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]

B3.3.1 (HL)—Movement adaptations

B3.3.2 (HL)—Sliding filament model

B3.3.3 (HL)—Titin and antagonistic muscles

B3.3.4 (HL)—Motor units

B3.3.5 (HL)—Skeletons as anchorage and levers

B3.3.6 (HL)—Synovial joint movement

B3.3.7 (HL)—Range of motion

B3.3.8 (HL)—Intercostal muscles

B3.3.9 (HL)—Reasons for locomotion

B3.3.10 (HL)—Swimming adaptations in marine mammals

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

C3.2 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 B3.3.4 (HL)—Motor units Question Bank

• Motor neurons connect to skeletal muscle fibres at neuromuscular junctions

• Acetylcholine release at motor end plates triggers sarcolemma excitation

• Excitation releases calcium from sarcoplasmic reticulum to start contraction

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