Photosynthesis & Cellular Respiration Review

Photosynthesis

The process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen.

Chloroplast

The organelle in plant cells where photosynthesis occurs.

Chlorophyll

A green pigment that absorbs light energy, mainly blue and red wavelengths.

Light reactions

The first stage of photosynthesis that uses light energy to produce ATP, NADPH, and oxygen.

Calvin cycle

The second stage of photosynthesis that uses ATP and NADPH to build sugar (G3P).

Thylakoid

A membrane structure inside the chloroplast where the light reactions occur.

Stroma

The fluid-filled space surrounding the thylakoids where the Calvin cycle occurs.

Photosystem I & II

Groups of proteins and pigments that absorb light energy and excite electrons.

Water splitting (photolysis)

The splitting of water molecules during the light reactions to produce oxygen, electrons, and hydrogen ions.

Oxygen (O₂)

A waste product of photosynthesis and a reactant in cellular respiration.

ATP

The main energy-carrying molecule used by cells.

NADPH

An electron carrier produced in the light reactions and used in the Calvin cycle.

ADP

A low-energy molecule that becomes ATP when a phosphate is added.

NADP⁺

An electron carrier that becomes NADPH after gaining electrons.

Glucose

A six-carbon sugar that stores chemical energy.

RuBisCO

An enzyme that attaches carbon dioxide to RuBP in the Calvin cycle.

Chemiosmosis

The process of making ATP using a proton gradient and ATP synthase.

Endergonic reaction

A reaction that requires energy input (photosynthesis).

Cellular respiration

The process by which cells break down glucose to release energy in the form of ATP.

Glucose

The primary fuel molecule used in cellular respiration.

Glycolysis

The first stage of cellular respiration that breaks glucose into pyruvate in the cytoplasm.

Pyruvate

A three-carbon molecule produced during glycolysis.

Citric acid cycle (Krebs cycle)

The stage of respiration that releases CO₂ and transfers energy to electron carriers.

Electron transport chain (ETC)

A series of proteins that transfer electrons and create a proton gradient.

Oxidative phosphorylation

ATP production using the ETC and chemiosmosis.

ATP synthase

An enzyme that produces ATP as protons flow through it.

Proton gradient

A difference in hydrogen ion concentration across a membrane.

NADH

An electron carrier that delivers electrons to the ETC.

FADH₂

Another electron carrier that delivers electrons to the ETC.

Oxygen (final electron acceptor)

The molecule that accepts electrons at the end of the ETC, forming water.

Carbon dioxide (CO₂)

A waste product released during the citric acid cycle.

Water (H₂O)

A product of cellular respiration formed when oxygen accepts electrons.

Aerobic respiration

Respiration that requires oxygen.

Anaerobic respiration

Respiration that occurs without oxygen.

Fermentation

An anaerobic pathway that allows glycolysis to continue without oxygen.

Mitochondrial matrix

The inner space of the mitochondrion where the citric acid cycle occurs.

Inner mitochondrial membrane

The location of the electron transport chain.

Exergonic reaction

A reaction that releases energy (cellular respiration).

ATP (energy currency)

The molecule cells use for immediate energy.

Electrons

High-energy particles transferred during chemical reactions.

Energy transfer

The movement of energy through chemical reactions.

Enzymes

Proteins that speed up chemical reactions.

1. Explain how light energy is converted into chemical energy during photosynthesis.

Light energy is absorbed by chlorophyll, exciting electrons. This energy is used to make ATP and NADPH, which store chemical energy.

2. Describe the role of water in the light reactions and explain how oxygen is produced.

Water is split during the light reactions to provide electrons and hydrogen ions. Oxygen is released as a waste product.

3. Compare the inputs and outputs of the light reactions and the Calvin cycle.

Light reactions use light and water to produce ATP, NADPH, and oxygen. The Calvin cycle uses ATP, NADPH, and CO₂ to produce G3P.

4. Why does the Calvin cycle depend on the light reactions even though it does not require light directly?

The Calvin cycle needs ATP and NADPH, which are only produced during the light reactions.

5. How does chlorophyll’s absorption of light affect the rate of photosynthesis?

Photosynthesis occurs faster at wavelengths where chlorophyll absorbs the most light.

6. Trace the path of a glucose molecule through cellular respiration.

Glucose is broken down in glycolysis (cytoplasm), then enters the citric acid cycle (mitochondrial matrix), and finally the ETC (inner membrane).

7. Explain why oxygen is essential for aerobic respiration.

Oxygen accepts electrons at the end of the ETC, allowing ATP production to continue.

8. Describe how ATP synthase uses a proton gradient to make ATP.

Protons flow through ATP synthase, releasing energy used to combine ADP and phosphate into ATP.

9. Why does blocking the electron transport chain cause cells to die?

Without the ETC, ATP cannot be produced efficiently, leading to an energy shortage.

10. Compare aerobic respiration and fermentation.

Aerobic respiration uses oxygen and produces much more ATP. Fermentation occurs without oxygen and produces only a small amount of ATP.

11. Explain how photosynthesis and cellular respiration are interdependent.

Photosynthesis produces glucose and oxygen, which are used in respiration. Respiration produces CO₂ and water, which are used in photosynthesis.

12. Describe how energy flows through both processes.

Energy enters ecosystems as sunlight, is stored in glucose during photosynthesis, and is released as ATP during respiration.

13. Why is the transfer of electrons central to both photosynthesis and cellular respiration?

Electron transfers release energy that is used to produce ATP in both processes.