NCERT Exemplar: Plant Kingdom

Multiple Choice Questions

Q.1. Cyanobacteria are classified under
(a) Protista 
(b) Plantae 
(c) Monera 
(d) Algae
Ans. (c)

Cyanobacteria are classified under Kingdom Monera.

• They are commonly called blue-green algae but are prokaryotic organisms (lack nucleus and membrane-bound organelles) and therefore not true algae.
• Cyanobacteria are photosynthetic bacteria; they contain chlorophyll a and accessory pigments such as phycocyanin and phycoerythrin and are capable of oxygenic photosynthesis.

(i) Protista - unicellular eukaryotes.
(ii) Plantae - eukaryotic, chloroplast-containing, predominantly autotrophic organisms commonly called plants.

Q.2. The fusion of two motile gametes that are dissimilar in size is termed as
(a) Oogamy 
(b) Isogamy 
(c) Anisogamy 
(d) Zoogamy
Ans. (c)

The fusion of two motile gametes that are dissimilar in size is termed anisogamy.

• In anisogamy the two gametes differ in size and/or form; usually the smaller gamete is motile (sperm) and the larger gamete is less motile or non-motile (egg).
• Oogamy is a specialised form of anisogamy in which the female gamete (egg) is large and non-motile while the male gamete (sperm) is small and motile.
• Isogamy is fusion of gametes of similar size and shape; zoogamy sometimes refers to motile gametes but is not commonly used to define size-difference categories.

Anisogamy of two Motile gametes

Q.3. Holdfast, stipe, and frond constitutes the plant body in case of
(a) Rhodophyceae
(b) Chlorophyceae
(c) Phaeophyceae
(d) All of the above
Ans. (c)

• Holdfast, stipe and frond are typical vegetative structures of brown algae (Phaeophyceae).
• The holdfast anchors the thallus to the substratum, the stipe is a stem-like supportive structure and the frond is a leaf-like expanded blade where photosynthesis occurs.
• Most brown algae are large, multicellular marine algae (e.g., kelps) and show advanced organisation among the algae.

Q.4. A plant shows a thallus level of organization. It shows rhizoids and is haploid. It needs water to complete its life cycle because the male gametes are motile. Identify the group to which it belongs to
(a) Pteridophytes 
(b) Gymnosperms
(c) Monocots 
(d) Bryophytes
Ans. (d)

• These characters-thalloid body, presence of rhizoids, predominant haploid phase and requirement of water for motile male gametes-are diagnostic of bryophytes.
• Bryophytes are non-vascular, small plants (mosses, liverworts, hornworts) in which the gametophyte is the dominant, photosynthetic and free-living generation.

Q.5. A prothallus is
(a) A structure in pteridophytes formed before the thallus develops
(b) A sporophytic free-living structure formed in pteridophytes
(c) A gametophyte free-living structure formed in pteridophytes
(d) A primitive structure formed after fertilization in pteridophytes
Ans. (c)

In pteridophytes the spores germinate to give rise to small, multicellular, usually photosynthetic and free-living gametophytes called prothalli (singular: prothallus). The prothallus represents the gametophyte phase.

Q.6. Plants of this group are diploid and well adapted to extreme conditions. They grow bearing sporophylls in compact structures called cones. The group in reference is
(a) Monocots 
(b) Dicots
(c) Pteridophytes 
(d) Gymnosperms
Ans. (d)

• The description refers to Gymnosperms: diploid, vascular seed plants whose seeds are not enclosed in an ovary and which typically bear reproductive structures (sporophylls) aggregated as cones.
• Gymnosperms (conifers, cycads, Ginkgo, gnetophytes) are often adapted to cold, dry or nutrient-poor habitats and have a dominant sporophyte generation.

Q.7. The embryo sac of an Angiosperm is made up of
(a) 8 cells 
(b) 7 cells and 8 nuclei
(c) 8 nuclei 
(d) 7 cells and 7 nuclei
Ans. (b)

The mature embryo sac (female gametophyte) of most angiosperms is the typical 7-celled, 8-nucleate structure.

Its organisation: three antipodal cells (at chalazal end), two synergids plus one egg cell (at micropylar end) and one central cell containing two polar nuclei (which may fuse to form a single diploid polar nucleus prior to fertilisation).

Q.8. If the diploid number of a flowering plant is 36. what would be the chromosome number in its endosperm?
(a) 36 
(b) 18 
(c) 54 
(d) 72
Ans. (c)

The endosperm in angiosperms is typically triploid (3n), formed by fusion of one sperm nucleus with the two polar nuclei (triple fusion).

2n = 36

n = 36 ÷ 2 = 18

Endosperm = 3n = 3 × 18 = 54

Q.9. Protonema is
(a) Haploid and is found in mosses
(b) Diploid and is found in liverworts
(c) Diploid and is found in pteridophytes
(d) Haploid and is found in pteridophytes
Ans. (a)

Protonema is a juvenile, filamentous or plate-like, haploid stage of the moss gametophyte. The protonema gives rise to the leafy gametophore (adult gametophyte) in mosses.

Q.10. The giant Redwood tree (Sequoia sempervirens) is a/an.
(a) Angiosperm 
(b) Free fern
(c) Pteridophyte 
(d) Gymnosperm
Ans. (d)

Sol: One of the gymnosperms, the giant redwood tree Sequoia sempervirens, is one of the tallest extant tree species.

Very Short Answer Type Questions

Q.1. Food is stored as Floridean starch in Rhodophyceae. Mannitol is the reserve food material of which group of algae?
Ans. Mannitol is the reserve food material of brown algae (Phaeophyceae).

Q.2. Give an example of plants with
(a) Haplontic life cycle
(b) Diplontic life cycle
(c) Haplo-diplontic life cycle
Ans.

• (a) Haplontic life cycle - Volvox, Spirogyra, some species of Chlamydomonas (dominant phase is haploid; zygote is the only diploid stage and undergoes meiosis).
• (b) Diplontic life cycle - All seed-bearing plants (gymnosperms and angiosperms) where the dominant free-living phase is diploid and gametes are produced by meiosis in specialised structures.
• (c) Haplo-diplontic life cycle - Bryophytes and pteridophytes (both multicellular haploid gametophyte and multicellular diploid sporophyte occur, though one phase may be dominant).

Q.3. The plant body in higher plants is well-differentiated and well developed. Roots are the organs used for the purpose of absorption. What is the equivalent of roots in the less developed lower plants?
Ans. In lower plants like many algae the holdfast acts as an anchoring structure while in bryophytes rhizoids perform anchorage and limited absorption; they are not true roots as they lack vascular tissue.

Q.4. Most algal genera show haplontic life style. Name an alga which is
(a) Haplo-diplontic
(b) Diplontic
Ans.

• (a) Haplo-diplontic - Ectocarpus, Polysiphonia, kelps (some stages diploid and multicellular, some haploid and multicellular).
• (b) Diplontic - Fucus, where the plant body (thallus) is diploid and gametes are formed by meiosis.

Q.5. In Bryophytes male and female sex organs are called ______ and ______.
Ans. In bryophytes the male sex organ is called antheridium and the female sex organ is called archegonium.

Short Answer Type Questions

Q.1. Why are bryophytes called the amphibians of the plant kingdom?
Ans. Bryophytes are called the amphibians of the plant kingdom because they are primarily terrestrial but remain dependent on water for sexual reproduction. They grow on land like higher plants but require a film of water for the motile male gametes (antherozoids) to reach the female gametes (eggs).

Bryophytes

Q.2. The male and female reproductive organs of several pteridophytes and gymnosperms are comparable to floral structures of angiosperms. Make an attempt to compare the various reproductive parts of pteridophytes and gymnosperms with reproductive structures of angiosperms
Ans.

Explanation (summary):

• In pteridophytes the sporophyll bears sporangia (which produce spores); clusters of sporophylls may form sori. In angiosperms the flower contains sporophylls modified as stamens (microsporophylls) and carpels/ovules (megasporophylls).
• In gymnosperms the male cone bears pollen-bearing microsporophylls and the female cone bears ovule-bearing megasporophylls; pollen grains are analogous to microspores/pollen of angiosperms, while ovules develop into seeds after fertilisation.

Q.3. Heterospory i.e., the formation of two types of spores - microspores and megaspores is a characteristic feature in the life cycle of a few members of pteridophytes and all spermatophytes. Do you think heterospory has some evolutionary significance in the plant kingdom?
Ans. Yes. Heterospory is evolutionarily significant because:

• It leads to differentiation of male and female gametophytes (microgametophyte and megagametophyte), often with the female gametophyte retained on or within the sporophyte, providing protection and nourishment to the developing embryo.
• This retention and protection of the megagametophyte and developing embryo is a precursor to the seed habit seen in gymnosperms and angiosperms, allowing offspring to survive unfavourable conditions and promoting dispersal.

Q.4. How far does Selaginella one of the few living members of lycopodiales (pteridophytes) fall short of seed habit?
Ans. Selaginella is heterosporous, producing megaspores and microspores which develop into female and male gametophytes respectively. However, it falls short of true seed habit because the megasporangium (and its developing megagametophyte and embryo) is not enclosed within an integument forming a seed; there is no true seed with an integument, testal layers and a dormant embryo with nutritive tissue protected as in spermatophytes.

Q.5. Each plant or group of plants has some phylogenetic significance in relation to evolution: Cycas, one of the few living members of gymnosperms is called the 'relic of past'. Can you establish a phylogenetic relationship of Cycas with any other group of plants that justifies the above statement?
Ans. Cycas shows several primitive features reminiscent of pteridophytes and thus is often regarded as a living fossil or 'relic'. These features include flagellated antherozoids (motile sperm), leaf-like megasporophylls, presence of archegonia on the female gametophyte and circinate vernation (circinate ptyxis) of young leaves-characters that suggest a phylogenetic link to earlier vascular plants (pteridophytes).

Q.6. The heterosporous pteridophytes show certain characteristics, which are precursors to the seed habit in gymnosperms. Explain.
Ans. Heterosporous pteridophytes (e.g., Selaginella, Salvinia, Marsilea, Azolla) exhibit:

• Production of two kinds of spores - megaspores (female) and microspores (male).
• Development of differentiated male and female gametophytes from these spores; female gametophytes are often larger and retained near the sporangium for some time.
• Retention of the female gametophyte on the parent sporophyte and development of the zygote within this retained structure; these features are precursors to the embryo retention and protection seen in seed plants.

Q.7. Comment on the lifecycle and nature of a fern prothallus.
Ans.

• Ferns exhibit a haplo-diplontic life cycle with two multicellular phases: a dominant, long-lived diploid sporophyte and a smaller, short-lived haploid gametophyte (prothallus).
• The gametophyte (prothallus) is usually a small, green, thalloid, free-living photosynthetic structure bearing antheridia and archegonia.
• Water is required for the motile antherozoids released from antheridia to swim to the egg in archegonium; fertilisation produces a zygote that develops into the new sporophyte.
• Prothalli require cool, damp, shaded habitats; these ecological requirements limit their geographic distribution.

Q.8. How are the male and female gametophytes of pteridophytes and gymnosperms different from each other?
Ans. In pteridophytes the gametophytes (male and female) are generally free-living and independent (e.g., fern prothallus). In gymnosperms the gametophytes are highly reduced and not free-living; they develop within the sporangia (microsporangia produce pollen grains - male gametophyte; megasporangia produce megagametophyte inside the ovule) and remain dependent on the sporophyte.

Q.9. In which plant will you look for mycorrhiza and coralloid roots? Also, explain what these terms mean.
Ans.

• Mycorrhiza - a symbiotic association between roots of vascular plants and fungi; it enhances water and mineral absorption (especially phosphorus) and is common in many angiosperms and gymnosperms.
• Coralloid roots - specialised, often branched roots resembling coral, found in cycads (e.g., Cycas); these roots harbour nitrogen-fixing cyanobacteria (e.g., Nostoc) in their cortex, contributing to the plant's nitrogen nutrition.

Long Answer Type Questions

Q.1. The gametophyte is a dominant phase in the life cycle of a bryophyte. Explain.
Ans.

• In bryophytes the predominant and persistent plant body is the haploid gametophyte, which is photosynthetic and independent.
• The gametophyte bears multicellular sex organs: antheridia (male) producing motile biflagellate antherozoids (sperms) and archegonia (female) - flask-shaped structures each containing a single egg.
• Sperm are released into water films and swim to the archegonium where fertilisation occurs producing a diploid zygote.
• The zygote divides mitotically to form the multicellular sporophyte, which is usually physically attached to and nutritionally dependent on the gametophyte; the sporophyte produces spores by meiosis that disperse to form new gametophytes.
• Because the gametophyte is larger, photosynthetic and free-living, while the sporophyte is smaller and dependent, bryophytes are described as having gametophyte-dominant life cycles.

Q.2. With the help of a schematic diagram, describe the haplo-diplontic life cycle pattern of a plant group.
Ans.

• In sexually reproducing plants there is an alternation of generations between multicellular haploid (gametophyte, n) and multicellular diploid (sporophyte, 2n) phases.
• The sporophyte produces haploid spores by meiosis (reduction division); each spore germinates by mitotic divisions to form a gametophyte.
• The gametophyte produces gametes by mitosis; fusion of two gametes forms a diploid zygote which grows into the sporophyte by mitosis.

In haplo-diplontic life cycles (e.g., pteridophytes, bryophytes) both phases are multicellular. In pteridophytes the sporophyte is dominant and independent while the gametophyte is free-living but smaller and short-lived; in bryophytes the gametophyte is dominant.

Q.3. Lichen is usually cited as an example of symbiosis in plants where an algal and a fungal species live together for their mutual benefit. Which of the following will happen if algal and fungal partners are separated from each other?
(a) Both will survive and grow normally and independently from each other.
(b) Both will die.
(c) Algal component will survive while the fungal component will die.
(d) Fungal component will survive while the algal partner will die.
Based on your answer how do you justify this association as symbiosis?
Ans.

• Empirical observations show that algal partners (photobionts) can often be cultured separately and survive independently; fungal partners (mycobionts), when isolated from the algal partner, generally fail to thrive in natural conditions and often die.
• Thus option (c) is correct: the algal component can usually survive alone, while the fungal component often cannot.
• Justification: In the lichen association the alga (or cyanobacterium) provides photosynthates (organic carbon) while the fungus provides a protected microenvironment, mechanical support, water retention and mineral absorption. The association is therefore a close and usually mutually beneficial relationship; however, because the fungus is often dependent on the alga for carbon, the relationship has been termed mutualism with some authors describing aspects of controlled parasitism in certain lichens.

Q.4. Explain why sexual reproduction in angiosperms is said to take place through double fertilization and triple fusion. Also, draw a labeled diagram of the embryo sac to explain the phenomena.
Ans.

• In angiosperms the pollen grain (male gametophyte) produces two male gametes (sperm nuclei).
• During fertilisation one sperm nucleus fuses with the egg cell nucleus to form the diploid zygote (this is one fertilisation event).
• The second sperm nucleus fuses with the two polar nuclei (or with a fused diploid polar nucleus) in the central cell of the embryo sac to form the triploid (3n) endosperm nucleus - this process is called triple fusion.
• Because two fusion events occur involving two different cells of the embryo sac, the phenomenon is called double fertilization.
• The zygote develops into the embryo while the triploid endosperm develops into nutritive tissue that supports embryo development; double fertilization ensures that endosperm formation is coupled with embryo formation and fertilisation success.

Triple Fusion

Double Fertilisation

Q.5. Draw labelled diagrams of
(a) Female and male thallus of a liverwort.
(b) Gametophyte and sporophyte of Funaria.
(c) Alternation of generation in Angiosperm.
Ans.

(a)

(b) Gametophyte and sporophyte of Funaria.

Funaria

(c) Alternation of generation in Angiosperm.

Alternation of Generation