Students should be able to explain how the structures of plant tissues are…

The idea

Plant tissues are groups of similar cells working together for a shared job, and each tissue's structure matches that job. Epidermal tissue forms a thin, flat protective covering; its waxy cuticle reduces water loss. Palisade mesophyll is packed with chloroplasts and sits near the upper surface, so it absorbs light for photosynthesis. Spongy mesophyll has rounded cells with large air spaces, allowing carbon dioxide to diffuse to photosynthesising cells. Xylem contains dead, hollow, lignified cells that carry water and mineral ions upward and give support. Phloem contains living cells with sieve plates that translocate dissolved sugars. Meristem tissue at shoot and root tips divides to produce new growth. Explaining means linking each structural feature to the function it performs, not merely naming the tissue.

What earns the marks

• Epidermal tissue is a thin protective layer; in leaves it is covered by a waxy cuticle that reduces water loss by evaporation.
• Palisade mesophyll cells contain many chloroplasts and are positioned near the upper leaf surface, increasing light absorption for photosynthesis.
• Spongy mesophyll cells are loosely packed with air spaces between them, so carbon dioxide can diffuse quickly to palisade cells.
• Xylem tissue is made of dead, hollow cells strengthened with lignin; this allows water and mineral ions to move upward and provides support.
• Phloem tissue contains living cells with sieve plates; dissolved sugars are translocated from sources such as leaves to sinks such as roots and growing regions.
• Meristem tissue at the growing tips of shoots and roots contains cells that divide by mitosis, producing new cells for growth.

Common mistakes and how to put them right

• Naming tissues without linking structure to function.

  Put it right: State the feature and then explain the job it enables, for example air spaces allow faster carbon dioxide diffusion.

• Claiming that xylem cells are living.

  Put it right: Mature xylem cells are dead and hollow, which allows unimpeded water movement.

• Saying phloem carries water.

  Put it right: Phloem translocates dissolved sugars, while xylem transports water and mineral ions.

Exam tips

• Use the connectives 'because' and 'so that' to turn each structural feature into a functional explanation.
• When a question asks about a named tissue, refer to its location in the plant as well as its structure.
• Check that every tissue named in the question has been addressed before finishing your answer.