A-LevelBiologyTransport in plants9700/23 · May/June 2025 · Q17 Marks

Ranunculus is a group (genus) of dicotyledonous plants that includes more than 1600 species. (a) Fig. 1.1 is a photomicrograph of a transverse section through part of a root of a Ranunculus species. [Figure 1.1]

(a)(i)Name the cells labelled A and B in Fig. 1.1. A B[2]
(a)(ii)The procambium tissue shown in Fig. 1.1 consists of stem cells. Suggest a role of the procambium tissue in the roots of this plant.[1]
(b)Some species in the Ranunculus genus are xerophytes. State and explain two adaptations of the leaves of xerophytic plants that reduce water loss. adaptation explanation adaptation explanation[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[2] A = endodermal (cell);
[2] B = xylem vessel element ; A vessel elements ; A xylem elements ; I xylem
[1] (has cells that can) divide continuously by mitosis;
[1] idea that forms cells that can, differentiate / AW, into cells in, vascular tissue / xylem (tissue) / phloem (tissue);
[1] (for) repair / growth, of, vascular tissue / xylem / phloem ;
[1] divide to maintain pool of procambial cells ;
[4] mark as pairs (adaptation A + explanation E), max two pairs
[4] A thick (waxy) cuticle;
[4] E increased / long, diffusion distance for water vapour or idea of (greater) impermeability to, water vapour ;
[4] A needle-shaped / narrow / AW, leaves ;
[4] E low surface area to volume ratio, qualified; e.g. less transpiration / AW ; allow ecf if adaptation is spines
[4] A multilayered epidermis / hypodermis ;
[4] E increased diffusion distance for water vapour ;
[4] A low stomatal density ; A few(er) stomata (per unit area) ; A small(er) stomata
[4] E less, transpiration / diffusion of water vapour out of the plant (because most water loss is via stomata) ; I evaporation
[4] A sunken stomata ; A other examples e.g. stomata in, grooves / crypts / chambers
[4] A trichomes / (stomatal) hairs;
[4] A rolled / curled, leaves ;
[4] E maintains humid air around stomata / reduced water potential gradient / (creates) still / non-moving, air; I concentration gradient
[4] AVP ;; e.g. A midday closure of stomata
[4] E close at times when transpiration is highest / AW
[4] A close packing of mesophyll cells / fewer (intercellular) air spaces
[4] E reduces evaporation from mesophyll
[4] A stomata open at night
[4] E lowers transpiration as, higher humidity / lower temperature
[4] A lighter gray / pale coloured, leaves
[4] E reflect light to keep temperature cooler