Photosynthesis & Cellular Respiration

Photosynthesis

The process by which a cell captures energy in sunlight and uses it to make food.

Nearly all living things obtain energy directly or indirectly from the sun.

Autotrophs-An organism that makes its own food.

Heterotrophs- An organism that cannot make its own food.

Two Stages of Photosynthesis

Stage 1- Capturing the Sun’s Energy- This happens inside the chloroplast!

Plants use energy from the sun to convert CO2 (carbon dioxide) and H2O (water) into O2 (oxygen) and sugars.

Pigments-Compounds that absorb light. In plants these are green!

Chlorophyll- The main photosyntheticpigment, found inside chloroplasts.

Stage 2

Using energy to make food- The cell needs H2O and CO2 for this stage.

The roots of the plant absorbwater. Then H2O moves to the chloroplasts.

CO2 enters the plant throughsmall openings in the leaves called stomata, then moves to the chloroplasts.

Photosynthesis Equation

6 CO2 + 6H2O –light energy---- C6H12O6 + 6 O2

H2O & CO2 with energy from the sun, go through complex chemical reactions to make O2 & sugars.

Respiration

Respiration is the process by which cells obtain energy from glucose (sugar).

During respiration, cells break down simple food molecules and release energy.

The Two Stages of Respiration

Step 1- Takes place in the cytoplasm, occurs without oxygen, and only a little energy is released.

Step 2- Takes place in the mitochondria, requires oxygen, and release a lot of energy.

The Respiration Equation

C6H12O6 + 6 O2 ------ 6 CO2 + 6 H2O + EnergyThe raw materials (or reactants) for

respiration are sugar and oxygen. The process of cellular respiration produces

CO2, H2O, and energy!

Comparing Photosynthesis and

RespirationHow do the equations for photosynthesis and

respiration relate to each other?

Review Questions

Why do living things need energy? What is the primary source of energy for all living

things? What are the substances needed for cellular

respiration? What substances are produced during

photosynthesis? Explain why cellular respiration adds carbon dioxide

to the atmosphere, but photosynthesis does not.