STEM Readiness: Physics Readiness - : Forces Newton’s, Laws Springs, and Hooke’s, Law Fkx, Elastic Potential Energy, SeriesParallel Springs

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.
• 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 endosymbiotic theory.
• Bacterial cell walls contain peptidoglycan; archaea lack peptidoglycan and have different cell wall chemistry.
• Plant cell walls are made of cellulose; fungal cell walls are made of chitin; animal cells lack cell walls.
• Mycoplasma, a bacterium, lacks a cell wall—an exception among prokaryotes.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Eukaryotes have membrane-bound organelles (e.g., nucleus, mitochondria, lysosomes); prokaryotes lack these.
• Endoplasmic reticulum (ER) is present only in eukaryotes: rough ER has ribosomes; smooth ER synthesizes lipids.
• Golgi apparatus modifies, sorts, and packages proteins for secretion—only in eukaryotes.
• Mitochondria generate ATP via aerobic respiration and have double membranes—eukaryote-specific organelle.
• Chloroplasts perform photosynthesis in plants and algae; contain thylakoids and chlorophyll—eukaryotic organelle.
• Lysosomes contain hydrolytic enzymes for degradation—found in animal cells, rare in plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; animal vacuoles are small.
• Nuclear envelope is a double membrane with nuclear pores regulating transport—only in eukaryotes.
• Nucleolus within the nucleus synthesizes ribosomal RNA and assembles ribosomes—eukaryotic feature.
• Cytoskeleton (microtubules, actin filaments, intermediate filaments) is complex in eukaryotes, minimal in prokaryotes.
• Flagella in prokaryotes are made of flagellin and rotate; in eukaryotes, made of dynein and tubulin, moving in whip-like motion.
• Red blood cells in mammals lack a nucleus and organelles—maximizing hemoglobin capacity.
• Plasmids are small, circular DNA molecules found in prokaryotes and some yeast (eukaryote exception).
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Archaea lack peptidoglycan and have ether-linked lipids in membranes—distinct from bacteria and eukaryotes.
• Gram-positive bacteria have thick peptidoglycan; Gram-negative have thin peptidoglycan and an outer membrane.

Difficulty Level

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

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 correlates with cell 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 some have protein-based microcompartments.
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 host and bacterial endosymbiont (endosymbiotic theory).

Practice MCQs

Question: Which of the following is a feature found in prokaryotic cells but not in eukaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Peptidoglycan in the cell wall
D) Plasma membrane with phospholipid bilayer
Answer: C
Explanation: Peptidoglycan is unique to bacterial cell walls and absent in eukaryotes.
Why the top distractor is wrong: 70S ribosomes are in prokaryotes but also in mitochondria and chloroplasts of eukaryotes.

Question: Which structure is present in plant cells but not in animal cells?
A) Mitochondria
B) Golgi apparatus
C) Central vacuole
D) Rough endoplasmic reticulum
Answer: C
Explanation: The large central vacuole is a defining feature of mature plant cells.
Why the top distractor is wrong: Mitochondria are present in both plant and animal cells.

Question: What is the primary evidence supporting the endosymbiotic theory for mitochondria?
A) They are surrounded by a single membrane
B) They contain linear DNA and 80S ribosomes
C) They have circular DNA and 70S ribosomes
D) They synthesize proteins using mRNA from the nucleus
Answer: C
Explanation: Mitochondria have circular DNA and 70S ribosomes, similar to bacteria.
Why the top distractor is wrong: Mitochondria have double membranes and do not have 80S ribosomes.

Question: Which of the following cells lacks a nucleus?
A) Yeast cell
B) Human liver cell
C) Escherichia coli
D) Onion root cell
Answer: C
Explanation: E. coli is a prokaryote and lacks a membrane-bound nucleus.
Why the top distractor is wrong: Yeast is a eukaryotic fungus and has a nucleus.

Question: Which component is found in both prokaryotes and eukaryotes?
A) Nucleoid
B) 80S ribosomes
C) Phospholipid bilayer
D) Mitochondria
Answer: C
Explanation: Both cell types have a plasma membrane made of phospholipid bilayer.
Why the top distractor is wrong: Nucleoid is only in prokaryotes; 80S ribosomes are only in eukaryotes.

Question: Which organism has a cell wall made of chitin?
A) Rose bush
B) Escherichia coli
C) Saccharomyces cerevisiae
D) Homo sapiens
Answer: C
Explanation: Saccharomyces cerevisiae (yeast) is a fungus with a chitin-containing cell wall.
Why the top distractor is wrong: Rose bush (plant) has cellulose; E. coli has peptidoglycan.

Question: Where is ribosomal RNA synthesized in eukaryotic cells?
A) Rough ER
B) Nucleolus
C) Cytoplasm
D) Mitochondria
Answer: B
Explanation: The nucleolus within the nucleus synthesizes rRNA and assembles ribosomal subunits.
Why the top distractor is wrong: Rough ER is involved in protein synthesis, not rRNA production.

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 and circular DNA—evidence for endosymbiosis.
• Bacterial cell walls contain peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal = chitin; animal = no cell wall.
• Mycoplasma lacks a cell wall—only known bacteria without one.
• Red blood cells lack a nucleus and mitochondria.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have membrane-bound organelles; prokaryotes do not.
• Rough ER has ribosomes; smooth ER makes lipids and detoxifies.
• Golgi apparatus modifies and packages proteins—only in eukaryotes.
• Lysosomes are in animal cells; plant vacuoles perform similar function.
• Nuclear pores regulate transport between nucleus and cytoplasm.
• Nucleolus makes ribosomal RNA—located inside nucleus.
• Cytoskeleton components: microtubules (tubulin), actin filaments, intermediate filaments.
• Prokaryotic flagella = flagellin, rotate; eukaryotic = axoneme (9+2), whip-like motion.
• Plasmids are common in bacteria; also found in some yeast.
• Archaea have ether-linked lipids in membranes—unlike bacteria and eukaryotes.
• Gram-positive bacteria: thick peptidoglycan; Gram-negative: thin peptidoglycan + outer membrane.
• Mitochondria have double membrane—outer from host, inner from symbiont.
• Chloroplasts have thylakoids and perform photosynthesis in plants and algae.
• Endosymbiotic theory: mitochondria from alpha-proteobacteria; chloroplasts from cyanobacteria.
• All organelles with double membranes (nucleus, mitochondria, chloroplasts) are linked to endosymbiosis or invagination.
• Eukaryotes include protists, fungi, plants, animals; prokaryotes are only Bacteria and Archaea.
• Verify from standard textbook: exact lipid composition in archaeal membranes.