STEM Readiness: Chemistry Readiness - Electrochemistry: Redox Reactions - Oxidation States, Half-Reactions, Balancing in Acidic/Basic Solution

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 mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
• Ribosomes in prokaryotes are 70S (50S + 30S subunits); eukaryotes have 80S ribosomes (60S + 40S) in the cytoplasm.
• 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.
• Eukaryotes have internal membrane systems including the nuclear envelope, ER, and Golgi; prokaryotes do not.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate RNA and protein transport.
• Chromosomes in prokaryotes are typically a single, circular DNA molecule; eukaryotes have multiple linear chromosomes.
• Plasmids are small, circular DNA molecules found in some prokaryotes and used in genetic engineering; rare in eukaryotes.
• Binary fission is the method of asexual reproduction in prokaryotes; eukaryotes divide by mitosis and cytokinesis.
• Cilia and flagella in prokaryotes are made of flagellin and rotate; in eukaryotes, they are composed of microtubules (9+2 arrangement) and move in a whip-like fashion.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own circular DNA, 70S ribosomes, and double membranes.
• Red blood cells in mammals lack a nucleus and organelles, maximizing space for hemoglobin; they cannot divide or repair themselves.
• Plant cells contain chloroplasts for photosynthesis, a large central vacuole for turgor pressure, and plasmodesmata for intercellular communication.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; they are rare in plant cells.
• Peroxisomes in eukaryotes break down fatty acids and detoxify hydrogen peroxide; absent in prokaryotes.
• Archaea are prokaryotes but have ribosomal RNA sequences and membrane lipids more similar to eukaryotes than bacteria.
• Gram-positive bacteria have thick peptidoglycan layers; gram-negative bacteria have thin peptidoglycan and an outer membrane with lipopolysaccharides.
• Cyanobacteria are photosynthetic prokaryotes with thylakoid membranes but no chloroplasts.
• Eukaryotic cilia and flagella are anchored by basal bodies; prokaryotic flagella lack basal bodies.

Difficulty Level

Intermediate – expected foundational knowledge in first-semester biology but requires precise differentiation of structures and exceptions.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plant cell walls are made of cellulose, fungal walls of chitin.
Trap: Ribosome size is the same across all organisms – Fact: Prokaryotes have 70S ribosomes; eukaryotes have 80S in cytoplasm (but 70S in mitochondria/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 nucleoid-associated proteins, though not histones.
Trap: All eukaryotic cells have mitochondria – Fact: Some eukaryotes (e.g., Giardia) lack mitochondria and use anaerobic metabolism in organelles called mitosomes.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of prokaryotic cells?
A) Membrane-bound nucleus
B) 80S ribosomes
C) Linear chromosomes
D) Nucleoid region
Answer: D
Explanation: Prokaryotes lack a nucleus and instead have DNA concentrated in the nucleoid.
Why the top distractor is wrong: A is incorrect because a membrane-bound nucleus is exclusive to eukaryotes.

Question: A cell is observed to have a cell wall, chloroplasts, and a large central vacuole. It most likely belongs to which domain?
A) Bacteria
B) Archaea
C) Animalia
D) Plantae
Answer: D
Explanation: Chloroplasts, a large central vacuole, and a cellulose cell wall are characteristic of plant cells.
Why the top distractor is wrong: A is incorrect because bacteria lack membrane-bound organelles like chloroplasts.

Question: Which structure is found in both prokaryotes and eukaryotes?
A) Mitochondria
B) Golgi apparatus
C) Plasma membrane
D) Endoplasmic reticulum
Answer: C
Explanation: Both cell types have a phospholipid bilayer plasma membrane.
Why the top distractor is wrong: A is incorrect because mitochondria are exclusive to eukaryotes.

Question: Mitochondria contain 70S ribosomes. This observation supports which theory?
A) Cell theory
B) Endosymbiotic theory
C) Germ theory
D) Theory of evolution
Answer: B
Explanation: 70S ribosomes in mitochondria resemble those in prokaryotes, supporting their origin from symbiotic bacteria.
Why the top distractor is wrong: D is too broad; the specific evidence relates to endosymbiosis, not general evolution.

Question: Which of the following cells lacks a nucleus?
A) Neuron
B) Leukocyte
C) Erythrocyte
D) Hepatocyte
Answer: C
Explanation: Mature mammalian red blood cells (erythrocytes) lose their nucleus to carry more hemoglobin.
Why the top distractor is wrong: B (leukocyte) is a white blood cell and contains a nucleus.

Question: What is the primary component of fungal cell walls?
A) Peptidoglycan
B) Cellulose
C) Chitin
D) Silica
Answer: C
Explanation: Fungi have cell walls made of chitin, a nitrogen-containing polysaccharide.
Why the top distractor is wrong: A is found in bacteria, not fungi.

Question: Which of the following is true about archaea?
A) They have peptidoglycan in their cell walls
B) They are eukaryotic
C) Their ribosomal RNA sequences resemble those of eukaryotes
D) They possess mitochondria
Answer: C
Explanation: Archaea are prokaryotes but share molecular similarities with eukaryotes, especially in rRNA.
Why the top distractor is wrong: A is incorrect because archaea lack peptidoglycan.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: nucleoid; eukaryotes: membrane-bound nucleus.
• 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 lacks a cell wall – naturally resistant to penicillin.
• Both cell types have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Nuclear envelope has nuclear pores for transport.
• Prokaryotes have circular DNA; eukaryotes have linear chromosomes.
• Plasmids are small, circular DNA molecules common in bacteria.
• Binary fission = prokaryotic division; mitosis = eukaryotic nuclear division.
• Prokaryotic flagella: made of flagellin, rotate; eukaryotic: 9+2 microtubules, whip-like motion.
• Red blood cells (erythrocytes) lack a nucleus and organelles.
• Plant cells: chloroplasts, central vacuole, plasmodesmata.
• Lysosomes: contain hydrolytic enzymes, found in animal cells.
• Peroxisomes: break down fatty acids, detoxify H?O?; absent in prokaryotes.
• Archaea: no peptidoglycan, ether-linked membrane lipids, rRNA similar to eukaryotes.
• Gram-positive: thick peptidoglycan; gram-negative: thin peptidoglycan + outer LPS membrane.
• Cyanobacteria perform photosynthesis using thylakoid membranes (no chloroplasts).
• Basal bodies anchor eukaryotic cilia and flagella; absent in prokaryotes.
• Mitochondria have double membranes – supports endosymbiotic theory.
• Some eukaryotes (e.g., Giardia) lack mitochondria but have mitosomes.
• Histones are found in eukaryotes and some archaea, but not in bacteria.
• Verify from standard textbook: exact lipid composition in archaeal membranes.