Chloroplasts

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.

Structure of chloroplasts

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.