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CNMS ICSE - 7 Std
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Chapter: 04. Photosynthesis

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SECTION A: MULTIPLE CHOICE QUESTIONS

© Green light (Photosynthesis is minimum in green light as chlorophyll reflects it).
(b) Photolysis (The splitting of water molecules in the presence of light energy).
(a) Crescograph (Sir Jagdish Chandra Bose invented the crescograph to measure plant growth).
(d) Destroy and remove chlorophyll (Boiling in alcohol removes the green pigment, decolourising the leaf so that color changes during the starch test are clearly visible).
© To absorb carbon dioxide from the air inside the bell jar (KOH removes CO₂ to test if photosynthesis can happen without it).
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SECTION B: FILL IN THE BLANKS

autotrophs
blue-black
20°C - 30°C
translocation
turgid
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SECTION C: TRUE OR FALSE QUESTIONS

False. Correct statement: Photosynthesis occurs mainly in leaves but can also take place in other green parts of the plant, such as green stems.
True.
False. Correct statement: Stomata get closed at night when there is no light to avoid loss of water by transpiration.
True.
True.
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SECTION D: EXPLANATIONS OF TERMS

Autotrophic nutrition: The process of nutrition in which organisms (like green plants) synthesise their own organic food (glucose) from inorganic raw materials (CO₂ and water) using solar energy.
Stomata: Minute microscopic pores present in the epidermis of leaves, guarded by kidney-shaped guard cells, which facilitate the exchange of gases (CO₂ and O₂) and transpiration.
Photolysis of water: The chemical process during photosynthesis where solar energy trapped by chlorophyll is used to split water molecules into hydrogen (H⁺) and hydroxyl (OH⁻) radicals.
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SECTION E: SHORT ANSWER QUESTIONS

Too much bright, intense light destroys the green pigment chlorophyll, which hampers the plant’s ability to trap solar energy and consequently slows down the rate of photosynthesis.
When water availability is reduced, the guard cells lose water and become flaccid, causing the stomata to close. Closed stomata prevent the entry of carbon dioxide from the atmosphere into the leaf cells.
Variegated leaves are leaves that have both green and non-green patches (regions containing chlorophyll and regions lacking it). Example: Coleus or Croton.
Fates of glucose (any two):
A part of it is immediately used by cells to release energy during respiration.
Extra glucose is converted into insoluble starch for storage in different plant parts.
It is used to synthesise other organic nutrients like proteins and fats.
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SECTION F: DIAGRAM-BASED QUESTIONS

The two major cell structures are:
Guard cells (the kidney-shaped cells flanking the opening)
Chloroplasts (the small green organelles inside the guard cells)
Stomatal pore (the central opening)
When water enters the guard cells, they swell and become turgid. Their thin, elastic outer walls bulge outwards, which pulls the inner thick, rigid walls apart, widening the stomatal pore between them.
At night, when there is no light, photosynthesis does not occur. The stomata close to prevent unnecessary loss of water through transpiration.
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SECTION G: DIFFERENTIATE BETWEEN CONCEPTS

Xylem vs. Phloem:
Xylem: Transports water and minerals absorbed by the roots to every cell of the leaf.
Phloem: Transports (translocates) the prepared soluble food (glucose) from the leaves to other growing and storage parts of the plant.
Turgid vs. Flaccid guard cells:
Turgid guard cells: Contain a large amount of water, are swollen/curved outwards, and keep the stomatal pore open.
Flaccid guard cells: Have lost water, are shrunk/relaxed, and keep the stomatal pore closed.
Photosynthesis vs. Respiration:
Photosynthesis: Consumes carbon dioxide (CO₂) and releases oxygen (O₂).
Respiration: Consumes oxygen (O₂) and releases carbon dioxide (CO₂).
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SECTION H: LONG ANSWER QUESTIONS

Experiment to show that sunlight is necessary for photosynthesis:
Materials required: A green potted plant, a strip of black paper, paper clips, beaker, burner, test tube, alcohol, water, iodine solution, dropper, Petri dish.
Procedure:
Keep the healthy green potted plant in a dark room for 48 hours to destarch its leaves (allowing the plant to consume all pre-existing starch).
Pluck a leaf and test it with iodine to confirm it is starch-free.
Take another leaf on the same plant and cover a middle section of it on both sides with a strip of black paper secured with clips.
Place the potted plant in bright sunlight for about 4 to 5 hours.
Pluck this leaf, remove the black paper strip, and boil the leaf first in water, and then in alcohol (using a water bath) to decolourise it by removing chlorophyll.
Wash the decolourised leaf with warm water, place it in a Petri dish, and add a few drops of iodine solution over it.
Observations: Only the uncovered portions of the leaf that were exposed to sunlight turn blue-black with iodine. The covered portion remains unchanged (brownish/pale), showing a negative starch test.
Conclusion: Starch is only formed in those parts of the leaf that received sunlight. Therefore, sunlight is indispensable for photosynthesis.
Chemical Equation of Photosynthesis:
math
⁠
math
⁠
Anatomical Adaptations of a Leaf (any four):
Presence of Chlorophyll: Leaf cells contain chloroplasts filled with chlorophyll, which specifically traps solar energy.
Broad and Flat Surface (Lamina): Offers a large surface area to maximize the absorption of sunlight and carbon dioxide.
Arrangement: Leaves are arranged mostly at right angles to the branches to capture maximum solar rays.
Stomata: Numerous minute pores are located primarily on the lower epidermis, allowing easy intake of CO₂ and release of O₂.
Intercellular Spaces: Spongy parenchyma cells have large intercellular spaces that allow carbon dioxide to diffuse freely to all photosynthetic cells.
Vascular Bundles (Veins): A dense network of veins containing xylem (to supply water) and phloem (to carry away food) reaches every corner of the leaf.
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