STEM Readiness: Physics Readiness - Waves/Sound: Standing Waves - Harmonics in Strings and Pipes, Open and Closed Ends

Must?Know

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• 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 endosymbiosis.
• Prokaryotic cell walls (in bacteria) are made of peptidoglycan; archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Eukaryotic plant cells have cell walls made of cellulose; fungal cell walls are composed of chitin.
• Animal cells lack a cell wall; their outer boundary is the plasma membrane only.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes possess membrane-bound organelles (e.g., nucleus, mitochondria, lysosomes); prokaryotes do not.
• The endoplasmic reticulum (ER) is a eukaryotic organelle involved in protein (rough ER) and lipid (smooth ER) synthesis.
• The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery in eukaryotic cells.
• Mitochondria generate ATP via aerobic respiration and have double membranes; they are present in nearly all eukaryotes.
• Chloroplasts are found in plant and algal cells and perform photosynthesis using chlorophyll.
• Lysosomes contain hydrolytic enzymes for intracellular digestion and are found in animal cells (rare in plants).
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small, temporary vacuoles.
• Nuclear envelope is a double membrane with nuclear pores that regulate transport between nucleus and cytoplasm.
• Nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) is present in eukaryotes and maintains cell shape and enables motility.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Pili (or fimbriae) are protein appendages in bacteria used for attachment or conjugation; absent in eukaryotes.
• Mycoplasma species are bacteria without a cell wall, making them resistant to antibiotics like penicillin.
• Mature mammalian red blood cells lack a nucleus and most organelles, maximizing space for hemoglobin.
• 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 the ability to divide independently.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, with several exceptions and overlapping features.

Common Traps

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.
• Trap: Ribosome size is the same across all cells – Fact: Prokaryotes have 70S ribosomes; eukaryotes have 80S in cytoplasm, but 70S in mitochondria and chloroplasts.
• Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
• Trap: Prokaryotes have no internal membrane structures – Fact: Some prokaryotes have protein-bound compartments (e.g., carboxysomes), but no true membrane-bound organelles.
• Trap: Eukaryotes evolved from archaea – Fact: Eukaryotes share genetic similarities with archaea, but their origin involves endosymbiosis and remains an active research area (verify from standard textbook).

Practice MCQs

Question: Which of the following is a structural feature shared by both prokaryotic and eukaryotic cells?
A) Membrane-bound nucleus
B) Mitochondria
C) Phospholipid bilayer membrane
D) 80S ribosomes
Answer: C
Explanation: Both cell types have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: A is exclusive to eukaryotes; prokaryotes lack a nucleus.

Question: A cell is observed to contain 70S ribosomes, a nucleoid, and peptidoglycan in its cell wall. This cell is most likely:
A) A plant cell
B) A fungal cell
C) A bacterial cell
D) An animal cell
Answer: C
Explanation: Presence of nucleoid, 70S ribosomes, and peptidoglycan are diagnostic of bacteria.
Why the top distractor is wrong: Plant cells have cellulose walls, 80S ribosomes, and a nucleus.

Question: Which organelle is responsible for modifying and packaging proteins for secretion in eukaryotic cells?
A) Nucleolus
B) Smooth ER
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies and sorts proteins from the ER for secretion or delivery.
Why the top distractor is wrong: Smooth ER synthesizes lipids, not packaging proteins.

Question: Mitochondria are thought to have originated from endosymbiotic bacteria. Which evidence best supports this theory?
A) Mitochondria have a single membrane
B) Mitochondria contain 80S ribosomes
C) Mitochondria have circular DNA and 70S ribosomes
D) Mitochondria synthesize their own proteins using nuclear DNA
Answer: C
Explanation: Circular DNA and 70S ribosomes in mitochondria resemble bacterial features.
Why the top distractor is wrong: Mitochondria have double membranes, not single.

Question: Which of the following cells lacks a nucleus at maturity?
A) Yeast cell
B) Onion root cell
C) Human hepatocyte
D) Human erythrocyte
Answer: D
Explanation: Mature red blood cells (erythrocytes) eject their nucleus to carry more hemoglobin.
Why the top distractor is wrong: Hepatocytes (liver cells) are nucleated eukaryotic cells.

Question: Which component is found in fungal cells but not in animal cells?
A) Plasma membrane
B) Ribosomes
C) Chitin in the cell wall
D) Mitochondria
Answer: C
Explanation: Fungi have cell walls made of chitin; animal cells lack cell walls entirely.
Why the top distractor is wrong: Both fungi and animals have mitochondria and plasma membranes.

Question: What distinguishes the flagellum of a eukaryotic cell from that of a prokaryotic cell?
A) Eukaryotic flagella are made of flagellin
B) Prokaryotic flagella use ATP directly for movement
C) Eukaryotic flagella have a 9+2 microtubule arrangement
D) Prokaryotic flagella are thicker and shorter
Answer: C
Explanation: Eukaryotic flagella have a 9+2 array of microtubules; prokaryotic flagella are composed of flagellin and lack microtubules.
Why the top distractor is wrong: Flagellin is the protein in prokaryotic, not eukaryotic, flagella.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have nucleoid; eukaryotes have nucleus with nuclear envelope.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes – evidence for endosymbiosis.
• Bacterial cell wall contains peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal cell wall = chitin; animal cells = no cell wall.
• Both prokaryotes and eukaryotes have phospholipid bilayer membranes.
• Eukaryotes have membrane-bound organelles; prokaryotes do not.
• Rough ER has ribosomes; smooth ER does not.
• Golgi apparatus modifies and packages proteins.
• Mitochondria produce ATP and have double membranes.
• Chloroplasts perform photosynthesis and contain thylakoids.
• Lysosomes are in animal cells; contain hydrolytic enzymes.
• Large central vacuole is characteristic of plant cells.
• Nuclear pores regulate transport through the nuclear envelope.
• Nucleolus makes rRNA and assembles ribosomes.
• Cytoskeleton includes microtubules, actin filaments, intermediate filaments.
• Prokaryotic flagellum = flagellin, rotates; eukaryotic = microtubules (9+2), bends.
• Pili are in bacteria; used for attachment or DNA transfer.
• Mycoplasma lacks a cell wall – resistant to penicillin.
• Mature red blood cells lack a nucleus and organelles.
• Archaea are prokaryotes but share molecular traits with eukaryotes.
• Endosymbiotic theory: mitochondria/chloroplasts had bacterial origin.
• Mitochondria have circular DNA and divide by binary fission.
• Verify from standard textbook: exact evolutionary relationship between archaea and eukaryotes.