STEM Readiness: Biology Readiness - Chemistry of Life: pH and Buffers - Acid-Base Chemistry, Relevant to, Biology Henderson-Hasselbalch

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 endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and (in plants) chloroplasts.
• 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, supporting their origin via endosymbiotic theory.
• Cell walls in bacteria contain peptidoglycan; archaea lack peptidoglycan but may have pseudopeptidoglycan or other polymers.
• Plant cell walls are made of cellulose; fungal cell walls are composed of chitin; animal cells lack cell walls.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane that regulates transport.
• Eukaryotes have internal membrane systems (nuclear envelope, ER, Golgi) forming compartments; prokaryotes do not.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis.
• Plasmids are small, circular extrachromosomal DNA molecules common in prokaryotes; rare in eukaryotes.
• Eukaryotic nuclei are surrounded by a double membrane (nuclear envelope) with nuclear pores for RNA and protein transport.
• Nucleolus is present in eukaryotic nuclei and is the site of ribosomal RNA synthesis and ribosome assembly; absent in prokaryotes.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and undulate.
• Cilia are present in some eukaryotes (e.g., Paramecium, human respiratory tract); prokaryotes lack cilia.
• Mycoplasma species are bacteria without a cell wall, making them resistant to antibiotics like penicillin that target peptidoglycan.
• Human red blood cells lack a nucleus and mitochondria in maturity, maximizing space for hemoglobin; they are an exception among eukaryotic cells.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Chloroplasts are found in plants and some protists (e.g., Chlamydomonas); absent in animals and fungi.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; plant vacuoles perform similar functions.
• Peroxisomes are present in both plant and animal eukaryotic cells and are involved in fatty acid breakdown and detoxification of hydrogen peroxide.
• Archaea are prokaryotes but have ribosomal RNA and membrane lipids more similar to eukaryotes than bacteria.
• Gram-positive bacteria have a thick peptidoglycan layer; Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide (LPS).
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells may have small, temporary vacuoles.

Difficulty Level

Intermediate – requires precise differentiation of structural and functional features across domains and kingdoms, with attention to exceptions.

Common Traps (3–5 factual traps)

Trap: All prokaryotes have cell walls – Fact: Mycoplasma, a bacterium, lacks a cell wall entirely.
Trap: Ribosome size is the same across all organelles in eukaryotes – Fact: Mitochondria and chloroplasts have 70S ribosomes, unlike the 80S ribosomes in the eukaryotic cytoplasm.
Trap: Eukaryotes are always larger than prokaryotes – Fact: Some giant bacteria (e.g., Thiomargarita namibiensis, up to 750 ?m) exceed typical eukaryotic cells in size.
Trap: The nucleus is the only site of DNA in eukaryotes – Fact: Mitochondria and chloroplasts contain their own circular DNA.
Trap: Archaea are structurally identical to bacteria – Fact: Archaea lack peptidoglycan, have distinct membrane lipids (ether-linked), and share transcriptional machinery with eukaryotes.

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 is incorrect because mitochondria are exclusive to eukaryotes.

Question: A cell is observed to contain 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 is incorrect because fungi have chitin, not cellulose, in their cell walls.

Question: Which structure is evidence supporting the endosymbiotic theory?
A) Presence of a nucleolus
B) 70S ribosomes in mitochondria
C) 80S ribosomes in the cytoplasm
D) Nuclear envelope with pores
Answer: B
Explanation: Mitochondria having 70S ribosomes, like prokaryotes, supports their bacterial origin.
Why the top distractor is wrong: C describes standard eukaryotic ribosomes, not evidence of endosymbiosis.

Question: Which of the following cells lacks a nucleus at maturity?
A) Yeast cell
B) Human liver cell
C) Escherichia coli
D) Human red blood cell
Answer: D
Explanation: Mature human red blood cells expel their nucleus to carry more hemoglobin.
Why the top distractor is wrong: C is incorrect because E. coli is prokaryotic and never has a nucleus.

Question: What is the primary component of fungal cell walls?
A) Peptidoglycan
B) Cellulose
C) Chitin
D) Lipopolysaccharide
Answer: C
Explanation: Fungi synthesize chitin, a nitrogen-containing polysaccharide, for structural support.
Why the top distractor is wrong: A is incorrect because peptidoglycan is found in bacterial, not fungal, cell walls.

Question: Which of the following best describes the DNA in prokaryotes?
A) Linear chromosomes within a nucleus
B) Circular chromosome in the nucleoid
C) Multiple linear chromosomes in the cytoplasm
D) Circular plasmids only
Answer: B
Explanation: Prokaryotes have a single circular chromosome located in the nucleoid region.
Why the top distractor is wrong: A is incorrect because prokaryotes lack a nucleus.

Question: Which organelle is found in both plant and animal cells but is typically larger and more central in plant cells?
A) Mitochondrion
B) Golgi apparatus
C) Central vacuole
D) Chloroplast
Answer: C
Explanation: Plant cells have a large central vacuole; animal cells have smaller, multiple vacuoles.
Why the top distractor is wrong: D is incorrect because chloroplasts are absent in animal cells.

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.
• Bacterial cell walls contain peptidoglycan; archaeal walls do not.
• Plant cell walls = cellulose; fungal = chitin; animal cells = no cell wall.
• Both cell types have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Mycoplasma lacks a cell wall – exception among bacteria.
• Mature human red blood cells lack a nucleus and mitochondria.
• Archaea are prokaryotes but share molecular features (e.g., RNA polymerase) with eukaryotes.
• Gram-negative bacteria have an outer membrane with LPS (endotoxin).
• Flagellin = prokaryotic flagella protein; microtubules (9+2) = eukaryotic flagella.
• Cilia are only found in eukaryotes.
• Plasmids = small circular DNA, common in bacteria.
• Nuclear envelope = double membrane with nuclear pores in eukaryotes.
• Nucleolus = site of rRNA synthesis and ribosome assembly in eukaryotes.
• Lysosomes = in animal cells; vacuoles perform similar roles in plants.
• Peroxisomes break down fatty acids and detoxify H?O? in eukaryotes.
• Endosymbiotic theory supported by: double membranes, 70S ribosomes, circular DNA in mitochondria/chloroplasts.
• Chloroplasts present in plants and some protists, absent in animals/fungi.
• Binary fission = prokaryotic division; mitosis/meiosis = eukaryotic.
• Thiomargarita namibiensis can be up to 750 ?m – larger than many eukaryotes.
• Mitochondria are present in nearly all eukaryotes; absent in some protists (e.g., Giardia – verify from standard textbook).
• Eukaryotic flagella move via bending; prokaryotic flagella rotate.
• Archaea have ether-linked lipids in membranes; bacteria and eukaryotes have ester-linked.