Organisation of Plant Tissues

Meristematic tissue

Meristematic tissue is made of small, thin-walled cells with dense cytoplasm and no vacuole that divide actively by mitosis. It is found at the root tip and shoot tip (apical meristem) and in the cambium (lateral meristem), and it is the source of all new plant cells.

Permanent tissue

Cells produced by meristematic tissue stop dividing and differentiate into permanent tissue with a fixed shape and job. Permanent tissue is divided into simple tissue, made of one cell type, and complex tissue, made of more than one cell type working together.

• Parenchyma, thin-walled, unspecialised cells for storage and packing; makes up the cortex and pith.
• Collenchyma, cells with unevenly thickened walls that give flexible support to young stems.
• Sclerenchyma, cells with thick, lignified walls (often dead at maturity) that give rigid support.
• Xylem, a complex tissue that transports water and mineral salts and gives mechanical support.
• Phloem, a complex tissue that transports manufactured food such as sucrose.

How tissues are arranged

In a dicotyledonous root, the vascular tissue forms a central star shape for anchorage against pulling forces. In a dicotyledonous stem, vascular bundles are arranged in a ring near the outer edge, which gives strength against bending, with xylem towards the centre and phloem towards the outside of each bundle.

How it is examined

Questions often show a labelled cross-section of a root or stem and ask you to identify a tissue, state its function, or explain why its arrangement suits the organ's role, for example why xylem forms a central star in a root but a ring in a stem.

Worked exam-style question

Question. A transverse section of a young dicotyledonous stem shows several vascular bundles arranged in a ring near the outer region of the stem. In each bundle, a tissue of thick-walled, lignified cells lies towards the centre, and a tissue of living, thin-walled cells lies towards the outside.

(a) Identify the two tissues described, and state one function of each. (b) Explain why arranging the vascular bundles in a ring near the periphery, rather than as a single solid mass, suits a stem's need to resist bending.

(c) State how the arrangement of the equivalent water-conducting tissue differs in a dicotyledonous root, and explain why this different arrangement suits a root's main function. (d) Name the meristematic tissue responsible for producing new vascular tissue as this stem increases in girth.

Model answer. (a) The tissue towards the centre of each bundle is xylem, which transports water and mineral salts and gives mechanical support; the tissue towards the outside is phloem, which transports manufactured food such as sucrose. (b) A ring of bundles near the periphery acts like a hollow supporting cylinder, giving the stem strength to resist bending from any direction while using less rigid tissue than a solid core would need, similar to how a hollow tube resists bending efficiently.

(c) In a root, xylem is arranged as a central solid star shape rather than a ring, because a root mainly experiences pulling (tension) forces during anchorage, and a central core resists these pulling forces most effectively. (d) The (vascular) cambium, a lateral meristem, produces new xylem and phloem as the stem grows in girth.

Practice question

Try this. A student examines a piece of plant tissue under a microscope and records: "cells with thin walls, no visible lignification, packed together with no obvious gaps, apparently functioning for storage." Identify the tissue, and explain why the description rules out two other named tissues that might otherwise seem similar.

Exam tip

Key terms

These glossary terms connect directly to this standard:

• Tissue, a group of similar cells working together to carry out a shared function.
• Meristem, tissue made of small, actively dividing cells that is the source of all new plant cells.
• Xylem, a complex tissue that transports water and mineral salts and gives mechanical support.
• Phloem, a complex tissue that transports manufactured food such as sucrose.

Source:SRC-DSKP-EN

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