Selina ICSE Class 10 Biology Solutions Chapter 5 Photosynthesis Provider of Food for All

Exercise 1 Multiple choice type
(choose the best option out of the four alternatives a,b,c, and d)

Question A1. 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

Question A2. 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

Question A3. The rate of photosysnthesis is affected by
(a) light intensity
(b) humidity
(c) temperature
(d) CO2 concentration

Question A4. 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

Question A5. If the rate of respiration becomes moree than the rate of photosynthesis, plants will:
(a) continue to live, but will not be able to store food
(b) be killed instantly
(c) frow more vigorously because more energy will be available
(d) stop growing and die gradually of starvation

Question A6. 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 cardon dioxide and water are reduced

Question A7. 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

Question A8. 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

Question A9. During photosynthesis, the oxygen in glucose comes from
(a) Co2
(b) water
(c)both CO2 and water
(d) oxygen via air

Question B1. 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 organism that can be called “natural purifiers” of the air.
(f) The source of carbon dioxide for aquatic plants.
(g) The parts 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 B1.
(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 C1. Mention one difference between the following on 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 C1.
(a)

Respiration	Photosynthesis
Carbon dioxide is the gas that is emitted during breathing.	During photosynthesis, process of cellular respiration.

(b)

Light Reaction	Dark Reaction
ADP is transformed to ATP by the producing hydrogen and oxygen, as well as the release of electrons.	The main consequence of the dark reaction is glucose.

(c)

Producers	Consumers
Producers have an autotrophic mode of nutrition, which implies they can make their own food from raw ingredients. For example: green plants	Consumers have a heterotrophic mode of nutrition, which means they rely on producers for for food either directly or indirectly. For example: Animals

(d)

Grass	Grasshopper
As a producer, green grass can manufacture its own food through photosynthesis.	The grasshopper is a main consumer (herbivore) which feeds on grass directly.

(e)

Chlorophyll	Chloroplast
Chlorophyll is a green pigment present in chloroplasts, which are cell organelles.	Chloroplasts are plant cell organelles that reside in the cytoplasm. They’re mostly found in the mesophyll cells and stomata’s guard cells.

Question C2. 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 weels before it is used by other part of the plant.
(d) photosynthesis requires enzymes.
(e) Green plants are consumers.
(f) photosynthesis result in loss of dry weight of the plants.
(g) photosynthesis stops at a temperature of about 53o C.
(h) photosynthesis occurs only in cells containing chloroplasts.
(i) Green plants perform photosynthesis.
(j) Algae are autotrophs.
Solution C2.
(a) False
Correct Statement: Photosynthesis’ dark reaction is light-independent and proceeds at the same time as the light reaction.
(b) True
(c) False
Correct Statement: The starch synthesized in a leaf is temporarily retained in the leaf until the photosynthesis process begins. It is converted back into soluble sugar at night and translocated to different organs, either for use or storage.
(d) True
(e) False
Correct Statement: Green plants are producers.
(f) False
Correct Statement: Plants lose dry weight as a result of respiration.
(g) False
Correct Statement: Photosynthesis stops at a temperature of above 40oC.
(h) True
(i) True
(j) True

Fill in the blanks with the appropriate answer from the choice 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)

Question C4. 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 C4.
(a) False
Only up to a certain amount does photosynthesis grow with light intensity before stabilizing.
(b) False
The temperature of the atmosphere has a significant impact on photosynthesis. The rate of net photosynthetic until the temperature reaches 35°C, following which it decreases and ceases at 40°C.
(c) False
(d) Even if there is enough sunlight, ice cold water will stymie the process of photosynthesis in the submerged leaf since temperature is a key element in photosynthesis rate.
(e) False
The potted plant can be kept in a dark room for 24-48 hours to destarch.
(f) False
(g) The carbon cycle has no beginning or finish since carbon is constantly exchanged between the environment and living organisms.
(h) False
(i) Because the dark reaction (biosynthetic phase) is light independent and happens simultaneously with the light dependent response, if a plant is kept in bright light 24 hours a day for a few days, the dark reaction (biosynthetic phase) will continue to happen.
(j) True

Question C5. 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 C5.
Photons, grana, water molecules, hydrogen and hydroxyl ions, oxygen

Question C6. State any four differences between photosynthesis and respiration
Solution C6.

Photosynthesis	Respiration
Carbon dioxide is depleted, allowing oxygen to be released.	Carbon dioxide is produced as oxygen is depleted.
Photosynthesis is a process that occurs in plants and microbes.	Respiration is a natural process that happens in all living things.
Plants gain dry weight as a result of photosynthesis.	Plants lose dry weight as a result of respiration.
Water, carbon dioxide, and sunlight are the raw components for photosynthesis.	Glucose is the starting ingredient for respiration.

Question C7. “Oxygen is a waste product of photosynthesis.” Comment.
Solution C7.
During photosynthesis, oxygen is released. While some of this oxygen is needed in leaf cell respiration, the majority of it is not required and diffuses into the atmosphere through the stomata. However, in some senses, even this oxygen is not a waste because all creatures, including plants, require it to survive.

Question C8. Why is it necessary to place a plant in the dark before starting an experiment on Photosynthesis? Explain.
Solution C8.
Photosynthesis is demonstrated by the existence of starch. As a result, before beginning a photosynthesis experiment, the plant should be left in the dark for 24-48 hours to destarch the leaves. During this time, all of the starch from the leaves will be carried to the storage organs, and the leaves will be starch-free. As a result, diverse photosynthesis experiments may be carried out effectively.

Question C9. What is meant by destarching?
Solution C9.
The phrase “destarching” relates to the procedure of removing starch from a dish. Destarching is done to ensure that each of the starch from the leaves is directed to the storage organs. As a result, all of the leaves will be free of starch, allowing researchers to study photosynthesis. Destarching assures that any starch left over from the experiment was produced in the laboratory.

Question C10. Why is it not possible to demonstrate respiration in a green plant kept in sunlight?
Solution C10.
When a green plant is exposed to intense light, it will use up all of the CO2 created during respiration for photosynthesis. As a result, the release of CO2 cannot be proven. As a result, demonstrating respiration is challenging because these two processes happen at the same time.

Question C11. Most leaves have the upper surface more green and shiny than the lower one. Why?
Solution C11.
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 C12. How would you demonstrate that green plants release oxygen when exposed to light.
Solution C12.
• In a beaker filled with pond water, place a hydrilla plant (a water plant) and cover it with a short-stemmed funnel. (Make sure the water level in the beaker is higher than the funnel’s stem.) •Invert a test tube full of water over the funnel’s stem.
• Leave the setup in the sun for a couple of hours.
Observation: Bubbles form in the stem and rise to the top, where they are collected in the test tube. A luminous splinter will be inserted into the test tube once enough gas has been collected, and it will burst into flames.
Inference: Because there is oxygen in the test tube, the splinter lights, indicating that the gas collected in the test is released by hydrilla during photosynthesis.

Question C13. Describe the main chemical change which occur during photosynthesis in:
i) Light reaction
ii) Dark reaction
Solution C13.
(i) Light Reaction:
There are two basic processes in the light reaction:
1. Chlorophyll activation – Chlorophyll is activated by absorbing photons when exposed to light energy.
2. Water splitting – The absorbed energy is released by splitting the water molecule into hydrogen and oxygen. Photolysis of water is the name for this reaction.

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.

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 Pi.
ADP + Pi → ATP
This process is called photophosphorylation.
(ii) Dark reaction: This phase’s reactions don’t require light energy and happen at the same time as the light reaction. The difference in time between the light and dark reactions is a thousandth of a second. ATP and NADPH molecules (made during the light reaction) are employed in the dark reaction to create glucose (C6H12O6) from carbon dioxide. A variety of events take place in the stroma of the chloroplast to fix and reduce carbon dioxide. The glucose produced is either utilised up by the cells right away or stored as starch.

Question C14. Complete the following food chain by writing the names of appropriate organisms in the blanks:
i)  Grass                         __________ Snake                 ________
ii) ______                         Mouse ______                     Peacock
Solution C.14.
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 C15. How do non- green plants such as fungi and bacteria obtain their nourishment?
Solution C15.
Fungi and bacteria are non-green plants that get their nutrition from decaying organic substances in their environment. This material is derived from the remains of deceased animals and plants. To gain sustenance, fungi and bacteria break down organic matter and release carbon dioxide into the atmosphere.

Question C16. All life owes its existence to chlorophyll. Give reason.
Solution C.16.
In green plants, chlorophyll serves as the primary location for photosynthesis. When the light energy is trapped by the chlorophyll molecule, photosynthesis begins. Carbon dioxide (CO2) from the atmosphere and water (H2O) from the soil are used to transform light energy into chemical energy in the form of glucose. All other species rely on this food for survival, whether directly or indirectly. A plant is always the beginning point of any food chain. If green plants vanished overnight, practically all life on Earth would go with them. As a result, we can claim that chlorophyll is responsible for the existence of all life.

Question C17. Complete the following by filling the blanks 1 to 5 with appropriate words/ terms/ phases:
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 C17.
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 D1. Acandidate investigates the role of many components in photosynthesis. He kept a potter plant in the dark for more than 24 hours. He covered one of the leaves with black paper in the centre only in the early hours of the next morning. After that, he exposed the plant to sunlight for a few hours and examined the leaf for starch, which was covered in black paper. 
Solution D1.
a. The student wanted to show that photosynthesis necessitates the presence of sunlight. The role of sunlight in photosynthesis is being investigated.
b. Yes, The other uncovered leaf on the potted plant acts as a control.
c. Destarching ensures that any leftover starch from the experiment was made in the lab. As a result, during the duration of the experiment, the plant was kept in the dark.
d.
• After killing the cells by soaking the leaf in boiling water for a minute, the student removes the chlorophyll by boiling the leaf in alcohol/methylated spirit over a water bath.
• After killing the cells by soaking the leaf in boiling water for a minute, the student removes the chlorophyll by boiling the leaf in alcohol/methylated spirit over a water bath.
• After that, the student spreads out the leaf on a plate and covers it with iodine solution. The presence of starch is indicated by a blue-black colour.
• The open (sun-exposed) area turned blue-black, whereas the covered area turned brown. The colour difference between the covered and uncovered regions of the leaves demonstrates the importance of sunlight for photosynthesis.

Question D2. Photosynthesis in green plants is directly and indirectly dependent on so many plant structures. Explain briefly the role of the following structure in this process.
a) Guard cell
b) Cuticle
c) Mesophyll cells
d) Xylem tissue in the leaf veins
e) Phloem tissue in the leaf veins
f) Stomata
Solution D2.
(a) Guard cells: They control the opening and closing of stomata, and hence the carbon dioxide entrance through them.
(b) Cuticle: Because the cuticle is clear and water resistant, light can readily pass through it.
(c) Mesophyll cells: Mesophyll cells are the primary photosynthesis sites. Mesophyll cells contain the majority of chloroplasts. The light energy is trapped by the chlorophyll of the higher layers of mesophyll, particularly the palisade cells, when sunlight falls on the leaf.
(d) Leaf Vein Xylem Tissue: Water is required for photosynthesis to take place. Water is drawn up from the earth by the roots, transmitted up the stem, and finally delivered to the leaves (photosynthesis site) via the xylem tissue. After then, the water is dispersed throughout the mesophyll tissue.
(e) Phloem Tissue in the Leaf Veins: Phloem tissue transports the prepared food from the leaves to all areas of the plant. The glucose is transformed to insoluble starch and then to soluble sugar, sucrose, which is carried in solution through the phloem in the leaf veins and down the stem phloem.
(f) Stoma: The stoma’s primary function is to allow carbon dioxide from the atmosphere into the body for photosynthesis. The stomata also allow the majority of the oxygen created during photosynthesis to seep into the atmosphere.

Question D3. 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 name of the correct items.
b. What phenomenon do the thick arrows A and B indicated?

Solution D3.
a.
1. Sunlight
2. Oxygen
3. Glucose
4. Xylem
b. A – Transpiration B –Translocation

Question D4. 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 oricess which was the starting point of the whole chin.
d. Name one natural element which all the organisms 2-4 and even 5 and gettinh from No. 1 for their survival.
Solution D4.
a. Food chain
b. Hawk, eagle
c. Photosynthesis
d. Carbon

Question D5. Enumerated the steps involved in testing a green leaf for the presence of starch.
Solution D5.
To detect whether a leaf contains starch, use the following test:
• Kill the cells by dipping a leaf in boiling water for a minute.
• To remove the chlorophyll, boil the leaf in methylated spirit in a water bath until it becomes pale blue and becomes hard and brittle.
• To soften the leaf, soak it in hot water.
• Place the leaf in a Petri dish and cover it with an iodine solution.
• The presence of starch is indicated by the presence of a blue-black colour on the leaf.
• A brown coloration indicates the absence of starch.

Question D6. Given alongside is the diagram of an experimental set-up:
a. What is 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 nay step before starting the experiment? Describe this step and explain its necessity.
Solution D6.
a. To show how important carbon dioxide is in photosynthesis
b. No, the experiment will not work since the beaker contains lime water rather than potassium hydroxide, which is needed to absorb CO2.
c. Instead of lime water, put potassium hydroxide in the beaker.
d. Before beginning the experiment, the plant’s leaves must be destarch by exposing it to complete darkness for 48 hours. Because starch accumulated previously in the leaf placed in the beaker may be identified even if no starch is created during the experiment if the plant is not destarched, the experiment will yield inaccurate data.

Question D7. 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 D7.