Notes on Photosynthesis & Cellular Respiration

Autotrophs and Heterotrophs

Organisms that use light energy from the sun to produce food are autotrophs (auto = self).
- Examples: plants and some microorganisms (some bacteria and protists).
Organisms that cannot use the sun's energy to make food are heterotrophs.
- Examples: animals and most microorganisms.

Photosynthesis is the process by which the energy of sunlight is converted into the energy of glucose.
Inputs: sunlight (light energy), carbon dioxide, and water.
Outputs: glucose and oxygen.
Key idea: energy from sunlight is converted into chemical energy stored in glucose.
Occurs in plants and some algae; takes place in chloroplasts using chlorophyll, the green pigment in plants.
Chlorophyll absorbs light for photosynthesis; as chlorophyll decays in autumn, green fades and oranges/reds appear due to carotenoids and other pigments.

The process of changing light energy to chemical energy.
Energy stored as sugar (glucose).
Occurs in plants and some algae.
Plants need light energy, CO₂, and H₂O.
Takes place in the chloroplasts, using chlorophyll, the green pigment in plants.

Chlorophyll is the pigment inside the chloroplast that absorbs light for photosynthesis.
As chlorophyll in leaves decays in autumn, the green color fades and is replaced by oranges and reds of carotenoids and other pigments.

Plants capture light energy and use that energy to make glucose.
Sunlight provides the energy needed by chlorophyll to change molecules of carbon dioxide and water into glucose.
Oxygen is also released in this reaction.

Carbon dioxide enters the leaf through holes called stomata.
CO₂ combines with the stored energy in the chloroplasts through a chemical reaction to make glucose.

Photosynthesis occurs in the chloroplasts of plants.
Leaf anatomy: Mesophyll, Leaf cross section, Stomata, Vein.
Internal chloroplast structures: Chloroplast, Granum (grana), Thylakoid, Thylakoid space, Stroma, Outer membrane, Inner membrane, Intermembrane space.
Scale reference shown: about 5 (\mu\text{m}) (5 μm).

The sugar is moved through tubes in the leaf to the roots, stems, and fruits.
Some sugar is used immediately by the plant for energy; some is stored as starch; some is built into plant tissue.

Once energy from sunlight has been captured and stored as chemical energy in glucose, organisms transform that chemical energy into a form usable by the organism (ATP) through cellular respiration.
Cellular respiration is the process by which the energy of glucose is released in the cell to be used for life processes (movement, breathing, blood circulation, etc.).

Respiration occurs in ALL cells and can take place either with or without oxygen present.
Occurs in plant and animal cells; mitochondria are the main site.

CO₂ + H₂O + Light energy (from the sun) drives photosynthesis in chloroplasts.
Cellular respiration in mitochondria releases energy stored in organic molecules, producing ATP.
Overall energy flow: Organic molecules + O₂ → ATP + Heat energy; photosynthesis stores energy as glucose, respiration releases it for cellular work and heat.