STEM Readiness: Chemistry Readiness - Kinetics: Reaction Rates - Average vs. Instantaneous, Rate Laws, Determining Order Experimentally

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 contain organelles such as mitochondria, lysosomes, and the Golgi apparatus.
• Ribosomes in prokaryotes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S).
• Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, similar to prokaryotes, supporting the endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (especially in bacteria); archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are made of cellulose; fungal cell walls contain chitin; animal cells lack a cell wall.
• Mycoplasma, a genus of bacteria, lacks a cell wall and is resistant to antibiotics like penicillin that target peptidoglycan synthesis.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane that regulates transport and maintains integrity.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER) and Golgi apparatus; prokaryotes do not.
• The nucleus in eukaryotes is surrounded by a double membrane (nuclear envelope) with nuclear pores that regulate RNA and protein transport.
• Nuclear pores allow selective passage of molecules; small molecules diffuse freely, but large proteins require signal sequences for active transport.
• The nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome subunit assembly.
• Prokaryotes can have plasmids (small circular DNA molecules); eukaryotes rarely have plasmids (except in some yeast and cancer cells).
• Eukaryotic mitochondria have their own circular DNA, similar to bacterial chromosomes, supporting endosymbiotic origin.
• Chloroplasts in plant cells are double-membraned organelles with thylakoids and circular DNA, also supporting endosymbiotic theory.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis for cell division.
• Cytoskeleton is present in both: prokaryotes have homologs of actin and tubulin (e.g., MreB, FtsZ); eukaryotes have microtubules, microfilaments, and intermediate filaments.
• Red blood cells in mammals lack a nucleus and most organelles at maturity, maximizing hemoglobin content for oxygen transport.
• Plant cells contain central vacuoles that maintain turgor pressure; animal cells may have small vacuoles but no central vacuole.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; plants use vacuoles for similar degradative functions.
• Flagella in prokaryotes are made of flagellin and rotate like a propeller; eukaryotic flagella are composed of microtubules (9+2 arrangement) and move in a whip-like fashion.
• Eukaryotic cilia and flagella are covered by the plasma membrane; prokaryotic flagella are not membrane-bound.
• Archaea lack peptidoglycan and have ether-linked lipids in their membranes, distinguishing them from bacteria despite being prokaryotic.

Difficulty Level

Intermediate – expected foundational knowledge in first-semester biology but requires precise distinctions between cell types and organelle functions.

Common Traps (3–5 factual traps)

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

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

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

Trap: Prokaryotes do not have any internal membranes – Fact: Some prokaryotes (e.g., photosynthetic bacteria) have infoldings of the plasma membrane (like thylakoids) but lack membrane-bound organelles.

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: A membrane-bound nucleus is exclusive to eukaryotes.
Why the top distractor is wrong: Circular DNA is found in prokaryotes and also in mitochondria and chloroplasts, so it is not exclusive to prokaryotes.

Question: A cell is observed to have a cell wall, chloroplasts, and a large central vacuole. Which type of cell is it most likely to be?
A) Fungal cell
B) Animal cell
C) Bacterial cell
D) Plant cell
Answer: D
Explanation: Chloroplasts and a central vacuole are characteristic of plant cells.
Why the top distractor is wrong: Fungal cells have cell walls but lack chloroplasts and central vacuoles.

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

Question: Which of the following provides the strongest evidence for the endosymbiotic theory?
A) Presence of a nucleus in eukaryotes
B) 70S ribosomes in mitochondria
C) Peptidoglycan in bacterial cell walls
D) Binary fission in prokaryotes
Answer: B
Explanation: Mitochondria having 70S ribosomes and circular DNA resembles free-living bacteria, supporting endosymbiosis.
Why the top distractor is wrong: The nucleus is not evidence for endosymbiosis; it evolved via membrane invagination.

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 expel their nucleus to carry more hemoglobin.
Why the top distractor is wrong: Neurons are highly specialized eukaryotic cells but retain a nucleus.

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 cell wall contains peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal = chitin; animal cells = no cell wall.
• Mycoplasma lacks a cell wall – resistant to penicillin.
• Both cell types have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Nuclear envelope has double membrane and nuclear pores for transport.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Prokaryotes reproduce by binary fission; eukaryotes by mitosis/meiosis.
• Plasmids: common in prokaryotes, rare in eukaryotes.
• Cytoskeleton: FtsZ in prokaryotes (tubulin analog); tubulin/actin in eukaryotes.
• Mature red blood cells lack a nucleus and organelles.
• Plant central vacuole maintains turgor pressure; animal cells do not have one.
• Lysosomes = in animal cells; plants use vacuoles for degradation.
• Prokaryotic flagellum = flagellin, rotates; eukaryotic = 9+2 microtubules, bends.
• Eukaryotic flagella are membrane-covered; prokaryotic are not.
• Archaea have ether-linked lipids in membranes – different from bacterial ester-linked lipids.
• Endosymbiotic theory: mitochondria evolved from alpha-proteobacteria; chloroplasts from cyanobacteria.
• Mitochondria divide by binary fission, independent of the host cell cycle.
• Nuclear pores allow passive diffusion of small molecules; large molecules require nuclear localization signals (NLS).
• Verify from standard textbook: exact lipid composition of archaeal membranes.
• Verify from standard textbook: presence of cytoskeletal elements in archaea.