NEET Practice Questions (MCQs) with Answers & Solutions

In an animal cell, cytokinesis is achieved by the appearance of a furrow in the plasma membrane in centripetal direction while in plant cell, it is achieved by the cell plate formation in the centre of the cell and grows outward to meet the existing lateral walls (centrifugal).

(page-166)

In some organisms karyokinesis is not followed by cytokinesis as a result of which multinucleate condition arises leading to the formation of syncytium (e.g., liquid endosperm in coconut).

(page-166)

In prophase I of meiosis I, synapse formation i.e. crossing over takes place whereas no such event occurs in prophase of mitosis.

G1 phase corresponds to the interval between mitosis and initiation of DNA replication. During G1 phase the cell is metabolically active and continuously grows but does not replicate its DNA.

Meiosis ensures the production of haploid phase in the life cycle of sexually reproducing organisms whereas fertilisation restores the diploid phase. We come across meiosis during gametogenesis in plants and animals. This leads to the formation of haploid gametes.

(page-167)

Generation time = 1 minute

Cells divide in 1 minute = 2^1 = 2

                        2 minutes = 2^2 = 4

                        20 minutes = 2^20 = 1/8 of tube filled with cells

Total volume tube can hold = 2^20 X 8

                                             =  2^20 X 2^3

                                             = 2^23

                                             = 23 minutes

In anaphase I, the homologous chromosomes separate, while sister chromatids remain associated at their centromeres.

(page-169)

Transpiration cause water to rise in plants by pulling through xylem elements.
Root pressure causes water to rise in plants by pushing water in xylem components.

So, the rise of water in plants is done by pulling and  pushing via transpiration and root pressure respectively.

Element like calcium are a part of structural component of the cell and hence, are not released. The deficiency symptoms tend to appear first in the young tissues whenever, the elements are not demobilized.

(b) The vertical conduction of water from root to aerial parts of plant is called ascent of sap. The water molecules remain joined to each other due to a force of attraction called cohesion force. This attraction is due to the presence of hydrogen bonds between them. The magnitude of this force is very high therefore, the continuous water column in the xylem cannot be broken easily due to the force of gravity or other obstructions offered by internal tissues in the upward movement of water. This adhesive property of water, i.e., attraction between the water molecules and the walls of xylem ensures the continuity of water column in xylenm Due to transpiration water evaporates to outer atmosphere through stomata. As a result leaf cells develop low water potential and water from leaf veins moves into leaf cells. The xylem vessel in turn draw water from xylem of main stem. A pressure (pull) is thus, exerted by all the leaves on the stems, which is called transpiration pull. This is strong enough to pull up the column of water to a great height.