Unit 1 Topic 3 Biology 2025

Metabolism

All the chemical reactions occurring in a living organism.

Catabolism

Breakdown of complex molecules into simpler ones, releasing energy.

Anabolism

Synthesis of complex molecules from simpler ones, requiring energy.

ATP (Adenosine triphosphate)

A molecule that stores and transfers energy for use in cellular processes.

Energy coupling

The use of energy released from catabolic reactions to drive anabolic reactions via ATP.

Aerobic respiration

Cellular process that uses oxygen to convert glucose into ATP.

Glycolysis

First stage of respiration in the cytosol; breaks glucose into pyruvate, producing 2 ATP.

Krebs cycle

Second stage of aerobic respiration in mitochondria; produces CO₂, ATP, and electron carriers.

Electron transport chain (ETC)

Final stage in mitochondria that uses oxygen and produces most of the ATP.

Mitochondrion

Organelle where aerobic respiration takes place.

Overall equation (aerobic)

Glucose + Oxygen → Carbon dioxide + Water + ATP.

Anaerobic respiration

Respiration without oxygen; produces less ATP and by-products like lactic acid or ethanol.

Lactic acid

A by-product of anaerobic respiration in animals.

Fermentation

Anaerobic breakdown of glucose in yeast and bacteria, producing alcohol or acids.

Alveoli

Tiny air sacs in the lungs where gas exchange occurs.

Capillaries

Small blood vessels that allow exchange of gases and nutrients between blood and tissues.

Gas exchange

Movement of oxygen and carbon dioxide between alveoli and capillaries.

Diffusion

Passive movement of gases from high to low concentration.

Partial pressure

The concentration of a gas in a mixture; drives diffusion direction.

Oxygen gradient

Higher in alveoli than in capillary blood, so O₂ diffuses into blood.

Carbon dioxide gradient

Higher in blood than in alveoli, so CO₂ diffuses out.

Tissue exchange

Oxygen moves from blood to muscles; CO₂ moves from muscles to blood.

Photosynthesis

Process by which plants convert light energy into chemical energy (glucose).

Chloroplast

Organelle where photosynthesis occurs.

Light-dependent reactions

Occur in thylakoid membranes; use sunlight to produce ATP and NADPH.

Light-independent reactions

(Calvin cycle) Occur in the stroma; use ATP and NADPH to fix carbon into glucose.

Stomata

Pores in leaves that allow gas exchange.

Guard cells

Cells that control the opening and closing of stomata.

Overall equation (photosynthesis)

CO₂ + H₂O + light → glucose + O₂.

Xylem

Plant tissue that transports water and minerals from roots to leaves.

Phloem

Plant tissue that transports sugars from leaves to other parts of the plant.

Transpiration

Evaporation of water from plant leaves, driving water movement through xylem.

Cohesion-tension theory

Explains how water moves up through xylem due to water sticking together and being pulled by transpiration.

Light intensity

More light increases stomatal opening and transpiration rate.

Temperature

Higher temperature increases evaporation and transpiration.

Wind

Increases transpiration by removing humid air around leaves.

Humidity

High humidity slows transpiration; low humidity increases it.