LIFE PROCESSES

1. How are the alveoli designed to maximise the exchange of gases?

Ans. A) small pouches or sacs like structure. B) richly supplied with blood
capillaries. C) large surface area maximises the exchange of gases. D) thin walls

2. Why do the walls of the trachea not collapse when there is less air in it?
Ans. Rings of cartilages are present in trachea. These rings support the trachea
and do not allow the trachea to collapse when there is less air in it.

3. State the role of the following in human digestive system:

(i) Digestive enzymes (ii) Hydrochloric acid (iii) Villi
Ans. (i) Digestive enzymes – Foods need to be broken into their small or simpler
molecules so that they can be absorbed into the bloodstream. Enzymes are hence
needed for the chemical breakdown of food and speeding up the digestive
process. The products of digestion can hence be small enough to be absorbed.
(ii) Hydrochloric acid – Hydro chloric acid helps to kill the germs which might
have entered in to the system through food. It creates acidic medium for the
pepsin to act on food to breakdown proteins.
(iii) Villi – Villi are finger like projections in the small intestine. They help to
increase the surface area for absorption of the digested food. Villi are richly
supplied with blood vessel which help to absorb digested food in to the blood
stream.

4. List in tabular form three differences between arteries and veins.

Arteries Veins

Carries blood from body towards heart Carries blood from heart to body parts

Thick walled as blood flows with high Thin walled as blood flows with low
pressure pressure

Deeply seated Superficial situated

Does not contain valves Contains valves to prevent back flow of

blood

5. Explain the process of breakdown of glucose in a cell.

Ans. The process of breakdown of glucose in a cell are as follows:
6. List the three events that occur during the process of photosynthesis.
Ans. The three events that occur during the process of photosynthesis are:
(i) Absorption of light energy by the green pigment chlorophyll.
(ii) Conversion of light energy into chemical energy and the splitting of water
molecule into hydrogen and oxygen.
(iii) Reduction of carbon dioxide into carbohydrate.

7. Explain the role of stomata in this process.

Stomata are tiny pores present on the surface of leaves. They are also present
on the surface of young stems. Stomata are mainly engaged in the exchange
of gases (entry of CO2 and release of O2 ) associated with photosynthesis.
Plant closes the stomata when it does not need CO2 for photosynthesis.

8. (a) State the roles of Liver and Pancreas.

(b) Name the organ which performs the following functions in humans:
(i) Absorption of digested food (ii) Absorption of water.
Ans:
(a) Liver: It synthesize and store bile juice secreted by gall bladder which
breaks down fats into fat globules. Pancreas: It secretes pancreatic juice which
contains protein-digesting and starch- digesting enzymes.
(b) The organ which performs the following functions in humans are as follows:
(i) Absorption of digested food – Small intestine.
(ii)Absorption of water – Large intestine

9. What advantage over an aquatic organism does a terrestrial organism have

with regard to obtaining oxygen for respiration? [Advantage of terrestrial
animals over aquatic for respiration].
 Ans. The amount of oxygen dissolved in water is very low, as compared to
amount of oxygen in air. Thus, terrestrial organism has to make less efforts to
obtain oxygen than an aquatic organism to obtain oxygen for respiration.

CONTROL AND COORDINATION

1. Write one example each of the following tropic movements:
(i) Positive phototropism (ii) Negative phototropism
(iii) Positive geotropism (iv) Negative geotropism
(v) Hydrotropism (vi) Chemotropism
Ans.
(i) Positive phototropism: shoots growing towards light.
(ii)Negative phototropism: roots growing away from light towards ground.
(iii) Positive geotropism: growth of roots towards earth due to the pull of the earth.
(iv)Negative geotropism: shoots growing away from the earth.
(v) Hydrotropism: roots growing towards the source of water.
(vi)Chemotropism: growth of pollen tubes towards the ovules.

2. What is a reflex arc?

Ans: Reflex arc is the pathway taken by the nerve impulses and responses in a
reflex action, i.e. from the receptor organs like skin to the spinal cord and from the
spinal cord to the effector organs like muscles.

3. Give functions of various parts of human brain.

Ans.
1. Fore Brain a) Cerebrum: It is the thinking part of the brain and controls
voluntary actions.
It is responsible for reasoning, speech, intelligence, sight, hearing and usage of
information.
b) Olfactory lobes: It is responsible for detecting smell from different receptors.
c) Hypothalamus: this part controls the body temperature, urge of eating, drinking
(hunger and thirst).
2. Mid Brain: Controls reflex actions
 Controls the movement of head, neck and trunk to locate sounds and visual
reflexes. Also controls the movements of eye muscles, pupil size etc.
3. Hind Brain:
a) Cerebellum: Maintains balance, posture and equilibrium of body during
various actions like walking, drinking, catching, riding etc.
b) Pons: controls respiration and breathing.
c) Medulla: Controls involuntary actions such as heart beat, breathing, blood
pressure etc. Also regulates reflex responses of swallowing, coughing,
sneezing, vomiting etc.

4. Name the hormone and function of endocrine glands.

Gland Hormone Function
Pituitary gland Growth hormone Controls growth
Thyroid gland Thyroxin Controls metabolism of carbohydrate,
protein and fat
Control calcium level
Adrenal gland Adrenaline Increases blood pressure, heart beat,
(emergency breathing rate
hormone) Prepares body for emergency situation
Pancreas insulin Controls blood glucose (sugar) level
5. What are phytohormones? Name them.
Ans. Plant hormones are phytohormones. They are
1. Growth promoter: Auxin and gibberellin
2. Growth inhibitor: Cytokinin and abscisic acid

How do organisms reproduce?

1. (a) In the human body what is the role of

(i) seminal vesicles, and (ii) prostate gland?
Ans. The role of seminal vesicles and the prostate gland are as follows:
(i) Seminal vesicles produce seminal plasma which is in the form of fluid makes
the transport of sperms smooth.
(ii) Prostate gland secretes prostatic fluid that keeps the sperms alive and helps
them to swim vigorously.

2. List two functions performed by testis in human beings.

Ans. Two functions performed by testis in human beings are as follows:
(i) Formation of sperms takes place in testis.
(ii) They secrete the hormone testosterone which regulates the formation of
sperms and brings changes in appearance of boys at the time of puberty.
3. Name two sexually transmitted disease each caused due to bacterial infection
and viral infection.
Ans: Bacterial disease: Gonorrhea, syphilis
Viral diseases: AIDS, warts

4. (a) Name the following parts.

(i) Production of an egg: Ovaries
(ii) Fertilisation takes place: oviduct or fallopian tube
(iii) Implantation of zygote: uterus
(b) What happens to the lining of uterus:
(i) before release of a fertilised egg?
(ii) if no fertilisation occurs?
Ans.
(i) The lining of uterus becomes
(ii) The lining of uterus slowly breaks and comes out through the vagina as blood
and mucous, if no fertilisation occurs.

5. (a) Explain the terms: (i) Implantation (ii) Placenta

Ans: (a) (i) Implantation: The embedding of a fertilised mammalian egg (embryo)
into the inner thick wall of the uterus (womb) where it will continue its development
is called implantation.
(ii) Placenta: It is a complex double-layered spongy vascular tissue in human female
formed by the joint activity of maternal and foetal tissues in the wall of uterus that is
meant for attachment, nourishment and waste disposal for the foetus.

6. List any three differences between pollination and fertilisation.

Ans:

7. List and explain in brief three methods of contraception.

Answer. Methods of contraception are:
a. Use of condom for penis or for vagina as a mechanical barrier for the sperms
to reach the egg.
b. Use of oral pills which change the hormonal balance so that eggs are not
released.
 c. Surgical method where either the vas deferens of male is blocked or the
fallopian tube of female is blocked.

8. List different asexual reproduction types with one example of each.

Ans:
a. Binary fission: amoeba, paramecium, leishmania
b. Multiple fission: plasmodium
c. Budding: yeast, hydra
d. Regeneration: Planaria
e. Fragmentation: Spirogyra
f. Spore formation: fungus (rhizopus)

9. List two advantages of vegetative propagation.

Ans: (i)Vegetative propagation is a cheaper, easier and more rapid method of
propagation in plants than growing plants from their seeds.
(ii) Better quality of the plants can be maintained by this method.
(iii) new plants are exact copies of parent plants.

10. Name the following parts:

(i) Part that produces pollen grain: anther
(ii)Part that transfers male gametes to the female gametes: pollen grain
(iii) Part that is sticky to trap the pollen grain: stamen
(iv) Part that develops into a fruit: ovary
(v) Part that develops into a seed: ovule

HEREDITY

1. Define variation in relation to a species. Why is variation beneficial to the species?

Ans. Variation refers to the differences in the characters or traits among the
individuals of a species. Variations are beneficial to the species because:
a) They enable the organisms to adapt themselves in changing environment.
b) Variations form the basis of heredity.
c) They form the raw materials for evolution and development of new species.

2. Explain the mechanism of sex determination in humans.

Or
With the help of a flow chart explain in brief how the sex of a newborn is
genetically determined in human beings. Which of the two parents, the mother or
the father, is responsible for determination of sex of a child?
Ans. Mechanism of Sex Determination in Human Beings
In human beings, the sex of the individual is genetically determined.
a. Sex determination is the process by which sex of a new born individual can be
determined.
b. Human beings have 1 unpaired sex chromosome. Sex chromosome of male is
XY and of female is XX.
c. Sex of a child depends on what happens at fertilisation.
Thus, father is responsible for the determination of the sex of a child.

3. Differentiate between inherited trait and acquired trait.

Ans:

4. Note:
Mono hybrid cross
F1 generation: all dominant character in phenotype (appearance)
F2 generation: Phenotypic ratio- 3:1 (3 dominant and 1 recessive)
Genotypic ratio- 1:2:1 (2 old combination and 2 new combination)
Dihybrid cross
F1 generation: all dominant character in phenotype (appearance)
F2 generation: Phenotypic ratio- 9:3:3:1

5. Why did Mendel choose green pea for his experiment?

Ans. Mendel chose pea plants for studying inheritance because
• pea plants had a number of contrasting characters. For example: tall and dwarf
pea plants, round yellow seeds, wrinkled green seeds etc.
• pea plants are self pollinating.
• Short life span, more generations can be produced in one year.
 OUR ENVIRONMENT

1. What will happen if we kill all the organisms in one trophic level?
Ans. If we kill all the organisms in one trophic level, the following effects will take
place:
• The population of organisms in previous trophic level will increase.
• The organisms in next trophic level will not be able to get the food, so they will
migrate to some other ecosystem or die.
• It will cause an ecological imbalance in the food chain.

2. What is the role of decomposers in the ecosystem?

Answer. Role of decomposers in the environment:
• They return the nutrients to the nutrient pool.
• They help in completing the different bio-geochemical cycles, thus they
maintain the balance in the ecosystem.

3. What step is being taken to limit the damage to the ozone layer?
Answer. Judicious use of aerosol spray propellants such as fluorocarbon and
chlorofluorocarbons which cause depletion or hole in ozone layer.
Control over large scale nuclear explosions and limited use of supersonic planes.

4. How is ozone formed in the upper atmosphere? How is ozone important to us?
Why is the damage of ozone layer a cause of concern to us? State a cause of
this damage.
Answer. Ozone is formed in upper atmosphere by the reaction of ultraviolet (UV)
radiations on oxygen (O2) molecule.
The important function of presence of ozone in earth’s atmosphere is that it shields
the surface of the earth from ultraviolet (UV) radiations of the sun.
The damage to ozone layer is a cause of concern to us as due to its damage, more
ultraviolet rays reach the earth’s surface causing various health hazards.

A cause of this damage is the presence of large amount of chlorofluorocarbons in

the atmosphere.

5. Explain ‘biological magnification’ with the help of an example.

Answer. The increase in concentration of harmful chemicals in the bodies of
organisms at higher trophic levels is called biological magnification.
Example: increase in amount of pesticides