Chapter 2Cell Processes and Energy

Section 1Photosynthesis

What Is Photosynthesis?

• Every living thing needs energy to carry out its functions.

• Our food contains the energy we need, but plants and bacteria-like organisms get energy in a different way.

• Photosynthesis is the process by which a cell captures the energy in sunlight and uses it to make food.

A Two-Stage Process

• During photosynthesis, plants and some other organisms use energy from the sun to convert carbon dioxide and water into oxygen and sugars, including glucose.

• The entire process can be put into two stages:– Capturing the sun’s energy– Producing sugars

Capturing the Sun’s Energy

• The chloroplasts of a cell give the plant its green color due to the presence of pigments, which are colored chemical compounds that absorb light (like a solar panel).

• The main pigment found in the chloroplasts of plants is chlorophyll.

Producing Sugars

• The cell needs H2O and CO2 to produce sugars.

• The plant can obtain H2O from its roots and CO2 from the air around it through little openings on the underside of leaves called stomata (the singular would be stoma).

Producing Sugars

• Once inside the chloroplasts, H2O and CO2 undergo a number of chemical reactions powered by the sunlight captured by the pigments.

• These reactions create O2 and sugars, including glucose (C6H12O6)

The Photosynthesis Equation

• The cells break down the sugars to use for energy or to store them for later use.

• Most of the oxygen is released through the stomata and into the air.

Photosynthesis and Life

• About 21% of our atmosphere contains oxygen, thanks to photosynthesis, which we need to survive.

• Nearly all living things obtain energy either directly (autotrophs) or indirectly (heterotrophs) from the energy of sunlight captured during photosynthesis.

Photosynthesis and the Circle of Life