AQA GCSE Combined Science Foundation (8464), Foundation tier · Biology › Organisation › Plant tissues, organs and systems
Practise Plant tissues. 8 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The tissues that make up a leaf (a plant organ) and how the structure of each tissue relates to its function: epidermis, palisade and spongy mesophyll, xylem, phloem, guard cells and stomata, plus meristem tissue. Questions ask you to label a leaf cross-section and explain adaptations for photosynthesis and gas exchange.
Key facts
Leaf = an organ; epidermis, palisade, spongy mesophyll, xylem and phloem = tissues
Waxy cuticle: reduces water loss
Palisade mesophyll: many chloroplasts; most photosynthesis
Spongy mesophyll: air spaces for gas diffusion
Stomata (mostly in the lower epidermis): CO2 in; O2 and water vapour out
Guard cells: open and close the stomata
Xylem: water and mineral ions, from the roots upwards
Phloem: dissolved sugars, from the leaves to the rest of the plant
Meristem: at the tips of shoots and roots; cells divide and differentiate
Notes
The leaf is an organ
diagram
A leaf is a plant organ made of several tissues that work together, mainly for photosynthesis and gas exchange.
Upper epidermis: a single layer of transparent cells, so light passes through. It is covered by a waxy cuticle that reduces water loss.
Palisade mesophyll: tall, tightly packed cells near the top of the leaf, with many chloroplasts. Most photosynthesis happens here because these cells receive the most light.
Spongy mesophyll: rounded, loosely packed cells with many air spaces, so carbon dioxide and oxygen diffuse quickly through the leaf.
Lower epidermis: contains most of the stomata (tiny pores). Each stoma is surrounded by two guard cells that open and close it. Carbon dioxide diffuses in, and oxygen and water vapour diffuse out, through the stomata.
Leaf cross-section. Green dots are chloroplasts: most are in the palisade mesophyll.
Transport and growth tissues
Xylem: hollow tubes strengthened by lignin, which carry water and mineral ions from the roots to the leaves.
Phloem: tubes of elongated cells, which carry dissolved sugars from the leaves to the rest of the plant.
Xylem and phloem run together in the veins of the leaf.
Meristem tissue is found at the growing tips of shoots and roots. Its cells divide by mitosis, and the new cells can differentiate into many types of plant cell.
How to answer each type of question
Name or label a leaf tissue
1 mark eachGrade 4
Work from top to bottom: cuticle, upper epidermis, palisade, spongy mesophyll, lower epidermis.
Stomata and guard cells are mostly on the lower surface.
The veins (xylem and phloem) are in the middle of the leaf.
Example. Name the tissue in a leaf that: (a) contains the most chloroplasts (b) transports water into the leaf (c) contains air spaces for gas exchange.
Say where it is: the growing tips of shoots and roots.
Say what it does: its cells divide to make new cells, which differentiate.
Example. Where in a plant is meristem tissue found, and what is its function?
Show the model answerHide the model answer
At the growing tips of shoots and roots (1). Its cells divide (by mitosis) to produce new cells for growth, which can differentiate into different types of cell (1).
Don’t lose marks
Calling the leaf a tissue. The leaf is an organ; palisade mesophyll, xylem and so on are tissues.
Saying most photosynthesis happens in the epidermis or spongy mesophyll. Most happens in the palisade mesophyll.
Calling the guard cells the pores. The stoma is the pore; the guard cells surround it and open and close it.
Mixing up xylem (water and mineral ions) and phloem (dissolved sugars).
Saying the waxy cuticle stops all water loss. It reduces water loss.
More tips
Memory tricks
Leaf layers, top to bottom: 'Can Unicorns Paint Silly Little Goats?' = Cuticle, Upper epidermis, Palisade, Spongy mesophyll, Lower epidermis, Guard cells.
Palisade = Packed with chloroplasts. Spongy = Spaces for gases.
Phloem: 'ph' sounds like 'f' for food (sugars). Xylem carries water.
Exam technique
For 'explain how it is adapted' questions, give feature + function pairs.
Name the gas and the direction: carbon dioxide diffuses in; oxygen and water vapour diffuse out.
When labelling a diagram, make sure each label line ends exactly on the correct layer.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Name the tissues in a leafUpper and lower epidermis, palisade mesophyll, spongy mesophyll, xylem and phloem, with guard cells around the stomata.
Grade 4
Label a leaf cross-sectionFrom top to bottom: waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll with air spaces and veins, lower epidermis with stomata.
Grade 4
State where meristem tissue is foundAt the growing tips of shoots and roots, where cells divide to make new cells.
Grade 5
State the function of each leaf tissueEpidermis covers the leaf, palisade does most photosynthesis, spongy mesophyll lets gases diffuse, xylem carries water and phloem carries sugars.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Light enters a leaf through its upper surface. Put these tissues in the order that light passes through them.