AQA A Level Biology Topic 3 – Organisms Exchange Substances with Their Environment – Exam Questions with Model Answers

AQA A Level Biology Topic 3 Exam Questions with
varied answers
The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary.
Explain why - CORRECT ANSWERS-Loss of water



High blood pressure leads to an accumulation of tissue fluid. Explain how [3] - CORRECT ANSWERS-High
blood pressure = high hydrostatic pressure;

Increase outward pressure from (arterial) end of capillary;

(So) more tissue fluid



The water potential of the blood plasma is more negative at the venule end of the capillary than at the
arteriole end of the capillary. Explain why [3] - CORRECT ANSWERS-Water has left the capillary;

Proteins too large to leave capillary;

Increasing higher concentration of blood proteins;



Describe and explain the mechanism that causes forced expiration [4] - CORRECT ANSWERS-Contraction
of internal intercostal muscles;

Relaxation of diaphragm muscles;

Causes decrease in volume of thoracic cavity;

Air pushed down pressure gradient;



One theory of translocation states that organic substances are pushed from a high pressure in the leaves
to a lower pressure in the roots.



Describe how a high pressure is produced in the leaves. [3] - CORRECT ANSWERS-Water potential
becomes lower;

Water enters phloem by osmosis;

Increased volume (of water) causes increased pressure;

,During their experiment, the scientists ensured the rate of photosynthesis of their plants remained
constant.



Explain why this was important [2] - CORRECT ANSWERS-Rate of photosynthesis related to rate of
sucrose production;

Rate of translocation higher when sucrose concentration is higher;



Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing
are not required. [5] - CORRECT ANSWERS-Trachea and bronchi and bronchioles;

Down pressure gradient;

Down diffusion gradient;

Across alveolar epithelium;

Across capillary endothelium;



The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the
advantage of this shift. [3] - CORRECT ANSWERS-Lower affinity for oxygen;

(To) muscles;

(For) rapid respiration;



Explain how the body shape of a Weddel seal is an adaptation to living in a cold environment [2] -
CORRECT ANSWERS-Small SA:Vol;

reduces heat loss;



Describe the role of enzymes in the digestion of proteins in a mammal. [5] - CORRECT ANSWERS-
(Reference to) hydrolysis of peptide bonds;

Endopeptidase act in the middle of protein/polypeptide OR

Endopeptidase produces short(er) polypeptides/ increase number of ends;

, Exopeptidases act at end of protein/polypeptide

OR

Exopeptidase produces dipeptides/amino acids;

Dipeptidase acts on dipeptide/amino acids

OR

Dipeptidase produces (single) amino acids;



Describe the processes involved in the absorption and transport of digested lipid molecules from the
ileum into lymph vessels. [5] - CORRECT ANSWERS-Micelles contain bile salts and fatty
acids/monoglycerides;

Make fatty acids/monoglycerides (more) soluble (in water)

OR

Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);

Fatty acids/monoglycerides absorbed by diffusion;

Triglycerides (re)formed (in cells);

Vesicles move to cell membrane;



Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions.
Explain how. [3] - CORRECT ANSWERS-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;



Explain the advantages of lipid droplet and Michelle formation [3] - CORRECT ANSWERS-Droplets
increase surface areas (for lipase/ enzyme action);

(So) faster hydrolysis/ digestion (of triglycerides/ lipids);

Micelles carry fatty acids and glycerol/ monoglycerides carry fatty acids and glycerol/monoglycerides
to/through membrane/ to (intenstinal epithelial) cell;