STEM Readiness: Physics Readiness - Mathematical Tools: Calculus in Physics - Derivatives as Rates, Integrals as Accumulation

Must?Know

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotes lack a membrane-bound nucleus; DNA is located in the nucleoid region.
• Eukaryotes have a membrane-bound nucleus containing linear DNA organized into chromosomes.
• Prokaryotic ribosomes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiosis.
• Prokaryotes include bacteria and archaea; both lack membrane-bound organelles.
• Eukaryotes include animals, plants, fungi, and protists.
• Bacterial cell walls contain peptidoglycan; archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are made of cellulose; fungal cell walls are made of chitin.
• Animal cells lack a cell wall; Mycoplasma (a bacterium) also lacks a cell wall.
• All cells have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER), Golgi apparatus, and lysosomes.
• The rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies drugs.
• The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery.
• Mitochondria generate ATP via aerobic respiration; they have double membranes and their own DNA.
• Chloroplasts (in plants and algae) perform photosynthesis; they have thylakoids and their own DNA.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion.
• Peroxisomes break down fatty acids and detoxify hydrogen peroxide.
• Nuclear envelope is a double membrane with nuclear pores that regulate molecule transport.
• Nucleolus within the nucleus synthesizes ribosomal RNA (rRNA) and assembles ribosome subunits.
• Red blood cells in mammals lack a nucleus and organelles, maximizing hemoglobin capacity.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Cilia and flagella in eukaryotes are made of microtubules (9+2 arrangement); prokaryotic flagella are made of flagellin and lack microtubules.
• Vacuoles in plant cells are large and central; in animal cells, vacuoles are small or absent.

Difficulty Level

Intermediate – requires precise differentiation between structural and functional features across domains and kingdoms.

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 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 inclusions or 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 ancestors with endosymbiotic events.

Practice MCQs

Question: Which of the following is a feature shared by both prokaryotic and eukaryotic cells?
A) Membrane-bound nucleus
B) Mitochondria
C) Phospholipid bilayer membrane
D) 80S ribosomes
Answer: C
Explanation: Both cell types have a plasma membrane composed of a phospholipid bilayer.
Why the top distractor is wrong: A is exclusive to eukaryotes; prokaryotes lack a nucleus.

Question: A cell is observed to contain circular DNA, 70S ribosomes, and peptidoglycan in its cell wall. It lacks a nucleus. This cell is most likely:
A) A plant cell
B) A fungal cell
C) A bacterial cell
D) An animal cell
Answer: C
Explanation: Bacteria have circular DNA, 70S ribosomes, peptidoglycan, and no nucleus.
Why the top distractor is wrong: Plant cells have cellulose walls and 80S ribosomes, and are eukaryotic.

Question: Which organelle is responsible for modifying and packaging proteins for secretion?
A) Nucleolus
B) Rough ER
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins from the ER.
Why the top distractor is wrong: Rough ER synthesizes proteins but does not package them for secretion.

Question: Which of the following provides evidence for the endosymbiotic theory?
A) Eukaryotic cells have linear DNA
B) Mitochondria have 70S ribosomes and circular DNA
C) Prokaryotes lack membrane-bound organelles
D) Plant cells have chloroplasts
Answer: B
Explanation: Mitochondria resemble bacteria in ribosome type and DNA structure, supporting bacterial origin.
Why the top distractor is wrong: D is true but not direct evidence; B provides structural and genetic evidence.

Question: Which cell type lacks a nucleus and has 80S ribosomes?
A) Bacterium
B) Fungal cell
C) Mature human red blood cell
D) Plant cell
Answer: C
Explanation: Mature mammalian red blood cells lose their nucleus but retain cytoplasm with 80S ribosomes during development.
Why the top distractor is wrong: Bacteria have 70S ribosomes, not 80S.

Question: Which structure is found in plant cells but not in animal cells?
A) Mitochondria
B) Central vacuole
C) Plasma membrane
D) Lysosome
Answer: B
Explanation: The large central vacuole is a defining feature of plant cells.
Why the top distractor is wrong: Mitochondria are present in both plant and animal cells.

Question: What distinguishes the prokaryotic nucleoid from the eukaryotic nucleus?
A) The nucleoid contains RNA, while the nucleus contains DNA
B) The nucleoid is surrounded by a lipid bilayer, while the nucleus is not
C) The nucleoid lacks a surrounding membrane, while the nucleus has a nuclear envelope
D) The nucleoid contains histone proteins, while the nucleus does not
Answer: C
Explanation: The nucleoid is not enclosed by a membrane; the nucleus is surrounded by a double-membrane nuclear envelope.
Why the top distractor is wrong: B reverses the truth—nucleus has membrane, nucleoid does not.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: DNA in nucleoid; no nuclear membrane.
• Eukaryotes: DNA in nucleus with nuclear envelope and pores.
• Prokaryotic ribosome = 70S (50S + 30S); eukaryotic cytoplasmic ribosome = 80S (60S + 40S).
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacteria: peptidoglycan cell wall; Archaea: no peptidoglycan.
• Plants: cellulose cell wall; Fungi: chitin cell wall; Animals: no cell wall.
• All cells have phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, lysosomes, etc.); prokaryotes do not.
• Rough ER: protein synthesis; Smooth ER: lipid synthesis, detoxification.
• Golgi apparatus: modifies, sorts, packages proteins and lipids.
• Mitochondria: ATP production, double membrane, own DNA.
• Chloroplasts: photosynthesis, contain thylakoids, own DNA.
• Lysosomes: contain hydrolytic enzymes, found in animal cells.
• Peroxisomes: break down fatty acids, neutralize H?O?.
• Nuclear pores regulate mRNA and protein transport.
• Nucleolus: site of rRNA synthesis and ribosome assembly.
• Mature human red blood cells lack nucleus and organelles.
• Mycoplasma is a bacterium without a cell wall.
• Eukaryotic flagella: 9+2 microtubule array; prokaryotic flagella: flagellin, rotary motion.
• Endosymbiotic theory: mitochondria and chloroplasts originated from engulfed prokaryotes.
• Mitochondria and chloroplasts have double membranes – outer from host, inner from original prokaryote.
• Plant cells: large central vacuole; animal cells: small or no vacuoles.
• Archaea are prokaryotes but genetically closer to eukaryotes in transcription and translation.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.