A Unity and Diversity

A1.1 Water

A1.2 Nucleic acids

A2.1 Origins of cells

A2.2 Cell structure

A2.3 Viruses [HL only]

A3.1 Diversity of organisms

A3.2 Classification and cladistics [HL only]

A4.1 Evolution and speciation

A4.2 Conservation of biodiversity

B Form and Function

B1.1 Carbohydrates and lipids

B1.2 Proteins

B2.1 Membranes and membrane transport

B2.2 Organelles and compartmentalization

B2.3 Cell specialization

B3.1 Gas exchange

B3.2 Transport

B3.3 Muscle and motility [HL only]

B4.1 Adaptation to environment

B4.2 Ecological niches

C Interaction and Interdependence

C1.1 Enzymes and metabolism

C1.2 Cell respiration

C1.3 Photosynthesis

C2.1 Chemical signalling [HL only]

C2.2 Neural signalling

C3.1 Integration of body systems

C3.1.1—System integration

C3.1.2—Hierarchy in multicellular organisms

C3.1.3—Integration of organs

C3.1.4—Brain as information integration organ

C3.1.5—Spinal cord

C3.1.6—Input through sensory neurons

C3.1.7—Output through motor neurons

C3.1.8—Nerves as bundles

C3.1.9—Pain reflex arcs

C3.1.10—Cerebellum role

C3.1.11—Melatonin and sleep

C3.1.12—Epinephrine (adrenaline)

C3.1.13—Hypothalamus and pituitary control

C3.1.14—Heart rate feedback control

C3.1.15—Ventilation rate feedback control

C3.1.16—Peristalsis control

C3.1.17 (HL)—Tropic responses in seedlings

C3.1.18 (HL)—Positive phototropism

C3.1.19 (HL)—Phytohormones

C3.1.20 (HL)—Auxin efflux carriers

C3.1.21 (HL)—Auxin promotes cell growth

C3.1.22 (HL)—Auxin and cytokinin interactions

C3.1.23 (HL)—Ethylene and fruit ripening

C3.2 Defence against disease

C4.1 Populations and communities

C4.2 Transfers of energy and matter

D Continuity and Change

D1.1 DNA replication

D1.2 Protein synthesis

D1.3 Mutation and gene editing

D2.1 Cell and nuclear division

D2.2 Gene expression [HL only]

D2.3 Water potential

D3.1 Reproduction

D3.2 Inheritance

D3.3 Homeostasis

D4.1 Natural selection

D4.2 Stability and change

D4.3 Climate change

IB Biology HL C3.1.21 (HL)—Auxin promotes cell growth Question Bank

• Auxin activates proton pumping into the apoplast

• Acidified cell walls loosen, allowing water uptake, elongation, and bending

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