STEM Readiness: Chemistry Readiness - Nuclear Chemistry: Radioactive Decay Kinetics - First-Order, Half-Life, Calculations Carbon, Dating

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, an unenclosed region; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain organelles such as mitochondria, lysosomes, and peroxisomes.
• Ribosomes in prokaryotes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan; archaea lack peptidoglycan and have different wall chemistries.
• Plant cell walls are made of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• All cells have a plasma membrane composed of a phospholipid bilayer with embedded proteins.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER) and Golgi apparatus; prokaryotes do not.
• The nucleus in eukaryotes contains chromatin (DNA + histones) and a nucleolus where ribosomal RNA is synthesized.
• Nuclear pores regulate transport between the nucleus and cytoplasm; prokaryotes lack such structures.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and bend.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; rare in eukaryotes.
• Mycoplasma species are bacteria without a cell wall, making them resistant to antibiotics like penicillin.
• Human red blood cells lack a nucleus and mitochondria, maximizing space for hemoglobin.
• Endosymbiotic theory proposes that mitochondria and chloroplasts originated from engulfed prokaryotes; evidence includes their own DNA, 70S ribosomes, and double membranes.
• Chloroplasts are found in plants and algae; perform photosynthesis; contain thylakoids and chlorophyll.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes for digestion; rare in plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small or temporary vacuoles.
• The rough ER is studded with ribosomes and synthesizes proteins for secretion or membranes; smooth ER synthesizes lipids and detoxifies.
• The Golgi apparatus modifies, sorts, and packages proteins into vesicles for transport; absent in prokaryotes.
• Peroxisomes contain catalase and break down fatty acids and hydrogen peroxide; present in eukaryotes only.
• Cytoskeleton elements (microtubules, microfilaments, intermediate filaments) are found in eukaryotes; prokaryotes have analogous proteins (e.g., FtsZ) but no true cytoskeleton.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, 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 (cellulose), fungal (chitin), and archaeal (pseudopeptidoglycan or other) walls differ chemically.

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

Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes; nuclear envelope is continuous with the ER.

Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, inclusions, and sometimes protein-based cytoskeletal analogs (e.g., MreB, FtsZ).

Practice MCQs (5–7 questions)

Question: Which of the following is a feature found in eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) 70S ribosomes
C) Circular DNA
D) Membrane-bound nucleus
Answer: D
Explanation: Only eukaryotes have a membrane-bound nucleus.
Why the top distractor is wrong: Circular DNA is present in both prokaryotes and eukaryotic organelles like mitochondria.

Question: A cell is observed to contain cellulose in its cell wall, chloroplasts, and a large central vacuole. This cell is most likely from a:
A) Fungus
B) Animal
C) Bacterium
D) Plant
Answer: D
Explanation: Cellulose, chloroplasts, and a large central vacuole are characteristic of plant cells.
Why the top distractor is wrong: Fungi have chitin in their cell walls and lack chloroplasts.

Question: Which structure is evidence supporting the endosymbiotic theory?
A) Presence of a nucleoid
B) 80S ribosomes in the cytoplasm
C) Mitochondria with 70S ribosomes and circular DNA
D) Peptidoglycan in the cell wall
Answer: C
Explanation: Mitochondria resemble prokaryotes in ribosome type and DNA structure, supporting their origin via endosymbiosis.
Why the top distractor is wrong: The nucleoid is a prokaryotic feature, not evidence for endosymbiosis.

Question: Which of the following cells lacks a nucleus?
A) Human liver cell
B) Yeast cell
C) Escherichia coli
D) Onion root cell
Answer: C
Explanation: Escherichia coli is a prokaryote and lacks a membrane-bound nucleus.
Why the top distractor is wrong: Human red blood cells lack a nucleus but are not listed; E. coli is the only prokaryote among the options.

Question: The organelle responsible for modifying and packaging proteins for secretion is the:
A) Nucleolus
B) Mitochondrion
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins into vesicles for transport.
Why the top distractor is wrong: The lysosome functions in intracellular digestion, not secretion.

Question: Which of the following is true of both prokaryotic and eukaryotic cells?
A) Presence of mitochondria
B) 80S ribosomes
C) Phospholipid bilayer plasma membrane
D) Nuclear envelope
Answer: C
Explanation: All cells have a plasma membrane made of a phospholipid bilayer.
Why the top distractor is wrong: Mitochondria are only in eukaryotes; prokaryotes generate ATP at the plasma membrane.

Question: Which component is found in animal cells but typically absent in plant cells?
A) Centrioles
B) Plasma membrane
C) Ribosomes
D) Vacuoles
Answer: A
Explanation: Centrioles are involved in spindle formation during mitosis in animal cells; most plant cells lack them.
Why the top distractor is wrong: Both plant and animal cells have vacuoles, though plant vacuoles are larger and more central.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have no nucleus; DNA in nucleoid.
• Eukaryotes have 80S ribosomes; prokaryotes have 70S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence for endosymbiosis.
• Bacteria cell wall contains peptidoglycan; archaea do not.
• Plant cell wall: cellulose; fungal: chitin; animal: no cell wall.
• All cells have a phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Nuclear pores allow selective transport between nucleus and cytoplasm.
• Human red blood cells lack a nucleus and mitochondria.
• Prokaryotes reproduce by binary fission; eukaryotes by mitosis/meiosis.
• Prokaryotic flagella: flagellin, rotating; eukaryotic: microtubules (9+2), bending.
• Plasmids: small circular DNA, common in bacteria.
• Mycoplasma has no cell wall – smallest known cells.
• Lysosomes contain hydrolytic enzymes; mainly in animal cells.
• Plant vacuole: large and central, maintains turgor pressure.
• Rough ER: ribosome-studded, synthesizes proteins.
• Smooth ER: lipid synthesis, detoxification, Ca²? storage.
• Golgi apparatus: modifies and packages proteins in vesicles.
• Peroxisomes: break down fatty acids and H?O? using catalase.
• Cytoskeleton: microtubules, microfilaments, intermediate filaments – eukaryote-specific.
• FtsZ protein in prokaryotes is homologous to tubulin.
• MreB protein in bacteria is analogous to actin.
• Mitochondria and chloroplasts have double membranes.
• Nucleolus: site of rRNA synthesis and ribosome assembly.
• Verify from standard textbook: exact protein composition of archaeal cell walls.