Bioenergetics

Photosynthesis

"Endothermic reaction where plants use light energy to convert CO₂ and water into glucose and oxygen."

Photosynthesis word equation

"Carbon dioxide + water → glucose + oxygen."

Photosynthesis balanced symbol equation

"6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂."

Chlorophyll

"Green pigment in chloroplasts that absorbs light energy."

Limiting factor

"Factor that stops photosynthesis increasing when others are in excess."

Limiting factors of photosynthesis

"Light intensity

Light intensity effect

"Higher light increases rate until another factor becomes limiting."

Temperature effect

"Rate increases to optimum; too high → enzymes denature."

CO₂ concentration effect

"Higher CO₂ increases rate until plateau."

Chlorophyll effect

"Less chlorophyll reduces photosynthesis (e.g.

Inverse square law

"Light intensity ∝ 1 ÷ distance²."

Inverse square law formula

"Light intensity = 1 ÷ distance²."

Why light decreases with distance

"Light spreads out

Uses of glucose

"Respiration

Why store glucose as starch

"Insoluble so does not affect osmosis; compact energy store."

Amino acid production in plants

"Glucose + nitrate ions → amino acids for protein synthesis."

Respiration

"Exothermic reaction releasing energy from glucose."

Uses of respiration energy

"Muscle contraction

Aerobic respiration word equation

"Glucose + oxygen → carbon dioxide + water."

Aerobic respiration balanced equation

"C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O."

Where aerobic respiration occurs

"Mitochondria."

Anaerobic respiration in animals

"Glucose → lactic acid."

Why anaerobic releases less energy

"Glucose not fully oxidised."

Anaerobic respiration in plants and yeast

"Glucose → ethanol + carbon dioxide."

Fermentation use

"Yeast fermentation used in making bread and alcoholic drinks."

Oxygen debt

"Extra oxygen needed to oxidise lactic acid after exercise."

How lactic acid is removed

"Transported to liver to be broken down."

Why heart rate increases during exercise

"More oxygen and glucose delivered to muscles; more CO₂ removed."

Metabolism

"Sum of all chemical reactions in the body."

Examples of metabolic reactions

"Protein synthesis

Factors affecting photosynthesis practical

"Light intensity

Required practical: photosynthesis

"Investigate effect of light intensity on photosynthesis using pondweed."

How to measure photosynthesis rate

"Count oxygen bubbles or measure volume of gas produced."

Why use LED lamp

"Produces less heat

Why repeat measurements

"Improves reliability and reduces anomalies."

Why green light is least effective

"Chlorophyll reflects green light instead of absorbing it."

Starch test

"Use iodine to detect starch → blue-black result."

De-starching leaves

"Leave plant in darkness to use all stored starch."

Temperature and enzyme activity

"Higher temperature increases collisions until enzymes denature."

Why plants need nitrates

"To make amino acids and proteins."

Why plants need magnesium ions

"To make chlorophyll; deficiency causes yellow leaves."

Adaptations of leaves

"Large surface area

Stomata role in photosynthesis

"Allow CO₂ to diffuse in and O₂ out."

Guard cells

"Control stomatal opening to balance photosynthesis and water loss."

Glucose for cellulose

"Used to strengthen cell walls."

Glucose for lipids

"Stored in seeds for energy."

Glucose stored as starch

"Insoluble and ideal for long-term storage."

Muscle fatigue

"When muscles are unable to contract efficiently due to lactic acid build-up."

Breathing rate during exercise

"Increases to supply oxygen and remove CO₂ faster."

Heart rate sensor

"Measures pulse to monitor respiration rate changes."

Advantages of anaerobic respiration

"Provides rapid energy when oxygen supply is limited."

Disadvantages of anaerobic respiration

"Causes lactic acid build-up and fatigue."

Respiration vs photosynthesis relationship

"Photosynthesis stores energy; respiration releases energy."

Why plants respire at night

"No light available so no photosynthesis."

Endothermic process example

"Photosynthesis (takes in energy)."

Exothermic process example

"Respiration (releases energy)."