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Theme C — Interaction and interdependence

Theme C — Interaction and interdependence — IB Biology SL Revision Notes & Topical Questions

5 min read 11 parts Lesson 1 of 9 Unit quiz

📚 IB Biology SL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Lesson summary

Theme C — Interaction and interdependence — IB BIOLOGY SL notes: Connect enzymes, respiration, photosynthesis, neural signalling, defence and populations in Theme C.Optimum = the temperature or pH at which the enzyme rate is highestThe rate falls on either side of the optimum as …

  • Cell respiration
  • Stage locations
  • Respirometer
  • Respiration compared with breathing
  • Oxygen source
  • Action spectrum

Part 1 of 9Enzymes

  • Optimum = the temperature or pH at which the enzyme rate is highest
    • The rate falls on either side of the optimum as bonds in the enzyme are disrupted.

Part 2 of 9Cell respiration

1
Cell respiration
Cell respiration the controlled release of energy from organic compounds to produce ATP
  • Oxidation is the loss of electrons or hydrogen and releases energy.
  • Respiration releases energy and does not make energy.
2
Stage locations
  • Stage locations glycolysis occurs in the cytoplasm and not in the mitochondria
3
ATP yield
  • ATP yield aerobic respiration gives far more ATP than anaerobic respiration
4
Anaerobic products depend on the organism
  • Human muscle cells make lactate.
  • Yeast makes ethanol and carbon dioxide.
5
ATP
  • ATP an immediate, short-term energy carrier and not a store lasting for days
6
Respirometer
  • Respirometer a control tube with dead seeds or glass beads shows that changes are caused by living tissue
7
Respiration compared with breathing
  • Respiration compared with breathing respiration is a chemical process in cells and breathing is ventilation of the lungs

Part 3 of 9Photosynthesis

Oxygen source
  • Oxygen source the oxygen released comes from water
Pigments
  • Pigments chlorophyll absorbs mostly red and blue light
Action spectrum
Action spectrum a graph of the rate of photosynthesis at each wavelength
Limiting factors
  • If the rate stays the same as light rises but rises with CO2, then CO2 is limiting.
  • The rate falls above 40 °C because enzymes denature.
Rf
Rf distance moved by a pigment divided by distance moved by the solvent front
  • Distances of 2 cm and 8 cm give an Rf of 0.25.
  • A pigment with a very low Rf has a strong affinity for the stationary phase.
Pondweed experiment
  • Pondweed experiment the water is boiled and cooled before sodium hydrogencarbonate is added
  • This removes dissolved CO2 so that the concentration is known.
FACE experiments
  • FACE experiments costly and hard to replicate

Part 4 of 9Action potential

Generating an action potential
Generating an action potential
1
The stimulus raises the membrane to threshold, about -50 mV from a resting potential of -70 mV.
2
Voltage-gated Na+ channels open.
3
Na+ enters and the inside becomes positive, reaching about +40 mV.
4
Na+ channels close and K+ channels open.
5
K+ leaves and the membrane repolarises.
6
The pump restores the resting distribution of ions.
Sodium-potassium pump
  • Sodium-potassium pump uses ATP to move 3 Na+ out and 2 K+ in
Propagation
  • Propagation an action potential is propagated along the axon and is not electricity flowing
Stimulus strength
  • Stimulus strength a stronger stimulus gives a higher frequency of impulses and not a bigger impulse
Myelin
  • Myelin insulates the axon, and impulses jump between the gaps

Part 5 of 9Synapse

  • Cholinergic synapse transmission
1
The action potential reaches the presynaptic terminal.
2
Ca2+ channels open and Ca2+ enters.
3
Vesicles release acetylcholine by exocytosis.
4
Acetylcholine diffuses across the cleft and binds receptors.
5
Na+ enters and the postsynaptic membrane depolarises.
6
Acetylcholinesterase breaks down the acetylcholine.
  • Signal transfer
    • a chemical neurotransmitter crosses the synapse and the impulse itself does not jump across

Part 6 of 9Neural and defence terms

Dendrite
Dendrite a short branch of a neurone that receives signals
Interneurone
Interneurone a relay neurone inside the CNS
Neuromuscular junction
Neuromuscular junction the synapse between a motor neurone and a muscle fibre
Feedback
  • Feedback involves a receptor, a control centre and an effector, and signals are nerve impulses
Phototropism
  • Phototropism involves efflux carriers and cell elongation
Phagocyte
Phagocyte a white blood cell that engulfs and digests pathogens by endocytosis
Signs and symptoms
  • Signs and symptoms signs are measurable features of disease and symptoms are what the patient feels

Part 7 of 9Sampling populations

Transect
  • Transect a line across a habitat along which samples are taken
  • It is better than random quadrats when an environmental gradient exists, such as from shore to dunes.
  • Systematic sampling shows how species change along the gradient.
Lincoln index
  • Lincoln index population size = first catch × second catch / marked recaptures
  • Round estimates to whole organisms.
Saprotroph
Saprotroph a decomposer that secretes enzymes externally and absorbs the digested products
Omnivore
  • Omnivore hard to place in a pyramid because it feeds at several trophic levels and its energy must be split between them

Part 8 of 9Population growth and relationships

Sigmoid growth
  • Sigmoid growth has three phases, with limiting factors setting the carrying capacity
  • At carrying capacity births and deaths fluctuate around a balance.
Competition
  • Competition interspecific between species and intraspecific within a species, for a named resource
Parasites
  • Parasites they harm hosts, usually without killing them quickly
Chi-squared test
  • Chi-squared test state the null hypothesis, give the degrees of freedom and the critical value
  • A significant result shows an association and does not prove that species depend on each other.

Part 9 of 9More from the specification

1Catalytic reaction rates and amino acids
  • Catalytic reaction rates and amino acids enzyme catalytic rates depend on correct three-dimensional folding of constituent amino acids forming active binding sites.
2Enzyme Active Site Specificity
  • An enzyme molecule features a distinct three-dimensional active site whose catalytic shape is complementary to specific substrate molecules.
3Enzyme-Substrate Complex Formation
  • Catalysis begins when substrate molecules collide with and bind to the active site,
  • forming a temporary enzyme-substrate complex that lowers the activation energy of the chemical reaction.
4Induced Fit Model
  • Upon substrate binding, the active site undergoes conformational changes that strain chemical bonds in the substrate molecule, accelerating metabolic conversion into products.
5Enzymatic Digestion of Starch
  • The enzyme amylase breaks down complex starch polysaccharides into maltose disaccharide molecules through specific enzyme-substrate interactions.
6Amylase
  • Enzyme that breaks starch into maltose.
7Enzyme-substrate complex
  • The temporary structure formed when a substrate binds to an enzyme's active site.
8Activation energy
  • The energy needed for a substrate to become unstable enough to react.
9Anabolic reaction
  • Builds large molecules from small ones using energy.
10Catabolic reaction
  • A reaction breaking larger molecules into smaller ones.
11Amino acid
  • The unit from which proteins are made; the sequence decides the protein's shape and function.
12Immobilised enzyme
  • An enzyme fixed to a surface or trapped in a matrix so it can be reused.
13Substrate
  • The molecule that an enzyme acts on and which binds to the active site.
14Complex
  • Two or more molecules joined, such as an antibody and antigen.
15Starch
  • An insoluble polysaccharide of glucose used by plants for energy storage.
16Metabolism
  • The chemical reactions in a cell that release energy and build molecules.

Key terms

TermMeaning
OptimumThe condition giving the highest enzyme rate.
Rf valueDistance moved by the pigment divided by distance moved by the solvent front.
Sodium-potassium pumpA pump that uses ATP to move 3 Na+ out and 2 K+ in.
PhagocyteA white blood cell that engulfs and digests pathogens.
Lincoln indexA mark-recapture estimate of population size.
SaprotrophA decomposer that secretes enzymes externally and absorbs the products.

Avoid these mistakes

1
Saying respiration makes energy — it releases energy from organic compounds to make ATP
2
Saying that the impulse jumps across the synapse — a neurotransmitter diffuses across the cleft
3
Saying that the chi-squared test proves dependence — it shows a significant association only
4
Saying glycolysis happens in the mitochondria — it happens in the cytoplasm

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