6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
A single-celled amoeba can exchange all the substances it needs directly across its cell surface, but a large animal such as a mouse has a heart, blood vessels and lungs.
Explain why large, multicellular organisms need transport systems and specialised exchange surfaces, whereas single-celled organisms do not. Use ideas about surface area to volume ratio and diffusion distance in your answer. (6 marks)
Cells can be modelled as cubes. A student compares a small cube of side 2 cm with a large cube of side 4 cm.
The formulae are: surface area of a cube =6×(side×side); volume of a cube =side×side×side.
(a) Calculate the surface area to volume ratio of the 2 cm cube. Show your working and give the ratio in the form n : 1. (2 marks)
(b) The 4 cm cube has a surface area to volume ratio of 1.5 : 1. State which cube has the larger surface area to volume ratio, and explain what this means for the exchange of substances. (2 marks)
A student investigated osmosis by placing a cube of potato into a concentrated sugar solution. The results are shown below.
| Mass | |
|---|---|
| Mass at start | 5.0 g |
| Mass after 40 minutes | 4.4 g |
(a) Calculate the percentage change in mass of the potato cube. Show your working. (2 marks)
(b) State, in terms of osmosis, why the potato cube lost mass. (1 mark)
The human circulatory system contains three types of blood vessel: arteries, veins and capillaries.
(a) Name the type of blood vessel that carries blood away from the heart. (1 mark)
(b) State one structural feature of a capillary and explain how it helps the exchange of substances with the tissues. (2 marks)
Water travels up a plant in the xylem and evaporates from the leaves in a process called transpiration.
Explain why the rate of transpiration increases on a warm, windy day. (2 marks)
Stem cells are unspecialised cells that can divide and differentiate.
Define the term differentiation. (1 mark)