Autotroph: Organism that produces its own food (usually via photosynthesis).
Heterotroph: Organism that obtains energy by consuming other organisms.

Chloroplast.

To allow gas exchange (CO₂ enters, O₂ exits).

They lacked structures to prevent water loss and required water for reproduction.

Similarities: Both involve electron transport chains and ATP production.
Differences: Photosynthesis stores energy (makes glucose); respiration releases energy (breaks glucose).

Light reactions: Occur in thylakoid membranes, require light, produce ATP & NADPH.
Calvin Cycle: Occurs in stroma, uses ATP & NADPH to fix CO₂ into sugar.

It builds complex molecules (glucose) from simpler ones (CO₂ and H₂O).

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

Red.

Shorter blue wavelengths scatter more in the atmosphere (Rayleigh scattering).

Chlorophyll a: Primary pigment in reaction center.
Chlorophyll b: Accessory pigment that broadens light absorption.

Accessory pigments that absorb excess light and provide photoprotection.

Chlorophyll breaks down, revealing carotenoids and anthocyanins.

Chlorophyll reflects green wavelengths.

C3: Direct CO₂ fixation via Calvin Cycle.
C4: CO₂ initially fixed into 4-carbon compounds to reduce photorespiration.
CAM: CO₂ fixed at night to conserve water.

C3: Cool, moist environments.
C4: Hot, sunny environments.
CAM: Arid/desert environments.

C3: Efficient in cool/moist climates; prone to photorespiration.
C4: Reduces photorespiration; requires extra ATP.
CAM: Conserves water; slower growth.