BIOLOGY FORM ONE

1.4.0 Cell structure and organization

1.4.1 The concept of a cell

Main parts of a cell - Cell membrane, nucleus, cell wall, cytoplasm, chloroplasts, cell vacuole

Cell Membrane - Made of living material. Its function is to enclose and protect the inner parts of the cell by selectively allowing certain substances to pass through while preventing others making it selectively permeable

Nucleus - Is a spherical or oval body which is seen when cells are stained. It is composed of a fluid called nucleoplasm and is surrounded by a membrane called the nucleo-membrane. The nucleus controls the life processes of a of a cell such as growth, respiration and synthesis of materials. The nucleus also controls the hereditary characteristics of an organism

Cell Wall - Is made up of non living material called cellulose. The major function is to give shape and

support to the cell. The cell wall is freely permeable to water and gases Cytoplasm - Is composed of a mixture of chemicals and water whose role is to store food Chloroplasts (Plants Only) - Small bodies within cytoplasm containing chlorophyll. It is the where

photosynthesis occurs producing carbohydrates for the plant

Cell Vacuole - Cavity within cytoplasm filled with sap and enclosed by a membrane called vacuolar membrane. The accumulation of water in the vacuole creates pressure to exert on the cytoplasm and the cell wall to make plant cells firm and strong

Examples of cells in the human body -

The longest cell - Nerve cell (neuron)

A motile cell - Sperm

A cell with strong contractile ability - Muscle cell

A cell which moves and feeds like an amoeba - White blood cell

Cell - A unit of living matter consisting of a nucleus, cytoplasm and a cell membrane

Cell Membrane - The semi-permeable membrane which forms the outer surface of all cells

Cell Wall - Outer membrane surrounding a cell which is made of cellulose and controls the flow of particles

in and out of the cell through osmosis

Cytoplasm - All of the contents of a cell except its nucleus

Internal Environment - The tissue fluid that bathes every cell of the body and supplies all of their food and

oxygen requirements

Mitochondria - Rod-shaped organelles in the cytoplasm of cells which is concerned with respiration Nucleus - Part of the cell which contains chromosomes and controls cell metabolism and division

Wall Pressure - A cell taking in water by osmosis inflates until its cellulose wall cannot be stretched further,

this restraining force is called wall pressure

Cholesterol - A substance found mainly in animal fats which form part of the cell membranes. Excessive cholesterol in ones diet can lead to blocked arteries

Cilia - Small hair-like strands on the surface of certain cells i.e. paramecium.  They flick back and forth

allowing for movement in fluids

Differentiation - The process by which cells become specialized to perform a particular function Semi-permeable Membrane - A membrane which allows certain substances to pass through but prevents

others e.g. the cell membrane

Tissue - A collection of similar cells which work together to perform a particular function

Organ - Part of a living organism formed when different tissues work together to perform a general function

Characteristics of all living things - Nutrition, respiration, excretion, response, reproduction, growth,

movement