GRADE 10

BIOLOGY

CHPTER 6 LIFE PROCESSES

QUESTION BANK

JUNE 2022

Q1) In amoeba, food is digested in the:

a) Food vacuole
b) Mitochondria
c) pseudopodia
d) Chloroplast
Correct Answer: Option (a)
Q2) In which of the following groups of organisms, food materials are broken down outside
the body and absorbed?

a) Mushroom, green plants, Amoeba

b) Yeast, mushroom, bread mould
c) Paramecium, Amoeba, Cuscuta
d) Cuscuta, lice, tapeworm

Correct Answer: Option (b)

Q3) The contraction and expansion movement of the walls of the food pipe is called:
a) Translocation
b) Transpiration
c) peristaltic movement
d) Digestion
Correct Answer: Option ©
Q4) What are the products obtained by anaerobic respiration in plants?
a) Lactic acid + Energy
b) Carbon dioxide + Water + Energy
c) Ethanol + Carbon dioxide + Energy
d) Pyruvate
Correct Answer: Option ©
Q5) When a few drops of iodine solution are added to rice water, the solution turns blue-
black in colour. This indicates that rice water contains:
a) Fats
b) Complex proteins
c) starch
d) .Simple proteins
Correct Answer: Option ©

Q6.The respiratory pigment in human beings is:

a) Carotene
b) Chlorophyll
c) haemoglobin
d) Mitochondria
Correct Answer: Option ©
Q7) Which of the following is the important characteristic of Emphysema?
a) Destruction of the alveolar wall and air sacs in the lungs are damaged.
b) Increase in the growth of the lung tissue.
c) Inflammation in the wall of bronchi.
d) Thickening of the artery walls of the lungs.
Correct Answer: Option (a)
Q8) The image shows the bread moulds on a bread

How do these fungi obtain nutrition?

a) By eating the bread on which it is growing
b) By using nutrients from the bread to prepare their own food
c) by breaking down the nutrients of bread and then absorbing them
d) By allowing other organisms to grow on the bread and then consuming them
Correct Answer: Option ©
Q9) The characteristic processes observed in anaerobic respiration are
i) Presence of oxygen
ii) Release of carbon dioxide
iii) Release of energy
iv) Release of lactic acid
a) I), ii) only
b) I), ii), iii) only
 c) ii), iii), iv) only
d) Iv) only
Correct Answer: Option ©

Q10) The opening and closing of the stomatal pore depends upon
a) Oxygen
b) Temperature
c) water in the guard cells
d) Concentration of CO2
Correct Answer: Option ©
Q11) The image shows how Amoeba obtains nutrition.
How is this process advantageous for Amoeba?

a) Capturing of food takes less time

b) Complex food can be digested easily
c) more amount of food can be consumed
d) Fast distribution of nutrition within the body
Correct Answer: Option (d)

Q11) A plant gets rid of excess water through transpiration. Which is a method used by plants
to get rid of solid waste products?
a) Shortening of stem
b) Dropping down of fruits
c) shedding of yellow leaves
d) Expansion of roots into the soil
Answer: Option ©
Q12) Chemicals present in the tobacco smoke lead to the breakdown of the elastic tissue in
the alveoli. Name this specific condition.
a) Heart disease
b) Emphysema
c) Bronchitis
d) Lung cancer
Correct Answer: Option (b)
Q13) Digestion of food starts from which organ of the human digestive system?
a) Mouth due to the presence of saliva
 b) Oesophagus that moves the food in gut
c) that releases juices for fat breakdown
d) Which helps in mixing food with digestive juices

Correct Answer: Option (a)

Q14) The image shows the excretory system in humans.
What is the importance of the labelled part in the excretory system?
a) It produces urine.
b) It filters waste from the blood.
c) It the urine till urination.
d) It carries urine from the kidney to the outside.
Correct Answer: Option ©

Q15.The image shows the transport of gases in the body through the heart and lungs.
Which option correctly shows the transport of oxygen to the cell?
a) Lungs →pulmonary vein →left atrium →left ventricle →aorta → body cells
b) Lungs →pulmonary vein →right atrium →right ventricle → aorta → body cells
c) Lungs →pulmonary artery →left atrium → left ventricle → vena cava → body cells
d) Lungs →pulmonary artery →right atrium → right ventricle→ vena cava → body cells
Correct Answer: Option (a)

ASSERTION REASON QUESTIONS FOR CLASS 10 SCIENCE

Following questions consist of two statements – Assertion (A) and Reason ®. Answer these
questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not the correct explanation of A.
© A is true but R is false.
(d) A is false but R is true.

Q.1. Assertion (A) : Plants lack excretory organs.

Reason ® : Plants usually absorb essential nutrients.
Answer(b)
Q.2. Assertion (A) : In anaerobic respiration, one of the end product is alcohol.
Reason ® : There is an incomplete breakdown of glucose.

Answer(a)
Q.3. Assertion (A) : In plants there is no need of specialised respiratory organs.
Reason ® : Plants do not have great demands of gaseous exchange.
Answer(a)

Q.4. Assertion (A) : Bile is essential for digestion of lipids.

Reason ® : Bile juice contains enzymes.

Answer©

Q.5. Assertion (A) : Carbohydrate digestion mainly takes place in small intestine.
Reason ® : Pancreatic juice contains the enzyme lactase.
Answer©
Q.6. Assertion (A) : Aerobic respiration requires less energy as compared to anaerobic
respiration.

Reason ® : Mitochondria is the powerhouse of the cell.

Answer(d)
Q.7. Assertion (A): Arteries are thick-walled and elastic in nature.
Reason ® : Arteries have to transport blood away from the heart.
Answer(b)
Q.8. Assertion (A) : Human heart is four-chambered.
Reason ® : Vena cava is the only artery that supplies deoxygenated blood to the heart.
Answer©

Q.9. Assertion (A): Energy is required to carry out different life processes.
Reason ® : Energy is obtained in the form of ATP in the mitochondria.
Answer(a)
Q.10. Assertion (A): Rings of cartilage are present in the throat,
Reason ® : These ensure that the air-passage does not collapse
Answer(a)

ANSWER THE FOLLOWING (SHORT ANSWERS)

1.What are enzymes? Name any one enzyme of our digestive system and write its function.
Answer. Enzymes are biological catalysts. Catalysts are proteins that increase the rate of
chemical reactions
without being used up. For example: Amylase catalyses the breakdown of starch into sugars in
the mouth and small intestine
2. When do the desert plants take up carbon dioxide and perform photosynthesis ?
Answer.
Desert plants open up their stomata during night and take in CO2. Stomata remains close
during the day time to prevent the loss of water by i transpiration. They store the CO 2 in their
cells until the sun comes out and they can carry on with photosynthesis during the day time.
3.In single celled organisms diffusion is sufficient to meet all their requirements of food,
exchange of gases or removal of wastes but it is not in case of multicellular organisms.
Explain the reason for this difference.
Answer. Unicellular organisms can absorb sufficient oxygen because of its complete contact
with the atmosphere, but in multicellular organisms the rate of absorption and diffusion
becomes very less because all cells are not in direct contact with the atmosphere. Multicellular
organisms require greater amount of oxygen to sustain life processes which cannot be fulfilled
by the process of diffusion.
4. Draw a diagram of human excretory system and label kidneys, ureters on it.

5.Name the acid presents in the following:

(i) Tomato (ii) Vinegar (iii) Tamarind
Answer.Oxalic acid (ii) citric acid (iii) Tartaric acid.
6.State the role of the following in human digestive system :

(i) Digestive enzymes (ii) Hydrochloric acid (iii) Villi

Answer.
Digestive enzymes – Foods need to be broken into their small or simpler
Molecules so that they can be absorbed into the bloodstream. However, the physical
breakdown of food is not enough. 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.

7.(a)Explain how does the exchange of gases occur in plants across the surface of stems, roots
and leaves.
(b) How are water and minerals transported in plants ?
(a) In plants there are tiny pores called stomata on leaves and lenticels in stem which facilitate
the exchange of gases. Carbon dioxide is taken in and oxygen given out {during photosynthesis}
and vice versa during respiration.

(b) Water and minerals are transported within the plant by the Xylem vessels (mainly in an
upward direction); these are part of the vascular system which also includes Phloem vessels.
8. Mention the raw materials required for photosynthesis.
Answer. The following raw materials are required for photosynthesis:
Carbon Dioxide: Plants get CO2 from atmosphere through stomata.

Water: Plants absorb water from soil through roots and transport to leaves.
Sunlight: Sunlight, which is absorbed by the chlorophyll and other green parts of the plant.
9. Why do herbivores have longer, small intestine than carnivores ?
Answer. Digestion of cellulose takes a longer time. Hence, herbivores eating grass need a
longer small intestine to allow complete digestion of cellulose. Carnivorous animals cannot
digest cellulose due to the absence of enzyme CELLULASE, hence they have a shorter intestine.
10.What would be the consequences of deficiency of hemoglobin in your body?
Answer. The deficiency of hemoglobin in our body is called anemia. In anemia, the blood is
unable to carry the sufficient amount of oxygen required by the body. So, respiration would be
less and less energy will be available to the body. The hemoglobin deficient person will feel
weak, pale, lethargic and will be Unable to perform heavy physical work.
11.

a) What is the role of HCl in our stomach ?

(b) What is emulsification of fats ?
© Which protein digesting enzyme is present in pancreatic juice ?
Answer.
(a)(i) It sterilises food by killing pathogens and other microbes.
(ii) It has a pH of 2, which is perfect for entyaus such as pepsin to break down proteins as
effectively as possible.
(iii) Helps emulsify food (digestion of protein and stimulates the pancreas to produce digestive
enzymes and bile) and protects against harmful ‘ bacteria
(b) Breakdown of large gloubule fats into smaller fats droplets is known as emulsification.

© Trypsin is the enzyme secreted by the pancreas which aids in digestion of proteins.
12. Why do the walls of the trachea not collapse’when there is less air in it?
Answer. 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.

13.(a) Draw a diagram to show open stomatal pore and label on it:
(i) guard cells
(ii) chloroplast
(b) State two functions of stomata.

© How do guard cells regulate the opening and closing of stomatal pore?
Answer.
(b) Two functions of stomata are:
(i) Exchange of gases between the plant and the atmosphere takes place through stomata.

(ii)Transpiration in plants takes place through stomata.

© Opening and Closing of Stomatal Pore: The opening and closing of the pore is a function of
the guard cells. The guard cells swell when water flows into them causing the stomatal pore to
open. Similarly, the pore closes if the guard cells shrink. As large amount of water is lost
through these stomata, the plant closes these pores when it does not require carbon dioxide
for photosynthesis
14.(a) Draw a diagram of human respiratory system and label the following:
(i) part where air is filtered by fine hair and mucus

(ii) part which terminates in balloon – like structures

(iii) balloon – like structures where exchange of gases takes place. (iv) part which separates
chest cavity from abdominal cavity.
(b) Why is the rate of breathing in aquatic organisms much faster than in terrestrial
organisms?
(b) Quantity of dissolved oxygen is fairly low in water as compared to the amount of oxygen in
air. Aquatic organisms therefore have to breath faster than terrestrial organisms to absorb the
required amount of oxygen from the water.

15. Draw a neat diagram of excretory system of human beings and label the following:
Kidney
Ureter
Urinary Bladder

Urethra
16.What are the final products after digestion of carbohydrates and proteins?
Answer.
The final product produced after digestion of carbohydrates is glucose and of proteins is amino
acids.

17.What is saliva? State its role in the digestion of food.

Answer. Saliva is a watery fluid secreted by the salivary glands in the mouth. The digestive
functions of saliva include moistening food, and helping to create a food bolus, so it can be
swallowed easily. Saliva contains the enzyme amylase that breaks some starches down into
maltose and dextrin.
18. State two differences between arteries and veins.
Answer. Arteries
Arteries carry oxygenated blood, away from the heart except pulmonary artery.

These are thick-walled, highly muscular except arteries of cranium and vertebral column.
Valves are absent.
Blood in arteries moves with pressure.Veins

Veins carry deoxygenated blood, towards the heart except pulmonary veins.
These are thin-walled.
Valves are present which provide unidirectional flow of blood.
Blood in veins moves under very low pressure.
19. How are the alveoli designed to maximise the exchange of gases?

Answer. Alveoli are small pouches or sacs like structure. They are surrounded by blood
capillaries. Thus a large amount of air is brought in contact with the air in the lungs. More than
millions of alveoli are present in the lungs. The presence of millions of alveoli in the lungs
provides a very large surface area for the exchange of gases. The availability of large surface
area maximises the exchange of gases.
20. Name two excretory products other than 02 and CO2 in plants.
Answer. The two excretory products other than 02 and CO2 in plants are resins and gums.
21.(a) “The breathing cycle is rhythmic whereas exchange of gases is a continuous process”.
Justify this statement.
(b) What happens if conducting tubes of circulatory system develops a leak? State in brief,
how could this be avoided?
© How opening and closing of stomata takes place?
Answer. (a) The breathing cycle involves inhalation and exhalation of air due to alternate
expansion and contraction of thoracic cavity. Thus it is a rhythmic process. But exchange of
gases is a continuous process as it takes place between the blood and each and every cell, by
diffusion.
(b) The circulatory system will become inefficient if it develops a leak. This could be avoided by
maintaining a normal blood pressure.
© When water flows into the guard cells, the guard cells swell and the stomatal pore opens up.
When water moves out the guard cells shrinks and the stomatal pore closes.
22.Draw a diagram of the front view of human heart and label any six parts including at least
two, that are concerned with arterial blood supply to the heart muscles.
23.(a) Draw a schematic representation of transport and exchange of oxygen and carbon
dioxide during transportation of blood in human beings and label on it:
Lung capillaries, Pulmonary artery to lungs, Aorta to body, Pulmonary veins from lungs.

(b) What is the advantage of separate channels in mammals and birds for oxygenated and
deoxygenated blood?
Answer.(a) A schematic representation of transportation and exchange of oxygen and
Carbon dioxide during transportation of blood in human beings
(b) It is necessary to separate oxygenated and deoxygenated blood in mammals and birds
because they need high energy and large amount of oxygen. The separation of oxygenated and
deoxygenated blood provides high oxygen supply to the organs.

24.(a) Draw a diagram depicting Human Alimentary Canal and label on it: Gall bladder, Liver
and Pancreas.
(b) State the roles of Liver and Pancreas.
© Name the organ which performs the following functions in humans:

(i) Absorption of digested food

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

Absorption of water – Large intestine.

25.(a) Draw a labelled diagram of the respiratory system of human beings with diaphragm at
the end of expiration.
(b) List four conditions required for efficient gas exchange in an organism.

Answer.(a)
(b) (i) A large surface area over which exchange can take place.
(ii) A concentration gradient without which nothing will diffuse.
A thin surface across which gases diffuse.

Warm conditions.
26.(a) Draw a diagram to show the nutrition in Amoeba and label the parts used for this
purpose. Mention any other purpose served by this part other than nutrition.
(b) Name the glands associated with digestion of starch in human digestive tract and mention
their role.
© How is required pH maintained in the stomach and small intestine?
Answer.(a)
Pseudopodia serves the purpose of locomotion apart from nutrition.
(b) The salivary gland is associated with digestion of starch in human digestive tract.

It secretes saliva which contains enzyme salivary amylase. This enzyme converts starch into
maltose (sugar).
© Gastric glands present on the walls of the stomach release HC1. HC1 creates an acidic
medium, which facilitates the action of enzyme pepsin. Bile juice from liver makes the food
alkaline in small intestine for the pancreatic enzymes to act.
27.(a) Leaves of a healthy potted plant were coated with vaseline to block the stomata. Will
this plant remain healthy for long? State three reasons for your answer.
(b) State any two differences between autotrophic nutrition and heterotrophic nutrition.

Answer. (a) No, this plant will not remain healthy for long. The plant will begin to die because
(i) Gaseous exchange will not take place.
(ii) No absorption of C02, hence no photosynthesis.
(iii) Transpiration will not occur; hence no transportation of water.
28.Name the green dot like structures in some cells observed by a student when a leaf peel
was viewed under a microscope. What is this green colour due to?
Answer. The green dot-like structures in some cells observed by a student when a leaf peel is
viewed under a microscope are chloroplasts. The green colour is due to the presence of green
pigment, chlorophyll.

29.State any one difference between autotrophic and heterotrophic modes of nutrition.
Answer. In autotrophic nutrition, organisms obtain their food from inorganic substances. In
heterotrophic nutrition, organisms derive their food from organic substances.
30. A Give one reason why multicellular organisms require special organs for exchange of
gases between their body and their environment. :
Answer. In unicellular organisms the entire body of the organism is in contact with the
environment hence exchange of materials can take place but, in multicellular organisms the
entire body of the organism is not in contact with the environment and hence simple diffusion
is not helpful.
31. What is‘translocation’in plants?
Answer. Translocation is the movement of soluble materials, products of photosynthesis from
leaves to other tissues throughout the plant.
32. In the experiment “Light is essential for photosynthesis”, why does the uncovered part of
the leaf turn blue-black after putting iodine solution?
Answer. Starch is produced in the uncovered part of the leaf because it is exposed to sunlight
allowing it to photosynthesize, which turns blue-black in presence of iodine solution.
33. Name the component of blood that helps in the formation of blood clot in the event of a
cut.
Answer. Platelets help in clotting of blood in the event of a cut.

34.Mention how organisms like bread moulds and mushrooms obtain their food.
Answer. Organisms like bread moulds and mushrooms breakdown the food materials outside
the body and then absorb the nutrients of the bread.
35.Describe in brief the function of kidneys, ureters, urinary bladder and urethra.

Answer.The Kidneys filter the blood and concentrate the filtrate to make urine. They also help
regulate blood pressure.
Ureters transport the urine to the urinary bladder.
Urinary bladder is like a holding tank for the urine until it’s ready to be excreted. Urethra is the
tube that connects the urinary bladder to the outside of the body for excretion.

35. What will happen to a plant if its xylem is removed?

Answer. Xylem in plant transports water and dissolved mineral nutrients from the roots to all
parts of the vascular plant. So, if xylem is removed from the plant, the water and mineral supply
to the plant will stop and therefore, the plant will die.

36. Where does digestion of fat take place in our body?

Answer. Digestion of fat takes place in the small intestine of our body.
37. What is the mode of nutrition in human beings?
Answer. Holozoic nutrition.

38.(a) What is meant by breathing? What happens to the rate of breathing during
Vigorous exercise and why?
(b) Define translocation with respect to transport in plants. Why is it essential for plants?
Where in plants are the following synthesised?

(i) Sugar (iii) Hormone

Answer.(a) The process of taking in of oxygen from air in to the lungs and expulsion of carbon
dioxide out of the lungs is called breathing. The rate of breathing during vigorous exercise
increases by about 20 to 25 times per minute. It is because, during vigorous exercise the
demand for oxygen increases. Breathing occurs involuntarily but its rate is controlled by the
respiratory center of the brain.
(b) Translocation is the transport of food from the leaves to other parts of the plant and occurs
in the part of the vascular tissue known as phloem.

It is essential for plants because every part of the plant needs food for obtaining energy for
building its parts and maintaining its life.
(i) Sugar is synthesised in the leaves of the plant.
(ii) Hormones are synthesised at the tips of roots and stems of a plant.

39.(a) Draw the structure of a nephron and label the following on it:
Glomerulus, Bowman’s capsule, Renal artery, Collecting duct.
(b) What happens to glucose that enters the nephron along with filtrate?
Answer.(a)

(b) During excretion in human beings, glucose which enters the nephron along with filtrate gets
reabsorbed by blood capillaries surrounding the nephron.

ANSWER IN DETAIL

1. How is urine produced and eliminated ?

Answer.
Blood from the heart comes into the kidneys afferent and efferent arteriols from the renal
arteries where it enters about 2-3 million nephrons per kidney. Then, it goes through the
glomerulus a tuft or bunch of blood capillaries and get rid of some of the unwanted substances
like urea, uric acid, creatinine in the blood and then continues through the renal tubules. The
loop of Henley, reabsorb certain substances such as water (actually if body is dehydrated, body
will send anti-diuretic hormone (ADH) to kidneys to prevent extra water from going into urine
and thus saving water for body and get rid of anything else that isn’t wanted, then the urine
goes through ureters to bladder and then to urethra where it is excreted out of body as urine.
2. In human alimentary canal, name the site of complete digestion of various components of
food. Explain the process of digestion.
Answer.In small intestine, complete digestion of various components of food take place. The
process of digestion of food in mouth, stomach and small intestine in human
Body are as follows:
Mouth: Digestion of food begins in the mouth. Saliva present in mouth contains a digestive
enzyme, called salivary amylase, maltose and dextrins, which breaks down starch into sugar.

Stomach: Stomach stores and mixes the food received from the oesophagus with gastric juices.
The main components of gastric juice are hydrochloric acid, mucus and pepsinogen.
Hydrochloric acid dissolves bits of food and creates an acidic medium. In this medium,
pepsinogen is converted to pepsin which is a protein-digesting enzyme. Mucus protects the
inner lining of the stomach from the action of HC1.
Small Intestine: Small intestine is the site of complete digestion of carbohydrates, proteins and
fats. Small intestine produces intestinal juice from the glands present in its wall. The intestinal
juice helps in further digestion of food. Small intestine also obtains digestive juices from liver
and pancreas. The liver produces bile juice that causes emulsification of fats and the pancreas
produces pancreatic juice for digesting proteins and emulsified fats. This digested food is finally
absorbed through the intestinal walls.

3.Explain the process of nutrition in Amoeba.

Answer. Amoeba is an important protozoa found in fresh water. It feeds on microscopic plants
and animals present in water. The mode of nutrition in amoeba is Holozoic. And the process of
obtaining food by amoeba is called phagocytosis. The different processes involved in the
nutrition of amoeba are:

Ingestion: Ingestion is the process of taking food in the body. Amoeba is a unicellular animal, so
it doesn’t have a mouth for ingestion of food. Amoeba ingests the food by encircling it by
forming pseudopodia. When the food is completely encircled , the food is engulfed in the form
of a bag called food vacuole.

Digestion: Digestion is the process of breaking the large and insoluble molecules in small and
water soluble molecules. In amoeba, several digestive enzymes react on the food present in the
food vacuoles and break it down into simple and soluble molecules.
Absorption: The food digested by digestive enzymes is then absorbed in the cytoplasm by the
process of diffusion. While the undigested food remains in the food vacuole. If a large amount
of food is absorbed by amoeba, the excess food is stored in the cytoplasm ih the form of
glycogen and lipids.
Assimilation: During this step the food absorbed by the cytoplasm is used to obtain energy,
growth and repair. This process of utilizing absorbed food for obtaining energy, repair and
growth is called assimilation.

Egestion: When a sufficient amount of undigested food gets collected in the food vacuole, it is
thrown out of the body by rupturing cell membrane. The process of removal of undigested food
from the body is called egestion.
4.(a) Draw a sectional view of the human heart and label on it – Aorta, Right ventricle and
Pulmonary veins.
(b) State the functions of the following components of transport system:
(i) Blood (ii) Lymph
Answer.(a)

(b) The functions of blood and lymph are as follows:

(i) Blood
Oxygen is transported by the blood to the tissues of the body for the breakdown of digested
food.
Carbon dioxide is transported to the lungs by the blood plasma.

The digested and absorbed nutrients are transported by blood to the tissues. Nitrogenous
wastes are transported to the kidneys.
It regulates the body temperature and maintains the pH of the body tissues.
It transports various hormones from one region to another and bring about the coordination.

It maintains water balance to constant level.

The lymphocytes produce antibodies against the invading antigens and protect from diseases.
It helps in rapid healing of wounds by forming a clot at the site of injury.
(i) Lymph

It cleans the cellular environment.

It returns proteins and tissue fluids to the blood (drainage)
It provides a pathway for the absorption of fats and fat-soluble vitamins into the bloodstream.
It defends the body against disease.
5. Explain the process of breakdown of glucose in a cell (ii) in the absence of oxygen.
Answer. The process of breakdown of glucose in a cell are as follows:

Life-processes-chapter-wise-important-questions-class-10-science-21
The first step in the breakdown of glucose both in presence of 02 and in absence of Os is same.
In this step, glucose is broken down into pyruvate.
Second step which involves further breakdown of private into simple compounds can take place
in two different ways:
(i) In presence of Oz: In the presence of 02, private is converted into C02 and water.
Energy released during aerobic respiration is much greater than that released during
an anaerobic respiration.

(ii)In absence of Oz: In the absence of 02 in yeast, pyruvate is converted into ethanol and C02
and the process is called fermentation. In absence of 02, in our muscle cells, pyruvate is
converted into lactic acid. The build up of lactic acid in muscle cells causes cramps.
6.a) List the three events that occur during the process of photosynthesis.
Explain the role of stomata in this process.

(b) Describe an experiment to show that “sunlight is essential for photosynthesis.”

Answer.
(a) 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.
(i) Reduction of carbon dioxide into carbohydrate.
Role of Stomata

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.

(b) Sunlight is essential for photosynthesis

Procedure:
 (i) Place a healthy green potted plant in a dark room for 1-2 days. This is done to
ensure
That the plant consumes all its reserve food and the leaves do not contain any starch.

(ii) Then, cover a portion of a leaf of this plant on both sides with two uniform pieces of
black paper, fixed in position with two paper clips.
(iii) Now, expose this plant to bright light. After a few hours, remove the leaf and
decolorize it with alcohol and test the presence of food (starch) with iodine solution.

Observation: It can be observed that the portion of the leaf covered with black paper does not
(food),
Conclusion: This is because the food prepared by plants through the process of photosynthesis
is stored as starch. Starch reacts with the iodine solution to give blue-black colour. Only those
portions of the leaf that were exposed to sunlight could photosynthesise. Hence, gives blue-
black colour when tested with iodine. The portion of the leaf covered with black paper did not
receive sunlight. Hence, starch was not produced. Thus, it can be
Concluded that the sunlight is essential for photosynthesis.