CLASS 9 Science CHAPTER 2 Is Matter Around Us Pure ? (NCERT Solution)

CLASS 9 Science                                                                                                   

CHAPTER 2                                                                                                                         

Is Matter Around Us Pure ? (NCERT Solution)

Intext Questions

On Page 15

Question 1: What is meant by a pure substance?

Answer: Substance having single type of particles is known as pure substance. For example: Hydrogen, Water etc., are pure. Note: All elements and compounds are considered to be pure.

Question 2: List the points of differences between homogeneous and heterogeneous mixtures.

Answer: Homogeneous mixture

Its constituent’s particles cannot be seen easily.

There are no visible boundaries of separation in a homogeneous mixture.

Its constituents cannot be easily separated.

Examples: Alloys, solution of salt in water etc.

Heterogeneous mixture

Its constituent particles can be seen easily.

Have visible boundaries of separation between the constituents.

Its constituents can be separated by simple methods.

Examples: Mixture of sand and common salt, mixture of sand and water etc.

On Page 18

Question 1: Differentiate between homogeneous and heterogeneous mixture with example.

Answer: Homogeneous mixture

Its constituent’s particles cannot be seen easily.

There are no visible boundaries of separation in a homogeneous mixture.

Its constituents cannot be easily separated.

Examples: Alloys, solution of salt in water etc.

Heterogeneous mixture

Its constituent particles can be seen easily.

Have visible boundaries of separation between the constituents.

Its constituents can be separated by simple methods.

Examples: Mixture of sand and common salt, mixture of sand and water etc.

Questions 2: How are sol, solution and suspension different from each other?

Answer: Solution or true solution is homogeneous.

NO Tyndall effect.

Solute particles cannot be filtered by using a filter paper

True solution is transparent.

Examples: Sea water, alloys, solution of lemon juice in water etc.

Sol (colloidal solution) :

Sol or colloidal solution is heterogeneous.

Tyndall effect.

Cannot be separated by ordinary filter paper.

It may be transparent or translucent.

Examples: Milk of magnesia, cough syrup, mist, fog, clouds, smoke, mudetc.

Suspension :

Suspension is also heterogeneous.

Tyndall effect.

It may be transparent or translucent.

Separated easily by filter paper.(because of large particles)

Examples: Mixture of sand in water, mixture of chalk in water.

Question 3: To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

Answer: Mass of sodium chloride (solute) = 36 g

Mass of water (solvent) = 100 g

We know that, mass of solution = mass of solute + mass of solvent

= 36 g+ 100 g= 136 g

Concentration (mass percentage) of the solution = Mass of Solute/Mass of Solution x 100

=36g/136 g x 100 = 26.47%

On Page 24

Question 1: How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?

Answer: Simple distillation is the method which can separate the mixture of kerosene and petrol (b.p. differ by more than 25°C).

Method: In a distillation flask, a mixture of kerosene and petrol is taken as shown in figure. The mixture is heated slowly and the temperature is recorded with the help of thermometer. Petrol (b.p. = 70° C to 1200 ° C) vaporizes first and the temperature becomes constant for some time (till all petrol evaporates from the mixture). Vapours of petrol are condensed and collected in another container while the kerosene remains in the distillation flask. As soon as the temperature starts’ rising again, the heating is stopped and both the components are collected separately.

Question 2: Name the technique to separate

(i) Butter from curd

(ii) Salt from sea water

(iii) Camphor from salt

Answer: (i) By using centrifugation method, butter can be separated from curd.

(ii) By using evaporation method, salt from sea water can be separated . Water vaporises on evaporation leaving behind the salt.

(iii) Camphor from salt can be separated by sublimation method. On subliming camphor will be converted into vapour leaving behind the salt.

Question 3: What types of mixtures are separated by the technique of crystallisation?

Answer: Crystallisation method can be used for the purification of those mixtures which Contain insoluble and/or soluble impurities. Have crystalline nature. Cannot be separated by filtration as some impurities are soluble.

Question 4: Classify the following as chemical or physical changes

(a) Cutting of trees,

(b) Melting of butter in a pan,

(c) Rusting of almirah,

(d) Boiling of water to form steam,

(e) Passing of electric current, through water and the water breaking down into hydrogen and oxygen gases,

(f) Dissolving common salt in water,

(g) Making a fruit salad with raw fruits, and

(h) Burning of paper and wood

Answer: Physical Change :

Cutting of trees

Melting of butter in a pan

Boiling of water to form steam

Dissolving common salt in water

Making a fruit salad with raw fruits

Chemical Change :

Rusting of almirah.

Passing of electric current, through water and the water breaking down into hydrogen and oxygen gases.

Burning of paper and wood.

Question 5: Try segregating the things around you as pure substances or mixtures.

(a) Wood

(b) Coal

(c) Milk

(d) Sugar

(e) Common salt

(f) Soap

(g) Soil

(h) Rubber

Answer: (a) Mixture

(b) Mixture

(c) Mixture

(d) Pure substance

(e) Pure substance

(f) Compound/mixture

(g) Mixture

(h) Pure substance

Exercises

Question 1: Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from its solution in water.

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.

(c) Small pieces of metal in the engine oil of a car.

(d) Different pigments from an extract of flower petals.

(e) Butter from curd.

(f) Oil from water.

(g) Tea leaves from tea.

(h) Iron pins from sand.

(i) Wheat grains from husk.

(j) Fine mud particles suspended in water.

Answer: (a) Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography.

(e) centrifugal machine or churning the curd by hand.

(f) Decantation

(g) Filtration.

(h) Magnetic Separation.

(i) Winnowing.

(j) Coagulation and decantation:

Question 2: Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Answer: Method of preparation of tea

(i) Take some water (solvent) in a pan and heat it.

(ii) Add some sugar (solute) and boil to dissolve the sugar completely the obtained homogeneous mixture is called solution.

(iii) Add tea leaves (or tea) in the solution and boil the mixture.

(iv) Now add milk and boil again.

(v) Filter the mixture through the tea stainer and collect the filtrate or soluble substances, i.e., tea in a cup. The insoluble tea leaves left behind as residue in the 8 trainer.

Question 3: Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?

(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?

(d) What is the effect of change of temperature on the solubility of a salt?

Answer: (a) Mass of potassium nitrate needed to produce its saturated solution

in 100 g of water at 313 K = 62 g

Mass of potassium nitrate needed to produce its saturated solution in

50 g of water at 313

K = 62/100 x 50g = 31g

(b) Crystals of potassium chloride are formed. This happens as solubility of solid decreases with decreasing the temperature.

(c) Solubility of each salt at 293 K

Potassium nitrate 32 g per 100 g water

Sodium chloride 36 g per 100 g water

Potassium chloride 35 g per 100 g water

Ammonium chloride 37 g per 100 g water

Note: Solubility of a solid is that amount in gram which can be dissolved in 100 g of water (solvent) to make saturated solution at a particular temperature.

Ammonium chloride has the maximum solubility (37 g per 100 g of water) at 293 K.

(d) Solubility of a (solid) salt decreases with decrease in temperature while it increases with rise in temperature.

Question 4: Explain the following giving examples.

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) Suspension

Answer: (a) Saturated solution: A solution in which no more amount of solute can be dissolved at a particular temperature is called saturated solution. Example: when sugar is dissolved repeatedly in a given amount of water, a condition is reached at which further dissolution of sugar is not possible in that amount of water at room temperature.

(b) Pure substance: A substance made up of single type of particles (atoms and/or molecules) is called pure substance. All elements and compounds are said to be pure, Example: water, sugar etc.

(c) Colloid: A heterogeneous mixture in which the solute particle size is too small to be seen with the naked eye, but is big enough to scatter light is known as Colloid. There are two phases in colloidal solution

Dispersed phase: solute particles are said to be dispersed phase

Dispersion medium: the medium in which solute particles are spread is called the dispersion medium.

Example: Milk, clouds etc., are the example of colloid.

(d) Suspension: A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of suspension are visible to the naked eye. Example: Mixture of sand, Water and Muddy water etc.

Question 5: Classify each of the following as a homogeneous or heterogeneous mixture. Soda water, wood, air, soil, vinegar, filtered tea.

Answer: Homogeneous mixtures: Air, soda water, vinegar, filtered tea. Heterogeneous mixtures: Wood, soil,

Question 6: How would you confirm that a colorless liquid given to you is pure water?

Answer: If the given colorless liquid boils at 100°C sharp, it is pure water, otherwise not.

Question 7: Which of the following materials fall in the category of a "pure substance"?

(a) Ice (b) Milk (c) Iron (d) Hydrochloric acid (e) Calcium oxide (f) Mercury (g) Brick (h)Wood (i) Air

Answer: Ice, iron, calcium oxide, mercury are pure substance as they have definite composition.

Milk is a colloid, so it is a heterogeneous mixture. Hydrochloric acid is also a mixture of hydrogen chloride gas and water.

Question 8: Identify the solutions among the following mixtures.

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water

Answer: Sea water, air and soda water: Homogeneous mixture Coal, Soil: Heterogeneous solution.

Question 9: Which of the following will show "Tyndall effect"?

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution

Answer: Milk and starch solution will show "Tyndall effect" as both of these are colloids.

Question 10: Classify the following into elements, compounds and mixtures.

(a) Sodium (b) Soil (c) Sugar solution (d) Silver (e) Calcium carbonate (f) Tin (g) Silicon (h) Coal (i) Air (j) Soap (k) Methane (l) Carbon dioxide (m) Blood

Answer: Elements : Sodium, silver, tin and silicon

Compounds : Calcium carbonate, methane, and carbon dioxide

Mixtures : Soil, sugar solution, coal, air, soap and blood.

Question 11: Which of the following are chemical changes?

(a) Growth of a plant

(b) Rusting of iron

(c) Mixing of iron filings and sand

(d) Cooking of food

(e) Digestion of food

(f) Freezing of water

(g) Burning of a candle

Answer: Growth of a plant, rusting of iron, cooking of food, digestion of food, burning of a candle are chemical changes, because here the chemical composition of substance changes.

( From www.ncrtsolutions.in )

CLASS 9 Science CHAPTER 15 Improvement In Food Resources (NCERT Notes)

CLASS 9 Science 

CHAPTER 15 

Improvement In Food Resources ( NCERT Notes)

All living organisms need food. Food supplies proteins, carbohydrates, fats, vitamins and minerals, all of which we require for body development, growth and health. Both plants and animals are major sources of food for us. We obtain most of this food from agriculture and animal husbandry.

India is a very populous country. Our population is more than one billion people, and it is still growing. As food for this growing population, we will soon need more than a quarter of a billion tonnes of grain every year. This can be done by farming on more land. But India is already intensively cultivated. As

a result, we do not have any major scope for increasing the area of land under cultivation. Therefore, it is necessary to increase our production efficiency for both crops and livestock.

Simply increasing grain production for storage in warehouses cannot solve the problem of malnutrition and hunger. People should have money to purchase food. Food security depends on both availability of food and access to it. The majority of our population depends on agriculture for their livelihood. Increasing the incomes of people working in agriculture is therefore necessary to combat the problem of hunger. Scientific management practices should be undertaken to obtain high yields from farms.

Improvement in Crop Yields

Cereals such as wheat, rice, maize, millets and sorghum provide us carbohydrate for energy requirement. Pulses like gram (chana), pea (matar), black gram (urad), green gram (moong), pigeon pea (arhar), lentil (masoor), provide us with protein. And oil seeds including soyabean, ground nut, sesame, castor, mustard, linseed and sunflower provide us with necessary fats. Vegetables, spices and fruits provide a range of vitamins and minerals in addition to small amounts of proteins, carbohydrates and fats. In addition to these food crops, fodder crops like berseem, oats or sudan grass are raised

as food for the livestock.

Different crops require different climatic conditions, temperature and photoperiods for their growth and completion of their life cycle:

Photoperiods are related to the duration of sunlight. Growth of plants and flowering are dependent on sunlight. Plants manufacture their food in sunlight by the process of photosynthesis. There are some

crops, which are grown in rainy season, called the kharif season from the month of June to October. Some of the crops are grown in the winter season, called the rabi season from November to April. Paddy, soyabean, pigeon pea, maize, cotton, green gram and black gram are kharif crops, whereas wheat, gram, peas, mustard, linseed are rabi crops.

In India there has been a four times increase in the production of food grains from 1960 to 2004 with only 25% increase in the cultivable land area.

How has this increase in production been achieved?

We can divide it into three stages:

The first is the choice of seeds for planting. 

The second is the nurturing of the crop plants.

The third is the protection of the growing and harvested crops from loss. 

Major groups of activities for improving crop yields can be classified as:

• Crop variety improvement

• Crop production improvement

• Crop protection management.

CROP VARIETY IMPROVEMENT

Finding a crop variety that can give a good yield. Varieties or strains of crops can be selected by breeding for various useful characteristics such as disease resistance, response to fertilisers, product quality and high yields. 

Incorporating desirable characters into crop varieties is by hybridisation. Hybridisation refers to crossing between genetically dissimilar plants. This crossing may be intervarietal (between different varieties), interspecific (between two different species of the same genus) or intergeneric (between different genera). 

Improving the crop is by introducing a gene that would provide the desired characteristic. This results in genetically modified crops.

For new varieties of crops to be accepted, it is necessary that the variety produces high yields under different conditions that are found in different areas. Farmers would need to be provided with good quality seeds of a particular variety, that is, the seeds should all be of the same variety and germinate under the same conditions.

Cultivation practices and crop yield are related to weather, soil quality and availability of water. Since weather conditions such as drought and flood situations are unpredictable, varieties that can be grown in diverse climatic conditions are useful. Similarly, varieties tolerant to high soil salinity have been developed. 

Some of the factors for which variety improvement is done are:

Higher yield: To increase the productivity of the crop per acre.

Improved quality: Quality considerations of crop products vary from crop to crop. Baking quality is important in wheat, protein quality in pulses, oil quality in oilseeds and preserving quality in fruits and vegetables.

Biotic and abiotic resistance: Crops production can go down due to biotic (diseases, insects and nematodes) and abiotic (drought, salinity, water logging, heat, cold and frost) stresses under different situations. Varieties resistant to these stresses can improve crop production.

Change in maturity duration: The shorter the duration of the crop from sowing to harvesting, the more economical is the variety. Such short durations allow farmers to grow multiple rounds of crops in a year. Short duration also reduces the cost of crop production. Uniform maturity makes the harvesting process easy and reduces losses during harvesting.

Wider adaptability: Developing varieties for wider adaptability will help in stabilising the crop production under different environmental conditions. One variety can then be grown under different climatic conditions in different areas.

Desirable agronomic characteristics: Tallness and profuse branching are desirable characters for fodder crops. Dwarfness is desired in cereals, sothat less nutrients are consumed by these crops. Thus developing varieties of desired agronomic characters help give higher productivity. 

CROP PRODUCTION MANAGEMENT

In India, as in many other agriculture-based countries, farming ranges from small to very large farms. Different farmers thus have more or less land, money and access to information and technologies. In short, it is the money or financial conditions that allow farmers to take up different farming practices and agricultural technologies. There is a correlation between higher inputs and yields. Thus, the farmer’s purchasing capacity for inputs decides cropping system and production practices. Therefore, production practices can be at different levels. They include ‘no cost’ production, ‘low cost’ production and ‘high cost’ production practices.

(i) NUTRIENT MANAGEMENT

Plants require nutrients for growth. Nutrients are supplied to plants by air, water and soil. There are sixteen nutrients which are essential for plants. Air supplies carbon and oxygen, hydrogen comes from water, and soil supplies the other thirteen nutrients to plants. Amongst these thirteen nutrients.

Nutrient which are required in large quantities are called macro-nutrients. They are six in no. For example: nitrogen, phosphorus, potassium, calcium, magnesium, sulphur.

Nutrient which are required in small quantities are called micro-nutrients. They are seven in no. For example: iron, manganese, boron, zinc, copper, molybdenum, chlorine.

Deficiency of these nutrients affects physiological processes in plants including reproduction, growth and susceptibility to diseases. To increase the yield, the soil can be enriched by supplying these nutrients in the form of manure and fertilizers.

MANURE

Manure contains large quantities of organic matter and also supplies small quantities of nutrients to the soil. Manure is prepared by the decomposition of animal excreta and plant waste. Manure helps in enriching soil with nutrients and organic matter and increasing soil fertility. The bulk of organic matter in manure helps in improving the soil structure. This involves increasing the water holding capacity in sandy soils. In clayey soils, the large quantities of organic matter help in drainage and in avoiding water logging. Using manure we use biological waste material, which is advantageous in protecting our environment from excessive use of fertilizers. Or biological waste material is also a way of recycling farm waste. 

Based on the kind of biological material used, manure can be classified as:

(i) Compost and vermi-compost: The process in which farm waste material like livestock excreta (cow dung etc.), vegetable waste, animal refuse, domestic waste, sewage waste, straw, eradicated weeds etc. is decomposed in pits is known as composting. The compost is rich in organic matter and nutrients. Compost is also prepared by using earthworms to hasten the process of decomposition of plant and animal refuse. This is called vermi-compost.

(ii) Green manure: Prior to the sowing of the crop seeds, some plants like sun hemp or guar are grown and then mulched by ploughing them into the soil. These green plants thus turn into green manure which helps in enriching the soil in nitrogen and phosphorus.

FERTILIZERS

Fertilizers are commercially produced plant nutrients. Fertilizers supply nitrogen, phosphorus and potassium. They are used to ensure good vegetative growth (leaves, branches and flowers), giving rise to healthy plants. Fertilizers are a factor in the higher yields of high-cost farming. Fertilizers should be applied carefully in terms of proper dose, time, and observing pre- and post-application precautions for their complete utilisation. 

For example, sometimes fertilizers get washed away due to excessive irrigation and are not fully absorbed by the plants. This excess fertilizer then leads to water pollution.

Continuous use of fertilizers in an area can destroy soil fertility because the organic matter in the soil is not replenished and micro-organisms in the soil are harmed by the fertilizers used. Short-term benefits of using fertilizers and long-term benefits.

Organic farming is a farming system with minimal or no use of chemicals as fertilizers, herbicides, pesticides etc. and with a maximum input of organic manures, recycled farm-wastes (straw and livestock excreta), use of bio-agents such as culture of blue green algae in preparation of biofertilizers, neem leaves or turmeric specifically in grain storage as bio-pesticides, with healthy cropping systems. These cropping systems are beneficial in insect, pest and wheat control besides providing nutrients.

(ii) IRRIGATION

Most agriculture in India is dependent on timely monsoons and sufficient rainfall spread through most of the growing season. Hence, poor monsoons cause crop failure. Ensuring that the crops get water at the right stages during their growing season can increase the expected yields of any crop. Therefore, many measures are used to bring more and more agricultural land under irrigation.

Droughts occur because of scarcity or irregular distribution of rains. Drought poses a threat to rain-fed farming areas, where farmers do not use irrigation for crop production and depend only on rain. Light soils have less water retention capacity. In areas with light soils, crops get adversely affected by drought conditions. Scientists have developed some crop varieties which can tolerate drought conditions.

India has a wide variety of water resources and a highly varied climate. Under such conditions, several different kinds of irrigation systems are adopted to supply water to agricultural lands depending on the kinds of water resources available. These include wells, canals, rivers and tanks.

Wells: There are two types of wells, namely dug wells and tube wells. In a dug well, water is collected from water bearing strata. Tube wells can tap water from the deeper strata. From these wells, water is lifted by pumps for irrigation.

Canals: Canals receive water from one or more reservoirs or from rivers. The main canal is divided into branch canals having further distributaries to irrigate fields.

River Lift Systems: In areas where canal flow is insufficient or irregular due to inadequate reservoir release, the lift system is more rational. Water is directly drawn from the rivers for supplementing irrigation in areas close to rivers.

Tanks: These are small storage reservoirs, which intercept and store the run-off of smaller catchment

areas.

Fresh initiatives for increasing the water available for agriculture include rainwater harvesting and watershed management. This involves building small check-dams which lead to an increase in ground water levels. The check-dams stop the rainwater from flowing away and also reduce soil erosion.

(iii) CROPPING PATTERNS

Mixed cropping is growing two or more crops simultaneously on the same piece of land, for example, wheat + gram, or wheat + mustard, or groundnut + sunflower. This reduces risk and gives some insurance against failure of one of the crops.

Inter-cropping is growing two or more crops simultaneously on the same field in a definite pattern. A few rows of one crop alternate with a few rows of a second crop, for example, soyabean + maize, or finger millet (bajra) + cowpea (lobia). The crops are selected such that their nutrient requirements are different. This ensures maximum utilisation of the nutrients supplied, and also prevents pests and

diseases from spreading to all the plants belonging to one crop in a field. This way, both crops can give better returns.

The growing of different crops on a piece of land in a pre-planned succession is known as crop rotation. Depending upon the duration, crop rotation is done for different crop combinations. The availability of

moisture and irrigation facilities decide the choice of the crop to be cultivated after one harvest. If crop rotation is done properly then two or three crops can be grown in a year with good harvests.

CROP PROTECTION MANAGEMENT

Field crops are infested by a large number of weeds, insect pests and diseases. If weeds and pests are not controlled at the appropriate time then they can damage the crops so much that most of the crop is lost. Weeds are unwanted plants in the cultivated field, for example, Xanthium (gokhroo), Parthenium (gajar ghas), Cyperinus rotundus (motha). They compete for food, space and light. Weeds take up

nutrients and reduce the growth of the crop. Therefore, removal of weeds from cultivated fields during the early stages of crop growth is essential for a good harvest.

Generally insect pests attack the plants in three ways: (i) they cut the root, stem and leaf, (ii) they suck the cell sap from various parts of the plant, and (iii) they bore into stem and fruits. They thus affect the health of the crop and reduce yields.

Diseases in plants are caused by pathogens such as bacteria, fungi and viruses. These pathogens can be present in and transmitted through the soil, water and air. Weeds, insects and diseases can be

controlled by various methods. 

Most commonly used methods is the use of pesticides, which include herbicides, insecticides and fungicides. These chemicals are sprayed on crop plants or used for treating seeds and soil. However, excessive use of these chemicals creates problems, since they can be poisonous to many plant and animal species and cause environmental pollution.

Weed control methods also include mechanical removal. Preventive methods such as proper seed bed preparation, timely sowing of crops, intercropping and crop rotation also help in weed control. Some other preventive measures against pests are the use of resistant varieties, and summer ploughing,

in which fields are ploughed deep in summers to destroy weeds and pests.

STORAGE OF GRAINS

Storage losses in agricultural produce can be very high. Factors responsible for such losses are biotic— insects, rodents, fungi, mites and bacteria, and abiotic— inappropriate moisture and temperatures in the place of storage. These factors cause degradation in quality, loss in weight, poor germinability,

discolouration of produce, all leading to poor marketability. These factors can be controlled by proper treatment and by systematic management of warehouses.

Preventive and control measures are used before grains are stored for future use. They include strict cleaning of the produce before storage, proper drying of the produce first in sunlight and then in shade, and fumigation using chemicals that can kill pests.

Animal Husbandry

Animal husbandry is the scientific management of animal livestock. It includes various aspects such as feeding, breeding and disease control. Animal-based farming includes cattle, goat, sheep, poultry and fish farming. 

As the population increases and as living standards increase, the demand for milk, eggs and meat is also going up. Also, the growing awareness of the need for humane treatment of livestock has brought

in new limitations in livestock farming. Thus, livestock production also needs to be improved.

CATTLE FARMING

Cattle husbandry is done for two purposes- milk and draught labour for agricultural work such as tilling, irrigation and carting. Indian cattle belong to two different species, Bos indicus , cows, and Bos bubalis, buffaloes.

Milk-producing females are called milch animals (dairy animals), while the ones used for farm labour are called draught animals. Milk production depends, to some extent, on the duration of the lactation period, meaning the period of milk production after the birth of a calf. So, milk production can be

increased by increasing the lactation period. Exotic or foreign breeds (for example, Jersey, Brown Swiss) are selected for long lactation periods, while local breeds (for example, Red Sindhi, Sahiwal) show excellent resistance to diseases. The two can be cross-bred to get animals with both the desired qualities.

Proper cleaning and shelter facilities for cows and buffaloes are required for humane farming, for the health of the animals and for production of clean milk as well. Animals require regular brushing to remove dirt and loose hair. They should be sheltered under well-ventilated roofed sheds that protect them from rain, heat and cold. The floor of the cattle shed needs to be sloping so as to stay dry

and to facilitate cleaning.

The food requirements of dairy animals are of two types: (a) maintenance requirement, which is the food required to support the animal to live a healthy life, and (b) milk producing requirement, which is the type of food required during the lactation period. Animal feed includes: (a) roughage, which is largely fibre, and (b) concentrates, which are low in fibre and contain relatively high levels of proteins and other nutrients.

Cattle need balanced rations containing all nutrients in proportionate amounts. Besides such nutritious food material, certain feed additives containing micronutrients promote the health and milk output of dairy animals.

Cattle suffer from a number of diseases. The diseases, besides causing death, reduce milk production. A healthy animal feeds regularly and has a normal posture. The parasites of cattle may be both external

parasites and internal parasites. The external parasites live on the skin and mainly cause skin diseases. The internal parasites like worms, affect stomach and intestine while flukes damage the liver. Infectious diseases are also caused by bacteria and viruses. Vaccinations are given to farm animals against many major viral and bacterial diseases.

POULTRY FARMING

Poultry farming is to raise domestic fowl for egg production and chicken meat. Therefore, improved poultry breeds are developed and farmed to produce layers for eggs and broilers for meat. The cross-breeding programmes between Indian (indigenous, for example, Aseel) and foreign (exotic, for example, Leghorn) breeds for variety improvement to develop new varieties for the following :

(i) number and quality of chicks;

(ii) dwarf broiler parent for commercial chick production;

(iii) summer adaptation capacity/ tolerance to high temperature;

(iv) low maintenance requirements;

(v) reduction in the size of the egg-laying bird with ability to utilise more fibrous cheaper diets formulated using agricultural by-products.

EGG AND BROILER PRODUCTION

Broiler chickens are fed with vitamin-rich supplementary feed for good growth rate and better feed efficiency. Care is taken to avoid mortality and to maintain feathering and carcass quality. They are produced as broilers and sent to market for meat purposes.

For good production of poultry birds, good management practices are important. These include maintenance of temperature and hygienic conditions in housing and poultry feed, as well as prevention and control of diseases and pests. The housing, nutritional and environmental requirements of broilers are somewhat different from those of egg layers.

The ration (daily food requirement) for broilers is protein rich with adequate fat. The level of vitamins A and K is kept high in the poultry feeds.

Poultry fowl suffer from a number of diseases caused by virus, bacteria, fungi, parasites, as well as from nutritional deficiencies. These necessitate proper cleaning, sanitation, and spraying of

disinfectants at regular intervals. Appropriate vaccination can prevent the occurrence of infectious diseases and reduce loss of poultry during an outbreak of disease.

FISH PRODUCTION

Fish is a cheap source of animal protein for our food. Fish production includes the finned true fish as well as shellfish such as prawns and molluscs. There are two ways of obtaining fish. One is from natural resources, which is called capture fishing. The other way is by fish farming, which is called culture fishery.

The water source of the fish can be either seawater or fresh water, such as in rivers and ponds. Fishing can thus be done both by capture and culture of fish in marine and freshwater ecosystems.

(i) MARINE FISHERIES

India’s marine fishery resources include 7500 km of coastline and the deep seas beyond it. Popular marine fish varieties include pomphret, mackerel, tuna, sardines, and Bombay duck. Marine fish are caught using many kinds of fishing nets from fishing boats, using satellites and echo-sounders.

Some marine fish of high economic value are also farmed in seawater. This includes finned fishes like mullets, bhetki, and pearl spots, shellfish such as prawns , mussels and oysters as well as seaweed.

Oysters are also cultivated for the pearls they make. 

(ii) INLAND FISHERIES 

Fresh water resources include canals, ponds, reservoirs and rivers. Brackish water resources, where seawater and fresh water mix together, such as estuaries and lagoons are also important fish reservoirs. 

Most fish production from these resources is through aquaculture. Fish culture is sometimes done in

combination with a rice crop, so that fish are grown in the water in the paddy field. 

More intensive fish farming can be done in composite fish culture systems. In such a system, a combination of five or six fish species is used in a single fishpond. These species are selected so that they do not compete for food among them having different types of food habits. As a result, the

food available in all the parts of the pond is used. As Catlas are surface feeders, Rohus feed in the middle-zone of the pond, Mrigals and Common Carps are bottom feeders, and Grass Carps feed on the weeds, together these species can use all the food in the pond without competing with each other. This

increases the fish yield from the pond.

Major problem with such composite fish culture is that many of these fish breed only during monsoon. Even if fish seed is collected from the wild, it can be mixed with that of other species as well. So, a major problem in fish farming is the lack of availability of good- quality seed. To overcome this problem now breed these fish in ponds is carried out by using hormonal stimulation. This has ensured the supply of pure fish seed in desired quantities.

BEE-KEEPING

Raring or catching of bee is called bee- keeping or Apic culture. Honey is widely used and obtained from bees. Bee- keeping for making honey has become an agricultural enterprise. Bee-keeping needs low investments, farmers use it as an additional income generating activity. In addition to honey, the beehives are a source of wax which is used in various medicinal preparations.

Varieties of bees used for commercial honey production are Apis cerana indica, commonly known as the Indian bee, A. dorsata, the rock bee and A. florae, the little bee. An Italian bee variety, A. mellifera  ,has also been brought in to increase yield of honey. This variety commonly used for  commercial honey production. The Italian bees have high honey collection capacity. They sting somewhat less. They stay in a given beehive for long periods, and breed very well. The value or quality of honey depends upon the pasturage, or the flowers available to the bees for nectar and pollen collection.

In addition to adequate quantity of pasturage, the kind of flowers available will determine the taste of the honey.

( From NCERT Book )

CLASS 9 Science CHAPTER 14 Natural Resources (NCERT Notes)

CLASS 9 Science               

CHAPTER 14                                                                                                                          

Natural Resources (NCERT Notes) 

Earth is the only planet on which life exists. Life on Earth is dependent on many factors. Most life-forms need an ambient temperature, water, and food. The resources available on the Earth and the energy from the Sun are necessary to meet the basic requirements of all life-forms on the Earth.

What are these resources on the Earth?

These are the land, the water and the air. The outer crust of the Earth is called the lithosphere. Water covers 75% of the Earth’s surface. It is also found underground. These comprise the hydrosphere. The air that covers the whole of the Earth like a blanket, is called the atmosphere. Living things are found where these three exist. This life-supporting zone of the Earth where the atmosphere, the  hydrosphere and the lithosphere interact and make life possible, is known as the biosphere. Living      things constitute the biotic component of the biosphere. The air, the water and the soil form the non-living or abiotic component of the biosphere.

The Breath of Life: Air

 Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour. It is interesting to note that even the composition of air is the result of life on Earth. In planets such as Venus and Mars, where no life is known to exist, the major component of the atmosphere is found to be carbon dioxide. Carbon dioxide constitutes up to 95-97% of the atmosphere on Venus and Mars.

Eukaryotic cells and many prokaryotic cells need oxygen to break down glucose molecules and get energy for their activities. This results in the production of carbon dioxide. Another process which results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion. This includes not just human activities, which burn fuels to get energy, but also forest fires. 

Despite this, the percentage of carbon dioxide in our atmosphere is a mere fraction of a percent because carbon dioxide is ‘fixed’ in two ways: (i) Green plants convert carbon dioxide into glucose in the presence of Sunlight and (ii) many marine animals use carbonates dissolved in sea-water to make their shells.

ROLE OF THE ATMOSPHERE IN CLIMATE CONTROL

Atmosphere covering the Earth, like a blanket. We know that air is a bad conductor of heat. The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year. The atmosphere prevents the sudden increase in temperature during the daylight hours. And during the night, it slows down the escape of heat into outer space. 

Moon which is about the same distance from the Sun that the Earth is. Despite that, on the surface of the moon, with no atmosphere, the temperature ranges from –190° C to 110° C. 

MOVEMENT OF AIR: WINDS

Changes that take place in our atmosphere due to the heating of air and the formation of water vapour. Water vapour is formed due to the heating of water bodies and the activities of living organisms. The atmosphere can be heated from below by the radiation that is reflected back or re-radiated by the land or water bodies. On being heated, convection currents are set up in the air.

When air is heated by radiation from the heated land or water, it rises. But since land gets heated faster than water, the air over land would also be heated faster than the air over water bodies.

In coastal regions during the day, the air above the land gets heated faster and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land.

At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land.

The movements of air resulting in diverse atmospheric phenomena are caused by the uneven heating of the atmosphere in different regions of the Earth. But various other factors also influence these winds – the rotation of the Earth and the presence of mountain ranges in the paths of the wind.

RAIN 

When water bodies are heated during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it. As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function.

Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain. Sometimes, when the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.

Rainfall patterns are decided by the prevailing wind patterns. In large parts of India, rains are mostly brought by the south- west or north-east monsoons. We have also heard weather reports that say ‘depressions’ in the Bay of Bengal have caused rains in some areas.

AIR POLLUTION

The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur. Not only is the inhalation of these gases dangerous, they also dissolve in rain to give rise to acid rain. The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons. Presence of high levels of all these pollutants cause visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution. 

Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases. An increase in the content of these harmful substances in air is called air pollution.

Water: A Wonder Liquid

Water occupies a very large area of the Earth’s surface and is also found underground. Some amount of water exists in the form of water vapour in the atmosphere. Most of the water on Earth’s surface is found in seas and oceans and is saline. Fresh water is found frozen in the ice-caps at the two poles and on snow-covered mountains. The underground water and the water in rivers, lakes and ponds is also fresh. However, the availability of fresh water varies from place to place. Most places have to face a shortage of water.

Why is water so necessary? And do all organisms require water?

All cellular processes take place in a water medium. All the reactions that take place within our body and within the cells occur between substances that are dissolved in water. Substances are also transported from one part of the body to the other in a dissolved form. Hence, organisms need to maintain the level of water within their bodies in order to stay alive. Terrestrial life-forms require fresh water for this because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water.

WATER POLLUTION

Water dissolves the fertilisers and pesticides that we use on our farms. So some percentage of these substances are washed into the water bodies. Sewage from our towns and cities and the waste from factories are also dumped into rivers or lakes. Specific industries also use water for cooling in various operations and later return this hot water to water-bodies.

Another manner in which the temperature of the water in rivers can be affected is when water is released from dams. The water inside the deep reservoir would be colder than the water at the surface which gets heated by the Sun. 

All this can affect the life-forms that are found in these water bodies in various ways. It can encourage the growth of some life-forms and harm some other life-forms. This affects the balance between various organisms which had been established in that system. So we use the term water-pollution to cover the following effects:

1. The addition of undesirable substances to water -bodies. These substances could be the fertilisers and

pesticides used in farming or they could be poisonous substances, like mercury salts which are used by

paper-industries. These could also be disease-causing organisms, like the bacteria which cause cholera.

2. The removal of desirable substances from water-bodies. Dissolved oxygen is used by the animals and plants that live in water. Any change that reduces the amount of this dissolved oxygen would adversely affect these aquatic organisms. Other nutrients could also be depleted from the water bodies.

3. A change in temperature. Aquatic organisms are used to a certain range of temperature in the water -body where they live, and a sudden marked change in this temperature would be dangerous for them or affect their breeding. The eggs and larvae of various animals are particularly susceptible to temperature changes. 

What is the soil and how is it formed?

The outermost layer of our Earth is called the crust and the minerals found in this layer supply a variety of nutrients to life-forms. But these minerals will not be available to the organisms if the minerals are bound up in huge rocks. Over long periods of time, thousands and millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical and some biological processes. The end product of this breaking down is the fine particles of soil. 

What are the factors or processes that make soil?

•The Sun: The Sun heats up rocks during the day so that they expand. At night, these rocks cool down and contract. Since all parts of the rock do not expand and contract at the same rate, this results in the formation of cracks and ultimately the huge rocks break up into smaller pieces.

•Water: Water helps in the formation of soil in two ways. One, water could get into the cracks in the rocks formed due to uneven heating by the Sun. If this water later freezes, it would cause the cracks to widen. Two flowing water wears away even hard rock over long periods of time. Fast flowing water often carries big and small particles of rock downstream. These rocks rub against other rocks and the resultant abrasion causes the rocks to wear down into smaller and smaller particles. The water then takes these particles along with it and deposits it further down its path. Soil is thus found in places far away from its parent-rock.

•Wind: In a process similar to the way in which water rubs against rocks and wears them down, strong winds also erode rocks down. The wind also carries sand from one place to the other like water does.

•Living organisms also influence the formation of soil. The lichen that grows on the surface of rocks. While growing, they release certain substances that cause the rock surface to powder down and form a thin layer of soil. Other small plants like moss, are able to grow on this surface now and they cause the rock to break up further. The roots of big trees sometimes go into cracks in the rocks and as the roots grow bigger, the crack is forced bigger.

Soil is a mixture. It contains small particles of rock (of different sizes). It also contains bits of decayed living  organisms which is called humus. In addition, soil also contains various forms of microscopic life. The type of soil is decided by the average size of particles found in it and the quality of the soil is decided by the amount of humus and the microscopic organisms found in it. Humus is a major

factor in deciding the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground. The mineral nutrients that are found in a particular soil depends on the rocks it was formed from. The nutrient content of a soil, the amount of humus present in it and the depth of the soil are some of the factors that decide which plants will thrive on that soil. 

The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil. The quality of the topsoil is an important factor that decides biodiversity in that area. Modern farming practices involve the use of large amounts of fertilizers and pesticides. Use of these substances over long periods of time can destroy the soil structure by killing the soil micro-organisms that recycle nutrients in the soil. It also kills the Earthworms which are instrumental in

making the rich humus. Fertile soil can quickly be turned barren if sustainable practices are not followed. Removal of useful components from the soil and addition of other substances, which adversely affect the fertility of the soil and kill the diversity of organisms that live in it, is called soil pollution.

The soil that we see today in one place has been created over a very long period of time. However, some of the factors that created the soil in the first place and brought the soil to that place may be responsible for the removal of the soil too. The fine particles of soil may be carried away by flowing water or wind. If all the soil gets washed away and the rocks underneath are exposed, we have

lost a valuable resource because very little will grow on the rock. 

The roots of plants have an important role in preventing soil erosion. The large-scale deforestation that is happening all over the world not only destroys biodiversity, it also leads to soil erosion. Topsoil that is bare of vegetation, is likely to be removed very quickly. And this is accelerated in hilly or

mountainous regions. This process of soil erosion is very difficult to reverse. Vegetative cover on the ground has a role to play in the percolation of water into the deeper layers too. 

Biogeochemical Cycles

A constant interaction between the biotic and abiotic components of the biosphere makes it a dynamic, but stable system. These interactions consist of a transfer of matter and energy between the different components of the biosphere. 

THE WATER-CYCLE 

The water evaporates from the water bodies and subsequent condensation of this water vapour leads to rain. Or The whole process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as the water-cycle.

All of the water that falls on the land does not immediately flow back into the sea. Some of it seeps into the soil and becomes part of the underground reservoir of fresh-water. Some of this underground water finds its way to the surface through springs. Or we bring it to the surface for our use through wells or tube- wells. Water is also used by terrestrial animals and plants for various life-processes.

Water is capable of dissolving a large number of substances. As water flows through or over rocks containing soluble minerals, some of them get dissolved in the water. Thus rivers carry many nutrients from the land to the sea, and these are used by the marine organisms. 

THE NITROGEN-CYCLE

Nitrogen gas makes up 78% of our atmosphere and nitrogen is also a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and some vitamins. Nitrogen is found in other  biologically important compounds such as alkaloids and urea too. Nitrogen is an essential nutrient for all life-forms and life would be simple if all these life-forms could use the atmospheric nitrogen directly.

Few forms of bacteria life-forms are not able to convert the comparatively inert nitrogen molecule into

forms like nitrates and nitrites which can be taken up and used to make the required molecules. These ‘nitrogen-fixing’ bacteria may be free-living or be associated with some species of dicot plants. 

Most commonly, the nitrogen-fixing bacteria are found in the roots of legumes (generally the plants which give us pulses) in special structures called root- nodules. 

Nitrogen molecule is converted to nitrates and nitrites is by a physical process. During lightning, the high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilised by various life- forms.

Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins. Some other biochemical pathways are used to make the other complex compounds containing

nitrogen. These proteins and other complex compounds are subsequently consumed by animals. Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites. A different type of bacteria converts the nitrates and nitrites into elemental

nitrogen. Thus, there is a nitrogen-cycle in nature in which nitrogen passes from its elemental form in the atmosphere into simple molecules in the soil and water, which get converted to more complex molecules in living beings and back again to the simple nitrogen molecule in the atmosphere.

CARBON-CYCLE

Carbon is found in various forms on the Earth. It occurs in the elemental form as diamonds and graphite. In the combined state, it is found as carbon dioxide in the atmosphere, as carbonate and hydrogen- carbonate salts in various minerals, while all life-forms are based on carbon-containing

molecules like proteins, carbohydrates, fats, nucleic acids and vitamins. 

The endoskeletons and exoskeletons of various animals are also formed from carbonate salts. Carbon is incorporated into life-forms through the basic process of photosynthesis which is performed in the presence of Sunlight by all life-forms that contain chlorophyll. This process converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules. These glucose molecules are either converted into other substances or used to provide energy for the synthesis of other biologically  important molecules.

The utilisation of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide. This carbon dioxide then goes back into the atmosphere. Another process that adds to the carbon dioxide in the atmosphere

is the process of combustion where fuels are burnt to provide energy for various needs like heating, cooking, transportation and industrial processes. In fact, the percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started

burning fossil fuels on a very large scale. Carbon, like water, is thus cycled repeatedly through different forms by the various physical and biological activities.

THE GREENHOUSE EFFECT

Heat is trapped by glass as the temperature inside a glass enclosure will be much higher than the surroundings. This phenomenon was used to create an enclosure where tropical plants could be kept warm during the winters in colder climates. Such enclosures are called greenhouses

Some gases prevent the escape of heat from the Earth. An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase world-wide and this is called the greenhouse effect. Carbon dioxide is one of the greenhouse gases. An increase in the carbon dioxide content in the atmosphere would cause more heat to be retained by the atmosphere and lead to global warming. 

OXYGEN-CYCLE

Oxygen is a very abundant element on our Earth. It is found in the elemental form in the atmosphere to the extent of 21%. It also occurs extensively in the combined form in the Earth’s crust as well as also in the air in the form of carbon dioxide. In the crust, it is found as the oxides of most metals and silicon, and also as carbonate, sulphate, nitrate and other minerals. It is also an essential component of most biological molecules like carbohydrates, proteins, nucleic acids and fats (or lipids).

Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process,

that is, photosynthesis. 

Some forms of life, especially bacteria are poisoned by elemental oxygen. In fact, even the process of nitrogen-fixing by bacteria does not take place in the presence of oxygen. 

Ozone Layer

Elemental oxygen is normally found in the form of a diatomic molecule. However, in the upper reaches of the atmosphere, a molecule containing three atoms of oxygen is found. This would mean a formula of O3 and this is called ozone. Unlike the normal diatomic molecule of oxygen, ozone is poisonous and

we are lucky that it is not stable nearer to the Earth’s surface. 

Function of ozone layer: It absorbs harmful radiations from the Sun. This prevents those harmful radiations from reaching the surface of the Earth where they may damage many forms of life.

Recently it was discovered that this ozone layer was getting depleted. Various man-made compounds like CFCs (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process) were found to persist in the atmosphere. Once they reached the ozone layer, they would react with the ozone molecules. This resulted in a reduction of the ozone layer and recently they have discovered a hole in the ozone layer above the Antartica.

( From NCERT Book )