Photosynthesis (Cambridge O Level Biology 6.1) – Key Vocabulary

Vocabulary flashcards covering definitions and key terms related to photosynthesis, experiments, factors affecting the rate, and associated plant processes.

Photosynthesis

The process by which green plants manufacture carbohydrates from carbon dioxide and water using light energy, releasing oxygen as a by-product.

Chlorophyll

Green pigment in chloroplasts that absorbs light energy and converts it into chemical energy for photosynthesis.

Glucose (C₆H₁₂O₆)

Main carbohydrate product of photosynthesis that can be used in respiration or converted into other molecules.

Word equation for photosynthesis

Carbon dioxide + water —(light, chlorophyll)→ glucose + oxygen.

Balanced chemical equation for photosynthesis

6CO₂ + 6H₂O —(light, chlorophyll)→ C₆H₁₂O₆ + 6O₂.

Raw materials of photosynthesis

Carbon dioxide and water (light energy is needed but is not a raw material).

Chloroplast

Organelle containing chlorophyll where photosynthesis occurs.

Chemical energy

Energy stored in the bonds of glucose molecules produced during photosynthesis.

Starch

Insoluble carbohydrate used by plants to store glucose made in photosynthesis.

Cellulose

Structural polysaccharide formed from glucose; makes up plant cell walls.

Sucrose

Transport form of carbohydrate in phloem, produced from glucose.

Lipids

Energy-rich compounds that plants can synthesise from carbohydrates.

Amino acids

Building blocks of proteins, synthesised by plants from carbohydrates and nitrate ions.

Starch test (iodine test)

Blue-black colour change with iodine solution indicating starch presence in a leaf.

Ethanol (in starch test)

Solvent used to remove chlorophyll from a leaf so iodine colour changes are visible.

Variegated leaf experiment

Test showing chlorophyll is required for photosynthesis; only green areas turn blue-black with iodine.

Aluminium foil experiment

Method to demonstrate that light is needed for photosynthesis by covering part of a leaf.

Sodium hydroxide (CO₂ removal)

Chemical placed in a bell jar to absorb carbon dioxide and show its necessity for photosynthesis.

Bell jar setup

Closed container used with chemicals (e.g., NaOH or water) to create controlled atmospheres for plant experiments.

Limiting factor

Environmental factor in shortest supply that restricts the rate of photosynthesis.

Light intensity

Amount of light energy reaching a plant; directly affects photosynthetic rate until another factor becomes limiting.

Carbon dioxide concentration

Level of CO₂ available; increasing it raises photosynthetic rate until another factor limits.

Temperature (photosynthesis)

Affects enzyme activity; rate rises with temperature until enzymes denature at high levels.

Denaturation

Loss of specific enzyme shape at extreme temperatures, stopping catalytic activity.

Kinetic energy (molecules)

Energy of molecular motion that increases with temperature, influencing reaction rates.

Elodea / Cabomba

Aquatic pondweeds commonly used to measure photosynthetic oxygen production in lab experiments.

Sodium hydrogencarbonate

Chemical dissolved in water to vary carbon dioxide concentration for photosynthesis investigations.

Hydrogencarbonate indicator

pH indicator that changes colour with CO₂ concentration, used to assess photosynthetic activity.

Hydrogencarbonate indicator colours

Yellow (high CO₂), orange (above atmospheric), red (atmospheric), magenta (low), purple (very low).

Aerobic respiration equation

Exact reverse of photosynthesis: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy).

Phloem

Plant tissue that transports sucrose and other organic nutrients.

Enzymes (in photosynthesis)

Protein catalysts controlling photosynthetic reactions; temperature sensitive.

Gas volume / bubble count

Quantitative measure of oxygen production used to estimate photosynthetic rate in aquatic plants.

Control variables

Factors kept constant (e.g., distance of lamp, temperature) to ensure a valid photosynthesis experiment.

Glass tank (heat shield)

Barrier placed between lamp and beaker to stop temperature from varying when investigating light intensity.