Topic 3: Organisms Exchange Substances with Their Environment

Question 1

Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.
Explain the importance of the xylem being kept open as a continuous tube. (3 marks)

Answer 1

1. Allows unbroken column of water
2. Cohesion from H bonds between water molecules
3. Evaporation/transpiration creates tension

Question 2

The dengue virus causes damage to capillaries so that blood proteins move out of the
capillaries into the tissue fluid.

Explain how this would affect the return of tissue fluid into the capillaries. (2 marks)

Answer 2

1. Increases water potential of blood/capillary
   OR
   Decreases water potential of tissue fluid;
2. (So) less water returns to blood/capillaries (by
   osmosis)
   OR
   (So) more water leaves blood/capillaries (by
   osmosis);

Question 3

some hospital patients suffer from dairrhoea cuased by infection with the bacterium c difficile, which releases toxins. These toxins cause diarrhoea.
The toxins damage the cells lining the ileum, causing them to lose their microvilli. The damage to the cells reduces the absorption of the products of digestion and reduces the absorption of water, resulting in diarrhoea.

Explain why the damage to the cells lining the ileum reduce absorption of the products of the digestion and why this reduces absorption of water. (3)
some hospital patients suffer from dairrhoea cuased by infection with the bacterium c difficile, which releases toxins. These toxins cause diarrhoea.
The toxins damage the cells lining the ileum, causing them to lose their microvilli. The damage to the cells reduces the absorption of the products of digestion and reduces the absorption of water, resulting in diarrhoea.

Explain why the damage to the cells lining the ileum reduce absorption of the products of the digestion and why this reduces absorption of water. (3)

Answer 3

-reduced surface area
-reduces water potential in ileum
-so less water absorbed into cells by osmosis.

Question 4

to be used as passive immunity treatement, the anti toxin antobody would be injected. If it wasz given by mouth, it would be digested. Describe how the anti toxin antibody would be digested. (4)

Answer 4

-peptide bonds hydrolysed
-endopeptidades hydrolyse internal peptide bonds
-exopeptidades hydrolyse terminal peptide bonds
-dipeptidades break dipeptides into amino acids.