Complete notes for Chapter 19 Growth and Development. Covers plant growth patterns, chick embryology, differentiation, aging, regeneration, and abnormal development.
Development: It is a programmed series of stages from a simple to complex form.
Growth: It is an irreversible increase in size.
The growth pattern in plants is called open growth. Open growth means the growth throughout of the life which involves adding of new organs like branches, leaves, roots etc. In lower plants the whole body can grow but in higher plants the entire body cannot show growth.
The groups of cells (called growing points) which are capable of division are called meristem. The higher plants have meristematic cells at stem and root for growth.
The reciprocal relationship between growth and development is called correlation.
The apical bud when grows suppresses the growth of lower axillary bud. It was proved by an experiment that auxin of the terminal bud is responsible for inhibiting the growth of lateral buds.
Thimann and Skoog in 1934 concluded that auxin are responsible for apical dominance as they diffuse from lateral bud and cause inhibition to the growth of lateral shoots (inhibitory effect). The removal of apex releases the lateral buds from apical dominance (compensatory effect).
Hormonal Interaction: Basically auxin controls the apical dominance but cytokinin also plays a role. If cytokinin is applied on the inhibited bud, it allows lateral buds to be released from apical dominance.
Importance: Apical dominance is important for taproot development and inhibition of sprouting of lateral buds in potato tubers.
Embryology: The study of the growth and differentiation experienced by an organism during its development from single fertilized egg to highly complex living being.
Fertilization is internal. The zygote produced is protected in a shell secreted by shell glands. The egg contains yolk.
Chick needs suitable temperature (36-38°C) for development. It takes 21 days.
In chick there is a discoidal cleavage where cell division is confined to small disc of protoplasm lying on the surface of yolk at animal pole. The first two cleavage planes are vertical while third is horizontal. The cells formed are called blastomeres. Cleavage results in formation of rounded closely packed mass of blastomeres called morula.
Morula consists of disc shaped mass of cells called blastoderm. It has two types of cells: smaller central cells and flattened peripheral cells.
Morula changes to blastula. It consists of blastomeres and a cavity called blastocoele. The discoidal cap of cells above blastocoele is blastoderm.
The marginal area of blastoderm in which cells remain undetached from yolk and closely adherent to it.
The movement and rearrangement of cells in the embryo is called gastrulation.
Mesodermal cells migrate medially and caudally to form a mid-line thickening called primitive streak. It grows lengthwise changing blastoderm from circular to pear shaped. The anterior end is Primitive Node (Hensen's Node) containing notochordal cells. Primitive streak represents dorsal and lateral lips of blastopore.
Separated sea urchin egg at two-cell stage. Both cells developed into normal larvae. Concluded that both cells contain all genetic information.
Cytoplasm has different morphogenetic determinants responsible for differentiation. Example: Ascidian egg has clear cytoplasm (epidermis), yellow (muscles), gray vegetal (gut), and gray equatorial (notochord/neural tube).
Hammerling experimented on Acetabularia (algae). A. mediterranea has regular cap, A. crenulata has irregular cap. He grafted stalk of one to base (containing nucleus) of other. The regenerated cap always matched the species of the base (nucleus), proving nucleus determines characteristics.
The capacity of some cells to evoke a specific development response in others is called embryonic induction.
Transplanted a piece of dorsal lip of blastopore from one salamander gastrula to ventral position of another. The grafted tissue induced formation of a second embryo (neural tube and nervous system). The dorsal lip cells were called Primary Organizer and the phenomenon Primary Induction.
Aging: The negative physiological changes in our body.
Gerontology: The study of aging.
The ability to regain or recover the lost or injured part of the body is called regeneration.
Planaria has unspecialized cells called neoblasts. When amputated, neoblasts migrate to site and differentiate into special cells.
Study of abnormal developments is called teratology.