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Chloroplasts
Chloroplasts have two membranes, inner and outer. The membranes allow carbon dioxide, oxygen and water to pass through them. Chloroplasts contain pigments, proteins and membranes that absorb light and perform chemical reactions. Plant cells contain 50 or more chloroplasts per cell. During photosynthesis, chloroplasts in plant cells use chlorophyll to collect energy from the sun. Energy, carbon dioxide and water are converted into sugars that the plant uses to carry out life process such as growth and development.
Pigments and Antenna Complexes
Chlorophyll a and b are the primary pigments in chloroplasts that absorb light for photosynthesis. They give leaves their green color. Secondary pigments, such as carotenoids, help plants to photosynthesize during low light conditions. Carotenoids give leaves and fruit yellow, orange and red color in the absence of chlorophyll. Molecules of pigment band together on thykaloids to form antenna complexes. The antenna complexes take in photons of light energy and transfer them to the photosystems.
Thykaloids
Thykaloids are membranes that form flattened sacs within the main body of the chloroplast. They are also called photosynthetic membranes. These sacs are stacked together to form grana. The thykaloid membranes contain chlorophyll a and b. Thykaloids also contain proteins used in the chemical reactions of photosynthesis. These proteins bind to chlorophyll molecules.
Photosystems
Chloroplasts have two photosystems located within the thykaloids that facilitate light absorption through a series of light reactions. These photosystems are composed of interconnected proteins that use light energy to power chemical reactions. The photosystems oxidize water, which causes the release of oxygen. The remaining hydrogen is used during the Calvin cycle. Photosystems convert light energy into adenosine triphosphate (ATP), a form of chemical energy used with carbon dioxide during photosynthesis to produce carbohydrates.