STEM Readiness: Physics Readiness - : Forces Newton’s, Laws Friction, Static vs. Kinetic, Coefficient of Friction, Inclined Planes

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 in eukaryotic cells contain 70S ribosomes, similar to prokaryotes.
• Peptidoglycan is present in bacterial cell walls; absent in archaea and eukaryotes.
• Archaea lack peptidoglycan but may have pseudopeptidoglycan or other wall types.
• Plant cells have cell walls made of cellulose; fungal cells have walls made of chitin.
• Animal cells lack a cell wall entirely.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Only eukaryotes have membrane-bound organelles such as the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria, and nucleus.
• Bacteria (e.g., Escherichia coli) and archaea (e.g., Methanogens) are prokaryotes.
• Animals, plants, fungi, and protists are eukaryotes.
• Mycoplasma species are bacteria that lack a cell wall—an exception among prokaryotes.
• Mature red blood cells in mammals lack a nucleus and most organelles—unlike typical eukaryotic cells.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; rare in eukaryotes.
• 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.
• Cytoskeleton elements (microtubules, actin filaments) are present in eukaryotes and homologs exist in some prokaryotes (e.g., FtsZ).
• Endosymbiotic theory proposes mitochondria evolved from aerobic bacteria; chloroplasts from cyanobacteria.
• Evidence for endosymbiosis includes mitochondrial 70S ribosomes, circular DNA, and binary fission reproduction.
• Lysosomes are membrane-bound organelles in animal cells that contain hydrolytic enzymes; absent in most plant cells.
• Vacuoles in plant cells are large and central; in animal cells, vacuoles are small and temporary.
• Chloroplasts are present in plant cells and some protists (e.g., Chlamydomonas), but not in animals or fungi.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Pili (or fimbriae) are present in many prokaryotes for attachment; not found in eukaryotes.

Difficulty Level

Intermediate – routinely tested in first-year biology with emphasis on comparison and exceptions.

Common Traps

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (other polymers) do not.
• Trap: Ribosome size is the same across all domains – Fact: Prokaryotes use 70S ribosomes; eukaryotes use 80S in cytoplasm (but 70S in mitochondria/chloroplasts).
• Trap: Eukaryotes are always larger because they have more DNA – Fact: Genome size does not always correlate with cell size or organism complexity (C-value paradox).
• Trap: The nucleus is the only organelle that contains DNA in eukaryotes – Fact: Mitochondria and chloroplasts also contain their own DNA.
• Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, inclusions, and some have protein-based cytoskeletal elements.

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) 80S ribosomes
Answer: C
Explanation: Both cell types have a phospholipid bilayer as the plasma membrane.
Why the top distractor is wrong: A is exclusive to eukaryotes; prokaryotes lack a nucleus.

Question: A cell is observed to have a cell wall made of cellulose, chloroplasts, and a large central vacuole. What type of cell is this most likely?
A) Fungal
B) Bacterial
C) Animal
D) Plant
Answer: D
Explanation: Cellulose cell walls, chloroplasts, and large central vacuoles are diagnostic of plant cells.
Why the top distractor is wrong: Fungal cells have chitin walls and lack chloroplasts.

Question: Which structure is found in prokaryotes but not in eukaryotes?
A) 70S ribosome
B) Circular DNA
C) Peptidoglycan cell wall
D) Flagella
Answer: C
Explanation: Peptidoglycan is unique to bacterial cell walls.
Why the top distractor is wrong: 70S ribosomes occur in prokaryotes and also in mitochondria/chloroplasts of eukaryotes.

Question: Which of the following provides evidence for the endosymbiotic theory?
A) Eukaryotic cells have a nucleus
B) Mitochondria have their own 70S ribosomes and circular DNA
C) Prokaryotes lack membrane-bound organelles
D) Plant cells have cell walls
Answer: B
Explanation: Mitochondrial 70S ribosomes and circular DNA resemble those of bacteria.
Why the top distractor is wrong: A is a general feature of eukaryotes but not evidence of endosymbiosis.

Question: Which of the following cells lacks a nucleus at maturity?
A) Escherichia coli
B) Saccharomyces cerevisiae (yeast)
C) Human hepatocyte
D) Human erythrocyte
Answer: D
Explanation: Mature human red blood cells (erythrocytes) lose their nucleus to carry more hemoglobin.
Why the top distractor is wrong: E. coli is prokaryotic and never had a nucleus, but the question implies loss during maturation.

Question: What distinguishes the flagellum of a eukaryotic cell from that of a prokaryotic cell?
A) Eukaryotic flagella are composed of flagellin
B) Prokaryotic flagella use ATP for movement
C) Eukaryotic flagella have a 9+2 microtubule arrangement
D) Prokaryotic flagella are powered by proton motive force
Answer: C
Explanation: The 9+2 axoneme structure of microtubules is unique to eukaryotic flagella.
Why the top distractor is wrong: A is false—flagellin is in prokaryotes, not eukaryotes.

Question: Which organelle is responsible for modifying and packaging proteins for secretion in eukaryotic cells?
A) Nucleus
B) Rough endoplasmic reticulum
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins from the ER.
Why the top distractor is wrong: The rough ER synthesizes proteins but does not package them for secretion.

Last?Minute Revision

• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA—evidence for endosymbiosis.
• Prokaryotes: 0.1–5.0 ?m; eukaryotes: 10–100 ?m.
• DNA in prokaryotes: nucleoid (no membrane); eukaryotes: nucleus (double membrane).
• Peptidoglycan = only in bacteria.
• Cellulose = plant cell wall; chitin = fungal cell wall.
• Animal cells: no cell wall, no chloroplasts, small vacuoles.
• Mycoplasma = bacteria without cell wall.
• Mature mammalian red blood cells = no nucleus, no mitochondria.
• Archaea lack peptidoglycan but are prokaryotes.
• Plasmids = small circular DNA, common in bacteria.
• Nuclear pores regulate mRNA and protein transport across nuclear envelope.
• Eukaryotic chromosomes are linear; prokaryotic chromosome is circular.
• FtsZ protein in prokaryotes is homologous to eukaryotic tubulin.
• Lysosomes present in animal cells, generally absent in plant cells.
• Central vacuole in plants stores water and maintains turgor pressure.
• Chloroplasts perform photosynthesis; found in plants and some protists.
• Eukaryotic flagellum: 9+2 microtubule arrangement; powered by ATP.
• Prokaryotic flagellum: made of flagellin; rotates using proton motive force.
• Pili = prokaryotic structures for adhesion or conjugation; not in eukaryotes.
• Endoplasmic reticulum (rough and smooth) is part of the endomembrane system in eukaryotes.
• Golgi apparatus modifies proteins with carbohydrate tags.
• Mitochondria generate ATP via aerobic respiration in eukaryotes.
• Nuclear envelope is a double membrane with nuclear pores.
• Verify from standard textbook: exact size ranges may vary slightly by source.