Rate of diffusion

Figure 3 shows a diagram of the skin.

Structures in the skin, shown in Figure 3, help to control body temperature.

Explain how the action of the hair erector muscle helps to keep the body warm.

Explain how sweating decreases body temperature.

A scientist investigated the air temperature at which women start to shiver.

The scientist recorded the air temperature at which a 40‑year‑old woman started to shiver.

Which would improve the quality of the results in this investigation?

State the optimum body temperature as shown in Figure 4.

Temperature affects the rate of diffusion of gases into and out of cells.

State two other factors that affect the rate of diffusion.

A teacher was demonstrating a process to students.

The teacher had a beaker of water and added five drops of food colouring to the beaker.

State the process being demonstrated.

A student asked if different food colourings spread evenly in the same amount of time.

Give two variables that would need to be controlled if the investigation was repeated with different food colourings.

The teacher repeated this process with water at different temperatures. Figure 11 shows the results of this experiment.

Draw a line graph to show the results in Figure 11.

Explain why the time taken decreased.

7 (a) Figure 13 shows three organisms that live in pond water. Oxygen diffuses across the cell membranes of these organisms.

species A species B species C

Figure 13

(i) Which row of the table shows the conditions needed for oxygen to diffuse from species A into the pond water?

(ii) Species B has a surface area of 9 000μm² and a volume of 6 000μm³. Calculate surface area to volume ratio for species B.

(iii) The surface area to volume ratio for a cell of species A is 1: 1. The surface area to volume ratio for each cell in species C is 1: 4. Explain how the different surface areas will affect the diffusion of oxygen out of the cells of species A and species C.

(b) Some species of algae that photosynthesise have vacuoles that are filled with gas. These vacuoles help the algae to float in water. State how these vacuoles help the algae survive.

*(c) Figure 14 shows leaves on a branch of a tree.

(Source: © Butus/Shutterstock)

Figure 14

Explain how leaves are adapted for photosynthesis.

Gas exchange happens in the alveoli in the lungs.

Figure 12 shows an alveolus and a capillary.

(adapted from: sciencepics/shutterstock)

Figure 12

Name the gas used in respiration that moves from the alveolus into the capillary.

Name the gas produced by respiration that moves from the capillary into the alveolus.

The capillary wall is only one cell thick.

Explain how gases move from the alveolus to the capillary.

Explain the advantages of red blood cells passing one at a time through this narrow capillary.

The average number of alveoli in each human lung is 280 million.

The surface area of 1 million alveoli is 0.25 m².

Calculate the total surface area of a human lung.

1 (a) Bloodworms in a pond indicate that the water is polluted.

(i) Which species also indicates that the water is polluted?

(ii) Bloodworms have a high level of haemoglobin in their blood. Give a reason why this helps them survive in polluted water.

(iii) Carbon dioxide diffuses from the body of the bloodworm into the water. Give two factors that affect the rate of diffusion.

(b) Figure 1 shows part of a diseased rose plant from a garden.

(Source: © Manfred Ruckszio/Shutterstock)

Figure 1

Explain what Figure 1 indicates about the air quality in the garden.

10 (a) When training, an athlete noticed some types of T‑shirts became wetter and heavier due to sweating. This athlete has three T‑shirts, each made of a different material. Devise a method this athlete could use to find the best T‑shirt for training.

(b) Athletes often eat a high protein diet.

(i) Which is the test and result for a food containing protein?

(ii) Digested protein is absorbed in the small intestine by diffusion. Figure 15 shows part of the small intestine.

(Source: © Science Photo Library C047/6177)

Figure 15

Using Figure 15 and Fick’s law, explain the effect of the villi on the rate of diffusion.

(iii) Digested protein enters the blood as amino acids. State which component of the blood transports amino acids.

(c) Explain how high levels of amino acids in the blood cause a high concentration of urea in urine.

(a) Figure 10 shows alveoli from a lung.

Figure 10

Explain why these alveoli have the internal structure shown in Figure 10.

How does oxygen move across the alveolar membrane into the capillary?

Figure 11 shows the movement of molecules across a membrane.

at start
after 2 seconds
after 4 seconds

Figure 11

Describe how Figure 11 illustrates movement of molecules across a membrane.

*(c) Explain, using Fick’s law, the factors that affect the diffusion rate of molecules into and out of cells.