Photosynthesis and Plants

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.

Inside a Leaf

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).

Chloroplasts

Photosynthetic reaction: 6CO2 + 12H2O + Light C6H12O6 + 6H2O + 6O2

Photosynthesis

Made up of Light dependant reactions and light independent reactionsLight reactions and dark reactions.Light reactions capture sunlight, release O2 and produce high energy compounds like ATP.Dark reactions in the stroma use the energy from light reactions with enzymes and CO2 to produce organic molecules.

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.

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.

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 O2.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.