Flashcards · IB Diploma Programme Biology · Topic 3

Interaction and interdependence flashcards

54 cards on Topic 3, subtopics C1.1 to C4.2. Pick a subtopic or study them all.

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C1.1 Enzymes and metabolism

Anabolism and catabolism: Anabolism: building larger molecules from smaller ones by condensation (protein synthesis, glycogen formation, photosynthesis). Catabolism: breaking larger molecules into smaller ones by hydrolysis or oxidation (digestion, respiration).
Induced fit: Enzyme and substrate both change shape on binding, which strains bonds in the substrate.
Effect of increasing substrate concentration on enzyme activity: Rate rises as there are more collisions with active sites, then plateaus when all active sites are occupied. The plateau is not the enzyme being used up.
How does an enzyme affect the energy of a reaction?: It lowers the activation energy (peak energy minus reactant energy). The energies of reactants and products, and so the overall energy change, are unchanged.
End-product (feedback) inhibition: The end product of a pathway inhibits an enzyme early in it. Example: isoleucine inhibits threonine deaminase in the pathway that makes isoleucine. (HL only)
Competitive, non-competitive and mechanism-based inhibitors: Competitive: resembles substrate, binds the active site reversibly; more substrate reduces the inhibition (statins). Non-competitive: binds an allosteric site reversibly; more substrate does not remove it. Mechanism-based: binds the active site irreversibly (penicillin and transpeptidase). (HL only)

C1.2 Cell respiration

Properties and uses of ATP: Soluble, small and mobile; releases a usable amount of energy on hydrolysis (ATP + water → ADP + phosphate) and is rapidly regenerated. Used for active transport, anabolism and movement of the cell or its parts.
Cell respiration compared with gas exchange: Cell respiration: release of energy from carbon compounds in cells to make ATP (chemical). Gas exchange: physical movement of oxygen in and carbon dioxide out across a surface.
Aerobic and anaerobic respiration in humans: Aerobic: carbohydrate, lipid and others; oxygen needed; large ATP yield; CO₂ and water; cytoplasm and mitochondria. Anaerobic: carbohydrate only; no oxygen; small yield; lactate; cytoplasm.
Krebs cycle: what happens in each turn?: An acetyl group joins oxaloacetate (4C) to form citrate (6C). Each turn has four oxidations (dehydrogenations) and two decarboxylations, producing CO₂, ATP and reduced NAD, and regenerates oxaloacetate. (HL only)
How does the electron transport chain produce ATP?: Reduced NAD passes electrons to carriers on the inner mitochondrial membrane; energy released pumps protons into the intermembrane space; protons flow back through ATP synthase, phosphorylating ADP (chemiosmosis). Oxygen accepts electrons and protons, forming water. (HL only)
Anaerobic respiration in humans and yeast: Humans: pyruvate accepts hydrogen from reduced NAD, forming lactate. Yeast: pyruvate → ethanal + CO₂; ethanal accepts hydrogen, forming ethanol. Both regenerate NAD so glycolysis continues; net 2 ATP per glucose. (HL only)

C1.3 Photosynthesis

Where does the oxygen released in photosynthesis come from, and how is this known?: From water, which is split; carbon dioxide is reduced. Water labelled with ¹⁸O gives labelled oxygen gas. Word equation: carbon dioxide + water → glucose + oxygen.
Chromatography of leaf pigments: Rf and order: Rf = distance moved by pigment ÷ distance moved by solvent front, both from the start line; no units, below 1. Order up the paper: carotene (highest), xanthophyll, chlorophyll a, chlorophyll b (lowest).
Absorption spectrum and action spectrum: Absorption spectrum: light absorbed by an extracted pigment at each wavelength. Action spectrum: rate of photosynthesis of whole organisms or cells at each wavelength. Both are high in blue-violet and red, low in green.
A lamp is moved from 10 cm to 20 cm from a plant. How does light intensity change?: Intensity ∝ 1 ÷ distance², so it falls to (10 ÷ 20)² = 0.25, one quarter.
Photosystem: An array of chlorophyll and accessory pigments in a membrane, with a special chlorophyll as the reaction centre where an excited electron is emitted. The array absorbs a wider range of wavelengths and passes energy to the reaction centre. (HL only)
Calvin cycle in outline: Rubisco fixes CO₂ onto RuBP (5C) to give glycerate 3-phosphate (3C); this is reduced to triose phosphate using ATP and reduced NADP; five triose phosphates are converted to three RuBP using ATP; the rest leave to make glucose and other compounds. (HL only)

C2.1 Chemical signalling (HL only)

Ligand and receptor: Ligand: the signalling chemical that binds to a receptor. Receptor: a protein with a binding site specific to a ligand, complementary in shape and charge; binding is reversible. (HL only)
Quorum sensing in bacteria: Each bacterium releases a little autoinducer. At high density its concentration passes a threshold and binds receptors, switching genes on across the population together. Example: Vibrio fischeri bioluminescence. (HL only)
Transmembrane and intracellular receptors: Transmembrane: for hydrophilic or large ligands that stay outside (acetylcholine, epinephrine, insulin); hydrophobic amino acids in the membrane-spanning region. Intracellular: for hydrophobic ligands that enter the cell (oestradiol, progesterone, testosterone). (HL only)
Epinephrine signal transduction: Epinephrine binds a G protein-coupled receptor; the G protein swaps GDP for GTP and activates an enzyme that makes cAMP (second messenger); cAMP starts a kinase cascade. Response in seconds. (HL only)
How does insulin's receptor cause glucose uptake?: Insulin binds a tyrosine kinase receptor; tyrosines inside are phosphorylated; relay reactions follow; vesicles carrying glucose transporters fuse with the plasma membrane. Response in minutes. (HL only)
Chemical groups of hormones and neurotransmitters: Hormones: amines (epinephrine), proteins (insulin), steroids (oestradiol, progesterone, testosterone). Neurotransmitters: amino acids, peptides, amines and nitric oxide (a gas). (HL only)

C2.2 Neural signalling

How is the resting potential of a neuron produced?: The sodium–potassium pump uses ATP to move 3 Na⁺ out and 2 K⁺ in per cycle. K⁺ leaks out through open channels while few Na⁺ channels are open, and negative molecules stay inside, so the inside is about −70 mV.
Transmission across an excitatory chemical synapse: Action potential depolarises the presynaptic membrane; voltage-gated Ca²⁺ channels open and Ca²⁺ enters; vesicles fuse and release neurotransmitter by exocytosis; it diffuses across the cleft and binds receptors; positive ions enter, giving an EPSP; the neurotransmitter is removed.
Which nerve fibres conduct impulses fastest?: Wider fibres (such as giant axons, with low resistance to ion flow) and myelinated fibres conduct faster than narrow non-myelinated ones.
EPSP: Excitatory postsynaptic potential: a small depolarisation of the postsynaptic membrane. It is graded, unlike an all-or-nothing action potential.
Ion movements in an action potential: Depolarisation: after threshold (about −55 mV), voltage-gated Na⁺ channels open and Na⁺ enters; potential rises to about +30 mV. Repolarisation: Na⁺ channels close, K⁺ channels open, K⁺ leaves; potential falls below rest before the pump restores it. (HL only)
Resting −70 mV, threshold −55 mV. Three EPSPs of +6 mV arrive together; then one IPSP of −4 mV is added. Does the neuron fire each time?: −70 + 6 + 6 + 6 = −52 mV: threshold reached, it fires. With the IPSP: −52 − 4 = −56 mV: below threshold, it does not fire. (HL only)

C3.1 Integration of body systems

Emergent property: A feature of the whole that its separate parts do not have. Example: a cardiac muscle cell cannot pump blood, but the heart can.
Nervous and endocrine signalling compared: Nervous: electrical impulses then chemicals across synapses; to specific targets; very fast; brief. Endocrine: hormones in the blood; reach any cell with the receptor; slower; longer lasting.
The pain reflex arc in order: Pain receptor (free nerve ending in the skin) → sensory neuron entering the cord by the dorsal root → one interneuron in the grey matter → motor neuron leaving by the ventral root → skeletal muscle contracts to withdraw the hand.
Dorsal and ventral roots of the spinal cord: Dorsal root: sensory fibres in (the dorsal root ganglion holds sensory neuron cell bodies). Ventral root: motor fibres out.
Effects of epinephrine in preparing for vigorous activity: Raises heart rate and stroke volume; diverts blood to skeletal muscle from gut and skin; widens bronchioles; makes the liver convert glycogen to glucose; widens pupils.
How does auxin make plant cells elongate?: Auxin causes proton pumps to move H⁺ into the cell wall; the lower pH loosens cellulose cross-links; water enters and turgor stretches the wall, so the cell elongates. In phototropism auxin is moved to the shaded side by efflux carriers. (HL only)

C3.2 Defence against disease

Blood clotting in order: Platelets release clotting factors; a cascade of reactions follows; thrombin forms; thrombin converts soluble fibrinogen to insoluble fibrin; a fibrin mesh traps erythrocytes, forming the clot.
Innate and adaptive immunity: Innate: broad, unchanged through life, no memory; phagocytes. Adaptive: specific to one pathogen, develops through life, builds memory; B-cells and T-cells.
Clonal selection and antibody production: A B-cell binds its specific antigen; a helper T-cell activated by the same antigen contacts it; the activated B-cell divides by mitosis; the clone becomes plasma cells (secrete antibody) and memory cells.
How does HIV infection lead to AIDS?: HIV infects and kills helper T-cells, so fewer B-cells are activated and less antibody is made. Opportunistic infections follow; AIDS is the later condition caused by this loss of immune function.
Why do antibiotics harm bacteria but not human cells or viruses?: They target bacterial cell wall synthesis or bacterial ribosomes, which differ from human cells (no cell wall; different ribosomes). Viruses have no metabolism or ribosomes of their own, so there is no target.
Zoonosis: An infectious disease that transfers from other species to humans. Examples: tuberculosis (some cases, from cattle), rabies, Japanese encephalitis, COVID-19.

C4.1 Populations and communities

25 snails are marked; a second sample of 30 contains 6 marked. Estimate the population with the Lincoln index.: Population = M × N ÷ R = 25 × 30 ÷ 6 = 125.
Carrying capacity, and the phases of a sigmoid growth curve: Carrying capacity: the largest population the environment can support indefinitely. Phases: exponential (resources plentiful), transition (density-dependent factors build), plateau near carrying capacity (births roughly equal deaths).
Density-dependent and density-independent factors: Density-dependent: effect grows as density rises (competition, predation, pathogens); negative feedback towards carrying capacity. Density-independent: same effect whatever the density (fire, drought); makes numbers fluctuate.
Legume root nodules as a mutualism: Rhizobium bacteria fix nitrogen for the plant; the plant supplies carbohydrate and a low-oxygen home. Both partners gain.
Chi-squared test for association: 100 sites, species A at 40, species B at 30. Expected number of sites with both?: Expected = row total × column total ÷ grand total = 40 × 30 ÷ 100 = 12. Degrees of freedom for a 2 × 2 table = 1; critical value 3.84 at 5%.
Why do lynx numbers peak after snowshoe hare numbers?: Predator–prey cycles are delayed negative feedback: more hares feed more lynx after a delay; more lynx then reduce the hares, and lynx numbers fall. The cycle is roughly ten years; hare food supply matters too.

C4.2 Transfers of energy and matter

Open and closed systems: Open: exchanges both energy and matter with its surroundings (an ecosystem). Closed: exchanges energy only (a sealed jar ecosystem).
Photoautotroph and chemoautotroph: Both make carbon compounds from CO₂. Photoautotrophs use light (plants, algae, cyanobacteria); chemoautotrophs use energy from oxidation of inorganic substances (iron-oxidising bacteria).
Why do food chains rarely have more than four or five trophic levels?: Energy is lost at every transfer (respiration as heat, faeces, uneaten parts, excretion), so the top level would receive too little energy to support a viable population. Energy is not recycled.
Units of an energy pyramid: Energy per unit area per unit time, for example kJ m⁻² year⁻¹. One bar per trophic level, producers at the bottom, drawn to one scale.
Carbon sink and carbon source: Sink: takes up more CO₂ than it releases (photosynthesis exceeds respiration). Source: releases more than it takes up. Judged on net flux, not the size of the store.
Explain the two patterns in the Keeling Curve: Annual fluctuation: CO₂ falls in the northern hemisphere growing season (photosynthesis exceeds respiration) and rises in autumn and winter. Long-term rise: combustion of fossil fuels adds carbon that photosynthesis does not offset.