Questions & explanations
1. Which of the following is a distinguishing feature between dicotyledons and monocotyledons?
- Dicots have parallel venation, while monocots have reticulate venation
- Dicots have fibrous roots, while monocots have taproots
- Dicots have flowers with floral parts in multiples of 4 or 5, while monocots have floral parts in multiples of 3
- Monocots have two cotyledons, while dicots have one cotyledon
Answer: Dicots have flowers with floral parts in multiples of 4 or 5, while monocots have floral parts in multiples of 3
Floral parts in dicots are typically in multiples of 4 or 5, whereas in monocots they are in multiples of 3. Other features: dicots have reticulate venation, taproots, and two cotyledons; monocots have parallel venation, fibrous roots, and one cotyledon.
2. Which type of reproduction in algae involves the fusion of morphologically similar gametes?
- Isogamy
- Anisogamy
- Oogamy
- Fragmentation
Answer: Isogamy
Isogamy is the fusion of morphologically similar gametes. Anisogamy involves fusion of dissimilar gametes, oogamy involves fusion of a large non-motile egg and a small motile sperm, and fragmentation is a vegetative method.
3. Why are bryophytes often called 'amphibians of the plant kingdom'?
- They can live both on land and in water.
- They require water for sexual reproduction.
- They have both aquatic and terrestrial adaptations.
- They are found only in moist environments.
Answer: They require water for sexual reproduction.
Bryophytes need water for the flagellated antherozoids to swim to the archegonium, making sexual reproduction dependent on water. This amphibious requirement gives them the name 'amphibians of the plant kingdom'.
4. Which group of plants exhibits a diplontic life cycle?
- Bryophytes
- Pteridophytes
- Seed plants (gymnosperms and angiosperms)
- Algae like Spirogyra
Answer: Seed plants (gymnosperms and angiosperms)
In seed plants, the dominant phase is the diploid sporophyte, and the only haploid cells are the gametes. This is a diplontic life cycle, where the gametophyte is highly reduced and dependent on the sporophyte.
5. Which of the following is an economic importance of algae?
- They are a source of agar, obtained from red algae.
- They cause harmful algal blooms only.
- They are not used as food for humans.
- They contribute less than 10% of global CO2 fixation.
Answer: They are a source of agar, obtained from red algae.
Agar is obtained from red algae like Gelidium and Gracilaria. Algae are used as food (e.g., Porphyra), and they contribute about half of total CO2 fixation. Harmful algal blooms are not the only importance.
6. In the life cycle of a plant, which of the following statements correctly describes the ploidy of the gametophytic and sporophytic phases?
- Gametophyte is diploid and sporophyte is haploid
- Gametophyte is haploid and sporophyte is diploid
- Both gametophyte and sporophyte are haploid
- Both gametophyte and sporophyte are diploid
Answer: Gametophyte is haploid and sporophyte is diploid
In plant life cycles, the gametophyte phase is haploid (n) and produces gametes, while the sporophyte phase is diploid (2n) and produces spores. This is a fundamental concept in alternation of generations.
7. What is meant by 'alternation of generations' in plants?
- The alternation between asexual and sexual reproduction
- The regular alternation between a haploid gametophyte and a diploid sporophyte
- The alternation between a sporophyte and a gametophyte that are both diploid
- The alternation between a dominant sporophyte and a reduced gametophyte
Answer: The regular alternation between a haploid gametophyte and a diploid sporophyte
Alternation of generations refers to the life cycle pattern where a multicellular haploid gametophyte alternates with a multicellular diploid sporophyte. This is a defining feature of plant life cycles.
8. Which evolutionary trend is observed in the life cycles of land plants?
- Increase in gametophyte dominance and reduction of sporophyte
- Reduction of gametophyte and dominance of sporophyte
- Both gametophyte and sporophyte remain equally dominant
- Loss of alternation of generations
Answer: Reduction of gametophyte and dominance of sporophyte
In the evolution of land plants, there is a trend from a dominant gametophyte in bryophytes to a dominant sporophyte in pteridophytes and seed plants, with the gametophyte becoming increasingly reduced.
9. Which of the following is a characteristic feature of pteridophytes that distinguishes them from bryophytes?
- Presence of vascular tissue (xylem and phloem)
- Dominant gametophyte generation
- Absence of true roots
- Requirement of water for fertilization
Answer: Presence of vascular tissue (xylem and phloem)
Pteridophytes are the first terrestrial plants to possess vascular tissue (xylem and phloem), which allows them to transport water and nutrients efficiently. Bryophytes lack true vascular tissue.
10. Which of the following is a characteristic feature of a haplontic life cycle?
- The dominant phase is diploid sporophyte
- The zygote is the only diploid stage
- Both gametophyte and sporophyte are multicellular
- Meiosis occurs during gamete formation
Answer: The zygote is the only diploid stage
In a haplontic life cycle, the dominant phase is the haploid gametophyte, and the only diploid stage is the zygote, which undergoes meiosis to produce haploid spores. This is seen in many algae.
11. In which plant group is the gametophyte the dominant, independent phase?
- Pteridophytes
- Gymnosperms
- Bryophytes
- Angiosperms
Answer: Bryophytes
In bryophytes, the gametophyte is the dominant, photosynthetic, and independent phase, while the sporophyte is dependent on it. In pteridophytes and seed plants, the sporophyte is dominant.
12. Fertilization in pteridophytes requires water because:
- Antherozoids need to swim to the archegonium
- The sporophyte is dependent on water
- Spores are dispersed by water
- The prothallus is aquatic
Answer: Antherozoids need to swim to the archegonium
In pteridophytes, the male gametes (antherozoids) are flagellated and require a film of water to swim to the archegonium for fertilization. This dependence on water is a primitive feature.