STEM Readiness: Chemistry Readiness - Equilibrium: Buffers - Henderson-Hasselbalch, Buffer Capacity, Buffer Range

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 true nucleus enclosed by a double membrane (nuclear envelope) with nuclear pores.
• Prokaryotic DNA is typically a single, circular chromosome; eukaryotic DNA is linear and organized into multiple chromosomes.
• 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 endosymbiotic origin.
• Prokaryotes include Bacteria and Archaea; eukaryotes include animals, plants, fungi, and protists.
• Bacterial cell walls contain peptidoglycan; archaeal cell walls lack peptidoglycan and have unique lipids.
• Plant cell walls are made of cellulose; fungal cell walls are made of chitin.
• Animal cells lack a cell wall; plant and fungal cells have cell walls.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have membrane-bound organelles (e.g., nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus); prokaryotes do not.
• Mitochondria are the site of aerobic respiration and have their own DNA and ribosomes.
• Chloroplasts are found in plant and algal cells, perform photosynthesis, and contain thylakoids and chlorophyll.
• The endoplasmic reticulum (ER) in eukaryotes exists as rough ER (with ribosomes) and smooth ER (lipid synthesis, detoxification).
• The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery to other organelles.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion.
• Peroxisomes break down fatty acids and detoxify hydrogen peroxide.
• Mycoplasma species are bacteria without a cell wall, an exception among prokaryotes.
• Mature mammalian red blood cells lack a nucleus and mitochondria, an exception among eukaryotic cells.
• Archaea are prokaryotes but share some molecular features with eukaryotes (e.g., RNA polymerase, histones).
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Cilia in eukaryotes are structurally similar to flagella but shorter and more numerous.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small or temporary vacuoles.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, with several exceptions and numerical values to recall.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacterial cell walls contain peptidoglycan; plant (cellulose), fungal (chitin), and archaeal (pseudopeptidoglycan or other) walls differ.

Trap: Ribosome size correlates with cell complexity (larger ribosomes = more advanced) – Fact: Mitochondria and chloroplasts have 70S ribosomes like prokaryotes, despite being in eukaryotic cells.

Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., cyanobacteria) have thylakoid membranes for photosynthesis.

Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes, consistent with endosymbiotic origin.

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 plasma membrane.
Why the top distractor is wrong: D (mitochondria) are only found in eukaryotic cells.

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) Plant
D) Animal
Answer: C
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 evidence supporting the endosymbiotic theory?
A) Presence of a nucleoid in bacteria
B) 70S ribosomes in mitochondria
C) 80S ribosomes in the cytoplasm
D) Nuclear envelope with pores
Answer: B
Explanation: Mitochondria have 70S ribosomes, like prokaryotes, indicating bacterial origin.
Why the top distractor is wrong: A describes a standard prokaryotic feature, not evidence of endosymbiosis.

Question: Which of the following cells lacks a nucleus at maturity?
A) Yeast cell
B) Escherichia coli
C) Human red blood cell
D) Amoeba
Answer: C
Explanation: Mature mammalian red blood cells eject their nucleus to carry more hemoglobin.
Why the top distractor is wrong: B (E. coli) is prokaryotic and never has a nucleus, but the question implies a eukaryotic cell that loses it.

Question: What is the primary component of the cell wall in fungi?
A) Peptidoglycan
B) Cellulose
C) Chitin
D) Lipopolysaccharide
Answer: C
Explanation: Fungal cell walls are composed of chitin, a nitrogen-containing polysaccharide.
Why the top distractor is wrong: A (peptidoglycan) is found in bacterial, not fungal, cell walls.

Question: Which of the following organelles is responsible for modifying and packaging proteins for secretion?
A) Nucleus
B) Rough endoplasmic reticulum
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins from the ER.
Why the top distractor is wrong: B (rough ER) synthesizes proteins but does not package them for secretion.

Question: Which statement correctly compares prokaryotic and eukaryotic flagella?
A) Both are made of microtubules and use ATP to move
B) Prokaryotic flagella are composed of flagellin and rotate; eukaryotic flagella are made of microtubules and bend
C) Eukaryotic flagella are smaller and simpler than prokaryotic flagella
D) Prokaryotic flagella contain dynein motors for movement
Answer: B
Explanation: Prokaryotic flagella are composed of flagellin and rotate via proton motive force; eukaryotic flagella have a 9+2 microtubule arrangement and bend using dynein.
Why the top distractor is wrong: A is incorrect because prokaryotic flagella do not use ATP directly and are not made of microtubules.

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 membrane-bound nucleus with nuclear pores.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacterial cell wall contains peptidoglycan; archaeal does not.
• Plant cell wall = cellulose; fungal = chitin; animal = no cell wall.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes generally do not.
• Mycoplasma – bacteria without a cell wall.
• Mature red blood cells lack nucleus and mitochondria.
• Archaea are prokaryotes but share some traits with eukaryotes (e.g., histones).
• Mitochondria produce ATP via aerobic respiration.
• Chloroplasts perform photosynthesis; contain thylakoids and chlorophyll.
• Rough ER has ribosomes; smooth ER lacks them.
• Golgi apparatus: modifies, sorts, packages proteins.
• Lysosomes: contain hydrolytic enzymes; found in animal cells.
• Peroxisomes break down fatty acids and H?O?.
• Eukaryotic flagella: 9+2 microtubule arrangement; use dynein for bending.
• Prokaryotic flagella: made of flagellin; rotate via proton gradient.
• Cilia and flagella in eukaryotes share same internal structure.
• Mitochondria and chloroplasts have double membranes – supports endosymbiotic theory.
• Nucleus contains chromatin (DNA + proteins); site of DNA replication and transcription.
• Verify from standard textbook: exact lipid composition in archaeal membranes.
• Endosymbiotic theory: mitochondria evolved from alpha-proteobacteria, chloroplasts from cyanobacteria.