CBSE Class 8

On this page, you will find Force and Pressure Class 8 Notes Science Chapter 11 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 11 Force and Pressure will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 11 Force and Pressure

Force and Pressure Class 8 Notes Understanding the Lesson

1. A push or pull on an object is called force.

2. Forces applied on an object in the same direction add to one another.

3. If two forces act in the opposite directions on an object, the net force acting on it is the difference between the two forces.

4. The strength of a force is usually expressed by its magnitude.

5. Force on an object may change its state of motion, speed, direction and shape.

6. The force resulting due to the action of muscles is known as the muscular force.

7. Muscular force can only be applied when it is in contact with an object, it is also called as contact force.

8. The force responsible for changing the state of motion of an object is known as the force of friction.

9. The force exerted on an object without touching it is known as non-contact force.

10. The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.

11. The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity. This force is known as gravitational force.

12. The force acting on a unit area of a surface is called pressure.

13. The envelop of air around us is known as atmosphere.

14. The pressure exerted by the atmosphere is known as atmospheric pressure.

Class 8 Science Chapter 11 Notes Important Terms

Atmospheric pressure: The pressure exerted by air around us is termed as atmospheric pressure.

Contact force: The type of force which acts only when the object are in physical contact with each other is called contact force.

Electrostatic force: The force exerted by an electrified body is called electrostatic force.

Force: A push or pull which tends to change the state of rest, motion direction, size and shape is called as force.

Friction: The force acting between two surfaces in contact which opposes the motion of one body over the another body is called the force of friction.

Gravitational force: The force of attraction between any two objects which have mass is called gravitational force.

Gravity: The force of gravitation which acts on the bodies close to the surface of the earth is called the force of gravity of the earth.

Magnetic force: The type of force which is exerted by a magnet is called magnetic force.

Muscular force: The type of force which is exerted by the muscles of a human or animal body is called muscular force.

Non-contact force: The type of force which is exerted by a body on another body without any direct contact with it is called non-contact force.

Pressure: Force acting per unit area is called pressure.

Pull: The type of force which move the object towards source of the force.

Push: The type of force which move the object forward or away from the source of force.

On this page, you will find Reaching the Age of Adolescence Class 8 Notes Science Chapter 10 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 10 Reaching the Age of Adolescence will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 10 Reaching the Age of Adolescence

Reaching the Age of Adolescence Class 8 Notes Understanding the Lesson

1. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. It begins around the age of eleven and lasts upto eighteen or nineteen years of age. Hence adolescence occurs between childhood and adulthood.

2. The human body undergoes several changes during adolescence such as change in body shape, voice change, development of sex organs, etc.

3. The phase wherein the bodily changes occurs in terms of sexual growth, is known as puberty. Therefore puberty is defined as the onset of reproductive maturity, starting at the age of 11 years and lasts till the age of 18 years. It starts earlier in females than in males.

4. During adolescence, in girls, the region below the waist becomes wider whereas in boys, shoulders broaden and the muscles of the body grow more prominently than girls.

5. At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes and produce hoarse voice whereas girls have a high pitched or shrilled voice. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

6. There is a sudden change in height of human beings during puberty. The height increases faster in girls than boys and both reach their maximum height at the age of 18.

7. During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases which results in development of acne and pimples on the face of boys and girls.

8. In the period of adolescence, a person reaches the maturity level of mental, intellectual and emotional thinking.

9. During puberty, breasts begins to develop in girls; facial hair, i.e., moustache and beard in boys. These features which distinguish the male from female are called secondary sexual characters.

10. The changes which occur at adolescence are controlled by hormones which are chemical substances. They are secreted from endocrine glands, or endocrine system.

11. The male hormone or testosterone is released by the testes and the female hormone or estrogen is produced by ovaries are responsible for secondary sexual characters in both of them. The production of these hormones are under the control of pituitary gland.

12. Hormones from pituitary stimulate testes and ovaries to release male (testosterone) and female (estrogen) hormone into the blood stream which reach a particular body part called target site. The target site responds to the hormones. The testes and ovaries secrete sex hormones which are responsible in the male and female secondary characters.

13. Reproductive phase of life in humans start when their testes and ovaries begin to produce gametes. In male, the reproductive phase begins at puberty at the ages 14 – 15 and lasts, as long as he is healthy whereas in female it begins at the ages 10-12 and lasts until the age of 45-50 years.

14. The uterine wall in females prepare itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down along with blood. This is called menstruation.

15. The first menstrual flow begins at puberty is termed as menarche.

16. Stoppage of menstruation at the age of 45-50 is termed as menopause.

17. Sex of unborn child depends on whether the egg is fertilised with sperm having X or Y chromosome.

18. The thyroid gland produces the thyroxine hormone which prevents from ‘goitre’ disease. Similarly, the pancreas produces the insulin hormone which checks the disease ‘diabetes’. The adrenals produce hormone 1 adrenaline which helps the body to adjust to stress when one is very angry, embarrassed or worried.

19. The adrenals and thyroid secrete their hormone when they receive orders from the pituitary through its I hormones. The pituitary also secretes growth hormone which is necessary for the normal growth of a person.

20. Hormones play a vital role in completing life cycle in insects and frogs. For example, metamorphosis (changing of larva into adult) in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by thyroid. The production of thyroxine needs the presence of iodine in water.

21. Nutritional needs of the adolescents: At the stage of adolescence, the human body grows at an extremely fast rate and requires adequate intake of a balanced diet which should contain proportionate I amount of proteins, carbohydrates, fats, vitamins and minerals, etc. They can be obtained from green vegetables, normal Indian meal of roti/dal/rice, milk, fruits, etc.

21. Maintaining personal hygiene and doing physical exercise is of utmost important to stay fit and healthy.

22. We should avoid drug to avoid physical, mental and emotional ailments.

Class 8 Science Chapter 10 Notes Important Terms

Adam’s apple: At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

Adolescence: The period of life, when the body undergoes changes, which leads to reproductive maturity, is called adolescence. It starts around the age of 11 and lasts upto 18 or 19 years of age.

Adrenaline: The hormone produced by adrenals is called adrenaline. It helps the body to adjust to stress when one is very angry, embarrassed and worried.

Balanced diet: A balanced diet or meal is one which includes proteins, vitamins, fats, carbohydrates, minerals, etc., in adequate quantity and proportion.

Chromosomes: These are thread-like structures present inside the nucleus of a cell and helps in for carrying genetic information from one generation to next generation.

Endocrine glands: Different types of hormones are secreted from particular glands called endocrine glands or endocrine system.

Female hormone or estrogen: The female hormone is secreted by ovaries at the onset on puberty and causes development of secondary sexual characters in female.

Growth hormones: Pituitary gland secretes growth hormones which is necessary for the normal growth of a person.

Hormones: Hormones are chemical substances secreted from endocrine glands. They are responsible for regulating metabolic and other activities of the body.

Insulin: The hormone produced by pancreas is called insulin.

Male hormone or testosterone: The male hormone is released by the testes at the onset of puberty and causes changes in secondary sexual characters.

Menarche: The first menstrual flow begins at puberty is known as menarche.

Menopause: When the menstruation ceases, the stage is called menopause.

Menstruation: The process in a woman of discharging blood and other material from the lining of uterus at intervals of about 28-30 days is called menstruation.

Pituitary gland: A pea-sized body attached to the base of the brain that is important in controlling growth and development and functioning of the other endocrine gland.

Puberty: The period of life, during which the human body undergoes several changes and reaches sexual maturity and the human beings become capable of reproduction, is called puberty.

Reproductive health: Good health is essential for adolescence and for reproductive phase of life. For good health one should have a balanced diet, do physical exercises, avoid smoking, drinking and drugs, maintain hygiene and take proper sleep and rest.

Secondary sexual characters: In adolescence period, there are several changes including growth of facial hair, i.e., moustaches and beard on boys’ face, development of breast in girls, etc. These features or characters that help to distinguish the male from the female are called secondary sexual characters.

Sex chromosomes: All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chro-mosomes out of these are the sex chrmosomes named X and Y. A male has one X and one Y chromosome while a female has two X chromosomes.

Thyroxine: The hormone produced by the thyroid gland is called thyroxine.

On this page, you will find Reproduction in Animals Class 8 Notes Science Chapter 9 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 9 Reproduction in Animals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 9 Reproduction in Animals

Reproduction in Animals Class 8 Notes Understanding the Lesson

1. Reproduction is the process of continuation of similar kinds of individuals, generation after generation. In this process, all living beings produce their young ones for continuity of life on the planet earth.

2. There are two modes by which animals reproduce. These are:

• Sexual reproduction and
• Asexual reproduction.

3. Reproduction resulting from the fusion of male and female gametes is called sexual reproduction; e.g., frog, fish, cow, human beings, etc., reproduce by sexual reproduction.

4. Reproduction in which young ones are formed from the cells of a single parent and are identical copies of their parents is called asexual reproduction. This type of reproduction is seen in Amoeba, yeast, worms, etc.

5. There are different reproductive organs in male and female. The main reproductive organs in males are testes, sperm ducts, urethra and penis , whereas those in females are ovaries, oviducts, uterus and vagina

6. In male, the testes produce the male gametes called sperms , whereas in female, the ovary produces female gametes called ova (eggs)
In human beings, a single matured egg is released into the oviduct by one of the ovaries every month.

7. Uterus is the part where development of the baby takes place.

8. When sperms come in contact with an egg, one of them may fuse with the egg. Such fusion of egg and the sperm is called fertilisation

9. The nuclei of the sperm and the egg fuse to form a single nucleus forming a fertilised egg called zygote

10. Fertilisation which takes place inside the female body is called internal fertilisation and that in which the fusion of a male and a female gametes takes place outside the female body is called external fertilisation. Internal fertilisation occurs in many animals including humans, cows, dogs and hens whereas external fertilisation is very common in aquatic animals like fish, frogs, starfish, etc.

11. The zygote formed after fertilisation begins to develop into an embryo . The zygote divides repeatedly to give rise to a ball of cells which then begin to form groups that develop into different tissues and organs of the body termed as embryo.

12. The embryo gets embedded in the wall of the uterus for further development.

13. The stage of the embryo in which all the body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby.

14. The animals which give birth to their young ones are called viviparous animals and those which lay eggs to reproduce are called oviparous animals.

15. The immature free-living form of most invertebrates (animals lacking a backbone) and amphibians and fish which at hatching from the egg is fundamentally unlike its parent and must metamorphose is called larva.

16. The transformation of the larva into an adult through drastic changes is called metamorphosis.

17. In Hydra, new individuals develop from buds. This method of asexual reproduction is called budding.

18. Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.

Class 8 Science Chapter 9 Notes Important Terms

Asexual reproduction: The mode of reproduction in which a single organism is able to produce one or more of its kind by itself is known as asexual reproduction; e.g., Amoeba, yeast, Hydra, etc., undergo asexual reproduction.

Binary fission: The type of reproduction in which an animal reproduces by dividing into two individuals is called binary fission; e.g., Amoeba reproduces by dividing itself into two.

Budding: This kind of reproduction is seen in Hydra and yeast. It is the process of reproduction in which new individuals develop as outgrowths from a single parent. The outgrowths developed on parent body is called buds and the process of reproduction is known as budding.

Embryo: When cells produced by the division of the zygote begin to form groups that develop into different tissues and organs of the body is called embryo.

External fertilisation: The fusion of male and female gametes takes place outside the female body. This is called external fertilisation. Most of the aquatic animals undergo this type of fertilisation.

Fertilisation: The process of union of male gametes or sperms and female gametes or ova (egg) is called fertilisation.

Foetus: The stage of the development of embryo in which the development and emergence of the various body parts like the hands, the feet and eyes, etc., can be identified is called the foetus.

Internal fertilisation: The fusion of male and female gametes or fertilisation that takes place inside the female body is called internal fertilisation. All insects, birds and mammals including human beings undergo this type of fertilisation.

Metamorphosis: A biological process in which larva drastically changes into an adult in an invertebrate or amphibian during their life cycle is known as metamorphosis.

Ova or Eggs: Female gametes produced by ovary in female are called ova or eggs.

Oviparous animals: The animals which lay eggs and hatch them to produce their young ones are called oviparous animals; e.g., frog, butterflies, hen, crow, etc.

Reproduction: The process of producing the offspring of one’s own kind for continuity of life in the earth is known as reproduction.

Sexual reproduction: The type of reproduction which involves fusion of male and female gametes is called sexual reproduction.

Sperms: Sperms are the male gametes produced by the testes in male.

Viviparous animals: The animals which give birth to their young ones are called viviparous animals; e.g., cow, buffalo, cat, dog, human beings, etc.

Zygote: The nucleus of the sperms and the egg fuse to form a single nucleus during the process of fertilisation. The fertilised egg is called zygote.

On this page, you will find Cell Structure and Function Class 8 Notes Science Chapter 8 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 8 Cell Structure and Function will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 8 Cell Structure and Function

Cell Structure and Function Class 8 Notes Understanding the Lesson

1. The basic structural and functional units of all the organs of the living organisms is called cell.

2. Cells were first discovered by Robert Hooke in 1665.

3. Cells of living organisms could be observed only after the discovery of improved microscopes.

4. Cells exhibit a variety of shapes and sizes.

5. Number of cells also varies from organism to organism.

6. Organisms made of more than one cell are called multicellular organisms while organisms made up of single cell are called unicellular organisms.

7. A single-celled organism, e.g., Amoeba captures and digests food, respires, excretes, grows and reproduces. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues.

8. A white blood cell (WBC) in human blood is an example of a single cell which can change its shape.

9. The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

10. The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm x 130 mm, is the egg of an ostrich.

11. Each organ is further made up of smaller parts called tissues.

12. A tissue is a group of similar cells performing a specific function.

13. The basic components of a cell are cell membrane, cytoplasm and nucleus.

14. Cell membrane is also called plasma membrane or cytoplasmic membrane. The cell membrane separates cells from one another and also the cell from the surrounding medium. It is porous and allows the movement of substances or materials both inward and outward.

15. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to these cells.

16. The jelly-like substance between the nucleus and the cell membrane is called cytoplasm. Various components or organelles, like mitochondria, golgi bodies, ribosomes, etc., are present in cytoplasm.

17. The central dense round body in the centre is called the nucleus.

18. The membrane which separates nucleus from the cytoplasm is called the nuclear membrane.

19. Cells without well-organised nucleus, i.e., lacking nuclear membrane, are called prokaryotic cells.

20. The smaller spherical body in the nucleus is called the nucleolus.

21. Chromosomes are the thread-like structures which carry genes and help in inheritance or transfer of characters from the parents to the offspring.

22. Plant cell differs from animal cell in having a central large vacuole, cell wall and plastids.

23. The blank-looking structures in the cytoplasm are called vacuole.

24. Plastids are the coloured organelles, that are found in plant cells only.

25. Green coloured plastids are called chloroplasts.

Class 8 Science Chapter 8 Notes Important Terms

Cell: Cell is the basic structural and functional unit of all living organisms.

Cell membrane: The membrane around the cell is called cell membrane. It is also called plasma membrane or cytoplasmic membrane.

Cell wall: The hard and rigid covering of plasma membrane which are found in plant cells only is called cell wall.

Chloroplasts: The green coloured plastids having chlorophyll, which is essential for photosynthesis is called chloroplasts.

Chromosomes: The thread like structures found in the nucleus which carry genes are called chromosomes.

Eukaryotes: Organisms which have eukaryotic cells, i.e., which contains a well developed nucleus are called eukaryotes.

Gene: Genes are located in chromosomes. It is a unit of inheritance in living organisms.

Multicellular: The category of organism like plants and animals which contains a large number of cells are called multicellular organisms.

Nuclear membrane: Nuclear membrane separates nucleus from cytoplasm.

Nucleolus: The smaller, spherical and dense body inside the nucleus is called nucleolus.

Nucleus: The denser region of the cell that may be present at the centre of the cell is called nucleus.

Organ: The group of tissues, which are specialised to perform specific functions is called organ.

Organelle: One of the smaller component of cell is known as organelle.

Plasma membrane: The other name of cell membrane is plasma membrane. It is a membrane around the cell.

Plastids: The coloured organelles, that are found in plant cells only are called plastids.

Prokaryotes: The organisms which have prokaryotic cells, i.e., lack true nucleus are called prokaryotes, e.g., bacteria and blue green algae.

Protoplasm: The viscous fluid inside the cell which provides living nature to it is called protoplasm.

Pseudopodia: The temporary projections protruding out of the body of Amoeba for locomotion and taking food. These appear and disappear as Amoeba moves.

Tissue: A group of similar cells performing a specific function is called tissue.

Unicellular: The category of organisms containing single cell are called unicellular organisms.

Vacuoles: Vacuoles are the empty or blank looking structures in the cytoplasm.

White Blood Cell (WBC): It is the component of blood cells. It is an example of a single cell which can change its shape.

On this page, you will find Conservation of Plants and Animals Class 8 Notes Science Chapter 7 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 7 Conservation of Plants and Animals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 7 Conservation of Plants and Animals

Conservation of Plants and Animals Class 8 Notes Understanding the Lesson

1. There are a number of plants and animals that exist on earth.

2. Deforestation means cutting down of forests.

3. The chances of natural calamities like droughts and floods increase due to the deforestation.

4. An ecosystem is made of all the plants, animals and microorganisms in an area along with non-living components such as climate, soil, river, deltas, etc.

5. Plants and animals of a particular area are known as flora and fauna, respectively, of that area.

6. The conversion of fertile lands into deserts is known as desertification.

7. To protect our flora and fauna and their habitats, protected areas called sanctuaries, national parks and biosphere reserves have been earmarked. Activities like plantation, cultivation, grazing, felling trees, hunting and poaching are prohibited there.

8. Biosphere reserves are large areas of protected land for conservation of wildlife, plant and animal resources and traditional life of the tribals living in that area.

9. A sanctuary is an area where animals are kept protected from the disturbances to them and their habitats.

10. National Parks are areas reserved for wildlife where they can freely use the habitats and natural resources.

11. Those species of plants and animals which are found exclusively in a particular area are termed as ‘endemic species’.

12. Species is a group of population which are capable of interbreeding.

13. Project Tiger was launched by the government to protect tigers in the country.

14. Extinct species are those which have disappeared completely from the earth. Example, Dodo and passenger pigeon.

15. Critically endangered species are those which are under highest risk of extinction as their number has decreased drastically. Example, Andean catfish, Abe’s salamander.

16. Endangered animals are those whose numbers are diminishing to such a level that they might face I extinction. Example, great Indian bustard and blue whale.

17. Vulnerable species are those which are most likely to become endangered if not taken care of.

18. Near threatened species are found in small numbers and are scattered all over the world.

19. A sourcebook that keeps a record of all the endangered plants and animals is called ‘Red Data Book’.

20. Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for a specific purpose like breeding.

21. Reforestation is restocking of the destroyed forests by planting new trees.

Class 8 Science Chapter 7 Notes Important Terms

Biodiversity: It is the variety of different types of plant and animal life in a particular habitat (or in the world as a whole).

Biosphere reserve: A large; protected area of land meant for conserving wildlife, biodiversity, and the traditional lifestyle of the tribal people living in the area is known as a ‘biosphere reserve’.

Deforestation: The cutting down of trees on a large scale is called deforestation.

Desertification: The conversion of fertile lands into deserts is called desertification.

Ecosystem: It is a system formed by the interaction of a community of organisms with their physical environment.

Endangered species: Those species whose numbers are so small that the species are at risk of extinction are called endangered species.

Endemic species: They are the species of plants and animals which are found exclusively in a place.

Extinct animals: Animals which no more exist anywhere on the earth are known as extinct animals.

Fauna: The animals of a particular area are known as fauna of that area.

Flora: They are the plants of a particular area.

Migratory birds: Birds which move from one place to another for some reasons like breeding, climatic changes, etc., are known as migratory birds.

National park: The areas reserved for wildlife where they can freely use the habitats and natural resources are known as national parks.

Red Data Book: A source book that keeps a record of all the endangered animals, plants and other species.

Reforestation: The replanting or restoration of a forest that had been reduced by fire or cutting is called reforestation.

Sanctuary: The area where animals are kept protected from any disturbance to them or their habitat is known as a sanctuary.