Chapter 6 Photosynthesis - Concise Biology Part II - Selina Solutions for Class 10 Biology ICSE

Question 1

The production of starch, and not glucose, is often used as a measure of photosynthesis in leaves because

a) starch is immediate product of photosynthesis

b) glucose formed in photosynthesis soon gets converted into starch

c) starch is soluble in water

d) sugar cannot be used

Solution 1

b) glucose formed in photosynthesis soon gets converted into starch

Question 2

The number of water molecules required in the chemical reactions to produce one molecule of glucose during photosynthesis is

a) six

b) twelve

c) eighteen

d) twenty-four

Solution 2

b) twelve

Question 3

The rate of photosynthesis is not affected by

a) light intensity

b) humidity

c) temperature

d) CO₂ concentration

Solution 3

b) humidity

Question 4

Chlorophyll in a leaf is required for

a) breaking down water into hydrogen and oxygen

b) emitting green light

c) trapping light energy

d) storing starch in the leaves

Solution 4

c) trapping light energy

Question 5

If the rate of respiration becomes more than the rate of photosynthesis, plants will:

a) continue to live, but will not be able to store food

b) be killed instantly

c) grow more vigorously because more energy will be available

d) stop growing and die gradually of starvation

Solution 5

a) continue to live, but will not be able to store food

Question 6

Which one chemical reaction occurs during photosynthesis?

a) Carbon dioxide is reduced and water is oxidised

b) Water is reduced and carbon dioxide is oxidised

c) Both carbon dioxide and water are oxidised

d) Both carbon dioxide and water are reduced

Solution 6

a) Carbon dioxide is reduced and water is oxidised

Question 7

The specific function of light energy in the process of photosynthesis is to

a) reduce carbon dioxide

b) synthesise glucose

c) activate chlorophyll

d) split water molecule

Solution 7

c) activate chlorophyll

Question 8

A plant is kept in a dark cupboard for 48 hours before conducting any experiment on photosynthesis in order to

a) remove chlorophyll from leaves

b) remove starch from the leaves

c) ensure that no photosynthesis occurred

d) ensure that the leaves are free from starch

Solution 8

d) ensure that the leaves are free from starch

Question 9

During photosynthesis, the oxygen in glucose comes from

a) CO₂

b) water

c) both CO₂ and water

d) oxygen via air

Solution 9

a) CO₂

Question 10

Name the following:

(a) The category of organisms that prepare their own food from basic raw materials.

(b) The kind of plastids found in the mesophyll cells of the leaf.

(c) The compound which stores energy in the cells.

(d) The first form of food substance produced during photosynthesis.

(e) The organisms that can be called "natural purifiers" of the air.

(f) The source of carbon dioxide for aquatic plants.

(g) The part of chloroplast where the dark reaction of photosynthesis takes place.

(h) The tissue that transports manufactured type of starch from leaves to all parts of the plants.

Solution 10

(a) Producers / Autotrophs

(b) Chloroplasts

(c) ATP (Adenosine triphosphate)

(d) Glucose

(e) Green plants

(f) Carbon dioxide dissolved in water

(g) Stroma

(h) Phloem

Question 11

Mention one difference between the following on the basis of what is given in brackets.

(a) Respiration and photosynthesis (gas released)

(b) Light and dark reactions (products formed)

(c) Producers and consumers (mode of nutrition)

(d) Grass and grasshopper (mode of nutrition)

(e) Chlorophyll and chloroplast (part of plant cell)

Solution 11

(a)

Respiration	Photosynthesis
The gas released during respiration is carbon dioxide.	The gas released during photosynthesis is oxygen.

(b)

Light Reaction	Dark Reaction
Hydrogen and oxygen are produced here, along with release of electrons, which converts ADP into ATP.	Glucose is the main product formed during dark reaction.

(c)

Producers

Consumers

Producers show autotrophic mode of nutrition i.e. they are able to produce their own food from basic raw materials.

For example: green plants

Consumers show heterotrophic mode of nutrition i.e. they depend directly or indirectly on the producers for their food.

For example: Animals

(d)

Grass	Grasshopper
Green grass being a producer is capable of producing its own food by photosynthesis.	Grasshopper is a primary consumer (herbivore) and directly feeds on producers like grass.

(e)

Chlorophyll	Chloroplast
Chlorophyll is the green pigment present in cell organelles called chloroplasts.	Chloroplasts are cell organelles, situated in the cytoplasm of plant cells. They are present mainly in the mesophyll cells and in the guard cells of stomata.

Question 12

Identify the false statements and rewrite them correctly by changing the first or last word only.

(a) Dark reaction of photosynthesis occurs during night time.

(b) Immediate product of photosynthesis is glucose.

(c) Starch produced in a leaf remains stored in it for 2-3 weeks before it is used by other parts of the plant.

(d) Photosynthesis requires enzymes.

(e) Green plants are consumers.

(f) Photosynthesis results in loss of dry weight of the plants.

(g) Photosynthesis stops at a temperature of about 35^oC.

(h) Photosynthesis occurs only in cells containing chloroplasts.

(i) Green plants perform photosynthesis.

(j) Algae are autotrophs.

Solution 12

(a) False

Correct Statement: Dark reaction of photosynthesis is independent of light and occurs simultaneously with light reaction.

(b) True

(c) False

Correct Statement: Starch produced in a leaf is stored temporarily in the leaf until the process of photosynthesis. At night it is converted back into soluble sugar and translocated to different part of the body either for the utilization or for the storage.

(d) True

(e) False

Correct Statement: Green plants are producers.

(f) False

Correct Statement: Respiration results in loss of dry weight of the plants.

(g) False

Correct Statement: Photosynthesis stops at a temperature of above 40^oC.

(h) True

(i) True

(j) True

Question 13

Fill in the blanks with the appropriate answer from the choices given in the brackets.

(a) The site of light reaction in the cells of a leaf is ............ (cytoplasm, stroma, grana)

(b) The chemical substance used to test the presence of starch in the cell of a leaf is ............. (CaCl₂, iodine solution, Benedict solution)

(c) Stroma is ground substance in ................ (cytoplasm, chloroplast, ribosomes)

(d) The dark reaction of photosynthesis is known as .............. (Hill reaction, cyclic phosphorylation, Calvin cycle)

(e) In the flowering plants, food is transported in the form of .................. (sucrose, glucose, starch)

Solution 13

(a) grana

(b) iodine solution

(c) chloroplast

(d) Calvin cycle

(e) Sucrose

Question 14

Are the following statements true or false? Give reason in support of your answer.

(a) The rate of photosynthesis continues to rise as long as the intensity of light rises.

(b) The outside atmospheric temperature has no effect on the rate of photosynthesis.

(c) If you immerse a leaf intact on the plant in ice cold water, it will continue to photosynthesise in bright sunshine.

(d) Destarching of the leaves of a potted plant can occur only at night.

(e) The starting point of carbon cycle is the release of carbon dioxide by animals during respiration.

(f) If a plant is kept in bright light all the 24 hours for a few days, the dark reaction (biosynthetic phase) will fail to occur.

(g) Photosynthesis is considered as a process supporting all life on earth.

Solution 14

(a) False

Photosynthesis increases with the light intensity up to a certain limit only and then it gets stabilized.

(b) False

The atmospheric temperature is an important external factor affecting photosynthesis. The rate of photosynthesis increases up to the temperature 35^oC after which the rate falls and the photosynthesis stops after 40^oC.

(c) False

Ice cold water will hamper the process of photosynthesis in the immersed leaf, even if there is sufficient sunshine because the temperature is an important factor for the rate of photosynthesis.

(d) False

For destarching, the potted plant can kept in a dark room for 24-48 hours.

(e) False

There is no start point or end point in the carbon cycle, the carbon is constantly circulated between the atmosphere and the living organisms.

(f) False

If a plant is kept in bright light all the 24 hours for a few days, the dark reaction (biosynthetic phase) will continue to occur because the dark reaction is independent of light and it occurs simultaneously with the light dependent reaction.

(g) True

Question 15

Given below are five terms. Rewrite the terms in the correct order so as to be in logical sequence with regard to photosynthesis: (i) water molecules, (ii) oxygen, (iii) grana, (iv) hydrogen and hydroxyl ions, (v) photons.

Solution 15

Photons, grana, water molecules, hydrogen and hydroxyl ions, oxygen

Question 16

State any four differences between photosynthesis and respiration.

Solution 16

Photosynthesis	Respiration
Carbon dioxide is used up and oxygen is released.	Oxygen is used up and carbon dioxide is released.
Photosynthesis occurs in plants and some bacteria.	Respiration occurs in all living organisms.
Photosynthesis results in gain of dry weight of the plants.	Respiration results in loss of dry weight of the plants.
Glucose is produced which is utilized by the plants.	Glucose is broken down to obtain energy.
The raw materials for the photosynthesis are water, carbon dioxide and sunlight.	The raw material for respiration is glucose.

(Any 4)

Question 17

"Oxygen is a waste product of photosynthesis." Comment.

Solution 17

Oxygen is released during photosynthesis. Some of this oxygen may be used in respiration in the leaf cells, but the major portion of it is not required and it diffuses out into the atmosphere through the stomata. However, in a sense, even this oxygen is not a waste because all organisms require it for their existence including the plants.

Question 18

Why is it necessary to place a plant in the dark before starting an experiment on photosynthesis? Explain.

Solution 18

The presence of starch is regarded as evidence of photosynthesis. Hence before starting an experiment on photosynthesis, the plant should be placed in the dark for 24-48 hours to destarch the leaves. During this period, all the starch from the leaves will be sent to the storage organs and the leaves will not show the presence of starch. So the various experiments on photosynthesis can be carried out effectively.

Question 19

Why is it not possible to demonstrate respiration in a green plant kept in sunlight?

Solution 19

If a green plant is kept in bright light, it tends to use up all the CO₂ produced during respiration, for photosynthesis. Thus, the release of CO₂ cannot be demonstrated. Hence, it is difficult to demonstrate respiration as these two processes occur simultaneously.

Question 20

Most leaves have the upper surface more green and shiny than the lower one. Why?

Solution 20

The chloroplasts are concentrated in the upper layers of the leaf which helps cells to trap the sunlight quickly. Also the epidermis is covered by a waxy, waterproof layer of cuticle. This layer is thicker on the upper surface than the lower one. Hence most leaves have the upper surface more green and shiny than the lower one.

Question 21

How would you demonstrate that green plants release oxygen when exposed to light?

Solution 21

Place hydrilla plant (a water plant) in a beaker containing pond water and cover it by a short-stemmed funnel. (Make sure the level of water in the beaker is above the level of the stem of the funnel)

Invert a test tube full of water over the stem of the funnel.

Place the set up in the sun light for a few hours.

Observation:

Bubbles appear in the stem which rise and are collected in the test tube. When sufficient gas gets collected, a glowing splinter will be introduced in the test tube, which will burst into flames.

Inference:

The splinter glows due the presence of oxygen in the test tube which proves that the gas collected in the test is released by hydrilla during photosynthesis.

Question 22

Describe the main chemical changes which occur during photosynthesis in:

(i) Light reaction

(ii) Dark reaction

Solution 22

(i) Light Reaction:

The light reaction occurs in two main steps:

(1) Activation of chlorophyll - On exposure to light energy, chlorophyll becomes activated by absorbing photons.

(2) Splitting of water - The absorbed energy is used in splitting the water molecule into hydrogen and oxygen, releasing energy. This reaction is known as photolysis of water.

2H₂O

4H⁺ + 4e^- + O₂

The fate of H⁺, e^- and (O) component are as follows:

The hydrogen ions (H⁺) obtained from above are picked up by a compound NADP (Nicotinamide adenine dinucleotide phosphate) to form NADPH.

NADP⁺ + e^- + H⁺

NADPH

The oxygen (O) component is given out as molecular oxygen (O₂).

2O

O₂

The electrons (e^-) are used in converting ADP into energy rich ATP by adding one inorganic phosphate group P_i.

ADP + P_i

ATP

This process is called photophosphorylation.

(ii) Dark reaction: The reactions in this phase does not require light energy and occur simultaneously with the light reaction. The time gap between the light and dark reaction is less than one thousandth of a second. In the dark reaction, ATP and NADPH molecules (produced during light reaction) are used to produce glucose (C₆H₁₂O₆) from carbon dioxide. Fixation and reduction of carbon dioxide occurs in the stroma of the chloroplast through a series of reactions. The glucose produced is either immediately used up by the cells or stored in the form of starch.

Question 23

Complete the following food chains by writing the names of appropriate organisms in the blanks:

(i) Grass → ............ Snake → ...............

(ii) ........... → Mouse ............... → Peacock

Solution 23

Complete the following food chains by writing the names of appropriate organisms in the blanks:

(i) Grass → Rabbit. → Snake → Hawk

(ii) Grass/Corn → Mouse → Snake → Peacock

Question 24

How do non-green plants such as fungi and bacteria obtain their nourishment?

Solution 24

Non-green plants such as fungi and bacteria obtain their nourishment from decaying organic matter in their environment. This matter comes from dead animals and plants. Fungi and bacteria break down the organic matter to obtain the nourishment and they release carbon dioxide back in the atmosphere.

Question 25

All life owes its existence to chlorophyll. Give reason.

Solution 25

Chlorophyll is the foundation site for the photosynthesis in green plants. The initiation of photosynthesis takes place when the chlorophyll molecule traps the light energy. The light energy is then converted into chemical energy in the form of glucose using carbon dioxide (CO₂) from the atmosphere, and water (H₂O) from the soil. All other organisms, directly or indirectly depend on this food for their survival. The starting point of any food chain is always a plant. If green plants were to suddenly disappear, then so would virtually all life on Earth. Thus, we can say that all life owes its existence to chlorophyll.

Question 26

Complete the following by filling the blanks 1 to 5 with appropriate words/ terms/ phrases:

To test the leaf for starch, the leaf is boiled in water to …………… (1). It is next boiled in methylated spirit to ……………(2). The leaf is placed in warm water to soften it. It is then placed in a dish and ………….(3) solution in added. The region, which contains starch, turns ……………. (4) and the region, which dose not contain starch, turns ………………(5)

Solution 26

To test the leaf for starch, the leaf is boiled in water to kill the cells. It is next boiled in methylated spirit to remove chlorophyll. The leaf is placed in warm water to soften it. It is then placed in a dish and iodine solution in added. The region, which contains starch, turns blue-black and the region, which does not contain starch, turns brown.

Question 27

A candidate studied the importance of certain factors in photosynthesis. He took a potted plant and kept in the dark for over 24 hours. In the early hours of the next morning, he covered one of the leaves with black paper in the centre only. Then he placed the plant in sunlight for a few hours and tested the leaf which was covered with black paper for starch.

a. What aspect of photosynthesis was being investigated?

b. Is there any control in this experiment? If so, state it.

c. Why was the plant kept in the dark before the experiment?

d. Describe step by step, how the candidate proceeded to test the leaf for the presence of starch?

Solution 27

a. The student wanted to show that sunlight is necessary for photosynthesis. / The role of sunlight in photosynthesis is being investigated.

b. Yes. The other uncovered leave of the potted plant act as a control.

c. Destarching ensures that any starch present after the experiment has been formed under experimental conditions. Therefore, the plant was kept in the dark before the experiment.

d.

The student dipped the leaf in boiling water for a minute to kill the cells.

Then he boiled the leaf in alcohol/methylated spirit over a water bath to remove chlorophyll. The leaf becomes hard and brittle.

He then places the leaf in hot water to soften it.

Next the student spreads the leaf in a dish and pours iodine solution on it. The presence of starch is indicated by a blue-black colour.

The uncovered portion (exposed to sunlight) turned blue-black colour and the covered portion showed brown colour. The difference in the colours of covered and uncovered part of leaves indicates the importance of sunlight in photosynthesis.

Question 28

Photosynthesis in green plants is directly and indirectly dependent on so many plant structures. Explain briefly the role of the following structures in this process. (a) Guard cells (b) Cuticle (c) Mesophyll cells (d) Xylem tissue in the leaf veins (e) Phloem tissue in the leaf veins (f) Stomata...

Solution 28

(a) Guard cells: They regulate the opening and closing of stomata and thus regulate the entry of carbon dioxide through the stomata.

(b) Cuticle: Cuticle is transparent and water proof due to which light can penetrate this later easily.

(c) Mesophyll cells: Mesophyll cells are the main sites for photosynthesis. Chloroplasts are mainly contained in the mesophyll cells. When sunlight falls on the leaf, the light energy is trapped by the chlorophyll of the upper layers of mesophyll, especially the palisade cells.

(d) Xylem Tissue in the Leaf Veins: Water is essential for photosynthesis to occur. Water is taken up by the roots from the soil, sent up through the stem and finally brought to the leaves (site of photosynthesis) through the xylem tissue. The water is then distributed in the mesophyll tissue.

(e) Phloem Tissue in the Leaf Veins: The prepared food is transported from leaves to all parts of the plant by the phloem tissue. The glucose is converted into insoluble starch and later into soluble sugar i.e. sucrose, which is transported in solution through the phloem in the veins of the leaf and down through the phloem of the stem.

(f) Stoma: The main function of stoma is to let in carbon dioxide from the atmosphere for photosynthesis. Also most of the oxygen produced during photosynthesis diffuses out into the atmosphere through the stomata.

Question 29

Given below is a schematic diagram to illustrate some aspects of photosynthesis.

a. Fill up the gaps, in blank spaces (1-4), by writing the names of the correct items.

b. What phenomenon do the thick arrows A and B indicate?

Solution 29

a.

1 - Sunlight

2 - Oxygen

3 - Glucose

4 - Xylem

b. A - Transpiration

B - Translocation

Question 30

Given below is the representation of a certain phenomenon in nature. With four organisms 1-4.

a. Name the phenomenon represented.

b. Name any one organism that could be shown at No .5

c. Name the biological process which was the starting point of the whole chain.

d. Name one natural element which all the organisms 2-4 and even 5 are getting from No. 1 for their survival.

Solution 30

a. Food chain

b. Hawk, eagle

c. Photosynthesis

d. Carbon

Question 31

Enumerate the steps involved in testing a green leaf for the presence of starch.

Solution 31

Test to determine the presence of starch in a leaf:

• Dip a leaf in boiling water for a minute to kill the cells.

• Boil the leaf in methylated spirit in a water bath to remove the chlorophyll, till the leaf turns pale blue and becomes hard and brittle.

• Now place the leaf in hot water to soften it.

• Place the leaf in a Petri dish and pour iodine solution over it.

• The appearance of a blue-black colour on the leaf is indicative of the presence of starch.

• The absence of starch is indicated by a brown colouration.

Question 32

Given alongside is the diagram of an experimental set-up:

a. What is the objective of this experiment?

b. Will it work satisfactorily? Given reason.

c. What alteration (s) will you make in it for obtaining expected result?

d. Would you take any step before starting the experiment? Describe this step and explain its necessity.

Solution 32

a. To demonstrate the importance of carbon dioxide in photosynthesis

b. No, the experiment will not work satisfactorily, as the beaker contains lime water and not potassium hydroxide to absorb CO₂.

c. Place potassium hydroxide in the beaker instead of lime water

d. Before starting the experiment, it is necessary to destarch the leaves of the plant by keeping the plant in complete darkness for 48 hours. This is because if the plant is not destarched, then the experiment will give false results because starch stored previously may be detected in the leaf placed in the beaker even if no starch is produced during the experiment.

Question 33

Draw a neat diagram of the stomatal apparatus found in the epidermis of leaves and label the Stoma, Guard cells, Chloroplast, Epidermal cells, Cell wall and Nucleus.

Solution 33

Question 34

A potted plant was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours. One of the leaves was covered with black paper in the centre. The potted plant was then placed in sunlight for a few hours.

(a) What aspect of photosynthesis was being tested?

(b) Why was the plant placed in the dark before beginning the experiment?

(c) During the starch test, why was the leaf

(1) boiled in water

(2) boiled in methylated spirit

(d) Write a balanced chemical equation to represent the process of photosynthesis.

(e) Draw a neat diagram of a chloroplast and label its parts.

Solution 34

(a) Light is required for photosynthesis.

(b) Before beginning the experiment, the plant was kept in dark in order to destarch it, i.e. to remove the pre-existing starch from the storage organs.

(c)

(1) The leaf was boiled in water to destroy enzymes so that further chemical changes do not take place in the leaf.

(2) The leaf was boiled in methylated spirit to dissolve chlorophyll.

(d) Chemical equation for the process of photosynthesis:

(e) Chloroplast:

Question 35

The diagram below shows two test-tubes A and B. Test-tube A contains a green water plant. Test-tube B contains both a green water plant and a snail. Both test-tubes are kept in sunlight. Answer the questions that follow:

(a) Name the physiological process that releases the bubbles of oxygen.

(b) Explain the physiological process as mentioned above in (a).

(c) What is the purpose of keeping a snail in test-tube B?

(d) Why does test-tube B have more bubbles of oxygen?

(e) Give an example of a water plant that can be used in the above experiment.

(f) Write the overall chemical equation for the above process.

Solution 35

(a) Photosynthesis releases bubbles of oxygen.

(b) Photosynthesis is a physiological process by which plant cells containing chlorophyll produce food in the form of carbohydrates by using carbon dioxide, water and light energy. Oxygen is released as a by-product.

(c) Carbon dioxide released by the snail during respiration is used by the plant for photosynthesis. This increases the rate of photosynthesis in the plant placed in test tube B. This also suggests that both respiration and photosynthesis are complementary processes to maintain the concentration of oxygen and carbon dioxide in the atmosphere.

(d) A plant and a snail are kept in test tube B. The plant in test tube B has more concentration of CO₂ available because the snail releases CO₂ during respiration. This increases the rate of photosynthesis in the plant placed in test tube B which leads to the release of more amount of oxygen.

(e) Hydrilla

(f) Chemical equation for photosynthesis:

Chapter 6 : Photosynthesis - Selina Solutions for Class 10 Biology ICSE

Chapter 6 - Photosynthesis Excercise Ex. 1

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Chapter 6 : Photosynthesis - Selina Solutions for Class 10 Biology ICSE

Chapter 6 - Photosynthesis Excercise Ex. 1

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