General BiologyCHAPTER 1

Biology is the study of all living organisms (bio = life; logy = study).

The recent system of classification proposed by RH Whittaker in 1969 is a five kingdoms system. Under this system, all living organisms are grouped into five kingdoms as explained below.

This group consists of individuals which are single-celled. These may or may not move; they have a cell wall. Nucleus, chloroplasts, other organelles are absent. No visible feeding mechanism. They absorb nutrients through cell wall. Animals with such cells are called prokaryotes.

Examples: Bacteria and blue-green bacteria.

Protista are single-celled tiny organisms. These usually move by cilia, flagella, or by amoeboid mechanisms. There is usually no cell wall, although some forms may have a cell wall. They have organelles including a nucleus and may have chloroplasts, so some will be green, while others will not be green in color. Nutrients are acquired by photosynthesis, ingestion of other organisms, or both. Animals with such cells are called eukaryotes.

Examples: Amoeba, Diatom, Euglena, Paramecium and some algae (unicellular), etc.

Fungi are multicellular, with a cell wall, organelles including a nucleus, but no chloroplasts. They have no mechanisms for locomotion. Fungi4 range in size from microscopic to very large (such as mushrooms). Nutrients are acquired by absorption. For the most part, fungi acquire nutrients from dead and decaying material.

Examples: Mushroom, Mucor, Puffball, Yeast, etc.

Plants are multicellular and most do not move, although gametes of some plants move using cilia or flagella. Organelles including nucleus, chloroplasts are present they have a cell wall. Nutrients are acquired by photosynthesis (they all require sunlight).

Examples: Multicellular algae, mosses, ferns, flowering plants (dandelions, roses, etc.), trees, etc.

Animals are multicellular, and move with the aid of cilia, flagella, or muscular organs based on contractile proteins. They have organelles including a nucleus, but no chloroplasts or cell walls. Animals acquire nutrients by ingestion.

Examples: Sponge, jellyfish, insect, fish, frog, bird, man, etc.

Prokaryotes: (from Old Greek pro: before + karyon: nucleus)

These are organisms without a cell nucleus, or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular.

Eukaryotes: (from Old Greek eu: good or true + karyon: nucleus)

These are organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. The most characteristic membrane-bound structure is the nucleus. This feature gives them their name.