Plant tissues: Students should be able to explain how the structures of plant tissues are related to their functions.

The idea

Plants contain tissues adapted to specific jobs. Epidermal tissue covers surfaces and often has a waxy cuticle that reduces water loss. Palisade mesophyll cells near the upper surface contain many chloroplasts for photosynthesis. Spongy mesophyll has loosely packed cells with air spaces that let carbon dioxide and oxygen diffuse to and from cells. Xylem tissue contains dead, hollow cells strengthened with lignin; it transports water and mineral ions upward and supports the stem. Phloem tissue contains living cells that transport dissolved sugars and amino acids up and down the plant. Meristem tissue at growing tips and roots divides to produce new cells for growth. Explaining structure and function together shows understanding.

What earns the marks

• Epidermal tissue covers plant surfaces and its waxy cuticle reduces water loss.
• Palisade mesophyll cells contain many chloroplasts and are near the upper surface, increasing light absorption for photosynthesis.
• Spongy mesophyll has air spaces that allow carbon dioxide and oxygen to diffuse through the leaf.
• Xylem tissue is made of dead, hollow cells strengthened with lignin, transporting water and mineral ions and providing support.
• Phloem tissue contains living cells that transport dissolved sugars and amino acids around the plant.
• Meristem tissue divides to produce new cells, enabling growth at tips and roots.

Common mistakes and how to put them right

• Saying xylem transports food.

  Put it right by stating xylem transports water and mineral ions, while phloem transports dissolved sugars and amino acids.

• Describing spongy mesophyll as tightly packed.

  Put it right by explaining that its air spaces allow gas diffusion.

• Confusing the waxy cuticle with a waterproof barrier that stops all gas exchange.

  Put it right by saying it reduces water loss while stomata still allow gas exchange.

Exam tips

• Link each named tissue to its function in the same sentence, for example 'palisade cells contain many chloroplasts so they absorb more light for photosynthesis'.
• Use correct tissue names such as epidermis, palisade mesophyll, spongy mesophyll, xylem, phloem and meristem.
• When asked to explain, give a structural feature and then state the advantage it provides rather than only naming the tissue.