Tag: structure of chromosome, cell cycle and cell division

In sexual reproduction, an egg cell from female and a sperm from a male fuse to form a zygote, precursor to an embryo offspring. The offspring is generally distinct from parents. Both the gametes contain half the number of required chromosomes, that is they are haploid in nature. The zygote contains the exact number of chromosomes required. This is how chromosome number is conserved from generation to generation. The zygote undergoes further cell division to form an embryo. 

1. In G$ _1$  phase the amount of DNA is the same as 40 because the cell is metabolically active but no division of DNA is observed.
   
2. In G$ _2$ phase the DNA gets doubled as it has gone through the synthesis phase which is characterized by the replication of DNA.
3. In mitosis since equational division occurs the DNA content remain 4C through the process before the transfer of DNA into daughter cells.

G$ _1$ , S , G$ _2$, M , cytokinesis. The correct sequence has G$ _1$ as a preparation for S and G$ _2$ as the time between the completion of S and entry into M. Cytokinesis occurs after the other stages to create two daughter cells.

In the maturation phase, the enlarged cells eventually acquire a specific size and form according to their location and role following biochemical, physiological and morphological changes, i.e., the cells undergo specialization or transformation. As a result, various kinds of cells get differentiated. These differentiated cells form different kinds of simple and complex tissues that perform different functions. This includes cell wall growth and protoplasm modification.

The cell cycle mainly consists of 4 stages G$ _1$, S, G$ _2$, and M. The G$ _{0}$ phase also known as the extended G1 phase is a period in which the cell exits from the cell cycle. In this stage, the cell exists in a quiescent state and does not divide. Thus the correct answer is option A.

During the cell cycle, RNA and protein synthesis takes place during G$ _1$ and G$ _2$ phase. The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells. Non-dividing cells not considered to be in the cell cycle. The stages are G$ _1$-S-G$ _2$-M.

G1 phase and the other subphases of the cell cycle may be affected by limiting growth factors such as nutrient supply, temperature, and room for growth. Sufficient nucleotides  and amino acids must be present in order to synthesize mRNA and proteins. Physiological temperatures are optimal for cell growth. In humans, the normal physiological temperature is around 37 C. Therefore, the correct answer is option D.