Question

What are the three zones found in a root tip in the region of primary growth? Discuss each.

How does the structure of xylem relate to its function?

Why would all plants not be short-day plants? Why would plants develop a variety of responses to environmental seasonal changes?

What is the difference between fertilization and pollination in flowering plants?

What is meant by double fertilization in flowering plants?

Answer 1

1) zones found in the root tip in the region of primary growth:

The root has main three main zones :

a) a zone of cell division ( cells are actively dividing)

b) a zone of elongation (cells increasing thier length)

c) a zone of maturation (cell differentiate into different kinds of cells)

ZONE OF CELL DIVISION:

This zone found behind root cap, it produces the cell that give rise to the primary body of the plant.most cell division occurs along along the edges of this center and give rise to columns of cells arranged parallel to the root axis . the apical meristem of the root organizes to foarm the primary meristems: proctoderm, which give rise to epidermis ; procambium ,which produces xylem and phloem and the ground meristem which produces the cortex.

ZONE OF ELONGATION:

the cells in this zone stretches and lengthen as small vacuoles within the cytoplasma coalesce and fill with water . one or two large vacuoles occupy almost all of the cell volume in fully elongated cell . cellular expansion in this zone is responsible for pushing the root cap and apical tip forward through soil.

ZONE OF MATURATION:

The elongation cells complete their differntiation into yhe tissues of the primary body in this zone .it is easily reconized because of the numerous root hair that extended into the soil as outgrowth of single epidermal cells .

2) DIFFERENCE BETWEEN FERTILIZATION AND POLLINATION :

POLLINATION: it is a process of transferring of pollens from one flower to another , either in same flower or different flower in same palnt or from different plant.

FERTILIZATION: it is the process after successful transfer of pollination , which involves the fusion of male gamets and female gamets of plants.

both of these are natural process , but only flowering plants undergo the process of pollination , while fertilizatiion is common process in almost all living beings.

COMPARISON :

BASIS FOR COMPARION POLLINATION FERTILIZATION

a) pollen tube no formation of pollen tube formation of pollen tube take place, which helps in pollen movement.

b) Time of process before fertilization Takes place after pollination

c) Types Self and cross pollination No any types

d)External factors required for pollination no external factors

e) It occurs in flowering plants only almost all living beings

3) DOUBLE FERTILIZATION:

double fertilization is a complex fertilization mechanism of flowering plants ( angiosperms) this process involes the joining of a female gametophyte with two male gamets .

the cells of unfertilized ovule are 8 in number and arranged in the form of 3+2+3 ( from top to bottom ) 3 antipodal cells, 2 polar cental cells, 2 synergids & 1 egg cell . one sperm fertilizes the egg cell and combine to foarm a diploid zygote , the process is being called syngamy , while the other sperm and the two haploid polar nuclei of the large central of the megagametophyte form a triploid nucleus ( triple fusion).

The process of fusion of male gamete with the female gamete to form the diploid zygote is known as fertilization. the fusion of one male gamet with egg and that of another male gamet with secondary nucleus is callad double fertilization.

4) structure of xylem relate to its function :

xylem is the specilized tissue of vascular plants that transports water and nutrients from the plant-soil interface to stems and leave , and provides mechanical support and storage .

The xylem cells also support the weight of the water tranported upward in the plant and the weight of the plant itself.

In most woody plants , xylem grows by the division and differentiation of cells of a bifacial lateral meristem , the vascular cambium which produces secondary xylem and phloem.