STEM Readiness: Physics Readiness - : Forces Newton’s, Laws Circular, Dynamics Centripetal, Force as, Net Force, Vertical and Horizontal Circles

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 lack a membrane-bound nucleus; DNA resides in the nucleoid region.
• Eukaryotes have a membrane-bound nucleus containing linear chromosomes.
• Prokaryotic ribosomes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting endosymbiotic origin.
• Bacteria have cell walls made of peptidoglycan; thickness distinguishes Gram-positive (thick) from Gram-negative (thin + outer membrane).
• Archaea lack peptidoglycan; their cell walls are made of pseudopeptidoglycan or other polysaccharides.
• Plant cells have cellulose-based cell walls; fungal cells have chitin-based walls.
• Animal cells lack a cell wall entirely.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have extensive internal membranes forming organelles; prokaryotes do not.
• Endoplasmic reticulum (ER) is present only in eukaryotes; rough ER synthesizes proteins, smooth ER synthesizes lipids and detoxifies.
• Golgi apparatus modifies, sorts, and packages proteins into vesicles; absent in prokaryotes.
• Mitochondria generate ATP via aerobic respiration; have double membranes, circular DNA, and 70S ribosomes.
• Chloroplasts perform photosynthesis in plants and algae; contain thylakoids, chlorophyll, circular DNA, and 70S ribosomes.
• Lysosomes contain hydrolytic enzymes for degradation; found in animal cells, rare in plant cells (vacuoles perform similar function).
• Vacuoles in plant cells maintain turgor pressure and store ions; central vacuole can occupy up to 90% of cell volume.
• Cytoskeleton (microtubules, actin filaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologous proteins (e.g., FtsZ) but no true cytoskeleton.
• Flagella differ structurally: prokaryotic flagella are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 array) and undulate.
• Binary fission is the method of prokaryotic cell division; mitosis occurs in eukaryotes.
• Mycoplasma species are bacteria without a cell wall; smallest known cells (~0.2 ?m).
• Human red blood cells lack a nucleus and organelles; maximize hemoglobin content for oxygen transport.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having double membranes, independent division, circular DNA, and 70S ribosomes.
• Archaea are prokaryotes in cell structure but share transcription and translation machinery with eukaryotes.
• Nuclear envelope is a double membrane with nuclear pores that regulate transport; absent in prokaryotes.

Difficulty Level

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

Common Traps (3–5 factual traps)

Trap: All prokaryotes have cell walls – Fact: Mycoplasma and related bacteria lack cell walls entirely.
Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: Eukaryotes are always larger than prokaryotes – Fact: Some bacteria (e.g., Thiomargarita namibiensis) can exceed 100 ?m, larger than typical eukaryotic cells.
Trap: The nucleus is the only site of DNA in eukaryotes – Fact: Mitochondria and chloroplasts contain their own DNA.
Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (pseudopeptidoglycan) differ.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature shared by both prokaryotic and eukaryotic cells?
A) Membrane-bound nucleus
B) 80S ribosomes
C) Phospholipid bilayer plasma membrane
D) Mitochondria
Answer: C
Explanation: Both cell types have a phospholipid bilayer as the plasma membrane.
Why the top distractor is wrong: D (mitochondria) are present only in eukaryotes.

Question: A cell is observed to have a nucleus, mitochondria, and a cell wall made of cellulose. From which organism is this cell most likely derived?
A) Fungus
B) Bacterium
C) Animal
D) Plant
Answer: D
Explanation: Plants have cellulose cell walls, a nucleus, and mitochondria.
Why the top distractor is wrong: A (fungi) have chitin, not cellulose, in their cell walls.

Question: Which structure is found in eukaryotes but not in prokaryotes?
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 endosymbiotic bacteria. Which of the following supports this theory?
A) Mitochondria lack DNA
B) Mitochondria have 80S ribosomes
C) Mitochondria divide by binary fission
D) Mitochondria are surrounded by a single membrane
Answer: C
Explanation: Mitochondria divide independently via binary fission, similar to bacteria.
Why the top distractor is wrong: B is incorrect because mitochondria have 70S ribosomes, not 80S.

Question: Which of the following cells lacks a nucleus?
A) Yeast cell
B) Human neuron
C) Escherichia coli
D) Onion root cell
Answer: C
Explanation: E. coli is a prokaryote and lacks a membrane-bound nucleus.
Why the top distractor is wrong: A (yeast) is a eukaryotic fungus and has a nucleus.

Question: What is the sedimentation coefficient of cytoplasmic ribosomes in human liver cells?
A) 50S
B) 70S
C) 80S
D) 30S
Answer: C
Explanation: Eukaryotic cytoplasmic ribosomes are 80S.
Why the top distractor is wrong: B (70S) refers to prokaryotic or organellar ribosomes, not cytoplasmic eukaryotic ones.

Question: Which organism has a cell wall but lacks peptidoglycan?
A) Streptococcus pneumoniae
B) Saccharomyces cerevisiae
C) Escherichia coli
D) Mycoplasma genitalium
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 have peptidoglycan in their cell walls.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have nucleoid, not nucleus.
• Eukaryotes have membrane-bound nucleus with nuclear pores.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA.
• Bacteria: peptidoglycan cell wall; Archaea: no peptidoglycan.
• Plants: cellulose cell wall; Fungi: chitin cell wall.
• Animal cells: no cell wall.
• Both cell types have phospholipid bilayer plasma membrane.
• Only eukaryotes have internal membrane systems (ER, Golgi, nucleus).
• Rough ER has ribosomes; smooth ER does not.
• Golgi apparatus: modifies and packages proteins.
• Mitochondria: ATP synthesis, double membrane, own DNA.
• Chloroplasts: photosynthesis, thylakoids, chlorophyll.
• Lysosomes: contain hydrolytic enzymes, found in animal cells.
• Plant vacuole: can occupy up to 90% of cell volume.
• Cytoskeleton: eukaryotes only (microtubules, actin, intermediate filaments).
• Prokaryotic flagellum: made of flagellin, rotates.
• Eukaryotic flagellum: 9+2 microtubule array, bends.
• Binary fission: prokaryotic division; mitosis: eukaryotic.
• Mycoplasma: smallest cells, no cell wall.
• Human red blood cells: no nucleus, no organelles.
• Endosymbiotic theory evidence: organelles have double membranes, circular DNA, 70S ribosomes, divide by binary fission.
• Archaea: prokaryotic structure but transcription/translation like eukaryotes.
• Nuclear envelope: double membrane with pores; regulates transport.