Bioenergetics

What is the word equation for photosynthesis?

Carbon dioxide + Water → Glucose + Oxygen (in the presence of light and chlorophyll).

What is the balanced symbol equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy and chlorophyll required).

Why is photosynthesis described as an endothermic reaction?

Photosynthesis is endothermic because it absorbs energy from the surroundings (light energy from the sun). Energy is taken in to convert simple inorganic molecules into complex organic glucose molecules. .

Explain the role of chloroplasts and light in photosynthesis.

Chloroplasts: Contain chlorophyll which absorbs light energy. They are the site of photosynthesis with specialized structures.

Light: Provides the energy needed to drive the endothermic reaction. Different wavelengths are absorbed by chlorophyll, with red and blue light being most effective.

How does temperature affect the rate of photosynthesis?

Low temperatures: Rate is slow because enzyme activity is reduced.

Optimum temperature (25-35°C): Maximum rate as enzymes work efficiently.

High temperatures (>40°C): Rate decreases rapidly as enzymes denature.

How does light intensity affect the rate of photosynthesis?

Low light intensity: Rate is directly proportional to light intensity (limiting factor).

Medium light intensity: Rate increases but levels off.

High light intensity: Rate plateaus as other factors become limiting.

How does carbon dioxide concentration affect the rate of photosynthesis?

Low CO₂: Rate is limited as insufficient raw material for glucose production.

Increasing CO₂: Rate increases proportionally up to optimum level.

High CO₂: Rate plateaus as CO₂ is no longer the limiting factor.

How does chlorophyll level affect the rate of photosynthesis?

More chlorophyll = Higher rate up to saturation point.

Chlorophyll is essential for light absorption, so plants with variegated leaves have lower rates in white areas (no chlorophyll)

mineral deficiencies reduce chlorophyll production

disease damages chloroplasts reducing photosynthesis.

How do you measure and calculate the rate of photosynthesis?

Methods: 1) Count oxygen bubbles produced by aquatic plants

2) Measure volume of gas collected over time

3) Measure mass change in plants.

Rate Calculation: Rate = Change in measurement ÷ Time taken (e.g., Rate = Volume of O₂ produced (cm³) ÷ Time (minutes))

How do you interpret photosynthesis graphs with one limiting factor?

Three phases: 1) Steep increase: Factor is limiting, rate proportional to factor

2) Leveling off: Factor becoming less limiting

3) Plateau: Factor no longer limiting, another factor now limits rate. .

How do you interpret graphs showing multiple limiting factors in photosynthesis?

Key features: Multiple plateaus at different levels,

step-like increases when conditions change,

different curves for different factor combinations.

Example: Light intensity graph with different CO₂ concentrations shows higher plateaus at higher CO₂ levels.

How do you identify the limiting factor from photosynthesis graphs?

1) Rising section: The x-axis variable is limiting

2) Plateau section: Another factor (not on x-axis) is limiting

3) Compare multiple curves: The factor that separates the curves is limiting at plateau. Look for the factor that, when increased, causes the rate to increase.

What is the inverse square law and how does it apply to photosynthesis?

Law: Light intensity is proportional to 1/distance².

Formula: Light intensity = k/d² (where k is constant, d is distance).

Application: As distance from light source doubles, intensity becomes ¼ of original value. This explains why moving a lamp from 10cm to 20cm from a plant quarters the light intensity.

Discuss greenhouse conditions and economic considerations for photosynthesis.

Optimal conditions: Temperature: 25-30°C (heating costs vs. productivity),

CO₂: Enriched to 0.1% (cost of CO₂ vs. increased yield)

Light: Supplementary lighting in winter (electricity costs).

Economic balance: Cost of providing conditions vs. value of increased crop yield.

How do plants use glucose for respiration?

Plants use glucose in cellular respiration to release energy for: metabolic processes (growth, transport, reproduction), active transport of minerals, synthesis reactions (making proteins, lipids).

Equation: Glucose + Oxygen → Carbon dioxide + Water + ATP. This occurs continuously in all living plant cells.

Why do plants convert glucose to starch for storage?

Advantages of starch storage: Insoluble: Doesn't affect water potential/osmosis

Large molecule: Cannot pass through cell membranes

Compact: Stores more energy per unit volume than glucose

Chemically inactive: Doesn't interfere with metabolism.

How and why do plants convert glucose to fats and oils?

Process: Glucose → Glycerol + Fatty acids → Lipids.

Uses: Energy storage in seeds (more concentrated than starch), membrane components (phospholipids), protective coatings (waxy cuticles). Lipids contain more than twice the energy per gram compared to carbohydrates.

How is glucose used to make cellulose for cell walls?

Process: Glucose molecules join by condensation reactions to form cellulose chains.

Function: Cellulose provides structural support to maintain cell shape, tensile strength to resist stretching, rigidity for plant structure.

How do plants use glucose to make amino acids and proteins?

Process: 1) Glucose provides carbon skeleton for amino acids

2) Nitrate ions (NO₃⁻) provide nitrogen for amino groups

3) Amino acids join by peptide bonds to form proteins. Plants absorb nitrate ions from soil through active transport.

Why do plants need nitrate ions for protein production?

Essential for: amino acid synthesis (contain -NH₂ groups), protein formation (enzymes, structural proteins), chlorophyll production (contains nitrogen), DNA/RNA synthesis (contain nitrogen bases).

Deficiency symptoms: Yellowing leaves, stunted growth, reduced yield. Nitrogen is often the limiting nutrient in plant growth.

Why is respiration described as an exothermic reaction?

Respiration is exothermic because it releases energy to the surroundings. Chemical energy stored in glucose bonds is transferred to ATP and some is lost as heat.

Evidence: Body temperature increases during exercise due to heat release from increased respiration.

Compare aerobic and anaerobic respiration in terms of oxygen requirement, products, and energy yield.

Aerobic: Requires oxygen, produces CO₂ + H₂O, high energy yield (38 ATP), complete glucose breakdown.

Anaerobic: No oxygen required, produces lactic acid OR ethanol + CO₂, low energy yield (2 ATP), incomplete glucose breakdown. Aerobic respiration produces 19 times more ATP per glucose molecule.

What is the word and symbol equation for aerobic respiration?

Word equation: Glucose + Oxygen → Carbon dioxide + Water (+ Energy).

Symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ ATP).

What is the equation for anaerobic respiration in muscles?

Word equation: Glucose → Lactic acid (+ Energy).

Symbol equation: C₆H₁₂O₆ → 2C₃H₆O₃ (+ ATP).

When it occurs: During intense exercise when oxygen supply cannot meet demand in muscle cells. Lactic acid buildup causes muscle fatigue and burning sensation.

What is the equation for anaerobic respiration in yeast?

Word equation: Glucose → Ethanol + Carbon dioxide (+ Energy).

Symbol equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (+ ATP).

Applications: Bread making (CO₂ makes dough rise), alcohol production. This process is called alcoholic fermentation.

Define fermentation and explain its commercial uses.

Definition: Anaerobic respiration in microorganisms (especially yeast) that produces useful products.

Uses: Bread making (CO₂ makes dough rise, ethanol evaporates), alcohol production (wine, beer, spirits from fermented sugars), industrial (biofuels, pharmaceuticals, food additives).

Describe how heart rate and breathing change during exercise.

Heart rate increases: Pumps blood faster to supply oxygen and glucose to muscles, removes carbon dioxide and lactic acid more quickly.

Breathing rate and depth increase: Takes in more oxygen per minute, removes more carbon dioxide from blood, maintains blood pH by removing CO₂.

Explain why anaerobic respiration may occur during exercise.

Cause: Oxygen demand by muscles exceeds oxygen supply from breathing and circulation.

1) Exercise increases energy demand

2) Aerobic respiration cannot provide enough ATP

3) Anaerobic respiration supplements energy production

4) Lactic acid accumulates in muscles.

Define oxygen debt and explain why it occurs.

Definition: The amount of oxygen needed to remove lactic acid that built up during anaerobic respiration.

Why it occurs: Lactic acid must be oxidized to CO₂ and water or converted back to glucose. This requires additional oxygen after exercise ends. Heavy breathing continues until oxygen debt is repaid.

Explain how lactic acid is transported and converted after exercise.

Transport: Lactic acid moves from muscles into bloodstream and is carried to the liver.

Conversion in liver: 80% of lactic acid is oxidized to CO₂ and water (releases energy), 20% is converted back to glucose (gluconeogenesis).

Glucose can be stored as glycogen or returned to muscles.

Explain why muscle fatigue occurs during prolonged activity.

Causes of fatigue: Lactic acid accumulation interferes with muscle contraction, glucose depletion reduces available fuel for respiration, oxygen debt builds up as anaerobic respiration increases, pH changes affect enzyme function in muscle cells.

Recovery: Rest allows lactic acid removal and glucose/oxygen replenishment.

How would you design an investigation into the effects of exercise on the body?

Variables to measure: Heart rate (pulse counter/monitor), breathing rate (count breaths per minute), recovery time (time to return to resting rates). Method:

1) Measure resting rates

2) Exercise for set time/intensity

3) Measure rates immediately after and during recovery

4) Control variables: age, fitness, room temperature.

Define metabolism and explain its importance.

Definition: The sum of all chemical reactions taking place in a living organism.

Includes: Anabolic reactions (building up complex molecules/synthesis), catabolic reactions (breaking down complex molecules).

Importance: Controls growth, reproduction, maintenance, and response to environment.

Describe the metabolic conversions involving glucose.

Glucose can be converted to: Starch (plants) – energy storage,

glycogen (animals) – energy storage in liver/muscles,

cellulose (plants) – structural component of cell walls.

Process: Condensation reactions join glucose molecules with removal of water. These are anabolic reactions requiring energy input.

Explain how lipids are formed from glycerol and fatty acids.

Process: Condensation reactions join glycerol with fatty acids to form lipids . Metabolic significance: Energy storage (more concentrated than carbohydrates), membrane structure, insulation and protection.

Each molecule forms from one glycerol and three fatty acids.

Describe amino acid and protein synthesis in metabolism.

Amino acid synthesis: Requires carbon skeleton (from glucose) + nitrogen (from nitrates/ammonia).

Protein synthesis: Condensation reactions join amino acids with peptide bonds.

Metabolic importance: Enzymes control all metabolic reactions, structural proteins (collagen, keratin), transport proteins (hemoglobin).

Explain how proteins are broken down to form urea.

Process: 1) Proteins → Amino acids (hydrolysis with protease enzymes)

2) Amino acids → Ammonia + Organic acids (deamination in liver)

3) Ammonia → Urea (detoxification in liver – less toxic).

Why necessary: Excess amino acids cannot be stored and ammonia is toxic.

Explain the role of sugars, amino acids, fatty acids, and glycerol in metabolic synthesis and breakdown.

Building blocks: Sugars make (starch, glycogen, cellulose),

amino acids make proteins and enzymes,

fatty acids + glycerol make lipids for energy storage and membranes.

Breakdown products: Complex molecules broken down to these simple units, used for respiration (energy release) or resynthesis.