STEM Readiness: Pre-Calculus Readiness - Exponentials/Logs: Exponential Models - Doubling Time, Half-Life, Newton’s Law of Cooling

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 contain 70S ribosomes, supporting their origin via endosymbiosis.
• Prokaryotic cell walls typically contain peptidoglycan; archaea lack peptidoglycan and have pseudopeptidoglycan or other polymers.
• Plant cells have cell walls made of cellulose; fungal cells have chitin; animal cells lack a cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes possess membrane-bound organelles including the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria, and nucleus; prokaryotes lack these.
• Bacteria (e.g., Escherichia coli) and archaea (e.g., Methanogens) are prokaryotes; animals, plants, fungi, and protists are eukaryotes.
• Plasma membrane fluidity is maintained by cholesterol in animal cells and hopanoids in many bacteria.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport.
• Nuclear pores allow selective passage of molecules like mRNA and proteins; prokaryotes lack nuclear pores.
• Chromosomes in prokaryotes are typically a single, circular DNA molecule; eukaryotes have multiple linear chromosomes.
• Histones package DNA in eukaryotes; most prokaryotes lack histones (archaea have histone-like proteins).
• Binary fission is the primary mode of reproduction in prokaryotes; eukaryotes divide via mitosis and cytokinesis.
• Flagella in prokaryotes are composed of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Pili and fimbriae are present in some prokaryotes for attachment and conjugation; absent in eukaryotes.
• Plasmids are small, circular DNA molecules common in prokaryotes; rare in eukaryotes (e.g., 2? plasmid in yeast).
• Mycoplasma species lack a cell wall, making them resistant to antibiotics like penicillin that target peptidoglycan.
• Mature red blood cells in mammals lack a nucleus and most organelles, maximizing hemoglobin content.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own DNA (circular, like bacteria) and double membranes.
• Mitochondria replicate independently of the cell via binary fission, similar to bacterial division.
• Lysosomes are membrane-bound organelles in eukaryotes containing hydrolytic enzymes; absent in prokaryotes.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; small or absent in animal cells.
• Cytoskeleton elements (microtubules, microfilaments, intermediate filaments) are present in eukaryotes; prokaryotes have homologs (e.g., FtsZ, MreB) but no true cytoskeleton.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and recognizing exceptions.

Common Traps

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; archaea, plants, and fungi have different wall compositions.
Trap: Ribosome size is the same across all cells – Fact: Prokaryotes have 70S ribosomes; eukaryotes have 80S (except in mitochondria/chloroplasts, which have 70S).
Trap: The nucleus is the only organelle that contains DNA – Fact: Mitochondria and chloroplasts also contain DNA.
Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., cyanobacteria) have thylakoid membranes for photosynthesis.
Trap: Eukaryotic cells are always larger than prokaryotic cells – Fact: While generally true, some giant bacteria (e.g., Thiomargarita namibiensis, up to 750 ?m) exceed typical eukaryotic size.

Practice MCQs

Question: Which of the following is a feature found in prokaryotic cells but not in eukaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Peptidoglycan in the cell wall
D) Plasma membrane with phospholipid bilayer
Answer: C
Explanation: Peptidoglycan is unique to bacterial cell walls.
Why the top distractor is wrong: 70S ribosomes are also found in mitochondria and chloroplasts of eukaryotes, so not exclusive to prokaryotes.

Question: Which structure is present in plant cells but not in animal cells?
A) Mitochondria
B) Golgi apparatus
C) Central vacuole
D) Nucleus
Answer: C
Explanation: The large central vacuole is a defining feature of plant cells.
Why the top distractor is wrong: Mitochondria are present in both plant and animal cells.

Question: Where is DNA located in a eukaryotic cell?
A) Nucleoid only
B) Nucleus, mitochondria, and chloroplasts
C) Nucleus only
D) Cytoplasm and nucleus
Answer: B
Explanation: Eukaryotic DNA is in the nucleus, mitochondria, and (in plants) chloroplasts.
Why the top distractor is wrong: The nucleoid is a prokaryotic structure.

Question: Which of the following provides the strongest evidence for the endosymbiotic theory?
A) Mitochondria are surrounded by a single membrane
B) Mitochondria have 80S ribosomes
C) Mitochondria have circular DNA and divide by binary fission
D) Mitochondria are smaller than bacteria
Answer: C
Explanation: Circular DNA and binary fission in mitochondria mirror bacterial characteristics.
Why the top distractor is wrong: Mitochondria have a double membrane, not single, and 70S ribosomes, not 80S.

Question: Which organism lacks a cell wall?
A) Saccharomyces cerevisiae
B) Escherichia coli
C) Mycoplasma pneumoniae
D) Arabidopsis thaliana
Answer: C
Explanation: Mycoplasma species are bacteria without a cell wall.
Why the top distractor is wrong: Saccharomyces cerevisiae (yeast) is a fungus with a chitin-containing cell wall.

Question: What is the primary function of the nuclear envelope in eukaryotes?
A) Protein synthesis
B) ATP production
C) Separation of transcription and translation
D) Lipid storage
Answer: C
Explanation: The nuclear envelope separates transcription (nucleus) from translation (cytoplasm).
Why the top distractor is wrong: Protein synthesis occurs on ribosomes, not in the nucleus.

Question: Which of the following is true of both prokaryotes and eukaryotes?
A) Presence of mitochondria
B) Use of 80S ribosomes
C) Phospholipid bilayer plasma membrane
D) Membrane-bound nucleus
Answer: C
Explanation: Both domains have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: Mitochondria are only in eukaryotes.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotic DNA in nucleoid; eukaryotic DNA in nucleus.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacteria: peptidoglycan cell wall; archaea: no peptidoglycan.
• Plants: cellulose cell wall; fungi: chitin; animals: no cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Eukaryotes have ER, Golgi, lysosomes, mitochondria, nucleus – prokaryotes lack these.
• Bacteria and archaea are prokaryotes; animals, plants, fungi are eukaryotes.
• Cholesterol in animal cell membranes; hopanoids in bacterial membranes.
• Nuclear envelope is double membrane with nuclear pores.
• Nuclear pores regulate mRNA and protein transport.
• Prokaryotes: single circular chromosome; eukaryotes: multiple linear chromosomes.
• Eukaryotic DNA wrapped around histones; prokaryotes generally lack histones.
• Prokaryotes divide by binary fission; eukaryotes by mitosis.
• Prokaryotic flagella: flagellin, rotates; eukaryotic: microtubules (9+2), bends.
• Pili for conjugation and attachment – found in prokaryotes only.
• Plasmids common in bacteria; rare in eukaryotes.
• Mycoplasma has no cell wall – resistant to penicillin.
• Mature mammalian red blood cells lack a nucleus and organelles.
• Mitochondria and chloroplasts have double membranes and replicate by binary fission.
• Lysosomes contain hydrolytic enzymes – only in eukaryotes.
• Plant central vacuole maintains turgor pressure.
• Prokaryotes have FtsZ (tubulin homolog) and MreB (actin homolog) – not true cytoskeleton.
• Some prokaryotes (e.g., cyanobacteria) have internal membranes (thylakoids).
• Thiomargarita namibiensis can be 750 ?m – larger than most eukaryotes.