11.1 Photosynthesis

Question 1

What is the main photosynthetic structure of eukaryotic plants

Answer 1

The leaf

Question 2

How are leaves adapted to their function

Answer 2

1. They have a large surface area that absorbs as much sunlight as possible
2. An arrangement of leaves that prevents overlapping to stop shadowing
3. Thin, as most light is absorbed in the first few micrometres of the leaf and the diffusion distance for gases is kept short
4. A transparent cuticle and epidermis that allows light to be let through to the photosynthetic mesophyll cells beneath
5. Long, narrow upper mesophyll cells packed with chloroplasts that collect light
6. Numerous stomata for gas exchange, so that all mesophyll cells are only a short diffusion pathway from one
7. Stomata that open and close depending on light intensity
8. A network of xylem and phloem to transport water to the leaves and carry sugars away

Question 3

What are the 3 stages of photosynthesis

Answer 3

1. Capture of light energy by chlorophyll
2. The light Dependent reaction, in which some of the light energy absorbed is stored in chemical bonds. During the process an electron flow is created by the effect of light on chlorophyll causing water to split into protons, electrons and oxygen
3. The light independent reaction, in which the protons are used to produce sugars and other organic molecules

Question 4

Describe briefly the structure of chloroplasts

Answer 4

Disc shaped

2-10 micrometres long

Surrounded by a double membrane

Question 5

What are the 2 main structures of chloroplasts

Answer 5

1. Grana - stacks of thylakoids, where the light dependent reaction occurs. Chlorophyll is found in thylakoids
2. Stroma - Fluid filled matrix where the light independent reaction takes place. Other structures are present, like starch grains