STEM Readiness: Physics Readiness - : Forces Newton’s, Laws Free, Body Diagrams, Drawing All Forces, Sign Convention, Identifying Normal Force

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.
• Prokaryotic DNA is located in the nucleoid, an unenclosed region; eukaryotic DNA is enclosed within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes.
• 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.
• Bacterial cell walls contain peptidoglycan; archaeal cell walls lack peptidoglycan and may contain pseudopeptidoglycan or other polymers.
• Plant cell walls are composed of cellulose; fungal cell walls are made of chitin; animal cells lack cell walls.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to penicillin.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotic cells have extensive internal membranes forming organelles; prokaryotes have no internal membranes (except some invaginations like mesosomes).
• Plasmids are small, circular DNA molecules commonly found in prokaryotes; eukaryotes rarely have plasmids (e.g., in yeast).
• Binary fission is the primary mode of reproduction in prokaryotes; mitosis occurs in eukaryotes.
• Eukaryotic nuclei are surrounded by a double membrane (nuclear envelope) with nuclear pores regulating transport.
• Nucleolus within the nucleus is the site of ribosomal RNA synthesis and ribosome assembly.
• Endoplasmic reticulum (ER): Rough ER has ribosomes and synthesizes proteins; smooth ER lacks ribosomes and synthesizes lipids and detoxifies drugs.
• Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery to other organelles.
• Mitochondria generate ATP via aerobic respiration and contain their own circular DNA and 70S ribosomes.
• Chloroplasts (in plants and algae) perform photosynthesis, contain thylakoids, and have circular DNA and 70S ribosomes.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion; plant vacuoles perform similar functions.
• Centrioles are present in animal cells and aid in spindle formation during mitosis; absent in most plant cells.
• Red blood cells in mammals lack a nucleus and organelles, maximizing space for hemoglobin.
• Archaea resemble prokaryotes in size and structure but have eukaryote-like transcription and translation machinery.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having double membranes, independent division, and own DNA.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologs (e.g., FtsZ) but no true cytoskeleton.

Difficulty Level

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

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacterial cell walls contain peptidoglycan; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.
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 some have protein-based microcompartments or cytoskeletal analogs.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: All eukaryotic cells have a cell wall – Fact: Animal cells lack cell walls; only plants, fungi, and some protists have them.

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 (mitochondria) are present only in eukaryotes.

Question: A cell is observed to contain a nucleus, mitochondria, and a cell wall made of cellulose. From which organism is this cell most likely derived?
A) Fungus
B) Bacterium
C) Animal
D) Plant
Answer: D
Explanation: Cellulose cell walls and chloroplasts (implied by context) are characteristic of plants; fungi have chitin.
Why the top distractor is wrong: A (fungus) has a chitin cell wall, not cellulose.

Question: Which structure is evidence supporting the endosymbiotic theory?
A) Presence of a nucleoid in bacteria
B) 70S ribosomes in mitochondria
C) Peptidoglycan in bacterial walls
D) Nuclear pores in eukaryotes
Answer: B
Explanation: Mitochondria having 70S ribosomes like prokaryotes supports their bacterial origin.
Why the top distractor is wrong: A describes a standard prokaryotic feature, not endosymbiosis evidence.

Question: Which of the following cells lacks a nucleus?
A) Yeast cell
B) Human neuron
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: A (yeast) is a eukaryotic fungus and has a nucleus.

Question: What distinguishes the ribosomes in eukaryotic cytoplasm from those in prokaryotes?
A) Eukaryotes have 70S; prokaryotes have 80S
B) Eukaryotes have 80S; prokaryotes have 70S
C) Eukaryotes lack ribosomes
D) Prokaryotes use 80S ribosomes in mitochondria
Answer: B
Explanation: Cytoplasmic ribosomes in eukaryotes are 80S; prokaryotes have 70S.
Why the top distractor is wrong: A reverses the correct sizes.

Question: Which of the following is absent in animal cells but present in plant cells?
A) Lysosome
B) Centriole
C) Large central vacuole
D) Plasma membrane
Answer: C
Explanation: Mature plant cells have a large central vacuole for storage and turgor; animal cells have small vacuoles.
Why the top distractor is wrong: A (lysosomes) are present in animal cells.

Question: Which organism lacks a cell wall?
A) Streptococcus
B) Saccharomyces
C) Mycoplasma
D) Arabidopsis
Answer: C
Explanation: Mycoplasma is a bacterium without a cell wall.
Why the top distractor is wrong: A (Streptococcus) is a Gram-positive bacterium with peptidoglycan.

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.
• Bacterial cell wall contains peptidoglycan; archaeal does not.
• Plant cell wall = cellulose; fungal = chitin; animal cells = no cell wall.
• Mycoplasma is a bacterium without a cell wall.
• Both cell types have phospholipid bilayer membranes.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes do not.
• Plasmids are common in prokaryotes, rare in eukaryotes (e.g., yeast).
• Binary fission = prokaryotes; mitosis = eukaryotes.
• Nuclear pores regulate mRNA and protein transport in/out of nucleus.
• Nucleolus = site of rRNA synthesis and ribosome subunit assembly.
• Rough ER = protein synthesis; smooth ER = lipid synthesis, detoxification.
• Golgi apparatus = modifies, sorts, packages proteins.
• Mitochondria = ATP production via oxidative phosphorylation.
• Chloroplasts = photosynthesis in plants and algae.
• Lysosomes = digestive enzymes in animal cells.
• Plant vacuoles function like lysosomes and maintain turgor pressure.
• Centrioles = in animal cells, absent in most plants.
• Mammalian red blood cells lack a nucleus and organelles.
• Archaea lack peptidoglycan but resemble bacteria in size and shape.
• Endosymbiotic theory supported by double membranes, independent division, DNA in mitochondria/chloroplasts.
• Cytoskeleton (microtubules, actin) is eukaryotic feature; prokaryotes have FtsZ, MreB analogs.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.