The composition of blood.

The composition of blood. 

ZIMSEC O Level Combined Science Notes: Blood and its properties

  • Blood circulating in a mammal constitutes about 7.5% of its body mass.
  • An average human weighing between 68-80 kgs has about 4.7 to 5 litres of blood in their body
  • Blood can be considered as tissue because it contains millions of cells.
  • These cells tend to be similar and they also perform similar functions:
  • They carry out transport functions and protect the mammal disease
  • Blood tissue is made up of a fluid called plasma
  • Red and white blood cells float within this plasma
  • Glucose and amino acid molecules are also found in the plasma in dissolved form

Functions of Blood

  • Blood has several major functions.
  • First it acts as a transport medium
  • It carries substances around the body
  • These substances include dissolved food, oxygen and plasma proteins which are all carried to where they are needed
  • Blood also carries waste substances produced by the body cells to excretion organs such as lungs and kidneys
  • Blood also helps with heat distribution from the internal organs to the fingers and toes
  • Homeostasis-is the maintenance of temperature, water, salt and glucose levels at a constant optimum levels
  • Blood plays a critical role in the homeostasis process
  • The white blood cells attack foreign particles and germs( viruses and bacteria) which invade the mammal’s body
  • The blood’s platelets are responsible for clotting of the blood where there is a wound or injury.
  • They release enzymes which convert special plasma proteins into  a blood clot to stop the flow of blood.
  • This prevents the mammal from dying as a result of excessive blood loss
  • The clot also prevents the further entry of germs into the mammal’s body

To access more topics go to the Combined Science Notes page.


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