**What is the physical difference between plants that grow in the direct sunlight and those that grow in the shade?**
Some plants produce "sun leaves" in direct sun and "shade leaves" where the leaves are shaded by others.
Shade leaves are typically larger in area, but thinner than sun leaves. Sun leaves become thicker than shade leaves because they develop longer palisade cells or an additional layer of palisade cells.
On a weight basis, shade leaves generally have more chlorophyll. (This is because the chloroplasts have more grana - you can look this up in a more advanced text book if you would like to know the details of chloroplast structure).
In shade leaves, the chloroplasts move within the cells to take up a position where they will absorb the maximum light without shading other chloroplasts below them. (In sun leaves, the chloroplasts take turns in the bright light and then shelter in the shade of others whilst they make use of the light they have absorbed - too much bright light would destroy the chloroplasts).
Sun and shade leaves can differ in the amount of photosynthesis by a factor of up to 5 - for the same amount of light.
Most of these adaptations take place during leaf development - there is little a leaf (or a plant) can do if its light conditions change.
