Biology project.. plz help!?

Question

I'm doing a biology project as part of my A2 course... Its based on leaf length and width and light intensity. I found that length and width of leaves are greater when light intensity is less (Leaves found in the shade).

But in my criteria it says I need a subtitle called "research and rationale" where i need to *Justify my investigation with appropriate and relevant biological principles*

So erm... Confused on what to right here? can you give me some tips and start me of please... Thanks advance =)

Answer 1

Hi Sham,

I am not exactly a leaf expert here but here are 2 reasons why I think leaves are longer and wider in low intensity light.

Photosynthesis: Leaves contain chlorophyll, which when exposed to light causes photosynthesis. In bright light, leaves only need to expose a smaller area to the light because photosynthesis is more effective in brighter light. In dim light/shade, leaves need to open up more surface area to expose more chlorophyll to the light.

Evaporation: Sunlight causes water in the leaves to evaporate. This is natural but in bright light, evaporation is higher and therefore the plant may be reducing its surface area to prevent excess evaporation. In dim light, the leaves can open up more without risking large moisture loss.

You can see some examples of this in cacti and coniferous plants.

Did this help?

Answer 2

Basically in less light, its "better" for leaves to be larger in order to be in the best situtation to get the most of the limited light ( so they can photosynthesise enough)....leaves in high light intesities do not need to be so large as they can get enough light energy with smaller leaves ( so do not need to spend so much energy making larger leaves)....

Answer 3

Well, you will have to do the research, but I could start you off with a heading for the project.

"Correlations Between Leaf Structure and Biological Surroundings"

Then continue into what the proposed hypothesis is, and find relevant examples to confirm or reject your hypothesis.

To support for investigation, you would have to understand the principles of photosynthesis, and why leaves in the shade would need more surface area to gather the same amount of light as a leaf in the sun.