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