Biology 121 – Energy, Photosynthesis & Cellular Respiration (Ch. 6–8)

60 Question-and-Answer flashcards covering key concepts from Chapters 6–8: energy types, thermodynamics, metabolism, enzymes, photosynthesis, and cellular respiration.

What is potential energy?

Stored energy possessed by an object or molecule.

Which type of energy is defined as the energy of motion?

Kinetic energy.

What kind of energy is stored in chemical bonds such as those in glucose or ATP?

Chemical energy.

Which law of thermodynamics states that energy cannot be created or destroyed but only transformed?

The First Law of Thermodynamics.

According to the Second Law of Thermodynamics, energy transformations increase a system’s .

Entropy (disorder).

What term describes the sum of all chemical reactions occurring in a cell or organism?

Metabolism.

Which metabolic pathway builds complex molecules and requires energy input?

Anabolism.

Which metabolic pathway breaks molecules down and releases energy?

Catabolism.

A reaction that releases energy is called an reaction.

Exergonic.

A reaction that consumes or requires energy input is called an reaction.

Endergonic.

Define activation energy.

The minimum amount of energy required to start a chemical reaction.

What is a catalyst?

A substance that speeds up a reaction without being consumed in the process.

What is a biological catalyst that possesses an active site for substrate binding?

An enzyme.

How do enzymes affect activation energy?

They lower the activation energy needed for a reaction.

What is competitive inhibition of an enzyme?

Inhibitor competes with the substrate for the enzyme’s active site.

In noncompetitive inhibition, where does the inhibitor bind?

To an allosteric (non-active) site, altering the enzyme’s shape.

What is an allosteric site on an enzyme?

A regulatory site other than the active site where molecules can bind to influence activity.

What is feedback inhibition?

When the end product of a metabolic pathway inhibits an enzyme earlier in the same pathway.

List four factors that can affect enzyme activity.

Enzyme concentration, substrate concentration, temperature, pH (and vitamins/coenzymes).

What is a biochemical pathway?

A series of enzyme-catalyzed reactions where the product of one step becomes the substrate for the next.

Name the three structural components of an ATP molecule.

Adenine, ribose sugar, and three phosphate groups.

How is energy released from ATP?

By breaking the bond between the last two phosphate groups (forming ADP + Pi).

Write the overall equation for photosynthesis.

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.

Which colors of visible light are most strongly absorbed and used in photosynthesis?

Red and blue wavelengths.

Identify the primary photosynthetic pigments in plants.

Chlorophyll a and chlorophyll b.

What accessory pigments help broaden the absorption spectrum of plants?

Carotenoids (including xanthophylls).

Through what leaf openings does CO₂ enter for photosynthesis?

Stomata.

In which leaf tissue do most photosynthetic reactions occur?

Mesophyll cells.

Name the two main regions of a chloroplast and the processes that occur in each.

Thylakoids – light reactions; Stroma – Calvin cycle (dark reactions).

Where do the light-dependent reactions of photosynthesis take place?

On the thylakoid membrane of the chloroplast.

What are the three chief products of the light reactions?

ATP, NADPH, and O₂.

Which enzyme catalyzes CO₂ fixation in the Calvin cycle?

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase).

What three-carbon sugar is produced in the Calvin cycle and later used to form glucose?

Glyceraldehyde-3-phosphate (G3P).

Which two energy carriers produced by the light reactions power the Calvin cycle?

ATP and NADPH.

Provide the overall equation for cellular respiration.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP).

Where in the cell does glycolysis occur?

The cytoplasm.

What are the end products of glycolysis?

Pyruvate, NADH, and a net gain of 2 ATP.

Is glycolysis an aerobic or anaerobic process?

Anaerobic (does not require oxygen).

What molecule is formed from pyruvate during the transition (preparatory) reaction?

Acetyl-CoA.

Where does the citric acid (Krebs) cycle occur?

In the mitochondrial matrix.

What is the first stable compound produced in the citric acid cycle?

Citrate (citric acid).

How many ATP molecules are produced directly by the citric acid cycle per glucose?

2 ATP.

Where is the electron transport chain (ETC) located in eukaryotic cells?

The inner mitochondrial membrane (cristae).

Which two molecules donate high-energy electrons to the ETC?

NADH and FADH₂.

What is the final electron acceptor in the mitochondrial ETC?

Oxygen (O₂).

Approximately how many ATP are generated by the ETC per molecule of glucose?

About 32–34 ATP.

Under anaerobic conditions, how many total ATP are produced via glycolysis followed by fermentation?

2 ATP.

What are the fermentation products of yeast?

Ethanol and carbon dioxide.

What compound accumulates in muscle cells during lactic acid fermentation?

Lactic acid.

Which stage of aerobic respiration yields the majority of ATP?

The electron transport chain (oxidative phosphorylation).

Organisms that synthesize their own glucose through photosynthesis are called .

Autotrophs.

Organisms that must consume other organisms for glucose are called .

Heterotrophs.

Which molecule is often referred to as an “uncharged battery” relative to ATP?

ADP (adenosine diphosphate).

How many total ATP are typically produced from complete aerobic respiration of one glucose molecule?

About 36 ATP (sometimes cited as 36–38).

During photosynthesis, what is the role of NADPH?

It carries high-energy electrons for the reduction of CO₂ in the Calvin cycle.

What enzyme synthesizes ATP using the proton motive force in both chloroplasts and mitochondria?

ATP synthase.

What happens to most enzymes when temperature rises far above their optimum?

They denature, causing a decrease in activity.

What is irreversible inhibition of an enzyme?

Permanent inactivation where the inhibitor covalently binds to the enzyme.

In biological systems, what is mechanical energy?

Energy of movement, such as muscle contraction.

If chemical energy is converted to mechanical energy, what happens to the total amount of energy in the system according to the First Law?

It remains constant; energy is conserved.