Cell Biology and Structure

Animals have two systems of co-ordination i.e., nervous system and endocrine system. Neurones are the basic structural and functional units of the nervous system which spread through out the organism forming a complex communication network. Endocrine system release hormones for intercellular communication.

Germ cells produce gametes and are the only cells that can undergo meiosis as well as mitosis. These cells are sometimes said to be immortal because they are the link between generations.

Adipose tissue is a fat storing connective tissue which consists of several sphereical or oval adipose cells (= adipocytes or fat cells). There are two types of tissues white or yellow fat and brown fat. White fat cells are monolocular or unilocular whereas brown fat cells are multilocular. 

Cancer is characterized by uncontrolled growth and division of cells. Abnormal and persistent cell division localized in a particular region is called benign tumour. Tumour cells may be carried by blood steam or lymph or penetrate directly to other parts of the tissue resulting in dangerous malignant tumour. The spread of cancerous cells to distant sites is termed as metastasis. 

Growth is an irreversible process seen at all organizational levels. It consist of cell growth. Growth is the result of the excess of the anabolic (synthetic) over the catabolic (destructive) processes in the organism. 

Nexin is a proteinous inter-doublet linkage that prevents microtubules in the outer layer of axonemes from movement with respect to each other.

Semi-autonomous organelles are organelles with DNA. In eukaryotic cells, mitochondrion and chloroplast are semi-autonomous organelles.

Electron microscope is a microscope with high magnification and resolution, employing electron beams in the place of light and using electron lenses. It is used to visualise plasma membrane.

Microtubules are a component of the cytoskeleton found throughout the cytoplasm. In eukaryotes, microtubules are long and hollow cylinders made up of polymerised α- and β-tubulin dimers.

A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae.

A vacuole is a membrane-bound organelle which is present in all plant and fungal cells. A vacuole is surrounded by a membrane called the tonoplast.

The glycocalyx is a glycoprotein-polysaccharide covering that surrounds the cell membranes of some bacteria, epithelia and other cells.

The thickness of the plasma membrane is 70-100 A.

Chloroplast is a double membrane cell organelle found in plants.

One of the key organelles involved in digestion and waste removal is the lysosome. Lysosome has one membrane or single membrane.