Reading: Diagram Label Completion: Question 10

A leaf's internal structure, viewed in cross-section, reveals several distinct layers, each fine-tuned by evolution to maximise the amount of light captured for photosynthesis while limiting the loss of water to the surrounding air. Botanists studying leaf anatomy at the Fenmarsh Plant Sciences Institute in 2020 used thin-sectioned samples from a broad-leaved shrub to illustrate the arrangement common to most flowering plants.

Covering the entire outer surface of the leaf is a waxy cuticle, a thin, transparent layer secreted by the cells beneath it that dramatically reduces water loss through evaporation while still allowing sunlight to pass through largely unhindered. Directly beneath the cuticle on the upper surface lies the upper epidermis, a single layer of tightly packed, transparent cells that contains no chloroplasts of its own but instead acts chiefly as a protective barrier, letting light pass down into the tissue below.

Immediately under the upper epidermis sits the palisade mesophyll, a layer of tall, closely packed, column-shaped cells crammed with chloroplasts and oriented so that their long axes run perpendicular to the leaf surface, an arrangement that captures the maximum amount of direct sunlight for photosynthesis. Below this dense layer lies the spongy mesophyll, made up of loosely arranged, irregularly shaped cells with large air spaces between them; these air spaces allow carbon dioxide and oxygen to diffuse freely through the tissue and reach the photosynthesising cells above.

Running through the spongy mesophyll is a vascular bundle, which bundles together the xylem, carrying water and dissolved minerals up from the roots, and the phloem, carrying the sugars produced by photosynthesis away to the rest of the plant. On the lower surface of the leaf sits the lower epidermis, broadly similar to its upper counterpart but interrupted at intervals by small pores called stomata; each stoma is flanked by a pair of guard cells, which change shape to open or close the pore and so control the movement of water vapour and gases into and out of the leaf.

The diagram below shows a cross-section of a leaf, from the upper surface (top) to the lower surface (bottom). Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The thin, waxy, transparent layer covering the entire outer surface of the leaf, which reduces water loss 2 ____________________. The single layer of tightly packed, transparent cells directly beneath this waxy layer on the upper surface 3 ____________________. The layer of tall, column-shaped cells packed with chloroplasts, arranged perpendicular to the leaf surface, just below the upper layer 4 ____________________. The layer of loosely arranged cells with large air spaces between them, lying below the column-shaped layer 5 ____________________. The structure running through this loosely arranged layer that bundles together the leaf's water- and sugar-transporting tissues 6 ____________________. The layer on the lower surface of the leaf, broadly similar to its upper counterpart 7 ____________________. The small pore within this lower layer, through which gases and water vapour move into and out of the leaf 8 ____________________. The pair of specialised cells flanking this pore that change shape to open or close it