Organisms exchange substances with their environment

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake. (2 marks)

• Larger organisms have a smaller surface area : volume ratio

• Overcomes long diffusion pathway

Suggest how the environmental conditions have resulted in adaptations of systems using Model A rather than Model B. (2 marks)

• Water has lower oxygen concentration than air

• So system on outside gives large surface area in contact with water

Mammals such as a mouse and a horse are able to maintain a constant body temperature. Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. (4 marks)

• The mouse is smaller so larger surface area to volume ratio

• More heat loss

• Faster rate of respiration releases heat

Tubifex worms are small, thin animals that live in water. They have no specialised gas exchange or circulatory system.

The figure shows a tubifex worm.

Using the information provided, explain how two features of the body of the tubifex worm allow efficient gas exchange. (2 marks)

• Thin so short diffusion pathway

• small so large surface area to volume ratio

Abdominal pumping takes place during vigorous activity in insects. This causes regular squeezing of tubes of the gas exchange system, A scientist investigated the effect of abdominal pumping on the pressure in the tubes and the volume of carbon dioxide released by the insect. Her results are shown.

Describe and explain these results. (3 marks)

• Abdominal pumping in tubes is linked to carbon dioxide release

• Abdominal pumping raises the pressure in the body

• Carbon dioxide is pushed out of the body

The ends of the tracheoles connect directly with the insect’s muscle tissue. When flying, water is absorbed into muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why. (1 mark)

Water is denser than air so when it is removed oxygen can diffuse faster through air than water

A scientist used grasshoppers to investigate the effect of composition of air on breathing rate in insects. He changed the composition of air they breathed in by varying the concentrations of oxygen and carbon dioxide. The scientist collected 20 mature grasshoppers from a meadow. He placed the grasshoppers in a small chamber where he could adjust and control the composition of air surrounding them. The small chamber restricted the movement of the grasshoppers. His results for three of the grasshoppers are shown in the table below in the form in which he presented them.

Use all the data to describe the effect of concentration of carbon dioxide on the breathing rate of grasshoppers

• Breathing rate increases when carbon dioxide than 0.1%

• Breathing rate of grasshoppers increase as concentration of carbon dioxide increases

• Breathing rate of grasshoppers actually lowest when there is no CO₂

The estimate does not provide a reliable value for the mean breathing rate of all insect species in the meadow. Other than being an estimate, suggest and explain three reasons why this value would not be reliable. (3 marks)

• Only 3 grasshoppers used, small sample size

• Grasshoppers not the only species

• Movement not restricted, rate of respiration increases

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5 marks)

• Micelles contain bile salts and fatty acids

• Bring fatty acids to the cells lining the epithelium

• Fatty acids are absorbed by diffusion

• Triglycerides reformed in cells

• Vesicles move to cell membrane

Describe the role of enzymes in the digestion of proteins in a mammal. (4 marks)

• Hydrolysis of peptide bonds

• Endopeptidase produces shorter polypeptides

• Exopeptidase produces dipeptides

• Dipeptidase produces single amino acids