Biological Classification — Important Questions

Euglena is photosynthetic in sunlight and becomes heterotrophic in the absence of sunlight, and has plant-like pigments

Step 1: Euglena is a euglenoid under Kingdom Protista that uniquely shows both plant-like and animal-like features. Step 2: Like plants, Euglena has pigments identical to those in higher plants and performs photosynthesis in the presence of sunlight. Step 3: Like animals, when deprived of sunlight, Euglena becomes heterotrophic and feeds on other smaller organisms by predation. Step 4: Option A is wrong – Euglena does NOT have a cell wall; instead it has a protein-rich layer called pellicle that makes its body flexible. It also does not use pseudopodia. Step 5: Option C is wrong – Euglena's re

Ascomycetes and Basidiomycetes

Step 1: In fungi, sexual reproduction involves three steps – plasmogamy (cytoplasm fusion), karyogamy (nucleus fusion), and meiosis. Step 2: In some fungi, plasmogamy occurs first but karyogamy is delayed. During this interval, each cell has two haploid nuclei (n+n) – this is called the dikaryotic or dikaryophase. Step 3: This intermediate dikaryotic phase occurs specifically in Ascomycetes and Basidiomycetes. Step 4: In Phycomycetes, the two haploid cells fuse directly to form diploid cells – there is no prolonged dikaryotic stage. Step 5: Deuteromycetes are called 'imperfect fungi' because t

Only their asexual or vegetative phases are known; their sexual stage has not been observed

Step 1: In biology, 'perfect' fungi refers to fungi where the sexual stage (perfect stage) is known, while 'imperfect' refers to those where only the asexual stage is known. Step 2: Deuteromycetes are called imperfect fungi because scientists have only observed their asexual reproduction (by conidia) – the sexual phase is unknown or absent. Step 3: When the sexual stage of some Deuteromycetes was later discovered, those species were reclassified into Ascomycetes or Basidiomycetes. Step 4: Option A is wrong – Deuteromycetes have well-developed, septate, and branched mycelium. Step 5: Option C i

Sex organs are absent; plasmogamy occurs by fusion of somatic cells, leading to a dikaryotic stage, followed by karyogamy and meiosis in the basidium to produce exogenous basidiospores

Step 1: Basidiomycetes lack sex organs entirely, which sets them apart from many other organisms. Step 2: Instead, plasmogamy (cytoplasm fusion) occurs between two vegetative somatic cells of different strains (genotypes), creating a dikaryotic cell (n+n). Step 3: This dikaryotic structure develops into the basidium, where karyogamy (nuclear fusion) occurs, creating a diploid (2n) cell. Step 4: Meiosis then occurs in the basidium, producing four haploid basidiospores that are borne EXOGENOUSLY (on the outside of the basidium). Step 5: Option A is wrong – sex organs are absent and spores are ex