Leaf structure

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Key points

  • The leaf is one of the most important organs of a plant.
  • Leaves produce food for the plant through a process called photosynthesis.
  • The leaves of different plants vary widely in size, shape and colour and are adapted to carry out photosynthesis.

Leaves and photosynthesis

Video - Leaf structure

is a vital process that occurs in the leaves of a plant. During photosynthesis, the leaves use and light energy to convert carbon dioxide and water into oxygen and glucose. The glucose acts as a source of food for the plant.

The equation for photosynthesis is:

Carbon dioxide + water → glucose + oxygen

Adaptations for photosynthesis

Leaves have several adaptations which play an important role in photosynthesis.

Plant adaptationFunction
Broad leavesProvide a large surface area to absorb as much sunlight as possible.
Thin leavesProvide a short pathway for gases to move into and out of cells.
Network of tubes (xylem and phloem)To transport water, mineral ions and glucose (food) around the plant.
Lots of chloroplastContain a green substance called chlorophyll, which traps energy from the sun for photosynthesis.
StomataTiny holes found mainly underneath the leaf to allow gases to diffuse into and out of the leaf. Each hole is a single stoma.
Guard cellsControls the opening and closing of stomata.
MidribProvides strength throughout the leaf, keeping it upright and sturdy in the wind.
PetioleAttaches the leaf to the stem.
cross section of a leaf showing the sunlight hitting the upper layer, below it the palisade layer, spongy layer, lower layer and stomata, where gasses are exchanged in and out of the cell
A cross-section through a leaf showing its main parts

Light

A leaf usually has a large surface area, so that it can absorb a lot of light. Its top surface is protected from water loss, disease and weather damage by a waxy layer.

The upper part of the leaf is where the light falls, and it contains a type of cell called a palisade cell. This is adapted to absorb a lot of light. It has lots of chloroplasts and is shaped like a tall box.

Carbon dioxide

Plants get the carbon dioxide they need from the air through their leaves. It moves by diffusion through small holes in the underside of the leaf called stomata. Guard cells control the size of the stomata so that the leaf does not lose too much water in hot, windy or dry conditions.

The lower part of the leaf is a spongy layer with loose-fitting cells. These let carbon dioxide reach the other cells in the leaf due to the air spaces around them, and also let the oxygen produced in photosynthesis leave the leaf easily.

Water

The water needed for photosynthesis is absorbed through the roots and transported through tubes to the leaf. The roots have a type of cell called a root hair cell. These project out from the root into the soil, and have a big surface area and thin walls. This lets water pass into them easily.

Root cells do not contain chloroplasts, as they are normally in the dark and cannot carry out photosynthesis.

Diagram of the root hair cell in water and soil. The root hair is long and thin.
Water is absorbed from the soil by root hair cells

Video - Parts of the leaf

Watch the video to see how a horticulturist uses science in her job

Can you answer these questions based on the video?

1. What is a horticulturist?

2. What are the four main features of a leaf which are mentioned in the video?

  1. An expert who looks after plants, including feeding, watering, pruning and training. They must also have extensive knowledge about trees, flowers, vegetables, nuts, bushes and fruits.

  2. Midrib, Veins, Edge, Petiole.

The importance of leaves

Leaves provide food for plants, and plants provide the food for all living organisms on Earth. Without plants, all other food chains would cease to exist.

Some leaves also have medicinal uses, for example the leaves of the snapdragon plant are used to reduce fever and inflammation. Knowledge of leaves is also important to horticulturists. They need to know the best conditions for different types of plants in order to grow flowers, fruit and vegetables.

Botany is the study of plants and are scientists who need to understand how plants relate to other organisms and the of an area. For example, botanists may learn about how to classify and protect plants, which in turn can provide us with the knowledge to develop new medicines. The more we know about botany, the more we understand about life on Earth.

Test your knowledge

Label the leaf

Quiz