STEM Readiness: Physics Readiness - Waves/Sound: Wave Properties - Speed, Frequency, Wavelength, Amplitude, Intensity

Must?Know

• 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, a region without a membrane; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotic ribosomes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S subunits).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan; archaea lack peptidoglycan and have pseudopeptidoglycan or other polymers.
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin; animal cells lack a cell wall.
• 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 generally do not.
• Organelles unique to eukaryotes include the nucleus, mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus, and chloroplasts (in plants).
• Prokaryotes reproduce by binary fission; eukaryotes use mitosis and meiosis.
• Eukaryotic chromosomes are linear and associated with histone proteins; prokaryotic DNA is circular and not bound by histones (though archaea have histone-like proteins).
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and bend.
• Endosymbiotic theory proposes mitochondria and chloroplasts originated from engulfed prokaryotes; evidence includes double membranes, own DNA, and 70S ribosomes.
• Red blood cells in mammals lack a nucleus and organelles, maximizing space for hemoglobin.
• Plant cells have chloroplasts, a central vacuole, and plasmodesmata; animal cells do not.
• Lysosomes are membrane-bound organelles in animal cells containing hydrolytic enzymes for digestion; rare in plant cells.
• Peroxisomes contain enzymes for breaking down fatty acids and detoxifying hydrogen peroxide; present in both plant and animal cells.
• The 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 synthesis and ribosome subunit assembly.
• Prokaryotes may have plasmids (small circular DNA); eukaryotes rarely have plasmids (except in some yeast and cancer cells).
• Cytoskeleton elements (microtubules, microfilaments, intermediate filaments) are present in eukaryotes; prokaryotes have homologs (e.g., FtsZ, MreB) but no true cytoskeleton.
• Gram-positive bacteria have thick peptidoglycan and no outer membrane; Gram-negative have thin peptidoglycan and an outer membrane with lipopolysaccharide.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and recognizing exceptions.

Common Traps

Trap: All cells with cell walls contain peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (other polymers) do not.
Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, and sometimes protein-based microcompartments (e.g., carboxysomes).
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Eukaryotes evolved from prokaryotes directly – Fact: Eukaryotes likely arose from archaeal ancestors, with bacterial contributions via endosymbiosis.

Practice MCQs

Question: Which of the following is a defining feature of prokaryotic cells?
A) Membrane-bound nucleus
B) 80S ribosomes
C) Linear chromosomes associated with histones
D) DNA located in a nucleoid region
Answer: D
Explanation: Prokaryotes lack a membrane-bound nucleus; DNA resides in the nucleoid.
Why the top distractor is wrong: A is incorrect because a membrane-bound nucleus is a eukaryotic feature.

Question: Which structure is found in plant cells but not in animal cells?
A) Mitochondria
B) Lysosomes
C) Central vacuole
D) Plasma membrane
Answer: C
Explanation: The large central vacuole is a hallmark of plant cells, maintaining turgor pressure.
Why the top distractor is wrong: B is incorrect because lysosomes are primarily in animal cells, not plants.

Question: Which of the following provides evidence for the endosymbiotic theory?
A) Eukaryotic cells have 80S ribosomes
B) Mitochondria have circular DNA and 70S ribosomes
C) Prokaryotes lack a cytoskeleton
D) Plant cells have cell walls made of cellulose
Answer: B
Explanation: Mitochondria resemble bacteria in having circular DNA and 70S ribosomes, supporting bacterial origin.
Why the top distractor is wrong: A describes a eukaryotic feature but does not support endosymbiosis.

Question: A bacterial cell is identified as lacking a cell wall. Which organism is most likely?
A) Escherichia coli
B) Bacillus subtilis
C) Mycoplasma pneumoniae
D) Staphylococcus aureus
Answer: C
Explanation: Mycoplasma species naturally lack a cell wall and are resistant to cell wall-targeting antibiotics.
Why the top distractor is wrong: A is a Gram-negative bacterium with a peptidoglycan layer and outer membrane.

Question: Which of the following is true about ribosomes in eukaryotic cells?
A) All ribosomes are 80S, including those in mitochondria
B) Chloroplast ribosomes are 70S
C) Ribosomes are synthesized in the Golgi apparatus
D) Free ribosomes are larger than bound ribosomes
Answer: B
Explanation: Chloroplasts contain 70S ribosomes, similar to prokaryotes.
Why the top distractor is wrong: A is incorrect because mitochondrial ribosomes are 70S, not 80S.

Question: Which component is present in both prokaryotes and eukaryotes?
A) Nucleus
B) Endoplasmic reticulum
C) Phospholipid bilayer membrane
D) Mitochondria
Answer: C
Explanation: Both domains have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: A is incorrect because only eukaryotes have a nucleus.

Question: What distinguishes the flagellum of a eukaryotic cell from that of a prokaryotic cell?
A) Prokaryotic flagella are made of microtubules
B) Eukaryotic flagella use a rotary motion
C) Eukaryotic flagella have a 9+2 microtubule arrangement
D) Prokaryotic flagella are powered by ATP hydrolysis
Answer: C
Explanation: Eukaryotic flagella have a 9+2 array of microtubules; prokaryotic flagella are composed of flagellin and rotate.
Why the top distractor is wrong: A is incorrect because microtubules are in eukaryotic flagella, not prokaryotic.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: DNA in nucleoid; eukaryotes: DNA in nucleus.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacterial cell walls contain peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal = chitin; animal = no cell wall.
• Mycoplasma has no cell wall – naturally resistant to penicillin.
• Both domains have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes generally do not.
• Organelles like mitochondria, ER, lysosomes, Golgi are exclusive to eukaryotes.
• Prokaryotes divide by binary fission; eukaryotes by mitosis/meiosis.
• Eukaryotic chromosomes are linear and histone-bound; prokaryotic DNA is circular and not histone-wrapped (except archaea).
• Prokaryotic flagellum = flagellin, rotary; eukaryotic = microtubules (9+2), bending motion.
• Double membranes in nucleus, mitochondria, chloroplasts.
• Red blood cells lack a nucleus and organelles.
• Plant cells have chloroplasts, central vacuole, plasmodesmata.
• Lysosomes are common in animal cells, rare in plants.
• Peroxisomes break down fatty acids and detoxify H?O?.
• Nuclear pores regulate transport through the nuclear envelope.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Plasmids = small circular DNA; common in prokaryotes, rare in eukaryotes.
• Cytoskeleton (microtubules, actin) is eukaryotic; prokaryotes have FtsZ, MreB homologs.
• Gram-negative bacteria have outer membrane with LPS; Gram-positive do not.
• Endosymbiotic theory supported by: double membrane, 70S ribosomes, circular DNA in mitochondria/chloroplasts.
• Archaea have histone-like proteins but no peptidoglycan.