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Quizzes > Science

Source of Energy in Food: Test What You Know

Quick, free quiz to test your knowledge of where food energy comes from. Instant results.

Editorial: Review CompletedCreated By: Catie SullivanUpdated Aug 27, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration of food energy molecules and enzyme catalysts on golden yellow background for fun quiz

This quiz helps you check your understanding of the source of energy in food and how that energy moves through food webs. For a deeper look, try the energy flow in ecosystems quiz or practice with a food chain energy quiz. You will see answers and brief explanations as you go.

What is the primary molecule that stores and transfers chemical energy in cells?
Glucose
ADP
ATP
NADH
Adenosine triphosphate (ATP) is the main energy currency of the cell because its terminal phosphate bonds store significant energy. When ATP is hydrolyzed to ADP and inorganic phosphate, energy is released to power cellular processes. Cells continually regenerate ATP through metabolic pathways such as glycolysis and oxidative phosphorylation. .
Which macronutrient yields the highest number of kilocalories per gram when metabolized?
Fats
Proteins
Carbohydrates
Alcohol
Fats provide about 9 kilocalories per gram, making them the most energy-dense macronutrient. Carbohydrates and proteins each yield about 4 kilocalories per gram, and alcohol yields about 7 kilocalories per gram. This high energy yield explains why fats are the body's preferred long-term storage form of energy. .
Which of the following is a simple carbohydrate commonly used by cells as fuel?
Glucose
Alanine
Cholesterol
Triglyceride
Glucose is a monosaccharide and a primary substrate for cellular respiration. It is broken down during glycolysis to produce ATP and intermediates for further metabolism. Other molecules like triglycerides and cholesterol are lipids, and alanine is an amino acid, not a carbohydrate. .
On nutrition labels, the term Calorie actually refers to which unit of energy?
1 kilocalorie
1 joule
1 calorie
1 kilojoule
The Calorie listed on food labels is actually a kilocalorie (kcal), equivalent to 1,000 small calories. This unit measures the amount of energy needed to raise the temperature of 1 kilogram of water by 1C. Scientists and nutritionists use kilocalories to quantify the energy content of foods. .
Which metabolic pathway breaks down glucose into pyruvate and generates a small amount of ATP?
Gluconeogenesis
Beta-oxidation
Glycogenesis
Glycolysis
Glycolysis is the ten-step enzymatic process that converts one molecule of glucose into two molecules of pyruvate, producing a net gain of two ATP molecules and two NADH molecules. Gluconeogenesis runs pathways in reverse to synthesize glucose, and beta-oxidation breaks down fatty acids. .
The standard free energy change (?G') for ATP hydrolysis under physiological conditions is approximately:
-7.3 kJ/mol
-30.5 kJ/mol
+30.5 kJ/mol
-200 kJ/mol
Under standard biochemical conditions (pH 7, 1 M concentrations), the hydrolysis of ATP to ADP and phosphate releases about 30.5 kJ/mol of free energy. This large negative ?G' drives many endergonic reactions in cells. The -7.3 kJ/mol value refers to calories rather than kilojoules. .
Which enzyme is responsible for producing ATP in the mitochondria during oxidative phosphorylation?
Hexokinase
Pyruvate kinase
ATP synthase
NADH dehydrogenase
ATP synthase harnesses the proton gradient across the inner mitochondrial membrane to catalyze the formation of ATP from ADP and inorganic phosphate. It is the final enzyme in the electron transport chain. Other enzymes like pyruvate kinase act in glycolysis, not oxidative phosphorylation. .
Niacin (vitamin B3) is a precursor for which essential coenzyme in cellular respiration?
Coenzyme A
NAD+
Biotin
FAD
Niacin is converted in cells to nicotinamide adenine dinucleotide (NAD+), which serves as an electron carrier in glycolysis, the citric acid cycle, and oxidative phosphorylation. Without NAD+, cells cannot effectively shuttle electrons or generate ATP. FAD is derived from riboflavin, and CoA from pantothenic acid. .
Which stage of cellular respiration produces the most ATP per glucose molecule?
Citric acid cycle
Fermentation
Electron transport chain
Glycolysis
The electron transport chain and oxidative phosphorylation together generate about 2628 ATP molecules per glucose by using the proton gradient to drive ATP synthase. Glycolysis yields 2 ATP, and the citric acid cycle yields 2 GTP (equivalent to ATP) per glucose. Fermentation yields no additional ATP beyond glycolysis. .
Enzymes accelerate biochemical reactions by:
Lowering the activation energy
Raising the temperature of the reaction
Changing the equilibrium constant
Increasing the overall free energy change
Enzymes function as catalysts by lowering the activation energy barrier of a reaction, making it easier for reactants to reach the transition state. They do not alter the net free energy change (?G) or equilibrium constant, nor do they change temperature. This property speeds up reaction rates significantly. .
In aerobic respiration, what is the final electron acceptor in the electron transport chain?
Oxygen
NAD+
Carbon dioxide
FADH2
Molecular oxygen serves as the terminal electron acceptor in the mitochondrial electron transport chain. It combines with electrons and protons to form water. Without oxygen, the chain backs up, and ATP production stops, leading to anaerobic metabolism. .
Which membrane in mitochondria maintains the proton gradient used for ATP synthesis?
Cell plasma membrane
Inner mitochondrial membrane
Thylakoid membrane
Outer mitochondrial membrane
The inner mitochondrial membrane is impermeable to most ions and harbors the protein complexes that pump protons to generate a gradient. This proton motive force drives ATP synthase. The outer membrane is more permeable and does not contribute to the gradient. .
Which reaction is exergonic and releases energy that can be harnessed by cells?
ADP + Pi ? ATP + H?O
Glucose + CO? ? C?H??O?
Amino acids ? proteins
ATP + H?O ? ADP + Pi
The hydrolysis of ATP to ADP and inorganic phosphate is exergonic, releasing about 30.5 kJ/mol under standard conditions. This reaction powers many cellular processes. The reverse reaction is endergonic and requires energy input. .
In enzyme kinetics, the Michaelis constant (Km) represents:
Turnover number of the enzyme
Substrate concentration at half Vmax
Maximum velocity of the reaction
Activation energy of the reaction
Km is defined as the substrate concentration at which the reaction rate is half of its maximum (Vmax). It reflects the affinity of the enzyme for its substratea lower Km indicates higher affinity. It is a key parameter in the MichaelisMenten equation. .
Which enzyme catalyzes the rate-limiting step of glycolysis, making it a key regulatory point in glucose metabolism?
Pyruvate kinase
Hexokinase
Phosphofructokinase-1 (PFK-1)
Aldolase
Phosphofructokinase-1 (PFK-1) catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, committing substrate to glycolysis. It is allosterically regulated by ATP, ADP, AMP, and citrate, controlling the flux based on cellular energy status. This regulation ensures efficient energy production. .
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Study Outcomes

  1. Identify the Ultimate Source of Energy in Food -

    After completing the quiz, readers can pinpoint the primary origin of energy in food at the cellular level, recognizing how nutrients are converted into usable fuel.

  2. Explain Photosynthesis and Energy Transformation -

    Readers will be able to outline the process by which sunlight is captured and stored in food molecules, connecting solar input to dietary energy.

  3. Describe Enzyme Catalysis -

    Participants will understand the role of enzyme catalysts in biochemical reactions, including how they accelerate reaction rates without being consumed.

  4. Analyze Factors Affecting Enzyme Activity -

    Quiz takers will learn to evaluate how variables like temperature and pH influence enzyme efficiency and reaction rates in living systems.

  5. Apply Knowledge in Food Energy Trivia -

    After engaging with the quiz, learners can confidently tackle energy in food trivia and enzyme catalyst questions across academic or casual settings.

Cheat Sheet

  1. Sunlight Powers Photosynthesis -

    The ultimate source of energy in food is sunlight, captured by chlorophyll during photosynthesis (6 CO₂ + 6 H₂O → C₆H₝₂O₆ + 6 O₂). This reaction stores solar energy in glucose, which plants and algae use as their primary fuel. Remember: "Light in, sugar out" to recall how the sun drives the food energy cycle.

  2. ATP: Cellular Energy Currency -

    Adenosine triphosphate (ATP) is the direct source of energy in food within our cells, releasing about 7.3 kcal/mol when its terminal phosphate bond is hydrolyzed. Enzyme catalysts like ATPases speed up this hydrolysis, ensuring quick energy delivery for muscle contraction and biosynthesis. Think "ATP pays the bills" to remember it fuels nearly every cellular process.

  3. Enzymes Lower Activation Energy -

    Enzyme catalysts reduce the activation energy needed for biochemical reactions, boosting reaction rates by factors of up to 10¹² (Source: National Center for Biotechnology Information). These protein catalysts bind substrates at the active site, forming enzyme - substrate complexes that ease transition states. Mnemonic trick: "Lock and Key" helps visualize substrate specificity in enzyme action.

  4. Macronutrient Oxidation Yields Energy -

    When glucose (carbs), fatty acids (fats), or amino acids (proteins) are oxidized, they generate ATP through glycolysis, β-oxidation, and the citric acid cycle (Journal of Biological Chemistry). Carbs and proteins yield ~4 kcal/g, while fats give ~9 kcal/g - key figures for energy in food trivia. Use the ratio "4-4-9" to quickly recall caloric values per gram of each macronutrient.

  5. Memory Aids for Metabolic Pathways -

    To ace enzyme catalyst questions and energy in food quiz items, memorize glycolysis steps with "Goodness Gracious, Father Franklin Didn't Go Buy Perfect Pumpkins" (Glucose to Pyruvate). For the citric acid cycle, try "Oh, Citrate Is Krebs' Starting Substrate For Making Oxaloacetate" to cue each intermediate. These mnemonic phrases streamline recall of complex metabolic routes.

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