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.
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.
Given below are two statements: One is labelled as Assertion A and the other islabeled as Reason R: Assertion A: A flower is defined as modified shoot wherein the shoot apical meristem changes to floral meristem. Reason R: Internode of the shoot gets condensed to produce different floral appendages laterally at successive nodes instead of leaves.
In the light of the above statements, choose the correct answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
Assertion A: A flower is defined as a modified shoot where the shoot apical meristem changes to a floral meristem. This is the NCERT view: the floral meristem is formed from the shoot apical meristem and gives rise to floral organs. Reason R: Internode of the shoot condenses to produce floral appendages laterally at successive nodes instead of leaves. According to the statement, R provides a mechanism that corresponds to how floral structures arise from the meristematic region, aligning with the idea that floral parts are modified shoot structures. Hence, both statements are true and R explains A.
? Did You Know?
NCERT describes flowers as determinate shoot systems arising from a floral meristem, which differentiates into sepals, petals, stamens, and carpels.
? NCERT Memory Line:
Flower = modified shoot; floral meristem forms from shoot apical meristem to develop floral organs.
Identify the correct statements:
A. Lenticels are the lens-shaped openings permitting the exchange of gases.
B. Bark formed early in the season is called hard bark.
C. Bark is a technical term that refers to all tissues exterior to vascular cambium.
D.Bark refers to periderm and secondary phloem.
E. Phellogen is single-layered in thickness. Choose the correct answer from the options given below:
Read the following statements about the vascular bundles :
A. In roots, xylem and phloem in a vascular bundle are arranged in an alternate manner along the different radii.
B. Conjoint closed vascular bundles do not possess cambium.
C. In open vascular bundles, cambium is present in between xylem and phloem.
D. The vascular bundles of dicotyledonous stem possess endarch protoxylem.
E. In monocotyledonous root, usually there are more than six xylem bundles present.
Choose the correct answer from the options given below :
AI-generated explanation. Check against your textbook.
Explanation:
From NCERT:
- B: Conjoint closed vascular bundles do not have cambium (true).
- C: In open vascular bundles, cambium is present between xylem and phloem (true).
- D: Dicot stem vascular bundles show endarch protoxylem (true).
- E: Monocot root typically has more than six xylem bundles (true, polyarch arrangement).
- A is not consistent with NCERT: in roots, the arrangement is radial and the vascular bundles are organised with xylem and phloem in a specific radial pattern, but the phrasing “alternate along the different radii” does not correctly describe the standard root bundle arrangement. Therefore A is not a correct standalone statement. Thus the correct combination is B, C, D and E.
? Did You Know?
In monocot roots, there is more than one xylem bundle forming a radial pattern around the central pith, unlike the typical dicot root.
? NCERT Memory Line:
Open vascular bundles have cambium between xylem and phloem; dicot stem shows endarch protoxylem; monocot root often has many xylem bundles (polyarch).
In old trees the greater part of secondary xylem is dark brown and resistant to insect attack due to:
A. secretion of secondary metabolities and their deposition in the lumen of vessels.
B. deposition of organic compounds like tannins and resins in the central layers of stem.
C. deposition of suberin and aromatic substances in the outer layer of stem.
D. deposition of tannins, gum, resin and aromatic substances in the peripheral layers of stem.
E. presence of parenchyma cells, functionally active xylem elements and essential oils.
Choose the correct answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
In old trees, the inner, old secondary xylem stores secondary metabolites like tannins and resins that darken the wood and deter insect attack. These compounds are deposited in central layers of the stem and in the luminal walls of vessels, giving the wood its dark brown color and resistance. This corresponds to options A and B.
? Did You Know?
NCERT explains that secondary metabolites accumulate in the central tissues of old xylem, contributing to durability and defense.
? NCERT Memory Line:
Secondary xylem in old trees becomes dark due to deposition of tannins, resins, and other metabolites in central layers and vessel lumens.