(a) The movement of molecules within an organism can occur by diffusion and active transport.
Complete Table 1.1 by placing ticks (✓) to show the correct features of each process.
(b) Explain why active transport is important in root hair cells.
▶️ Answer/Explanation
(a)
Explanation: Active transport requires energy (✓) as it moves substances against their concentration gradient, while diffusion is passive (no ✓ for energy). Diffusion is responsible for gas exchange (✓) and its rate increases with a steeper concentration gradient (✓). Both processes occur across membranes, but the question specifies “always” for active transport (✓) since diffusion can also occur in open spaces.
(b)
Active transport is crucial in root hair cells because:
- It allows absorption of mineral ions even when their concentration in the soil is lower than inside the root cells
- It enables movement of ions against their concentration gradient, which is essential for nutrient uptake
- It helps create a water potential gradient that facilitates water absorption by osmosis
- Specific ions like nitrates and magnesium are often in low concentration in soil but needed in large amounts by plants
Detailed Explanation: Root hair cells are specialized for absorbing water and minerals from the soil. The concentration of essential mineral ions in the soil water is usually much lower than their concentration inside the root hair cells. Diffusion alone couldn’t move these ions into the roots because it only works along the concentration gradient. Active transport uses energy from respiration to pump these ions into the root against their concentration gradient. This process not only provides the plant with necessary nutrients but also lowers the water potential inside the root, causing water to follow by osmosis. Without active transport, plants would struggle to obtain enough minerals, especially in nutrient-poor soils.