Chapter 3: Plant Kingdom Application Questions | biology Class 11 CBSE

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Chapter 3: Plant Kingdom Application Questions | biology Class 11 CBSE | ByteNotes.in

Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 1

Applied Concept

A marine biologist collects a red-coloured alga from a depth of 200 metres where very little sunlight penetrates. With reference to the pigment composition and adaptations of Rhodophyceae, explain how this alga is able to survive at such great depths.

The alga belongs to Rhodophyceae (red algae), which contains the red pigment r-phycoerythrin that is capable of absorbing blue-green light wavelengths, which penetrate deepest into ocean water.
While red and orange wavelengths are absorbed by water in the upper layers, blue-green light reaches great depths, and r-phycoerythrin efficiently captures this light for photosynthesis.
Red algae also contain chlorophyll a and d, which assist in photosynthesis at low light intensities, making the organisms capable of surviving in light-limited deep-ocean environments.
Because red algae are also found in well-lit surface waters, the presence of r-phycoerythrin provides a significant advantage in deep water environments, allowing them to colonise habitats inaccessible to other algal groups.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 2

Applied Concept

A food technologist wants to produce a solid medium to culture bacteria and also needs a stabiliser for an ice-cream product. With reference to the chapter on Plant Kingdom, suggest which algae-derived products can fulfil these needs and explain their origin.

Agar, obtained from red algae Gelidium and Gracilaria, is the ideal product for use as a solid culture medium for growing bacteria and other microorganisms in laboratory settings.
For use as a food stabiliser in ice-cream production, agar from Gelidium and Gracilaria can also be used; additionally, carrageen from red algae is used commercially as a hydrocolloid and emulsifier in food products.
Algin, obtained from brown algae (Phaeophyceae), is another hydrocolloid (water-holding substance) that can be used as a thickener and stabiliser in food, cosmetic, and pharmaceutical preparations.
Both agar and algin are natural polysaccharide products extracted from marine algae that are safe for consumption and have wide industrial applications, making algae commercially valuable organisms.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 3

Applied Concept

During a trek in the Himalayas, a student observes that bare rocky slopes eventually become covered by mosses and lichens first, followed later by grasses and shrubs. With reference to bryophytes, explain this ecological phenomenon.

Mosses and lichens are pioneer organisms that are capable of colonising bare, inhospitable rocks where no other plants can establish; this is the beginning of primary ecological succession.
Mosses and lichens decompose rocks through their physical and chemical activities, gradually converting rock surfaces into a fine layer of soil rich in organic matter and minerals.
As organic matter accumulates and the substrate becomes fertile, conditions become suitable for the growth of higher plants like grasses and shrubs; mosses thus facilitate the succession of vegetation.
Dense moss mats also retain moisture on the rock surface and prevent soil erosion by reducing rain impact, creating a stable, moist microhabitat that supports the establishment of subsequent plant communities.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 4

Applied Concept

A botanist studying a garden pool finds algae that reproduce by both zoospores and gamete fusion. In one sample, the fusing gametes appear identical in size and both are flagellated, while in another, the gametes are similar in size but lack flagella. Identify the type of reproduction in each case and name one example of each.

When two gametes that are flagellated and similar in size fuse, this is called isogamy; Ulothrix is an example of an alga that shows flagellated isogamy.
When two gametes that are non-flagellated (non-motile) but similar in size fuse, this is also classified as isogamy; Spirogyra is an example of this type of non-flagellated isogamy.
Isogamy is defined broadly as fusion between morphologically similar gametes, regardless of whether or not they are flagellated, as long as both gametes are equal in size.
Oogamy, by contrast, involves fusion between a large non-motile female gamete and a smaller motile male gamete (as in Volvox and Fucus), which is distinct from both forms of isogamy described.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 5

Applied Concept

A student is confused about why mosses can survive on rocky hill slopes but cannot establish themselves in a dry, sunny desert. With reference to the reproductive biology and structural features of bryophytes, explain this limitation.

Bryophytes, including mosses, require water for sexual reproduction because the biflagellate antherozoids (male gametes) must swim through a film of water to reach the archegonium for fertilisation; a dry desert provides no such water film.
The gametophyte (main plant body of bryophytes) is not protected by a cuticle or vascular tissue, making it extremely vulnerable to desiccation; rocky hill slopes in the hills provide shade and moisture, while deserts are hot and arid.
The protonema stage of mosses requires a moist, shaded substrate to germinate and establish; the extreme heat and UV radiation of a sunny desert would destroy this delicate stage before it matures.
The absence of vascular tissue in bryophytes means they cannot efficiently transport water from the substrate to upper parts of the plant body, limiting them to habitats where ambient moisture is consistently available.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 6

Applied Concept

A student is examining Marchantia under a hand lens and notices cup-shaped structures on the upper surface of the thallus containing tiny green bodies. Identify these structures and explain their role in reproduction.

The cup-shaped structures are gemma cups and the tiny green bodies inside them are gemmae (singular: gemma), specialised structures for asexual reproduction in liverworts like Marchantia.
Gemmae are green, multicellular, asexual buds that develop within the gemma cups; they are entirely vegetative structures not formed through any sexual process.
When mature, gemmae detach from the parent thallus either naturally (by rain splash or other physical disturbance) and land on suitable substrates where they germinate to produce new, independent gametophyte individuals.
This method of vegetative reproduction through gemmae allows rapid colonisation of suitable habitats and does not require water or gamete fusion, making it an efficient asexual propagation strategy for liverworts.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 7

Applied Concept

With reference to the features of pteridophytes, explain why a fern growing in a dense, damp rainforest is able to reproduce successfully while the same fern species fails to reproduce in a dry, exposed garden bed.

Fern reproduction requires the formation of a free-living photosynthetic gametophyte called prothallus, which needs cool, damp, shady conditions; these conditions are available in the dense rainforest but not in a dry garden bed.
The prothallus bears archegonia and antheridia; the antherozoids (male gametes) released from antheridia must swim through a film of water to reach the archegonium — a process that requires continuous moisture on the soil surface.
In the dry, exposed garden bed, the prothallus would desiccate before reaching maturity, and even if it survived, the lack of surface water would prevent antherozoid transfer and fertilisation.
The cool, shaded rainforest microclimate also maintains consistent humidity and temperature suitable for gametophyte survival, whereas direct sunlight and low humidity in the garden bed create conditions lethal to the delicate, thin-tissued prothallus.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 8

Applied Concept

An ecologist studying a coniferous forest notices that Pinus trees growing in highly rocky, nutrient-poor soil are thriving well. How do the root associations of Pinus help it adapt to such nutrient-poor conditions? Also mention the different type of root association found in Cycas.

Pinus roots form mycorrhizal associations with fungi; the fungal hyphae significantly increase the effective absorptive surface area of the roots, enabling efficient uptake of water and minerals (especially phosphorus) from nutrient-poor, rocky soils.
The mycorrhizal fungi also produce enzymes that break down organic matter in soil, releasing nutrients that the Pinus tree can then absorb, effectively supplementing its mineral nutrition in poor soils.
Cycas, another gymnosperm, has specialised roots called coralloid roots that are associated with nitrogen-fixing cyanobacteria; these cyanobacteria fix atmospheric nitrogen (N2) and convert it into a form usable by the plant.
Both associations — mycorrhiza in Pinus and cyanobacteria in Cycas coralloid roots — represent mutualistic relationships that allow gymnosperms to thrive in environments that are otherwise limiting in key nutrients.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 9

Applied Concept

Compare the significance of the following observation: in Selaginella (a pteridophyte), megaspores and microspores remain briefly associated with the parent plant, whereas in Pinus (a gymnosperm), the female gametophyte is permanently retained within the megasporangium. What evolutionary conclusion can you draw?

In Selaginella, heterospory produces microspores (male) and megaspores (female); the female gametophyte develops within the retained megaspore and the embryo begins development within it, but megaspores may eventually be shed from the parent plant.
In Pinus, the female gametophyte is permanently retained within the megasporangium on the parent sporophyte and is never shed; the ovule (megasporangium + integuments) remains on the megasporophyll throughout development.
This permanent retention in gymnosperms, combined with the development of protective integuments around the ovule, represents the fully established seed habit, providing the developing embryo with continuous nutrition and protection.
Evolutionarily, the progression from free spore dispersal in homosporous pteridophytes through partial retention in heterosporous pteridophytes to permanent retention in gymnosperms illustrates the step-by-step evolution of the seed — one of the most significant innovations in plant evolution.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 10

Applied Concept

A scientist working on space nutrition is looking for a plant-based protein supplement that can be grown in minimal space in zero-gravity conditions. With reference to the economic importance of algae mentioned in the chapter, identify a suitable organism and justify your answer.

Chlorella is the most suitable organism; it is a unicellular green alga that is exceptionally rich in proteins, making it a high-value nutritional supplement in minimal volumes.
According to the chapter, Chlorella is already used as a food supplement by space travellers, directly validating its suitability for space nutrition programmes.
Being unicellular, Chlorella can be grown in compact photobioreactors with minimal space; it reproduces rapidly through cell division, allowing continuous protein production in controlled environments.
Its autotrophic nature means it requires only light, carbon dioxide, water, and simple mineral salts for growth, making it self-sustaining and ideal for closed life-support systems in space missions.

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Chapter 3: Plant Kingdom | Application Questions

A marine biologist collects a red-coloured alga from a depth of 200 metres where very little sunlight penetrates. With reference to the pigment composition and adaptations of Rhodophyceae, explain how this alga is able to survive at such great depths.

A food technologist wants to produce a solid medium to culture bacteria and also needs a stabiliser for an ice-cream product. With reference to the chapter on Plant Kingdom, suggest which algae-derived products can fulfil these needs and explain their origin.

During a trek in the Himalayas, a student observes that bare rocky slopes eventually become covered by mosses and lichens first, followed later by grasses and shrubs. With reference to bryophytes, explain this ecological phenomenon.

A student is confused about why mosses can survive on rocky hill slopes but cannot establish themselves in a dry, sunny desert. With reference to the reproductive biology and structural features of bryophytes, explain this limitation.

A student is examining Marchantia under a hand lens and notices cup-shaped structures on the upper surface of the thallus containing tiny green bodies. Identify these structures and explain their role in reproduction.

With reference to the features of pteridophytes, explain why a fern growing in a dense, damp rainforest is able to reproduce successfully while the same fern species fails to reproduce in a dry, exposed garden bed.

An ecologist studying a coniferous forest notices that Pinus trees growing in highly rocky, nutrient-poor soil are thriving well. How do the root associations of Pinus help it adapt to such nutrient-poor conditions? Also mention the different type of root association found in Cycas.

A scientist working on space nutrition is looking for a plant-based protein supplement that can be grown in minimal space in zero-gravity conditions. With reference to the economic importance of algae mentioned in the chapter, identify a suitable organism and justify your answer.

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