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C Interaction and Interdependence

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  1. C1.1 Enzymes and metabolism

    1. C1.1.1Enzymes as catalysts

      • Enzymes are mostly protein biological catalysts, with some RNA examples • They work in small amounts and remain unchanged after catalysis

    2. C1.1.2Role in metabolism

      • Metabolism is all enzyme-controlled chemical reactions in cells • Specific enzymes control which metabolic reactions occur and when

    3. C1.1.3Anabolic and catabolic reactions

      • Anabolism builds complex molecules by condensation and requires energy • Catabolism breaks molecules by hydrolysis or oxidation and releases energy

    4. C1.1.4Enzymes as globular proteins

      • Enzymes are usually globular proteins with a small active-site pocket • The active site binds substrate, forms an ES complex, and catalyses reaction

    5. C1.1.5Induced-fit binding

      • Substrate binding induces shape changes in both enzyme and substrate • Induced fit aligns catalytic groups and raises substrate toward transition state

    6. C1.1.6Molecular motion

      • Molecular motion brings substrates and active sites into collision • Higher kinetic energy increases successful active-site collisions

    7. C1.1.7Relationships between structure and function

      • Active-site amino acid arrangement determines substrate specificity • Denaturation changes tertiary structure and active-site shape, not peptide bonds

    8. C1.1.8Effects on enzyme activity

      • Temperature increases rate to an optimum, then denaturation lowers activity • pH changes active-site bonding; substrate concentration rises to saturation plateau

    9. C1.1.9Measuring enzyme reactions

      • Measure substrate loss or product formation per unit time • Use initial rate, replicates, controls, and graphs from amylase or catalase assays

    10. C1.1.10Effect of enzymes on activation energy

      • Enzymes lower activation energy by providing an alternative pathway • They stabilize transition states but do not remove the energy barrier

  2. C1.2 Cell respiration

    1. C1.2.1ATP distributes energy

      • ATP is a small soluble nucleotide and universal energy currency • It links energy-yielding respiration to energy-requiring cellular processes

    2. C1.2.2Life processes using ATP

      • ATP supplies active transport, anabolic synthesis, and movement • Examples include membrane pumps, macromolecule synthesis, and chromosome movement

    3. C1.2.3ATP ↔ ADP interconversions

      • ATP hydrolysis to ADP and phosphate releases energy for coupled reactions • Respiration phosphorylates ADP to ATP; ATP is recycled rather than stored

    4. C1.2.4Cell respiration system

      • Cell respiration is enzyme-controlled release of energy from organic compounds • Carbon compounds are oxidized stepwise so energy can be transferred to ATP

    5. C1.2.5Anaerobic vs. aerobic respiration in humans

      • Aerobic respiration uses oxygen and mitochondria, producing CO₂, water, and high ATP • Anaerobic respiration in human cytoplasm produces lactate and low ATP

    6. C1.2.6Variables affecting rate

      • Rate depends on metabolic demand, organism size, oxygen, substrate, temperature, and pH • Respirometers measure oxygen uptake while soda lime absorbs CO₂

  3. C1.3 Photosynthesis

    1. C1.3.1Light energy → chemical energy

      • Photosynthesis converts light energy into chemical energy in carbon compounds • Photoautotrophs use chlorophyll in chloroplasts or cyanobacterial membranes

    2. C1.3.2CO₂ → glucose

      • Carbon dioxide is reduced to carbohydrate using hydrogen from water • Glucose represents the main stored product, though many compounds are synthesized

    3. C1.3.3Oxygen as by-product

      • Oxygen is released from photolysis of water, not directly from CO₂ • Oxygenic photosynthesis occurs in plants, algae, and cyanobacteria

    4. C1.3.4Photosynthetic pigment separation

      • Paper chromatography separates chlorophylls and accessory pigments • Rf values compare pigment movement relative to solvent front

    5. C1.3.5Absorption of specific wavelengths

      • Chlorophyll and accessory pigments absorb specific wavelengths • Absorbed light excites electrons for light-dependent reactions

    6. C1.3.6Absorption vs. action spectra

      • Absorption spectra show wavelengths absorbed by pigments • Action spectra show wavelengths most effective for photosynthesis rate

    7. C1.3.7Limiting factors investigation

      • Light intensity, CO₂ concentration, and temperature can limit photosynthesis • Investigations change one variable and estimate rate from O₂ production or CO₂ uptake

    8. C1.3.8CO₂ enrichment experiments

      • CO₂ enrichment tests whether increased CO₂ raises photosynthesis or growth • Greenhouse and FACE experiments compare realistic crop and ecosystem responses

  4. C2.2 Neural signalling

    1. C2.2.1Neurons

      • Neurons carry electrical impulses in the nervous system • Motor, sensory, and relay neurons differ in axon, dendrite, and cell body arrangement

    2. C2.2.2Resting potential generation

      • Sodium-potassium pumps use ATP to move 3 Na⁺ out and 2 K⁺ in • Ion gradients make the resting axon polarized at about -70 mV

    3. C2.2.3Nerve impulses as action potentials

      • A nerve impulse is a propagated action potential along a nerve fibre • Stimulus-triggered sodium influx reverses membrane polarity

    4. C2.2.4Variation in impulse speed

      • Larger axon diameter lowers resistance and increases impulse speed • Myelin sheaths and nodes of Ranvier enable faster saltatory conduction

    5. C2.2.5Synapses as junctions

      • Synapses connect neurons to neurons, muscles, or glands • Chemical synapses transmit one way across a narrow synaptic cleft

    6. C2.2.6Neurotransmitter release

      • Action potentials open voltage-gated Ca²⁺ channels in presynaptic terminals • Ca²⁺ causes vesicle fusion and neurotransmitter exocytosis into the cleft

    7. C2.2.7Excitatory postsynaptic potential

      • Neurotransmitters diffuse and bind receptors on the postsynaptic membrane • EPSPs depolarize the membrane and make threshold more likely

  5. C3.1 Integration of body systems

    1. C3.1.1System integration

      • Integration lets interacting parts coordinate an overall biological function • Systems interact across molecular, cellular, organ, organism, and ecosystem levels

    2. C3.1.2Hierarchy in multicellular organisms

      • Cells form tissues, organs, organ systems, and whole organisms • Emergent properties arise when subsystems interact, such as gut peristalsis and absorption

    3. C3.1.3Integration of organs

      • Organs are integrated by nervous signals, hormones, and blood transport • Transport links nutrients, gases, wastes, hormones, and energy substrates between organs

    4. C3.1.4Brain as information integration organ

      • The brain integrates sensory input and coordinates complex responses • Cerebral hemispheres, cerebellum, hypothalamus, and medulla have distinct roles

    5. C3.1.5Spinal cord

      • The spinal cord links brain and peripheral nervous system • It integrates unconscious processes such as reflex arcs

    6. C3.1.6Input through sensory neurons

      • Sensory neurons carry impulses from receptors to spinal cord and brain • Inputs may reach cerebral hemispheres for conscious perception

    7. C3.1.7Output through motor neurons

      • Motor neurons carry impulses from CNS to skeletal muscle effectors • Voluntary muscle contraction is coordinated through cerebral hemispheres

    8. C3.1.8Nerves as bundles

      • Nerves are bundles of sensory and motor nerve fibres in connective tissue • Mixed nerves carry impulses both to and from the CNS

    9. C3.1.9Pain reflex arcs

      • Pain reflexes are rapid involuntary withdrawal responses • Reflex arcs use receptors, sensory neurons, relay neurons, motor neurons, and skeletal muscle

    10. C3.1.10Cerebellum role

      • The cerebellum coordinates timing and force of skeletal muscle contractions • It maintains balance, posture, and smooth learned movements

    11. C3.1.11Melatonin and sleep

      • The pineal gland secretes melatonin according to light-dark cycles • Melatonin modulates sleep timing as part of circadian rhythms

    12. C3.1.12Epinephrine (adrenaline)

      • Adrenal glands secrete epinephrine during stress or danger • It increases heart rate, ventilation, and respiratory substrate availability

    13. C3.1.13Hypothalamus and pituitary control

      • The hypothalamus links nervous inputs to endocrine control • Pituitary hormones regulate glands including thyroid, gonads, adrenals, and mammary glands

    14. C3.1.14Heart rate feedback control

      • Baroreceptors monitor blood pressure; chemoreceptors monitor CO₂, pH, and O₂ • The medulla adjusts sinoatrial node activity by sympathetic and parasympathetic nerves

    15. C3.1.15Ventilation rate feedback control

      • Chemoreceptors detect CO₂-driven pH changes in blood and cerebrospinal fluid • The medulla alters diaphragm and intercostal muscle activity to change ventilation rate

    16. C3.1.16Peristalsis control

      • The CNS controls voluntary swallowing and egestion • The enteric nervous system coordinates involuntary peristalsis in gut smooth muscle

  6. C3.2 Defence against disease

    1. C3.2.1Pathogens cause infectious diseases

      • Pathogens are disease-causing viruses, bacteria, fungi, protists, or parasites • Archaea are not currently known to cause human infectious diseases

    2. C3.2.2Skin and mucous membranes

      • Keratinized skin, shedding, lysozyme, mucus, and cilia are primary defences • Mucous membranes protect respiratory and digestive surfaces

    3. C3.2.3Blood clotting

      • Platelets and damaged tissue release clotting factors at wounds • Thrombin converts fibrinogen to fibrin, trapping blood cells and sealing entry points

    4. C3.2.4Innate vs. adaptive immune system

      • Innate immunity is broad, rapid, and does not become more specific over life • Adaptive immunity is antigen-specific and produces memory cells

    5. C3.2.5Phagocytes

      • Phagocytes use amoeboid movement to reach infection sites • They recognize, engulf, and digest pathogens using lysosomal enzymes

    6. C3.2.6Lymphocytes

      • B-cells produce antibodies after activation; T-cells assist or destroy infected cells • Lymphocytes originate in bone marrow and circulate through blood, lymph, and lymph nodes

    7. C3.2.7Antigens

      • Antigens are non-self molecules that trigger specific immune responses • They are often proteins or glycoproteins recognized by antibodies or lymphocyte receptors

    8. C3.2.8B-lymphocyte activation

      • B-cells bind antigen, internalize it, and present it with MHC proteins • Helper T-cells activated by the same antigen stimulate B-cell activation

    9. C3.2.9Clones of plasma cells

      • Activated B-cells divide by mitosis through clonal selection • Plasma cells rich in rough ER secrete large amounts of one specific antibody

    10. C3.2.10Immunity from memory cells

      • Memory B- and T-cells remain after the primary response declines • Re-exposure triggers faster, stronger secondary immunity

    11. C3.2.11HIV transmission

      • HIV is transmitted through infected blood, semen, vaginal fluids, or breast milk • Transmission risk depends on fluid exchange, barriers, and viral load

    12. C3.2.12HIV infection and AIDS

      • HIV infects helper T-cells using CD4 receptors and reverse transcriptase • AIDS results when helper T-cell loss weakens antibody production and immune coordination

    13. C3.2.13Antibiotics

      • Antibiotics block bacterial processes absent from eukaryotic cells • They do not treat viruses; antivirals target viral replication processes

    14. C3.2.14Antibiotic resistance evolution

      • Antibiotic use selects resistant variants that survive and reproduce • Multi-resistant strains arise through mutation, plasmids, and overuse of antibiotics

    15. C3.2.15Zoonoses

      • Zoonoses transfer from animal reservoirs to humans, sometimes through vectors • Examples include rabies, tuberculosis, Japanese encephalitis, and COVID-19

    16. C3.2.16Vaccines and immunization

      • Vaccines contain weakened/inactivated pathogens, antigens, or genetic instructions • Immunization produces active artificial immunity and memory cells

    17. C3.2.17Herd immunity

      • Herd immunity indirectly protects susceptible people when many are immune • Thresholds depend on transmission route and pathogen contagiousness

    18. C3.2.18COVID-19 pandemic data evaluation

      • Evaluate COVID-19 data using source reliability, trends, and controlled comparisons • Calculate percentage change, percentage difference, incidence, and vaccine efficacy

  7. C4.1 Populations and communities

    1. C4.1.1Populations

      • A population is interacting organisms of the same species in one area • Members have opportunities to interbreed and may be reproductively isolated from others

    2. C4.1.2Population size estimation

      • Population size is estimated when full counts are impractical • Random sampling reduces bias; stratified and systematic sampling fit different habitats

    3. C4.1.3Random quadrat sampling

      • Quadrats estimate density, frequency, cover, or abundance of sessile organisms • Random coordinates and known quadrat area support representative population estimates

    4. C4.1.4Capture-mark-release-recapture

      • Capture-mark-release-recapture estimates motile animal populations • Lincoln index assumes marks persist, mixing occurs, and marking does not affect survival

    5. C4.1.5Carrying capacity

      • Carrying capacity is the maximum population an environment can sustain • Limited food, space, mates, and other resources create competition near capacity

    6. C4.1.6Negative feedback control

      • Density-dependent factors regulate populations by negative feedback • Competition, predation, waste, and disease intensify as population density rises

    7. C4.1.7Population growth curves

      • Exponential growth occurs when resources are abundant and limiting factors are weak • Sigmoid growth slows as resources limit growth near carrying capacity

    8. C4.1.8Modelling sigmoid growth

      • Sigmoid curves can be modelled with yeast, duckweed, or other fast-growing organisms • Lag, exponential, transition, and plateau phases show changing growth rate

    9. C4.1.9Competition vs. cooperation

      • Intraspecific competition occurs for food, mates, space, or light • Cooperation such as social hunting or parental care can increase survival and reproduction

    10. C4.1.10Community

      • A community is all interacting populations in an ecosystem • Species interactions make populations interdependent within the abiotic environment

    11. C4.1.11Interspecific relationships

      • Interspecific relationships occur between different species in communities • Categories include herbivory, predation, competition, mutualism, parasitism, and pathogenicity

    12. C4.1.12Mutualism as interspecific relationship

      • Mutualism benefits both species through exchanged resources or protection • Examples include legumes and Rhizobium, orchids and mycorrhizae, corals and zooxanthellae

    13. C4.1.13Endemic vs. invasive species

      • Endemic species are native to a restricted geographic area • Invasive species can escape controls and compete with endemic species for niche resources

    14. C4.1.14Tests for interspecific competition

      • Competition is tested using lab experiments, field observations, or removal studies • Connell's barnacle study links removal experiments to fundamental and realized niches

    15. C4.1.15Chi-squared test

      • Chi-squared tests association between two species from quadrat presence/absence data • Compare observed and expected counts, degrees of freedom, and critical values

    16. C4.1.16Predator-prey relationships

      • Predator-prey relationships regulate populations through density-dependent feedback • Snowshoe hare and lynx cycles show time-lagged predator and prey changes

    17. C4.1.17Top-down vs. bottom-up control

      • Top-down control begins with predators and cascades to lower trophic levels • Bottom-up control begins with producers or resources and affects higher trophic levels

    18. C4.1.18Allelopathy and antibiotics

      • Allelopathy releases chemicals that inhibit competitor germination or growth • Antibiotics are microbial allelochemicals, such as penicillin from Penicillium

  8. C4.2 Transfers of energy and matter

    1. C4.2.1Ecosystems as open systems

      • Ecosystems are open systems exchanging energy and matter with surroundings • Energy flows through ecosystems while matter can enter, leave, and recycle

    2. C4.2.2Sunlight as principal energy source

      • Sunlight is the principal energy source for most ecosystems • Exceptions include caves and deep-ocean vents supported by chemosynthesis

    3. C4.2.3Chemical energy flow

      • Chemical energy flows from producers to consumers through feeding • Energy enters as light or chemical energy and leaves ecosystems as heat

    4. C4.2.4Food chains and food webs

      • Food chains and food webs model feeding relationships in communities • Arrows point in the direction of energy and biomass transfer

    5. C4.2.5Supply to decomposers

      • Decomposers obtain energy from carbon compounds in detritus • Dead organisms, faeces, fallen leaves, and shed tissues supply organic matter

    6. C4.2.6Autotrophs as self-feeders

      • Autotrophs synthesize carbon compounds from simple inorganic substances • They use external energy sources to fix carbon and build biomass

    7. C4.2.7Energy sources

      • Photoautotrophs use light captured by photosynthetic pigments • Chemoautotrophs use oxidation of inorganic substances, such as iron or sulfur compounds

    8. C4.2.8Heterotrophs

      • Heterotrophs obtain carbon compounds from other organisms or organic matter • They use these compounds for respiration and synthesis of their own biomass

    9. C4.2.9Energy release

      • Both autotrophs and heterotrophs release energy by cell respiration • Oxidation of carbon compounds transfers energy to ATP and heat

    10. C4.2.10Trophic levels

      • Trophic levels classify organisms as producers, primary consumers, and higher consumers • Omnivores and decomposers may feed across more than one trophic level

    11. C4.2.11Energy pyramids

      • Energy pyramids represent energy flow per unit area per unit time • Each bar shows energy available to one trophic level

    12. C4.2.12Energy reductions

      • Energy availability decreases at each transfer between trophic levels • Losses occur through respiration, heat, egestion, excretion, and uneaten biomass

    13. C4.2.13Heat loss

      • Cell respiration converts some chemical energy to heat in all trophic levels • Heat dissipates to the environment, so energy cannot be recycled

    14. C4.2.14Restrictions on trophic levels

      • Large energy losses restrict food chains to a few trophic levels • Higher trophic levels usually support less biomass and fewer individuals

    15. C4.2.15Primary production

      • Primary production is accumulation of carbon compounds in autotroph biomass • Gross production minus respiration gives net primary production

    16. C4.2.16Secondary production

      • Secondary production is biomass accumulation by heterotrophs • It depends on food intake, assimilation, respiration losses, and biomass conversion

    17. C4.2.17Carbon cycle diagrams

      • Carbon cycle diagrams show stores as boxes and fluxes as labelled arrows • Include CO₂, photosynthesis, feeding, respiration, decomposition, fossil fuels, and combustion

    18. C4.2.18Carbon sinks and sources

      • Carbon sinks absorb more carbon than they release, such as forests, soils, and oceans • Carbon sources release more carbon than they absorb, such as fossil fuel combustion

    19. C4.2.19CO₂ release during combustion

      • Combustion of biomass, peat, coal, oil, and natural gas releases CO₂ • Draining peat and forest fires increase carbon flux to the atmosphere

    20. C4.2.20Keeling Curve analysis

      • The Keeling Curve records atmospheric CO₂ at Mauna Loa since the late 1950s • Long-term rise reflects combustion; annual oscillation reflects Northern Hemisphere photosynthesis

    21. C4.2.21Dependence between respiration and photosynthesis

      • Photosynthesis supplies atmospheric O₂ used in aerobic respiration • Respiration supplies CO₂ used by photosynthesis, linking autotrophs and heterotrophs

    22. C4.2.22Recycling of all chemical elements

      • All chemical elements required by organisms are recycled in ecosystems • Decomposers convert detritus and waste into inorganic nutrients for producers