bio 120 - chapter 4and 5 - photosynthesis and cellular respiration

Photosynthesis overall equation

CO₂ + H₂O + light energy → C₆H₁₂O₆ + O₂.

Photosynthesis vs. cellular respiration

Photosynthesis stores light energy in glucose; cellular respiration breaks down fuel molecules to make ATP.

Photosynthesis inputs

Water, carbon dioxide, and light energy.

Role of water in photosynthesis

Water provides electrons and hydrogen; oxygen is released when water is split during the light-dependent reactions.

Role of light

Provides energy that excites electrons during the light-dependent reactions.

Role of carbon dioxide

Provides carbon atoms that are incorporated into organic molecules during the Calvin cycle.

Why are many plants green?

Chlorophyll absorbs much of the red and blue light but reflects green light.

Chlorophyll location

In the thylakoid membranes of chloroplasts.

Chloroplast

The organelle where photosynthesis occurs in plant and algal cells.

Stroma

Fluid-filled space inside a chloroplast where the Calvin cycle occurs.

Thylakoid

A flattened membrane sac inside a chloroplast where the light-dependent reactions occur.

Granum/grana

A stack of thylakoids.

Light-dependent reactions

The first major stage of photosynthesis; they use light and water to make ATP and NADPH and release oxygen.

Light-dependent reaction inputs

Light, water, ADP + phosphate, and NADP⁺.

Light-dependent reaction outputs

Oxygen, ATP, and NADPH.

Location of light-dependent reactions

Thylakoid membranes of the chloroplast.

Calvin cycle

A series of reactions that use CO₂, ATP, and NADPH to build G3P, which can be used to make sugars.

Calvin cycle inputs

CO₂, ATP, and NADPH.

Calvin cycle outputs

G3P and regenerated ADP/Pi and NADP⁺.

Location of Calvin cycle

Stroma of the chloroplast.

C3 plants

Plants that use the standard Calvin-cycle pathway and initially fix CO₂ into a three-carbon compound.

C4 plants

Plants that use an additional carbon-fixation pathway that helps reduce photorespiration, especially in hot, bright conditions.

CAM plants

Plants that open stomata at night to take in CO₂ and store it for use during the day, conserving water.

Stomata

Tiny openings, usually in leaves, that allow gas exchange and help regulate water loss.

Cellular respiration equation

C₆H₁₂O₆ + O₂ → CO₂ + H₂O + ATP.

What organisms perform cellular respiration?

Cells of essentially all living organisms use cellular respiration or related metabolic pathways to obtain usable energy.

Aerobic respiration

Energy-releasing pathways that use oxygen.

Anaerobic metabolism

Energy-releasing pathways that do not require oxygen.

Three main stages of aerobic cellular respiration

Glycolysis → Krebs/citric acid cycle → electron transport chain and oxidative phosphorylation.

ATP

Adenosine triphosphate; the cell's main immediately usable energy currency.

Glycolysis

The pathway that splits one glucose molecule into two pyruvate molecules and produces a net gain of ATP and NADH.

Where does glycolysis occur?

In the cytosol.

Does glycolysis require oxygen?

No. Glycolysis does not directly require oxygen.

Glycolysis starting material

One glucose molecule.

Glycolysis products

Two pyruvate, net ATP, and NADH.

Krebs/citric acid cycle location

Mitochondrial matrix in eukaryotic cells.

What enters the Krebs cycle?

Acetyl-CoA.

Krebs cycle products

CO₂, ATP (or GTP), NADH, and FADH₂.

Major players in the Krebs cycle

Acetyl-CoA, NAD⁺, FAD, ADP/GDP, and enzymes of the cycle.

Electron transport chain location

Inner mitochondrial membrane in eukaryotic cells.

What enters the electron transport chain?

Electrons carried by NADH and FADH₂.

Role of oxygen in the ETC

Oxygen is the final electron acceptor and combines with electrons and hydrogen ions to form water.

Which stage produces the most ATP?

The electron transport chain and oxidative phosphorylation produce the largest share of ATP.

How is the respiratory ETC similar to the photosynthetic ETC?

Both use electron carriers and a proton gradient across a membrane to power ATP production.

What happens if oxygen is unavailable after glycolysis?

Cells can use fermentation to regenerate NAD⁺ so glycolysis can continue producing a small amount of ATP.

Lactic acid fermentation

A pathway that converts pyruvate into lactate and regenerates NAD⁺; it can occur in muscle cells when oxygen availability is limited.

Alcoholic fermentation

A pathway used by organisms such as yeast that produces ethanol and CO₂ while regenerating NAD⁺.

Aerobic vs. fermentation

Aerobic respiration uses oxygen and produces much more ATP; fermentation does not use oxygen and allows glycolysis to continue but produces much less ATP.

What happens during hard exercise when oxygen is limited?

Muscle cells may rely more on fermentation, producing lactate.