International Baccalaureate Diploma Programme (IB) Group 4: Sciences (Biology) Syllabus

List the taxonomic hierarchy from broadest to most specific used in classification.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Name the three domains of life.

Bacteria, Archaea and Eukarya.

State the binomial nomenclature convention for naming species.

A two-part Latin name: the genus (capitalised) followed by the species epithet (lowercase), both italicised, e.g. $Homo\ sapiens$.

Define the biological species concept.

A group of organisms that can interbreed to produce fertile, viable offspring and are reproductively isolated from other such groups.

What is a dichotomous key used for?

Identifying organisms by working through a series of paired (either/or) statements about observable characteristics until a name is reached.

Explain how the fluid mosaic model describes the cell membrane.

A phospholipid bilayer (fluid) with embedded and surface proteins forming a mosaic; phospholipids and proteins can move laterally, with cholesterol, glycoproteins and glycolipids also present.

Contrast simple diffusion, facilitated diffusion and active transport across a membrane.

Simple diffusion: passive movement down a gradient directly through the bilayer. Facilitated diffusion: passive movement down a gradient via protein channels/carriers. Active transport: movement against the gradient using carrier proteins and ATP.

How is the structure of a red blood cell adapted to its function?

Biconcave shape gives a large surface-area-to-volume ratio for gas exchange, no nucleus gives more room for haemoglobin, and flexibility allows passage through narrow capillaries.

Describe the pathway of air through the human respiratory system.

Nasal cavity $\to$ pharynx $\to$ larynx $\to$ trachea $\to$ bronchi $\to$ bronchioles $\to$ alveoli.

List three adaptations of alveoli for efficient gas exchange.

Large total surface area, thin (one-cell-thick) walls giving a short diffusion distance, and a dense capillary network maintaining a steep concentration gradient (plus a moist surface).

Distinguish between the systemic and pulmonary circulations in a double circulatory system.

Pulmonary circulation carries blood between the heart and lungs (for gas exchange); systemic circulation carries oxygenated blood from the heart to the rest of the body and returns deoxygenated blood.

State the oxygen dissociation behaviour shown by the haemoglobin curve and the Bohr shift.

Haemoglobin shows a sigmoidal (S-shaped) oxygen dissociation curve due to cooperative binding; the Bohr shift moves the curve right when $\ce{CO2}$ or $\ce{H+}$ rises, releasing more oxygen to active tissues.

Define homeostasis.

The maintenance of a stable internal environment within narrow limits despite changes in external conditions, typically by negative feedback.

Explain how negative feedback maintains blood glucose concentration.

High blood glucose triggers insulin release (promoting glucose uptake and glycogen storage, lowering glucose); low blood glucose triggers glucagon release (promoting glycogenolysis, raising glucose), each correction reversing the original change.

What are the roles of the kidney's nephron in osmoregulation?

Ultrafiltration at the glomerulus, selective reabsorption of useful substances, and water reabsorption controlled by ADH in the collecting duct to regulate blood water potential.

Describe the structure of a typical motor neuron.

A cell body with dendrites, a long myelinated axon insulated by Schwann cells with nodes of Ranvier, ending in axon terminals (synaptic knobs).

What is the resting potential of a neuron and how is it maintained?

Approximately $-70\ \text{mV}$, maintained by the sodium-potassium pump ($\ce{Na+}$/$\ce{K+}$ ATPase) pumping $\ce{3Na+}$ out and $\ce{2K+}$ in, plus differential membrane permeability.

Outline how an action potential is transmitted across a chemical synapse.

The action potential triggers $\ce{Ca^2+}$ influx, vesicles release neurotransmitter into the synaptic cleft, it diffuses and binds receptors on the postsynaptic membrane, opening ion channels to generate a new potential.

Distinguish between the central and peripheral nervous systems.

The central nervous system (CNS) comprises the brain and spinal cord; the peripheral nervous system (PNS) comprises all the nerves connecting the CNS to the rest of the body.

Define a trophic level and explain the approximate 10% energy transfer rule.

A trophic level is a feeding position in a food chain; only about 10% of the energy at one level is passed to the next, the rest being lost as heat (respiration), in movement, and in undigested material.

Distinguish between a habitat, a population, a community and an ecosystem.

Habitat: where an organism lives. Population: members of one species in an area. Community: all interacting populations in an area. Ecosystem: the community plus its abiotic environment.

State the four stages of the nitrogen cycle and the bacteria involved.

Nitrogen fixation (Rhizobium/Azotobacter), nitrification ($\ce{NH4+ -> NO2- -> NO3-}$ by Nitrosomonas and Nitrobacter), denitrification (Pseudomonas), and ammonification by decomposers.

Write the formula for calculating the Simpson's reciprocal diversity index.

$$D = \frac{N(N-1)}{\sum n(n-1)}$$ where $N$ is the total number of organisms and $n$ is the number of each species.

Distinguish between gross primary productivity (GPP) and net primary productivity (NPP).

GPP is the total energy fixed by producers in photosynthesis; NPP is GPP minus energy lost in respiration: $$\text{NPP} = \text{GPP} - R$$

What is the difference between the innate (non-specific) and adaptive (specific) immune responses?

Innate immunity is rapid, non-specific and lacks memory (e.g. skin, phagocytes, inflammation); adaptive immunity is slower, specific to antigens, and produces immunological memory via lymphocytes.

Compare the roles of B-lymphocytes and T-lymphocytes.

B-lymphocytes mediate humoral immunity by producing antibodies (and plasma/memory cells); T-lymphocytes mediate cell-mediated immunity, with helper T-cells activating other cells and cytotoxic T-cells killing infected cells.

Explain the basis of vaccination.

A vaccine introduces a harmless antigen so the adaptive immune system produces memory cells, giving a faster, stronger secondary response on later exposure to the real pathogen (active artificial immunity).

Name the stages of mitosis in order.

Prophase, metaphase, anaphase and telophase (preceded by interphase and followed by cytokinesis). Mnemonic: PMAT.

State the key difference in outcome between mitosis and meiosis.

Mitosis produces two genetically identical diploid daughter cells; meiosis produces four genetically distinct haploid gametes (halving the chromosome number).

What two processes during meiosis generate genetic variation?

Crossing over (recombination) during prophase I and independent assortment of homologous chromosomes during metaphase I (plus random fertilisation).

State the four conditions Darwin's theory of evolution by natural selection requires.

Variation exists within a population, more offspring are produced than can survive (overproduction), there is a struggle for survival, and individuals with favourable heritable traits reproduce more (survival of the fittest), changing allele frequencies over generations.

How does climate change threaten ecosystem stability, and what is a tipping point?

Rising $\ce{CO2}$ and temperatures cause ocean acidification, coral bleaching, range shifts and phenology mismatches; a tipping point is a threshold beyond which an ecosystem shifts abruptly and often irreversibly to a new state.