Exchange and transportEdexcel A-Level Biology B: Topic test

20 questions, 54 marks

Edexcel A-Level Biology B

Exchange and transport topic test

Total 54 marks

Name

Class

Date

1
Shrews are very small mammals with a body mass of about 5 g. A shrew eats almost continuously and may die if it goes without food for a few hours. An elephant has a body mass of about 5 000 kg and can survive for days without food.
(a)
What happens to the surface area to volume ratio of an animal as its body size increases?
[1 mark]
AIt increases because surface area increases faster than volume
BIt decreases because volume increases faster than surface area
CIt stays the same because both increase in proportion
DIt increases because volume increases more slowly than mass
(b)
Why does an elephant need a mass transport system, whereas a very small organism can rely on diffusion alone?
[1 mark]
AElephant cells need a different type of respiration
BElephant cells are much larger than those of small organisms
CThe surface area to volume ratio is too small and diffusion distances are too long for diffusion alone to supply the cells
DDiffusion does not occur across the cell surface membranes of large animals
(c)
Explain why a shrew loses heat faster per gram of body mass than an elephant does, and why this means it must eat so frequently.
[2 marks]
Total for question 1: 4 marks
2
A scientist investigates how different substances cross a cell surface membrane. Some pass directly across the phospholipid bilayer, some need membrane proteins, and some cannot cross without help because of their size or charge.
(a)
Which substance would cross the phospholipid bilayer most rapidly by simple diffusion?
[1 mark]
AOxygen
BChloride ions
CGlucose
DSodium ions
(b)
Which statement about facilitated diffusion is correct?
[1 mark]
AIt requires ATP
BIt moves substances against a concentration gradient
CIt takes place directly through the phospholipid bilayer
DIt uses channel or carrier proteins and moves substances down a concentration gradient
(c)
Explain why chloride ions cannot diffuse directly through the phospholipid bilayer but can cross the membrane through channel proteins.
[2 marks]
Total for question 2: 4 marks
3
A neurone uses a pump protein in its cell surface membrane to move sodium ions out of the cell and potassium ions into the cell, against their concentration gradients. The neurone also releases a neurotransmitter, which is stored in small membrane-bound sacs inside the cell, into the gap between it and the next cell.
(a)
Explain why moving sodium ions out of the neurone requires a carrier protein and ATP.
[3 marks]
(b)
Describe how the neurone releases the neurotransmitter by exocytosis, and explain why ATP is needed for this process.
[4 marks]
Total for question 3: 7 marks
4
A man receives a heart-lung transplant. The donor heart has no nerve connections to the rest of the recipient's body, yet it beats regularly. The recipient's breathing is normal and the donor lungs ventilate as expected. Before the operation he had pulmonary fibrosis, a condition in which scar tissue makes the walls of the alveoli much thicker.
(a)
Explain how the donor heart can beat regularly without nerve connections, and how the excitation of the heart muscle leads to coordinated contraction of the atria and ventricles.
[6 marks]
(b)
Explain how the structure of normal alveoli allows efficient gas exchange and why pulmonary fibrosis reduces the efficiency of gas exchange.
[6 marks]
Total for question 4: 12 marks
5
Llamas live in the Andes at altitudes above 4 000 m, where the partial pressure of oxygen in the air is much lower than at sea level. Llama haemoglobin has a different amino acid sequence from human haemoglobin and has a higher affinity for oxygen.
(a)
How does the oxygen dissociation curve of llama haemoglobin compare with that of human haemoglobin?
[1 mark]
AIt is shifted to the right
BIt is identical because both haemoglobins have four polypeptide chains
CIt is shifted to the left
DIt is shifted to the right at low partial pressures only
(b)
In the respiring tissues of a llama the partial pressure of carbon dioxide increases. What is the effect on haemoglobin?
[1 mark]
AIt releases oxygen more readily
BIt binds oxygen more tightly
CIt releases oxygen less readily
DIt loses its haem groups
(c)
Explain why a higher affinity for oxygen is an advantage for llamas living at high altitude.
[2 marks]
Total for question 5: 4 marks
6
Aphids feed on plant sap by pushing a needle-like mouthpart into a single sieve tube element of the phloem. When an aphid is anaesthetised and its mouthpart is cut, sap continues to flow out of the cut end at a measurable rate for hours.
(a)
What does the flow of sap from the cut mouthpart show about the contents of the phloem?
[1 mark]
AThey are under negative pressure
BThey are under tension, as in the xylem
CThey are under no pressure
DThey are under positive pressure
(b)
Which feature of sieve tube elements allows sap to flow along the phloem?
[1 mark]
AThick walls reinforced with lignin
BPerforated end walls (sieve plates) and few organelles
CDead, hollow cells with no end walls
DA large central vacuole and a nucleus in every cell
(c)
Suggest one weakness of the mass-flow hypothesis for the movement of sugars in the phloem.
[2 marks]
Total for question 6: 4 marks
7
A man with heart failure is short of breath because fluid collects in the tissue of his lungs. His heart cannot pump blood out of the veins effectively, so the blood pressure in his veins and capillaries is higher than normal. A healthy adult at rest has a heart rate of 70 beats per minute and a stroke volume of 70 cm³. The patient's ECG shows 0.60 seconds between successive R waves and his stroke volume is 45 cm³.
(a)
Explain how raised blood pressure in the veins causes tissue fluid to accumulate in his lungs.
[3 marks]
(b)
Calculate the patient's heart rate and cardiac output, and explain what the values show about his heart compared with that of a healthy adult at rest.
[4 marks]
Total for question 7: 7 marks
8
A grower fits fans to a glasshouse to circulate the air around tomato plants. The plants take in carbon dioxide for photosynthesis during the day, and the leaves have stomata mainly on their lower surfaces.
(a)
Describe how carbon dioxide reaches the photosynthesising cells of a leaf, and explain why water vapour is lost from the leaf by the same route.
[6 marks]
(b)
Explain how the loss of water vapour from the leaves leads to the movement of water up the xylem, and how the fans would affect the rate of this movement.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).