Summary
Flat, thin organs adapted to capture light and exchange gases for photosynthesis.
In depth
Layers: waxy cuticle, upper epidermis, palisade mesophyll (dense chloroplasts), spongy mesophyll (air spaces for gas diffusion), lower epidermis with stomata. Veins supply water and remove sugar.
Leaf structure reflects the trade-off between capturing light and avoiding water loss. Sun leaves are thicker, shade leaves thinner and broader. Leaf shape, hairs and waxy layers adjust to climate.
Example: needle leaves reduce water loss in conifers.
Leaf shape varies with environment: broad thin leaves capture light in shade, small thick leaves reduce water loss in dry areas, and spines (cactus) are leaves modified for defence. Veins bring water and take away sugar, and dense venation supports high rates of photosynthesis. Sun leaves are thicker with more palisade layers than shade leaves.
Leaves can be simple or compound, and arranged alternate, opposite or whorled. Special forms include tendrils, bud scales and the traps of carnivorous plants. In deciduous trees, leaf fall is controlled by an abscission layer, regulated by ethylene and auxin.
Key idea: the leaf's structure shows a trade-off between capturing light and CO2 and losing water.
Frequently asked questions
What is Leaves?
Flat, thin organs adapted to capture light and exchange gases for photosynthesis.
Which area of biology covers Leaves, and how advanced is it?
Leaves is one of the 56 topics in Plant Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Transpiration, Stomata, Stems.
Can you give an example of Leaves?
Cacti have spines as reduced leaves to cut water loss.
What should I learn before Leaves?
Leaves is a Beginner topic, so no earlier topic is required. Other Beginner topics in Plant Biology that pair well with it include Plant Kingdom, Photosynthesis, Chlorophyll.
What topics are related to Leaves?
The closest topics to Leaves are Transpiration, Stomata, Stems, Apical Dominance. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Leaves?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Leaves. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Leaves different from Transpiration?
Leaves: Flat, thin organs adapted to capture light and exchange gases for photosynthesis. Transpiration: Evaporation of water from leaves that pulls water up the plant through the xylem. Read both side by side and note what each one explains.
How should I study Leaves step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Transpiration and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.