Question

Answer in detail.
a. Explain the glycolysis in detail.
b. With the help of suitable diagrams, explain the mitosis in detail.
c. With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.
d. How all the life processes contribute to the growth and development of the body?
e. Explain the Kreb's cycle with reaction.

Answer 1

a. Glycolysis was first given by Embden, Meyerhof and Parnas, and is referred to as EMP pathway. This process occurs in the cytoplasm of the cell and is present in all living organisms.

In this pathway, glucose undergoes partial oxidation to form two molecules of pyruvic acid, which can enter either Krebs cycle (in the case of aerobic respiration) or fermentation pathway (in the case of anaerobic respiration). In the course of conversion of glucose into pyruvate, energy is produced in the form of two molecules of ATP.

The steps involved in the partial oxidation of glucose to form pyruvate are as follows:

b.

Mitosis is the process of equational cell division where daughter cells, so produced, contain an equal number of chromosomes as that in the parent cell. The various stages of mitosis in an animal cell are as follows:

(i) Prophase: It is the first stage of mitosis that is marked by the initiation of the condensation of chromosomal material. Each chromosome is composed of two chromatids, which are attached by the centromere. At the end of prophase, the mitotic spindle begins to form from the centrioles. The nuclear membrane and the nucleolus disappear completely by the end of this stage.

(ii) Metaphase: It is the second stage of mitosis in which the condensation of the chromosomal material and the spindle formation gets complete. The spindle fibres get attached to the kinetochores of the chromosomes and the chromosomes get aligned along the metaphase plate in the middle of the nucleus.

(iii) Anaphase: It is the stage of mitosis where the centromere of the chromosomes split and the chromatids get separated. The contraction of the spindle fibres moves the sister chromatid apart, towards the two opposite poles.

(iv) Telophase: It is the last stage of mitosis. In this stage, chromosomes finally reach their respective poles. The spindle fibres disappear and the nuclear envelope reappears around the chromosome cluster. Also, the nucleolus, Golgi complex, endoplasmic reticulum, and other cell organelles re-appear.

c. Prophase I is the longest phase of meiosis and is further sub divided into 5 phases:

Leptotene − Condensation makes chromosomes become distinct and compact.

Zygotene − Homologous chromosomes start pairing together by a process called synapsis to form a complex structure called synaptonemal complex. Two synapsed homologous chromosomes form a complex called bivalent or tetrad.

Pachytene − Longest phase of prophase I
Recombination nodules appear in this stage at the sites where crossing over has to take place between non-sister chromatids of homologous chromosomes.

Diplotene − Synaptonemal complex dissolves and recombinants separate from each other except at crossover sites to form X-shaped structure called chiasmata.

Diakinesis − Chiasmata terminalises and chromosomes condense. Meiotic spindle assembles and nucleolus and nuclear envelope disappear.

d. Life processes are processes which are required to maintain body functions and are necessary for survival. The important life processes are nutrition, transportation, metabolism, reproduction, respiration, and excretion. All these processes work together and result in the growth and development of the body. For example, nutrition is the process by which we take up nutrients which are used by the cells to meet their respective needs. This is a vital process which helps living beings to obtain their energy from various sources. Respiration is associated with the exchange of gases as well as burning of food. It results in the breakdown of glucose and release of oxygen. Similarly, cell cycle and cell division play an important role in the growth and development of the organisms. They help in the formation of new organisms as well as repair of dead and damaged cells and tissues.

e. Krebs cycle is a cyclic process that occurs in the mitochondrial matrix, in the presence of oxygen.

Step 1: The cycle starts with the condensation of an acetyl group with oxaloacetic acid and water to form citric acid, with a release of CoA molecule. The enzyme involved in this conversion is citrate synthase.

Step 2: Citrate then isomerises to form isocitrate.

Step 3: The synthesis of citrate is followed by two successive steps of decarboxylation − first, the formation of α-ketoglutaric acid, and then, that of succinyl-CoA.

Step 4: This succinyl-CoA gets oxidised to form malic acid, which in turn gets converted into oxaloacetic acid, thereby allowing the cycle to continue.

The entire process of Krebs cycle can be represented as follows: