STEM Readiness: Physics Readiness - Electricity Foundations: Electric Charge - and Coulomb’s, Law Superposition, Field Lines

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 peroxisomes.
• Prokaryotic ribosomes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S subunits).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting endosymbiotic theory.
• Most prokaryotes have a cell wall made of peptidoglycan; archaea lack peptidoglycan and have other polysaccharides or proteins.
• Plant cells have a cell wall made of cellulose; fungal cells have chitin; animal cells lack a cell wall.
• Mycoplasma species are bacteria that lack a cell wall, making them resistant to antibiotics like penicillin.
• Red blood cells in mammals lack a nucleus and most organelles, maximizing space for hemoglobin.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membranes forming organelles like the endoplasmic reticulum (ER), Golgi apparatus, and nuclear envelope.
• The nucleus contains chromatin (DNA + histone proteins) and a nucleolus where ribosomal RNA is synthesized.
• Nuclear pores regulate transport between nucleus and cytoplasm; prokaryotes lack such structures.
• Prokaryotes divide by binary fission; eukaryotes undergo mitosis and meiosis.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Eukaryotic cells may have centrioles (in animals) involved in spindle formation; prokaryotes lack centrioles.
• Lysosomes are membrane-bound organelles in eukaryotes containing hydrolytic enzymes; absent in prokaryotes.
• Peroxisomes break down fatty acids and detoxify alcohol in eukaryotes; not found in prokaryotes.
• Chloroplasts are present in plant and algal cells, perform photosynthesis, and contain thylakoids and chlorophyll.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Mitochondria are the site of aerobic respiration and ATP production in eukaryotes; prokaryotes perform respiration on the plasma membrane.
• The rough ER is studded with ribosomes and synthesizes proteins; smooth ER synthesizes lipids and detoxifies drugs.
• The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery to other organelles.
• Cytoskeleton (microfilaments, intermediate filaments, microtubules) is present in eukaryotes; prokaryotes have analogous proteins (e.g., FtsZ) but no true cytoskeleton.

Difficulty Level

Intermediate – expected foundational knowledge in first-semester biology, with detailed distinctions frequently tested.

Common Traps (3–5 factual traps)

Trap: All cells with a nucleus are eukaryotic, so any cell without a nucleus must be prokaryotic – Fact: Mature mammalian red blood cells lack a nucleus but are eukaryotic, derived from eukaryotic lineages.

Trap: Ribosome size correlates with cell complexity, so eukaryotic ribosomes are always larger – Fact: While cytoplasmic ribosomes are 80S, mitochondria and chloroplasts have 70S ribosomes, identical in size to prokaryotes.

Trap: Cell walls are only found in prokaryotes – Fact: Plants, fungi, and some protists have cell walls; only animal cells lack them among eukaryotes.

Trap: The plasma membrane is structurally different in prokaryotes and eukaryotes – Fact: Both have a phospholipid bilayer with embedded proteins; the fundamental structure is conserved across domains.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature found in eukaryotic cells but absent 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 a large central vacuole. This cell is most likely from which organism?
A) Fungus
B) Bacterium
C) Animal
D) Plant
Answer: D
Explanation: Cellulose cell walls, chloroplasts, and central vacuoles are characteristic of plant cells.
Why the top distractor is wrong: Fungi have chitin-based cell walls and lack chloroplasts.

Question: Which structure is present in both prokaryotes and eukaryotes?
A) Mitochondria
B) Nucleolus
C) Ribosomes
D) Golgi apparatus
Answer: C
Explanation: Ribosomes are present in all cells; prokaryotes have 70S, eukaryotes have 80S (and 70S in organelles).
Why the top distractor is wrong: Mitochondria are membrane-bound organelles found only in eukaryotes.

Question: Which of the following provides 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 resemble bacteria in having circular DNA and 70S ribosomes, supporting their origin from endosymbiotic prokaryotes.
Why the top distractor is wrong: Cell size difference does not provide evolutionary evidence.

Question: Which organism lacks a cell wall entirely?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Arabidopsis thaliana
Answer: C
Explanation: Mycoplasma is a bacterium that naturally lacks a cell wall.
Why the top distractor is wrong: E. coli has a peptidoglycan cell wall typical of bacteria.

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 cell wall contains peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal = chitin; animal cells = no cell wall.
• Mycoplasma – smallest known bacteria, lacks cell wall.
• Mature red blood cells lack a nucleus and mitochondria.
• Both prokaryotes and eukaryotes have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, lysosomes).
• Nuclear envelope is double membrane with pores; absent in prokaryotes.
• Chromatin = DNA + histone proteins; found in eukaryotic nucleus.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Prokaryotes divide by binary fission; eukaryotes by mitosis/meiosis.
• Prokaryotic flagella = flagellin, rotates; eukaryotic = microtubules (9+2), bends.
• Centrioles present in animal cells, not in plants or prokaryotes.
• Lysosomes contain hydrolytic enzymes for digestion; absent in prokaryotes.
• Peroxisomes break down fatty acids and detoxify H?O?.
• Chloroplasts have thylakoids, perform photosynthesis, contain chlorophyll.
• Smooth ER = lipid synthesis, detoxification, Ca²? storage.
• Rough ER = protein synthesis (due to ribosomes).
• Golgi apparatus = modifies, sorts, packages proteins in vesicles.
• Cytoskeleton elements: microfilaments (actin), intermediate filaments, microtubules (tubulin).
• FtsZ protein in prokaryotes is homologous to tubulin in eukaryotes.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.