STEM Readiness: Physics Readiness - Gravitation/Oscillations: Simple Harmonic Motion - Period of Spring and Pendulum, Energy Exchange

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, a region without a membrane; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain endoplasmic reticulum, Golgi apparatus, lysosomes, and mitochondria.
• Ribosomes in prokaryotes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan (e.g., Escherichia coli); archaea lack peptidoglycan and have different wall chemistry.
• Plant cells have cellulose in their cell walls; fungal cells have chitin; animal cells lack a cell wall.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to antibiotics like penicillin that target peptidoglycan synthesis.
• Red blood cells in mammals lack a nucleus and most organelles, maximizing space for hemoglobin.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems (nuclear envelope, ER, Golgi) that compartmentalize cellular functions.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport of RNA and proteins.
• Nucleolus within the nucleus is the site of ribosomal RNA synthesis and ribosome subunit assembly.
• Prokaryotes reproduce by binary fission; eukaryotes divide by mitosis and cytokinesis.
• Plasmids are small, circular DNA molecules found in prokaryotes and some yeasts (eukaryotes), often carrying antibiotic resistance genes.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and bend.
• Cilia are short, numerous motile structures in some eukaryotes (e.g., Paramecium); prokaryotes lack cilia.
• Endosymbiotic theory posits that mitochondria and chloroplasts originated from engulfed prokaryotes; evidence includes circular DNA, 70S ribosomes, and double membranes.
• Chloroplasts are found in plants and algae, perform photosynthesis, and contain thylakoids and chlorophyll.
• Lysosomes (in animal cells) contain hydrolytic enzymes for breaking down macromolecules; absent in most plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal cells have small, temporary vacuoles.
• Peroxisomes contain enzymes like catalase that break down hydrogen peroxide; present in both plant and animal eukaryotic cells.
• Cytoskeleton components (microtubules, microfilaments, intermediate filaments) are found only in eukaryotes and maintain cell shape and enable motility.
• Gram-positive bacteria have thick peptidoglycan layers and retain crystal violet stain; Gram-negative have thin peptidoglycan and an outer membrane.

Difficulty Level

Intermediate – expected foundational knowledge in first-semester biology but requires precise differentiation of structures and exceptions.

Common Traps (3–5 factual traps)

Trap: All cells with a nucleus are eukaryotic, so any cell without a nucleus must be prokaryotic – Fact: Mammalian red blood cells lack a nucleus but are eukaryotic; absence of nucleus does not imply prokaryotic origin.

Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells, due to their prokaryotic ancestry.

Trap: Cell walls are present in all non-animal cells – Fact: Mycoplasma (bacteria) lack a cell wall, and some eukaryotic cells (e.g., protozoa like Amoeba) also lack cell walls.

Trap: The nucleus is the only organelle that contains DNA in eukaryotes – Fact: Mitochondria and chloroplasts contain their own circular DNA, independent of nuclear DNA.

Practice MCQs (5–7 questions)

Question: Which of the following is a feature shared by both prokaryotic and eukaryotic cells?
A) Membrane-bound nucleus
B) 80S ribosomes
C) Phospholipid bilayer plasma membrane
D) Mitochondria
Answer: C
Explanation: Both cell types have a phospholipid bilayer as the plasma membrane.
Why the top distractor is wrong: D is incorrect because mitochondria are only found in eukaryotes.

Question: A cell is observed to have a nucleus, mitochondria, and a large central vacuole. Which of the following is most likely?
A) Bacterial cell
B) Animal cell
C) Fungal cell
D) Plant cell
Answer: D
Explanation: Large central vacuoles are characteristic of plant cells.
Why the top distractor is wrong: C is incorrect because fungal cells have smaller vacuoles and chitin in their walls, not cellulose.

Question: Which structure is evidence supporting the endosymbiotic theory?
A) Presence of a nucleoid
B) 70S ribosomes in mitochondria
C) Peptidoglycan in bacterial walls
D) 80S ribosomes in cytoplasm
Answer: B
Explanation: Mitochondria having 70S ribosomes suggests prokaryotic origin.
Why the top distractor is wrong: C describes a bacterial feature but does not support endosymbiosis directly.

Question: Which organism lacks a cell wall entirely?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Arabidopsis thaliana
Answer: C
Explanation: Mycoplasma is a bacterium without a cell wall.
Why the top distractor is wrong: A has a Gram-negative cell wall with peptidoglycan.

Question: Where is DNA located in a eukaryotic plant cell?
A) Nucleoid only
B) Nucleus and mitochondria only
C) Nucleus, mitochondria, and chloroplasts
D) Cytoplasm and nucleus
Answer: C
Explanation: Eukaryotic plant cells have DNA in the nucleus, mitochondria, and chloroplasts.
Why the top distractor is wrong: B is incorrect because chloroplasts also contain DNA.

Question: Which of the following best describes the ribosomes in the cytoplasm of a human liver cell?
A) 70S, composed of 30S and 50S subunits
B) 70S, composed of 40S and 30S subunits
C) 80S, composed of 40S and 60S subunits
D) 80S, composed of 50S and 30S subunits
Answer: C
Explanation: Eukaryotic cytoplasmic ribosomes are 80S with 40S and 60S subunits.
Why the top distractor is wrong: A describes prokaryotic ribosomes, not human cell ribosomes.

Question: Which of the following structures is found in prokaryotes but not in eukaryotes?
A) Flagella
B) Ribosomes
C) Nucleoid
D) Plasma membrane
Answer: C
Explanation: The nucleoid is a prokaryote-specific region for DNA.
Why the top distractor is wrong: A is incorrect because both prokaryotes and eukaryotes have flagella, though structurally different.

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.
• Peptidoglycan is found only in bacterial cell walls (not archaea or eukaryotes).
• Plant cell wall = cellulose; fungal = chitin; animal = no cell wall.
• Mycoplasma has no cell wall – smallest known cells.
• Mature mammalian red blood cells lack a nucleus and mitochondria.
• Both prokaryotes and eukaryotes have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, lysosomes); prokaryotes do not.
• Nuclear envelope is a double membrane with nuclear pores.
• Nucleolus synthesizes rRNA and assembles ribosomal subunits.
• Prokaryotes divide by binary fission; eukaryotes by mitosis.
• Plasmids are circular DNA molecules, common in bacteria.
• Prokaryotic flagella rotate; made of flagellin.
• Eukaryotic flagella and cilia have 9+2 microtubule arrangement.
• Cilia are short and numerous; flagella are long and few.
• Lysosomes contain hydrolytic enzymes; mainly in animal cells.
• Plant vacuole maintains turgor pressure via osmosis.
• Peroxisomes break down H?O? using catalase.
• Cytoskeleton (microtubules, actin) exists only in eukaryotes.
• Gram-positive bacteria: thick peptidoglycan, no outer membrane.
• Gram-negative bacteria: thin peptidoglycan, outer membrane with LPS.
• Endosymbiotic theory: mitochondria from alpha-proteobacteria, chloroplasts from cyanobacteria.