Photosynthesis, Cellular Respiration, and DNA – Exam Review

A comprehensive set of question-and-answer flashcards covering key concepts from Chapters 5 – 7: photosynthesis, cellular respiration, and DNA structure/function.

What are the reactants of photosynthesis?

Carbon dioxide (CO₂), water (H₂O), and light energy (sunlight).

What are the products of photosynthesis?

Glucose (C₆H₁₂O₆) and oxygen (O₂).

Which organelle carries out photosynthesis?

The chloroplast.

What powers the light reactions in photosynthesis?

Solar energy, specifically the mid-range wavelengths of visible light.

Which molecules supply energy for the carbon (Calvin) reactions?

ATP and NADPH.

Is NADP⁺ oxidized or reduced?

Oxidized (it has lost electrons).

Is NADPH oxidized or reduced?

Reduced (it has gained electrons and a hydrogen).

Which molecule donates electrons at the start of photosynthesis?

Water (H₂O).

After the photosynthetic electron transport chain, which carrier holds the electrons?

NADP⁺, which becomes NADPH after accepting the electrons and H⁺.

Differentiate autotrophs from heterotrophs.

Autotrophs make their own energy-rich compounds from inorganic sources; heterotrophs must consume other organisms for energy.

Why is a proton (H⁺) gradient essential in photosynthesis?

It drives ATP synthase; protons flow from high to low concentration through the enzyme, producing ATP.

Within which membrane are chlorophyll pigments embedded?

The thylakoid membrane inside chloroplasts.

Order these plant structures from smallest to largest: photosystem, thylakoid, granum, chloroplast, mesophyll cell, leaf.

Photosystem → thylakoid → granum → chloroplast → mesophyll cell → leaf.

What structures on leaves allow gas exchange?

Stomata.

Which enzyme catalyzes the first Calvin-cycle reaction?

Rubisco.

Define carbon fixation.

Incorporation of carbon from CO₂ into an organic compound during the Calvin cycle.

During Calvin reactions, PGA is converted into what?

Phosphoglyceraldehyde (PGAL).

What provides the energy for converting PGA to PGAL?

ATP and NADPH produced in the light reactions.

How many PGAL molecules form one glucose molecule?

Two PGAL molecules combine to make one glucose.

During glycolysis, one glucose yields how many pyruvate molecules?

Two pyruvate molecules.

Where does glycolysis occur?

In the cytosol (cytoplasm).

In which organelle does the Krebs cycle take place?

The mitochondrion.

Where is the electron transport chain located in eukaryotic cells?

The inner mitochondrial membrane.

List the reactants and products of cellular respiration.

Reactants: glucose and O₂. Products: CO₂, H₂O, and ATP.

Define chemiosmotic phosphorylation.

ATP synthesis driven by the flow of H⁺ down its gradient through ATP synthase.

Put these aerobic-respiration steps in order: glycolysis, formation of acetyl-CoA, Krebs cycle, electron transport chain, chemiosmotic phosphorylation.

Glycolysis → formation of acetyl-CoA → Krebs cycle → electron transport chain → chemiosmotic phosphorylation.

What is ATP synthase?

A membrane enzyme that uses proton flow to convert ADP + Pᵢ into ATP.

Does glycolysis require oxygen?

No; it is anaerobic.

Do the Krebs cycle and electron transport chain require oxygen?

Yes; both are aerobic.

What is the net yield of ATP from one glucose during cellular respiration?

About 36 ATP.

Define ATP.

Adenosine triphosphate, the energy currency of the cell.

What does the word “synthesis” mean?

To create or produce something.

What are endergonic reactions, and how are they linked to ATP?

Reactions that require an input of energy; ATP supplies that energy.

Why is a proton gradient necessary for cellular respiration?

It powers ATP synthase during oxidative phosphorylation.

What is the final electron acceptor at the end of the electron transport chain?

Oxygen.

Which organelle generates most ATP in animal cells?

The mitochondrion.

Name the two electron carriers produced during glycolysis and the Krebs cycle.

NADH (glycolysis & Krebs) and FADH₂ (Krebs only).

List the main products of one turn of the Krebs cycle.

2 CO₂, 1 ATP, 3 NADH, and 1 FADH₂ (per acetyl-CoA).

Can proteins and fats enter the cellular-respiration pathway?

Yes; their components can feed into glycolysis or the Krebs cycle.

During aerobic respiration, what happens to the carbon atoms from glucose?

They are released as CO₂.

State two structural differences between DNA and RNA.

DNA is double-stranded and uses thymine; RNA is single-stranded and uses uracil.

What region of DNA does RNA polymerase first bind?

The promoter.

List three mRNA modifications before nuclear exit.

5′ cap addition, poly-A tail addition, and removal of introns (splicing).

Differentiate introns from exons.

Exons code for amino acids and exit the nucleus; introns are non-coding regions removed during mRNA processing.

What is the function of tRNA?

Carries specific amino acids to the ribosome and matches them to codons on mRNA.

State the primary function of ribosomes.

They are the sites of protein synthesis (translation).

Define mutation.

A change in a cell’s DNA sequence.

What is a silent mutation?

A substitution that does not alter the encoded amino acid and therefore has no effect on the protein.

Define substitution mutation.

Replacement of one base pair with another in DNA.

Describe insertion and deletion mutations.

Insertion adds nucleotides; deletion removes nucleotides from the DNA sequence.

Why is the complementary strand to 5′-ATCGTACG-3′ written 3′-TAGCATGC-5′?

It is both complementary and antiparallel to the original strand.

What codon initiates translation?

AUG (methionine).

List the three stop codons.

UAA, UAG, and UGA.

In the mRNA 5′-GGAUAACUAUGCCCAAA-3′, which is the first codon translated and why?

AUG; it is the universal start codon signaling translation initiation.