‘The adventitious leaf bud plays significant role in natural vegetative propagation of plant’ – Evaluate the validity of the statement with a proper example?

Adventitious roots and buds are important when people propagate plants via cuttings, layering, and tissue culture. Plant hormones, termed auxins, are usually employed to stem, shoot or leaf cuttings to stimulate adventitious root formation, e.g., African violet and Sedum leaves and shoots of poinsettia and Coleus . Natural vegetative propagation occurs when an axillary bud grows into a lateral shoot and develops its roots (also known as adventitious roots).

Establish the relationship between the formation of malignant tumour in the human body with the loss of control in the cell cycle?

Cancer is the result of unchecked cell division caused by a breakdown of the mechanisms regulating the cell cycle. The loss of control begins with a change in the DNA sequence of a gene that codes for one of the regulatory molecules. Faulty instructions lead to a protein that does not function as it should. Dysregulation of the cell cycle components may lead to tumour formation. When some genes like the cell cycle inhibitors/ RB. P53 etc., mutate, they may cause the cell to reproduce uncontrollably, forming a tumour. Although the duration of the cell cycle in tumour cells is equal to or longer than the normal cell cycle, the proportion of cells that are inactive cell division in tumours is much higher than that in normal tissue. Thus, the number of cells increase and become malignant and may result in cancer.

How can you distinguish between mitosis of plant cells and that of animal cells on the basis of formation of spindle fibre and the process of cytokinesis?

Mitosis is the type of cell division, in which a single mother cell produces two daughter cells with the same number of chromosomes. Mitosis occurs in four steps; prophase, metaphase, anaphase, and telophase. The major difference between animal mitosis and plant mitosis is that the mitotic spindle in animal mitosis is formed with the help of two centrioles whereas, the mitotic spindle in plant mitosis is formed without any centrioles. Mitosis had followed by cytokinesis.

Distinguish between asexual and sexual reproduction on the basis of following features: i) Number of parents ii) Nature of offspring

Features Asexual Reproduction Sexual Reproduction Definition Occurs in prokaryotic microorganisms and in some eukaryotic unicellular and multicellular organisms, lower invertebrates and plants. Occurs almost in all types of multicellular organisms including humans, animals, and higher plants. Number of parents Only a single parent is involved. Both male and female parents are involved. Nature of offspring Identical to parents in case of asexual reproduction. They will be unique and a little different from parents in the case of sexual reproduction due to reductional division.

During the meiosis cell division, reduction in the number of chromosomes and exchange of segments between chromatids take place analyse what are the significance of these two phenomena.

Meiosis is the reproductive cell division that results in the formation of four daughter cells from a parent cell. There are the following significance of meiosis: Meiosis is responsible for the formation of sex cells or gametes that are responsible for sexual reproduction. It activates the genetic information for the development of sex cells. The daughter cells formed have half the number of chromosomes compared to the parent cell. Hence, the number of chromosome in the zygote can be restored. The possibilities of production of new characteristics increases because of the process of crossing over.

Explain the importance of the following parts of a eukaryotic chromosome: Centromere Telomere Analyse the role of cell divisions in controlling growth, reproduction and repair in an organism.

The importance of centromere are given below: The centromeres are the point of attachment of the kinetochore. The main functions include the attachment of sister chromatids, and it is the site for attachment of spindle fibre. Centromeres help in the proper alignment and segregation of the chromosomes during the process of cell division in eukaryotic cells. Centromeres play an important part in the production of a new cell. When the chromosomes are copied, these centromere serves as a binding site for the two replicated chromosomes, which are known as sister chromatids. The importance of telomere are given below: Telomeres are specialized chromosomal end structures composed of repeat TTAGGG sequences in humans. They shorten with each cell division and thus serve as the "mitotic clock" of the cell. The main function is the maintenance of chromosomal integrity and their excessive shortening is associated with DNA instability. All cells are produced from other cells by the process of cell division. Cell division occurs when one cell divides to produce two new cells. Unicellular organisms use cell division to reproduce. Multicellular organisms use cell division for growth and repair of damage such as wounds.

Distinguish between mitotic and meiotic cell division in animals on the basis of the following features: Site of occurrence Nature of division of chromosomes Number of cells produced List the changes in the sense organs and bones that occurred during the senescence phase of human development.

Features Mitotic cell Meiotic cell Site of occurrence This division takes place in somatic cells. This division takes place in germ cells. Features Mitotic cell Meiotic cell Nature of division of chromosomes Crossing over does not take place. Crossing over takes place in which the exchange of segments of chromatids occurs. Features Mitotic cell Meiotic cell Number of cells produced Mitotic cell gives two nuclei, and hence two cells. Meiosis gives four nuclei or cells. The changes in the sense organs and bones that occurred during the senescence phase of human development are listed below: Ageing includes a decline in accommodation, glare tolerance, adaptation, low-contrast activity, attentional visual fields and colour discrimination. Changes occur in central processing and in the components of the eye. Ageing causes conductive and sensory hearing losses, the loss is primarily high tones, making consonants in speech difficult to discriminate. Normal ageing is characterised by a decrease in bone and muscle mass and an increase in adiposity. A decline in muscle mass and a reduction in muscle strength lead to risk of fractures, frailty, reduction in the quality of life and loss of independence. These changes in musculoskeletal system reflect the ageing process as well as consequences of a reduced physical activity.

Write three features of the metaphase stage and two features of the anaphase stage of mitotic cell division in an animal cell.

Three features of the metaphase stage of mitotic cell division in an animal cell are given below: Spindle fibres attach to kinetochores of chromosomes. Chromosomes are moved to spindle equator and get aligned along with metaphase plate through spindle fibres to both poles. Chromosomes are the shortest and thickest in metaphase. Two features of the anaphase stage of mitotic cell division in an animal cell are given below: The splitting of the sister chromatids marks the onset of anaphase. These sister chromatids become the chromosome of the daughter nuclei. The chromosomes are then pulled towards the pole by the fibres attached to the kinetochores of each chromosome. The centromere of each chromosome leads at the edge while the arms trail behind it.