STEM Readiness: Chemistry Readiness - Kinetics: Integrated Rate Laws - First Order ln plot, Second Order, 1A plot, Half-Life

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 lacking 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.
• Prokaryotic ribosomes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S subunits).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting the endosymbiotic theory.
• Bacterial cell walls contain peptidoglycan; archaea lack peptidoglycan and have different cell wall compositions (e.g., pseudopeptidoglycan).
• Plant cell walls are made of cellulose; fungal cell walls are composed of chitin; animal cells lack a cell wall.
• Mycoplasma, a bacterium, 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 passage of substances.
• Eukaryotic cells have internal membranes forming organelles (e.g., nuclear envelope, endoplasmic reticulum); prokaryotes do not.
• The nucleus in eukaryotes contains linear DNA organized into chromosomes; prokaryotes have a single circular chromosome.
• Plasmids are small, circular DNA molecules found in prokaryotes and some yeasts (eukaryotes), often carrying antibiotic resistance genes.
• Eukaryotic cells divide by mitosis and cytokinesis; prokaryotes divide by binary fission.
• 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 motion.
• Cilia are short, numerous motile structures found on some eukaryotic cells (e.g., tracheal epithelium); absent in prokaryotes.
• Mitochondria are the site of aerobic respiration in eukaryotes; prokaryotes perform respiration on the plasma membrane.
• Chloroplasts are photosynthetic organelles in plant cells and algae; absent in prokaryotes, though some bacteria perform photosynthesis using thylakoid membranes.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having double membranes, circular DNA, and 70S ribosomes.
• Red blood cells (erythrocytes) in mammals lack a nucleus and most organelles, maximizing space for hemoglobin.
• Sieve tube elements in plants lose their nucleus at maturity but remain alive with support from companion cells.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; rare in plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small, temporary vacuoles.
• Peroxisomes contain enzymes for fatty acid oxidation and detoxify hydrogen peroxide; present in both plant and animal eukaryotic cells.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences between cell types, including exceptions and evolutionary implications.

Common Traps (3–5 factual traps)

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose) and fungi (chitin) have different wall compositions.
• Trap: Ribosome size is the same across all organisms – Fact: Prokaryotes use 70S ribosomes; eukaryotic cytoplasmic ribosomes are 80S, though mitochondria and chloroplasts retain 70S.
• 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 cytoplasm, ribosomes, nucleoid, and sometimes inclusions or protein microcompartments.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of prokaryotic cells?
A) Membrane-bound nucleus
B) 80S ribosomes
C) Presence of peptidoglycan in the cell wall
D) Mitochondria for ATP production
Answer: C
Explanation: Peptidoglycan is a key component of bacterial (prokaryotic) cell walls.
Why the top distractor is wrong: A is incorrect because prokaryotes lack a membrane-bound nucleus.

Question: Which structure is found in plant cells but not in animal cells?
A) Lysosome
B) Mitochondrion
C) Central vacuole
D) Golgi apparatus
Answer: C
Explanation: The large central vacuole is a hallmark of mature plant cells.
Why the top distractor is wrong: A is incorrect because lysosomes are primarily in animal cells, though plant vacuoles can have similar functions.

Question: Mitochondria are thought to have originated from free-living prokaryotes due to all of the following EXCEPT:
A) They have 70S ribosomes
B) They contain circular DNA
C) They are surrounded by a single membrane
D) They reproduce by binary fission
Answer: C
Explanation: Mitochondria have a double membrane, consistent with endosymbiotic engulfment.
Why the top distractor is wrong: C is the exception; the double membrane (not single) supports endosymbiosis.

Question: Which of the following cells lacks a nucleus?
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 carry more hemoglobin.
Why the top distractor is wrong: A is incorrect because yeast is a eukaryote and has a nucleus.

Question: Where does aerobic respiration occur in prokaryotes?
A) Mitochondria
B) Nucleoid
C) Cytoplasm
D) Plasma membrane
Answer: D
Explanation: Prokaryotes lack mitochondria; electron transport chain proteins are embedded in the plasma membrane.
Why the top distractor is wrong: A is incorrect because prokaryotes do not have mitochondria.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: nucleoid; eukaryotes: nucleus.
• 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 has no cell wall – resistant to penicillin.
• Both cell types have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes do not.
• Prokaryotes have single circular chromosome; eukaryotes have multiple linear chromosomes.
• Plasmids: small circular DNA, common in bacteria.
• Prokaryotes divide by binary fission; eukaryotes by mitosis.
• Prokaryotic flagella: made of flagellin, rotary motion.
• Eukaryotic flagella: 9+2 microtubule arrangement, dynein arms, bending motion.
• Cilia: found only in eukaryotes, used for movement or fluid propulsion.
• Mitochondria: site of Krebs cycle and oxidative phosphorylation in eukaryotes.
• Chloroplasts: site of photosynthesis in plants and algae.
• Red blood cells lack a nucleus and organelles.
• Sieve tube elements lose nucleus but stay alive via companion cells.
• Lysosomes: hydrolytic enzymes, mostly in animal cells.
• Plant vacuole: large central, maintains turgor pressure.
• Peroxisomes: break down fatty acids, detoxify H?O?.
• Nuclear envelope: double membrane with nuclear pores.
• Endosymbiotic theory supported by double membranes, 70S ribosomes, and independent division of mitochondria/chloroplasts.
• Verify from standard textbook: exact lipid composition of archaeal membranes.