Saturday, December 7, 2013

Chloroplasts: Capture of Light Energy

Plastids are a category of membrane-enclosed organelles that function in photosynthesis or storage in
plant and algal cells. Plastids called chloroplasts are organelles specialized for photosynthesis. Chloroplastscontain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis. Chloroplasts are found in leaves and other green organs of plants and in algae.

Chloroplast structure includes 

Stroma: Each has two outer membranes enclosing a semifluid interior, the stroma, that contains
enzymes and the chloroplast’s own DNA.

Thylakoids: Inside the stroma, a third, highly folded membrane forms a single, continuous compartment. The folded membrane resembles stacks of flattened disks. The stacks are called grana (singular, granum). Photosynthesis takes place at this membrane, which is called the thylakoid membrane. The abundance of chlorophylls in thylakoids is the reason most plants are green. By the process of photosynthesis, chlorophylls and other molecules in the thylakoid membrane harness the
energy in sunlight to drive the synthesis of ATP. The ATP is then used inside the stroma to build carbohydrates from carbon dioxide and water.