Photosynthesis takes place in chloroplasts within plant cells. Chloroplasts contain thylakoids where the two key reactions of photosynthesis - the light reactions and dark reactions - occur. The light reactions use energy from sunlight to convert water and carbon dioxide into oxygen and energy-carrying molecules like ATP. The dark reactions then use these energy-carrying molecules to produce sugars from carbon dioxide.

1. Photosynthesis and Plants

2. Photosynthesis Practically all life on earth today starts with the sun. All proteins, lipids, carbohydrates and any other kind of organic molecule comes because plants can trap the sun’s energy.

3. Inside a Leaf

4. Chloroplasts Chloroplasts are the organelles inside a cell where photosynthesis takes place. They have two outer membranes. Full of a semi-fluid medium called Stroma. Embedded in stroma are discs called Thylakoids. Stacks of thylakoids form grana (Granum).

5. Chloroplasts Photosynthetic reaction: 6CO 2 + 12H 2 O + Light C 6 H 12 O 6 + 6H 2 O + 6O 2

6. Photosynthesis Made up of Light dependant reactions and light independent reactions Light reactions and dark reactions. Light reactions capture sunlight, release O 2 and produce high energy compounds like ATP. Dark reactions in the stroma use the energy from light reactions with enzymes and CO 2 to produce organic molecules.

7. Photosynthesis Chlorophyll in thylakoid membranes absorb some wavelengths and alters shape. Thus they store the energy. The energy is transported through several chlorophylls to a specialized one called Reaction Center. The energy is then transferred to the electron transport system.

8. Photosynthesis There are two kinds of photosystem in modern plants. Old plants had only one and were not very efficient. A second photosystem evolved in front of it.

9. Photosynthesis Photosystem I pigment molecule absorbs light and excites an electron. The electron couples with a proton (H + ) from water and moves along a chain of membrane bound carriers. The breaking of water releases O 2 . The energy absorbed from the photon is used to transport the proton into the thylakoid. Diffusion of the proton out creates ATP in a process called Chemiosmosis .