STEM Readiness: Chemistry Readiness - Atomic Structure: Electron Configuration - Aufbau, Pauli Exclusion, Hunds Rule, Full and Abbreviated

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.
• Prokaryotic DNA is located in the nucleoid, a region without a membrane; eukaryotic DNA is enclosed within a membrane-bound nucleus.
• Prokaryotes have 70S ribosomes (30S + 50S subunits); eukaryotes have 80S ribosomes (40S + 60S subunits).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (absent in Archaea, which have pseudopeptidoglycan or other polymers).
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to antibiotics targeting peptidoglycan (e.g., penicillin).
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems (e.g., endoplasmic reticulum, Golgi apparatus); prokaryotes lack these.
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport.
• Nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly.
• Endoplasmic reticulum (ER): Rough ER has ribosomes and synthesizes proteins; smooth ER synthesizes lipids and detoxifies.
• Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery to organelles.
• Mitochondria are sites of aerobic respiration and contain their own circular DNA and 70S ribosomes.
• Chloroplasts (in plants and algae) perform photosynthesis, contain thylakoids, and have circular DNA and 70S ribosomes.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion; absent in most plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small, temporary vacuoles.
• Cytoskeleton (microfilaments, intermediate filaments, microtubules) is present in eukaryotes; prokaryotes have homologs (e.g., FtsZ) but no true cytoskeleton.
• Flagella differ structurally: prokaryotic flagella are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Pili (or fimbriae) are present in some prokaryotes for attachment or conjugation; absent in eukaryotes.
• Plasmids are small, circular DNA molecules common in prokaryotes; rare in eukaryotes (e.g., 2-micron plasmid in yeast).
• Red blood cells in mammals lack a nucleus and organelles, maximizing hemoglobin content for oxygen transport.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having double membranes, independent division, circular DNA, and 70S ribosomes.
• Archaea lack peptidoglycan and have ether-linked lipids in their membranes, distinguishing them from Bacteria.

Difficulty Level

Intermediate – integrates structural, functional, and evolutionary concepts commonly tested in first-year biology.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (pseudopeptidoglycan or other) have different compositions.
Trap: Ribosome size correlates with cell complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., photosynthetic bacteria) have infoldings like thylakoids but lack membrane-bound organelles.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of eukaryotic cells but absent in prokaryotes?
A) Plasma membrane
B) Ribosomes
C) Circular DNA
D) Membrane-bound nucleus
Answer: D
Explanation: Only eukaryotes have a membrane-bound nucleus enclosing their DNA.
Why the top distractor is wrong: Circular DNA is found in prokaryotes and also in mitochondria/chloroplasts, so it is not exclusive to prokaryotes.

Question: A cell is observed to have a cell wall, chloroplasts, and a large central vacuole. It most likely belongs to which domain?
A) Bacteria
B) Archaea
C) Animalia
D) Plantae
Answer: D
Explanation: Chloroplasts, a large central vacuole, and a cellulose cell wall are characteristic of plant cells.
Why the top distractor is wrong: Bacteria may have cell walls but lack membrane-bound organelles like chloroplasts.

Question: Which structure is present in both prokaryotes and eukaryotes?
A) Mitochondria
B) 80S ribosomes
C) Phospholipid bilayer
D) Golgi apparatus
Answer: C
Explanation: Both cell types have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: 80S ribosomes are only in eukaryotes; prokaryotes have 70S ribosomes.

Question: Which of the following provides the strongest evidence for the endosymbiotic origin of mitochondria?
A) Presence of a double membrane
B) Involvement in ATP production
C) Containing 80S ribosomes
D) Being enclosed by the nuclear envelope
Answer: A
Explanation: The double membrane, circular DNA, and 70S ribosomes in mitochondria support endosymbiotic theory.
Why the top distractor is wrong: 80S ribosomes are in the cytoplasm of eukaryotes; mitochondria have 70S ribosomes.

Question: Which organism lacks a cell wall and is therefore resistant to penicillin?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Bacillus subtilis
Answer: C
Explanation: Mycoplasma lacks a cell wall and thus is unaffected by antibiotics that target peptidoglycan synthesis.
Why the top distractor is wrong: E. coli has a peptidoglycan cell wall and is typically susceptible to penicillin.

Question: Where is ribosomal RNA (rRNA) synthesized in a eukaryotic cell?
A) Cytoplasm
B) Rough ER
C) Nucleolus
D) Mitochondria
Answer: C
Explanation: The nucleolus within the nucleus is the site of rRNA transcription and ribosome subunit assembly.
Why the top distractor is wrong: Rough ER is involved in protein synthesis, not rRNA production.

Question: Which of the following is true regarding flagella in prokaryotes and eukaryotes?
A) Both are powered by ATP hydrolysis in the same way
B) Both have a 9+2 microtubule arrangement
C) Prokaryotic flagella rotate; eukaryotic flagella undulate
D) Both are composed of actin filaments
Answer: C
Explanation: Prokaryotic flagella rotate like a propeller; eukaryotic flagella move in a whip-like motion due to microtubule sliding.
Why the top distractor is wrong: The 9+2 arrangement is only in eukaryotic flagella; prokaryotic flagella are made of flagellin, not 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.
• Bacterial cell walls contain peptidoglycan; archaeal walls do not.
• Plant cell wall = cellulose; fungal = chitin; animal = no cell wall.
• Mycoplasma lacks a cell wall-resistant to penicillin.
• Red blood cells lack a nucleus and mitochondria.
• Both cell types have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes do not.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Rough ER = protein synthesis; smooth ER = lipid synthesis, detoxification.
• Golgi apparatus = modifies and sorts proteins.
• Mitochondria = site of aerobic respiration; double membrane; own DNA.
• Chloroplasts = site of photosynthesis; thylakoids; double membrane.
• Lysosomes contain hydrolytic enzymes; mainly in animal cells.
• Plant vacuole maintains turgor pressure; large and central.
• Eukaryotic cytoskeleton includes microtubules, microfilaments, intermediate filaments.
• Prokaryotic flagellum = flagellin, rotates; eukaryotic = microtubules (9+2), undulates.
• Pili are present in some prokaryotes for attachment or DNA transfer.
• Plasmids = small circular DNA; common in bacteria.
• Evidence for endosymbiosis: double membrane, 70S ribosomes, circular DNA, autonomous division.
• Archaea have ether-linked lipids in membranes; Bacteria have ester-linked.
• Verify from standard textbook: exact lipid composition in Archaea varies by species.