Biology Exam Questions – Digestion
Complete Answers
Washing powders often contain enzymes from bacteria. These enzymes include
proteases that hydrolyse proteins in clothing stains. The graph shows the effect of
temperature on a protease that could be used in washing powder.
Explain the shape of the curves at 50 °C and 60 °C. (4) - ANSWER--both denatured
by high temperatures
-50°C- activity decreases over time as protein concentration becomes limiting factor
-60°C - higher denaturation rate due to more kinetic energy
-breaking ionic bonds between amino acids
Some proteases are secreted as extracellular enzymes by bacteria.
Suggest one advantage to a bacterium of secreting an extracellular protease in its
natural environment. Explain your answer. (2) - ANSWER--hydrolyses larger
polypeptides
-smaller polypeptides/dipeptides/amino acids can be directly absorbed by bacteria
for growth
Mammals have some cells that produce extracellular proteases. They also have cells
with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their
importance. (2) - ANSWER--hydrolyse polypeptides into amino acids
-allow larger polypeptides to be absorbed by the epithelium
Cells lining the ileum of mammals absorb the monosaccharide glucose by co-
transport with sodium ions. Explain how. (3) - ANSWER--sodium ions actively
transported from ileum cell to blood;
-maintains / forms diffusion gradient for sodium to enter cells from gut (and with it,
glucose);
-glucose enters by facilitated diffusion with sodium ions
A student set up the experiment shown in the diagram below
...
Complete the table by placing a tick in each box that you expect to have shown a
positive result. (3) - ANSWER-[Left to right, top to bottom]
X, ✔, X, ✔, ✔, ✔
Justify your answers to part (b). (3) - ANSWER--biuret: protein molecules too large to
pass through tubing
-iodine in potassium iodide solution: starch molecules too large to pass through
tubing;
-benedict's: starch hydrolysed to maltose, which is able to pass through tubing
Complete Answers
Washing powders often contain enzymes from bacteria. These enzymes include
proteases that hydrolyse proteins in clothing stains. The graph shows the effect of
temperature on a protease that could be used in washing powder.
Explain the shape of the curves at 50 °C and 60 °C. (4) - ANSWER--both denatured
by high temperatures
-50°C- activity decreases over time as protein concentration becomes limiting factor
-60°C - higher denaturation rate due to more kinetic energy
-breaking ionic bonds between amino acids
Some proteases are secreted as extracellular enzymes by bacteria.
Suggest one advantage to a bacterium of secreting an extracellular protease in its
natural environment. Explain your answer. (2) - ANSWER--hydrolyses larger
polypeptides
-smaller polypeptides/dipeptides/amino acids can be directly absorbed by bacteria
for growth
Mammals have some cells that produce extracellular proteases. They also have cells
with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their
importance. (2) - ANSWER--hydrolyse polypeptides into amino acids
-allow larger polypeptides to be absorbed by the epithelium
Cells lining the ileum of mammals absorb the monosaccharide glucose by co-
transport with sodium ions. Explain how. (3) - ANSWER--sodium ions actively
transported from ileum cell to blood;
-maintains / forms diffusion gradient for sodium to enter cells from gut (and with it,
glucose);
-glucose enters by facilitated diffusion with sodium ions
A student set up the experiment shown in the diagram below
...
Complete the table by placing a tick in each box that you expect to have shown a
positive result. (3) - ANSWER-[Left to right, top to bottom]
X, ✔, X, ✔, ✔, ✔
Justify your answers to part (b). (3) - ANSWER--biuret: protein molecules too large to
pass through tubing
-iodine in potassium iodide solution: starch molecules too large to pass through
tubing;
-benedict's: starch hydrolysed to maltose, which is able to pass through tubing
