STEM Readiness: Physics Readiness - Mathematical Tools: Trigonometry in Physics - Resolving Forces, Finding Angles, Right-Triangle Relations

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; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain organelles such as mitochondria, lysosomes, and the Golgi apparatus.
• Ribosomes in prokaryotes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S subunits).
• Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, supporting their origin via endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., Escherichia coli); archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are composed of cellulose; fungal cell walls are made of chitin; animal cells lack cell walls.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER) and Golgi apparatus; prokaryotes do not.
• The nucleus in eukaryotes is surrounded by a double membrane (nuclear envelope) with nuclear pores for RNA export.
• Nuclear pores regulate transport between nucleus and cytoplasm; prokaryotes lack such structures.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and undulate.
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; rare in eukaryotes.
• Mycoplasma species are bacteria that lack a cell wall; they are resistant to antibiotics like penicillin that target peptidoglycan.
• Human red blood cells are anucleate (lack a nucleus) in maturity, limiting their lifespan and repair capacity.
• Plant cells contain chloroplasts for photosynthesis; animal cells lack chloroplasts.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes; rare in plant cells (vacuoles perform similar function).
• The endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Mitochondria are the site of aerobic respiration in eukaryotes; prokaryotes perform respiration on the plasma membrane.
• Prokaryotes often have capsules or slime layers for protection and adhesion; some eukaryotes (e.g., fungi) have similar extracellular matrices.
• Cilia in eukaryotes have the same 9+2 microtubule arrangement as flagella; prokaryotes lack cilia.
• Eukaryotic cells may have centrioles (in animal cells) for organizing microtubules during cell division; prokaryotes lack centrioles.
• The nucleolus within the eukaryotic nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly.

Difficulty Level

Intermediate – requires precise differentiation between structural and functional features across domains and kingdoms.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plant (cellulose), fungal (chitin), and archaeal (varied, non-peptidoglycan) walls differ chemically.
Trap: Ribosome size is the same across all cells – Fact: Prokaryotes use 70S ribosomes; eukaryotes use 80S in cytoplasm, but mitochondria and chloroplasts retain 70S.
Trap: The nucleus is the only organelle that contains DNA in eukaryotes – Fact: Mitochondria and chloroplasts also contain their own DNA (circular, like prokaryotes).
Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., photosynthetic bacteria) have infolded plasma membranes (chromatophores), but lack membrane-bound organelles.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) Ribosomes
C) Mitochondria
D) Circular DNA
Answer: C
Explanation: Mitochondria are membrane-bound organelles found only in eukaryotes.
Why the top distractor is wrong: Circular DNA is present in prokaryotes and also in mitochondria and chloroplasts, so it is not exclusive to prokaryotes.

Question: A cell is observed to have a nucleus, 80S ribosomes, and a cell wall made of cellulose. This cell is most likely from a:
A) Fungus
B) Bacterium
C) Plant
D) Animal
Answer: C
Explanation: Cellulose cell walls are characteristic of plant cells; presence of nucleus and 80S ribosomes confirms eukaryotic origin.
Why the top distractor is wrong: Fungi have chitin in their cell walls, not cellulose.

Question: Which structure is found in both prokaryotes and eukaryotes?
A) Nuclear envelope
B) 80S ribosomes
C) Phospholipid bilayer membrane
D) Golgi apparatus
Answer: C
Explanation: Both cell types have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: The nuclear envelope is exclusive to eukaryotes.

Question: Which of the following provides the strongest evidence for the endosymbiotic origin of mitochondria?
A) Presence of a double membrane
B) Use of 80S ribosomes
C) Linear DNA with histones
D) Reproduction by mitosis
Answer: A
Explanation: Mitochondria have a double membrane and 70S ribosomes, with circular DNA—features consistent with bacterial origin.
Why the top distractor is wrong: Mitochondria use 70S ribosomes, not 80S; 80S are cytoplasmic in eukaryotes.

Question: Which organism lacks a cell wall and a nucleus?
A) Mycoplasma pneumoniae
B) Saccharomyces cerevisiae
C) Escherichia coli
D) Human red blood cell
Answer: D
Explanation: Mature human red blood cells lack both a nucleus and a cell wall.
Why the top distractor is wrong: Mycoplasma lacks a cell wall but is a prokaryote with a nucleoid (has DNA, though not enclosed).

Question: Where is DNA located in a prokaryotic cell?
A) Nucleus
B) Nucleolus
C) Nucleoid
D) Mitochondria
Answer: C
Explanation: Prokaryotes store DNA in the nucleoid, a region not enclosed by a membrane.
Why the top distractor is wrong: A nucleus is a membrane-bound organelle present only in eukaryotes.

Question: Which of the following structures is involved in protein modification and sorting in eukaryotic cells?
A) Plasma membrane
B) Nucleoid
C) Golgi apparatus
D) Capsule
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery to other organelles.
Why the top distractor is wrong: The plasma membrane regulates transport but does not modify or sort proteins.

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.
• Bacteria: peptidoglycan cell wall; Archaea: no peptidoglycan.
• Plant cell wall: cellulose; fungal: chitin; animal: no cell wall.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, lysosomes); prokaryotes do not.
• Mycoplasma – bacteria without cell wall.
• Mature red blood cells lack a nucleus.
• Flagellin-based flagella = prokaryotes; 9+2 microtubules = eukaryotes.
• Plasmids are common in prokaryotes, rare in eukaryotes.
• Binary fission = prokaryotes; mitosis/meiosis = eukaryotes.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Lysosomes: common in animal cells, rare in plants.
• Chloroplasts: found in plants and algae, not in animals.
• Centrioles: present in animal cells, absent in plants and prokaryotes.
• Endosymbiotic theory: mitochondria evolved from aerobic bacteria, chloroplasts from cyanobacteria.
• Mitochondria perform aerobic respiration; prokaryotes use plasma membrane for respiration.
• Capsules in prokaryotes = protection and adhesion.
• Nuclear envelope = double membrane with pores for RNA export.
• 70S ribosomes in mitochondria/chloroplasts – key evidence for endosymbiosis.
• Cilia and flagella in eukaryotes share 9+2 microtubule arrangement.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.