STEM Readiness: Physics Readiness - Kinematics: Relative Motion - Reference Frames, Galilean Transformation, River-Boat Problems

Must?Know

• 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 contain mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and (in plants) chloroplasts.
• Ribosomes in prokaryotes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., Escherichia coli); archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• Mycoplasma species are bacteria that lack a cell wall, making them resistant to penicillin.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems including nuclear envelope, ER, and Golgi; prokaryotes do not.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport.
• Chromosomes in prokaryotes are typically a single circular DNA molecule; eukaryotes have multiple linear chromosomes.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; rare in eukaryotes.
• Cytoskeleton is present in both: prokaryotes have FtsZ, MreB, CreS; eukaryotes have microtubules, actin filaments, intermediate filaments.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and bend.
• Red blood cells in mammals lack a nucleus and most organelles at maturity, increasing space for hemoglobin.
• Plant cells contain chloroplasts for photosynthesis and a large central vacuole for turgor pressure; animal cells do not.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; rare in plant cells (vacuoles perform similar function).
• Endosymbiotic theory is supported by: mitochondria and chloroplasts have their own 70S ribosomes, circular DNA, and double membranes.
• Mitochondria are present in nearly all eukaryotic cells; chloroplasts are limited to plants and algae.
• Archaea lack peptidoglycan and have ether-linked lipids in their membranes, unlike bacteria.
• Peroxisomes are single-membrane organelles in eukaryotes that break down fatty acids and detoxify hydrogen peroxide.
• Nuclear DNA in eukaryotes is associated with histone proteins to form chromatin; prokaryotic DNA is not.

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; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.
Trap: Ribosome size is the same across all organisms – Fact: Prokaryotes use 70S ribosomes; eukaryotic cytoplasmic ribosomes are 80S, but mitochondria and chloroplasts retain 70S.
Trap: The nucleus is the only place DNA is found in eukaryotes – Fact: Mitochondria and chloroplasts contain their own DNA.
Trap: Prokaryotes have no internal structure – Fact: They have nucleoids, ribosomes, cytoskeletal elements, and some have protein-bound microcompartments.
Trap: Eukaryotes evolved from prokaryotes directly – Fact: Eukaryotes likely arose from archaeal ancestors with endosymbiotic bacteria becoming mitochondria.

Practice MCQs

Question: Which of the following is a feature shared by both prokaryotic and eukaryotic cells?
A) Membrane-bound nucleus
B) Mitochondria
C) Phospholipid bilayer plasma membrane
D) Endoplasmic reticulum
Answer: C
Explanation: Both cell types have a phospholipid bilayer as the plasma membrane.
Why the top distractor is wrong: D (ER) is only found in eukaryotes; prokaryotes lack internal membrane systems.

Question: A cell is observed to contain a nucleoid, 70S ribosomes, and a cell wall with peptidoglycan. It is most likely:
A) A plant cell
B) A fungal cell
C) A bacterial cell
D) An animal cell
Answer: C
Explanation: Nucleoid, 70S ribosomes, and peptidoglycan are diagnostic of bacteria.
Why the top distractor is wrong: A (plant cells) have a nucleus, 80S ribosomes, and cellulose cell walls.

Question: Which structure is found in eukaryotic cells but absent in prokaryotic cells?
A) Ribosomes
B) Plasma membrane
C) Golgi apparatus
D) DNA
Answer: C
Explanation: The Golgi apparatus is a membrane-bound organelle unique to eukaryotes.
Why the top distractor is wrong: A (ribosomes) are present in both, though differing in size.

Question: Mitochondria are thought to have originated from free-living bacteria due to all of the following EXCEPT:
A) Presence of 70S ribosomes
B) Double membrane
C) Linear DNA molecules
D) Circular DNA
Answer: C
Explanation: Mitochondria have circular DNA, not linear; linear chromosomes are typical of nuclear DNA in eukaryotes.
Why the top distractor is wrong: D is correct evidence; C is false and thus the exception.

Question: Which of the following cells lacks a nucleus at maturity?
A) Yeast cell
B) Neuron
C) Human red blood cell
D) Leaf mesophyll cell
Answer: C
Explanation: Mature mammalian red blood cells eject their nucleus to accommodate hemoglobin.
Why the top distractor is wrong: A (yeast) are fungi and have a nucleus; they are eukaryotic.

Question: Which organism has a cell wall but does not contain peptidoglycan?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Bacillus anthracis
D) Mycoplasma pneumoniae
Answer: B
Explanation: Saccharomyces cerevisiae (yeast) is a fungus with a chitin-containing cell wall, not peptidoglycan.
Why the top distractor is wrong: A and C are bacteria and contain peptidoglycan.

Question: What is the primary structural component of the plant cell wall?
A) Chitin
B) Peptidoglycan
C) Cellulose
D) Collagen
Answer: C
Explanation: Cellulose is the main polysaccharide in plant cell walls.
Why the top distractor is wrong: A (chitin) is found in fungi and insect exoskeletons, not plants.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: nucleoid; eukaryotes: nucleus with nuclear envelope.
• 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.
• Plant cell wall: cellulose; fungal: chitin; animal: no cell wall.
• Mycoplasma – bacteria without cell walls.
• Both cell types have phospholipid bilayer membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Prokaryotes have single circular chromosome; eukaryotes have multiple linear chromosomes.
• Prokaryotes reproduce by binary fission; eukaryotes by mitosis/meiosis.
• Plasmids common in bacteria; rare in eukaryotes.
• Cytoskeleton: prokaryotes have FtsZ (tubulin homolog); eukaryotes have microtubules.
• Prokaryotic flagella: rotate, made of flagellin; eukaryotic: bend, 9+2 microtubule array.
• Mature mammalian red blood cells lack a nucleus and organelles.
• Chloroplasts only in plants and algae; mitochondria in nearly all eukaryotes.
• Lysosomes primarily in animal cells; plant vacuoles perform degradation.
• Nuclear pores regulate molecule transport across the double-membrane nuclear envelope.
• Endosymbiotic theory: mitochondria from alpha-proteobacteria; chloroplasts from cyanobacteria.
• Archaea have ether-linked lipids in membranes; bacteria and eukaryotes have ester-linked.
• Peroxisomes contain catalase to break down H?O?.
• Histones associate with eukaryotic DNA; prokaryotic DNA is not packaged with histones.
• Nuclear DNA is linear; mitochondrial DNA is circular.
• FtsZ protein in prokaryotes is homologous to eukaryotic tubulin.
• Verify from standard textbook: exact lipid composition in archaeal membranes.