Root hairs are found in large numbers on the roots of many plants. To investigate their importance, two identical bean seedlings were compared. Seedling A w...

This question tests why root hairs speed up water uptake, a ratio calculation, and the routes water takes into and through a plant.

(a) Which seedling absorbed more water [1] Seedling A (4.8 cm³), the one that kept its root hairs.

(b) How many times more [2] Divide the larger volume by the smaller: \( \frac{4.8}{1.2} = 4 \) times (1 mark working, 1 mark answer).

(c) Why it absorbed more water [3] Using Fig. 3.1, the root hair (structure X) gives a much larger surface area; so there is more area in contact with soil water for osmosis; therefore water is absorbed faster. This is the same surface-area principle that makes alveoli and villi efficient.

(d) Process of water absorption [1] Osmosis.

(e) Why seedling B might wilt on a hot day [2] Without root hairs it absorbs little water; so the water lost by transpiration cannot be replaced, the cells lose turgor and the plant wilts. On a hot day transpiration is fast, so the shortfall is greatest.

(f) Another condition that reduces water uptake [2] Name one condition and give its effect: for example dry soil / little soil water (less water available to absorb), a very low temperature (slows water uptake), or damaged roots (less surface for absorption). 1 mark for the named condition, 1 for the effect on uptake.

(g) Process for mineral ion uptake [1] Active transport - mineral ions are usually absorbed against a concentration gradient, so this requires energy from respiration, unlike osmosis.