STEM Readiness: Biology Readiness - Energy Metabolism: Photosynthesis - Light Reactions, ATP, NADPH, and Calvin, Cycle G3P

Must?Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotes lack a membrane-bound nucleus; DNA resides in the nucleoid region (e.g., Escherichia coli).
• Eukaryotes have a membrane-bound nucleus containing linear chromosomes (e.g., human liver cell).
• Prokaryotic ribosomes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, supporting endosymbiotic origin.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., bacterial cell walls in Staphylococcus aureus).
• Archaea lack peptidoglycan; their cell walls are made of pseudopeptidoglycan or other polysaccharides.
• Plant cells have cellulose-based cell walls; fungal cells have chitin-based walls.
• Animal cells lack a cell wall entirely (only plasma membrane).
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems (e.g., endoplasmic reticulum, Golgi apparatus); prokaryotes do not.
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores regulating transport.
• Nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly.
• Endoplasmic reticulum (ER): Rough ER has ribosomes and synthesizes proteins; smooth ER synthesizes lipids and detoxifies.
• Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery (e.g., glycosylation of proteins).
• Mitochondria are the site of aerobic respiration and have double membranes; inner membrane folded into cristae.
• Chloroplasts (in plants and algae) perform photosynthesis and contain thylakoids and grana.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion at low pH.
• Peroxisomes break down fatty acids and detoxify hydrogen peroxide (H?O?).
• Cytoskeleton components (microtubules, microfilaments, intermediate filaments) maintain cell shape and enable motility in eukaryotes.
• Prokaryotes have no cytoskeleton homologs with identical structure; however, proteins like FtsZ (tubulin analog) aid in division.
• Mycoplasma species are bacteria without a cell wall, making them resistant to penicillin.
• Mature mammalian red blood cells lack a nucleus and organelles, maximizing hemoglobin capacity.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Binary fission is the method of reproduction in prokaryotes; eukaryotes undergo mitosis and meiosis.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, with attention to exceptions.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; archaea, plants, and fungi use different structural materials.
Trap: Ribosome size correlates with cell complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, not 80S.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, and some have protein-based cytoskeletal analogs.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature found in eukaryotic cells but NOT in prokaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Membrane-bound nucleus
D) Plasma membrane
Answer: C
Explanation: A membrane-bound nucleus is exclusive to eukaryotes.
Why the top distractor is wrong: Circular DNA is present in prokaryotes and also in mitochondria and chloroplasts of eukaryotes.

Question: A cell is observed to have a cell wall made of cellulose, chloroplasts, and large central vacuoles. Which domain does it most likely belong to?
A) Bacteria
B) Archaea
C) Eukarya – Fungi
D) Eukarya – Plants
Answer: D
Explanation: Cellulose cell walls, chloroplasts, and central vacuoles are diagnostic of plant cells.
Why the top distractor is wrong: Fungi have chitin cell walls and lack chloroplasts.

Question: Which structure is present in both prokaryotes and eukaryotes?
A) Nucleolus
B) Mitochondria
C) 80S ribosomes
D) Plasma membrane
Answer: D
Explanation: All cells have a phospholipid bilayer plasma membrane.
Why the top distractor is wrong: The nucleolus is only found in eukaryotic nuclei.

Question: Which of the following provides the strongest evidence for the endosymbiotic theory?
A) Eukaryotic cells are larger than prokaryotic cells
B) Mitochondria have their own circular DNA and 70S ribosomes
C) Prokaryotes reproduce by binary fission
D) Lysosomes contain digestive enzymes
Answer: B
Explanation: Mitochondria’s independent DNA and ribosomes resemble those of bacteria.
Why the top distractor is wrong: Cell size differences do not indicate evolutionary origin.

Question: Which cell type lacks a nucleus and has 70S ribosomes?
A) Fungal cell
B) Plant cell
C) Bacterial cell
D) Animal cell
Answer: C
Explanation: Bacteria are prokaryotes with no nucleus and 70S ribosomes.
Why the top distractor is wrong: Fungal, plant, and animal cells are eukaryotes with 80S ribosomes and nuclei.

Last?Minute Revision (20–25 one?liners)

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• DNA in prokaryotes: nucleoid (no membrane); eukaryotes: nucleus (double membrane).
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacterial cell walls contain peptidoglycan; archaeal walls do not.
• Plant cell walls: cellulose; fungal: chitin; animal: no cell wall.
• Both cell types have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes do not.
• Nuclear pores regulate mRNA and protein transport in eukaryotes.
• Nucleolus = site of rRNA synthesis and ribosome subunit assembly.
• Rough ER = protein synthesis; smooth ER = lipid synthesis and detoxification.
• Golgi apparatus = modifies, sorts, packages proteins (e.g., adds carbohydrates).
• Mitochondria = site of ATP production via aerobic respiration.
• Mitochondrial inner membrane folds = cristae; increase surface area.
• Chloroplasts contain thylakoids (site of light reactions) stacked into grana.
• Lysosomes (animal cells) maintain acidic pH for hydrolytic enzyme activity.
• Peroxisomes break down very long chain fatty acids and neutralize H?O?.
• Cytoskeleton includes microtubules (tubulin), microfilaments (actin), intermediate filaments.
• Prokaryotic division protein FtsZ is a tubulin homolog.
• Mycoplasma = bacteria without cell wall; resistant to beta-lactams.
• Mature red blood cells = no nucleus, no mitochondria.
• Endosymbiotic theory: mitochondria evolved from alpha-proteobacteria; chloroplasts from cyanobacteria.
• Binary fission = asexual reproduction in prokaryotes.
• Mitosis and meiosis occur only in eukaryotes.
• Verify from standard textbook: exact composition of archaeal cell walls varies by species.