Blood and Blood Clotting

Question 1

what is blood?

Answer 1

blood is a complex tissue, consisting of a liquid component (plasma), cell fragments (platelets) and two types of cells (red and white blood cells)

Question 2

plasma features

Answer 2

• straw coloured liquid
• transports blood cells and many other substances, including: dissolved nutrients such as glucose and amino acids; dissolved waste products including urea and carbon dioxide; hormones; proteins; heat energy

Question 3

red blood cell features

Answer 3

• small red cells
• transport oxygen, bound to haemoglobin

Question 4

platelet features (p2)

Answer 4

• cell fragments
• release chemicals when the blood is exposed to air, which cause soluble fibrinogen to be converted to insoluble fibrin
• fibrin forms a mesh, which traps platelets and red blood cells - this is a clot

Question 5

phagocytes (white blood cell) features

Answer 5

• larger cells with a multi-lobed nucleus
• engulf and digest pathogens (microorganisms which can cause disease)

Question 6

lymphocytes (white blood cell) features

Answer 6

-cells with a very large nucleus
- make and release antibodies, which bind to and destroy pathogens

Question 7

how are red blood cells specialised for their job?

Answer 7

• they contain haemoglobin, a protein which combines with oxygen to form oxyhaemoglobin - this transports oxygen to respiring cells
• they have no nucleus, meaning more haemoglobin can be packed into each cell and so more oxygen can be transported
• they are biconcave - this increases their surface area; volume ratio and decreases the distance to the centre of the cell (this increases the rate of diffusion)

Question 8

what happens if platelets are exposed to oxygen (because of a cut)? (p2)

Answer 8

they release chemicals which start the clotting process

• these chemicals cause the soluble plasma protein fibrinogen to be changed into the insoluble protein fibrin
• the fibrin forms a network of fibres across the cut, which trap platelets and red blood cells
• this forms a clot, or scab, which prevents further loss of blood
• it also acts as a barrier to prevent the entry of pathogens
• (clots can also form within blood vessels if plaques cause red blood cells to be broken - this can cause heart attacks)