plant development, growth and structure

- Most life on Earth depends on photosynthesis.

• The process is carried out by plants, algae, and some types of bacteria, which capture energy from sunlight to produce oxygen (O2) and chemical energy stored in glucose (a sugar).

• Herbivores then obtain this energy by eating plants, and carnivores obtain it by eating herbivores.

- During photosynthesis

• plants take in carbon dioxide (CO2) and water (H2O) from the air and soil.

• Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons.

• This transforms the water into oxygen and the carbon dioxide into glucose.

• The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.

- Inside the plant cell are small organelles called chloroplasts,

• which store the energy of sunlight.

Within the thylakoid membranes of the chloroplast is

• a light-absorbing pigment called chlorophyll, (which is responsible for giving the plant its green color).

During photosynthesis,

• chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green.

- While there are many steps behind the process of photosynthesis, it can be broken down into two major stages:

• light-dependent reactions

• light-independent reactions.

The light-dependent reaction takes place within the

• thylakoid membrane and requires a steady stream of sunlight, hence the name light-dependent reaction

The chlorophyll absorbs energy from the light waves

• which is converted into chemical energy in the form of the molecules ATP and NADPH.

The light-independent stage, also known as the Calvin Cycle

• takes place in the stroma, the space between the thylakoid membranes and the chloroplast membranes, and does not require light, hence the name light-independent reaction. During this stage, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide.

Not all forms of photosynthesis are created equal, however.

• There are different types of photosynthesis, including C3 photosynthesis and C4 photosynthesis.