Primary activities include agriculture, animal husbandry, forestry, fishing, mining and quarrying, etc. Secondary activities include manufacturing industry, building and construction work, etc. Tertiary activities include transport, communications, commerce, administration and other services. The proportion of people working in different activities varies in developed and developing countries. Developed nations have a high proportion of people in secondary, and tertiary activities. Developing countries tend to have a higher proportion of their workforce engaged in primary activities. In India, about 64 per cent of the population is engaged only in agriculture. The proportion of population dependent on secondary and tertiary sectors is about 13 and 20 per cent respectively. There has been an occupational shift in favour of secondary and tertiary sectors because of growing industrialisation and urbanisation in recent times.

Health is an important component of population composition, which affects the process of development. Sustained efforts of government programmes have registered significant improvements in the health conditions of the Indian population. Death rates have declined from 25 per 1000 population in 1951 to 7.2 per 1000 in 2011 and life expectancy at birth has increased from 36.7 years in 1951 to 67.9 years in 2012. The substantial improvement is the result of many factors including improvement in public health, prevention of infectious diseases and application of modern medical practices in diagnosis and treatment of ailments.

Despite considerable achievements, the health situation is a matter of major concern for India. The per capita calorie consumption is much below the recommended levels and malnutrition afflicts a large percentage of our population. Safe drinking water and basic sanitation amenities are available to only one-third of the rural population. These problems need to be tackled through an appropriate population policy.

The most significant feature of the Indian population is the size of its adolescent population. It constitutes one-fifth of the total population of India. Adolescents are, generally, grouped in the age group of 10 to 19 years. They are the most important resource for the future. Nutrition requirements of adolescents are higher than those of a normal child or adult. Poor nutrition can lead to deficiency and stunted growth. But in India, the diet available to adolescents is inadequate in all nutrients. A large number of adolescent girls suffer from anaemia. Their problems have so far not received adequate attention in the process of development. The adolescent girls have to be sensitised to the problems they confront. Awareness among them can be improved through the spread of literacy and education.

Recognising that the planning of families would improve individual health and welfare, the Government of India initiated a comprehensive Family Planning Programme in 1952. The Family Welfare Programme has sought to promote responsible and planned parenthood on a voluntary basis. The National Population Policy (NPP) 2000 is a culmination of years of planned efforts.

The NPP 2000 provides a policy framework for imparting free and compulsory school education up to 14 years of age, reducing infant mortality rate to below 30 per 1000 live births, achieving universal immunisation of children against all vaccine preventable diseases, promoting delayed marriage for girls, and making family welfare a people-centred programme.

NPP 2000 identified adolescents as one of the major section of the population that need greater attention. Besides nutritional requirements, the policy puts greater emphasis on other important needs of adolescent including protection from unwanted pregnancies and sexually transmitted diseases (STDs). It called for programmes that aim towards encouraging delayed marriage and child-bearing, education of adolescents about the risks of unprotected sex, making contraceptive services accessible and affordable, providing food supplements, nutritional services, and strengthening legal measures to prevent child marriage. People are the nation’s most valuable resource. A well-educated healthy population provides potential power.


After land, labour is the next necessary factor for production. Farming requires a great deal of hard work. Small farmers along with their families cultivate their own fields. Thus, they provide the labour required for farming themselves. Medium and large farmers hire farm labourers to work on their fields.

Farm labourers come either from landless families or families cultivating small plots of land. Unlike farmers, farm labourers do not have a right over the crops grown on the land. Instead they are paid wages by the farmer for whom they work. Wages can be in cash or in kind e.g. crop. Sometimes labourers get meals also. Wages vary widely from region to region, from crop to crop, from one farm activity to another (like sowing and harvesting). There is also a wide variation in the duration of employment. A farm labourer might be employed on a daily basis, or for one particular farm activity like harvesting, or for the whole year.

Dala is a landless farm labourer who works on daily wages in Palampur. This means he must regularly look for work. The minimum wages for a farm labourer set by the government is Rs 300 per day (March 2019), but Dala gets only Rs 160. There is heavy competition for work among the farm labourers in Palampur, so people agree to work for lower wages. Dala complains about his situation to Ramkali, who is another farm labourer. Both Dala and Ramkali are among the poorest people in the village.

You have already seen that the modern farming methods require a great deal of capital, so that the farmer now needs more money than before.
1. Most small farmers have to borrow money to arrange for the capital. They borrow from large farmers or the village moneylenders or the traders who supply various inputs for cultivation. The rate of interest on such loans is very high. They are put to great distress to repay the loan.
2. In contrast to the small farmers, the medium and large farmers have their own savings from farming. They are thus able to arrange for the capital needed. How do these farmers have their own savings? You shall find the answer in the next section.

Let us suppose that the farmers have produced wheat on their lands using the three factors of production. The wheat is harvested and production is complete. What do the farmers do with the wheat? They retain a part of the wheat for the family’s consumption and sell the surplus wheat. Small farmers like Savita and Gobind’s sons have little surplus wheat because their total production is small and from this a substantial share is kept for their own family needs. So it is the medium and large farmers who supply wheat to the market. In the Picture 1.1, you can see the bullock cart streaming into the market each carrying loads of wheat. The traders at the market buy the wheat and sell it further to shopkeepers in the towns and cities.

Tejpal Singh, the large farmer, has a surplus of 350 quintals of wheat from all his lands! He sells the surplus wheat at the Raiganj market and has good earnings. What does Tejpal Singh do with his earnings? Last year, Tejpal Singh had put most of the money in his bank account. Later he used the savings for lending to farmers like Savita who were in need of a loan. He also used the savings to arrange for the working capital for farming in the next season. This year Tejpal Singh plans to use his earnings to buy another tractor. Another tractor would increase his fixed capital.

Like Tejpal Singh, other large and medium farmers sell the surplus farm products. A part of the earnings is saved and kept for buying capital for the next season. Thus, they are able to arrange for the capital for farming from their own savings. Some farmers might also use the savings to buy cattle, trucks, or to set up shops. As we shall see, these constitute the capital for non-farm activities.


Due to historical and cultural reasons there is a division of labour between men and women in the family. Women generally look after domestic chores and men work in the fields. Sakal’s mother Sheela cooks food, cleans utensils, washes clothes, cleans the house and looks after her children. Sakal’s father Buta cultivates the field, sells the produce in the market and earns money for the family.

Sheela is not paid for the services delivered for upbringing of the family. Buta earns money, which he spends on rearing his family. Women are not paid for their service delivered in the family. The household work done by women is not recognised in the National Income. Geeta, mother of Vilas, earned an income by selling fish. Thus women are paid for their work when they enter the labour market. Their earning like that of their male counterpart is determined on the basis of education and skill.

Education helps individual to make better use of the economic opportunities available before him. Education and skill are the major determinants of the earning of any individual in the market. A majority of women have meagre education and low skill formation. Women are paid low compared to men. Most women work where job security is not there. Various activities relating to legal protection is meagre. Employment in this sector is characterised by irregular and low income. In this sector there is an absence of basic facilities like maternity leave, childcare and other social security systems. However, women with high education and skill formation are paid at par with the men. Among the organised sector, teaching and medicine attract them the most. Some women have entered administrative and other services including job, that need high levels of scientific and technological competence.

The quality of population depends upon the literacy rate, health of a person indicated by life expectancy and skill formation acquired by the people of the country. The quality of the poulation ultimately decides the growth rate of the country. Literate and healthy population are an asset.

Sakal’s education in the initial years of his life bore him the fruits in the later years in terms of a good job and salary. We saw education was an important input for the growth of Sakal. It opened new horizon for him, provided new aspiration and developed values of life. Not only for Sakal, education contributes towards the growth of society also. It enhances the national income, cultural richness and increases the efficiency of governance. There is a provision made for providing universal access, retention and quality in elementary education with a special emphasis on girls. There is also an establishment of pace setting of schools like Navodaya Vidyalaya in each district. Vocational streams have been developed to equip large number of high school students with occupations related to knowledge and skills. The plan outlay on education has increased from Rs 151 crore in the first plan to Rs 99,300 crore in 2020–21. The expenditure on education as a percentage of GDP rose from 0.64% in 1951–52 to 3.1% in 2019–20 (B.E.) and has remained stagnant around 3% from past few years. The Budgetary Estimate as stated in the Budget Documents of Union State Governments, Reserve Bank of India, the expenditure on education as a percentage of GDP has declined to 2.8% in 2020–21 (B.E.) The literacy rates have increased from 18% in 1951 to 85% in 2018. Literacy is not only a right, it is also needed if the citizens are to perform their duties and enjoy their rights properly. However, a vast difference is noticed across different sections of the population. Literacy among males is nearly 16.1% higher than females and it is about 14.2% higher in urban areas as compared to rural areas. As per 2011 census, literacy rates varied from 94% in Kerala to 62% in Bihar. The primary school system (I–V) has expanded to over 7,78,842, lakh in 2019–20. Unfortunately this huge expansion of schools has been diluted by the poor quality of schooling and high dropout rates. “Sarva Siksha Abhiyan is a significant step towards providing elementary education to all children in the age group of 6–14 years by 2010... It is a time-bound initiative of the Central government, in partnership with the States, the local government and the community for achieving the goal of universalisation of elementary education.” Along with it, bridge courses and backto-school camps have been initiated to increase the enrolment in elementary education. Mid-day meal scheme has been implemented to encourage attendance and retention of children and improve their nutritional status. These policies could add to the literate population of India.

The Gross Enrolment Ratio (GER) in higher education in the age group of 18 to 23 years is 27% in 2019–20, which would be broadly in line with world average. The strategy focuses on increasing access, quality, adoption of state-specific curriculum modification, vocationalisation and networking on the use of information technology. There is also focused on distance education, convergence of formal, non-formal, distance and IT education institutions.

Over the past 60 years, there has been a significant growth in the number of university and institutions of higher learning in specialised areas. Let us read the table to see the increase in the number of college, universities, enrolment of students and recruitment of teachers from 1951 to 2019–20.


Education helps individual to make better use of the economic opportunities available before him. Education and skill are the major determinants of the earning of any individual in the market. A majority of women have meagre education and low skill formation. Women are paid low compared to men. Most women work where job security is not there. Various activities relating to legal protection is meagre. Employment in this sector is characterised by irregular and low income. In this sector there is an absence of basic facilities like maternity leave, childcare and other social security systems. However, women with high education and skill formation are paid at par with the men. Among the organised sector, teaching and medicine attract them the most. Some women have entered administrative and other services including job, that need high levels of scientific and technological competence.

The quality of population depends upon the literacy rate, health of a person indicated by life expectancy and skill formation acquired by the people of the country. The quality of the poulation ultimately decides the growth rate of the country. Literate and healthy population are an asset.

Sakal’s education in the initial years of his life bore him the fruits in the later years in terms of a good job and salary. We saw education was an important input for the growth of Sakal. It opened new horizon for him, provided new aspiration and developed values of life. Not only for Sakal, education contributes towards the growth of society also. It enhances the national income, cultural richness and increases the efficiency of governance. There is a provision made for providing universal access, retention and quality in elementary education with a special emphasis on girls. There is also an establishment of pace setting of schools like Navodaya Vidyalaya in each district. Vocational streams have been developed to equip large number of high school students with occupations related to knowledge and skills. The plan outlay on education has increased from Rs 151 crore in the first plan to Rs 99,300 crore in 2020–21. The expenditure on education as a percentage of GDP rose from 0.64% in 1951–52 to 3.1% in 2019–20 (B.E.) and has remained stagnant around 3% from past few years. The Budgetary Estimate as stated in the Budget Documents of Union State Governments, Reserve Bank of India, the expenditure on education as a percentage of GDP has declined to 2.8% in 2020–21 (B.E.) The literacy rates have increased from 18% in 1951 to 85% in 2018. Literacy is not only a right, it is also needed if the citizens are to perform their duties and enjoy their rights properly. However, a vast difference is noticed across different sections of the population. Literacy among males is nearly 16.1% higher than females and it is about 14.2% higher in urban areas as compared to rural areas. As per 2011 census, literacy rates varied from 94% in Kerala to 62% in Bihar. The primary school system (I–V) has expanded to over 7,78,842, lakh in 2019–20. Unfortunately this huge expansion of schools has been diluted by the poor quality of schooling and high dropout rates. “Sarva Siksha Abhiyan is a significant step towards providing elementary education to all children in the age group of 6–14 years by 2010... It is a time-bound initiative of the Central government, in partnership with the States, the local government and the community for achieving the goal of universalisation of elementary education.” Along with it, bridge courses and backto-school camps have been initiated to increase the enrolment in elementary education. Mid-day meal scheme has been implemented to encourage attendance and retention of children and improve their nutritional status. These policies could add to the literate population of India.

The Gross Enrolment Ratio (GER) in higher education in the age group of 18 to 23 years is 27% in 2019–20, which would be broadly in line with world average. The strategy focuses on increasing access, quality, adoption of state-specific curriculum modification, vocationalisation and networking on the use of information technology. There is also focused on distance education, convergence of formal, non-formal, distance and IT education institutions.

Over the past 60 years, there has been a significant growth in the number of university and institutions of higher learning in specialised areas. Let us read the table to see the increase in the number of college, universities, enrolment of students and recruitment of teachers from 1951 to 2019–20.

Firm maximise profit: Do you think any firm would be induced to employ people who might not work efficiently as healthy workers because of ill health? The health of a person helps him to realise his/her potential and the ability to fight illness. He/She will not be able to maximise his/her output to the overall growth of the organisation. Indeed; health is an indispensable basis for realising one’s well-being. Henceforth, improvement in the health status of the population has been the priority of the country. Our national policy, too, aims at improving the accessibility of healthcare, family welfare and nutritional service with a special focus on the underprivileged segment of the population. Over the last five decades, India has built a vast health infrastructure and has also developed the manpower required at primary, secondary and tertiary sector in government, as well as, in the private sector.

There are many places in India which do not have even these basic facilities. There are only 542 medical colleges in the country and 313 dental colleges. Just four states, like Andhra Pradesh, Karnataka, Maharashtra and Tamil Nadu have the maximum number of medical colleges.


Since poverty has many facets, social scientists look at it through a variety of indicators. Usually the indicators used relate to the levels of income and consumption. But now poverty is looked through other social indicators like illiteracy level, lack of general resistance due to malnutrition, lack of access to healthcare, lack of job opportunities, lack of access to safe drinking water, sanitation etc. Analysis of poverty based on social exclusion and vulnerability is now becoming very common.

At the centre of the discussion on poverty is usually the concept of the “poverty line”. A common method used to measure poverty is based on the income or consumption levels. A person is considered poor if his or her income or consumption level falls below a given “minimum level” necessary to fulfill the basic needs. What is necessary to satisfy the basic needs is different at different times and in different countries. Therefore, poverty line may vary with time and place. Each country uses an imaginary line that is considered appropriate for its existing level of development and its accepted minimum social norms. For example, a person not having a car in the United States may be considered poor. In India, owning of a car is still considered a luxury.

While determining the poverty line in India, a minimum level of food requirement, clothing, footwear, fuel and light, educational and medical requirement, etc., are determined for subsistence. These physical quantities are multiplied by their prices in rupees. The present formula for food requirement while estimating the poverty line is based on the desired calorie requirement. Food items, such as cereals, pulses, vegetable, milk, oil, sugar, etc., together provide these needed calories. The calorie needs vary depending on age, sex and the type of work that a person does. The accepted average calorie requirement in India is 2400 calories per person per day in rural areas and 2100 calories per person per day in urban areas. Since people living in rural areas engage themselves in more physical work, calorie requirements in rural areas are considered to be higher than in urban areas. The monetary expenditure per capita needed for buying these calorie requirements in terms of food grains, etc., is revised periodically taking into consideration the rise in prices.

On the basis of these calculations, for the year 2011–12, the poverty line for a person was fixed at Rs 816 per month for rural areas and Rs 1000 for urban areas. Despite less calorie requirement, the higher amount for urban areas has been fixed because of high prices of many essential products in urban centres. In this way in the year 2011-12, a family of five members living in rural areas and earning less than about Rs 4,080 per month will be below the poverty line. A similar family in the urban areas would need a minimum of Rs 5,000 per month to meet their basic requirements. The poverty line is estimated periodically (normally every five years) by conducting sample surveys. These surveys are carried out by the National Sample Survey Organisation (NSSO). However, for making comparisons between developing countries, many international organisations like the World Bank use a uniform standard for the poverty line: minimum availability of the equivalent of $1.90 per person per day.

It is clear from Table 3.1 that there is a substantial decline in poverty ratios in India from about 45 per cent in 1993-94 to 37.2 per cent in 2004–05. The proportion of people below poverty line further came down to about 22 per cent in 2011–12. If the trend continues, people below poverty line may come down to less than 20 per cent in the next few years. Although the percentage of people living under poverty declined in the earlier two decades (1973–1993), the number of poor declined from 407 million in 2004–05 to 270 million in 2011–12 with an average annual decline of 2.2 percentage points during 2004–05 to 2011–12.

The proportion of people below poverty line is also not same for all social groups and economic categories in India. Social groups, which are most vulnerable to poverty are Scheduled Caste and Scheduled Tribe households. Similarly, among the economic groups, the most vulnerable groups are the rural agricultural labour households and the urban casual labour households. Graph 3.1 shows the percentage of poor people in all these groups. Although the average for people below poverty line for all groups in India is 22, 43 out of 100 people belonging to Scheduled Tribes are not able to meet their basic needs. Similarly, 34 per cent of casual workers in urban areas are below poverty line. About 34 per cent of casual labour farm (in rural areas) and 29 per cent of Scheduled Castes are also poor. The double disadvantage of being a landless casual wage labour household in the socially disadvantaged social groups of the scheduled caste or the scheduled tribe population highlights the seriousness of the problem. Some recent studies have shown that except for the scheduled tribe households, all the other three groups (i.e. scheduled castes, rural agricultural labourers and the urban casual labour households) have seen a decline in poverty in the 1990s.


There were a number of causes for the widespread poverty in India. One historical reason is the low level of economic development under the British colonial administration. The policies of the colonial government ruined traditional handicrafts and discouraged development of industries like textiles. The low rate of growth persisted until the nineteeneighties. This resulted in less job opportunities and low growth rate of incomes. This was accompanied by a high growth rate of population. The two combined to make the growth rate of per capita income very low. The failure at both the fronts: promotion of economic growth and population control perpetuated the cycle of poverty.

With the spread of irrigation and the Green revolution, many job opportunities were created in the agriculture sector. But the effects were limited to some parts of India. The industries, both in the public and the private sector, did provide some jobs. But these were not enough to absorb all the job seekers. Unable to find proper jobs in cities, many people started working as rickshaw pullers, vendors, construction workers, domestic servants etc. With irregular small incomes, these people could not afford expensive housing. They started living in slums on the outskirts of the cities and the problems of poverty, largely a rural phenomenon also became the feature of the urban sector.

Another feature of high poverty rates has been the huge income inequalities. One of the major reasons for this is the unequal distribution of land and other resources. Despite many policies, we have not been able to tackle the issue in a meaningful manner. Major policy initiatives like land reforms which aimed at redistribution of assets in rural areas have not been implemented properly and effectively by most of the state governments. Since lack of land resources has been one of the major causes of poverty in India, proper implementation of policy could have improved the life of millions of rural poor.

Many other socio-cultural and economic factors also are responsible for poverty. In order to fulfil social obligations and observe religious ceremonies, people in India, including the very poor, spend a lot of money. Small farmers need money to buy agricultural inputs like seeds, fertilizer, pesticides etc. Since poor people hardly have any savings, they borrow. Unable to repay because of poverty, they become victims of indebtedness. So the high level of indebtedness is both the cause and effect of poverty.

Removal of poverty has been one of the major objectives of Indian developmental strategy. The current anti-poverty strategy of the government is based broadly on two planks (1) promotion of economic growth (2) targeted anti-poverty programmes.

Over a period of thirty years lasting up to the early eighties, there were little per capita income growth and not much reduction in poverty. Official poverty estimates which were about 45 per cent in the early 1950s remained the same even in the early eighties. Since the eighties, India’s economic growth has been one of the fastest in the world. The growth rate jumped from the average of about 3.5 per cent a year in the 1970s to about 6 per cent during the 1980s and 1990s. The higher growth rates have helped significantly in the reduction of poverty. Therefore, it is becoming clear that there is a strong link between economic growth and poverty reduction. Economic growth widens opportunities and provides the resources needed to invest in human development. This also encourages people to send their children, including the girl child, to schools in the hope of getting better economic returns from investing in education. However, the poor may not be able to take direct advantage from the opportunities created by economic growth. Moreover, growth in the agriculture sector is much below expectations. This has a direct bearing on poverty as a large number of poor people live in villages and are dependent on agriculture.

In these circumstances, there is a clear need for targeted anti-poverty programmes. Although there are so many schemes which are formulated to affect poverty directly or indirectly, some of them are worth mentioning. Mahatma Gandhi National Rural Employment Guarantee Act, 2005 aims to provide 100 days of wage employment to every household to ensure livelihood security in rural areas. It also aimed at sustainable development to address the cause of draught, deforestration and soil erosion. One-third of the proposed jobs have been reserved for women. The scheme provided employment to 220 crores person days of employment to 4.78 crore households. The share of SC, ST, Women person days in the scheme are 23 per cent, 17 per cent and 53 per cent respectively. The average wage has increased from 65 in 2006–07 to 132 in 2013–14. Recently, in March 2018, the wage rate for unskilled manual workers has been revised, state wise, the range of wage rate for different states and union territories lies in between Rs 281 per day (for the workers in Haryana) to Rs 168 per day (for the workers of Bihar and Jharkhand).

Prime Minister Rozgar Yozana (PMRY) is another scheme which was started in 1993. The aim of the programme is to create self-employment opportunities for educated unemployed youth in rural areas and small towns. They are helped in setting up small business and industries. Rural Employment Generation Programme (REGP) was launched in 1995. The aim of the programme is to create selfemployment opportunities in rural areas and small towns. A target for creating 25 lakh new jobs has been set for the programme under the Tenth Five Year plan. Swarnajayanti Gram Swarozgar Yojana (SGSY) was launched in 1999. The programme aims at bringing the assisted poor families above the poverty line by organising them into self help groups through a mix of bank credit and government subsidy. Under the Pradhan Mantri Gramodaya Yozana (PMGY) launched in 2000, additional central assistance is given to states for basic services such as primary health, primary education, rural shelter, rural drinking water and rural electrification. Another important scheme is Antyodaya Anna Yozana (AAY) about which you will be reading more in the next chapter.

The results of these programmes have been mixed. One of the major reasons for less effectiveness is the lack of proper implementation and right targeting. Moreover, there has been a lot of overlapping of schemes. Despite good intentions, the benefits of these schemes are not fully reached to the deserving poor. Therefore, the major emphasis in recent years is on proper monitoring of all the poverty alleviation programmes.


The food insecure people are disproportionately large in some regions of the country, such as economically backward states with high incidence of poverty, tribal and remote areas, regions more prone to natural disasters etc. In fact, the states of Uttar Pradesh (eastern and south-eastern parts), Bihar, Jharkhand, Orissa, West Bengal, Chattisgarh, parts of Madhya Pradesh and Maharashtra account for largest number of food insecure people in the country.

Hunger is another aspect indicating food insecurity. Hunger is not just an expression of poverty, it brings about poverty. The attainment of food security therefore involves eliminating current hunger and reducing the risks of future hunger. Hunger has chronic and seasonal dimensions. Chronic hunger is a consequence of diets persistently inadequate in terms of quantity and/or quality. Poor people suffer from chronic hunger because of their very low income and in turn inability to buy food even for survival. Seasonal hunger is related to cycles of food growing and harvesting. This is prevalent in rural areas because of the seasonal nature of agricultural activities and in urban areas because of casual labourers, e.g., there is less work for casual construction labourers during the rainy season. This type of hunger exists when a person is unable to get work for the entire year.

The percentage of seasonal, as well as, chronic hunger has declined in India as shown in the above table. India is aiming at Self-sufficiency in Foodgrains since Independence. After Independence, Indian policymakers adopted all measures to achieve self-sufficiency in food grains. India adopted a new strategy in agriculture, which resulted in ‘Green Revolution’, especially in the production of wheat and rice.

Indira Gandhi, the then Prime Minister of India, officially recorded the impressive strides of Green Revolution in agriculture by releasing a special stamp entitled ‘Wheat Revolution’ in July 1968. The success of wheat was later replicated in rice. The increase in foodgrains was, however, disproportionate. The highest rate of growth was achieved in Uttar Pradesh and Madhya Pradesh, which was 44.01 and 30.21 million tonnes in 2015–16. The total foodgrain production was 252.22 Million tonnes in 2015–16 and it has changed to 275.68 million tonnes in 2016–17. Uttar Pradesh and Madhya Pradesh recorded a significant production in field of wheat which was 26.87 and 17.69 million tonnes in 2015–16, respectively. West Bengal and UP, on the other hand, recorded significant production of rice 15.75 and 12.51 Million tonnes in 2015–16 respectively.

Since the advent of the Green Revolution in the early-1970s, the country has avoided famine even during adverse weather conditions.  India has become self-sufficient in foodgrains during the last 30 years because of a variety of crops grown all over the country. The availability of foodgrains (even in adverse weather conditions or otherwise) at the country level has further been ensured with a carefully designed food security system by the government. This system has two components: (a) buffer stock, and (b) public distribution system.

Buffer Stock is the stock of foodgrains, namely wheat and rice, procured by the government through the Food Corporation of India (FCI). The FCI purchases wheat and rice from the farmers in states where there is surplus production. The farmers are paid a pre-announced price for their crops. This price is called Minimum Support Price (MSP). The MSP is declared by the government every year before the sowing season to provide incentives to farmers for raising the production of these crops. The purchased foodgrains are stored in granaries. Do you know why this buffer stock is created by the government? This is done to distribute foodgrains in the deficit areas and among the poorer strata of the society at a price lower than the market price also known as Issue Price. This also helps resolve the problem of shortage of food during adverse weather conditions or during the periods of calamity.

The food procured by the FCI is distributed through government regulated ration shops among the poorer section of the society. This is called the Public Distribution System (PDS). Ration shops are now present in most localities, villages, towns and cities. There are about 5.5 lakh ration shops all over the country. Ration shops also, known as Fair Price Shops, keep stock of foodgrains, sugar, and kerosene for cooking. These items are sold to people at a price lower than the market price. Any family with a ration card* can buy a stipulated amount of these items (e.g. 35 kg of grains, 5 litres of kerosene, 5 kgs of sugar etc.) every month from the nearby ration shop.


Buffer Stock is the stock of foodgrains, namely wheat and rice, procured by the government through the Food Corporation of India (FCI). The FCI purchases wheat and rice from the farmers in states where there is surplus production. The farmers are paid a pre-announced price for their crops. This price is called Minimum Support Price (MSP). The MSP is declared by the government every year before the sowing season to provide incentives to farmers for raising the production of these crops. The purchased foodgrains are stored in granaries. Do you know why this buffer stock is created by the government? This is done to distribute foodgrains in the deficit areas and among the poorer strata of the society at a price lower than the market price also known as Issue Price. This also helps resolve the problem of shortage of food during adverse weather conditions or during the periods of calamity.

The food procured by the FCI is distributed through government regulated ration shops among the poorer section of the society. This is called the Public Distribution System (PDS). Ration shops are now present in most localities, villages, towns and cities. There are about 5.5 lakh ration shops all over the country. Ration shops also, known as Fair Price Shops, keep stock of foodgrains, sugar, and kerosene for cooking. These items are sold to people at a price lower than the market price. Any family with a ration card* can buy a stipulated amount of these items (e.g. 35 kg of grains, 5 litres of kerosene, 5 kgs of sugar etc.) every month from the nearby ration shop.

Public Distribution System (PDS) is the most important step taken by the Government of India (GoI) towards ensuring food security. In the beginning, the coverage of PDS was universal with no discrimination between the poor and the non-poor. Over the years, the policy related to PDS has been revised to make it more efficient and targeted. In 1992, Revamped Public Distribution System (RPDS) was introducted in 1,700 blocks in the country. The target was to provide the benefits of PDS to remote and backward areas. From June 1997, in a renewed attempt, Targeted Public Distribution System (TPDS) was introducted to adopt the principle of targeting the ‘poor in all areas’. It was for the first time that a differential price policy was adopted for poor and nonpoor. Further, in 2000, two special schemes were launched viz., Antyodaya Anna Yojana (AAY) and Annapurna Scheme (APS) with special target groups of ‘poorest of the poor’ and ‘indigent senior citizens’, respectively. The functioning of these two schemes was linked with the existing network of the PDS.

The PDS has proved to be the most effective instrument of government policy over the years in stabilising prices and making food available to consumers at affordable prices. It has been instrumental in averting widespread hunger and famine by supplying food from surplus regions of the country to the deficit ones. In addition, the prices have been under revision in favour of poor households in general. The system, including the minimum support price and procurement has contributed to an increase in foodgrain production and provided income security to farmers in certain regions.

However, the Public Distribution System has faced severe criticism on several grounds. Instances of hunger are prevalent despite overflowing granaries. FCI godowns are overflowing with grains, with some rotting away and some being eaten by rats. Graph 4.2 shows the difference in foodgrain stocks in Central pool and its stocking norms.

In 2014, the stock of wheat and rice with FCI was 65.3 million tonnes which was much more than the minimum buffer norms. However, these remained consistently higher than the buffer norms. The situation improved with the distribution of foodgrains under different schemes launched by the government. There is a general consensus that high level of buffer stocks of foodgrains is very undesirable and can be wasteful. The storage of massive food stocks has been responsible for high carrying costs, in addition to wastage and deterioration in grain quality. Freezing of MSP for a few years should be considered seriously.

The increased food grains procurement at enhanced MSP is the result of the pressure exerted by leading foodgrain producing states, such as Punjab, Haryana and Andhra Pradesh. Moreover, as the procurement is concentrated in a few prosperous regions (Punjab, Haryana, Western Uttar Pradesh, Andhra Pradesh and to a lesser extent in West Bengal) and mainly of two crops— wheat and rice— increase in MSP has induced farmers, particularly in surplus states, to divert land from production of coarse grains, which is the staple food of the poor, to the production of rice and wheat. The intensive utilisation of water in the cultivation of rice has also led to environmental degradation and fall in the water level, threatening the sustainability of the agricultural development in these states.

As per the NSSO report No. 558 in rural India, the per person per month consumption of rice has declined from 6.38 Kg. in 2004-05 to 5.98 Kg in 2011-12. In urban India, the per person per month consumption of rice, too has declined from 4.71 Kg in 2004-05 to 4.49 Kg in 2011-12. Per Capita consumption of PDS rice has doubled in rural India and increased by 66% in urban India since 2004-05. The per Capita consumption of PDS wheat has doubled since 2004-05 in both rural and urban India.

PDS dealers are sometimes found resorting to malpractices like diverting the grains to open market to get better margin, selling poor quality grains at ration shops, irregular opening of the shops, etc. It is common to find that ration shops regularly have unsold stocks of poor quality grains left. This has proved to be a big problem. When ration shops are unable to sell, a massive stock of foodgrains piles up with the FCI. In recent years, there is another factor that has led to the decline of the PDS. Earlier every family, poor and non-poor had a ration card with a fixed quota of items such as rice, wheat, sugar etc. These were sold at the same low price to every family. The three types of cards and the range of prices that you see today did not exist. A large number of families could buy foodgrains from the ration shops subject to a fixed quota. These included low income families whose incomes were marginally higher than the below poverty line families. Now, with TPDS of three different prices, any family above the poverty line gets very little discount at the ration shop. The price for APL family is almost as high as open market price, so there is little incentive for them to buy these items from the ration shop.


Activity 1.1 can be described as – when a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide. This description of a chemical reaction in a sentence form is quite long. It can be written in a shorter form. The simplest way to do this is to write it in the form of a word-equation.

The substances that undergo chemical change in the reaction (1.1), magnesium and oxygen, are the reactants. The new substance is magnesium oxide, formed during the reaction, as a product. A word-equation shows change of reactants to products through an arrow placed between them. The reactants are written on the left-hand side (LHS) with a plus sign (+) between them. Similarly, products are written on the right-hand side (RHS) with a plus sign (+) between them. The arrowhead points towards the products, and shows the direction of the reaction.

Is there any other shorter way for representing chemical equations? Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equation represents a chemical reaction.

Count and compare the number of atoms of each element on the LHS and RHS of the arrow. Is the number of atoms of each element the same on both the sides? If yes, then the equation is balanced. If not, then the equation is unbalanced because the mass is not the same on both sides of the equation. Such a chemical equation is a skeletal chemical equation for a reaction. Equation (1.2) is a skeletal chemical equation for the burning of magnesium in air.

Recall the law of conservation of mass that you studied in Class IX; mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation. Is the chemical Eq. (1.2) balanced? Let us learn about balancing a chemical equation step by step.

Step I: To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation.

Step II: List the number of atoms of different elements present in the unbalanced equation.

Step III: It is often convenient to start balancing with the compound that contains the maximum number of atoms. It may be a reactant or a product. In that compound, select the element which has the maximum number of atoms. Using these criteria, we select Fe3O4 and the element oxygen in it. There are four oxygen atoms on the RHS and only one on the LHS. To equalise the number of atoms, it must be remembered that we cannot alter the formulae of the compounds or elements involved in the reactions.

Step IV: Fe and H atoms are still not balanced. Pick any of these elements to proceed further. Let us balance hydrogen atoms in the partly balanced equation.

Step V: Examine the above equation and pick up the third element which is not balanced. You find that only one element is left to be balanced, that is, iron.

Step VI: Finally, to check the correctness of the balanced equation, we count atoms of each element on both sides of the equation. The numbers of atoms of elements on both sides of Eq. (1.9) are equal. This equation is now balanced. This method of balancing chemical equations is called hit-and-trial method as we make trials to balance the equation by using the smallest whole number coefficient.

Step VII: Writing Symbols of Physical States Carefully examine the above balanced Eq. (1.9). Does this equation tell us anything about the physical state of each reactant and product? No information has been given in this equation about their physical states. To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s), respectively. The word aqueous (aq) is written if the reactant or product is present as a solution in water.


In Section 2.1 we have seen that all acids have similar chemical properties. What leads to this similarity in properties? We saw in Activity 2.3 that all acids generate hydrogen gas on reacting with metals, so hydrogen seems to be common to all acids. Let us perform an Activity to investigate whether all compounds containing hydrogen are acidic.

The bulb will start glowing in the case of acids, as shown in Fig. 2.3. But you will observe that glucose and alcohol solutions do not conduct electricity. Glowing of the bulb indicates that there is a flow of electric current through the solution. The electric current is carried through the acidic solution by ions.

The process of dissolving an acid or a base in water is a highly exothermic one. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating. Look out for the warning sign (shown in Fig. 2.5) on the can of concentrated sulphuric acid and on the bottle of sodium hydroxide pellets. Mixing an acid or base with water results in decrease in the concentration of ions per unit volume. Such a process is called dilution and the acid or the base is said to be diluted.

We can do this by making use of a universal indicator, which is a mixture of several indicators. The universal indicator shows different colours at different concentrations of hydrogen ions in a solution. A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power. On the pH scale we can measure pH generally from 0 (very acidic) to 14 (very alkaline). pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value.

The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH–  ion concentration in the solution, that is, increase in the strength of alkali (Fig. 2.6). Generally paper impregnated with the universal indicator is used for measuring pH.

The strength of acids and bases depends on the number of H+ ions and OH– ions produced, respectively. If we take hydrochloric acid and acetic acid of the same concentration, say one molar, then these produce different amounts of hydrogen ions. Acids that give rise to more H+ ions are said to be strong acids, and acids that give less H+ ions are said to be weak acids. Can you now say what weak and strong bases are?

Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Plants require a specific pH range for their healthy growth. To find out the pH required for the healthy growth of a plant, you can collect the soil from various places and check the pH in the manner described below in Activity 2.12. Also, you can note down which plants are growing in the region from which you have collected the soil.

It is very interesting to note that our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids. One such remedy must have been suggested by you at the beginning of this Chapter. These antacids neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.

Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

Salts of a strong acid and a strong base are neutral with pH value of 7. On the other hand, salts of a strong acid and weak base are acidic with pH value less than 7 and those of a strong base and weak acid are basic in nature, with pH value more than 7. By now you have learnt that the salt formed by the combination of hydrochloric acid and sodium hydroxide solution is called sodium chloride. This is the salt that you use in food. You must have observed in the above Activity that it is a neutral salt.

Seawater contains many salts dissolved in it. Sodium chloride is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt. Beds of rock salt were formed when seas of bygone ages dried up. Rock salt is mined like coal.


You have learnt about oxidation reactions in the first Chapter. Carbon compounds can be easily oxidised on combustion. In addition to this complete oxidation, we have reactions in which alcohols are converted to carboxylic acids – We see that some substances are capable of adding oxygen to others. These substances are known as oxidising agents. Alkaline potassium permanganate or acidified potassium dichromate are oxidising alcohols to acids, that is, adding oxygen to the starting material. Hence they are known as oxidising agents.

Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected. This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.

You must have seen advertisements stating that some vegetable oils are ‘healthy’. Animal fats generally contain saturated fatty acids which are said to be harmful for health. Oils containing unsaturated fatty acids should be chosen for cooking.

Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents. However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. Chlorine can replace the hydrogen atoms one by one. It is called a substitution reaction because one type of atom or a group of atoms takes the place of another. A number of products are usually formed with the higher homologues of alkanes.

Many carbon compounds are invaluable to us. But here we shall study the properties of two commercially important compounds – ethanol and ethanoic acid.

Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids. 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles. The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.

The group of organic compounds called carboxylic acids are obviously characterised by their acidic nature. However, unlike mineral acids like HCl, which are completely ionised, carboxylic acids are weak acids.

Reactions of ethanoic acid:
(i) Esterification reaction: Esters are most commonly formed by reaction of an acid and an alcohol. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester – Generally, esters are sweet-smelling substances. These are used in making perfumes and as flavouring agents. On treating with sodium hydroxide, which is an alkali, the ester is converted back to alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap. Soaps are sodium or potassium salts of long chain carboxylic acid.
(ii) Reaction with a base: Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate or commonly called sodium acetate) and water:
(iii) Reaction with carbonates and hydrogencarbonates: Ethanoic acid reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide and water. The salt produced is commonly called sodium acetate.

This activity demonstrates the effect of soap in cleaning. Most dirt is oily in nature and as you know, oil does not dissolve in water. The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic-end of soap interacts with water while the carbon chain interacts with oil. The soap molecules, thus form structures called micelles (see Fig. 4.12) where one end of the molecules is towards the oil droplet while the ionic-end faces outside. This forms an emulsion in water. The soap micelle thus helps in pulling out the dirt in water and we can wash our clothes clean (Fig. 4.13).

Have you ever observed while bathing that foam is formed with difficulty and an insoluble substance (scum) remains after washing with water? This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. Hence you need to use a larger amount of soap. This problem is overcome by using another class of compounds called detergents as cleansing agents. Detergents are generally sodium salts of sulphonic acids or ammonium salts with chlorides or bromides ions, etc. Both have long hydrocarbon chain. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.


Even after the rejection of Newlands’ Law of Octaves, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.

The main credit for classifying elements goes to Dmitri Ivanovich Mendeléev, a Russian chemist. He was the most important contributor to the early development of a Periodic Table of elements wherein the elements were arranged on the basis of their fundamental property, the atomic mass, and also on the similarity of chemical properties.

When Mendeléev started his work, 63 elements were known. He examined the relationship between the atomic masses of the elements and their physical and chemical properties. Among chemical properties, Mendeléev concentrated on the compounds formed by elements with oxygen and hydrogen. He selected hydrogen and oxygen as they are very reactive and formed compounds with most elements. The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element for its classification. He then took 63 cards and on each card he wrote down the properties of one element. He sorted out the elements with similar properties and pinned the cards together on a wall. He observed that most of the elements got a place in a Periodic Table and were arranged in the order of their increasing atomic masses. It was also observed that there occurs a periodic recurrence of elements with similar physical and chemical properties. On this basis, Mendeléev formulated a Periodic Law, which states that ‘the properties of elements are the periodic function of their atomic masses’.

While developing the Periodic Table, there were a few instances where Mendeléev had to place an element with a slightly greater atomic mass before an element with a slightly lower atomic mass. The sequence was inverted so that elements with similar properties could be grouped together. For example, cobalt (atomic mass 58.9) appeared before nickel (atomic mass 58.7). Looking at Table 5.4, can you find out one more such anomaly?

Further, Mendeléev left some gaps in his Periodic Table. Instead of looking upon these gaps as defects, Mendeléev boldly predicted the existence of some elements that had not been discovered at that time. Mendeléev named them by prefixing a Sanskrit numeral, Eka (one) to the name of preceding element in the same group. For instance, scandium, gallium and germanium, discovered later, have properties similar to Eka–boron, Eka aluminium and Eka–silicon, respectively. The properties of Eka–Aluminium predicted by Mendeléev and those of the element, gallium which was discovered later and replaced Ekaaluminium, are listed as follows.

This provided convincing evidence for both the correctness and usefulness of Mendeléev’s Periodic Table. Further, it was the extraordinary success of Mendeléev’s prediction that led chemists not only to accept his Periodic Table but also recognise him, as the originator of the concept on which it is based. Noble gases like helium (He), neon (Ne) and argon (Ar) have been mentioned in many a context before this. These gases were discovered very late because they are very inert and present in extremely low concentrations in our atmosphere. One of the strengths of Mendeléev’s Periodic Table was that, when these gases were discovered, they could be placed in a new group without disturbing the existing order.

Electronic configuration of hydrogen resembles that of alkali metals. Like alkali metals, hydrogen combines with halogens, oxygen and sulphur to form compounds having similar formulae, as shown in the examples here. On the other hand, just like halogens, hydrogen also exists as diatomic molecules and it combines with metals and non-metals to form covalent compounds.

Certainly, no fixed position can be given to hydrogen in the Periodic Table. This was the first limitation of Mendeléev’s Periodic Table. He could not assign a correct position to hydrogen in his Table. Isotopes were discovered long after Mendeléev had proposed his periodic classification of elements. Let us recall that isotopes of an element have similar chemical properties, but different atomic masses.

Thus, isotopes of all elements posed a challenge to Mendeleev’s Periodic Law. Another problem was that the atomic masses do not increase in a regular manner in going from one element to the next. So it was not possible to predict how many elements could be discovered between two elements — especially when we consider the heavier elements.

In 1913, Henry Moseley showed that the atomic number (symbolised as Z) of an element is a more fundamental property than its atomic mass. Accordingly, Mendeléev’s Periodic Law was modified and atomic number was adopted as the basis of Modern Periodic Table and the Modern Periodic Law can be stated as follows: ‘Properties of elements are a periodic function of their atomic number.’ Let us recall that the atomic number gives us the number of protons in the nucleus of an atom and this number increases by one in going from one element to the next. Elements, when arranged in order of increasing atomic number, lead us to the classification known as the Modern Periodic Table (Table 5.6). Prediction of properties of elements could be made with more precision when elements were arranged on the basis of increasing atomic number.

As we can see, the Modern Periodic Table takes care of three limitations of Mendléev’s Periodic Table. The anomalous position of hydrogen can be discussed after we see what are the bases on which the position of an element in the Modern Periodic Table depends.

The Modern Periodic Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’. Let us see what decides the placing of an element in a certain group and period.

You will find that all these elements contain the same number of valence electrons. Similarly, you will find that the elements present in any one group have the same number of valence electrons. For example, elements fluorine (F) and chlorine (Cl), belong to group 17, how many electrons do fluorine and chlorine have in their outermost shells? Hence, we can say that groups in the Periodic Table signify an identical outershell electronic configuration. On the other hand, the number of shells increases as we go down the group.


Further, Mendeléev left some gaps in his Periodic Table. Instead of looking upon these gaps as defects, Mendeléev boldly predicted the existence of some elements that had not been discovered at that time. Mendeléev named them by prefixing a Sanskrit numeral, Eka (one) to the name of preceding element in the same group. For instance, scandium, gallium and germanium, discovered later, have properties similar to Eka–boron, Eka aluminium and Eka–silicon, respectively. The properties of Eka–Aluminium predicted by Mendeléev and those of the element, gallium which was discovered later and replaced Ekaaluminium, are listed as follows.

This provided convincing evidence for both the correctness and usefulness of Mendeléev’s Periodic Table. Further, it was the extraordinary success of Mendeléev’s prediction that led chemists not only to accept his Periodic Table but also recognise him, as the originator of the concept on which it is based. Noble gases like helium (He), neon (Ne) and argon (Ar) have been mentioned in many a context before this. These gases were discovered very late because they are very inert and present in extremely low concentrations in our atmosphere. One of the strengths of Mendeléev’s Periodic Table was that, when these gases were discovered, they could be placed in a new group without disturbing the existing order.

Electronic configuration of hydrogen resembles that of alkali metals. Like alkali metals, hydrogen combines with halogens, oxygen and sulphur to form compounds having similar formulae, as shown in the examples here. On the other hand, just like halogens, hydrogen also exists as diatomic molecules and it combines with metals and non-metals to form covalent compounds.

Certainly, no fixed position can be given to hydrogen in the Periodic Table. This was the first limitation of Mendeléev’s Periodic Table. He could not assign a correct position to hydrogen in his Table. Isotopes were discovered long after Mendeléev had proposed his periodic classification of elements. Let us recall that isotopes of an element have similar chemical properties, but different atomic masses.

Thus, isotopes of all elements posed a challenge to Mendeleev’s Periodic Law. Another problem was that the atomic masses do not increase in a regular manner in going from one element to the next. So it was not possible to predict how many elements could be discovered between two elements — especially when we consider the heavier elements.

In 1913, Henry Moseley showed that the atomic number (symbolised as Z) of an element is a more fundamental property than its atomic mass. Accordingly, Mendeléev’s Periodic Law was modified and atomic number was adopted as the basis of Modern Periodic Table and the Modern Periodic Law can be stated as follows: ‘Properties of elements are a periodic function of their atomic number.’ Let us recall that the atomic number gives us the number of protons in the nucleus of an atom and this number increases by one in going from one element to the next. Elements, when arranged in order of increasing atomic number, lead us to the classification known as the Modern Periodic Table (Table 5.6). Prediction of properties of elements could be made with more precision when elements were arranged on the basis of increasing atomic number.

As we can see, the Modern Periodic Table takes care of three limitations of Mendléev’s Periodic Table. The anomalous position of hydrogen can be discussed after we see what are the bases on which the position of an element in the Modern Periodic Table depends.

The Modern Periodic Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’. Let us see what decides the placing of an element in a certain group and period.

You will find that all these elements contain the same number of valence electrons. Similarly, you will find that the elements present in any one group have the same number of valence electrons. For example, elements fluorine (F) and chlorine (Cl), belong to group 17, how many electrons do fluorine and chlorine have in their outermost shells? Hence, we can say that groups in the Periodic Table signify an identical outershell electronic configuration. On the other hand, the number of shells increases as we go down the group.

You will find that these elements of second period do not have the same number of valence electrons, but they contain the same number of shells. You also observe that the number of valence shell electrons increases by one unit, as the atomic number increases by one unit on moving from left to right in a period. Or we can say that atoms of different elements with the same number of occupied shells are placed in the same period. Na, Mg, Al, Si, P, S, Cl and Ar belong to the third period of the Modern Periodic Table, since the electrons in the atoms of these elements are filled in K, L and M shells.

How many elements are there in the first, second, third and fourth periods? We can explain the number of elements in these periods based on how electrons are filled into various shells. You will study the details of this in higher classes. Recall that the maximum number of electrons that can be accommodated in a shell depends on the formula 2n squared where ‘n’ is the number of the given shell from the nucleus.

The position of an element in the Periodic Table tells us about its chemical reactivity. As you have learnt, the valence electrons determine the kind and number of bonds formed by an element. Can you now say why Mendeléev’s choice of formulae of compounds as the basis for deciding the position of an element in his Table was a good one? How would this lead to elements with similar chemical properties being placed in the same group?


We have discussed nutrition in organisms in the last section. The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Diverse organisms do this in different ways – some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen (Fig. 6.8). In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. Breakdown of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than in the anaerobic process. Sometimes, when there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

The energy released during cellular respiration is immediately used to synthesise a molecule called ATP which is used to fuel all other activities in the cell. In these processes, ATP is broken down giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell.

Since the aerobic respiration pathway depends on oxygen, aerobic organisms need to ensure that there is sufficient intake of oxygen. We have seen that plants exchange gases through stomata, and the large inter-cellular spaces ensure that all cells are in contact with air. Carbon dioxide and oxygen are exchanged by diffusion here. They can go into cells, or away from them and out into the air. The direction of diffusion depends upon the environmental conditions and the requirements of the plant. At night, when there is no photosynthesis occurring, CO2 elimination is the major exchange activity going on. During the day, CO2 generated during respiration is used up for photosynthesis, hence there is no CO2 release. Instead, oxygen release is the major event at this time. Animals have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced. Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water need to use the oxygen dissolved in water.

Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. Fishes take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood. Terrestrial organisms use the oxygen in the atmosphere for respiration. This oxygen is absorbed by different organs in different animals. All these organs have a structure that increases the surface area which is in contact with the oxygen-rich atmosphere. Since the exchange of oxygen and carbon dioxide has to take place across this surface, this surface is very fine and delicate. In order to protect this surface, it is usually placed within the body, so there have to be passages that will take air to this area. In addition, there is a mechanism for moving the air in and out of this area where the oxygen is absorbed.

In human beings (Fig. 6.9), air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage. The passage is also lined with mucus which helps in this process. From here, the air passes through the throat and into the lungs. Rings of cartilage are present in the throat. These ensure that the air-passage does not collapse.

Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures which are called alveoli (singular–alveolus). The alveoli provide a surface where the exchange of gases can take place. The walls of the alveoli contain an extensive network of blood-vessels. As we have seen in earlier years, when we breathe in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger as a result. Because of this, air is sucked into the lungs and fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. Instead, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it. In human beings, the respiratory pigment is haemoglobin which has a very high affinity for oxygen. This pigment is present in the red blood corpuscles. Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood.


In animals, such control and coordination are provided by nervous and muscular tissues, which we have studied in Class IX. Touching a hot object is an urgent and dangerous situation for us. We need to detect it, and respond to it. How do we detect that we are touching a hot object? All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect smell.

This information, acquired at the end of the dendritic tip of a nerve cell [Fig. 7.1 (a)], sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron. This is a general scheme of how nervous impulses travel in the body. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland [Fig. 7.1 (b)]. It is thus no surprise that nervous tissue is made up of an organised network of nerve cells or neurons, and is specialised for conducting information via electrical impulses from one part of the body to another. Look at Fig. 7.1 (a) and identify the parts of a neuron (i) where information is acquired, (ii) through which information travels as an electrical impulse, and (iii) where this impulse must be converted into a chemical signal for onward transmission.

‘Reflex’ is a word we use very commonly when we talk about some sudden action in response to something in the environment. We say ‘I jumped out of the way of the bus reflexly’, or ‘I pulled my hand back from the flame reflexly’, or ‘I was so hungry my mouth started watering reflexly’. What exactly do we mean? A common idea in all such examples is that we do something without thinking about it, or without feeling in control of our reactions. Yet these are situations where we are responding with some action to changes in our environment. How is control and coordination achieved in such situations?

Let us consider this further. Take one of our examples. Touching a flame is an urgent and dangerous situation for us, or in fact, for any animal! How would we respond to this? One seemingly simple way is to think consciously about the pain and the possibility of getting burnt, and therefore move our hand. An important question then is, how long will it take us to think all this? The answer depends on how we think. If nerve impulses are sent around the way we have talked about earlier, then thinking is also likely to involve the creation of such impulses. Thinking is a complex activity, so it is bound to involve a complicated interaction of many nerve impulses from many neurons.

If this is the case, it is no surprise that the thinking tissue in our body consists of dense networks of intricately arranged neurons. It sits in the forward end of the skull, and receives signals from all over the body which it thinks about before responding to them. Obviously, in order to receive these signals, this thinking part of the brain in the skull must be connected to nerves coming from various parts of the body. Similarly, if this part of the brain is to instruct muscles to move, nerves must carry this signal back to different parts of the body. If all of this is to be done when we touch a hot object, it may take enough time for us to get burnt!

How does the design of the body solve this problem? Rather than having to think about the sensation of heat, if the nerves that detect heat were to be connected to the nerves that move muscles in a simpler way, the process of detecting the signal or the input and responding to it by an output action might be completed quickly. Such a connection is commonly called a reflex arc (Fig. 7.2). Where should such reflex arc connections be made between the input nerve and the output nerve? The best place, of course, would be at the point where they first meet each other. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain. Of course, reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. In fact many animals have very little or none of the complex neuron network needed for thinking. So it is quite likely that reflex arcs have evolved as efficient ways of functioning in the absence of true thought processes. However, even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.

Is reflex action the only function of the spinal cord? Obviously not, since we know that we are thinking beings. Spinal cord is made up of nerves which supply information to think about. Thinking involves more complex mechanisms and neural connections. These are concentrated in the brain, which is the main coordinating centre of the body. The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it.

We also think about our actions. Writing, talking, moving a chair, clapping at the end of a programme are examples of voluntary actions which are based on deciding what to do next. So, the brain also has to send messages to muscles. This is the second way in which the nervous system communicates with the muscles. The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord. The brain thus allows us to think and take actions based on that thinking. As you will expect, this is accomplished through a complex design, with different parts of the brain responsible for integrating different inputs and outputs. The brain has three such major parts or regions, namely the fore-brain, mid-brain and hind-brain.


‘Reflex’ is a word we use very commonly when we talk about some sudden action in response to something in the environment. We say ‘I jumped out of the way of the bus reflexly’, or ‘I pulled my hand back from the flame reflexly’, or ‘I was so hungry my mouth started watering reflexly’. What exactly do we mean? A common idea in all such examples is that we do something without thinking about it, or without feeling in control of our reactions. Yet these are situations where we are responding with some action to changes in our environment. How is control and coordination achieved in such situations?

Let us consider this further. Take one of our examples. Touching a flame is an urgent and dangerous situation for us, or in fact, for any animal! How would we respond to this? One seemingly simple way is to think consciously about the pain and the possibility of getting burnt, and therefore move our hand. An important question then is, how long will it take us to think all this? The answer depends on how we think. If nerve impulses are sent around the way we have talked about earlier, then thinking is also likely to involve the creation of such impulses. Thinking is a complex activity, so it is bound to involve a complicated interaction of many nerve impulses from many neurons.

If this is the case, it is no surprise that the thinking tissue in our body consists of dense networks of intricately arranged neurons. It sits in the forward end of the skull, and receives signals from all over the body which it thinks about before responding to them. Obviously, in order to receive these signals, this thinking part of the brain in the skull must be connected to nerves coming from various parts of the body. Similarly, if this part of the brain is to instruct muscles to move, nerves must carry this signal back to different parts of the body. If all of this is to be done when we touch a hot object, it may take enough time for us to get burnt!

How does the design of the body solve this problem? Rather than having to think about the sensation of heat, if the nerves that detect heat were to be connected to the nerves that move muscles in a simpler way, the process of detecting the signal or the input and responding to it by an output action might be completed quickly. Such a connection is commonly called a reflex arc (Fig. 7.2). Where should such reflex arc connections be made between the input nerve and the output nerve? The best place, of course, would be at the point where they first meet each other. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain. Of course, reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. In fact many animals have very little or none of the complex neuron network needed for thinking. So it is quite likely that reflex arcs have evolved as efficient ways of functioning in the absence of true thought processes. However, even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.

Is reflex action the only function of the spinal cord? Obviously not, since we know that we are thinking beings. Spinal cord is made up of nerves which supply information to think about. Thinking involves more complex mechanisms and neural connections. These are concentrated in the brain, which is the main coordinating centre of the body. The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it.

We also think about our actions. Writing, talking, moving a chair, clapping at the end of a programme are examples of voluntary actions which are based on deciding what to do next. So, the brain also has to send messages to muscles. This is the second way in which the nervous system communicates with the muscles. The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord. The brain thus allows us to think and take actions based on that thinking. As you will expect, this is accomplished through a complex design, with different parts of the brain responsible for integrating different inputs and outputs. The brain has three such major parts or regions, namely the fore-brain, mid-brain and hind-brain.

The fore-brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing, smell, sight and so on. There are separate areas of association where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in the brain. Based on all this, a decision is made about how to respond and the information is passed on to the motor areas which control the movement of voluntary muscles, for example, our leg muscles. However, certain sensations are distinct from seeing or hearing, for example, how do we know that we have eaten enough? The sensation of feeling full is because of a centre associated with hunger, which is in a separate part of the fore-brain.

Let us look at the other use of the word ‘reflex’ that we have talked about in the introduction. Our mouth waters when we see food we like without our meaning to. Our hearts beat without our thinking about it. In fact, we cannot control these actions easily by thinking about them even if we wanted to. Do we have to think about or remember to breathe or digest food? So, in between the simple reflex actions like change in the size of the pupil, and the thought out actions such as moving a chair, there is another set of muscle movements over which we do not have any thinking control. Many of these involuntary actions are controlled by the mid-brain and hind-brain. All these involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain.

Think about activities like walking in a straight line, riding a bicycle, picking up a pencil. These are possible due to a part of the hind-brain called the cerebellum. It is responsible for precision of voluntary actions and maintaining the posture and balance of the body. Imagine what would happen if each of these events failed to take place if we were not thinking about it.


Animals have a nervous system for controlling and coordinating the activities of the body. But plants have neither a nervous system nor muscles. So, how do they respond to stimuli? When we touch the leaves of a chhui-mui (the ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down, the stem comes up into the air.

There is no growth involved in this movement. On the other hand, the directional movement of a seedling is caused by growth. If it is prevented from growing, it will not show any movement. So plants show two different types of movement – one dependent on growth and the other independent of growth.

Let us think about the first kind of movement, such as that of the sensitive plant. Since no growth is involved, the plant must actually move its leaves in response to touch. But there is no nervous tissue, nor any muscle tissue. How does the plant detect the touch, and how do the leaves move in response?

If we think about where exactly the plant is touched, and what part of the plant actually moves, it is apparent that movement happens at a point different from the point of touch. So, information that a touch has occurred must be communicated. The plants also use electrical-chemical means to convey this information from cell to cell, but unlike in animals, there is no specialised tissue in plants for the conduction of information. Finally, again as in animals, some cells must change shape in order for movement to happen. Instead of the specialised proteins found in animal muscle cells, plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.

Some plants like the pea plant climb up other plants or fences by means of tendrils. These tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it. More commonly, plants respond to stimuli slowly by growing in a particular direction. Because this growth is directional, it appears as if the plant is moving. Let us understand this type of movement with the help of an example.

Environmental triggers such as light, or gravity will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it. How does this help the plant?

Plants show tropism in response to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growth of shoots and roots, respectively, in response to the pull of earth or gravity is, obviously, geotropism.

Let us now once again think about how information is communicated in the bodies of multicellular organisms. The movement of the sensitive plant in response to touch is very quick. The movement of sunflowers in response to day or night, on the other hand, is quite slow. Growth-related movement of plants will be even slower. Even in animal bodies, there are carefully controlled directions to growth. Our arms and fingers grow in certain directions, not haphazardly. So controlled movements can be either slow or fast. If fast responses to stimuli are to be made, information transfer must happen very quickly. For this, the medium of transmission must be able to move rapidly.

Electrical impulses are an excellent means for this. But there are limitations to the use of electrical impulses. Firstly, they will reach only those cells that are connected by nervous tissue, not each and every cell in the animal body. Secondly, once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanisms before it can generate and transmit a new impulse. In other words, cells cannot continually create and transmit electrical impulses. It is thus no wonder that most multicellular organisms use another means of communication between cells, namely, chemical communication.

If, instead of generating an electrical impulse, stimulated cells release a chemical compound, this compound would diffuse all around the original cell. If other cells around have the means to detect this compound using special molecules on their surfaces, then they would be able to recognise information, and even transmit it. This will be slower, of course, but it can potentially reach all cells of the body, regardless of nervous connections, and it can be done steadily and persistently. These compounds, or hormones used by multicellular organisms for control and coordination show a great deal of diversity, as we would expect. Different plant hormones help to coordinate growth, development and responses to the environment. They are synthesised at places away from where they act and simply diffuse to the area of action.

Let us take an example that we have worked with earlier. When growing plants detect light, a hormone called auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

Another example of plant hormones are gibberellins which, like auxins, help in the growth of the stem. Cytokinins promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds. These are examples of plant hormones that help in promoting growth. But plants also need signals to stop growing. Abscisic acid is one example of a hormone which inhibits growth. Its effects include wilting of leaves.


Let us take an example that we have worked with earlier. When growing plants detect light, a hormone called auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

Another example of plant hormones are gibberellins which, like auxins, help in the growth of the stem. Cytokinins promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds. These are examples of plant hormones that help in promoting growth. But plants also need signals to stop growing. Abscisic acid is one example of a hormone which inhibits growth. Its effects include wilting of leaves.

How are such chemical, or hormonal, means of information transmission used in animals? What do some animals, for instance squirrels, experience when they are in a scary situation? Their bodies have to prepare for either fighting or running away. Both are very complicated activities that will use a great deal of energy in controlled ways. Many different tissue types will be used and their activities integrated together in these actions. However, the two alternate activities, fighting or running, are also quite different! So here is a situation in which some common preparations can be usefully made in the body. These preparations should ideally make it easier to do either activity in the near future. How would this be achieved?

If the body design in the squirrel relied only on electrical impulses via nerve cells, the range of tissues instructed to prepare for the coming activity would be limited. On the other hand, if a chemical signal were to be sent as well, it would reach all cells of the body and provide the wideranging changes needed. This is done in many animals, including human beings, using a hormone called adrenaline that is secreted from the adrenal glands. Look at Fig. 7.7 to locate these glands.

Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation. Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body.

Remember that plants have hormones that control their directional growth. What functions do animal hormones perform? On the face of it, we cannot imagine their role in directional growth. We have never seen an animal growing more in one direction or the other, depending on light or gravity! But if we think about it a bit more, it will become evident that, even in animal bodies, growth happens in carefully controlled places. Plants will grow leaves in many places on the plant body, for example. But we do not grow fingers on our faces. The design of the body is carefully maintained even during the growth of children.

Let us examine some examples to understand how hormones help in coordinated growth. We have all seen salt packets which say ‘iodised salt’ or ‘enriched with iodine’. Why is it important for us to have iodised salt in our diet? Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck. Can you correlate this with the position of the thyroid gland in Fig. 7.7?

Sometimes we come across people who are either very short (dwarfs) or extremely tall (giants). Have you ever wondered how this happens? Growth hormone is one of the hormones secreted by the pituitary. As its name indicates, growth hormone regulates growth and development of the body. If there is a deficiency of this hormone in childhood, it leads to dwarfism. You must have noticed many dramatic changes in your appearance as well as that of your friends as you approached 10–12 years of age. These changes associated with puberty are because of the secretion of testosterone in males and oestrogen in females.

Do you know anyone in your family or friends who has been advised by the doctor to take less sugar in their diet because they are suffering from diabetes? As a treatment, they might be taking injections of insulin. This is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects.

If it is so important that hormones should be secreted in precise quantities, we need a mechanism through which this is done. The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the sugar levels in blood rise, they are detected by the cells of the pancreas which respond by producing more insulin. As the blood sugar level falls, insulin secretion is reduced.