STEM Readiness: Chemistry Readiness - Equilibrium: ICE Tables - Setting Up and Solving for Equilibrium Concentrations

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 have endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and (in plants) chloroplasts.
• Ribosomes in prokaryotes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S subunits).
• 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 cell walls.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane that regulates transport.
• Eukaryotes have internal membrane systems (nuclear envelope, ER, Golgi) forming compartments; prokaryotes do not.
• Prokaryotes reproduce by binary fission; eukaryotes divide by mitosis and meiosis.
• Circular DNA is found in prokaryotic nucleoids and in mitochondria and chloroplasts of eukaryotes.
• Eukaryotic chromosomes are linear and associated with histone proteins; prokaryotic DNA is circular and not bound by histones (though archaea have histone-like proteins).
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and bend.
• Cytoskeleton is absent in prokaryotes (though some have cytoskeletal analogs); eukaryotes have actin, microtubules, and intermediate filaments.
• Mycoplasma species are bacteria without a cell wall, making them resistant to antibiotics like penicillin.
• Human red blood cells lack a nucleus and mitochondria at maturity, maximizing hemoglobin capacity.
• Plant cells have large central vacuoles, chloroplasts, and plasmodesmata; animal cells have centrioles and lysosomes.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own DNA, 70S ribosomes, and double membranes.
• Gram-positive bacteria have thick peptidoglycan and no outer membrane; Gram-negative have thin peptidoglycan and an outer lipid membrane.
• Archaea resemble prokaryotes in size and structure but have eukaryote-like transcription and translation machinery.
• Nuclear pores in the nuclear envelope allow RNA and proteins to move between nucleus and cytoplasm in eukaryotes.
• Rough endoplasmic reticulum has ribosomes attached and synthesizes proteins for secretion; smooth ER lacks ribosomes and synthesizes lipids and detoxifies drugs.
• Golgi apparatus modifies, sorts, and packages proteins into vesicles for transport to lysosomes, plasma membrane, or secretion.
• Lysosomes contain hydrolytic enzymes active at acidic pH and break down macromolecules, organelles, and pathogens.

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; plants (cellulose), fungi (chitin), and archaea (pseudopeptidoglycan or other) have different compositions.

Trap: Ribosome size correlates with cell complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, identical in size to prokaryotes, due to evolutionary origin.

Trap: Prokaryotes have no internal structure – Fact: Prokaryotes may have protein-based microcompartments (e.g., carboxysomes) and cytoskeletal analogs (e.g., FtsZ), but no membrane-bound organelles.

Trap: The nucleus evolved from the nucleoid – Fact: The nucleus is a eukaryotic innovation with no direct prokaryotic precursor; its origin is linked to invagination of the plasma membrane in some hypotheses.

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) Peptidoglycan in the cell wall
D) Plasma membrane with phospholipid bilayer
Answer: C
Explanation: Peptidoglycan is unique to bacterial cell walls and absent in eukaryotes.
Why the top distractor is wrong: 70S ribosomes are also in mitochondria and chloroplasts of eukaryotes, so not exclusive to prokaryotes.

Question: Which structure is present in plant cells but absent in animal cells?
A) Mitochondria
B) Lysosome
C) Central vacuole
D) Plasma membrane
Answer: C
Explanation: Mature plant cells have a large central vacuole for storage and turgor pressure; animal cells have small or transient vacuoles.
Why the top distractor is wrong: Lysosomes are typically associated with animal cells, though some plant vacuoles have degradative functions.

Question: Which of the following provides evidence for the endosymbiotic theory?
A) Eukaryotic cells are larger than prokaryotic cells
B) Mitochondria have their own 70S ribosomes and circular DNA
C) Prokaryotes lack a nucleus
D) Eukaryotes have linear chromosomes
Answer: B
Explanation: Mitochondria’s 70S ribosomes and circular DNA resemble those of bacteria, supporting bacterial origin.
Why the top distractor is wrong: Cell size difference is descriptive, not evidence of evolutionary origin.

Question: A cell is observed to have a nucleus, mitochondria, and a cell wall made of chitin. This cell is most likely from a:
A) Plant
B) Bacterium
C) Fungus
D) Animal
Answer: C
Explanation: Fungi have eukaryotic organelles and cell walls composed of chitin.
Why the top distractor is wrong: Plants have cell walls made of cellulose, not chitin.

Question: Which of the following is true of both prokaryotes and eukaryotes?
A) Presence of mitochondria
B) Use of 80S ribosomes for protein synthesis
C) Phospholipid bilayer as the plasma membrane
D) Membrane-bound nucleus
Answer: C
Explanation: Both domains use a phospholipid bilayer as the selectively permeable plasma membrane.
Why the top distractor is wrong: 80S ribosomes are only in eukaryotic cytoplasm; prokaryotes use 70S.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: DNA in nucleoid; eukaryotes: DNA in nucleus.
• 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 wall = cellulose; fungal = chitin; animal = no cell wall.
• Both domains have phospholipid bilayer plasma membranes.
• Only eukaryotes have membrane-bound organelles (ER, Golgi, lysosomes, nucleus).
• Prokaryotes divide by binary fission; eukaryotes by mitosis/meiosis.
• Eukaryotic chromosomes are linear and histone-associated; prokaryotic DNA is circular and not histone-wrapped (except archaea).
• Prokaryotic flagella = flagellin, rotating; eukaryotic = microtubules (9+2), bending.
• Cytoskeleton (actin, tubulin) is eukaryotic feature; prokaryotes have analogs (e.g., FtsZ, MreB).
• Mycoplasma lacks a cell wall – smallest known cells.
• Mature human red blood cells lack a nucleus and mitochondria.
• Plant cells have chloroplasts, central vacuole, plasmodesmata; animal cells have centrioles, lysosomes.
• Nuclear envelope has nuclear pores for RNA/protein transport.
• Rough ER = ribosomes attached, synthesizes proteins; smooth ER = lipid synthesis, detoxification.
• Golgi apparatus = modifies, sorts, packages proteins into vesicles.
• Lysosomes = contain acid hydrolases, break down materials.
• Gram-positive bacteria: thick peptidoglycan, no outer membrane.
• Gram-negative bacteria: thin peptidoglycan, outer lipid membrane.
• Archaea resemble prokaryotes structurally but have eukaryote-like transcription/translation.
• Endosymbiotic theory: mitochondria from alpha-proteobacteria, chloroplasts from cyanobacteria.
• Verify from standard textbook: exact composition of archaeal cell walls and membranes varies widely.
• No organelles in prokaryotes are membrane-bound.