STEM Readiness: Pre-Calculus Readiness - Sequences/Series: Limits - Intuitive Understanding, Basic Evaluation, Indeterminate Forms

Must?Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• DNA in prokaryotes is located in the nucleoid, a region without a membrane; in eukaryotes, DNA is enclosed within the membrane-bound nucleus.
• Ribosomes in prokaryotes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S).
• Mitochondria and chloroplasts in eukaryotic cells contain 70S ribosomes, similar to prokaryotes, supporting endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan; gram-positive bacteria have thick peptidoglycan, gram-negative have thin layer with outer membrane.
• Archaea lack peptidoglycan and have cell walls made of pseudopeptidoglycan or other polysaccharides.
• Plant cells have cell walls made of cellulose; fungal cells have walls made of chitin; animal cells lack a cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane; only eukaryotes have internal membrane-bound organelles.
• Eukaryotes possess endoplasmic reticulum (ER), Golgi apparatus, mitochondria, lysosomes, and peroxisomes; prokaryotes lack these.
• Prokaryotes reproduce by binary fission; eukaryotes divide by mitosis and meiosis.
• Prokaryotic DNA is typically a single, circular chromosome; eukaryotic DNA is linear and organized into multiple chromosomes.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; rare in eukaryotes (e.g., 2-micron plasmid in yeast).
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Cytoskeleton is present in both: prokaryotes have FtsZ, MreB, CreS (homologs of tubulin, actin, intermediate filaments); eukaryotes have microtubules, microfilaments, intermediate filaments.
• Transcription and translation occur simultaneously in the cytoplasm in prokaryotes due to lack of nucleus; in eukaryotes, transcription occurs in nucleus, translation in cytoplasm.
• Mycoplasma species are prokaryotes without a cell wall, resistant to penicillin.
• Human red blood cells lack a nucleus and mitochondria, maximizing space for hemoglobin.
• Endosymbiotic theory proposes mitochondria and chloroplasts originated from engulfed alpha-proteobacteria and cyanobacteria, respectively.
• Evidence for endosymbiosis includes: double membranes, circular DNA, 70S ribosomes, and independent replication of mitochondria and chloroplasts.
• Plant cells contain chloroplasts, large central vacuole, and plasmodesmata; animal cells have centrioles and lysosomes, which plant cells typically lack.
• Fungi are eukaryotes with chitin in cell walls and lack chloroplasts.
• Archaea are prokaryotes but share some molecular features with eukaryotes, such as RNA polymerase (multiple subunits, similar to eukaryotes).
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport; prokaryotes lack this structure.
• Lysosomes are membrane-bound organelles in eukaryotes containing hydrolytic enzymes for digestion; absent in prokaryotes.
• Peroxisomes contain catalase and break down fatty acids and hydrogen peroxide; found only in eukaryotes.

Difficulty Level

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

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; archaea, plants (cellulose), and fungi (chitin) 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, not 80S.
Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., cyanobacteria) have thylakoid membranes for photosynthesis, though not enclosed in organelles.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes, supporting their endosymbiotic origin.
Trap: Eukaryotes are always multicellular – Fact: Many eukaryotes (e.g., yeast, amoeba, paramecium) are unicellular.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature found in prokaryotic cells but NOT in eukaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Nucleoid region
D) Plasma membrane
Answer: C
Explanation: The nucleoid is a distinct, non-membrane-bound region in prokaryotes where DNA is located.
Why the top distractor is wrong: 70S ribosomes (B) are also found in mitochondria and chloroplasts of eukaryotes, so not exclusive to prokaryotes.

Question: Which structure is present in plant cells but absent in animal cells?
A) Mitochondria
B) Golgi apparatus
C) Central vacuole
D) Ribosomes
Answer: C
Explanation: The large central vacuole is a defining feature of mature plant cells, involved in storage and turgor pressure.
Why the top distractor is wrong: Mitochondria (A) are present in both plant and animal cells for ATP production.

Question: Which of the following provides the strongest evidence for the endosymbiotic origin of mitochondria?
A) Presence of a double membrane
B) Use of oxygen in metabolism
C) Involvement in ATP synthesis
D) Location in the cytoplasm
Answer: A
Explanation: The double membrane and presence of 70S ribosomes and circular DNA support mitochondrial origin from engulfed bacteria.
Why the top distractor is wrong: Use of oxygen (B) is a function, not structural evidence, and not unique to mitochondria.

Question: A cell is observed to have a nucleus, mitochondria, and a cell wall made of chitin. This cell is most likely from a:
A) Plant
B) Bacterium
C) Fungus
D) Animal
Answer: C
Explanation: Fungi are eukaryotes with chitin-based cell walls, distinguishing them from plants (cellulose) and animals (no wall).
Why the top distractor is wrong: Plants (A) have cellulose walls, not chitin.

Question: Which of the following organisms lacks a cell wall?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Bacillus subtilis
Answer: C
Explanation: Mycoplasma is a bacterium that naturally lacks a cell wall, making it resistant to antibiotics like penicillin.
Why the top distractor is wrong: Saccharomyces cerevisiae (B) is a fungus and has a chitin-containing cell wall.

Question: Where does transcription occur in a eukaryotic cell?
A) Cytoplasm
B) Nucleus
C) Ribosome
D) Mitochondrion
Answer: B
Explanation: Transcription of DNA to mRNA occurs in the nucleus before mRNA is exported for translation.
Why the top distractor is wrong: Cytoplasm (A) is where translation occurs, not transcription.

Question: Which of the following is true about ribosomes in eukaryotic cells?
A) All ribosomes are 80S
B) Mitochondrial ribosomes are 70S
C) Ribosomes are enclosed in a membrane
D) Ribosomes are made of DNA and protein
Answer: B
Explanation: Mitochondrial ribosomes are 70S, reflecting their prokaryotic ancestry.
Why the top distractor is wrong: Not all ribosomes in eukaryotes are 80S; mitochondrial and chloroplast ribosomes are 70S.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have nucleoid; eukaryotes have nucleus with nuclear envelope.
• 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 wall = cellulose; fungal = chitin; animal = no cell wall.
• Mycoplasma is a bacterium without a cell wall.
• Human red blood cells lack a nucleus and mitochondria.
• Plasma membrane = phospholipid bilayer in both prokaryotes and eukaryotes.
• Only eukaryotes have membrane-bound organelles (e.g., ER, Golgi, lysosomes).
• Prokaryotes reproduce by binary fission; eukaryotes by mitosis/meiosis.
• Prokaryotic DNA = single circular chromosome; eukaryotic = multiple linear chromosomes.
• Plasmids are common in bacteria, rare in eukaryotes.
• Prokaryotic flagella = flagellin, rotate; eukaryotic = microtubules (9+2), bend.
• Cytoskeletal proteins: prokaryotes have FtsZ (tubulin homolog), MreB (actin homolog).
• Transcription and translation are coupled in prokaryotes; separated in eukaryotes.
• Endosymbiotic theory: mitochondria from alpha-proteobacteria, chloroplasts from cyanobacteria.
• Mitochondria and chloroplasts have double membranes and replicate independently.
• Plant cells have chloroplasts, central vacuole, plasmodesmata.
• Animal cells have centrioles, lysosomes; most plant cells lack these.
• Fungi are eukaryotes with chitin in cell walls and no chloroplasts.
• Archaea are prokaryotes but have eukaryote-like RNA polymerase.
• Nuclear pores regulate mRNA export and protein import.
• Lysosomes contain acid hydrolases; function in intracellular digestion.
• Peroxisomes contain catalase and break down fatty acids and H?O?.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.