STEM Readiness: Physics Readiness - Waves/Sound: Doppler Effect - Qualitative and Quantitative, Moving Source vs. Moving Observer

Must?Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• DNA in prokaryotes is located in the nucleoid, an unenclosed region; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotic ribosomes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S subunits).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiosis.
• Prokaryotic cell walls typically contain peptidoglycan; archaea lack peptidoglycan and have pseudopeptidoglycan or other polymers.
• Plant cell walls are made of cellulose; fungal cell walls contain chitin; animal cells lack a cell wall.
• Mycoplasma species are bacteria that lack a cell wall, making them resistant to antibiotics like penicillin.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have extensive internal membrane systems, including the endoplasmic reticulum and Golgi apparatus; prokaryotes do not.
• Eukaryotic organelles include the nucleus, mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus, and (in plants) chloroplasts; prokaryotes lack these.
• Bacteria (e.g., Escherichia coli) and archaea (e.g., Methanogens) are prokaryotes; animals, plants, fungi, and protists are eukaryotes.
• Red blood cells in mammals lack a nucleus and most organelles, maximizing space for hemoglobin.
• Mitochondria have double membranes, their own circular DNA, and 70S ribosomes, consistent with endosymbiotic theory.
• Chloroplasts are found in plants and algae, perform photosynthesis, and also have double membranes, circular DNA, and 70S ribosomes.
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport.
• Nucleolus within the nucleus is the site of ribosomal RNA synthesis and ribosome subunit assembly.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.
• Cilia are short, numerous motile structures in some eukaryotes (e.g., Paramecium); prokaryotes lack cilia.
• Lysosomes (containing hydrolytic enzymes) are present in animal cells but generally absent in plant and prokaryotic cells.
• Peroxisomes contain enzymes for fatty acid oxidation and detoxification of hydrogen peroxide; found only in eukaryotes.
• Plasmids are small, circular extrachromosomal DNA molecules common in prokaryotes; rare in eukaryotes.
• Cell division in eukaryotes involves the mitotic spindle (microtubules); prokaryotes lack spindle fibers.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologous proteins but no true cytoskeleton.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having own DNA, ribosomes, and ability to replicate independently.

Difficulty Level

Intermediate – regularly tested in first-year biology with emphasis on comparison and organelle function.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; archaea, plants (cellulose), and fungi (chitin) have different wall compositions.

Trap: Ribosome size correlates with cell complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, like prokaryotes, due to evolutionary origin.

Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, and sometimes protein-based microcompartments, 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 feature found in eukaryotic cells but absent in prokaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Membrane-bound nucleus
D) Plasma membrane
Answer: C
Explanation: A membrane-bound nucleus is exclusive to eukaryotes.
Why the top distractor is wrong: Circular DNA is present in prokaryotes and also in mitochondria and chloroplasts.

Question: A cell is observed to have a cell wall, chloroplasts, and 80S ribosomes. It is most likely from which domain?
A) Bacteria
B) Archaea
C) Animal
D) Plant
Answer: D
Explanation: Plants have cell walls (cellulose), chloroplasts, and 80S ribosomes.
Why the top distractor is wrong: Bacteria have 70S ribosomes and lack chloroplasts.

Question: Which structure is evidence supporting the endosymbiotic theory?
A) Presence of a nucleoid
B) 70S ribosomes in mitochondria
C) Peptidoglycan in cell walls
D) Binary fission in bacteria
Answer: B
Explanation: Mitochondria having 70S ribosomes resembles prokaryotes, supporting endosymbiosis.
Why the top distractor is wrong: Nucleoid is a prokaryotic feature, not evidence for endosymbiosis.

Question: Which of the following cells lacks a nucleus?
A) Neuron
B) Leukocyte
C) Mature erythrocyte
D) Hepatocyte
Answer: C
Explanation: Mature mammalian red blood cells (erythrocytes) expel their nucleus during development.
Why the top distractor is wrong: Leukocytes are nucleated white blood cells.

Question: What is the primary component of fungal cell walls?
A) Peptidoglycan
B) Cellulose
C) Chitin
D) Silica
Answer: C
Explanation: Fungi have cell walls made of chitin, a nitrogen-containing polysaccharide.
Why the top distractor is wrong: Peptidoglycan is found in bacterial cell walls, not fungi.

Question: Which of the following is true of both prokaryotic and eukaryotic plasma membranes?
A) Composed of phospholipid bilayer
B) Contain membrane-bound organelles
C) Include nuclear pores
D) Synthesize proteins on 80S ribosomes
Answer: A
Explanation: Both cell types have a phospholipid bilayer as the fundamental membrane structure.
Why the top distractor is wrong: Membrane-bound organelles are only in eukaryotes.

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

Last?Minute Revision (20–25 one?liners)

• 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 and circular DNA – evidence of endosymbiosis.
• Bacteria: peptidoglycan cell wall; Archaea: no peptidoglycan.
• Plant cell wall: cellulose; Fungal cell wall: chitin; Animal: no cell wall.
• Mycoplasma lacks a cell wall – smallest known cells.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Lysosomes present in animal cells; generally absent in plants and prokaryotes.
• Red blood cells (mammals) lack nucleus and mitochondria.
• Nuclear pores regulate transport between nucleus and cytoplasm.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Prokaryotes divide by binary fission; eukaryotes by mitosis/meiosis.
• Eukaryotic flagella: 9+2 microtubule arrangement; prokaryotic: flagellin, rotary motion.
• Cilia only in some eukaryotes (e.g., Paramecium).
• Plasmids = small circular DNA; common in bacteria.
• Peroxisomes break down fatty acids and detoxify H?O?.
• Cytoskeleton (microtubules, actin) only in eukaryotes.
• Mitochondria have double membrane, own DNA, divide by fission.
• Chloroplasts found in plants and algae, perform photosynthesis.
• Endosymbiotic theory: mitochondria from aerobic bacteria, chloroplasts from cyanobacteria.
• Archaea lack peptidoglycan and have unique membrane lipids (ether linkages).
• 80S ribosomes in eukaryotic cytoplasm; 70S in mitochondria/chloroplasts.
• No organelles in prokaryotes – no nucleus, ER, Golgi, lysosomes.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.