Selina Biology Class 8 Solutions

Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants

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Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 1 Transportation in Plants. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 1 Transportation in Plants

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Diffusion occurs when molecules move:

  1. from lower concentration to higher concentration.
  2. from higher concentration to lower concentration through a membrane.
  3. from higher concentration to lower concentration.
  4. when energy is used.

Answer: (3) from higher concentration to lower concentration.

(b) Ascent of sap in plants takes place through:

  1. Cortex
  2. Epidermis
  3. Xylem
  4. Phloem

Answer: (3) Xylem

(c) If the xylem vessels of a plant are plugged:

  1. The leaves will turn yellow
  2. No food will be made
  3. The plant will wilt (shrivel)
  4. The plant will continue to grow

Answer: (3) The plant will wilt (shrivel)

(d) Force responsible for the ascent of sap is:

  1. Capillary force
  2. Root pressure
  3. Transpirational pull
  4. All the three

Answer: (4) All the three

(e) Raisins swell when put in:

  1. Rain water
  2. Tap water
  3. Mustard oil
  4. Saturated sugar solution

Answer: (1) Rain water

(f) The root-hairs are suited for absorbing water from the soil because:

  1. They have a large surface area
  2. They have a semi-permeable membrane
  3. They contain a solution of higher concentration than the surrounding water.
  4. All the three.

Answer: (4) All the three.

(g) Transpiration is defined as:

  1. the rise of water up to the stem of a plant.
  2. the elimination of water with dissolved water products.
  3. the loss of water as water vapour from the aerial parts of a plant.
  4. the loss of water as water vapour from the roots as well as the leaves of the plant.

Answer: (3) the loss of water as water vapour from the aerial parts of a plant.

(h) Which one of the following favours the fastest transpiration rate ?

  1. A cool, humid, windy day,
  2. A hot, humid, windy day,
  3. A hot, humid, still day,
  4. A hot, dry, windy day.

Answer: (4) A hot, dry, windy day.

Short Answer Questions:

Question 1.
An experiment was set up as shown in the figure below. After some time, the Water level in test tube A fell down but not in test tube B.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 1
Why was there a fall in the water level of test tube A and not in that of test-tube B ?
Answer:
In test tube A the water level falls because the water was absorbed by the plant through its roots dipped in water. Here no water loss occurs due to evaporation from the water surface due to presence of oil.
In test tube B the water level remains unchanged as it does not contain a rooted plant. Due to the presence of oil on surface no water loss occurs due to evaporation.

Question 2.
How are roots useful to the plants? Give any two points.
Answer:
Roots are useful to the plants in the following way:

  1. It absorbs water and minerals from the soil and transport it upward to various parts of a plant.
  2. Roots fix the plant firmly in the ground.

Question 3.
What do xylem vessels carry?
Answer:
The xylem vessels carry the water and minerals absorbed by the roots to the stem and leaves.

Question 4.
Name the plant tissue which helps in carrying the food to different parts.
Answer:
Phloem.

Question 5.
Define the terms:
(a) semi-permeable membrane
(b) osmosis.
Answer:

(a) Semi-permeable membrane: It is a membrane that allows the movement of solvent molecules (e.g. water molecules) through it but prevents the movement of solute particles (e.g. sugar or salt molecules).
For example: Egg membrane, parchment membrane, cellophane paper etc. are semi-permeable membranes.

(b) Osmosis: The diffusion of water molecules through a semi-permeable membrane from a region where water is more concentrated to a region where it is less concentrated is called osmosis.
In other words, osmosis is the diffusion of water from its pure state or dilute solution into a stronger or concentrated solution through a semi-permeable membrane.

Question 6.
Under what conditions do plant transpire (a) more quickly and (b) most slowly?
Answer:
(a) Transpiration is faster on hot summer days as compared to cold winters.
(b) Transpiration is reduced if the air is humid. Air cannot hold any water molecules when it is already laden with moisture (humidity).

Question 7.
Given here is an enlarged diagram of a part of the root. Draw arrows on the diagram to show the movement of water passing through different parts.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 2
Answer:
Path of water through the root hair to the xylem vessels.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 3

Question 8.
Why is the structure of the root hair is quite suitable for absorbing water from the soil ?
Answer:
The root hair are suitable for absorbing water from the soil in the following three ways:

  1. The root hairs present a large surface area. More the surface area, greater is absorption.
  2. The cell wall is of cellulose nature and forms permeable membrane and the plasma membrane around the vacuole forms the semi-permeable membrane.
  3. Root hairs have solution (cell sap) of a higher concentration than the surrounding soil water.

Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 4
Fig. Unicellular root hairs through the soil particles

Question PQ.
In an experimental set-up, a dye was placed at the bottom of a beaker filled with water as shown in figure A, below. After some time, the entire water in the beaker got coloured uniformly as shown in figure D.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 6
Answer:
(a) Name and define the phenomenon shown in the experiment.
Answer: The phenomenon is diffusion. Diffusion is the movement of the molecules or atoms of a substance (whether in a solid, liquid or gaseous state) from the region of higher concentration to the region of lower concentration.

(b) In all the four figures, two kinds of molecules are shown symbolically – larger and smaller. Which molecules are of the solute and which are of the solvent?
(a) Larger: ………… (b) Smaller: …………..
Answer: (a) The larger molecules are of the solute (dye)
(b) The smaller molecules are of the solvent (water)

(c) If all the dark shaded molecules in A are tightly enclosed in a cell membrane, what will be the nature of movement of the molecules, if any ?
Answer: As the concentration of solvent molecules is more in the left side of the figure A. The cell membrane will act as semi permeable membrane and will allow only the solvent molecules of water to move towards the solute particles. So the solvent molecules will move towards the solute particles. This will show the phenomenon or process of osmosis.

Question 9.
Briefly explain, how transpiration helps in upward conduction of water in plants? (a) ………… (b) ……………
Answer:
(a) Plants continuously absorb water through their roots. This water is sent up through the stem to all parts of the plant, including the leaves. Only a little amount, of water is retained in the plant or utilised by it in photosynthesis. The rest of it gets evaporated into the atmosphere as water vapour through the stomata present in the epidermis of the leaves and other aerial parts of the plant. This creates a suction pressure which pulls up water from xylem of the roots to the stem and then to the leaves.

(b) Xylem tissues are in the form of capillary tubes (tracheids and fibres) where narrower the diameter, greater will be the force. Whenever the xylem vessels lay empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force.
During day time, water is lost from the surface of the leaves by the process of transpiration. In this process, more and more water molecules are pulled up due to their tendency of rentainingjoined (cohesion). Such pulling force created by the leaves is very important in the case of tall trees where an upward conduction of water takes place.

Question 10.
How does temperature, light intensity and wind affect transpiration?
Answer:
Temperature: Transpiration is faster on hot summer days as compared to cold winters.
Light intensity: The transpiration rate is increased due to the increase in light intensity. During daytime in the sunlight, the rate of transpiration is faster. This is because the stomata remain open to allow the inward diffusion of carbon dioxide for photosynthesis. During dark, the stomata are closed, and hence transpiration hardly occurs at night.
Wind: Transpiration is more when the wind is blowing faster as water evaporates faster from the leaves.

Question 11.
The set up shown alongside was kept in sunlight for an hour. It was observed that drops of water appeared on the inside of the polyethylene bag.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 7
(a) Name the process which is being demonstrated.
(b) Why was the pot and its soil left uncovered by the polythene bag ?
(c) Why was the pot left in the sunlight?
(d) Suppose the pot in this experiment was placed inside a dark room instead of placing it in sunlight for some time. What difference will be noticed?
Answer:
(a) The process demonstrates the loss of water that has appeared in the polythene bag is transpiration.
As the potted plant covered with polythene bag is kept in the sunlight there will be loss of water through the stomata present on the leaves. The water drops will appear inside the polythene bag as a result of loss of water from the stomata. This is due to transpiration.

(b) As the potted plant is kept in the sun. The water vapours will also be given by the pot and the wet soil. These vapours (water drops) will also go inside the polythene if it covers the pot and the soil. We left the pot and soil uncovered by the polythene so that we may find the loss of water from the aerial parts of the plant covered with polythene bag. This shows that the water gets deposited in the polythene bag has come from the aerial parts of plant.

(c) As we keep the pot in the sunlight the stomata will open and the loss of water i.e., transpiration takes place from the aerial parts of the potted plant and the stomata. The loss of water will be more (transpiration) in the sun, and water vapours will appear in the polythene bag very soon.

(d) As we keep the pot inside the room, the stomata will not open fully and the rate of loss of water will be very-very less, and no water vapours will appear in the polythene bag. By keeping the pot in the room the loss of water will be very less and as a result the transpiration will be very less.

Question 12.
State whether the following statements are true or false. Rewrite the false statements correctly.
(a) Water absorption mainly occurs through the root-hair.
True
(b) Water enters the root-hair by osmosis.
True
(c) Water absorbed by the roots reaches the leaves and is used in producing food for the entire plant.
True
(d) A semi-permeable membrane allows larger molecules to pass through, but prevents the smaller ones.
False. A semi-permeable membrane allows smaller molecules to pass through, but prevents the smaller ones.
(e) Transpiration is the loss of water from the roots of the plant.
False. Transpiration is the loss of water from the aerial parts of the plant.
(f) Transpiration cools the plant when it is hot outside.
True
(g) During transpiration, the leaves lose more water from their upper surface.
False. During transpiration, the leaves lose more water from their lower surface.

Question 13.
Fill in the blanks with suitable terms given below: (Fast, Leaves, Stomata, Conducting, Ascent, Humid)
(a) Transportation in plants is carried out by a conducting system.
(b) The upward movement of sap that contains water and minerals is called ascent of sap.
(c) Transpiration is more when the wind is blowing fast.
(d) Most water gets evaporated from the plant from its leaves.
(e) Transpiration is reduced if the air is humid.
(f) The leaves have more stomata on their lower surface.

Long Answer Questions:

Question 1.
Draw a magnified view of the root-hair, and describe, how it helps in the absorption of water from the soil.
Answer:
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 8
Give above is a magnified view of a root-hair. It is a long protuberance of a cell. This cell contains a fluid called cell sap which is more concentrated than the surrounding soil water.
The root hair is covered by a very thin ceil membrane that allows water molecules to pass through, but prevents the larger molecules. So the water from the soil passes into the root hairs by osmosis.

Question PQ.
“Raisins swell in water, and grapes shrink in syrup.” Explain this phenomenon briefly.
Answer:
When we put some raisins in a bowl containing water, after 10-12 hours, we will notice that the raisins have swelled up. The raisins have absorbed water.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 9
But when we put some soft-skinned grapes in another bowl containing thick syrup of sugar. After 10-12 hours we will notice that grapes have shrunk. The grapes have lost water.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 10
In both cases the gain or loss of water is through the peel acting as a kind of semi-permeable membrane. This membrane has very minute pores which allow water molecules to pass through, but prevent the larger ones of sugar.

Question 2.
How does transpiration help the roots absorb water and minerals from the soil?
Answer:
Transpiration process in plants creates a suction pressure which pulls up water from xylem of the roots to the stem and then to the leaves.
Xylem tissues are in the form of capillary tubes (tracheids and fibres) where narrower the diameter, greater will be the force. Whenever the xylem vessels lay empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force.
Due to transpirational pull more and more water molecules are pulled up due to their tendency of remaining joined (cohesion). Such pulling force created by the leaves is very important in the case of tall trees where an upward conduction of water takes place.

Question 3.
Define the three processes by which plants absorb water and minerals from the soil.
Answer:
Following are the tree processes which help the plants to absorb water and minerals from the soil.

  1. Diffusion: Soil water moves into the root hairs through the process of diffusion from higher concentration to lower concentration as we put sugar in the milk and the sugar molecules are evenly distributed in the milk and occupy inter molecular spaces of milk.
  2. Osmosis: The cell sap and the cell walls act as semi- permeable membranes and permeable membranes. The concentration of the cell sap is more as compared to the water + minerals present in the soil. So the water and dissolved minerals enters the roots by the process of osmosis.
  3. Active transport: Root hairs absorb water and minerals from the soil. Water diffuses into the root hairs as the concentration of water is more as compared to root hair.
    But in case of minerals these move from lower concentration to molecules of higher concentration. So the minerals from the soil along with water move into the roots. So this is active transport in the opposite direction which needs energy.

Question 4.
How water absorbed by the roots is important for the plants?
Answer:
The water absorbed by the roots is important for the plant in three main ways:

  1. Transportation: The water in the plant body transports substances in solution from one part to another.
  2. Food production: Water is used in producing food (photosynthesis) by combining it with carbon-dioxide from the air in the presence of sunlight.
  3. Cooling: Water is used to cool the plant by evaporation through leaves when it is hot outside.

Question 5.
Name the factors which affect the rate of transpiration? State their role in each case.
Answer:
The following are the main factors that affect the rate of transpiration:

  1. Sunlight: During daytime, the rate of transpiration is faster. This is because the stomata remain open to allow the inward diffusion ofcarbondioxide for photosynthesis.
    During dark, the stomata are closed, and hence transpiration hardly occurs at night.
  2. Temperature: Transpiration is faster on hot summer days as compared to cold winter.
  3. Wind: Transpiration is more when the wind is blowing faster as water evaporates faster from the leaves.
  4. Humidity: Transpiration is reduced if the air is humid. Air cannot hold any water molecules when it is already laden with moisture (humidity).
  5. Low atmospheric pressure: The rate of transpiration increases when the pressure is low.

Question 6.
Mention the two ways in which transpiration helps the plants.
Answer:
Transpiration helps the plants in the following ways:

  1. Cooling effect: In transpiration, water gets evaporated from the plant. The heat required for this evaporation is obtained from the plant itself (latent heat) and thus the plant is able to cool itself w’hen it is hot outside.
  2. Transpiration helps in maintaining the concentration of the sap inside the plant body: The roots continue to absorb water from the soil. If excess water is not evaporated out, the sap would become dilute, preventing further absorption of water along with the minerals required by the plant.

Question 7.
Describe an experiment to show that the plant loses water through its leaves.
Answer:
Experiment: To demonstrate that the plants lose water through its leaves.

  • Take one small-sized, well-watered potted plant having a few branches. Place a polythene bag over its one branch as shown in A and tie it with a rubber band.
    Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 11
  • Remove all the leaves from another branch (B) of the same plant, cover this too with a polythene bag and tie it with a rubber band.
  • Place the plant in sunlight, and observe it after 4-6 hours. You will notice that drops have appeared on the inner surface of the polythene bag over branch A, while no water drops appear on branch B.
  • This set-up indicates that most water gets evaporated from the plant through its leaves.

Question 8.
Name any three minerals whose deficiency causes diseases in plants. Give the symptoms of each deficiency.
Answer:
The nutrient elements i.e. minerals are essential for the plants to grow well and complete their life-cycle properly. The minerals are divided into two main categories:

(i) Macro-Nutrients: They are required in larger concentrations and they are obtained from soil.
The three macro-nutrients (minerals) whose deficiency causes diseases in plants are:

  1. Nitrogen (N) – Yellowing of leaves,wrinkling of cereal grains.
  2. Phosphorus (P) – Purple and red spots on leaves, delay in seed germination.
  3. Potassium (K) – Poor Growth

(ii) Micro Nutrients: They are required in small amounts and they are also obtained from soil.
The three micro-nutrients(minerals) whose deficiency causes diseases in plants are:

  1. Iron (Fe) – Yellowing of Leaves.
  2. Manganese (Mn) – Yellowing of leaves, with grey spots.
  3. Zinc (Zn) Desphaped leaves, yellowing of leaves, stunted plant growth.

Question 9.
List out the differences between xylem and phloem.
Answer:
The Xylem tissue consists of four types of cells:

  1. Tracheids: They are elongated dead cells with tapering ends. Their main function is in upward conduction of water and provide mechanical support.
  2. Vessels: They are like tube-like structures placed one above the other forming long channels. They provide mechanical support and also transport water and mineral salts laterally and vertically upward.
  3. Fibres: They are long, narrow and tapering at both ends. They provide only mechanical support.
  4. Parenchyma: They are living cells and helps in the conduction of water and minerals, and serve for the storage of food.

The Phloem tissue consists of four types of cells:

  1. Seive tubes: They are formed of seive cells and form the main conducting part of the phloem. These are cylindrical cells arranged in vertical rows, joined end to end. Their end walls are perforated by pores and are called seive plates. Seive piates helps in passing food material from cell to cell.
  2. Companion Cells: They are associated with seive tubes. It help sieve tubes in the conduction of food material.
  3. Parenchyma: It is formed of thin-walled unspecialized parenchymatous cells and these cells store food.
  4. Phloem fibres: They are dead sclerenchyma fibres formed of elongated cells. These provide mechanical strength.

Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Humans

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Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Humans

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 3 Reproduction in Humans. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 3 Reproduction in Humans

REVIEW QUESTION

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) The testes are located within the:

  1. Penis
  2. Scrotum
  3. Ureter
  4. Urinary bladder

(b) Amoeba is most commonly reproduced by:

  1. Budding
  2. Regeneration
  3. Binary fission
  4. Multiple fission

(c) Identify the stage which is formed after the fertilisation of the egg by the sperm?

  1. Ovule
  2. Foetus
  3. Embryo
  4. Zygote

(d) Internally, the uterus opens into:

  1. Urethra
  2. Vagina
  3. Oviduct
  4. Vulva

(e) Which one of the following represents the correct sequence in the life history of a butterfly ?

  1. Egg → Larva → Adult → Pupa
  2. Egg → Pupa → Adult → Larva
  3. Egg → Larva → Pupa → Adult
  4. Egg → Pupa → Larva → Adult

Short Answer Questions:

Question 1.
Distinguish between the following pair of terms:
(a) Egg and sperm.
(b) Sexual reproduction and asexual reproduction.
(c) Budding and Regeneration.
Answer:
(a) Egg and sperm
Egg Sperm

  1. Egg is produced in the ovaries.
  2. Egg is spherical in shape with a nucleus.

Sperm

  1. Sperm is produced in the testes.
  2. Sperm has head with nucleus, middle piece and tail.

(b) Sexual reproduction and asexual reproduction.

Sexual reproduction

  1. In sexual reproduction the two sexes i.e., male and female produce special type of reproductive cells sperms in the male and eggs in the female.
  2. To produce a new individual the sperm has to reach the ovum and fuse with it. e.g. Humans, bird, reptile, etc.

Asexual reproduction:

  1. It involves the production of an offspring from a single parent without the fusion of reproductive cells (gametes).
  2. It is a rapid mode of multiplication, e.g. Lower plants and animals {Amoeba).

(c) Budding and Regeneration

Budding: Budding is a process in which buds grow on the outside of the parent body. The buds detach themselves when they are large enough.
Example: Hydra
Regeneration: Regeneration is the process that uses cell division to regrow lost body parts.
Example: Starfish, sponges

Question 2.
Define the following terms:
(a) Fetilization
(b) Implantation
(c) Puberty
Answer:
(a) Fetilization: When sperms and eggs from the opposite partners (males and females) fuse to form Zygote. It is called fertilization.
(b) Implantation: The fertilised egg (zygote) soon starts developing and by the time it reaches the uterus, a small ball of numerous cells is already formed. This is a kind of embryo which forms a pit in the wall of the uterus and gets fixed in it. This natural way of fixing of the embryo in the wall of the uterus is called implantation. This produces the state of pregnancy.
(c) Puberty: Puberty is the period during which the reproductive systems of boys and girls mature. In girls, it starts at the age of about ten and the first sign of puberty is the development of breasts. In boys, it starts at about 11 years of age of the^enlargement of the testes is its first sign. Sudden spurt in growth, shoulder girdle grows more than hip girdle.

Question 3.
State the reason why testes lie outside the abdomen in a scrotum?
Answer:
Both the testes remain in the scrotum because normal body temperature are to high, scrotum has smooth muscle tissues that keeps the testes at a cooler temperature than the body temperature 2°C to 3°C lower than the body temperature which is the most suitable temperature for sperm production.

Question 4.
Why is it important that a very large number of sperms should be present in the semen ?
Answer:
Single ejaculation of semen has 20,000,000 to 40,000,000 sperms. But only 1 or 2 sperms go into oviduct and fertilise the egg to form the Zygote. It forms embryo that forms an individual. It is the sperm in the semen that are of importance, and therefore semen quality involves both sperm quantity and quality.

Question 5.
List the structures, in their correct sequence, through which the sperms must pass from the time they are produced in the testes to the time they leave the urethra.
Answer:
Sperms are produced in testes. They pass as follows:
The testes consist of a mass of sperm producing tube. The tubes join to form ducts leading to the epididymis which in.turn leads into a muscular sperm duct. The two sperm ducts, one from each testes, open at the top of the urethra.

Question 6.
State the functions of the following:
(a) Ovary
(b) Testes
(c) Fallopian tubes
(d) Seminal vesicle
(e) Uterus
Answer:
(a) Ovary: Ovaries produce ova (eggs) and secrete female sex hormones, oestrogen and progestrone.
(b) Testes: A pair of testes are present in human male. The testes produce sperms.
(c) Fallopian tubes: There are two fallopian tubes in the human female reproductive system. Fertilization occurs in the fallopian tube. It also conveys fertilized egg to the uterus.
(d) Seminal vesicle: The function of seminal vesicle is to store sperms and to secrete seminal fluid.
(e) Uterus: The inner lining recieves, protects and nourishes embryo. Contractions of muscular wall expel baby during birth.

Question 7.
Given here is a section of the female reproductive system of human beings.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 1
(a) Name the parts labelled 1 to 4
(b) Name the part where fertilisation occurs in human beings.
Answer:
(a)

  1. Ovary
  2. Fallopian tube (Oviduct)
  3. Uterus (Inner lining or Muscular wall)
  4. Vagina

(b) Fertilisation occurs in the upper part of the oviduct. Sperm fuses withthe egg and zygote is formed this is called fertilisation.

Question 8.
Given alongside is a diagram of male reproductive system in humans. Label the parts indicated by numbers 1 to 5, and state their functions.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 2
Answer:

  1. Seminal vesicle: The seminal vesicles produce a secretion which serves as a medium for the transportation of the sperms.
  2. Prostate gland: Prostate gland which pours an alkaline secretion into the semen as it passes through the urethra.
  3. Testes: Sperms are produced in the testes.
  4. Urethra: Urethra passes through the penis and carries either urine or semen.
  5. Sperm duct: The sperm pass through the sperm ducts.

Long Answer Questions:

Question PQ.
Define the term metamorphosis. Briefly describe the various stages occurring in the life-cycle of a butterfly.
Answer:
Metamorphosis: A change in the form and often habits of an animal during normal development after embryonic stage complete transformation from an immature form to an adult form in two or more distinct stages.

Life cycle of butterfly: The butterfly lays its eggs on the leaves of the plants. The new born that comes out of the egg is called larva. It passes through various stages of development. The larva of butterfly is also called Caterpillar. It is very active. It is very voracious. It feeds and moves actively and gains size.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 3

It stops moving and eating and it is called pupa. It is a resting stage. The pupa spins thread around itself and thus is enclosed in a covering. It is called cocoon. This cocoon covers the pupa and is protective in function. During this stage it forms the features of an adult. After attaining adulthood the pupa comes out of the cocoon after breaking it as an adult butterfly. The wings of emerged butterfly are wrinkled and soft. After an hour these are fully stretched and it starts flying.

Question PQ.
What is fertilization? Describe the process in human beings.
Answer:
Fertilization: The fusion of male (sperm) and female (ova) gamete is called fertlization.

As the male performs sexual act with the female and as a result of it the semen is deposited in the vagina of the female. Thus the semen has millions of sperms. Only a few of these sperms are able to reach the upper part of the oviduct. If there is an egg in the oviduct it is fertilized by the sperm. As sperm enters the egg and this leads to the formation of zygote, this act is called fertilisation.

During fusion only the head part of the sperm, which has nucleus, enters the egg. The tail is left behind. The nucleus of the sperm and egg fuse and form the zygote. Soon this zygote becomes many called embryo and reaches the uterus and implants on the wall of the uterus and forms the foetus. Baby develops with in the gestation period of 280 days. After this the baby is delivered.

Question 1.
How does a single called fertilized egg grows into an adult in human beings?
Answer:
Fertilised egg i.e., zygote divides and redivides and forms a ball of cells. This is a kind of embryo and it reaches the uterus and gets attached to the wall of the uterus. This fixing of embryo to the uterus is called implantation. Now the embryo undergoes a process “specialisation of cells’’. It leads to the formation of different parts of the body. This process is called differentiation. It leads to the formation of various tissues and other organs and thus organ systems are formed. Organ system lead to the formation of an individual. Thus the zygote forms an embryo, it forms a baby and it forms an adult.

Question PQ.
Tabulate the important physical changes in the boys and girls that take place during puberty.
Answer:
Reproductive system of boys and girls mature during puberty. Puberty starts at 10 in girls and at 11 in boys. Testes enlarge in boys and breasts develop in girls. The following table shows the physical changed in boys and girls that take place during puberty.

Boys

  1. Testes become large
  2. Scrotal sac grows and penis becomes long.
  3. Length increases and shoulder girdle grows becomes more.
  4. Hair grow on the chest arm pits and on the sex organs.
  5. Facial hair and moustaches grow.
  6. Voice becomes hoarse and deep.

Girls

  1. Breasts become large.
  2. Ovaries become large and these release eggs. Size of uterus and vagina grows. Menstruation cycle starts.
  3. Sudden grow th takes place in length. Hip girdle becomes trough shaped, it larger than the shoulder girdle.
  4. Chest and abdomen do not have hair. But hair arise on the sex organs and the arm pits.
  5. No moustaches and facial hair.
  6. High pitch voice.

Question 2.
Describe the human female reproductive system with a labelled diagram.
Answer:
On each side of the uterus two white oval bodies lie. These are called ovaries. Eggs are produced in the ovaries. Nearer to the ovaries there lies expanded funnel shaped oviducts or fallopian tubes. The eggs go into the oviducts when released by the ovaries. The two oviducts open into the uterus. The walls of the uterus are muscular. The growing embryo lodges to the wall of the uterus. It is supplied by the food and blood through the placenta w hich is a connection betw een the growing embryo and the mother. The uterus joins the vagina. It is the vagina in which semen is lodged during sexual act. From here sperms go up into the oviduct and fertilise the egg. The urethra which brings urine from the urinary bladder opens into the.vulva just in front of the vaginal opening.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 4

Question PQ.
‘Adolescence is a crucial stage’. Justify this statement.
Answer:
During adolescence physical and emotional changes takes place in the body of boys and girls. This is period between the age of 10 to 19 and this is very critical period. Boys bear facial hair, muscular body, hair in the arm pits and on the sex organs, and have hoarse voice. The girls also have beautiful contours, raised breasts, wide lips and high pitch voice. The body increases in length in both cases. Boys and girls becomes conscious about the growth of the body. They become hesitant and shy to each other. They become body conscious and spend lot of time on dressing up and grooming. Hormonal level increases in their body and become restless.

Hormones affect their brains and control their emotions and moods. They cherish the company of their own sexes and show the attraction for the opposite sex. Thus it is very strange and crucial stage in their life. So adolescence is a very crucial stage in the life of the boys and the girls.

Selina Concise Biology Class 8 ICSE Solutions – Food Production

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Selina Concise Biology Class 8 ICSE Solutions – Food Production

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 9 Food Production. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 9 Food Production

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(i) Which one of the following is an indigenous breed of dairy cows ?

  1. Jersey
  2. Frieswal
  3. Sahiwal
  4. Dangi

(ii) Which one of the following is the common breed of buffalo found in Gujarat ?

  1. Surti
  2. Murrah
  3. Gir
  4. Mehsana

(iii) Identify the indigenous breed of poultry of India:

  1. White leghorn
  2. HH-260
  3. Aseel
  4. B-77

(iv) Which one of the following is a rabi crop

  1. Mustard
  2. Pea
  3. Rice
  4. Wheat

(v) Identify the Kharif crop:

  1. Barley
  2. Mustard
  3. Rice
  4. Wheat

(vi) One of the following is a bacterial disease of sheep and goat. Identify it.

  1. Sore mouth
  2. Rinderpest
  3. Goat pox
  4. Brucellosis

(vii) Which one of the following is a bacterial disease of cattle in which the animal gets swelling on body parts, especially on the neck ?

  1. Cow pox
  2. Anthrax
  3. Salmonellosis
  4. Rinderpest

(viii) The plants that live for more than two years are called:

  1. Annuals
  2. Perennials
  3. Biennials
  4. Triennials

(ix) Which one of the following is a viral disease of poultry?

  1. Ranikhet disease
  2. Cholera
  3. Coryze
  4. Aspergillosis

Short Answer Questions:

1. Fill in the blanks:

  1. Cattle feed made from cereals and wheat is called concentrates.
  2. Rearing of birds for egg and meat is called poultry.
  3. Animal food is rich in proteins.

2. Name the following:

  1. The popular indigienous breed of poultry of India …..
  2. Rearing of honey bee …..
  3. Architect of white revolution in India …..
  4. A kashmiri goat which gives expensive wool ….
  5. Scientist responsible for green revolution in India ……

Answer:

  1. The popular indigienous breed of poultry of India Aseel.
  2. Rearing of honey bee is called apiculture.
  3. Architect of white revolution in India Mr. Verghese Kurien.
  4. A kashmiri goat which gives expensive wool kashmiri pashmina.
  5. Scientist responsible for green revolution in India M.S. Swaminathan.

3. Match the columns

Selina Concise Biology Class 8 ICSE Solutions - Food Production 1

Answer:

Selina Concise Biology Class 8 ICSE Solutions - Food Production 2

4. Answer the following questions:

Question 1.
Name any four animals which provide us food.
Answer:
Buffalo, goat, pig, hen, fish give us food.

Question 2.
Name any two dual purpose breeds of cattle.
Answer:
Dangi and Tharparkar are dual purpose breeds of cattle.

Question 3.
Give two examples of milch animals.
Answer:
Cows, buffaloes, goat are milk yielding animals.

Question 4.
Name any two high-yielding indigenous breeds of cow.
Answer:
Gir, Sahiwal, Red sindhi are high yielding breeds of cow.

Question 5.
Name four varieties of edible fishes of India.
Answer:
Eel, Hilsa, Salmon, Sardine, Pomphret are edible fishes.

Question 6.
Name two breeds of buffaloes.
Answer:
Murrah, surti, mehsana are breeds of buffaloes.

Question 7.
Name any two diseases of cattle caused by viruses.
Answer:
Cow pox, foot and mouth disease.

Question 8.
Name any two bacterial iiseases of cattle.
Answer:
Anthrax and rinderpest are bacterial diseases of cattle.

Question 9.
What are the symptoms of foot and mouth disease ?
Answer:
Blisters on the foot and mouth, high body temperature, reduced appetite are symptoms of foot and mouth disease.

Question 10.
Name two bacterial diseases of poultry.
Answer:
Fowl cholera, salmonellosis, coryze are bacterial diseases.

5. Briefly explain the following terms:
Answer:

  1. Animal husbandry: The branch of Biology which deals with feeding, shelter, caring and breeding of domesticated animals is called animal husbandry.
  2. Sericulture: Artificial rearing of silk worm and getting of silk from the silk worms is called sericulture.
  3. Aquaculture: The production and farming of aquatic animals as fishes, prawns, shrimps, molluscs, lobsters etc. is called aquaculture.
  4. Hatcheries: We raise small nurseries where water is stored in small pits where we put fish seeds (fish eggs). From these fish eggs very small fish come out after hatching. Then these small fish are transferred to big ponds. These small nurseries where eggs hatch to give small fish are called hatcheries.
  5. Pisciculture: It deals with production and management of fishes. It is a scientific, systematic way of raising of fishes, their multiplication, their production and management. So it is used as food in a sensible way.

6. What is organic farming?
Answer:
Organic farming is the practice of raising crops without using inorganic fertilisers and pesticides. Farmers use organic manure that has been prepared scientifically. In order to maintain soil fertility, and for weed and pest control, they use a combination of crop rotation, hand weeding, mixed cropping and biological control.

Long Answer Questions:

Question 1.
Differentiate between an egger and a broiler.
Answer:
Following are the differences between the egger and the broiler:
Egger

  1. Egg laying chickens are called eggers or egg layers.
  2. The chicks are given calcium (bones, seeds) and are reared to produce eggs.
  3. Eggers should give large number of eggs as white leghorns give many eggs. Rhode island red breeds like HH-260, IBL-80, B-77.

Broiler

  1. Chickens which give us meat are called broilers.
  2. Those chicks are reared on a diet of fats so that they gain flesh on their body and these are used as broilers.
  3. Broilers should give flesh. Indigenous variety Aseel give high yield of meat and less number of eggs.

Question 2.
Name any two exotic breeds of fowl in India, and mention their usefulness
Answer:
Exotic breeds of fowl in India are as:

  1. White leghorn: Its size is small and needs less feed for maintenance. So to raise it is economical. It lays oval white eggs.
  2. Rhode island red: It serves both the purposes as it is a good egg layer and also provide enough of meat. It was raised on a farm in Rhode island of U.S.A. So it is named as Rhode island red.

Selina Concise Biology Class 8 ICSE Solutions - Food Production 3

Question 3.
What are “milch animals”? Give three examples of exotic breeds of cow.
Answer:
Milk-producing animals are known as “milch animals” e.g. cows, buffaloes, goats and camels. The milk from goats is nutritious and is sometimes preferred to cow milk. But the production of goat milk is much less than that of cows and buffaloes. Cow milk is quite nourishing and easy to digest, but as compared to buffaloes, cows produce less quantity of milk. Buffaloes are the major source of milk in our country.
Exotic (Foreign) breeds. For example. Jersey, Holstein- Friesian, and Brown Swiss.

Question 4.
What is the meaning of the term “aquaculture”? Name any three animals which can be cultured by this method.
Answer:
The term “aquaculture” is used for production or farming of useful aquatic animals in various types of water bodies. The animals which can be cultured by this method are: fish, prawns, lobsters, molluscous, etc.

Question 5.
Differentiate between food crops and cash crops and give two examples of each:
Answer:
Differences:
Food crops

  1. These are crops which are grown for food such as cereals: wheat, rice, maize, pulses, oil seeds.
  2. These grow in the plains generally.
  3. These are annuals and complete their cycle in one season as in case of wheat, rice maize, gram, beans, peas.

Cash crops

  1. These are crops which are cultivated for commercial purposes such as tea, coffee, rubber, coconut, spices.
  2. These grow in the hilly areas on the slopes as water of rain should not stand in the roots as in case of tea.
  3. These plants are perennials. These plants live for more than two years. Tea, coffee require pruning before winter.

Question 6.
What are Kharif crops ? Give the name of the most important cereal plant of such crops. Briefly describe any three methods for cultivation of Kharif crops.
Answer:
Kharif crops generally grow in rainy season. Rice is the most important cereal Kharif crop growing in India. It occupies the largest area in India. It needs rainfall from 150 to 200 cms. It requires flooded fields during its growth. It requires alluvial loamy soil.

Cultivation methods of Kharif crops:

  1. Broadcasting: After preparing the fields for growing the rice crop the seeds are thrown in the fields. This method is adopted in the areas where there is less of rain. The fields are not flooded with water. This method is being adopted in China and Japan.
  2. Dibbling: In this method seeds are dropped at regular interval in the furrows made by the plough.
  3. Transplantation: Here the seeds are soaked for 24 hours. The seeds get sprouted. Then these seeds are transferred to nurseries. Here the seeds grow and attain a height of 6” to 9” and then these seedlings are transferred to specially prepared flooded fields which have been properly ploughed. Then those seedlings start growing in the fields. Then the fields are watered and manured from time to time. Then the crop matures and ultimately for ripening they require a temperature ranging from 16°C to 20°C. When the crop become fully ripe and plants become golden yellowish, then the crop is harvested manually or with the help of combines.

Question 7.
Name the two main crop seasons of India. Give three examples of the crops grown during each season.
Answer:
The two main crops seasons in India are:

  1. Kharif season: The rainy season is from July to October and is known as the Kharif Season. The chief kharif crops are the milles, known as Bajra and Jowar, Paddy, Maize, Cotton.
  2. Rabi season: The winter season is from November to April and is known as rabi season. Wheat, Gram, Peas, Linseed and Mustard are important rabi crops.

Question 8.
List the uses of bacteria in the food industry.
Answer:
The bacterial action is involved in the following industrial processes.

  1. In the manufacture of vinegar, butter and cheese.
  2. The process of tanning hides in leather making and preparing sponges.
  3. The separation of flax and hemp fibres which are used for making linen cloth and ropes.
  4. Fermentation of green plants for the production of ensilage for animal food.
  5. Bacteria are used for forming lactic acid, vinegar, citric acid, and vitamins.
  6. For formation of antibiotics, serums and vaccines, vitamin B complex.

Question 9.
Name any one variety of edible mushrooms.
Answer:
White button mushroom (Agaricus bisporous) and paddy straw mushroom (Volvariella) the two varieties of edible mushrooms.
Five major steps in cultivation of the common edible mushroom are as below:

  1. Composting: The compost is prepared by mixing the following in certain proportions.
    • Wheat or paddy straw,
    • Chicken manure
    • Some organic and inorganic fertilizer
      This compost is kept at about 50°C for a week.
  2. Spawning: “mushroom seed” consisting of mycelium of the selected type of mushroom is introduced into the compost, and allowed to spread for a couple of days.
  3. Casting: A thin layer of soil is spread over the compost to give support to the mushroom and provide humidity. It also prevents quick drying of the compost and helps to regulate temperature.
  4. Cropping and Harvesting: The growth occurs in three stages:
    (a) Mycelium (a network of fibrous mass) grows within 2 to 6 weeks.
    (b) Tiny pin heads.
    (c) Button stage which grows bigger attaining marketable size.
    The full grown mushrooms are taken out.
  5. Preservation: Mushrooms are highly perishable. Their shelf life is increased by a variety of processes
    (a) Vacuum cooling
    (b) Giving gamma radiation and storing at 15°C
    (c) Freeze drying in a solution of citric acid, ascorbic acid and brine, etc.

Question 10.
Mention the benefits of “Green revolution” in our country.
Answer:
Green revolution: Knowledge of science has brought about manifold increase in the production of grains, pulses and other crops and led to green revolution. Factors leading to it are:

  1. development of high – yielding varities.
  2. development of early – maturing varities.
  3. disease – resistant varities.
  4. using of fertilizers and pesticides.
  5. development of drought – resistant and dwarf varities.

Dr. M.S. Swaminathan is known as the father of green revolution in India which has led to manifold increase in the production of wheat and rice using hybrid varities (wheat – Kalyan Sona and Sonalika, Rice – IR – 8 Padma, Jaya and Pusa 215, Maize – Ganga 101 and Rankit).

Question 11.
Mention the benefits of “White revolution” in our country.
Answer:
The benefits of “White Revolution” in our country:

  1. The purpose of this programme was to link the rural producer (dairy farmer) with the urban consumer.
  2. Rural farmer co-operatives were organized at the village level and connected to the urban consumer.
  3. It ensured that the dairy farmer got a major share of the price of milk which consumers pay.

The “Operation flood” ensured thre objectives:

  1. increased milk production
  2. strengthened the dairy farmer’s income.
  3. easy availability of milk at a fair price to all.

Question 12.
Write briefly the processes of

  1. wine (alcohol) making and
  2. bread making.

Answer:

The steps for making

  1. Wine (alcohol): Wine is usually made from grapes. The grapes are crushed and the juice is extracted. The juice contains sugar and wild yeast.The yeast ferments the sugar and gradually turns it into alcohol.
  2. Bread: Mix some flour and water with a small amount of sugar and yeast. This makes dough. Then leave the dough for an hour or so in a warm place. During this period the living yeast cells multiply and fermenting sugar to form alcohol give off carbon dioxide gas. The gas so produced makes the dough rise, more or less doubling its size. Then when you bake the dough in a hot oven: the heat kills the yeast and evaporates the alcohol.

Question 13.
Give any five features of good shelter for milch animals.
Answer:

  1. Animal shelter should be very clean, well ventilated and well-lit.
  2. Cattle should have proper sheds, so that animals are safe from rain, cold and heat.
  3. The floor should have a proper sloping so that urine and excreta can be disposed of easily.
  4. Animals should have proper feeding and drinking tubs.
  5. Animal shelter should be spacious and there should not be over crowding.
  6. It should have arrangements for clean fresh drinking water.
  7. The shelter should give protection from predators.
  8. Shelter should be located away from the residential areas and waste disposal sites.

Question 14.
What type of food you would suggest for cattle in order to get good quality of milk ?
Answer:s
Cattle should be given good quality type of food which is proper for their growth, development, health and for their maintenance. Animal food is feed.
This cattle feed has two types of substances.

  1. Roughage: The animals get roughage from hay (straw of cereals), berseem, cowpea, lucerne, silage, maize, bajra and other green plants.
    These plants generally provide fibrous substances and other minerals.
  2. Concentrates: These are rich in carbohydrates, proteins, fats, minerals, and vitamins, concentrates are given by.
    • Grains and seeds of bajra, maize, rye, gram, cotton, jowar, barley. These provide carbohydrates.
      Legume seeds and cotton seeds provide proteins and fats.
    • Oil cakes: These oil cakes are very good feed for the animals. These are formed from the remains of oil seeds after we get the oil from the seeds. We get oil cakes from the seeds of cotton, mustard.
    • Molasses are rich in proteins.
    • Wheat bran, rice bran, and gram bran also give concentrates.

Selina Concise Biology Class 8 ICSE Solutions – Nervous System

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Selina Concise Biology Class 8 ICSE Solutions – Nervous System

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 7 Nervous System. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 7 Nervous System

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Medulla oblongata controls

  1. Smelling
  2. Beating of heart and respiratory movement
  3. Intelligence and will power
  4. Balancing the body

(b) Balance of body is controlled by:

  1. Spinal cord
  2. Cerebellum
  3. Cerebrum
  4. Medulla

(c) The smell of good food causes watering of your mouth. It is a

  1. Natural reflex
  2. Acquired relfex
  3. Inborn reflex
  4. Ordinary reflex

(d) The structural and functional unit of nervous system is a

  1. Axon
  2. Nephron
  3. Neuron
  4. Texon

Short Answer Questions:

Question 1.
Name the two types of coordination which take place in our body.
Answer:
(a) Nervous coordination: By nerves and brain
(b) Chemical coordination: By hormones

Question 2.
Your are driving your bicycle at a fast speed. Suddenly, a small boy comes in front of your cycle and, without wasting any time in thinking, you immediately apply the brakes and accident is avoided. What name is given to such an action?
Answer:
Reflex action (acquired).

Question 3.
Given below is the diagram of a neuron. Name the parts numbered 1-5.
Selina Concise Biology Class 8 ICSE Solutions – Nervous System 1
Answer:

  1. Dendrite
  2. Nucleus
  3. Cell Body (Nyton)
  4. Axon (Nerve fibre)
  5. Node of Ranvier

Question 4.
Write one word in the space provided to complete the second pair of the related words pertaining to nervous system.
Memory : cerebrum : : breathing :
Balance : cerebellum : : reasoning :
Answer:
Memory : cerebrum : : breathing: medulla oblongata
Balance : cerebellum : : reasoning : cerebrum

Question 5.
Differentiate between the following pair of terms:
(a) Stimulus and impulse
(b) Receptor and effector
(c) Motor nerve and sensory nerve
Answer:
(a) Stimulus: Any change in the environment that usually results in change in the activity of the body.
Impulse: A wave of electrical disturbance that runs through the nerves.

(b) Receptor: The nerve cell on receiving the stimulus sets up the waves of impulses towards the central nervous system.
Effector: Any muscle or gland on receiving the impulse from the brain (or the spinal cord), contracts or secretes.

(c) Motor nerve: It contains only motor neurons,
Example: Nerves going to the muscles of the eyeball.
Sensory nerve: It contains only sensoiy neurons.
Example: optic nerve of the eye.

Question 6.
(a) Name the three major divisions of the human nervous system.
(b) Name the three main parts of human brain.
Answer:
(a)

  1. The central nervous system (brain and spinal cord)
  2. The peripheral nervous system
  3. The autonomic nervous system

(b)

  1. Cerebrum
  2. Cerebellum
  3. Medulla oblongata

Question 7.
Give the function of each of the following:
(a) Olfactory nerve:
(b) Optic nerve:
(c) Facial nerve:
Answer:
(a) Olfactory nerve: The sense of smell is present in the epithelial layers of the nasal chambers. The sense of smell is carried to the brain by the olfactory nerve. They arise from the anterior ends of the olfactory lobes and are distributed to lining of nasal chambers.
(b) Optic nerve: It carries the reflection of the object from the retina to the brain. The image formed on the retina is in a reverted position and the correct picture is formed in the brain as the object is. The optic nerves arise from the side of diencephalon. They innervate the retina of the eye and are sensory in nature.
(c) Facial nerve: It carries message and all expressions of the face, mastication work alone by the teeth, movement of the neck and the activities of the salivary glands to the brain. It arises from the side of medulla. On the whole facial nerves are mixed in nature.

Long answer questions

Question 1.
With the help of a suitable diagram describe the structures of a neuron.
Answer:
Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.
Selina Concise Biology Class 8 ICSE Solutions – Nervous System 2
The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this:
Organ → Message goes to dnedrites → Cell body → Axon → Muscles or glands

Question 2.
Briefly describe the structure of the cerebrum in human brain and mention its functions.
Answer:
Brain consists of main three parts and lies in the cranial cavity of skull.

  1. The cerebrum
  2. The cerebellum
  3. The medulla oblongata

Cerebrum: It is very large and form two third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.

Functions:

  1. It controls all the voluntary activities.
  2. It is the seat of intelligence, consciousness and will power.

Question 3.
Mention the three functions of spinal cord.
Answer:
Spinal cord has the following functions.

  1. It is the centre of reflex actions below the neck.
  2. It carries messages from the skin and muscles to the brain.
  3. All the stimuli and responses are passed from and to the brain through the spinal cord.

Question 4.
With the help of suitable example, describe reflex action.
Answer:
Reflex action: Reflex actions are automatic responses to stimuli. These actions are not under the control of the animal. They are of definite and mechanical type. Peripheral nervous system and spinal cord both control certain action and the brain is not in action.
Some examples of reflex actions are:

  1. Pupil becomes narrow when strong light falls on it.
  2. The aroma of the food makes the mouth watering.
  3. The hand is withdrawn as we touch the hot plate.
  4. Flow of bile from the gall bladder into the duodenum.
  5. A loud thud may lead to opening of the mouth.

In a reflex action brain is not involved, removing the hand on touching a hot plate is a reflex action. The impulse of heat goes from the hand to the spinal cord and the order is sent back to the muscles of the hand to remove the hand from the hot plate.

Question 5.
Describe three kinds of nerves, giving the example of each.
Answer:
A nerve is formed by a group of nerve fibres (axons) encased by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons (nerve fibres) We have three kinds of nerves:

Selina Concise Biology Class 8 ICSE Solutions – Nervous System 3

  1. Sensory nerve: It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
  2. Motor nerves: These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eye ball.
  3. Mixed nerve: It has both sensory and motors fibres as nerve going to the tongue.

Question 6.
Differentiate between natural reflex and conditioned reflex. Give examples to illustrate your answer.
Answer:
Natural reflex: It is one in which no previous experience or learning is required. These reflexes are inborn i.e. inherited from the parents.
Examples are

  1. Blinking, coughing, sneezing as these are protective reflexes
  2. Salivation, swallowing, peristalsis as it provides functional efficiency.
  3. Dilation of the eyes pupil to look in the dark and vice versa. It is muscular movement.
  4. Pushing along of swallowed food through the food canal. It is muscular movement.

Conditioned Reflex: It is one which develops during lifetime due to experience or learning.
Examples are:

  1. Watering of mouth (Salvination) at the sight of a tasty food.
  2. Surfing the channels while watching the television.
  3. Typing of a keyboard of a computer.
  4. Playing a musical instrument.