Photosynthesis Overview Quiz

Photosynthesis: Using Light to Make Food

Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy that can be used to fuel the organism's activities.
Autotrophs are organisms that can produce their own food, such as plants.
Photoautotrophs are a type of autotroph that uses light energy to produce food.
Producers are organisms that produce their own food and are the basis of most food chains.
Heterotrophs are organisms that cannot produce their own food and must obtain it from other organisms.
Benefits of photoautotrophs: Produce oxygen, provide food for heterotrophs, support diverse ecosystems.
Leaf Structure: Leaves are the primary sites of photosynthesis. Contains chloroplasts, which are responsible for capturing light energy.
Chloroplasts: Organelles within plant cells containing chlorophyll and other pigments that absorb light energy.
Redox Reactions: Photosynthesis and cellular respiration involve oxidation-reduction reactions in which electrons are transferred between molecules.
Photosynthesis Chemical Formula: 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2
Photosynthesis Stages: Two stages, the light-dependent reactions and the Calvin Cycle.
- Light-dependent reactions: Occur within the thylakoid membranes of chloroplasts and require light to convert light energy into chemical energy (ATP and NADPH).
- Calvin Cycle: Occurs in the stroma of chloroplasts and uses ATP and NADPH to convert carbon dioxide into glucose.
Photon: A particle of light energy.
Photosynthetic Pigments: Absorb different wavelengths of light.
- Chlorophyll a is the primary pigment that absorbs red and blue light.
- Chlorophyll b absorbs blue and orange light.
- Carotenoids absorb blue and green light and give plants their orange and yellow colors.
Photosystems: In chloroplasts, photosystems are groups of pigments and proteins that work together to capture light energy.
- Photosystem II: Captures light energy and uses it to split water molecules, releasing oxygen.
- Photosystem I: Captures light energy and uses it to generate NADPH.
Light Reactions:
- Step 1: Light energy is captured by photosystems II and I.
- Step 2: Water molecules are split, releasing oxygen.
- Step 3: Electrons flow through an electron transport chain, generating ATP.
- Step 4: Light energy is used to produce NADPH.
Photophosphorylation: The process by which light energy is used to generate ATP.
Calvin Cycle:
- Step 1: Carbon dioxide is incorporated into an organic molecule, RuBP (ribulose bisphosphate).
- Step 2: The molecule containing carbon dioxide is reduced, using energy from ATP and NADPH.
- Step 3: RuBP is regenerated.
Glucose Production: Six turns of the Calvin Cycle are required to produce one glucose molecule.
C3, C4, and CAM Plants: Differ in how they obtain and use carbon dioxide:
- C3 plants: Most common type of plant; the first stable product of carbon fixation is a 3-carbon compound (PGA).
- C4 plants: Adapt to hot, dry climates; first product of carbon fixation is a 4-carbon compound (oxaloacetate).
- CAM plants: Adapt to very dry climates; open their stomata at night to take in carbon dioxide and store it as a 4-carbon compound.
Uses of Sugars Made by Photosynthesis:
- Provide energy for growth and development of the plant.
- Used to make other molecules such as cellulose, starch, and proteins.
- Stored as food reserves.

Cellular Respiration vs. Photosynthesis

Cellular respiration occurs in all living organisms, breaking down glucose to release energy in the form of ATP
Photosynthesis is carried out by plants and some bacteria, capturing light energy to convert carbon dioxide and water into glucose and oxygen

Breathing and Cellular Respiration

Breathing provides oxygen needed for cellular respiration and removes carbon dioxide produced by cellular respiration

Cellular Respiration Overview

Chemical equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP)
Reactants: Glucose (C6H12O6) and oxygen (O2)
Products: Carbon dioxide (CO2), water (H2O), and ATP (energy)
Efficiency: Approximately 34% of energy from glucose is captured by cellular respiration, the remaining 66% is released as heat

Redox Reactions in Cellular Respiration

Oxidation: Loss of electrons, often accompanied by loss of hydrogen atoms
Reduction: Gain of electrons, often accompanied by gain of hydrogen atoms
Redox reactions involve the transfer of electrons from one molecule to another

Roles of NAD+ and FAD

NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are electron carriers
During cellular respiration, they accept electrons from glucose and shuttle them to the electron transport chain

Aerobic vs. Anaerobic

Aerobic: Requires oxygen
Anaerobic: Does not require oxygen

Stages of Cellular Respiration

Glycolysis: Occurs in the cytoplasm, yielding 2 ATP and 2 pyruvate molecules per glucose molecule, anaerobic
Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix, produces 2 ATP per glucose molecule, aerobic
Oxidative Phosphorylation: Occurs in the mitochondrial inner membrane, generates the majority of ATP (approximately 32 ATP per glucose molecule), aerobic

Glycolysis

Breakdown of glucose into two pyruvate molecules
Substrate-level phosphorylation: ATP is generated by directly transferring a phosphate group from a substrate molecule to ADP

Citric Acid Cycle

Series of reactions that oxidizes pyruvate, generating CO2, NADH, FADH2, and ATP
Requires two cycles to break down a single glucose molecule

Oxidative Phosphorylation

Uses electron transport chain and chemiosmosis
Electron transport chain: Electrons from NADH and FADH2 are passed from carrier to carrier, releasing energy that pumps protons (H+) across the inner mitochondrial membrane
Chemiosmosis: Protons flow back through ATP synthase, driving the synthesis of ATP

ATP Production

Total ATP produced: Approximately 38 ATP per glucose molecule
Substrate-level phosphorylation: 4 ATP (2 from glycolysis and 2 from the citric acid cycle)
Oxidative phosphorylation: Approximately 34 ATP

Fermentation

Anaerobic process that allows glycolysis to continue in the absence of oxygen
Produces only 2 ATP per glucose molecule
Lactic acid fermentation: Pyruvate is converted to lactate
Alcoholic fermentation: Pyruvate is converted to ethanol and CO2

Fuel Sources for Cellular Respiration

Carbohydrates: Primary fuel source
Fats: Can be broken down into glycerol and fatty acids, which enter cellular respiration at different stages
Proteins: Can be broken down into amino acids, which can be used to synthesize glucose or enter the citric acid cycle