Palisade mesophyll

Palisade mesophyll is a leaf tissue specialised for photosynthesis. It lies near the upper surface of the leaf, where it receives light passing through the epidermis, the outer layer of the leaf.

Palisade mesophyll cells are elongated and closely packed. Each cell contains many chloroplasts, which absorb light for photosynthesis. Their position near the upper surface helps the cells receive light, while their many chloroplasts help them absorb it.

Spongy mesophyll

Spongy mesophyll is a layer of loosely arranged cells inside a leaf. Large air spaces between the cells connect with the stomata, the pores through which gases enter and leave the leaf.

These air spaces provide routes for gases to diffuse between the stomata and photosynthesising cells. Carbon dioxide can diffuse from the stomata through the spaces to reach the cells. Oxygen and water vapour can diffuse through the spaces towards the stomata and leave the leaf.

Spongy mesophyll cells contain chloroplasts and carry out photosynthesis. They generally have fewer chloroplasts than palisade cells.

Plant meristem tissue

Plants grow at the tips of their roots and shoots because these regions contain meristem tissue. Meristem tissue contains unspecialised cells that can continue to divide by mitosis, producing new cells.

The new cells allow the root or shoot tip to grow. They can also differentiate: they develop the structures and functions of specialised plant cells. These specialised cells form the tissues needed as the plant develops.