What are the differences between sun and shade leaves?

Sun leaves are typically smaller, thicker, and have fewer chloroplasts than shade leaves, which are larger, thinner, and have more chloroplasts.

Sun leaves and shade leaves are adaptations of plants to different light conditions. Sun leaves are found on plants that are exposed to high light intensity. They are typically smaller in size to minimise water loss through transpiration. They are also thicker due to a higher density of cells, particularly the palisade mesophyll cells which contain chloroplasts for photosynthesis. Despite this, sun leaves have fewer chloroplasts per cell compared to shade leaves. This is because in high light conditions, too many chloroplasts can lead to photo-damage.

On the other hand, shade leaves are found on plants that grow in low light conditions, such as under the canopy of other plants. They are larger in size to maximise the surface area for light absorption. They are thinner as they have fewer cell layers, reducing the distance that light has to travel to reach the chloroplasts. Shade leaves have more chloroplasts per cell than sun leaves. This is to optimise the capture of light energy for photosynthesis in low light conditions.

The differences between sun and shade leaves are a result of the plant's need to balance light absorption for photosynthesis with water conservation and protection from photo-damage. This is a great example of how plants adapt to their environment at a cellular level, which is a key concept in biology and chemistry.