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

C3.2 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

D3.3.1—Homeostasis definition

D3.3.2—Negative feedback loops

D3.3.3—Blood glucose regulation

D3.3.4—Diabetes

D3.3.5—Thermoregulation

D3.3.6—Thermoregulation mechanisms

D3.3.7 (HL)—Kidney role

D3.3.8 (HL)—Glomerulus, Bowman's capsule, PCT

D3.3.9 (HL)—Loop of Henle

D3.3.10 (HL)—Osmoregulation by collecting ducts

D3.3.11 (HL)—Blood supply changes

D4.1 Natural selection

D4.2 Stability and change

D4.3 Climate change

IB Biology HL D3.3.9 (HL)—Loop of Henle Question Bank

• Ascending limb pumps Na⁺/Cl⁻ and is impermeable to water

• Descending limb loses water, creating a medulla gradient for water conservation

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