Questions & explanations
1. During unfavorable conditions, slime moulds form a structure called:
- Plasmodium
- Fruiting body
- Cyst
- Spore
Answer: Fruiting body
Slime moulds form a multinucleate, free-living mass called a plasmodium under suitable (favourable) conditions, when food is plentiful. When conditions become unfavourable, the plasmodium stops moving and differentiates to form fruiting bodies at its tips, which bear spores. The spores are the resistant, dispersal stage produced inside these fruiting bodies. Therefore the structure formed during unfavourable conditions is the fruiting body, not the plasmodium.
2. Lichens are considered excellent indicators of air pollution because they are particularly sensitive to which of the following pollutants?
- Sulfur dioxide
- Carbon dioxide
- Ozone
- Nitrogen
Answer: Sulfur dioxide
Lichens are highly sensitive to sulfur dioxide, a common air pollutant from industrial emissions. They absorb nutrients from the air and lack protective structures, making them vulnerable to SO₂, which damages their chlorophyll and disrupts photosynthesis. Thus, their presence or absence indicates air quality. Carbon dioxide is not toxic at ambient levels; ozone and nitrogen are less directly harmful to lichens compared to sulfur dioxide.
3. Which of the following statements about Deuteromycetes is correct?
- They are also known as imperfect fungi because only the asexual phase is known.
- They reproduce exclusively by sexual means.
- They include the genera Alternaria, Colletotrichum, and Trichoderma, which are all beneficial to humans.
- They are classified under Ascomycetes due to their sexual stages.
Answer: They are also known as imperfect fungi because only the asexual phase is known.
Deuteromycetes are called imperfect fungi because their sexual (perfect) stage is not known; only asexual reproduction has been observed. Examples include Alternaria, Colletotrichum, and Trichoderma. The other options are incorrect: they do not reproduce exclusively by sexual means, not all are beneficial (some are pathogens), and they are not classified under Ascomycetes as their sexual stage is absent.
4. Which of the following is the most common method of reproduction in bacteria?
- Binary fission
- Budding
- Fragmentation
- Sexual reproduction
Answer: Binary fission
Binary fission is the primary method of reproduction in bacteria, where a single cell divides into two identical daughter cells. Budding and fragmentation are common in other organisms like yeast and some algae, not bacteria. Bacteria do not undergo true sexual reproduction; they only transfer genetic material through processes like conjugation, transformation, and transduction.
5. A major limitation of the two-kingdom system (Plantae and Animalia) was that it could not accommodate:
- Fungi, which have cell walls but are heterotrophic
- Animals, which are motile
- Plants, which are autotrophic
- Bacteria, which are prokaryotic
Answer: Fungi, which have cell walls but are heterotrophic
In the two-kingdom system, organisms with cell walls were placed in Plantae, but fungi are heterotrophic, not autotrophic like plants. This discrepancy highlighted the limitation of the system. Bacteria were not well accommodated either, but the question specifically asks about a limitation, and fungi are a classic example.
6. Which of the following is a characteristic feature of Ascomycetes?
- Basidiospores produced on basidia
- Ascospores produced inside asci
- Aseptate mycelium
- Sporangiospores produced in sporangia
Answer: Ascospores produced inside asci
Ascomycetes, also known as sac fungi, produce sexual spores called ascospores inside sac-like structures called asci. Basidiospores are characteristic of Basidiomycetes. Aseptate mycelium is typical of Phycomycetes, and sporangiospores are asexual spores in Phycomycetes.
7. Lichens represent a symbiotic association between:
- Fungi and algae
- Fungi and roots of higher plants
- Two different fungi
- Fungi and bacteria
Answer: Fungi and algae
Lichens are symbiotic associations between fungi (mycobiont) and algae (phycobiont). The fungus provides structure and absorbs water and minerals, while the alga performs photosynthesis. Mycorrhiza is a symbiotic association between fungi and plant roots, not lichens.
8. Which of the following is a characteristic feature of fungi?
- Autotrophic nutrition
- Cell wall made of cellulose
- Heterotrophic nutrition
- Unicellular body organization
Answer: Heterotrophic nutrition
Fungi are heterotrophic organisms that obtain nutrients from organic sources. They lack chlorophyll and cannot perform photosynthesis. Their cell wall is made of chitin, not cellulose, and while some fungi are unicellular (yeasts), most are multicellular.
9. In the sexual reproduction of fungi, the dikaryophase refers to:
- A stage with two haploid nuclei per cell
- Fusion of two haploid nuclei
- Formation of diploid zygote
- Meiosis in the zygote
Answer: A stage with two haploid nuclei per cell
After plasmogamy (fusion of cytoplasm), the two haploid nuclei from the mating types remain separate in each cell, leading to a dikaryotic stage (n+n). Karyogamy (fusion of nuclei) occurs later, forming a diploid zygote, which then undergoes meiosis.
10. Which of the following is an asexual spore in fungi?
- Ascospore
- Basidiospore
- Conidium
- Oospore
Answer: Conidium
Conidia are asexual spores produced exogenously on conidiophores. Ascospores and basidiospores are sexual spores produced in asci and basidia, respectively. Oospores are sexual spores formed by the fusion of oogonia and antheridia in some fungi.
11. Which of the following best describes the kingdom Protista?
- Multicellular eukaryotes that include plants, animals, and fungi
- Single-celled eukaryotes that serve as a link between plants, animals, and fungi
- Prokaryotic organisms that are ancestors of all eukaryotes
- Single-celled prokaryotes that form colonies
Answer: Single-celled eukaryotes that serve as a link between plants, animals, and fungi
Protista are single-celled eukaryotes, and they are considered a connecting link because they include organisms that show characteristics similar to plants (e.g., photosynthetic algae), animals (e.g., protozoans), and fungi (e.g., slime moulds).
12. Which of the following kingdoms in Whittaker's five-kingdom classification includes organisms that are primarily prokaryotic?
- Monera
- Protista
- Fungi
- Plantae
Answer: Monera
Whittaker's five-kingdom classification places all prokaryotic organisms (bacteria and cyanobacteria) in the kingdom Monera. Protista includes unicellular eukaryotes, Fungi are eukaryotic heterotrophs, and Plantae are eukaryotic autotrophs.