STEM Readiness: Pre-Calculus Readiness - Functions/Algebra: Piecewise Functions - Graphing, Evaluating Continuity at Breakpoints

Must?Know

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotes store DNA in a nucleoid (not membrane-bound); eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotic ribosomes are 70S (30S + 50S subunits); eukaryotic cytoplasmic ribosomes are 80S (40S + 60S subunits).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiotic theory.
• Bacterial cell walls contain peptidoglycan; archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are made of cellulose; fungal cell walls contain chitin; animal cells lack a cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have membrane-bound organelles (e.g., nucleus, mitochondria, lysosomes); prokaryotes do not.
• 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—found only in eukaryotes.
• Mitochondria generate ATP via aerobic respiration and have double membranes and circular DNA.
• Chloroplasts perform photosynthesis in plants and algae; contain thylakoids, chlorophyll, and circular DNA.
• Lysosomes contain hydrolytic enzymes for degradation; present in animal cells, rare in plant cells.
• Vacuoles in plant cells are large and central, maintaining turgor pressure; smaller and multiple in animal cells.
• Cytoskeleton (microtubules, actin filaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologous proteins but no true cytoskeleton.
• Binary fission is the method of prokaryotic cell division; mitosis occurs in eukaryotes.
• Plasmids are small, circular DNA molecules common in prokaryotes; rare in eukaryotes.
• Mycoplasma species lack a cell wall, making them resistant to penicillin—exception among bacteria.
• Mature red blood cells in mammals lack a nucleus and mitochondria, maximizing hemoglobin capacity.
• Archaea are prokaryotes but have ribosomes and membrane lipids more similar to eukaryotes than bacteria.
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores regulating transport.
• Nucleolus within the nucleus synthesizes ribosomal RNA and assembles ribosome subunits.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having 70S ribosomes, circular DNA, and ability to self-replicate.
• Peroxisomes detoxify harmful substances (e.g., hydrogen peroxide) and are found only in eukaryotes.
• Centrioles organize microtubules during cell division in animal cells; absent in most plant cells.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, with attention to exceptions.

Common Traps

Trap: All prokaryotes have cell walls – Fact: Mycoplasma, a bacterium, lacks a cell wall entirely.
Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts have 70S ribosomes despite being in eukaryotic cells.
Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
Trap: Eukaryotes are always multicellular – Fact: Many eukaryotes (e.g., yeast, amoeba) are unicellular.
Trap: Plant cells have chloroplasts but no mitochondria – Fact: Plant cells have both chloroplasts and mitochondria for energy production.

Practice MCQs

Question: Which structure is found in prokaryotic cells but not in eukaryotic cells?
A) Circular DNA
B) 70S ribosomes
C) Nucleoid
D) Plasma membrane
Answer: C
Explanation: The nucleoid is a distinct, unenclosed region in prokaryotes where DNA resides.
Why the top distractor is wrong: 70S ribosomes (B) are also in mitochondria and chloroplasts of eukaryotes, so not exclusive to prokaryotes.

Question: Which of the following is a component of fungal cell walls?
A) Cellulose
B) Peptidoglycan
C) Chitin
D) Lignin
Answer: C
Explanation: Chitin is a polysaccharide found in fungal cell walls and insect exoskeletons.
Why the top distractor is wrong: Cellulose (A) is found in plant cell walls, not fungal.

Question: Which organelle is responsible for modifying and packaging proteins for secretion in eukaryotic cells?
A) Nucleolus
B) Smooth ER
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus processes and packages proteins from the ER into vesicles.
Why the top distractor is wrong: Smooth ER (B) synthesizes lipids and detoxifies, but does not package proteins.

Question: Which of the following provides evidence for the endosymbiotic theory?
A) Eukaryotic cells have linear DNA
B) Mitochondria have 80S ribosomes
C) Chloroplasts have circular DNA and 70S ribosomes
D) The nucleus is surrounded by a double membrane
Answer: C
Explanation: Chloroplasts resemble free-living cyanobacteria in having circular DNA and 70S ribosomes.
Why the top distractor is wrong: Mitochondria have 70S ribosomes, not 80S (B), so that statement is false.

Question: Which cell type lacks a nucleus at maturity?
A) Neuron
B) Leukocyte
C) Mature erythrocyte
D) Hepatocyte
Answer: C
Explanation: Mature mammalian red blood cells (erythrocytes) expel their nucleus to carry more hemoglobin.
Why the top distractor is wrong: Leukocytes (B) are nucleated white blood cells.

Question: What is the primary structural component of plant cell walls?
A) Chitin
B) Peptidoglycan
C) Cellulose
D) Collagen
Answer: C
Explanation: Cellulose is a polysaccharide that provides rigidity to plant cell walls.
Why the top distractor is wrong: Chitin (A) is found in fungi and arthropods, not plants.

Question: Which of the following is present in both prokaryotes and eukaryotes?
A) Mitochondria
B) 80S ribosomes
C) Phospholipid bilayer membrane
D) Nucleus
Answer: C
Explanation: All cells are bounded by a phospholipid bilayer plasma membrane.
Why the top distractor is wrong: 80S ribosomes (B) are only in eukaryotic cytoplasm, not prokaryotes.

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• DNA in prokaryotes: nucleoid; in eukaryotes: nucleus.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacteria: peptidoglycan cell wall; plants: cellulose; fungi: chitin; animals: no cell wall.
• All cells have a 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, sorts, ships proteins.
• Mitochondria: double membrane, produce ATP, have own DNA.
• Chloroplasts: site of photosynthesis, contain thylakoids and chlorophyll.
• Lysosomes: contain hydrolytic enzymes; mainly in animal cells.
• Plant vacuole: large central, maintains turgor pressure.
• Cytoskeleton: microtubules, actin, intermediate filaments – only in eukaryotes.
• Prokaryotes divide by binary fission; eukaryotes by mitosis.
• Plasmids: small circular DNA – common in bacteria.
• Mycoplasma has no cell wall – exception among bacteria.
• Mature red blood cells: no nucleus, no mitochondria.
• Archaea: prokaryotic but with some eukaryotic-like features (e.g., RNA polymerase).
• Nuclear envelope: double membrane with pores for transport.
• Nucleolus: makes rRNA and assembles ribosomal subunits.
• Peroxisomes: break down fatty acids, detoxify H?O?.
• Centrioles: in animal cells, organize spindle fibers.
• Endosymbiotic theory: mitochondria from aerobic bacteria, chloroplasts from cyanobacteria.
• Mitochondria have 70S ribosomes – not 80S.