Life Processes in Plants – Case-based Questions with Answers

CBSE Class 7 Science — Chapter 10: Life Processes in Plants — 20 Case-Based Questions

Content Bank — Focus Areas

Each case targets real exam-style situations covering photosynthesis, leaf structure, transport (xylem & phloem), transpiration, translocation, respiration, excretion, adaptations and simple experiments. Answers are concise, concept-focused and NCERT-aligned.

20 Case-Based Questions (Read the case, answer the questions)

Case 1 — Shaded Leaves

A gardener notices that the leaves on the shaded side of a hedge are larger and thinner than leaves on the sunny side.

Explain why shaded leaves are larger and thinner.
How does this structural difference help the plant?

Answers: Shaded leaves are larger and thinner to maximize light capture; they have fewer palisade layers and more surface area. Functionally, this increases light interception under low light so photosynthesis can proceed efficiently despite reduced light intensity.

Case 2 — Potted Plant Wilting

A potted plant wilts on a hot, dry day though the soil seems moist when touched superficially.

Suggest two possible reasons for wilting.
What immediate steps should be taken to help the plant?

Answers: Wilting can be due to excessive transpiration exceeding water uptake, or root damage/compacted soil preventing water absorption. Immediate steps: reduce transpiration (move to shade, mist leaves), check soil moisture deeply and water thoroughly, loosen soil or repot if roots are damaged.

Case 3 — Starch Test on Leaves

In an experiment, a leaf is covered with black paper for a day. After testing, the covered part does not turn blue-black with iodine, while the exposed part does.

What conclusion can be drawn?
Why is the iodine test used here?

Answers: Conclusion: Light is necessary for photosynthesis (starch formation). Iodine reacts with starch to give a blue-black colour, indicating presence of stored glucose as starch after photosynthesis.

Case 4 — Girdling a Fruit Tree

A farmer removes a ring of bark (including phloem) from a fruit tree trunk. After some days, sap accumulates above the ring and fruits below become small and weak.

Explain why sap accumulates above the girdle.
Why do roots and fruits below become weak?

Answers: Phloem transport is interrupted, preventing downward translocation of sugars, so food accumulates above the girdle. Roots and fruits below are deprived of sugars (sinks) so they weaken and growth is reduced.

Case 5 — Aquatic Plant Leaves

A biology student observes that many aquatic plant leaves have stomata on their upper surface only.

Explain this adaptation.
How does it affect gas exchange?

Answers: Aquatic plants have stomata on upper surface to exchange gases with air since the lower surface is submerged. This placement facilitates CO₂ uptake from air and O₂ release efficiently, aiding photosynthesis and respiration.

Case 6 — Desert Plant Features

A student lists features of a cactus: thick fleshy stem, spines instead of leaves, and a waxy cuticle.

Link each feature to water-saving function.
Why are spines advantageous in deserts?

Answers: Thick fleshy stems store water; spines (reduced leaves) reduce surface area and transpiration; waxy cuticle prevents evaporation. Spines also protect from herbivores and can provide shade, reducing water loss further.

Case 7 — High Humidity Greenhouse

Plants in a humid greenhouse show lower transpiration rates and lush foliage.

Explain why transpiration is lower in high humidity.
State one advantage and one disadvantage of low transpiration.

Answers: High humidity reduces water vapour gradient between inside leaf and outside air, lowering transpiration. Advantage: plants conserve water and maintain turgor; disadvantage: reduced transpiration pull can limit mineral uptake and cooling effect.

Case 8 — Potometer Reading

Using a potometer, you measure bubble movement faster on a windy day than on a calm day.

Explain the observation.
What does this tell you about environmental effects on transpiration?

Answers: Wind removes humid air from leaf surface, increasing vapour gradient and thus transpiration, so water uptake (bubble movement) increases. This shows transpiration rises with wind speed and environmental factors strongly influence water loss.

Case 9 — Yeast and Anaerobic Respiration

In waterlogged soil, some roots show signs of stress and anaerobic conditions promote fermentation in microorganisms nearby.

Describe differences between aerobic and anaerobic respiration relevant here.
How might waterlogging affect root health?

Answers: Aerobic respiration uses O₂ and yields more ATP; anaerobic yields less energy and produces ethanol/CO₂ in some microbes. Waterlogging reduces oxygen availability to roots, forcing anaerobic metabolism, causing energy shortage and root damage or death.

Case 10 — Leaf with Many Villi? (Trick)

A student writes that leaves have 'villi' to absorb nutrients like the intestine.

Identify and correct the mistake.
What structure in leaves increases surface area for absorption?

Answers: Correction: Leaves do not have villi; 'villi' are in animal intestines. Leaves have 'veins' (xylem/phloem) and 'palisade' cells plus a broad lamina that increases surface area for light absorption, while 'spongy mesophyll' provides air spaces for gas exchange.

Case 11 — Translocation During Spring

In spring, stored sugars in roots move to buds and young leaves for growth.

Explain the source-sink reversal that occurs.
Which vascular tissue is involved?

Answers: During spring, roots act as source (storage) and buds/leaves are sinks (growing tissues), so translocation flows upward from root to shoot. Phloem carries out this bidirectional movement of organic solutes.

Case 12 — Leaf Shedding in Autumn

Deciduous trees shed leaves in autumn after reabsorbing nutrients.

Why do trees reabsorb nutrients before leaf fall?
How does leaf fall help the plant?

Answers: Trees retrieve valuable nutrients (e.g., nitrogen) from leaves before abscission to conserve resources. Leaf fall reduces water loss and metabolic demand during unfavorable season, conserving energy for survival.

Case 13 — Guard Cells Experiment

Under microscope, guard cells look turgid in morning and flaccid by evening for a sample plant.

Explain the change in turgor of guard cells.
What effect does this have on gas exchange?

Answers: In daylight guard cells take up water (become turgid) due to active ion uptake, opening stomata for CO₂ entry. At night or under water stress they lose turgor, closing stomata, reducing gas exchange and transpiration.

Case 14 — Storage Organs

A farmer stores potatoes (tubers) that are rich in starch and uses them for planting later.

Explain why tubers are good storage organs.
How is stored starch mobilised when the tuber sprouts?

Answers: Tubers store starch (energy) in parenchyma cells, providing reserves for adverse periods. When sprouts form, enzymes (amylases) convert starch back to sugars which are translocated to growing buds as energy source.

Case 15 — Fungus on Dead Leaf

Dead leaves on the ground show fungal growth decomposing the material.

Is the fungus autotrophic or saprophytic? Explain.
Why is saprophytism ecologically important?

Answers: Fungus is saprophytic; it secretes enzymes to digest dead organic matter and absorbs nutrients. Saprophytes recycle nutrients back into soil, maintaining ecosystem nutrient cycles.

Case 16 — Plant in Polluted Area

Leaves of plants near a busy road have dust clogging stomata and appear pale.

How can clogged stomata affect photosynthesis and transpiration?
Suggest two remedies to help such plants.

Answers: Clogged stomata reduce CO₂ uptake (lower photosynthesis) and reduce transpiration, impairing cooling and nutrient transport. Remedies: gently wash leaves to remove dust, plant green barriers, or relocate sensitive plants away from pollution sources.

Case 17 — Pitcher Plant

A student reports that a pitcher plant derives nutrients by trapping insects.

Explain why this carnivorous habit evolved.
Which nutrients are mainly obtained from prey?

Answers: Carnivory evolved in nutrient-poor soils (low nitrogen); trapping insects supplements nitrogen and minerals required for growth. Prey provide nitrogenous compounds and phosphates.

Case 18 — Seasonal Dormancy

Bulbs remain dormant underground during winter and sprout in spring.

How do bulbs survive adverse conditions?
What role do stored food reserves play?

Answers: Bulbs store food (starch) and have protective scales that reduce desiccation; dormancy reduces metabolic demand. Stored reserves support rapid growth and shoot emergence when conditions improve.

Case 19 — Rapid Leaf Movement

Touching Mimosa pudica causes rapid folding of leaves.

What life process is involved and what causes the movement?
Is this movement related to photosynthesis?

Answers: Movement is a rapid response (nastic movement) triggered by change in turgor pressure in pulvini cells. It's a protective response, not directly related to photosynthesis, though energy for recovery comes from respiration.

Case 20 — Excessive Fertiliser Use

Overuse of fertiliser causes lush green growth but poor flowering and eventual leaf burn.

Explain how excess fertiliser affects plant life processes.
What balanced strategy should a gardener follow?

Answers: Excess fertiliser (especially nitrogen) promotes vegetative growth (more photosynthesis products directed to leaves) and may inhibit flowering; high salt concentration can cause osmotic stress, reducing water uptake and burning tissues. Strategy: use balanced NPK based on soil test, follow recommended doses and timing, and water well after application to prevent salt build-up.