Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R: Assertion A: The first stage of gametophyte in the life cycle of moss is protonema stage. Reason R: Protonema develops directly from spores produced
in capsule.
In the light of the above statements, choose the most appropriate answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
Assertion A is correct: in moss, the first stage of the gametophyte is the protonema. Reason R is also correct: protonema develops directly from the spores released from the capsule. Since protonema arises from germinating spores and then develops into the leafy gametophyte, R explains how the protonema (the first gametophyte stage) originates. Therefore, option 2 is correct.
? Did You Know?
In mosses, the gametophyte is dominant and photosynthetic, while the sporophyte is dependent on the gametophyte for nutrition.
? NCERT Memory Line:
Germination of a spore produces the protonema, from which the juvenile gametophyte (leafy moss) develops.
AI-generated explanation. Check against your textbook.
Explanation:
Axile placentation means ovules attached to a central axis in a multilocular ovary. In NCERT, axile placentation is observed in China rose (Hibiscus), Petunia, and Lemon, where ovules are arranged around the central axis of the locules. Hence option 1 is correct.
🧠 Did You Know?
Axile placentation is common in many plants with syncarpous ovaries, where all carpels are fused into a single ovary with a central column.
💡 NCERT Memory Line:
Axile placentation: ovules on central axis of a multilocular ovary (common in Hibiscus and Petunia).
Statement I: Endarch and exarch are the terms often used for describing the position of secondary xylem in the plant body.
Statement II: Exarch condition is the most common feature of the root system.
In the light of the above statements, choose the correct answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
Endarch and exarch describe the position of xylem elements during primary xylem development. They are not used to describe secondary xylem. Statement I is therefore incorrect. In roots, the common arrangement is exarch-type primary xylem. Statement II is true because exarch arrangement is typical for the root system in NCERT biology.
? Did You Know?
In exarch xylem, protoxylem lies toward the periphery and metaxylem toward the center; in endarch, protoxylem is toward the center. These terms pertain to primary vascular tissue development, not the secondary xylem formed later by cambium.
? NCERT Memory Line:
Exarch is the common arrangement for the root’s primary xylem; endarch/exarch describe primary xylem positions, not secondary xylem.
Family Fabaceae differs from Solanaceae and Liliaceae. With respect to the stamens, pick out the characteristics specific to family Fabaceae but not found in Solanaceae or Liliaceae.
AI-generated explanation. Check against your textbook.
Explanation:
In Fabaceae, the stamens are diadelphous: nine filaments are fused to form a common tube, leaving one filament free. The anthers are typically dithecous, i.e., each anther has two thecae. This combination (diadelphous stamens with dithecous anthers) is characteristic of Fabaceae and is not seen in Solanaceae or Liliaceae, according to NCERT descriptions of floral structure.
🧠 Did You Know?
Solanaceae and Liliaceae generally show stamens that are epipetalous (attached to petals), unlike the diadelphous condition seen in Fabaceae.
💡 NCERT Memory Line:
Fabaceae has diadelphous stamens (9 fused + 1 free) with dithecous anthers—distinct from the other families.
Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: Late wood has fewer xylary elements with narrow vessels.
Reason R: Cambium is less active in winters.
In the light of the above statements, choose the correct answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
In a tree, late wood (end of the growing season) has fewer xylary elements and narrower vessels compared with early wood. This is because cambial activity slows down as winter approaches, producing denser tissue with smaller vessels. Therefore, Assertion A is true. Reason R states that the cambium is less active in winters, which explains why late wood forms with fewer, narrower vessels. Hence, R correctly explains A. So, option 2 is correct.
? Did You Know?
NCERT notes that winter cambium activity decreases, leading to the formation of late wood with smaller vessels and thicker-walled cells.
? NCERT Memory Line:
Late wood forms under reduced cambial activity (in winter), resulting in fewer xylary elements with narrow vessels.
Among eukaryotes, replication of DNA takes place in
AI-generated explanation. Check against your textbook.
Explanation:
In eukaryotes, DNA replication occurs during the S (Synthesis) phase of the cell cycle. During this phase, the DNA is duplicated so that each daughter cell receives an identical copy. Other phases have different roles: G1 is cell growth, G2 checks and prepares for division, and M phase is when mitosis and cytokinesis occur, separating the duplicated chromosomes.
🧠 Did You Know?
DNA replication is a tightly regulated process ensuring each chromosome is copied once before division, preventing errors.
💡 NCERT Memory Line:
DNA replication occurs in the S phase of the cell cycle in eukaryotes.
Which of the following stages of meiosis involves division of centromere?
AI-generated explanation. Check against your textbook.
Explanation:
Centromere division (sister chromatids separate) occurs during anaphase II of meiosis. In meiosis I, homologous chromosomes separate, but sister chromatids stay together at the centromere. During metaphase I/II, chromosomes align at the equator; the centromere does not divide yet. Telophase involves chromosome de-condensation and cytokinesis begins, not centromere splitting. Therefore, the correct stage is Anaphase II, when the centromeres split and sister chromatids move to opposite poles.
🧠 Did You Know?
Only in Anaphase II do the duplicated chromatids become separate chromosomes that migrate to opposite poles.
The process of appearance of recombination nodules occurs at which sub stage of prophase I in meiosis?
AI-generated explanation. Check against your textbook.
Explanation:
The recombination nodules appear during the pachytene stage of prophase I. This is the stage when crossing-over between homologous chromosomes occurs, facilitated by synapsis. Thus, recombination nodules form to mediate genetic exchange.
🧠 Did You Know?
In later stages, chiasmata become visible as remnants of crossing-over during diplotene and are seen until metaphase I.
💡 NCERT Memory Line:
Crossing over and recombination nodules occur during pachytene of prophase I.