Antibiotics treat food poisoning because they kill Salmonella bacteria inside the human body. Some antibiotics work because they damage the bacterial cell wall. The bacteria die because the cells burst. Explain why the cells burst. 3 marks (2023)
Water moves into the bacterial cells by osmosis
Because the cytoplasm has a lower water potential than the surrounding solution
The weakened cell wall cannot withstand the pressure and bursts
Explain why the potato pieces in the 0.4 mol/dm3 salt solution decreased in mass. [3 marks] (2022)
The solution has a lower water potential than the potato cells
Water moves out of the potato cells by osmosis
This causes the cells to lose mass and become flaccid
When placed into a beaker of water:
• a red blood cell bursts
• a plant cell does not burst.
Explain why the red blood cell bursts, but the plant cell does not burst. [2 marks] (2021)
The red blood cell has no cell wall, so water moves in by osmosis and it bursts
The plant cell has a cell wall, which prevents it from bursting; instead, it becomes turgid
The body cells of a person with untreated diabetes lose more water than the body cells of a person who does not have diabetes. Explain how diabetes can cause the body cells to lose more water. [3 marks] (2019)
High blood glucose concentration creates a low water potential in the blood
Water moves out-of-body cells into the blood by osmosis
This causes the body cells to become dehydrated
Organism D and organism E both have alveoli in the lungs and villi in the small intestine. Figure 8 shows some alveoli and some villi.
Describe how the alveoli and the villi are adapted to increase absorption. [4 marks] (2022)
Large surface area (due to alveoli shape and villi/microvilli)
Thin walls (one cell thick) for short diffusion distance
Rich blood supply (many capillaries) to maintain a concentration gradient
Moist surfaces to allow gases/nutrients to dissolve and diffuse easily
The gorse plant has nodules on its roots. box The nodules are part of the living root tissue. Bacteria which convert nitrogen gas into soluble nitrate ions live in the nodule tissue. Explain how the nodules benefit the gorse plant. 2 marks (2020)
Bacteria in the nodules convert nitrogen gas into soluble nitrates
The plant uses these nitrates for protein synthesis, aiding growth
Glucose is absorbed into the blood in the small intestine by both diffusion and active transport. Describe how the small intestine is adapted for efficient absorption. [5 marks]
Large surface area due to villi and microvilli
Thin walls (one cell thick) for short diffusion distance
Rich blood supply to maintain a steep concentration gradient
Presence of mitochondria in cells for active transport of glucose
Membrane proteins for active transport of glucose and amino acids