Chloroplasts

1. Chloroplasts

2. What are chloroplasts? • They are small flattened organelles found in plant cells. • It is the main site of the light-dependent reactions in the process of photosynthesis.

3. Structure of chloroplasts

4. Thylakoids and Grana • Thylakoids are fluid-filled sacs. • They are stacked up in the chloroplast into structures called grana. • The grana are linked together by bits of thylakoid membrane called lamellae.

5. Stroma • Contained within the inner membrane of the chloroplasts and surrounding the thylakoids. • It contains enzymes, sugars, organic acids and oil droplets (which store non-carbohydrate organic material).

6. Photosynthetic Pigments (Chlorophyll a and b and carotene) • These are colored substances that absorb the light energy needed for photosynthesis. • They are found in the thylakoid membranes attached to proteins. • The protein and pigment is called a photosystem.

7. Two kinds of photosystem • Photosystem 1 : absorbs light best at a wavelength of 700nm • Photosystem 2 : absorbs light best at 680 nm

8. Absorption of light by chlorophyll • Most of the light is absorbed by the chlorophyll (blue and red spectrum). • The green part of the visible light spectrum is reflected off the chlorophyll therefore giving the leaf its green color.

10. Structure of chloroplasts in relation to its role in photosynthesis • The chloroplast aligned so that their broad surface runs parallel to the cell wall to maximize surface area for light absorption. • The grana are arranged in such a way to maximize the chances of the light ray passing through the leaf and hitting the chloroplast at the right areas for photosynthesis to take place.