BIO 1124 – Unit 3: Energy and Metabolism (Chs 46, 6–8)

55 question-and-answer style flashcards covering major concepts, terms, reactions, and processes from Unit 3 lecture notes on animal nutrition, thermodynamics, enzymes, cellular respiration, fermentation, and photosynthesis.

What are the four steps in animal food processing?

Ingestion, digestion, absorption, and egestion/defecation.

Name the three trophic categories of animals based on diet.

Herbivores (plant eaters), carnivores (consume animal flesh or fluids), and omnivores (eat both plant and animal material).

List the three primary things food provides for animals.

1) Energy that can be converted to ATP, 2) essential nutrients the body cannot synthesize, and 3) raw materials to build body tissues and molecules.

What are the four categories of essential nutrients?

Essential amino acids, essential fatty acids, vitamins, and minerals.

Define a vitamin and distinguish water-soluble from fat-soluble vitamins.

Vitamins are small organic molecules required in trace amounts. Water-soluble (C and B) must be eaten regularly; fat-soluble (A, D, E, K) are stored in body fat.

What is a mineral in nutritional terms?

An inorganic ion (e.g., Mg²⁺, Fe²⁺/³⁺, I⁻) required in trace amounts for normal physiological functions.

Why are some amino acids and fatty acids called “essential”?

Because an organism cannot synthesize them and must obtain them pre-formed in the diet.

What is micronutrient malnutrition and give two example effects.

Deficiency of one or more vitamins or minerals; examples include anemia (iron deficiency), xerophthalmia (vitamin A deficiency causing dry eyes), and goiter (iodine deficiency).

Define energy and name its two main forms.

Energy is the capacity to do work or cause change. The two main forms are kinetic (associated with motion) and potential (stored due to structure, position, or composition).

What is metabolism?

The sum of all chemical reactions (catabolic and anabolic) occurring in a cell or organism.

Which catalysts guide the steps of metabolic pathways?

Enzymes.

State the first law of thermodynamics and its implication for organisms.

Law of conservation of energy: energy cannot be created or destroyed, only transformed—organisms must obtain energy from their environment rather than create it.

Which thermodynamic law explains why 100 % of food energy is not converted to usable ATP?

The second law of thermodynamics (entropy increases; some energy is lost as heat).

Where does the energy lost from food conversion typically go?

It is dissipated as heat, contributing to metabolic heat production and limiting energy transfer up food chains.

What is Gibbs free energy (G) used to measure in reactions?

The usable energy available to do work during a chemical reaction at constant temperature and pressure.

What ΔG sign characterizes an exergonic reaction?

Negative ΔG (< 0); the reaction releases free energy and is spontaneous.

What ΔG sign characterizes an endergonic reaction, and what molecule usually supplies the needed energy?

Positive ΔG (> 0); ATP commonly provides the input energy.

Do enzymes alter the ΔG of a reaction?

No; they lower activation energy but do not change ΔG.

What type of biomolecule is an enzyme?

Most enzymes are proteins (some are catalytic RNA).

What is the region on an enzyme where substrates bind?

The active site.

What are the reactants in an enzyme-catalyzed reaction called?

Substrates.

Name and describe the model of fit between enzyme and substrate.

Induced-fit model: binding causes both enzyme and substrate to change shape slightly, improving catalytic efficiency and forming an enzyme–substrate complex.

List two environmental factors that influence enzyme activity.

Temperature and pH (others include ionic strength and cofactors).

Differentiate competitive and non-competitive inhibition.

Competitive: inhibitor binds the active site, blocking substrate access. Non-competitive (allosteric): inhibitor binds a separate site, changing enzyme shape and reducing activity.

What are coenzymes and cofactors?

Coenzymes are small organic molecules that temporarily carry chemical groups or electrons (e.g., NAD⁺). Cofactors are inorganic ions (often metals) that bind reversibly and are required for enzyme function.

Explain the boulder-on-a-hill analogy for activation energy.

Pushing a boulder over a hill requires an initial energy input (activation energy); enzymes lower this hill, making the reaction proceed more easily.

Define a redox reaction.

A reaction in which one substance is oxidized (loses electrons) and another is reduced (gains electrons).

In redox terms, what does it mean if a substance is oxidized? Reduced?

Oxidized: loses electrons (or hydrogen). Reduced: gains electrons (or hydrogen).

What molecule is most often used to pay for cellular work?

ATP (also NADH is an energy carrier but ATP directly powers work).

When ATP is hydrolyzed, what are the products?

ADP, inorganic phosphate (Pᵢ), and released free energy.

Provide the overall equation for cellular respiration.

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP (and heat).

List the four major stages of cellular respiration.

Glycolysis, transition reaction (pyruvate oxidation), citric acid (Krebs) cycle, and oxidative phosphorylation (electron transport chain + chemiosmosis).

Which respiratory stage actually contains two subprocesses?

Oxidative phosphorylation—composed of the electron transport chain and chemiosmosis/ATP synthase activity.

Which stages of cellular respiration require oxygen?

Transition reaction, citric acid cycle, electron transport chain, and chemiosmosis (all but glycolysis).

Name the two mechanisms by which ATP is produced in cells.

Substrate-level phosphorylation and oxidative phosphorylation (via chemiosmosis).

For glycolysis, state location, main reactants, and net products.

Location: cytoplasm. Reactant: glucose. Net products: 2 pyruvate, 2 ATP (net), and 2 NADH.

For the transition reaction, give location and products.

Location: mitochondrial matrix. Products per glucose: 2 acetyl-CoA, 2 CO₂, and 2 NADH.

For the citric acid (Krebs) cycle, give location and products.

Location: mitochondrial matrix. Products per glucose (two turns): 4 CO₂, 6 NADH, 2 FADH₂, and 2 ATP.

For the electron transport chain, give location and purpose.

Location: inner mitochondrial membrane. Purpose: transfer electrons from NADH/FADH₂ to O₂ while pumping protons to create an H⁺ gradient.

For chemiosmosis, what drives ATP synthesis and about how much ATP is made?

The proton (H⁺) gradient drives ATP synthase; about 26–28 ATP are produced per glucose.

How many net ATP are produced per glucose in glycolysis, citric acid cycle, and oxidative phosphorylation?

Glycolysis: 2 ATP, citric acid cycle: 2 ATP, oxidative phosphorylation: ~26–28 ATP, giving ~30 ATP total (varies by cell type).

Why is oxygen called the final electron acceptor in respiration, and what happens if it is absent?

O₂ accepts electrons at the end of the ETC, forming water; without O₂, electrons back up, the proton gradient collapses, ATP synthase stops, and cells quickly die from energy failure.

Can fats and proteins fuel cellular respiration? Briefly explain.

Yes; their breakdown products (glycerol, fatty acids, amino-acid carbon skeletons) enter at glycolysis, acetyl-CoA, or Krebs cycle intermediates to generate ATP.

Besides aerobic respiration, what metabolic options exist without oxygen?

Anaerobic respiration (uses an alternate final electron acceptor) and fermentation (e.g., lactic acid or alcoholic fermentation).

What molecule must be regenerated by fermentation to keep glycolysis running?

NAD⁺ (oxidized form).

Compare lactic acid fermentation in humans with alcoholic fermentation in yeast.

Humans (muscle, RBCs) reduce pyruvate to lactate; yeast reduce pyruvate to ethanol and CO₂. Both regenerate NAD⁺ for glycolysis.

Define autotroph and heterotroph.

Autotroph: organism that makes organic molecules from inorganic CO₂ (e.g., plants). Heterotroph: organism that must consume organic food (e.g., humans).

In which organisms does photosynthesis occur?

Photoautotrophs, including plants, algae, and some bacteria (cyanobacteria).

Give the summary equation of photosynthesis and explain its relation to respiration.

6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂; it is essentially the reverse of aerobic cellular respiration.

What pigment traps light energy in plants?

Chlorophyll (primarily chlorophyll a and b).

What wavelength range constitutes photosynthetically active radiation?

Approximately 400 nm – 700 nm (visible light).

Name the two main locations inside chloroplasts where photosynthetic reactions occur.

Thylakoid membranes (light reactions) and the stroma (Calvin cycle).

What occurs during the light reactions (location, main products)?

In thylakoid membranes: light energy drives water splitting and an ETC to produce ATP and NADPH, releasing O₂.

Where does the Calvin cycle occur and what are its products?

In the stroma; uses ATP and NADPH to fix CO₂ into glyceraldehyde-3-phosphate (G3P), which forms glucose and other carbohydrates.

What is carbon fixation and what does it reveal about the composition of trees?

Conversion of inorganic CO₂ into organic carbon (RuBP + CO₂ → 3-PGA); it shows that most of a tree’s mass comes from atmospheric CO₂, not soil.