STEM Readiness: Chemistry Readiness - Phases/Solutions: Colligative Properties - Boiling Point Elevation, Freezing Point Depression, Osmotic Pressure

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 (e.g., Escherichia coli).
• Eukaryotes have a membrane-bound nucleus containing linear DNA (e.g., human hepatocyte).
• Prokaryotic ribosomes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting endosymbiotic origin.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., Staphylococcus aureus).
• Archaea lack peptidoglycan; their cell walls are made of pseudopeptidoglycan or other polysaccharides.
• Plant cells have cellulose-based cell walls; fungal cells have chitin-based walls.
• Animal cells lack a cell wall entirely (e.g., neurons, erythrocytes).
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Eukaryotes have extensive internal membranes forming organelles; prokaryotes do not.
• Endoplasmic reticulum (ER) is present only in eukaryotes; rough ER synthesizes proteins, smooth ER synthesizes lipids.
• Golgi apparatus modifies, sorts, and packages proteins for secretion (e.g., antibody processing in plasma cells).
• Mitochondria generate ATP via oxidative phosphorylation; have double membranes and their own circular DNA.
• Chloroplasts perform photosynthesis in plants and algae; contain thylakoids, grana, and circular DNA.
• Lysosomes contain hydrolytic enzymes for degradation; found in animal cells, rare in plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; fungal and protist vacuoles vary in function.
• Nuclear envelope is a double membrane with nuclear pores regulating transport (e.g., mRNA export).
• Nucleolus within the nucleus synthesizes ribosomal RNA and assembles ribosomal subunits.
• Mycoplasma species lack a cell wall, making them resistant to penicillin (exception among bacteria).
• Mature mammalian red blood cells lack a nucleus and mitochondria, maximizing hemoglobin capacity.
• Cilia and flagella in eukaryotes have a 9+2 microtubule arrangement; prokaryotic flagella are composed of flagellin and lack microtubules.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having 70S ribosomes, circular DNA, and binary fission.
• Plasmids are small, circular DNA molecules in prokaryotes; eukaryotes rarely have plasmid-like elements (e.g., yeast 2-micron plasmid).
• Cytoskeleton (microfilaments, intermediate filaments, microtubules) is well-developed in eukaryotes; prokaryotes have homologs (e.g., FtsZ, MreB).

Difficulty Level

Intermediate – requires understanding of structural and functional differences across domains and organelle-specific roles.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; archaea, plants, and fungi use different structural components.
Trap: Ribosome size correlates directly with cell complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Prokaryotes have no internal compartmentalization – Fact: Some prokaryotes have protein-bound microcompartments (e.g., carboxysomes), though not membrane-bound organelles.
Trap: Eukaryotic DNA is always linear – Fact: Mitochondrial and chloroplast DNA is circular, like prokaryotic DNA.

Practice MCQs (5–7 questions)

Question: Which structure is found in eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) Ribosomes
C) Nucleus
D) Circular DNA
Answer: C
Explanation: The nucleus is a membrane-bound organelle unique to eukaryotes.
Why the top distractor is wrong: Circular DNA is present in prokaryotes and also in mitochondria and chloroplasts of eukaryotes.

Question: A cell is observed to have a cell wall made of cellulose and large central vacuoles. It most likely belongs to which domain?
A) Bacteria
B) Archaea
C) Animalia
D) Plantae
Answer: D
Explanation: Cellulose cell walls and central vacuoles are diagnostic features of plant cells.
Why the top distractor is wrong: Bacteria have peptidoglycan walls and lack membrane-bound vacuoles.

Question: Which of the following is true about ribosomes in mitochondria?
A) They are 80S, like cytoplasmic ribosomes
B) They are 70S, similar to bacterial ribosomes
C) They are synthesized entirely in the Golgi apparatus
D) They are absent in aerobic eukaryotes
Answer: B
Explanation: Mitochondrial ribosomes are 70S, supporting their endosymbiotic origin from bacteria.
Why the top distractor is wrong: 80S ribosomes are found in the eukaryotic cytoplasm, not in mitochondria.

Question: Which of the following cells lacks a nucleus?
A) Yeast cell
B) Neuron
C) Mature human red blood cell
D) Hepatocyte
Answer: C
Explanation: Mature mammalian red blood cells expel their nucleus to accommodate more hemoglobin.
Why the top distractor is wrong: Yeast is a eukaryotic fungus and has a well-defined nucleus.

Question: Which feature supports the endosymbiotic theory for the origin of mitochondria?
A) Presence of a single membrane
B) Use of 80S ribosomes
C) Ability to undergo mitosis
D) Possession of circular DNA and 70S ribosomes
Answer: D
Explanation: Mitochondria have circular DNA and 70S ribosomes, similar to bacteria, supporting bacterial origin.
Why the top distractor is wrong: Mitochondria have double membranes and divide by binary fission, not mitosis.

Question: Which organism has a cell wall but lacks peptidoglycan?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Bacillus anthracis
D) Mycoplasma pneumoniae
Answer: B
Explanation: Saccharomyces cerevisiae (yeast) is a fungus with a chitin-based cell wall, not peptidoglycan.
Why the top distractor is wrong: E. coli and B. anthracis are bacteria and have peptidoglycan.

Question: What is the primary function of the Golgi apparatus?
A) ATP synthesis
B) Protein synthesis
C) Protein modification and sorting
D) DNA replication
Answer: C
Explanation: The Golgi apparatus modifies (e.g., glycosylation), sorts, and packages proteins for transport.
Why the top distractor is wrong: Protein synthesis occurs on ribosomes, not in the Golgi.

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

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have nucleoid, not nucleus.
• Eukaryotes have nuclear envelope with pores.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA.
• Bacterial cell walls contain peptidoglycan.
• Archaeal cell walls lack peptidoglycan – use pseudopeptidoglycan or other polymers.
• Plant cell walls: cellulose; fungal: chitin; animal: no cell wall.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have membrane-bound organelles; prokaryotes do not.
• Rough ER: protein synthesis; smooth ER: lipid synthesis and detoxification.
• Golgi apparatus: modifies, sorts, packages proteins.
• Mitochondria: double membrane, ATP production, own DNA.
• Chloroplasts: photosynthesis, thylakoids, grana, own DNA.
• Lysosomes: contain hydrolytic enzymes; mainly in animal cells.
• Plant vacuole: large central, maintains turgor pressure.
• Nuclear pores regulate mRNA and protein transport.
• Nucleolus: site of rRNA synthesis and ribosome assembly.
• Mycoplasma lacks a cell wall – smallest known cells.
• Mature red blood cells lack nucleus and mitochondria.
• Eukaryotic flagella: 9+2 microtubule array; prokaryotic: flagellin-based, rotary.
• Endosymbiotic theory supported by: 70S ribosomes, circular DNA, binary fission in mitochondria/chloroplasts.
• Plasmids: common in bacteria (circular DNA); rare in eukaryotes (e.g., yeast 2-micron).
• Cytoskeleton: eukaryotes have microtubules, microfilaments, intermediate filaments.
• Prokaryotic cytoskeleton homologs: FtsZ (tubulin-like), MreB (actin-like).
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.