STEM Readiness: Pre-Calculus Readiness - Conic Sections: Ellipses and Hyperbolas - Standard Form, Foci, Asymptotes

Must?Know

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotes store DNA in a nucleoid (no membrane); eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotic ribosomes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiotic theory.
• Bacteria have peptidoglycan in their cell walls; archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cells have cellulose in their cell walls; fungal cells have chitin; animal cells lack a cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have membrane-bound organelles (e.g., ER, Golgi, lysosomes); prokaryotes do not.
• Endoplasmic reticulum (ER): rough ER has ribosomes; smooth ER synthesizes lipids and detoxifies.
• Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery.
• Mitochondria generate ATP via aerobic respiration; contain their own circular DNA and double membrane.
• Chloroplasts (in plants and algae) perform photosynthesis; contain thylakoids, grana, and circular DNA.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion; absent in most plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal vacuoles are small.
• Nuclear envelope is a double membrane with nuclear pores regulating transport.
• Nucleolus within the nucleus synthesizes ribosomal RNA (rRNA) and assembles ribosome subunits.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) maintains cell shape and enables motility; present in eukaryotes.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2) and undulate.
• Pili (in bacteria) are protein tubes for adhesion or conjugation; not found in eukaryotes.
• Mycoplasma species lack a cell wall, making them resistant to penicillin; exception among bacteria.
• Human red blood cells lack a nucleus and organelles, maximizing hemoglobin capacity; exception among eukaryotic cells.
• Archaea are prokaryotes but share some molecular features with eukaryotes (e.g., RNA polymerase).
• Endosymbiotic theory is supported by mitochondria and chloroplasts having 70S ribosomes, circular DNA, and binary fission.
• Plasma membrane fluidity is maintained by cholesterol in animal cells and hopanoids in some bacteria.
• Cell walls provide structural support and prevent osmotic lysis; absent in animal cells.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, including exceptions.

Common Traps

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.
• Trap: Ribosome size is the same across all organisms – Fact: Prokaryotes use 70S ribosomes; eukaryotes use 80S in cytoplasm, but 70S in mitochondria and chloroplasts.
• Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
• Trap: Eukaryotes are always larger and more complex than prokaryotes – Fact: Some bacteria (e.g., Thiomargarita namibiensis) can be larger than typical eukaryotic cells (up to 750 ?m).
• Trap: All eukaryotic cells have a cell wall – Fact: Animal cells lack a cell wall; only plants, fungi, and some protists have one.

Practice MCQs

Question: Which of the following is a defining feature of prokaryotic cells?
A) Membrane-bound nucleus
B) 80S ribosomes
C) Presence of nucleoid
D) Mitochondria for ATP production
Answer: C
Explanation: Prokaryotes lack a nucleus and instead have a nucleoid region containing DNA.
Why the top distractor is wrong: A is incorrect because a membrane-bound nucleus is exclusive to eukaryotes.

Question: Which structure is found in plant cells but not in animal cells?
A) Mitochondria
B) Large central vacuole
C) Plasma membrane
D) Ribosomes
Answer: B
Explanation: Plant cells have a large central vacuole for storage and turgor pressure; animal cells have small or multiple vacuoles.
Why the top distractor is wrong: A is incorrect because mitochondria are present in both plant and animal cells.

Question: What evidence supports the endosymbiotic theory for mitochondria?
A) They have 80S ribosomes
B) They are surrounded by a single membrane
C) They reproduce by binary fission and have circular DNA
D) They synthesize proteins using nuclear DNA
Answer: C
Explanation: Mitochondria divide independently via binary fission and contain circular DNA, similar to bacteria.
Why the top distractor is wrong: A is incorrect because mitochondria have 70S ribosomes, not 80S.

Question: Which of the following organisms lacks a cell wall?
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: A is incorrect because E. coli is a bacterium with a peptidoglycan cell wall.

Question: Where is DNA located in a eukaryotic liver cell?
A) Nucleoid only
B) Nucleus and mitochondria
C) Cytoplasm and nucleus
D) Nucleus only
Answer: B
Explanation: Eukaryotic nuclear DNA is in the nucleus; mitochondrial DNA is in mitochondria.
Why the top distractor is wrong: D is incorrect because mitochondria also contain DNA.

Question: Which component is common to both prokaryotic and eukaryotic plasma membranes?
A) Cholesterol
B) Peptidoglycan
C) Phospholipid bilayer
D) Nuclear pores
Answer: C
Explanation: Both cell types have a phospholipid bilayer as the fundamental membrane structure.
Why the top distractor is wrong: A is incorrect because cholesterol is typical in animal membranes, not prokaryotes.

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 into vesicles.
Why the top distractor is wrong: A is incorrect because rough ER synthesizes proteins but does not package them for secretion.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• DNA in prokaryotes: nucleoid; eukaryotes: nucleus.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA.
• Bacteria cell wall contains peptidoglycan; archaea do not.
• Plant cell wall: cellulose; fungal: chitin; animal: no cell wall.
• Both cell types have a phospholipid bilayer plasma membrane.
• Eukaryotes have membrane-bound organelles; prokaryotes do not.
• Rough ER has ribosomes; smooth ER makes lipids.
• Golgi apparatus: modifies and packages proteins.
• Mitochondria: ATP production, double membrane, own DNA.
• Chloroplasts: photosynthesis, thylakoids, grana, own DNA.
• Lysosomes: contain hydrolytic enzymes, mainly in animal cells.
• Plant vacuole: large and central; maintains turgor.
• Nuclear envelope: double membrane with nuclear pores.
• Nucleolus: makes rRNA and ribosome subunits.
• Cytoskeleton: present in eukaryotes, not in prokaryotes.
• Prokaryotic flagella: made of flagellin, rotary motion.
• Eukaryotic flagella: 9+2 microtubule arrangement, bending motion.
• Pili: found in bacteria, used for adhesion or conjugation.
• Mycoplasma: no cell wall – exception among bacteria.
• Human red blood cells: no nucleus or organelles.
• Archaea: prokaryotic but share transcription machinery with eukaryotes.
• Endosymbiotic theory evidence: organelles divide by binary fission, have 70S ribosomes, circular DNA.
• Cholesterol stabilizes animal plasma membranes; hopanoids in some bacteria.
• Not all eukaryotes have cell walls – animal cells lack them.