Bacteria

Bacteria are single-celled organisms that can cause infection if they gain entry into the body.

Capillary

Capillaries are small blood vessels with thin walls through which substances can pass in and out of the bloodstream.

Cellulose

This is a carbohydrate that makes up the cell walls of plant cells. It cannot be digested by enzymes in the human gut. A component of fibre.

Constipation

Constipation is a condition in which too much water is absorbed from the large intestine back into the bloodstream, leaving the faeces dry, hard and difficult to expel. Caused by a lack of fibre in the diet (fibre holds water, preventing the faeces becoming too hard).

Cytoplasm

Cytoplasm is the propoplasm (living material) of a cell excluding the nucleus. It contains a variety of small structures (organelles), for example, mitochondria where respiration takes place.

Haemoglobin

Haemoglobin is the red pigment in red blood cells. It combines with oxygen in the lungs, transports it around the body and releases the oxygen to cells that need it.

pH

This is a measurement of acidity. pH 1 is strongly acidic, ph 7 is neutral, pH 11 is strongly alkaline.

Each enzyme needs a particular pH to function efficiently.

Plasma

Plasma is the liquid part of blood in which blood cells are suspended. Consists largely of water and dissolved substances.

Red blood cells

These are the cells in the blood which contain haemoglobin. As blood flows through the lungs the haemoglobin combines with oxygen which is carried around the body in the red blood cells. Oxygen is released to body cells for use in respiration.

Respiration

Respiration is the chemical reaction in all living cells that releases energy from food. Usually, sugar is broken down by oxygen (aerobic respiration). Some cells can break down sugar without the need for oxygen - this is anaerobic respiration.