STEM Readiness: Pre-Calculus Readiness - Conic Sections: Circles and Parabolas - Standard Form, Completing the Square, Applications

Must?Know

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotic DNA is located in the nucleoid, a region without a membrane; eukaryotic DNA is enclosed within a membrane-bound nucleus.
• Prokaryotes have 70S ribosomes (30S + 50S subunits); eukaryotes have 80S ribosomes (40S + 60S subunits).
• Mitochondria and chloroplasts in eukaryotic cells contain 70S ribosomes, similar to prokaryotes.
• Peptidoglycan is present in bacterial cell walls; absent in archaea and eukaryotes.
• Archaea lack peptidoglycan but may have pseudopeptidoglycan or other wall materials.
• Plant cells have cell walls made of cellulose; fungal cells have walls made of chitin.
• Animal cells lack a cell wall; only have a plasma membrane.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Eukaryotes have extensive internal membrane systems including the endoplasmic reticulum (ER), Golgi apparatus, and lysosomes; prokaryotes do not.
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores; absent in prokaryotes.
• Linear chromosomes are typical in eukaryotes; circular chromosomes are typical in prokaryotes.
• Eukaryotic cells undergo mitosis using a mitotic spindle; prokaryotes divide by binary fission.
• Lysosomes are membrane-bound organelles in eukaryotes that contain hydrolytic enzymes; absent in prokaryotes.
• Peroxisomes are present in eukaryotes and involved in fatty acid oxidation; not found in prokaryotes.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologs (e.g., FtsZ) but lack true cytoskeleton.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and bend.
• Plasmids are common in prokaryotes as small circular DNA; rare in eukaryotes (e.g., 2? plasmid in yeast).
• Mycoplasma species are bacteria that lack a cell wall; resistant to penicillin.
• Mature red blood cells in mammals lack a nucleus and mitochondria; rely on glycolysis.
• Chloroplasts are found in plant and algal cells; absent in animal and fungal cells.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having own circular DNA, 70S ribosomes, and double membranes.
• Mitochondria are present in nearly all eukaryotic cells; absent in some protists like Giardia (mitosomes instead).
• Bacteria and archaea are prokaryotes; plants, animals, fungi, and protists are eukaryotes.

Difficulty Level

Intermediate – requires precise differentiation of structural and molecular features across domains.

Common Traps

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (other polymers) have different wall compositions.
• Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, identical in size to prokaryotes.
• Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., cyanobacteria) have thylakoid membranes for photosynthesis.
• Trap: The nucleus evolved from invagination of the plasma membrane – Fact: The nuclear envelope likely originated from endoplasmic reticulum membranes, not direct plasma membrane folding.
• Trap: All eukaryotic cells have mitochondria – Fact: Some anaerobic eukaryotes (e.g., Monocercomonoides) lack mitochondria entirely.

Practice MCQs

Question: Which of the following is a structural feature found in eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) 70S ribosomes
C) Mitochondria
D) Circular DNA
Answer: C
Explanation: Mitochondria are membrane-bound organelles unique to eukaryotes.
Why the top distractor is wrong: Circular DNA is typical in prokaryotes but also found in mitochondria and chloroplasts.

Question: A cell is observed to have a nucleus, mitochondria, and a cell wall made of chitin. This cell is most likely from which domain?
A) Bacteria
B) Archaea
C) Plant
D) Fungus
Answer: D
Explanation: Fungi are eukaryotes with chitin-based cell walls and possess mitochondria.
Why the top distractor is wrong: Plants have cellulose walls, not chitin.

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 proteins using 80S ribosomes
C) Linear DNA molecule
D) Division by binary fission
Answer: A
Explanation: The double membrane and presence of 70S ribosomes and circular DNA support endosymbiotic theory.
Why the top distractor is wrong: Mitochondria use 70S ribosomes, not 80S.

Question: Which organism lacks a cell wall and a nucleus?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Human red blood cell
D) Mycoplasma pneumoniae
Answer: C
Explanation: Mature human red blood cells lack both a nucleus and a cell wall.
Why the top distractor is wrong: Mycoplasma lacks a cell wall but is a prokaryote with a nucleoid.

Question: What is the sedimentation coefficient of cytoplasmic ribosomes in eukaryotic cells?
A) 50S
B) 70S
C) 80S
D) 100S
Answer: C
Explanation: Eukaryotic cytoplasmic ribosomes are 80S (40S + 60S subunits).
Why the top distractor is wrong: 70S ribosomes are found in prokaryotes and organelles, not in eukaryotic cytoplasm.

Question: Which of the following is true of the nucleoid region in prokaryotes?
A) It is surrounded by a lipid bilayer
B) It contains linear DNA molecules
C) It lacks a membrane boundary
D) It is associated with histone proteins like in eukaryotes
Answer: C
Explanation: The nucleoid is not enclosed by a membrane.
Why the top distractor is wrong: Prokaryotic DNA is circular and not packaged with histones (though some archaea have histone-like proteins).

Question: Which structure is present in plant cells but not in animal cells?
A) Lysosome
B) Peroxisome
C) Central vacuole
D) Smooth ER
Answer: C
Explanation: The large central vacuole is a defining feature of plant cells.
Why the top distractor is wrong: Lysosomes are present in animal cells; plant vacuoles can perform similar functions.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m
• Eukaryotic cell size: 10–100 ?m
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA
• Bacterial cell walls contain peptidoglycan
• Archaea lack peptidoglycan; may have pseudopeptidoglycan
• Plant cell wall = cellulose
• Fungal cell wall = chitin
• Animal cells = no cell wall
• Both prokaryotes and eukaryotes have phospholipid bilayer membranes
• Eukaryotes have membrane-bound organelles; prokaryotes do not
• DNA in prokaryotes = nucleoid (no membrane)
• DNA in eukaryotes = nucleus (double membrane, pores)
• Eukaryotes have linear chromosomes with histones; prokaryotes have circular DNA
• Prokaryotes divide by binary fission; eukaryotes by mitosis
• Mycoplasma – smallest known cells, no cell wall
• Mature red blood cells – no nucleus, no mitochondria
• Mitochondria absent in some eukaryotes (e.g., Monocercomonoides)
• Eukaryotic flagella = 9+2 microtubule arrangement
• Prokaryotic flagella = flagellin, rotary motion
• Endosymbiotic theory supported by organelle double membranes, 70S ribosomes, circular DNA
• Lysosomes and peroxisomes are eukaryotic-only organelles
• Cytoskeleton elements (actin, tubulin) are eukaryotic features; prokaryotes have FtsZ, MreB
• Plasmids common in bacteria; rare in eukaryotes
• Nuclear envelope derived from endoplasmic reticulum, not plasma membrane
• Verify from standard textbook: histone-like proteins in some archaea – not true histones