Everything Life Sciences Grade 10

Electron micrographs of blood cells

Figure 5.29: Scanning elec-

tron microscope image of cir-

culating blood showing sev-

eral red and white blood cells.

Figure 5.30: Scanning electron microscope image of a white

blood cell (right), a platelet (centre) and a red blood cell (left).

Red blood cells: called erythrocytes are made in the red bone marrow. They do not have

a nucleus and are biconcave in shape. Their biconcave shape makes them flexible so that

they can squeeze through narrow capillaries. It also gives them a bigger surface to volume

ratio, so that they absorb and release gases faster. Red blood cells have a short life span

of approximately 120 days. Red blood cells contain the protein known as haemoglobin.

Haemoglobin contains the pigment known as heme that has an iron (Fe) at its centre that

combines with oxygen. Haemoglobin releases oxygen as required and takes up carbon

dioxide. Red blood cells transport oxygen from the lungs to the tissues and returns carbon

dioxide from the tissues to the lungs.

Figure 5.31: Human red blood cells.

White blood cells: are commonly known as leukocytes and are produced in the yellow

bone marrow and lymph nodes. The cells have one or more nuclei. White blood cells are

slightly larger than red blood cells and are more irregular in shape. Their main function

is to protect the body from diseases. There are several types of leukocytes: neutrophils,

basophils, eosinophils, lymphocytes, monocytes and macrophages. The white blood cells

known as lymphocytes actively produce chemicals called antibodies which destroy disease

causing micro-organisms.

138 5.4. Animal tissues