Cellular Energy — Practice Quiz
A Biology cheat sheet for Cellular Energy — every key formula with its symbols defined — plus a medium-level practice quiz to test recall.
Formulas & key concepts
The primary energy currency of the cell. Composed of adenine, ribose, and three phosphate groups. Releases energy when a phosphate bond is broken to form ADP.
A lower-energy molecule that can be converted into ATP by the addition of a phosphate group. Acts like a rechargeable battery.
<b>Heterotrophs</b>: Organisms that obtain energy by consuming other living things (e.g., animals, fungi).<br><b>Autotrophs</b>: Organisms that make their own food using energy from sunlight or chemicals (e.g., plants, algae).
All chemical reactions inside a cell. <b>Anabolic</b>: Building complex molecules (requires energy). <b>Catabolic</b>: Breaking down molecules (releases energy).
<b>1st Law</b>: Energy cannot be created or destroyed, only transformed.<br><b>2nd Law</b>: Energy transfers increase entropy (disorder); some energy is lost as heat.
<b>Kinetic</b>: Energy of motion.<br><b>Potential</b>: Stored energy (position/structure).<br><b>Chemical</b>: Potential energy stored in chemical bonds.
<b>Exergonic</b>: Releases energy (spontaneous, negative ΔG).<br><b>Endergonic</b>: Absorbs energy (non-spontaneous, positive ΔG).
Biological catalysts (proteins) that speed up reactions by lowering <b>activation energy</b>. They have an <b>active site</b> where specific <b>substrates</b> bind (Induced Fit model).
Process of breaking down glucose to produce ATP. Three main stages: Glycolysis, Citric Acid Cycle, and Oxidative Phosphorylation.
First stage of respiration. Occurs in cytoplasm. Breaks 1 glucose (6C) into 2 pyruvate (3C). Produces net 2 ATP and 2 NADH. Anaerobic.
Second stage. Occurs in mitochondrial matrix. Pyruvate -> Acetyl-CoA -> Cycle. Produces CO2, ATP, NADH, and FADH2.
Third stage. Occurs in inner mitochondrial membrane. Electron Transport Chain uses electrons from NADH/FADH2 to pump H+ ions. <b>Chemiosmosis</b> (ATP Synthase) uses H+ gradient to make ATP. Oxygen is final electron acceptor (forms water).
Anaerobic process to regenerate NAD+ so glycolysis can continue. <b>Lactic Acid</b>: Muscles/bacteria (produces lactate). <b>Alcoholic</b>: Yeast (produces ethanol + CO2).
Practice quiz
Which of the following statements accurately describes the relationship between ATP and ADP?
- ATP is formed by breaking a phosphate bond from ADP, releasing energy.
- ADP is a higher-energy molecule than ATP, storing more chemical potential.
- ATP is converted to ADP by adding a phosphate group, storing energy.
- ADP is converted to ATP by adding a phosphate group, requiring energy.
Answer: ADP is converted to ATP by adding a phosphate group, requiring energy.
A mushroom obtains its energy by decomposing dead organic matter. Based on this, how would the mushroom be classified?
- Autotroph
- Heterotroph
- Chemotroph
- Phototroph
Answer: Heterotroph
The synthesis of a complex protein from individual amino acids is an example of what type of metabolic process?
- Catabolic, as it breaks down molecules.
- Anabolic, as it builds complex molecules and requires energy.
- Exergonic, as it releases energy spontaneously.
- Glycolytic, as it involves glucose breakdown.
Answer: Anabolic, as it builds complex molecules and requires energy.
According to the second law of thermodynamics, what is the general trend for energy transfers in a closed system?
- Energy is created to maintain order.
- Energy is destroyed, leading to increased complexity.
- Energy transfers increase the entropy of the universe, with some energy lost as heat.
- Energy is conserved, and all transformations are perfectly efficient.
Answer: Energy transfers increase the entropy of the universe, with some energy lost as heat.
A chemical reaction that has a positive change in Gibbs free energy ($ \Delta G > 0 $) would be classified as:
- Exergonic and spontaneous.
- Endergonic and non-spontaneous.
- Catabolic and energy-releasing.
- Anabolic and energy-releasing.
Answer: Endergonic and non-spontaneous.
How do enzymes primarily function to speed up biochemical reactions?
- By increasing the overall free energy change ($ \Delta G $) of the reaction.
- By providing additional energy to the reactants.
- By lowering the activation energy required for the reaction to proceed.
- By changing the equilibrium point of the reaction.
Answer: By lowering the activation energy required for the reaction to proceed.
Which of the following correctly lists the three main stages of cellular respiration in order?
- Citric Acid Cycle, Glycolysis, Oxidative Phosphorylation
- Glycolysis, Oxidative Phosphorylation, Citric Acid Cycle
- Glycolysis, Citric Acid Cycle, Oxidative Phosphorylation
- Fermentation, Glycolysis, Citric Acid Cycle
Answer: Glycolysis, Citric Acid Cycle, Oxidative Phosphorylation
During glycolysis, one molecule of glucose ($6$ carbons) is broken down into two molecules of pyruvate ($3$ carbons). This process occurs in the cytoplasm and results in a net production of:
- $2$ ATP and $2$ FADH$_2$
- $2$ ATP and $2$ NADH
- $32$ ATP and $2$ NADH
- $2$ CO$_2$ and $2$ ATP
Answer: $2$ ATP and $2$ NADH
In oxidative phosphorylation, what is the role of oxygen?
- It acts as the primary electron donor to the electron transport chain.
- It directly produces ATP via substrate-level phosphorylation.
- It serves as the final electron acceptor, forming water.
- It pumps protons ($ \text{H}^+ $) into the intermembrane space.
Answer: It serves as the final electron acceptor, forming water.
What is the primary purpose of fermentation in cells when oxygen is not available?
- To directly produce a large amount of ATP.
- To regenerate NAD$^+$ so that glycolysis can continue.
- To produce carbon dioxide for cellular respiration.
- To convert pyruvate into acetyl-CoA for the Citric Acid Cycle.
Answer: To regenerate NAD$^+$ so that glycolysis can continue.
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