Light Reactions- Photosynthesis

Photosynthesis Equation

sunlight + 6H₂O + 6CO₂ → C₆H₁₂O₆ + 6O₂

Photoautotrophs

use light as an energy source to produce organic compounds

Heterotrophs

must obtain energy and carbon by consuming other organisms or organic matter

Cellular Respiration Equation

C₆H₁₂O₆ + 6O₂ + ADP + P_i → 6H₂O + 6CO₂ + ATP + heat

Anabolic Process

build larger molecules from smaller ones

What process is photosynthesis?

anabolic

Catabolic Process

break down large molecules into smaller ones

What process is cellular respiration?

catabolic

How much of the earth’s oxygen comes from the ocean?

50%

Photosynthetic pigments

absorb different wavelengths of solar energy

Chlorophyll a

primary photosynthetic pigment in plants, algae, cyanobacteria

Chlorophyll b

accessory pigment that broadens light harvesting in plants, green algae, and a few cyanobacteria

Why are plants green?

the pigments do not absorb green wavelength

Why do leaves change color in fall/winter?

less sunlight so less wavelength to absorb so carotids are main factor; they absorb the complementary color to red/yellow

Chloroplasts

double-membraned organelles in plants and algae that contain chlorophyll a, chlorophyll b, and carotenoids

Stomata

openings that control the diffusion of CO₂ and O₂

Thylakoid membrane

stacked into grana and key component in ATP synthesis for photosynthesis

Where does photosynthesis occur in plants?

chloroplasts

Stroma

space surrounding thylakoid membrane but inside chloroplast membrane

Photosystems

complexes of proteins and pigments that harvest light energy; includes chlorophylls and carotenoids

Reaction Center

special pair of chlorophyll molecules where energy is focused, causing a high-energy electron to leave the photosystem

Light Reaction

light excites electrons in photosystem 2; water splits, releasing O₂, protons, and electrons; electrons travel down ETC to photosystem 1 which releases energy to pump H⁺ into thylakoid lumen, building a gradient; H⁺ flow down the gradient back into the stroma, passively passing through ATP synthase which drives ATP production; NADPH is also produced

ATP

adenosine triphosphate; universal energy-carrying molecule in cells that power biological processes

Chemiosmosis

H⁺ passing through ATP synthase to drive ATP production; all down passively

How far is photosynthesis after light reactions are completeed?

halfway

Matter is

CO₂