Answer to Question #97122 in Cell Biology for Abhishek

Question

Write a brief account of the following :

(1) Prophase of first meiotic division .

(2) Plant cell wall

(3) Components of of vertebrate blood and their functions.

Answer 1

(1) The prophase of the first meiotic division consists of five stages:

1. Leptotene - completion of DNA replication occurs.

2. Zygotene - the process of conjugation.

3. Pachytene - crossing of chromosome regions occurs.

4. Diplotene - chiasmas and chromatids are visible.

5. Diakinesis - chromosomes are shortened, centromeres are repelled from each other, nuclear membranes and the nucleolus are dissolved, a fission spindle is formed.

(2) The cell membrane is a derivative of protoplast, since it is formed from the secret of the Golgi apparatus with the participation of enzymes on the plasmalemma.

The cell membrane determines the shape of cells and the texture of tissues, performs supporting and protective functions. Also involved in the processes of absorption, movement of substances, transpiration and secretion.

Three parts are distinguished in the plant cover:

• The primary (growing) wall is the first membrane of its own to form in a developing cell. It contains cellulose, hemicellulose and pectin. Primary walls are associated with living protoplasts.

• The secondary wall appears after the primary wall and is superimposed on it from the side of the cell cavity. It consists mainly of cellulose or various mixtures of cellulose and hemicellulose, lignin, suberin and some other substances (proteins).

• The intercellular substance is located between the primary membranes of two adjacent cells and consists mainly of pectin substances.

In the walls of the primary wall there are areas in the form of numerous depressions - pore fields. No secondary wall forms above the fields. Their function is to facilitate the metabolism between cells.

(3) Blood consists of blood plasma (55-60%) and blood cells (40-45%).

Blood plasma is the yellow liquid in the blood. It contains 90-92% of water and 8-10% of dry matter: proteins, salts, lipids, carbohydrates, metabolic products, hormones, enzymes, vitamins and gases dissolved in it.

There are three main types of blood cells:

1. Red blood cells (erythrocytes) - nuclear-free cells in the form of a biconcave disk. The main function is respiratory. Cells carry oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs.

2. White blood cells (leukocytes) - spherical nuclear cells. The main function is protective. Provide humoral and cellular immunity. Also phagocytose microorganisms and various foreign particles .

3. Platelets (thrombocytes) are nuclear-free, demonless platinum. Responsible for blood coagulation and restoration of the vessel wall after damage.