Which of the following is incorrect about Cynobacteria?
Explanation:
The incorrect statement is option 2. Cyanobacteria are photoautotrophs and carry out photosynthesis. Many cyanobacteria form specialized cells called heterocysts for nitrogen fixation, so they do have heterocysts in several species. They often form blooms in polluted or nutrient-rich water bodies, and they contain chlorophyll a, along with other pigments, which is similar to green plants.
π§ Did You Know?
Cyanobacteria are sometimes called blue-green algae, but they are bacteria, not true algae. They play a key role in nitrogen cycling due to heterocysts in some species.
π‘ NCERT Memory Line:
Cyanobacteria are photosynthetic and may fix nitrogen in heterocysts; they form blooms in polluted waters and possess chlorophyll a similar to green plants.
The size of Pleuropneumonia - like Organism (PPLO) is:
Explanation:
PPLO stands for Pleuropneumonia-Like Organism, which is the organism Mycoplasma pneumoniae. According to NCERT biology, PPLOs are very small, about 0.1 ΞΌm in size, much smaller than many bacteria. Thus the correct size is 0.1 ΞΌm (option 4).
π§ Did You Know?
PPLOs lack a cell wall and have a flexible membrane, which helps them survive as small organisms in various environments.
π‘ NCERT Memory Line:
PPLO organisms are extremely small, around 0.1 ΞΌm, illustrating how some pathogens can be much smaller than typical bacteria.
Male and female gametophytes do not have an
independent free living existence in:
Explanation:
In angiosperms, the male and female gametophytes are microscopic and develop inside the sporophyte tissues (anther and ovule) and are dependent on the sporophyte for nutrition and development. Hence, they do not have an independent free-living existence.
π§ Did You Know?
The pollen grain (male gametophyte) and the embryo sac (female gametophyte) are produced inside the parent plant, not free in the environment.
π‘ NCERT Memory Line:
In angiosperms, the gametophytic phase is reduced and dependent on the sporophyte.
Which of the following options does correctly represent the characteristic features of phylum Annelida?
Explanation:
The correct statement is option 2. Annelida are triploblastic animals with bilateral symmetry and a segmented (metamerically arranged) body. They are coelomates, having a true coelom lined by peritoneum. This segmentation is a key feature emphasized in NCERT biology for phylum Annelida. Options 1, 3, and 4 describe incorrect features: 1 says unsegmented, which contradicts the segmented body; 3 mentions an acoelomate and flattened body, not true for annelids; 4 describes diploblastic and radial symmetry, which applies to cnidarians, not annelids. Understanding these contrasts helps reinforce the NCERT characterization of annelids as triploblastic, bilaterally symmetrical, and segmented.
π§ Did You Know?
Segmentation in annelids allows specialization of body segments for movement and function, a feature highlighted in NCERT discussions of Annelida.
π‘ NCERT Memory Line:
βAnnelids have a segmented (metamerically arranged) body and are triploblastic with bilateral symmetry.β
Match the following group of organisms with their
respective distinctive characteristics and select the correct option :
Organisms
Characteristics
(A)Platyhelminthes
(I)Cylindrical body with no segmentation
(B)Echinoderms
(II)Warm blooded
animals with direct development
(C)Hemichordates
(III)Bilateral symmetry with incomplete
digestive system
(D)Aves
(IV)Radial symmetry with indirect
development
Choose the correct answer from the options given below:
Explanation:
Matchings as per NCERT:
- Platyhelminthes (A) have bilateral symmetry and are unsegmented with an incomplete digestive system (only one opening). => (III)
- Echinoderms (B) show radial symmetry as adults and have indirect development (larval stage). => (IV)
- Hemichordates (C) are worm-like, unsegmented (cylindrical body, no segmentation) organisms. => (I)
- Aves (D) are warm-blooded and show direct development (hatching resembles the adult). => (II)
Thus the correct pairing is A-III, B-IV, C-I, D-II. The other options mismatch these standard NCERT characteristics.
π§ Did You Know?
Hemichordates and Echinoderms are considered deuterostomes, like chordates, in embryology.
