STEM Readiness: Biology Readiness - Energy Metabolism: Cellular Respiration - Glycolysis, Pyruvate Oxidation, Krebs Cycle, ETC, ATP Yield

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 include bacteria and archaea; eukaryotes include animals, plants, fungi, and protists.
• DNA in prokaryotes is located in the nucleoid, a region without a membrane; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain organelles such as mitochondria, lysosomes, and the Golgi apparatus.
• Ribosomes in prokaryotes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting the endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., Escherichia coli); archaea lack peptidoglycan and have different wall chemistry.
• Plant cell walls are made of cellulose; fungal cell walls contain chitin; animal cells lack a cell wall.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to antibiotics like penicillin that target peptidoglycan synthesis.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane that regulates transport and maintains cell integrity.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER) and Golgi apparatus; prokaryotes do not.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate RNA and protein transport.
• Nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly.
• Smooth ER synthesizes lipids and detoxifies drugs; rough ER (with ribosomes) synthesizes proteins for secretion.
• Golgi apparatus modifies, sorts, and packages proteins into vesicles for transport to lysosomes, plasma membrane, or secretion.
• Mitochondria are the site of aerobic respiration and ATP production; they have double membranes and their own circular DNA.
• Chloroplasts (in plants and algae) perform photosynthesis; they contain thylakoids, chlorophyll, and their own circular DNA.
• Lysosomes contain hydrolytic enzymes that break down macromolecules, old organelles, and pathogens; absent in most plant cells.
• Peroxisomes break down fatty acids and detoxify hydrogen peroxide; present in both plant and animal eukaryotic cells.
• Centrioles (involved in microtubule organization during cell division) are found in animal cells but not in most plant cells.
• Red blood cells in mammals lack a nucleus and mitochondria in maturity, maximizing space for hemoglobin.
• Cilia and flagella in eukaryotes have a 9+2 microtubule arrangement; prokaryotic flagella are composed of flagellin and lack microtubules.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having 70S ribosomes, circular DNA, and double membranes.
• Plant cells contain a large central vacuole for storage and turgor pressure; animal cells have smaller, multiple vacuoles.
• Plasmodesmata in plant cells and gap junctions in animal cells allow intercellular communication through cytoplasmic connections.

Difficulty Level

Intermediate – routinely tested in first?year biology with emphasis on structural and functional comparisons.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacterial prokaryotes have peptidoglycan; plant (cellulose) and fungal (chitin) cell walls have different compositions.
Trap: Ribosome size is the same across all cells – Fact: Prokaryotes have 70S ribosomes; eukaryotes have 80S in cytoplasm, but 70S in mitochondria and chloroplasts.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Prokaryotes have no DNA packaging – Fact: Prokaryotic DNA is supercoiled and associated with proteins, though not histones like in eukaryotes (except some archaea).
Trap: Eukaryotes evolved directly from bacteria – Fact: Eukaryotes likely arose from archaeal ancestors, with bacterial contributions via endosymbiosis.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature found in prokaryotic cells but not in eukaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Nucleoid region
D) Phospholipid bilayer
Answer: C
Explanation: The nucleoid is a distinct, non-membrane-bound region in prokaryotes where DNA is located.
Why the top distractor is wrong: 70S ribosomes (B) are also found in mitochondria and chloroplasts of eukaryotes, so not exclusive to prokaryotes.

Question: Which structure is present in plant cells but not in animal cells?
A) Mitochondria
B) Golgi apparatus
C) Central vacuole
D) Plasma membrane
Answer: C
Explanation: Mature plant cells have a large central vacuole for storage and turgor pressure, absent in animal cells.
Why the top distractor is wrong: Mitochondria (A) are present in both plant and animal cells.

Question: Which of the following provides the strongest evidence for the endosymbiotic origin of mitochondria?
A) Presence of a double membrane
B) Ability to synthesize proteins
C) Containing 70S ribosomes and circular DNA
D) Involvement in ATP production
Answer: C
Explanation: 70S ribosomes and circular DNA in mitochondria closely resemble those of prokaryotes.
Why the top distractor is wrong: Double membranes (A) can arise by other mechanisms; circular DNA and ribosomes are more specific evidence.

Question: A cell lacks a nucleus and has a cell wall containing peptidoglycan. Which domain does it most likely belong to?
A) Eukarya
B) Archaea
C) Bacteria
D) Protista
Answer: C
Explanation: Bacteria are prokaryotes with peptidoglycan in their cell walls.
Why the top distractor is wrong: Archaea (B) lack peptidoglycan, though they are also prokaryotes.

Question: Which organelle is responsible for modifying and packaging proteins for secretion?
A) Nucleolus
B) Rough endoplasmic reticulum
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins into vesicles for export.
Why the top distractor is wrong: Rough ER (B) synthesizes proteins but does not package them for secretion.

Question: Which of the following cells lacks mitochondria?
A) Fungal cell
B) Plant cell
C) Mature human red blood cell
D) Amoeba
Answer: C
Explanation: Mature human red blood cells lack mitochondria and generate ATP via glycolysis.
Why the top distractor is wrong: Fungal cells (A) are eukaryotic and contain mitochondria.

Question: What is the primary structural component of fungal cell walls?
A) Peptidoglycan
B) Cellulose
C) Chitin
D) Silica
Answer: C
Explanation: Fungal cell walls are composed primarily of chitin, a nitrogen-containing polysaccharide.
Why the top distractor is wrong: Peptidoglycan (A) is found in bacterial cell walls, not fungal.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have no nucleus; DNA in nucleoid.
• Eukaryotes have membrane-bound nucleus with nuclear pores.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacteria: peptidoglycan cell wall; plants: cellulose; fungi: chitin; animals: no cell wall.
• Mycoplasma has no cell wall – naturally resistant to penicillin.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Nucleolus synthesizes rRNA and assembles ribosome subunits.
• Rough ER has ribosomes; smooth ER makes lipids and detoxifies.
• Golgi apparatus modifies and sorts proteins into vesicles.
• Mitochondria produce ATP via aerobic respiration; double membrane; own DNA.
• Chloroplasts perform photosynthesis; contain thylakoids and chlorophyll.
• Lysosomes contain hydrolytic enzymes; absent in most plant cells.
• Peroxisomes break down fatty acids and neutralize H?O?.
• Centrioles present in animal cells, not in most plant cells.
• Mature mammalian red blood cells lack nucleus and mitochondria.
• Eukaryotic flagella: 9+2 microtubule array; prokaryotic: flagellin filament, no microtubules.
• Endosymbiotic theory supported by organelle 70S ribosomes, circular DNA, double membranes.
• Plant cells have large central vacuole; animal cells have small, multiple vacuoles.
• Plasmodesmata (plants) and gap junctions (animals) allow intercellular communication.
• Archaea lack peptidoglycan in cell walls – different from bacteria.
• Verify from standard textbook: histone-like proteins in some archaea resemble eukaryotic histones.
• Mitochondria and chloroplasts divide independently via binary fission.