STEM Readiness: Pre-Calculus Readiness - Sequences/Series: Arithmetic and Geometric Sequences - Formulas, Sums

Must?Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• 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 have endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes.
• Ribosomes in prokaryotes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S subunits).
• 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 composed of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to penicillin, which targets peptidoglycan synthesis.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have extensive internal membrane systems, including the nuclear envelope, ER, and Golgi; prokaryotes do not.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport; prokaryotes have no equivalent structure.
• Chromosomes in prokaryotes are typically a single, circular DNA molecule; eukaryotes have multiple linear chromosomes.
• Plasmids are small, circular DNA molecules common in prokaryotes; rare in eukaryotes (e.g., 2-micron plasmid in Saccharomyces cerevisiae).
• Binary fission is the primary mode of reproduction in prokaryotes; eukaryotes divide by mitosis and cytokinesis.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and undulate.
• Cytoskeleton is present in both: prokaryotes have homologs of actin and tubulin (e.g., MreB, FtsZ); eukaryotes have actin filaments, microtubules, intermediate filaments.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own circular DNA, 70S ribosomes, and double membranes.
• Red blood cells in mammals lack a nucleus and organelles, maximizing hemoglobin content; they are an exception among eukaryotic cells.
• Plant cells have chloroplasts, large central vacuoles, and plasmodesmata; animal cells do not.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; absent in most plant cells (vacuoles perform similar function).
• Peroxisomes are present in both plant and animal eukaryotic cells and contain enzymes for fatty acid oxidation and detoxification of hydrogen peroxide.
• Archaea lack peptidoglycan and have ether-linked lipids in their membranes; bacteria have ester-linked lipids.
• Gram-positive bacteria have thick peptidoglycan and no outer membrane; Gram-negative bacteria have thin peptidoglycan and an outer membrane with lipopolysaccharides.
• Nuclear DNA in eukaryotes is associated with histone proteins to form chromatin; prokaryotic DNA is not packaged with histones (though some archaea have histone-like proteins).

Difficulty Level

Intermediate – requires precise differentiation of structures, components, and exceptions across domains, commonly tested in first-semester biology.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plant cell walls are made of cellulose, fungal walls of chitin, and archaeal walls lack peptidoglycan.

Trap: Ribosome size is the same across all organisms – Fact: Prokaryotes have 70S ribosomes; eukaryotes have 80S ribosomes in the cytoplasm, but mitochondria and chloroplasts retain 70S ribosomes.

Trap: The nucleus is the only organelle that contains DNA in eukaryotes – Fact: Mitochondria and chloroplasts also contain their own DNA, distinct from nuclear DNA.

Trap: Prokaryotes do not have any internal membranes – Fact: Some prokaryotes (e.g., cyanobacteria) have internal membrane systems like thylakoids for photosynthesis.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) Ribosomes
C) Circular DNA
D) Membrane-bound nucleus
Answer: D
Explanation: The membrane-bound nucleus is unique to eukaryotes.
Why the top distractor is wrong: Circular DNA is common in prokaryotes but also found in mitochondria and chloroplasts of eukaryotes.

Question: A cell is observed to have a cell wall, chloroplasts, and a large central vacuole. It most likely belongs to which domain?
A) Bacteria
B) Archaea
C) Animalia
D) Plantae
Answer: D
Explanation: Chloroplasts, a large central vacuole, and a cellulose cell wall are characteristic of plant cells.
Why the top distractor is wrong: Bacteria may have cell walls but lack chloroplasts and membrane-bound organelles.

Question: Which structure is present in both prokaryotes and eukaryotes but differs in size and subunit composition?
A) Nucleus
B) Mitochondrion
C) Ribosome
D) Golgi apparatus
Answer: C
Explanation: Ribosomes are present in both, but prokaryotes have 70S and eukaryotes have 80S ribosomes.
Why the top distractor is wrong: The nucleus is only present in eukaryotes.

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
C) Containing 70S ribosomes and circular DNA
D) Having a role in ATP production
Answer: C
Explanation: 70S ribosomes and circular DNA in mitochondria are prokaryote-like features supporting endosymbiosis.
Why the top distractor is wrong: A double membrane is suggestive but not exclusive evidence; many organelles have double membranes.

Question: Which of the following cells lacks a nucleus?
A) Escherichia coli
B) Human neuron
C) Saccharomyces cerevisiae
D) Arabidopsis thaliana root cell
Answer: A
Explanation: E. coli is a prokaryote and lacks a membrane-bound nucleus.
Why the top distractor is wrong: Human neurons are eukaryotic and contain a nucleus.

Question: Which organism has a cell wall but does not contain peptidoglycan?
A) Staphylococcus aureus
B) Mycoplasma pneumoniae
C) Penicillium chrysogenum
D) Escherichia coli
Answer: C
Explanation: Penicillium, a fungus, has a chitin-based cell wall, not peptidoglycan.
Why the top distractor is wrong: Mycoplasma lacks a cell wall entirely.

Question: Which of the following is true about ribosomes in mitochondria?
A) They are 80S, like cytoplasmic ribosomes
B) They are 70S, similar to bacterial ribosomes
C) They are synthesized entirely in the nucleus
D) They are absent in plant cells
Answer: B
Explanation: Mitochondrial ribosomes are 70S, reflecting their bacterial ancestry.
Why the top distractor is wrong: 80S ribosomes are found in the eukaryotic cytoplasm, not in mitochondria.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• 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.
• Bacteria: peptidoglycan cell wall; plants: cellulose; fungi: chitin; animals: no cell wall.
• Mycoplasma has no cell wall – naturally resistant to penicillin.
• Both prokaryotes and eukaryotes have phospholipid bilayer membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes generally do not.
• Nuclear envelope has double membrane and nuclear pores.
• Prokaryotes have single circular chromosome; eukaryotes have multiple linear chromosomes.
• Plasmids are common in bacteria, rare in eukaryotes.
• Prokaryotes reproduce by binary fission; eukaryotes by mitosis.
• Prokaryotic flagella: rotate, made of flagellin; eukaryotic: 9+2 microtubules, bend.
• Cytoskeleton: prokaryotes have FtsZ (tubulin homolog), MreB (actin homolog).
• Mammalian red blood cells lack a nucleus and organelles.
• Plant cells: chloroplasts, central vacuole, plasmodesmata.
• Animal cells: lysosomes, centrioles, no cell wall.
• Lysosomes contain hydrolytic enzymes; absent in most plant cells.
• Peroxisomes: break down fatty acids and detoxify H?O?.
• Archaea: no peptidoglycan, ether-linked lipids in membranes.
• Gram-positive: thick peptidoglycan, no outer membrane; Gram-negative: thin peptidoglycan, outer membrane with LPS.
• Mitochondria have own DNA and ribosomes – supports endosymbiotic theory.
• Nuclear DNA is wrapped around histones; prokaryotic DNA is not (except some archaea).
• Chloroplasts have thylakoids for photosynthesis; cyanobacteria have similar structures.
• Verify from standard textbook: histone-like proteins in some archaea.