Lecture 7: CLASS VIII: SCIENCE: CHAPTER 2: CLASSIFICATION OF MICRO-ORGANISMS

Class VIII: SCIENCE:

                       Notes prepared by Subhankar Karmakar

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Micro-organisms: some of them are bad, but some of them are good too.

Those organisms which are too small to be seen without a microscope are called micro-organisms. Some of the microorganisms are useful to us, but some of the micro-organisms are harmful to us. 

Good micro-organisms:

For example, the microorganisms by certain bacteria help in making food products such as curd and cheese. Microorganisms are are also useful in making bread, cakes, pastries, alcohol, acetic acid or vinegar and medicines called antibiotics. 

Bad Micro-organisms;

On the other hand, the microorganisms like certain bacteria and fungi make our food rotten. The Microorganisms also caused diseases in humans, other animals and plants. The diseases like common cold, malaria, skin infections, typhoid, tuberculosis, tetanus, cholera, measles, chicken pox, smallpox, AIDS and of course covid-19 are all caused by the action of various types microorganisms.

Major groups of microorganisms:

Microorganisms are classified into 5 major groups. This groups are: 

1. Bacteria  

2. Viruses  

3. Protozoa

4. Fungi

5. Algae

Cellular structure of microorganisms: 

Some microorganisms are unicellular or single celled where as many microorganisms are multicellular or multi celled. 

1. Bacteria:

Bacteria are very small, single celled microorganisms which have cell walls but do not have an organised nucleus and other structures. They come in various shapes like spherical bacteria, rod shaped bacteria, and spiral bacteria. 

Example: Beneficial bacteria: 

Lactobacillus bacteria, which are useful for making foods like curd and Rhizobium bacteria which help in nitrogen fixation and decomposition of organic waste matter.

Harmful bacteria: Diseases like cholera, typhoid, tuberculosis or TB, diphtheria, whooping cough and food poisoning all are caused by actions of bacteria.

2. Viruses: 

Viruses are the smallest microorganisms which can develop only inside the cells of the host organisms. They are neither alive nor dead. They are not exactly living things.

Viruses can reproduce and multiply only inside the cells of other organisms like animal cells plant cells or bacteria cells.

Viruses are the agents of disease. The human diseases such as common cold, influenza, measles, polio, chicken pox, HIV, smallpox and covid-19 are all caused by viruses.

3. Protozoa: 

Protozoa are a group of single celled microorganisms which are classified as animals.

They are found in lakes, ponds, dirty water drains, sea water and damp soil. 

Some common examples of protozoa are:

Paramecium, Entamoeba and Plasmodium. 

Protozoa can be parasites also. 

Diseases caused by protozoa: 

• Entamoeba is a protozoan which causes a disease known as amoebic dysentery. 

• Plasmodium is a protozoan which causes a disease called malaria. Plasmodium is also known as Malarial Parasite.

4. Algae: 

Algae is a large group of simple plant like organisms. Like plants, they contain chlorophyll and produce food by photosynthesis.

Example:  Chlamydomonas, Spirogyra, blue green algae, Diatoms are example of algae.

Blue green algae have the ability to fix nitrogen gas of atmosphere.

5. Fungi:

Fungi are a  large group of organisms which do not have chlorophyll and do not photosynthesize. 

Some examples of fungi are: Yeast, Moulds like penicillium and aspergillus, mushrooms, toadstools, puffballs.

All fungi are made up of fine threads called hyphae except Yeast. 

Some of the human diseases caused by fungi are ringworm and athlete's foot. 

Lecture- 6: CLASS VIII : SCIENCE: CHAPTER- 1 : STORAGE

VIII-SCIENCE

Prepared By Subhankar Karmakar

7. STORAGE OF FOOD GRAINS

The fresh food grains (like wheat) obtained by the harvesting of crops contain more moisture than required for their safe storage. So, the food grains (like wheat) obtained by harvesting the crops are dried in the sunshine before storing, to reduce their moisture. It is necessary to reduce the moisture content of grains before storing to prevent their spoilage during storage.

 This is because the higher moisture content in food grains promotes the growth of fungus and mould on the stored grains which damages them (and makes them lose their germination capacity). 

The farmers store the dried food grains at home in metal bins (metal drums) and jute bags (called gunny bags). Dried neem leaves are used for storing food grains at home. For example, when wheat is stored at home in iron drums, then some dried been leaves are put on it. Dry been leaves protect the stored food grains from pests such as insects and micro-organisms. 

The large scale storage of food grains ( like wheat and rice) is done in two ways:

(a) in gunny bags, and

(b) in grain silos ( bulk storage of food grains)

FOOD FROM ANIMALS:

The food provided by animals consists of Milk, Eggs and Meat.

The animals which provide us food are mainly of two types:

(a) Milk yielding animals,

(b) Meat and Egg yielding animals.

Examples of milk yielding animals:

Cow, Buffalo and Goat

Examples of meat and egg yielding animals are: Goat, Sheep, Fish and Poultry.

ANIMAL HUSBANDRY:

The branch of agriculture which deals with the feeding, shelter, health and breeding of domestic animals is called animal husbandry.

The various practices necessary for raising animals for food and other purposes (or the elements of animal husbandry) are :

1. Proper feeding of animals,

2. Proper shelter for animals,

3. Prevention and cure of animal diseases, and

4. Proper breeding of animals.

FISH AS FOOD:

Fish is an important source of animal food. Many people living in the coastal areas (sea-side areas) consume fish as a major part of their diet. Fish is rich in proteins. It is a highly nutritious and easily digestible food. Fish liver oil is rich in vitamin A and vitamin D. For example, Cod liver oil (or Cod fish liver oil) is rich in vitamin A and vitamin D.

Lecture 5: CLASS VIII: SCIENCE: CHAPTER 1: HARVESTING

CLASS-VIII; SCIENCE

Prepared by Subhankar Karmakar

6. HARVESTING:

The cutting and gathering of the matured food crop is called harvesting. 

MANUAL HARVESTING:

In harvesting, the crops like wheat or rice are cut close to the ground by hand using a cutting tool called sickle and this is called manual harvesting.

MACHINE HARVESTING:

In large fields, wheat and paddy crops are cut by a motorised machine called harvester.

THRESHING:

After harvesting the crop, the grains are separated from the harvested crops. The process of beating out the grains from the harvested crops plants is called threshing. It can be done manually as well as with the help of a motorised machine called thresher.

WINNOWING: 

The process of threshing brings out grains from the cut and dried crop plants, but this grain is mixed with chaff ( outer inedible covering of grain) and hay. The process of separating grain from chaff and hay with the help of wind is called winnowing.

COMBINE: 

A combine is a large machine which cuts the standing cereal crop in the fields, threshes it, and separates the chaff from grain in one operation.

Lecture-4: CLASS VIII: SCIENCE: CHAPTER -1: WEEDS

CLASS-VIII; SCIENCE

Prepared by Subhankar Karmakar

5) REMOVING THE WEEDS OR WEEDING

Weeds: The unwanted plants or wild plants which grow along with a cultivated crop are called weeds. Like some of the common weeds found in wheat and rice fields are:

(a) Wild oat 

(b) Grass

(c) Amaranthus

(d) Chenopodium

HARMFUL EFFECTS OF WEEDS:

The growth of weeds in the fields is harmful because 

(i) they consume a lot of fertilisers, water, sunlight and space, meant for the crops plants, 

(ii) weeds reduce the crop yield and lower the quality of food grains,

(iii) some weeds are poisonous for human beings and animals,

(iv) some weeds interfere in harvesting.

WEEDING: 

The process of removing weeds from a crop field is called weeding. 

VARIOUS METHODS OF WEEDING:

(a) Removal of weeds by pulling them out with hand.

(b) Removal of weeds by using a trowel ( khurpa)

(c) Destroying the weeds by spraying special chemicals called weedicides.

WEEDICIDES: 

The poisonous chemicals which are used to kill weeds in the fields are called weedicides.  Some of the common weedicides are: 2,4-D, MCPA, Butachlor. 

Lecture 3: CLASS-VIII: SCIENCE: CHAPTER 1: MANURE & FERTILIZER

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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SCIENCE: CLASS VIII CBSE (CLASS NOTES)

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Lecture 3: 

ADDING MANURE AND FERTILISERS

1. NEED OF MANURE & FERTILISERS

Repeated growing of crops in the same field removes a lot of precious mineral elements, organic matter and other materials from the soil. The deficiency of plant nutrients and organic matter in the soil is made up by adding manures and fertilisers to the soil.

2. MANURES: 

Manure is a natural fertiliser. A manure is a natural substance obtained by the decomposition of animal wastes like cow-dung, human wastes and plant residues, which supplies essential elements and humus to the soil and makes it more fertile.

3. PREPARATION OF MANURES: 

Manures are prepared from animal wastes, human wastes and plant residues by the action of micro- organisms. In order to prepare manure, farmer dump animal wastes and plant wastes in pits at open places and allow it to decompose slowly. The decomposition is carried out by some micro-organisms. The decomposed animal and plant matter is used as organic manure.

4. FUNCTION OF MANURES:

Manures provide a lot of organic matter like humus to the soil. A manure improves the soil texture for better retention of water and aeration. 

5. CHEMICAL FERTILISERS:

A chemical fertiliser is a salt or an organic compound containing the necessary plant nutrients like nitrogen, phosphorus or potassium, to make the soil more fertile. A chemical fertiliser is rich in a particular plant nutrients such as nitrogen, phosphorus or potassium (NPK). Some examples of chemical fertilisers are Urea, Ammonium sulphate, Superphosphate, Potash and NPK.

6. DIFFERENCES BETWEEN MANURES AND FERTILISERS: 

1. A manure is a natural substance obtained by the decomposition of animal wastes like cow dung, human waste and plant residue. 

But a fertilizer is a salt or an organic compound.

2. Manure is not very rich in essential plant nutrients like nitrogen, phosphorus and potassium where as fertilizers are very rich in plant nutrients like nitrogen, phosphorus and potassium.

3. A manure provides a lot of organic matter like humus to the soil but a fertilizer does not provide any humus to the soil.

4. A manure is absorbed slowly by the plants because it is not much soluble in water but being soluble in water if fertilizer is readily absorbed by the plants.

5. Menure can be prepared in the field but fertilizers are prepared in factories.

7. ADVANTAGES OF MANURE:

Organic manure is considered better than Fertilisers because of the following reasons:

1. Manure enhances the water holding capacity of the soil.

2. Manure makes the soil porous due to which the exchange of gases becomes easy.

3. Manure increases the number of useful microbes in the soil.

4. Manure improves the texture of the soil.

8. LEGUMINOUS CROPS:

The pulses, peas, beans, groundnut, gram and clover are called leguminous crops. Leguminous crops have the ability to fix atmospheric nitrogen to form nitrogen compounds. The planting of leguminous crops in a field has the same effect as adding nitrogenous fertiliser in the field.

9. CROP ROTATION:

The practice in which different types of crops like leguminous crops and non-leguminous crops are grown in the same field or soil is called crop rotation. In crop rotation, cereal crops like Wheat, Maize, Paddy and Millet are grown alternately with leguminous crops pulses, peas, beans, groundnut and clover etc. in the same field.

10. ADVANTAGES OF CROP ROTATION:

Rotation of crops has the following advantages:

1. Rotation of crops improves the fertility of the soil and hence increases the production.

2. Rotation of crops saves a lot of nitrogenous fertiliser.

QUESTIONS BANK:

21. Why does soil needs manuring?

22. What are manures? Why it is needed?

23. What are the advantages of manures?

24. What are chemical fertilisers? Give examples.

25. Differentiate between manures and fertilisers.

26. What are leguminous plants? What they are being planted in the field?

27. What are crop rotation? What are their advantages?

Lecture 2: CLASS - VIII: SCIENCE: CROPS -2: IRRIGATION

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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• IRRIGATION

The process of supplying water to crop plants in the fields is called irrigation. 

• Why is Irrigation Necessary: 

1. Irrigation before ploughing the fields makes the soil soft due to which ploughing of fields becomes easier.

2. Irrigation is necessary to provide moisture for the germination of seeds. This is because seeds do not grow in dry soil.

3. Irrigation is necessary to maintain the moisture of soil for healthy crop growth so as to get good yield.

4. Irrigation is necessary for the absorption of nutrient elements by the plants from the soil.

5. Water supplied to the crops during irrigation protects the crop plants from hot air currents as well as frost.

• Factors Affecting Irrigation Requirements of Crops:

The irrigation requirements of crops depend on three factors:

• 1) Nature of the crop
• 2) Nature of the soil, and 
• 3) Season.

• NATURE OF THE CROP: 

Paddy crop is transplanted in standing water and requires continuous irrigation where as other other crops like wheat, gram, cotton etc. do not require so much water. Hence irrigation depends upon the nature of the crops.

• NATURE OF THE SOIL: 

There are two types of soil on which the crops are grown, (a) Sandy soil and (b) Clayey soil. The crops grown in a Sandy soil need irrigation more frequently where as the frequency of irrigation for the crops grown in a Clayey soil is comparatively less.

• SEASON: 

The frequency of irrigation of the crops is higher in summer season.

• SOURCES OF IRRIGATION:

Crops are supplied water for irrigation from different sources like: Rivers, Canals, Wells, Tube-wells, Dams, Ponds and Lakes.

• TRADITIONAL METHODS OF IRRIGATION:

The various traditional methods of irrigation are:

i) Most (Pulley system),

ii) Chain pump,

iii) Dhekli, and

iv) Rahat ( Lever system)

• MODERN METHODS OF IRRIGATION:

The two main modern methods of irrigation are:

(a) Sprinkler system, and

(b) Drip System.

• SPRINKLER SYSTEM:

In the sprinkler system of irrigation, a main pipeline is laid in the fields. Perpendicular pipes having rotating nozzles at the top are joined to the main pipeline at regular intervals. When water from a tube- well is allowed to flow through the main pipeline under pressure with the help of a pump, it escapes from the rotating nozzles. This water gets sprinkled on the crop plants. It is more useful for the uneven land where sufficient water is not available. It is also useful for Sandy soil.

• DRIP SYSTEM:

In the drip irrigation system, there is a network of narrow pipes with small holes, in the fields. When water flows through the narrow pipes, it falls drop by drop at the position of roots of the plants. This water is absorbed by the soil in the root zone of the plants and utilised by the plants. There is no wastage of water in this type of Irrigation. Drip system is the best technique for watering fruit plants, trees and gardens.

• ADVANTAGES OF DRIP SYSTEM:

Drip Irrigation system has the following advantages:

(a) Drip system provides water to plants drop by drop. So, water is not wasted.

(b) Drip system minimises the use of water in agriculture. So, drip system of irrigation is very useful in those regions where the availability of water is poor.

Lecture 1: Class VIII: SCIENCE: CROPS AND ITS MANAGEMENT (CBSE)- 1

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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Chapter: 1

• CROP PRODUCTION AND MANAGEMENT

CROP:  When the same kind of plants are grown in the fields on a large scale to obtain foods like cereals (wheat, rice, maize), pulses, vegetables and fruits, etc., it is called a crop.

(i) Cereals: Wheat, Paddy, Maize, Millet

(ii) Pulses: Gram, Peas, Beans

(iii) Oil Seeds: Mustard, Groundnut

(iv) Vegetables: Tomato, Cabbage, Spinach

(v) Fruits: Banana, Grapes, Guava, Mango

• TYPES OF CROPS:

All the crops are categorised into two main groups:

1. KHARIF CROPS: The crops are sown in the rainy season (from June to September) are called Kharif crops. Some of the examples of Kharif crops are: Paddy, Maize, Millet, Soyabean, Groundnut, and Cotton.
2.  RABI CROPS: The crops grown in the winter season (from October to March) are called Rabi crops. Some of the examples of Rabi crops are: Wheat, Gram, peas, Mustard and Linseed.

• AGRICULTURE: 

The growing of plants or crops in the fields for obtaining food ( like wheat, rice etc) is called agriculture.

• BASIC PRACTICES OF CROP PRODUCTION

The various tasks performed by a farmer to produce a good crop are called agricultural practices.

• 1. Preparation of soil,
• 2. Sowing,
• 3. Adding manure and fertilisers,
• 4. Irrigation,
• 5. Removal of weeds,
• 6. Harvesting and
• 7. Storage of food grains.

Sometimes another practice called Rotation of crops is also undertaken to improve soil fertility and to increase crop yield.

• 1. PREPARATION OF SOIL:

The soil is prepared for sowing the seeds of the crop by 

(i) ploughing (ii) levelling and (iii) manuring.

• (i) PLOUGHING: 

The process of loosening and turning the soil is called ploughing or tilling. 

• (ii) LEVELLING: 

The ploughed soil is levelled by pressing it with a wooden leveller so that the top soil is not blown away by wind or drained off by water and thus soil erosion is prevented.

• (iii) MANURING: 

Manuring means adding manure to the soil. It is done to increase the fertility of the soil before seeds are sown into it. 

Prepared by: Subhankar Karmakar 

• AGRICULTURAL IMPLEMENTS:

(i) PLOUGH: 

It is a large agricultural implement which is used for ploughing the soil and it is made of wood.

                       

 

.                             A wooden plough

The wooden plough consists of a long log of wood which is called plough shaft. There is a handle at one end of the ploughshaft. Below the handle is a strong triangular iron strip called ploughshare. The other end of ploughshaft can be attached to a wooden beam which is fixed at right angles to the ploughshaft. 

(ii) HOE:

Hoe is an agricultural implement or tool which is used for removing weeds, and loosening and turning the soil. It consists of a long rod of wood or iron. There is a handle at one end of the hoe. A strong, broad and bent plate of iron is fixed below the handle and acts like a blade. The other end of hoe has a beam which is put on the neck of bullocks.

Prepared by: Subhankar Karmakar 

(iii) CULTIVATOR:

The cultivator is a tractor driven agricultural implement which is used for loosening and turning the soil in the fields quickly. A cultivator has many ploughshares which can dig into a considerable area of soil at the same time, loosen it and turn it. Due to this, many fields can be ploughed in a short time by using a cultivator.

• 2. SOWING:

The process of scattering seeds or putting seeds in the ground soil for growing the crop plants is called sowing. It is the most important part of crop production.

(i) SELECTION OF SEEDS: Good quality seeds are clean and healthy seeds free from infection and diseases and which will give him yield of food grains.

(ii) METHODS OF SOWING SEEDS: There are two methods of sowing the seeds in the soil. These are

(a) Sowing by hand, and

(b) Sowing with a seed drill.

Prepared by: Subhankar Karmakar

(iii) PRECAUTIONS FOR SOWING SEEDS:

a) The seeds should be sown at right depth in the soil suitable for germination.

b) The seeds should be sown at right intervals or spacings.

c) The seeds should not be sown is dry soil.

d) The seeds should not be sown in a highly wet soil.

(iv) ADVANTAGES OF SOWING WITH A SEED DRILL:

a) By using a seed drill for sowing, the seeds are sown at correct depth and correct intervals.

b) The seeds sown with a seed drill are in regular rows.

c) When the seeds are sown in furrows by a seed drill, the seeds get covered by soil and hence these seeds can not be picked up and eaten by birds. This prevents damaged by birds. 

d) Sowing by using a tractor driven seed drill saves time and labour.

Prepared by: Subhankar Karmakar

(v) TRANSPLANTATION:

The process of transferring the seedlings from the nursery to the main field by hand is called transplantation or transplanting.

The Advantages of Transplantation:

a) It helps us to select the better and healthy seedlings for the cultivation by rejecting the damaged seedlings.

b) It allows better penetration of the roots in the soil.

c) It promotes better development of the shoot system of plants.

The practice of transplantation is used in the cultivation of Paddy (rice) crop and in the cultivation of many vegetables like tomatoes and chillies.

Prepared by: Subhankar Karmakar

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HOME TASKS:

1. What are crops? Give some examples.

2. Classify crops with suitable examples.

3. What are Kharif crops? Give examples.

4. What are Rabi crops? Give examples.

5. Which types of crops are also known as summer crops? 

6. What are the basic practices of crop production? 

7. What are agricultural practices? 

8. What are steps to prepare the soil for cultivation?

9. What are ploughing or tilling?

10. What do you understand by the term "manuring"?

11. Describe a plough with a neat sketch.

12. Describe a hoe with a neat sketch.

13. What are agricultural implements?

14. What is a cultivator?

15. What do you understand by " sowing"?

16. What type of seeds are selected for sowing?

17. What are the methods of sowing? 

18. Describe the precautions taken for sowing seeds.

19. Describe the Advantages of sowing with a seed drill.

20. What is transplantation?  Describe its advantages.

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SCIENCE: CLASS VIII CBSE (CLASS NOTES)