Question

Auxetic growth is
A. Increase in cell volume only
B. Increase in cell number only
C. Increase in fatty tissue
D. Increase in intercellular material

Answer 1

Hint: Growth can be termed as a gradual increase in size or number among all living organisms. Biological growth is usually considered as an increase in that part of the living system which is in its own turn capable of growth.

Complete answer:
There are different types of growth levels:
Molecular level: Growth involves synthesis of new molecules and their aggregation into organelles and storage products in the cells.
Cellular level: At the cellular level, the growth involves cell expansion (hypertrophy),cell division (hyperplasia) and cell differentiation
Individual level: Growth is visible increase in the body, dimension, size, volume and weight.

Physiological condition for growth: Variety of chemical reaction occurs in living organisms which are termed as metabolism. Metabolism has phases- anabolism and catabolism. A growth can be:
> Positive growth
> Negative growth
> Cell reproduction

Types of growth:-
- Auxetic growth: In some organisms growth occurs as a result of increase in the size of their cells. The number of cells remains the same. Body grows in size due to enlargement of cells. Example: Nematodes, rotifers and tunicates.
- Multiplicative growth: It is also named as embryonic growth where growth occurs due to an increase in the number of cells of the body by rapid mitosis division and appreciable growth of the cells. It involves both cell growth and cell reproduction. It is found in the embryo. In this type of growth, the average cell size remains the same, or increases insignificantly. Example: Growth of embryos, prenatal growth in mammals.
- Accretionary growth: During postembryonic growth and also in the adult, all the body cells are incapable of undergoing division. This is because they have become differentiated or due to the lost ability to division of specialized cells of organs and tissues. The undifferentiated cells divide mitotically and help in growth. This kind of growth is called accretionary growth. Example: Bone marrow of vertebrates have unspecialized cells which produce blood cells and replace worn out ones.
- Appositional growth: It involves addition of new layers on previously formed layers. It is a characteristic mode of growth in rigid materials. Example: Addition of lamellae in the formation of bone.

Therefore, the correct option is a) increase in cell volume only.

Note: Strategies of growth:
Cell proliferation: Growth of a structure by cell multiplication due to cell division e.g., growth of lens.
Cell enlargement: Cells do not divide but their size increases due to synthesis of cytoplasm e.g., growth in cardiac muscles, neurons and skeletal muscles.
Growth by accretion: Growth occurs due to secretion of a large amount of extracellular materials e.g., growth of cartilage and bones.
States of growth:
Pre-functional state of growth: Early embryonic stage during which developmental processes transform a zygote into an embryo.
Functional state of growth: The late embryonic and post embryonic developmental stage during which organ rudiments become functional and organogenesis begins.