Fig. 1.1 is a diagram of an animal cell.
(a) Complete Table 1.1 by writing the name and function of each of the labelled parts of the cell shown in Fig. 1.1.
(b) (i) Explain how water moves into and out of animal cells.
(ii) A sample of red blood cells was taken from a person. The red blood cells were put into three test‑tubes. Each test‑tube contained a different liquid:
- blood plasma
- pure water
- a very concentrated salt solution.
Fig. 1.2 shows the appearance of the red blood cells when examined using a microscope. Identify the liquids the red blood cells were immersed in. Write your answers in the spaces provided in Fig. 1.2.
(iii) State the name of the molecule in red blood cells that combines with oxygen.
(iv) Fig. 1.3 shows a drawing of a white blood cell.
Identify the type of white blood cell shown in Fig. 1.3.
▶️ Answer/Explanation
Ans:
(a) 
(b)(i) Water moves via osmosis—from high to low water potential through a partially permeable membrane, driven by the random motion of water molecules.
(b)(ii) From top to bottom in Fig. 1.2:
• Blood plasma (normal cell shape)
• Concentrated salt solution (shrunken cells, water leaves by osmosis)
• Pure water (swollen/burst cells, water enters by osmosis)
(b)(iii) Haemoglobin binds oxygen in red blood cells.
(b)(iv) The white blood cell is a phagocyte, identifiable by its lobed nucleus and ability to engulf pathogens.
Fungal cells and plant cells contain mitochondria.
(a) (i) State the function of mitochondria.
(ii) State one feature of plants that is used to distinguish them from fungi.
(b) Yeast is a fungus that can respire to produce ethanol. State the balanced chemical equation for this type of respiration in yeast.
(c) A scientist investigated the effect of sugar on respiration in yeast cells. One flask contained \(100cm^3\) of a sugar solution and another flask contained \(100cm^3\) of water. Both flasks contained the same mass of yeast. The temperature was maintained at 25°C. The scientist used the apparatus shown in Fig. 1.1.
Fig. 1.2 is a graph of the results of the investigation. 
(i) Using the gradient shown in Fig. 1.2, calculate the rate of carbon dioxide gas produced by the yeast in a sugar solution between 10 minutes and 15 minutes. Include the unit. Space for working.
(ii) Suggest the reason for the oil layer in the apparatus shown in Fig. 1.1.
(iii) State one reason why no more carbon dioxide gas was produced after 35 minutes by the yeast in a sugar solution, shown in Fig. 1.2.
(iv) The scientist repeated the investigation using yeast and the sugar solution at a temperature of 95°C. Explain why no carbon dioxide was produced at a temperature of 95°C.
(d) State one way in which humans use the carbon dioxide gas produced by yeast cells.
(e) State the name of one gas, other than carbon dioxide, that contributes to the enhanced greenhouse effect.
▶️ Answer/Explanation
Ans:
(a)(i) Mitochondria are the site of aerobic respiration, where glucose is broken down to release energy (ATP).
(a)(ii) Plants have cellulose cell walls or chloroplasts, while fungi have chitin cell walls and lack chloroplasts.
(b) The anaerobic respiration equation in yeast: \[ C_6H_{12}O_6 \to 2C_2H_5OH + 2CO_2 \]
(c)(i) The rate of CO₂ production between 10-15 minutes is 1.6 cm³/min, calculated from the gradient (rise/run) of the graph.
(c)(ii) The oil layer prevents oxygen entry, ensuring anaerobic conditions for ethanol fermentation.
(c)(iii) CO₂ production stops because the sugar is fully consumed by the yeast.
(c)(iv) At 95°C, yeast enzymes denature, halting respiration and CO₂ production.
(d) Humans use CO₂ from yeast in bread-making to make dough rise.
(e) Another greenhouse gas is methane (CH₄), which traps heat more effectively than CO₂.