STEM Readiness: Physics Readiness Mathematical Tools Dimensional Analysis SI Units Unit Conversion Checking Equations

Must‑Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 μm in diameter; eukaryotic cells range from 10–100 μm.
• 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.
• 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 pseudopeptidoglycan or other polymers.
• 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 with embedded proteins.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER), Golgi apparatus, and nuclear envelope; prokaryotes do not.
• The nucleus in eukaryotes is surrounded by a double membrane (nuclear envelope) with nuclear pores that regulate transport.
• Nuclear pores allow selective passage of molecules like mRNA and proteins; prokaryotes lack such structures.
• Prokaryotes reproduce by binary fission; eukaryotes divide by mitosis and meiosis.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; they can carry antibiotic resistance genes.
• Eukaryotic DNA is linear and associated with histone proteins to form chromatin; prokaryotic DNA is circular and not bound to histones (though archaea have histone-like proteins).
• Mycoplasma species are prokaryotes that lack a cell wall; they are resistant to antibiotics like penicillin that target cell wall synthesis.
• Human red blood cells are eukaryotic cells that lack a nucleus and mitochondria in maturity, maximizing space for hemoglobin.
• Chloroplasts are organelles found in plant and algal cells; they perform photosynthesis and contain thylakoids and chlorophyll.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own circular DNA, 70S ribosomes, and double membranes.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; plant cells use vacuoles for similar functions.
• The rough ER is studded with ribosomes and synthesizes proteins for secretion; smooth ER lacks ribosomes and synthesizes lipids.
• The Golgi apparatus modifies, sorts, and packages proteins for transport; it has cis (receiving) and trans (shipping) faces.
• Peroxisomes contain enzymes like catalase that break down hydrogen peroxide; they are present in both plant and animal eukaryotic cells.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and undulate.
• Cilia in eukaryotes have the same 9+2 microtubule structure as flagella and are shorter and more numerous.

Difficulty Level

Intermediate – requires precise differentiation between structural and functional features across domains, including exceptions and evolutionary implications.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacterial cell walls contain peptidoglycan; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.
Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, inclusions, and sometimes protein-based microcompartments.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature found in eukaryotic cells but NOT 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: 70S ribosomes are found in prokaryotes and also in mitochondria/chloroplasts, so they are 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 smaller vacuoles.
Why the top distractor is wrong: Lysosomes are typically associated with animal cells, though some plant vacuoles perform lysosomal functions.

Question: A cell is observed to have a cell wall, no nucleus, and 70S ribosomes. It is most likely:
A) A fungal cell
B) A plant cell
C) A bacterial cell
D) An animal cell
Answer: C
Explanation: Bacteria are prokaryotes with cell walls (peptidoglycan), no nucleus, and 70S ribosomes.
Why the top distractor is wrong: Fungal cells are eukaryotic and have 80S ribosomes and a nucleus.

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 ATP
C) Containing 70S ribosomes and circular DNA
D) Being involved in cellular respiration
Answer: C
Explanation: 70S ribosomes and circular DNA are prokaryotic traits, indicating bacterial origin.
Why the top distractor is wrong: A double membrane is supportive but not unique; other organelles also have double membranes.

Question: Which of the following lacks a cell wall?
A) Streptococcus pneumoniae
B) Saccharomyces cerevisiae
C) Mycoplasma genitalium
D) Arabidopsis thaliana
Answer: C
Explanation: Mycoplasma is a bacterium that naturally lacks a cell wall.
Why the top distractor is wrong: Saccharomyces cerevisiae (yeast) is a fungus with a chitin-containing cell wall.

Question: Where is DNA located in a prokaryotic cell?
A) Within the nucleus
B) In mitochondria
C) In the nucleoid region
D) Attached to the Golgi apparatus
Answer: C
Explanation: Prokaryotes lack a nucleus; DNA is concentrated in the nucleoid.
Why the top distractor is wrong: Prokaryotes do not have a nucleus or mitochondria.

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

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

• ⚠️ Prokaryotic cell size: 0.1–5.0 μm; eukaryotic: 10–100 μm.
• ⚠️ 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; archaea do not.
• Plant cell walls = cellulose; fungal = chitin; animal cells = no cell wall.
• Both domains have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Nuclear envelope has double membrane and nuclear pores.
• ⚠️ Human red blood cells lack a nucleus and mitochondria.
• ⚠️ Mycoplasma is a prokaryote without a cell wall.
• Plasmids are small circular DNA molecules common in bacteria.
• Eukaryotic DNA is linear and bound to histones; prokaryotic DNA is circular and mostly naked.
• Archaea have histone-like proteins but no peptidoglycan.
• Binary fission = prokaryotic division; mitosis/meiosis = eukaryotic.
• Chloroplasts perform photosynthesis and contain thylakoids.
• Lysosomes are in animal cells; plant vacuoles handle degradation.
• Rough ER = ribosome-studded, protein synthesis; smooth ER = lipid synthesis, detox.
• Golgi apparatus has cis (input) and trans (output) sides.
• Peroxisomes break down H₂O₂ with catalase.
• Prokaryotic flagella = flagellin, rotary motion; eukaryotic = microtubules (9+2), bending motion.
• Cilia and flagella in eukaryotes share the 9+2 microtubule arrangement.
• Mitochondria have double membrane, 70S ribosomes, circular DNA – supports endosymbiotic theory.
• ⚠️ Nucleus is not the only organelle with a double membrane – mitochondria and chloroplasts also have them.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.