Poop

What is the Role of enzymes in metabolism use specificity in answer (4 pts)

Enzymes act as biological catalysts, lowering activation energy.

• They speed up metabolic reactions that would otherwise be too slow.

• Enzymes provide substrate specificity, ensuring correct biochemical pathways.

What is the difference between Anabolic and catabolic reactions and give an example of each (4 pts)

•

Anabolic: builds larger molecules from smaller ones, requires energy. Example: protein synthesis.

• Catabolic: breaks larger molecules into smaller ones, releases energy. Example: glycolysis.

• Anabolic reactions are endergonic (require ATP input).

• Catabolic reactions are exergonic (produce ATP or energy).

What type of protein are enzymes? What is the active site composed of?

Enzymes are globular proteins.

• The active site is composed of specific amino acid side chains (R groups).

What is induced-fit binding? What changes shape when a substrate binds to an active site?

Induced fit: the enzyme slightly changes shape to fit the substrate better.

• The enzyme’s active site changes shape when substrate binds.

What is the Role of molecular motion and substrate-active site collisions in enzyme catalysis? (

• Substrate and enzyme molecules are in constant random motion.

• Successful collisions occur when substrates collide with the active site at correct orientation.

• Higher kinetic energy increases frequency of collisions.

• Collision theory explains enzyme activity rates.

What is the Relationships between the structure of the active site, enzyme–substrate specificity and denaturation

The active site has a specific 3D structure complementary to substrate.

• Enzyme–substrate specificity ensures only correct substrate binds.

• Denaturation alters active site shape, preventing binding.

• Denaturation can be caused by pH, heat, or chemicals.

• Specificity depends on precise bonding interactions (H-b

What are the Effects of temperature, pH and substrate concentration on the rate of enzyme activity? (

Temperature: increases activity until optimum, then denaturation occurs.

• pH: changes alter ionization of R groups, disrupting bonds in active site.

• Substrate concentration: increases rate until enzyme saturation.

• Extreme pH causes denaturation and loss of activity.

• Very low temperatures slow molecular motion, reducing collisions.

• Enzyme concentration also affects rate; more enzymes = more active sites.

How do you determine reaction rates of a chemical reaction and what would need to be controlled in a reaction using enzymes?

Reaction rates: measure decrease in substrate or increase in product over time.

• Use initial slope of concentration vs. time graph.

• Control variables: temperature, pH, enzyme concentration.

• Control substrate concentration to test effect properly.

• Use replicates to reduce error and increase reliability.

What is an example of Intracellular and extracellular enzyme-catalysedreactions?

Intracellular: glycolysis (cytoplasm).

• Intracellular: Krebs cycle (mitochondria).

How do animals use Generation of heat energy by the reactions of metabolism?

Heat is released as a byproduct of exergonic metabolic reactions.

• Maintains body temperature in homeothermic animals.

• Used in thermogenesis (shivering or brown fat metaboli

What is the difference between Cyclical and linear pathways in metabolism? What type of path is glycolysis, the Krebs cycle and the Calvin cycle? (3 pts)

Linear pathways: reactions proceed in one direction only, ending with a final product.

• Cyclical pathways: products of final step regenerate reactants of first step.

• Glycolysis is linear.

• Krebs cycle is cyclical.

• Calvin cycle is cyclical.

What is an allosteric site? What does binding cause to the allosteric site? (3 pts)

An allosteric site is a binding site distinct from the active site.

• Only specific substances can bind to an allosteric site.

• Binding causes conformational changes in enzyme structure.

What is the difference between non competitive and Competitive inhibition?

Competitive inhibition: inhibitor resembles substrate and binds active site, blocking substrate.

• Non-competitive inhibition: inhibitor binds at allosteric site, changing enzyme shape.

• Statins act as competitive inhibitors of HMG-CoA reductase in cholesterol synthesis.

• Competitive inhibition can be overcome by increasing substrate concentration.

How are metabolic pathways regulated by feedback inhibition (use isoleucine in answer)

End-product of pathway inhibits an earlier enzyme.

• Isoleucine inhibits threonine deaminase in its biosynthetic pathway.

• Prevents overproduction of isoleucine by shutting down pathway.

How is Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor? (3 pts) How is penicillin an example? (1 pt)

Mechanism-based inhibitors bind irreversibly to enzyme active site.

• Binding causes chemical change that permanently inactivates enzyme.

• Enzyme cannot catalyze further reactions once modified.

• Penicillin irreversibly binds to bacterial transpeptidases.

What does ATP do and what properties make it suitable as the energy currency?

ATP stores chemical energy in its phosphate bonds and releases it quickly by hydrolysis.

• It can be rapidly regenerated from ADP and phosphate.

• It is soluble and easily transported within the cell.

• It releases energy in small, usable amounts for cellular processes.

Life processes within cells that ATP supplies with energy

• ATP provides energy for active transport across membranes.

• ATP is required for synthesis of macromolecules (anabolism).

• ATP provides energy for movement of the whole cell or intracellular components such as chromosomes.

-muscle contraction

Energy transfers during interconversion of ATP and ADP

Energy is released by hydrolysis of ATP into ADP and phosphate.

• Energy is required to synthesize ATP from ADP and phosphate.

• Hydrolysis is exergonic, phosphorylation is endergonic.

• Released energy is used for cellular work.

Principal substrates for cell respiration; can anything else be used?

Glucose is the main substrate for cell respiration.

• Lipids can also be broken down and used.

• Amino acids can be used when carbohydrates and fats are low.

Differences between anaerobic and aerobic respiration in humans

Substrates: Both use glucose; aerobic can also use lipids and amino acids.

• Oxygen: Aerobic requires oxygen; anaerobic does not.

• ATP yield: Aerobic produces large amounts of ATP (~30–32 ATP); anaerobic produces 2 ATP.

• Waste products: Aerobic forms CO₂ and H₂O; anaerobic forms lactate.

• Location: Aerobic occurs in mitochondria (and glycolysis in cytosol); anaerobic occurs only in cytosol.

• Word equations:

o Aerobic: glucose + oxygen → carbon dioxide + water + ATP

o Anaerobic: glucose → lactate + ATP

• Aerobic is sustainable long-term; anaerobic is short-term and rapid.

• Anaerobic regenerates NAD quickly but causes acid buildup.

Variables that affect the rate of cell respiration (

Temperature affects enzyme activity.

• Substrate concentration such as glucose or oxygen availability.

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7Outline the process of AEROBIC cellular respiration (more detailed)

Glycolysis (in the cytosol)

o One glucose (6C) is phosphorylated using 2 ATP to make it more reactive.

o The 6C sugar is split into two 3C triose phosphate molecules.

o Each 3C molecule is oxidized; NAD is reduced to NADH + H⁺as it accepts hydrogen and electrons.

o A small yield of ATP (net 2 ATP per glucose) is produced by substrate-level phosphorylation.

o End products are two molecules of pyruvate (3C), which enter the mitochondrion in aerobic conditions.

• Link reaction (in the mitochondrial matrix)

o Pyruvate (3C) is transported into the mitochondrial matrix.

o Each pyruvate is decarboxylated (CO₂ removed) and oxidized; NAD is reduced to NADH + H⁺.

o The remaining 2C fragment combines with coenzyme A to form acetyl-CoA.

o This reaction links glycolysis to the Krebs cycle and produces CO₂ as a waste product.

• Krebs cycle (citric acid cycle in the mitochondrial matrix)

o Acetyl-CoA (2C) combines with a 4C acceptor molecule to form a 6C citrate.

o The 6C compound is progressively oxidized and decarboxylated, releasing two CO₂ per turn of the cycle.

o At several steps, hydrogen and electrons are removed and transferred to NAD (forming NADH + H⁺) and to FAD (forming FADH₂).

o A small amount of ATP is produced directly by substrate-level phosphorylation in each cycle turn.

o The 4C acceptor is regenerated, allowing the cycle to continue.

• Role of reduced NAD and FAD; electron transport chain (ETC) (inner mitochondrial membrane / cristae)

o NADH + H⁺ and FADH₂ carry high-energy electrons from glycolysis, link reaction, and Krebs cycle to the ETC in the inner mitochondrial membrane.

o NADH donates electrons to the first carrier protein; FADH₂ donates electrons further along the chain.

o Electrons pass along a series of electron carriers at progressively lower energy levels in redox reactions.

o The energy released as electrons move along the chain is used by carrier proteins to pump protons (H⁺) from the matrix into the intermembrane space, creating a proton gradient.

• Proton gradient and chemiosmosis (oxidative phosphorylation)

o The proton gradient represents stored potential energy (higher H⁺ concentration in the intermembrane space than in the matrix).

o Protons flow back into the matrix through ATP synthase channels down their electrochemical gradient.

o The flow of protons causes ATP synthase to rotate and catalyze the formation of ATP from ADP and inorganic phosphate.

o This process of using a proton gradient to drive ATP synthesis is called chemiosmosis.

• Role of oxygen as the terminal electron acceptor

o At the end of the ETC, low-energy electrons are transferred to oxygen.

o Oxygen combines with electrons and protons (H⁺) to form water.

o This removal of electrons keeps the ETC flowing and maintains the proton gradient needed for chemiosmosis.

o Without oxygen, the ETC stops, NADH cannot be reoxidizedefficiently, and aerobic ATP production greatly decreases.

8. How pyruvate is converted to lactate to regenerate NAD in

How pyruvate is converted to lactate to regenerate NAD in anaerobic respiration (

Pyruvate accepts hydrogen from reduced NAD, forming lactate.

• This oxidizes NAD so glycolysis can continue without oxygen.

• Lactate temporarily stores electrons until oxygen becomes available again.

Anaerobic respiration in yeast; how is it similar to humans? How is it used in baking? (

Both yeast and humans use glycolysis followed by NAD regeneration when oxygen is absent.

• Yeast converts pyruvate to ethanol and CO₂; humans convert pyruvate to lactate.

• CO₂ produced by yeast makes bread dough rise in baking.

Differences between lipids and carbohydrates as respiratory substrates

Lipids yield more energy per gram because they contain more hydrogen and less oxygen.

• Carbohydrates enter respiration through glycolysis; lipids require β-oxidation.

• Anaerobic respiration only occurs with carbohydrates.

• Fatty acids break into 2-carbon acetyl units that enter Krebs cycle via acetyl-CoA.

• Lipids provide slow but long-term energy; carbohydrates provide rapid energy supply.

• Lipids are stored anhydrously, giving more energy per mass.

Wrap

 

1. What kind of transfer of energy happens in photosynthesis? What is the word equation? How is oxygen formed

Light energy is converted into chemical energy stored in glucose.

• Word equation: carbon dioxide + water → glucose + oxygen.

• Oxygen is formed by photolysis of water in photosystem II.

What is chromatography? How do you calculate Rf values and identify pigments?

Chromatography separates pigments based on solubility and attraction to the paper.

• Rf value = distance moved by pigment ÷ distance moved by solvent.

• Pigments are identified by both color and their characteristic Rf values.

• More soluble pigments travel farther.

How do photosynthetic pigments absorb specific wavelengths? Include required detailsHow do photosynthetic pigments absorb specific wavelengths? Include required details

• Only certain wavelengths are absorbed because pigment structures absorb specific photon energies.

• Chlorophyll absorbs mainly red and blue light.

• Accessory pigments broaden the range of absorbed wavelengths.

• Energy not absorbed is reflected or transmitted.

• Excited electrons drive photochemical reactions.

• Each pigment has a unique absorption profile

4. What is an absorption spectrum? What is on the horizontal axis? (2 pts)

An absorption spectrum shows how much light a pigment absorbs at each wavelength.

• The horizontal axis is wavelength of light.

Similarities and differences of absorption and action spectra

Both relate to photosynthesis and light use.

• Absorption spectra show light absorbed; action spectra show effectiveness in photosynthesis.

• Both show strongest effects in red and blue wavelengths.

• Differences: absorption is pigment-based; action is whole photosynthesis-based.

• Action spectra reflect combined pigment activity.

• Absorption spectra do not prove which wavelengths drive photosynthesis.

What are the 3 limiting factors of photosynthesis? How test each? (6 pts)

Light intensity: vary distance from a lamp or change wattage.

• Carbon dioxide concentration: add sodium hydrogen carbonate to water or change CO₂ injection levels.

• Temperature: use heated/ice water baths or controlled environmental chambers.

• Each factor can be held constant while one is varied.

• Limiting factor determines the rate until saturation.

• Extremes can denature enzymes or damage pigments.

How can CO₂ enrichment experiments predict future photosynthesis and growth?

• Greenhouse CO₂ enrichment shows increased growth when CO₂ levels are raised.

• FACE experiments expose plants to elevated outdoor CO₂ to predict realistic future growth.

How can photosystems act as arrays of pigments that generate excited electrons?

photosystems are always located in membranes and they occur in cyanobacteria and chloroplasts… special chlorophyll reaction centre

9. Advantages of structured arrays of pigments in a photosystem (3

They capture a wider range of wavelengths.

• Energy transfers efficiently to the reaction centre.

• They increase the probability of electron excitation.

How is oxygen produced by photolysis in PSII? What else is produced? Is oxygen used?

Water is split into oxygen, protons, and electrons using light energy.

• Protons contribute to the proton gradient; electrons replace those lost by PSII.

• Oxygen is released as a waste gas and is not used in photosynthesis.

How is ATP made by chemiosmosis in thylakoids?

• Electrons from PSI (cyclic) or PSII (non-cyclic) flow through carriers that pump protons into the thylakoid space.

• This creates a proton gradient with high H⁺ concentration inside the thylakoid.

• Protons flow back to the stroma through ATP synthase.

• ATP synthase uses the energy from proton flow to phosphorylate ADP.

• Chemiosmosis produces ATP needed for the Calvin cycle

How is NADP reduced in photosystem I

NADP is reduced by accepting two electrons from PSI and a H⁺from the stroma.

What 3 things happen in the thylakoid for photosynthesis?

• Photolysis of water occurs in thylakoids.

• ATP is synthesized by chemiosmosis in thylakoids.

• NADP is reduced in thylakoids.

What is RUBISCO? Is it abundant? How is carbon fixed by it? Why high concentration?

• RUBISCO is the enzyme that catalyzes carbon fixation in the Calvin cycle.

• It is the most abundant protein on Earth.

• RUBISCO fixes CO₂ by attaching it to RuBP to form unstable 6C intermediates.

• It must be present in high concentration due to low catalytic rate.

• It competes with oxygen, requiring large quantities to maintain CO₂ fixation.

• Plants invest heavily in RUBISCO to drive carbon assimilation.

How is triose phosphate synthesized using reduced NADP and ATP? (3 pts)

• ATP provides energy to convert 3-carbon intermediates into triose phosphate.

• Reduced NADP donates hydrogen to reduce the intermediate.

• Triose phosphate is used to build glucose or regenerate RuBP.

How is RuBP regenerated using ATP?

Five molecules of triose phosphate are rearranged into three RuBP molecules.

• ATP supplies the energy for regeneration steps.

• RuBP regeneration allows the Calvin cycle to continue.

• Most triose phosphate (five-sixths) must be recycled rather than used for glucose.

How are carbohydrates, amino acids, and other carbon compounds produced using Calvin cycle products and mineral nutrients?

Triose phosphate is converted into glucose and other carbohydrates.

• Nitrogen and sulfur from minerals allow synthesis of amino acids.

• Calvin cycle intermediates form fatty acids and other organic molecules.

How are light-dependent and light-independent reactions dependent on each other?

• Light-dependent reactions supply ATP and reduced NADP for the Calvin cycle.

• Light-independent reactions regenerate ADP and NADP needed again in the light reactions.

• Neither set can function long-term without the other.

• Both interact through chloroplast metabolism.

19. What is the structure of a chloroplast? Where do the light-dependent and light-independent reactions occur? (4 pts)

Chloroplasts have a double envelope enclosing the stroma and thylakoid membranes.

• Thylakoids are arranged in stacks called grana where the light-dependent reactions occur.

• The Calvin cycle occurs in the stroma where enzymes and ribulose bisphosphate are located.

• Chloroplasts also contain DNA and ribosomes for protein synthesis.

What is the difference between cyclic and non-cyclic photophosphorylation? When is cyclic used more?

Cyclic uses only photosystem I and produces ATP only.

• Non-cyclic uses both photosystems and produces ATP, NADPH, and oxygen.

• Cyclic is used when the plant needs extra ATP relative to NADPH.

• Non-cyclic is required to supply NADPH to the Calvin cycle.

• Cyclic helps prevent photoinhibition by diverting electrons.

21. How do sun plants and shade plants differ in their photosynthetic adaptations?

Sun plants have thicker leaves and more palisade cells to harvest intense light.

• Shade plants have more accessory pigments to absorb a broader range of wavelengths.

• Shade plants reach light saturation at low light intensity.

• Sun plants have higher maximum photosynthetic rates.

How do you interpret a light saturation graph for photosynthesis? (3 pts)

At low light intensity, the rate increases proportionally because light is limiting.

• At higher intensity, the rate plateaus when photosystems reach maximum capacity.

• The plateau indicates another factor is limiting (CO₂ or temperature).

What is the CO₂ compensation point and what does it show? (2 pts)

pts)

• The CO₂ level where photosynthesis equals respiration.

• Below this point, the plant releases more CO₂ than it fixes.

24. What is the full Z-scheme pathway of electrons in photosynthesis? (6 pts)

pts)

• Electrons start in water and are excited in photosystem II.

• They flow down an electron transport chain to photosystem I.

• At PSI, electrons are re-energized by light absorption.

• Electrons reduce NADP to form NADPH.

• The pathway creates a proton gradient for ATP synthesis.

• The Z-shape represents rising and falling energy states of electrons.

5. What is the role of transporters in chloroplast envelopes such as the triose phosphate–phosphate antiporter? (

pts)

• The antiporter exports triose phosphate to the cytosol while importing inorganic phosphate.

• This maintains phosphate supply for ATP synthesis in the stroma.

• It enables sugar synthesis in the cytosol.

Why must ATP and NADPH remain in the stroma, and how does chloroplast compartmentalization support photosynthesis? (

• ATP and NADPH are needed immediately by Calvin cycle enzymes in the stroma.

• The thylakoid membrane separates proton gradients from the stroma.

• Compartmentalization concentrates enzymes for each stage.

• It prevents diffusion of gradients that drive chemiosmosis.

What structural adaptations of thylakoids maximize photosynthesis?

pts)

• Large surface area from grana increases space for pigments and carriers.

• High density of ATP synthase enhances ATP production.

• Stacked membranes optimize absorption of shorter wavelengths.

• Thylakoid lumen allows proton accumulation.

How does temperature affect photosynthesis according to enzyme activity graphs?

Rate increases with temperature as enzymes gain kinetic energy.

• At high temperatures, enzymes denature and rate drops sharply.

• Rubisco and Calvin cycle enzymes are most temperature sensitive.

1. What is a ligand? (

• A ligand is a molecule that binds specifically to a receptor to initiate a cellular response.

How is cell signaling used by bacteria in quorum sensing? What is an example? (

Bacteria release signaling molecules that increase in concentration as the population grows.

• When the concentration reaches a threshold, bacteria alter gene expression collectively.

• Vibrio fischeri uses quorum sensing to activate bioluminescence genes in high population density.

How are hormones, neurotransmitters, cytokines, and calcium ions examples of functional categories of signaling chemicals in animals? (

Hormones act as long-distance chemical messengers transported in the bloodstream.

• Neurotransmitters transmit signals across synapses between neurons or to muscles.

• Cytokines regulate immune responses and communication between immune cells.

• Calcium ions act as intracellular second messengers that trigger rapid cellular changes.

• These categories differ in distance traveled and speed of action.

• They bind to specific receptors, triggering signal transduction pathways.

• They coordinate complex functions such as growth, immunity, movement, and metabolism.

How are localized and distant effects of signaling molecules different? How are hormones transported by the blood system different than neurotransmitters diffusing across a synaptic gap? (4 pts)

Local signaling affects nearby cells; distant signaling affects cells throughout the body.

• Hormones travel long distances through the bloodstream to reach target tissues.

• Neurotransmitters diffuse only a short distance across the synaptic cleft to the next cell.

• Hormonal responses are often slower but longer lasting than neurotransmitter responses.

5. Give 3 reasons why hormones and neurotransmitters are so diverse. (3 pts)

•

Organisms require different signals to regulate many specialized processes.

• Different receptors allow cells to respond selectively to specific chemicals.

• Chemical diversity allows for differences in speed, distance, and strength of signaling.

What are 2 differences between transmembrane receptors in a plasma membrane and intracellular receptors in the cytoplasm or nucleus? (2 pts)

Transmembrane receptors bind hydrophilic signals; intracellular receptors bind hydrophobic or lipid-soluble signals.

• Transmembrane receptors activate cascades at the membrane; intracellular receptors directly affect gene expression when activated.

 

7. What does the initiation of signal transduction pathways by receptors do?

• It leads to specific cellular responses such as gene expression, secretion, or metabolic change.

• It causes changes in enzyme activity

How do transmembrane receptors for neurotransmitters cause changes to membrane potential?

When acetylcholine binds, the receptor’s ion channel opens and allows Na⁺ ions to enter.

• This ion movement changes the membrane voltage and may trigger an action potential.

How do transmembrane receptors activate G proteins? Do humans have these? (2 pts)

• Ligand bi

Ligand binding changes the receptor’s shape, allowing it to activate a nearby G protein by exchanging GDP for GTP.

• Activated G proteins trigger downstream signaling pathways.

What is the mechanism of action of epinephrine (adrenaline) receptors? Include the roles of a G protein and cyclic AMP (cAMP). (4 pts)

• Epinephrine binds to a G-protein-coupled receptor on the cell membrane.

• The activated receptor stimulates a G protein to exchange GDP for GTP.

• The G protein activates adenylate cyclase, which converts ATP to cAMP.

• cAMP acts as a second messenger to activate protein kinase A, leading to cellular responses such as glycogen breakdown.

How do transmembrane receptors affect tyrosine kinase activity?

binding of insulin to a receptor in the plasma membrane, causing phosphorylation of tyrosine inside a cell. This leads to a sequence of reactions ending with movement of vesicles containing glucose transporters to the plasma membrane.)

What are 3 intracellular receptors that affect gene expression and how do they affect it? (4 pts)

hormones oestradiol, progesterone and testosterone as examples. Students should understand that the signalling chemical binds to a site on a receptor, activating it. The activated receptor binds to specific DNA sequences to promote gene transcription.)

What are 2 effects of the hormones oestradiol and progesterone on target cells?

Oestradiol promotes development of female secondary sex characteristics.

• Progesterone prepares and maintains the uterine lining.

• Oestradiol regulates the menstrual cycle.

• Progesterone suppresses contractions during pregnancy.

What is the difference between positive and negative feedback? Give an example of each

Negative feedback reverses a change to maintain homeostasis (e.g., insulin lowering blood glucose).

• Positive feedback amplifies a change to drive a process to completion (e.g., oxytocin increasing uterine contractions in childbirth).

• Negative feedback keeps internal conditions stable.

• Positive feedback produces rapid, escalating responses.

Outline the structure of a neuron

cytoplasm and a nucleus form the cell body of a neuron, with elongated nerve fibres of varying length projecting from it. An axon is a long single fibre. Dendrites are multiple shorter fibres. Electrical impulses are conducted along these fibres.

2. How is the generation of the resting potential established by pumping sodium and potassium ions?

Why is resting potential negative?

• The sodium–potassium pump moves 3 Na⁺ ions out of the neuron for every 2 K⁺ ions pumped in.

• This creates a concentration gradient: high Na⁺ outside and high K⁺inside.

• K⁺ leaks out more easily through potassium channels, making the inside less positive.

• The unequal pumping and ion leakage produce an electrical gradient.

• ATP provides the energy for active transport to maintain these gradients.

• The resting potential is negative because more positive charges leave than enter the neuron, leaving the inside relatively negative.

How do nerve impulses act as action potentials? What is depolarization and repolarization? (

Action potentials are rapid changes in membrane potential that travel along neurons.

• Depolarization occurs when sodium ions flow into the neuron, making the inside more positive.

• Repolarization occurs when potassium ions flow out, restoring a negative potential.

Compare variation in speed of nerve impulses in giant vs. small, and in myelinated vs. non-myelinated fibres.

Giant axons (like in squid) conduct impulses faster due to larger diameter and lower resistance.

• Small non-myelinated fibres conduct more slowly.

• Myelinated fibres are much faster because the impulse jumps between nodes of Ranvier.

• Non-myelinated fibres conduct more slowly because ions must move along the entire membrane length.

. What is a synapse? Can a signal be passed in both directions? (2 pts)

A synapse is a junction where a neuron communicates with another cell via neurotransmitters.

• Signals pass only one direction—from presynaptic to postsynaptic cell.

Explain the release of neurotransmitters from a presynaptic membrane.

• An action potential arrives at the presynaptic terminal.

• Voltage-gated calcium channels open and Ca²⁺ enters the terminal.

• Vesicles fuse with the presynaptic membrane and release neurotransmitter by exocytosis.

• Neurotransmitter diffuses across the synaptic cleft to bind receptors.

How is an excitatory postsynaptic potential (EPSP) generated? (5 pts)

• N

Neurotransmitter binds to receptors on the postsynaptic membrane.

• Ion channels open and allow Na⁺ or other positive ions to enter.

• The influx of positive charges depolarizes the postsynaptic membrane.

• If threshold is approached, an action potential may occur.

• EPSPs make the neuron more likely to fire.

How is depolarization and repolarization generated during action potentials?

• Depolarization occurs when voltage-gated sodium channels open and Na⁺ rushes in.

• Repolarization occurs when sodium channels close and voltage-gated potassium channels open.

• K⁺ flows out, restoring a negative membrane potential.

• The membrane briefly becomes hyperpolarized before returning to resting potential.

• Sodium channels inactivate to prevent backward propagation.

• Potassium channels close slowly.

How is propagation of an action potential along a nerve fibrecaused by local currents?

Incoming sodium causes local depolarization that spreads to adjacent membrane.

• This opens voltage-gated sodium channels further down the axon, continuing the action potential.

How can oscilloscope traces show resting potentials and action potentials?

They graph voltage across a neuron membrane over time.

• They show a flat line at resting potential and a sharp spike during an action potential.

How does saltatory conduction in myelinated fibres make impulses faster?

Ranvier)

• The myelin sheath insulates the axon and prevents ion movement across most of the membrane.

• Action potentials occur only at nodes of Ranvier, causing the impulse to “jump” between nodes.

• This greatly increases conduction speed

 

12. What are the effects of exogenous chemicals on synaptic transmission

Neonicotinoids bind irreversibly to acetylcholine receptors, causing continuous stimulation and paralysis in insects.

• Cocaine blocks the reuptake of dopamine, increasing dopamine concentration in synapses.

• Exogenous chemicals can mimic or block neurotransmitters.

• They can overstimulate or inhibit neural pathways.

13. How are inhibitory neurotransmitters and inhibitory postsynaptic potentials (IPSPs) generated? (

Inhibitory neurotransmitters open channels that allow Cl⁻ in or K⁺ out.

• This hyperpolarizes the postsynaptic membrane, making firing less likely.

• IPSPs counteract EPSPs to regulate signaling.

What is meant by summation of excitatory and inhibitory neurotransmitters in a postsynaptic neuron? (

The postsynaptic neuron integrates multiple EPSPs and IPSPs.

• If total depolarization reaches threshold, the neuron fires; if IPSPs outweigh EPSPs, it does not.

How is the perception of pain by free nerve endings generated?

Pain receptors have ion channels that open when stimulated by heat, acids, or chemicals like capsaicin.

• Entry of positive ions depolarizes the neuron.

• When threshold is reached, impulses travel to the brain, where pain is interpreted.

How does consciousness emerge?

Consciousness results from integrated neural activity across multiple brain regions.

• It arises from coordinated communication between cortical and subcortical networks.