Rapid revision in Biology for CBSE Class X Examination-2026

Here is a detailed breakdown of the Biology topics included in the Science syllabus for March 2026 examinations.

Unit II: World of Living

This unit focuses on various aspects of living organisms and is allocated 25 marks in the examination.

1. Life Processes

• Key Concepts:
  • Understanding the essential processes that define living organisms.
  • Detailed study of nutrition, respiration, transport, and excretion in plants and animals.
• Topics Covered:
  • Nutrition:
    • Modes of nutrition in plants and animals.
    • Autotrophic and heterotrophic nutrition.
  • Respiration:
    • Aerobic and anaerobic respiration.
    • Respiratory system in humans.
  • Transport:
    • Transport of water, minerals, and nutrients in plants.
    • Circulatory system in humans.
  • Excretion:
    • Excretory system in humans.
    • Excretion in plants.

2. Control and Coordination in Animals and Plants

• Key Concepts:
  • Mechanisms by which organisms respond to stimuli.
  • Role of nervous and endocrine systems in animals.
  • Coordination in plants through hormones.
• Topics Covered:
  • Nervous System in Humans:
    • Structure and function of neurons.
    • Central and peripheral nervous systems.
    • Reflex actions.
  • Hormones in Animals:
    • Endocrine glands and their hormones.
    • Role of hormones in growth, metabolism, and reproduction.
  • Coordination in Plants:
    • Tropic movements.
    • Plant hormones (auxins, gibberellins, cytokinins, etc.).

3. Reproduction

• Key Concepts:
  • Modes of reproduction in single and multicellular organisms.
  • Detailed study of human reproductive system.
  • Introduction to reproductive health.
• Topics Covered:
  • Asexual Reproduction:
    • Binary fission, budding, fragmentation, spore formation, and vegetative propagation.
  • Sexual Reproduction in Plants:
    • Structure of flower.
    • Pollination, fertilization, seed formation, and dispersal.
  • Sexual Reproduction in Humans:
    • Male and female reproductive systems.
    • Menstrual cycle.
    • Fertilization and development of embryo.
  • Reproductive Health:
    • Contraceptive methods.
    • Sexually transmitted diseases (STDs).

4. Heredity and Evolution

• Key Concepts:
  • Principles of inheritance and variation.
  • Basic concepts of evolution.
• Topics Covered:
  • Mendel’s Laws of Inheritance:
    • Monohybrid and dihybrid crosses.
    • Concept of dominant and recessive traits.
  • Sex Determination in Humans:
    • Chromosomal basis of sex determination.
  • Evolution:
    • Brief introduction to theories of evolution.
    • Fossil records and their significance.
    • Evolutionary relationships among organisms.

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5. Our Environment

• This unit is allocated 5 marks in the examination.
• Key Concepts:
  • Understanding ecosystems and their components.
  • Impact of human activities on the environment.
• Topics Covered:
  • Ecosystems:
    • Components of ecosystems.
    • Food chains and food webs.
    • Energy flow in ecosystems.
  • Environmental Problems:
    • Ozone layer depletion.
    • Waste production and its management.
    • Biodegradable and non-biodegradable substances.

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6.Conservation of Nature and Natural Resources

1.What are natural resources?

The materials (living or nonliving things) which organisms can obtain from nature for the sustenance of their life are called natural resources.

2.Differentiate between renewable resources  and non-renewable resources.

Those resources that are replenished by the natural processes like quick recycling, reproduction etc. are called renewable resources . eg: soil, air, plants, animals, water, etc..

Those resources that are exhausted by continuous use and are not formed again by the   natural processes are called  non – renewable resources.eg: Fossil fuels (coal,petroleum,natural gas) and minerals.

3. What do you mean by conservation?

The sensible, wise and judicious use of the earth’s natural resources in order to avoid excessive degradation and rapid exhaustion but to have a scope for the future use.

4.What are the steps to be taken to conserve water?

    The steps involved in the conservation of water are :

     i)Prevention of wastage of water

    ii)Control of water pollution

5.What are the major causes of water pollution?

    Water pollution is defined as the addition of certain substances  (organic , inorganic, biological, radiological) which degrade the quality of water so that it becomes unfit for use, is called water pollution.

    The main causes of water pollution are the increase  of the human population  and the growth of towns and the development of industry.

Community Waste Waters:- (water carrying domestic waste materials)

    The community waste waters discharges from houses , commercial and industrial establishments connected to the public sewage system.

    The sewage contains human  and animal excreta, food residue, cleaning agents, detergents and other wastes.

    It is always rich in organic matter ,bacteria and other biological  pollutants and contaminate the water bodies like rivers and lakes.

    With the increase of the amount of organic waste  in water the bacteria multiply and use up the available oxygen.This results in the destruction of aquatic life due to de-oxygenation of water.

Industrial wastes:-

Various industrial wastes (organic and inorganic) get mixed with river, pond and lake water and makes it highly toxic. The oil products from industrial wastes prevents oxygen from diffusing in the water and affect the aquatic life.The detergents getting into water diminishes the capacity of water to retain oxygen besides being poisonous to fishes and aquatic plants.

Metallic waste materials from the factories like salts of copper, zinc, lead , nickel, etc.and fluorides act like poisons.

 

 Agrochemicals

Agrochemicals  include the fertilizers, insecticides, fungicides, etc. used to improve the crop production . They get carried away by water or wind and  get accumulated in the water bodies. These chemicals being highly toxic, cause serious health hazards to aquatic life and in turn the human life.

6.What are the harmful effects caused by  various detergents and oil products in water?

The detergents change the surface tension and diminishes the capacity of water to hold oxygen. Thus they inhibit the growth of bacteria which decompose the organic substances resulting in the production of froth that accumulates on the surface of water. They become toxic to the fishes and aquatic plants.

7.What are the causes of pollution of seas(Marine pollution)?

The main causes of marine pollution include sewage disposal and dumping of industrial effluents. Other causes are nuclear waste, offshore oil drilling, underwater nuclear explosions, and oil discharge or leakage from oil tankers. The discharge of pollutants carried by the rivers into the sea also pollute the sea water.

8.How does oil pollution result in the destruction of birds?

When birds come to the surface of the water which is polluted by oil , their feathers get soaked in oil. The feathers thus lose the water proofing properties and the birds die due to the poor regulation of body temperature.(the sea plants and small marine organisms are also destroyed due to oil pollution.)

9.Water borne diseases:

Those diseases spread/transmitted through contaminated water.

Eg: Cholera, dysentery, typhoid, jaundice

10.What do you mean by the “Ganga Action Plan”? What was its purpose?

The programme launched by the Indian Government on January 1984, to improve the water quality of the holy river Ganga is called the Ganga Action Plan. The main purpose of the Ganga Action Plan was to improve the quality of water by intercepting and diverting the sewage water to the towns for treatment and restore the ecological balnce in the Ganga basin. The treated sewage was supposed to be either used for irrigation or discharged back into the river.

11.What do you mean by the National River Plan?

National River Action Plan is a programme formulated by the government of Indiato improve the quality of water in major rivers across the country by intercepting and diverting the polluted water for treatment.

12.What are the main causes of air pollution ?

The introduction materials that produces an adverse effect on the health plants and animals into the atmosphere is called air pollution .

The main causes of air pollution are dust , storms, automobiles, factories, jet planes, power stations, steel plants, incinerators, atomic reactors, etc.

On the basis of their physical state the air pollutants can be divided into two groups:-

i)Particulate pollutants

ii)Gaseous Pollutants

Particulate pollutants are the solid particles like the metallic particles, dust, soot,etc.or liquid particles that are suspended in the air. The presence of particulate matter in the atmosphere reduces the visibility.

Gaseous pollutants includethe gases like carbon dioxide, carbon monoxide, chlorides, fluorides, sulphur dioxide which are released in the air due to the burning of woods, coal, fuel, oil, etc.The presence of acidic gases promotes corrosion of metals and causes tarnishing and erosion of buildings. Smog which is a mixture of smoke and fog causes the atmosphere cloudy leading to many health hazards. Traces of radioactive substances and radiation also pollute the air.The agrochemicals such as pesticides can also contaminate the air.

13.Consequences of air pollution:

Air pollution will cause adverse effects on the health of plants and animals.

The depletion opf the ozone layer results in the entry of most of the ultraviolet solar padiation which can cause skin cancer . The presence of particulate pollutants in the atmosphere reduces visibility. The carbon monoxide during the combusting of fuels causes harmful effects to the respiratory function of haemoglobin (present in animals) ie. Instead of oxygen, carbon monoxide is absorbed by haemoglobin and results in the formation of carboxy- haemoglobin. The partial combustion of  impurities in the fuels produce poisonous gases like sulphur dooxide which gets trans formed into sulphuric acid by dissolving in the atmosphere,leading to acid rain.The presence of acidic acid promotes corrosion of metals and causes tarnishing and erosion of buildings, sculptures, and paintings. It also causes serious irritation in the respiratory tract.

Smog causes respiratory ailments, nausea, eye irritation , etc.

Radiations emitted by radioactive substances can kill plant and animal tissues, causes leukaemia or induce mutation .

Leakage of poisonous substances results in heavy toll of life.Eg:-Leakage of MIC (Methyl Iso Cynate) in Bhopal in 1984.

The agrochemicals like pesticides (DDT,BHC, etc.)can cause many neuro- biological abnormalities in man.

14.What is noise pollution ?How does it affect human health?

Noise pollution is the undesirable sound released into the atmosphere.

The sources of noise pollution are machines, automobiles, aircrafts, loudspeakers, explosions. The high frequency of music poured out during festival etc.are other sources of noise pollution.

Noise pollution can cause physiological and psychological ill effects.The constant exposure to loud noise can impair the hearing ability andcause nervous disorders. It can also cause abnormal rise in heartbeat and blood pressure.

15.Enumerate efforts taken at the national and international levels to protect wild life?

Wild life includes all the organisms –plants, animals and microbes that live in natural habitat and flourish without human control.

The Indian Government has appointed a separate organisation called the Indian Board for Wild Life (IBWL) to protect our wild life.It observes a Wild Life Week throughout the country from the 1^st to 8^th October every year. This is done  in order to create a great awareness about the need for protecting our wild life.

The Wild Life Protection Act of 1972 bans killing of many endangered species.

In 1973 the Government started a special scheme to protect the tiger population in India called as the Project Tiger.At present 21 National Parks and Sanctuary are involved in Project Tiger.

Several National parks and Sanctuaries have been setup in the country to protect animals which are facing the threat of extinction.The export of tiger and panther’s skin, Rhino horn, snake and crocodile skin are now prohibited.

An International organization IUCNNR has been set up to advice various governments on the ecological problems. IUCNNR works through several commissions.  The survival service commission of IUCNNR collects data and maintains a list of wild animals that may be in danger of extinction and to initiate action to prevent it.

16.What are the main causes of destruction of wild life? What are the remedial measures to protect wild life?

• Hunting wild life for sport, or fur is partly responsible for the destruction of wild life.
• Clearing of Natural forest and wilderness to build cities or to increase agricultural land is the latest threat to wild life because it destroys the natural habit of animals.
• Afforestation and reforestation are to be given due importance in our developmental scheme.
• Preservation of the natural habitat of animals, monitoring their numbers in wild life sanctuaries and a total ban on pouching are the remedial measures required to conserve wild life.

17.Differentiate between biodegradable waste and non-biodegradable waste?

• The waste materials resulting from various human activities can be classified as biodegradable and non-biodegradable waste.
• Those waste materials which can be broken down into non-toxic substances by the action of certain bacteria on them are called biodegradable waste.
• Those waste materials which cannot be changed into non-toxic substances by the action of the bacteria are called non-biodegradable wastes.
• The biodegradable waste material can be recycled. Ex. Waste papers and rags are used for the manufacturing of new paper.
• Non-biodegradable waste material can not be recycled. Therefore they become the major pollutants.Eg;Aluminum cans, Plastics,Pesticides such as D.D.T, Radioactive waste materials etc.

18.How do radio active waste cause pollution?

• The sources of radioactive waste materials include nuclear reactors,laboratories and hospitals which use radioactive substances.
• They release high energy particles which are very harmful to living organisms.
• The ionizing radiations emitted by the radioactive substances can destroy plant and animal tissues and cause diseases like Leukemia.
• They induces mutations leading to many hereditary disorders.
• The nuclear pollution assumes a universal dimension because radioactive materials spread far and wide in relatively short time.
• It can be controlled by adopting special techniques for  the storage and disposal of radioactive wastes.