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Why do multicellular organisms need transport systems?

They have a small surface area to volume ratio so direct diffusion through the outer surface would be too slow because substances would have to travel large distances to every cell. Multicellular organisms need transport systems to move substances to and from individual cells quickly


Why don't unicellular organisms need transport systems?

They can rely on diffusion for movement of substances into and out of the cell because the substances only have a short distance to travel


What are the 4 main components of blood?

Plasma, platelets, red blood cells, white blood cells


What does blood plasma carry?

Digested food products (like glucose and amino acids) from the gut to all the body cells
Carbon dioxide from body cells to lungs
Urea from the liver to the kidneys
Hormones which act as chemical messengers
Heat energy


What happens in blood clotting?

When you damage a blood vessel platelets clump together to 'plug' the damaged area
This is known as blood clotting.
In a clot, platelets are held together by a mesh of protein called fibrin


Why does blood clot?

To stop you from losing too much blood
To stop the entry of pathogens and other micro organisms


How is fibrin formed?

Thrombin catalyses the reaction of fibrinogen, which is a soluble protein, to fibrin, which is insoluble


How are red blood cells adapted to their function?

Biconcave shape to give a large surface area for absorbing and releasing oxygen
Contain haemoglobin which reacts with oxygen to become oxyhaemoglobin
No nucleus which frees up more space for haemoglobin to carry oxygen


Why do we have an immune system?

Once pathogens have entered the body, they reproduce rapidly unless destroyed. The immune system and white blood cells are there to destroy pathogens


What do phagocytes do?

They detect things that are foreign to the body and ingulf and digest them
They are nonspecific - they attack anything that isn't supposed to be there


What do lymphocytes do?

Every pathogen has a unique molecule called an antigen on its surface
When lymphocytes detect foreign antigens they will start to produce proteins called antibodies that are specific to the pathogen which make them out for destruction
Antibodies are produced rapidly and flow around the body to mark all similar pathogens
Some lymphocytes stay around in the blood as memory cells so if the antigen infects the body again it can destroy it quickly