STEM Readiness: Physics Readiness - Mathematical Tools: Vectors - Components, Addition, Subtraction, Dot and Cross Products

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 membrane-bound nucleus containing linear DNA organized into chromosomes.
• Prokaryotic ribosomes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiosis.
• Bacterial cell walls contain peptidoglycan; archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin.
• Animal cells lack a cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Eukaryotes have internal membrane systems (e.g., endoplasmic reticulum, Golgi apparatus).
• Prokaryotes lack membrane-bound organelles (e.g., no mitochondria, lysosomes, or ER).
• Eukaryotes have mitochondria for aerobic respiration (except some anaerobic protists like Giardia).
• Plant cells have chloroplasts for photosynthesis; animal cells do not.
• Prokaryotes reproduce by binary fission; eukaryotes use mitosis and meiosis.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes, occasionally in yeast (eukaryote exception).
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores regulating transport.
• Nucleolus within the nucleus is the site of ribosomal RNA synthesis and ribosome assembly.
• Mycoplasma species are bacteria that lack a cell wall, making them resistant to penicillin.
• Human red blood cells lack a nucleus and mitochondria, maximizing hemoglobin capacity.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Archaea are prokaryotes but share some molecular features with eukaryotes (e.g., RNA polymerase).
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2) and undulate.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; absent in most plant cells.
• Peroxisomes contain enzymes for fatty acid oxidation and detoxify hydrogen peroxide; present in both plant and animal eukaryotic cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small, temporary vacuoles.

Difficulty Level

Intermediate – routinely tested in first-year biology courses with emphasis on comparative structure and functional 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 correlates with organism complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: Prokaryotes have no DNA packaging – Fact: Prokaryotic DNA is supercoiled and associated with nucleoid-associated proteins, though not histones.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Eukaryotes evolved from archaea – Fact: Current evidence suggests eukaryotes share a common ancestor with archaea but are a distinct domain.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of prokaryotic cells?
A) Presence of mitochondria
B) 80S ribosomes in the cytoplasm
C) DNA enclosed within a nuclear envelope
D) DNA located in a nucleoid region
Answer: D
Explanation: Prokaryotes lack a nucleus; DNA is in the nucleoid.
Why the top distractor is wrong: Distractor C describes eukaryotic cells, which have membrane-bound nuclei.

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, cell walls (cellulose), and large central vacuoles are characteristic of plant cells.
Why the top distractor is wrong: Bacteria may have cell walls but lack chloroplasts and membrane-bound organelles.

Question: Which structure is present in both prokaryotes and eukaryotes?
A) Golgi apparatus
B) Mitochondria
C) Plasma membrane
D) Endoplasmic reticulum
Answer: C
Explanation: All cells have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: Golgi apparatus is exclusive to eukaryotes.

Question: Which of the following provides evidence for the endosymbiotic theory?
A) Eukaryotic ribosomes are 80S
B) Mitochondria have circular DNA and 70S ribosomes
C) Prokaryotes lack a nucleus
D) Plant cells have cell walls
Answer: B
Explanation: Mitochondria resemble bacteria in having circular DNA and 70S ribosomes.
Why the top distractor is wrong: Eukaryotic cytoplasmic ribosomes being 80S does not support endosymbiosis.

Question: Which organism lacks a cell wall?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Streptococcus pyogenes
Answer: C
Explanation: Mycoplasma is a bacterium that naturally lacks a cell wall.
Why the top distractor is wrong: E. coli is a typical Gram-negative bacterium with peptidoglycan.

Question: Where are ribosomal subunits assembled in eukaryotic cells?
A) Cytoplasm
B) Rough endoplasmic reticulum
C) Nucleolus
D) Golgi apparatus
Answer: C
Explanation: The nucleolus synthesizes rRNA and assembles ribosomal subunits.
Why the top distractor is wrong: Ribosomes are translated on the RER but assembled in the nucleolus.

Question: Which of the following is found in animal cells but not in plant cells?
A) Plasma membrane
B) Lysosome
C) Mitochondria
D) Nucleus
Answer: B
Explanation: Lysosomes are common in animal cells; plant cells use vacuoles for degradation.
Why the top distractor is wrong: Both plant and animal cells have mitochondria.

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 80S ribosomes; prokaryotes have 70S.
• Mitochondria and chloroplasts have 70S ribosomes – verify from standard textbook.
• Bacterial cell walls contain peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal = chitin; animal = no cell wall.
• Plasma membrane = phospholipid bilayer in both domains.
• Only eukaryotes have membrane-bound organelles (ER, Golgi, nucleus, etc.).
• Mitochondria perform aerobic respiration in eukaryotes.
• Chloroplasts are present only in plant and algal cells.
• Binary fission = prokaryotic division; mitosis = eukaryotic nuclear division.
• Plasmids: circular DNA, common in bacteria, rare in eukaryotes (e.g., yeast).
• Nuclear envelope has double membrane and nuclear pores.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Mycoplasma = bacterium without cell wall.
• Human red blood cells lack nucleus and mitochondria.
• Endosymbiotic theory supported by: circular DNA, 70S ribosomes, double membranes in mitochondria/chloroplasts.
• Archaea are prokaryotes but share transcription machinery with eukaryotes.
• Prokaryotic flagella = flagellin, rotate; eukaryotic = microtubules (9+2), bend.
• Lysosomes = hydrolytic enzymes, found in animal cells.
• Peroxisomes = break down fatty acids, detoxify H?O?.
• Plant vacuole = large, central, maintains turgor; animal vacuoles = small.
• Mitochondria and chloroplasts have their own DNA and ribosomes.
• No histones in prokaryotes; DNA is supercoiled with nucleoid proteins.
• Golgi apparatus modifies, sorts, and packages proteins – eukaryote only.