Question 1 of 6: Plant Tissues and Cell Types

Question 1: Plant Tissues and Cell Types (12 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Each item pairs a tissue/cell name with the tissue system it belongs to, or a cell type with the mechanical/metabolic role its wall structure is built for. Working through the plant body from outside in: the epidermis is the plant's dermal tissue (D); pith (centre) and cortex (periphery of the stem, outside the vascular tissue) are both part of the ground tissue system (F); and xylem and phloem together make up the vascular tissue (E). For the cell types, the wall tells the story — a thin primary wall with no secondary wall marks a metabolically active, undifferentiated cell (parenchyma), an unevenly thickened primary wall in living cells at growing regions gives flexible support (collenchyma), and a thick, lignified secondary wall in cells that mature and then die gives rigid structural support (sclerenchyma).

Concrete examples make the distinctions easier to hold onto: the "strings" in celery petioles are collenchyma, still living and bendable, bracing a rapidly growing organ; the gritty "stone cells" in a pear are sclerenchyma (sclereids), dead at maturity with a thick lignified wall; and the bulk of a potato tuber, which stores starch and stays metabolically active right up until it sprouts, is parenchyma. Xylem itself is a composite tissue — its water-conducting vessels and tracheids are dead, lignified cells structurally allied with sclerenchyma, while phloem's sieve-tube elements stay alive, since active sugar transport requires a functioning cell.