STEM Readiness: Chemistry Readiness - Electrochemistry: Galvanic Cells - Cell Notation, Standard Reduction Potentials, Spontaneity

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, an unenclosed region; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain organelles such as mitochondria, ER, and Golgi.
• Ribosomes in prokaryotes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S).
• Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, supporting their origin via endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., Escherichia coli); archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems including the nuclear envelope, endoplasmic reticulum, and Golgi apparatus; prokaryotes do not.
• Prokaryotes reproduce by binary fission; eukaryotes divide by mitosis and meiosis.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; rare in eukaryotes (e.g., 2-micron plasmid in yeast).
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and undulate.
• Eukaryotic nucleus contains nuclear pores for regulated transport; prokaryotes lack nuclear pores.
• Chromosomes in prokaryotes are typically a single circular DNA molecule; eukaryotes have multiple linear chromosomes.
• Histone proteins in eukaryotes package DNA into chromatin; most prokaryotes lack histones (archaea have histone-like proteins).
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to antibiotics like penicillin that target peptidoglycan.
• Human red blood cells lack a nucleus and mitochondria in maturity, maximizing hemoglobin capacity.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own DNA, 70S ribosomes, and double membranes.
• Lysosomes are membrane-bound organelles in animal cells that contain hydrolytic enzymes; plant cells use vacuoles for similar functions.
• Plant cells contain large central vacuoles for turgor pressure; animal cells have small or transient vacuoles.
• Chloroplasts are present in plant and algal cells; absent in animal and fungal cells.
• Eukaryotic cytoskeleton includes microtubules, microfilaments, and intermediate filaments; prokaryotes have homologs (e.g., FtsZ) but no true cytoskeleton.
• Gram-positive bacteria have thick peptidoglycan layers and no outer membrane; Gram-negative bacteria have thin peptidoglycan and an outer lipid membrane.
• Nuclear envelope in eukaryotes is continuous with the rough endoplasmic reticulum; absent in prokaryotes.

Difficulty Level

Intermediate – requires precise differentiation between structural and genetic features across domains and kingdoms.

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, fungi use chitin.
Trap: Eukaryotes are always larger than prokaryotes – Fact: While typical, some bacteria (e.g., Thiomargarita namibiensis, up to 750 ?m) exceed most eukaryotic cells.
Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, like prokaryotes, due to endosymbiotic origin.
Trap: The nucleus is the only site of DNA in eukaryotic cells – Fact: Mitochondria and chloroplasts contain their own DNA.
Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, and some have protein-based microcompartments (e.g., carboxysomes).

Practice MCQs (5–7 questions)

Question: Which of the following is a feature shared by both prokaryotic and eukaryotic cells?
A) Membrane-bound nucleus
B) Mitochondria
C) Phospholipid bilayer plasma membrane
D) Endoplasmic reticulum
Answer: C
Explanation: Both cell types have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: D (endoplasmic reticulum) is exclusive to eukaryotes.

Question: A cell is observed to have 80S ribosomes, no cell wall, and lysosomes. It is most likely:
A) A bacterium
B) A plant cell
C) A fungal cell
D) An animal cell
Answer: D
Explanation: Animal cells lack cell walls, contain 80S ribosomes, and have lysosomes.
Why the top distractor is wrong: B (plant cells) have cell walls and lack lysosomes (use vacuoles instead).

Question: Which structure provides evidence for the endosymbiotic origin of mitochondria?
A) Presence of a single membrane
B) Linear DNA and 80S ribosomes
C) Circular DNA and 70S ribosomes
D) Connection to the nuclear envelope
Answer: C
Explanation: Mitochondria have circular DNA and 70S ribosomes, like bacteria.
Why the top distractor is wrong: A is incorrect because mitochondria have a double membrane, not single.

Question: Which organism lacks a cell wall and is therefore resistant to penicillin?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Bacillus subtilis
Answer: C
Explanation: Mycoplasma lacks a cell wall and is naturally resistant to cell wall-targeting antibiotics.
Why the top distractor is wrong: A (E. coli) has a peptidoglycan cell wall and is typically susceptible to penicillin.

Question: In which cellular component would you find the nucleoid?
A) Animal cell nucleus
B) Plant cell chloroplast
C) Bacterial cytoplasm
D) Fungal mitochondrion
Answer: C
Explanation: The nucleoid is the region in prokaryotes where DNA is located, not enclosed by a membrane.
Why the top distractor is wrong: A refers to a membrane-bound nucleus, which is eukaryotic, not a nucleoid.

Question: Which of the following is true about ribosomes in chloroplasts?
A) They are 80S and similar to cytoplasmic ribosomes
B) They are 70S and similar to prokaryotic ribosomes
C) They are synthesized in the Golgi apparatus
D) They are enclosed by a single membrane
Answer: B
Explanation: Chloroplast ribosomes are 70S, supporting their bacterial origin.
Why the top distractor is wrong: A is incorrect because 80S ribosomes are found in the eukaryotic cytoplasm, not chloroplasts.

Question: Which cell type has a large central vacuole that maintains turgor pressure?
A) Human liver cell
B) Streptococcus bacterium
C) Onion epidermal cell
D) Yeast cell
Answer: C
Explanation: Plant cells, like onion cells, have large central vacuoles for turgor pressure.
Why the top distractor is wrong: D (yeast) are fungi and have small vacuoles, not large central ones like plants.

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 – smallest known cells.
• Human red blood cells lack nucleus and mitochondria.
• Both prokaryotes and eukaryotes have phospholipid bilayer membranes.
• Only eukaryotes have endoplasmic reticulum, Golgi, lysosomes, mitochondria.
• Prokaryotes divide by binary fission; eukaryotes by mitosis/meiosis.
• Prokaryotic DNA is circular and naked; eukaryotic DNA is linear and bound to histones.
• Archaea lack peptidoglycan but may have similar cell wall structures.
• Eukaryotic flagella: 9+2 microtubule arrangement; prokaryotic: flagellin-based, rotary.
• Nuclear envelope is continuous with the rough ER.
• Lysosomes are primarily in animal cells; plants use vacuoles for degradation.
• Plant cells have plastids (e.g., chloroplasts); animal cells do not.
• Mitochondria have double membrane – outer from host, inner from symbiont.
• Chloroplasts perform photosynthesis; found in plants and algae.
• Cytoskeleton components: microtubules (tubulin), microfilaments (actin), intermediate filaments.
• Prokaryotes have FtsZ protein (tubulin homolog) for division.
• Gram-positive bacteria: thick peptidoglycan, no outer membrane.
• Gram-negative bacteria: thin peptidoglycan, outer lipid membrane with LPS.
• Plasmids: small, circular DNA, common in bacteria.
• Verify from standard textbook: histone-like proteins in archaea.