STEM Readiness: Pre-Calculus Readiness - Exponentials/Logs: Exponential Functions - Growth/Decay Base, e Continuous, Compounding

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.
• 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 organelles such as mitochondria, lysosomes, and peroxisomes.
• Ribosomes in prokaryotes are 70S (composed of 50S and 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S and 40S).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting the endosymbiotic theory.
• Prokaryotic cell walls typically contain peptidoglycan; archaea lack peptidoglycan and have different cell wall chemistry.
• Plant cell walls are made of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to antibiotics like penicillin that target peptidoglycan synthesis.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane that regulates transport.
• Eukaryotic cells have extensive internal membrane systems, including the endoplasmic reticulum (ER) and Golgi apparatus.
• The rough ER is studded with ribosomes and synthesizes proteins for secretion or membranes.
• The smooth ER synthesizes lipids, detoxifies drugs, and stores calcium ions (e.g., in muscle cells).
• The Golgi apparatus modifies, sorts, and packages proteins into vesicles for transport to lysosomes, plasma membrane, or secretion.
• Lysosomes contain hydrolytic enzymes that break down macromolecules, old organelles, and pathogens; absent in most plant cells.
• Mitochondria are the site of aerobic respiration; they have double membranes, their own circular DNA, and 70S ribosomes.
• Chloroplasts are found in plant and algal cells; they perform photosynthesis, have double membranes, circular DNA, and 70S ribosomes.
• Nuclear envelope is a double membrane with nuclear pores that regulate RNA and protein transport between nucleus and cytoplasm.
• Nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome subunit assembly.
• Cytoskeleton components (microtubules, microfilaments, intermediate filaments) are present in eukaryotes; prokaryotes have homologs like FtsZ but lack true cytoskeleton.
• Red blood cells in mammals lack a nucleus and most organelles, maximizing space for hemoglobin.
• Plant cells contain a central vacuole that maintains turgor pressure and stores ions and metabolites; animal cells have small or transient vacuoles.
• Peroxisomes break down very long chain fatty acids via beta-oxidation and detoxify hydrogen peroxide.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having circular DNA, 70S ribosomes, and double membranes.
• Gram-positive bacteria have thick peptidoglycan layers; Gram-negative bacteria have thin peptidoglycan and an outer membrane with lipopolysaccharides.

Difficulty Level

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

Common Traps

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; archaea, plants (cellulose), and fungi (chitin) have different wall compositions.

Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, like prokaryotes, due to evolutionary origin.

Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.

Trap: Prokaryotes have no internal structure – Fact: Prokaryotes have nucleoids, ribosomes, and some have protein-based microcompartments (e.g., carboxysomes).

Trap: Eukaryotic cells always have a nucleus – Fact: Mature mammalian red blood cells lack a nucleus, a key exception.

Practice MCQs

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 have a nucleus, mitochondria, and a cell wall made of cellulose. This cell is most likely from which domain?
A) Bacteria
B) Archaea
C) Animal
D) Plant
Answer: D
Explanation: Cellulose cell walls and mitochondria with a nucleus are characteristic of plant cells.
Why the top distractor is wrong: A (bacteria) lack nuclei and mitochondria and have peptidoglycan walls.

Question: Which structure is found in prokaryotes but not in eukaryotes?
A) 70S ribosome
B) Circular DNA
C) Nucleoid
D) Plasma membrane
Answer: C
Explanation: The nucleoid is a distinct, non-membrane-bound region in prokaryotes where DNA is located.
Why the top distractor is wrong: A (70S ribosomes) are also found in mitochondria and chloroplasts of eukaryotes.

Question: Which of the following provides the strongest evidence for the endosymbiotic origin of mitochondria?
A) Presence of a double membrane
B) Ability to synthesize ATP
C) Containing 70S ribosomes and circular DNA
D) Being involved in cellular respiration
Answer: C
Explanation: 70S ribosomes and circular DNA are prokaryotic traits retained in mitochondria.
Why the top distractor is wrong: A (double membrane) is suggestive but not exclusive evidence; other organelles also have double membranes.

Question: Which cell type lacks a nucleus and contains peptidoglycan in its cell wall?
A) Fungal cell
B) Plant cell
C) Gram-negative bacterium
D) Animal cell
Answer: C
Explanation: Gram-negative bacteria are prokaryotes with peptidoglycan and no nucleus.
Why the top distractor is wrong: A (fungal cells) are eukaryotes with chitin walls and nuclei.

Question: Where are ribosomal subunits assembled in eukaryotic cells?
A) Rough ER
B) Nucleus
C) Nucleolus
D) Golgi apparatus
Answer: C
Explanation: The nucleolus synthesizes rRNA and assembles ribosomal subunits.
Why the top distractor is wrong: B (nucleus) is correct location but not specific; nucleolus is the precise site.

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

Last?Minute Revision

• Prokaryotic size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: DNA in nucleoid; eukaryotes: DNA in nucleus.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence for endosymbiosis.
• Peptidoglycan is found only in bacterial cell walls.
• Archaea lack peptidoglycan; plants use cellulose; fungi use chitin.
• Mycoplasma has no cell wall – resistant to penicillin.
• Both cell types have phospholipid bilayer membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus).
• Rough ER = protein synthesis; smooth ER = lipid synthesis and detoxification.
• Golgi apparatus = modifies and sorts proteins.
• Lysosomes = contain hydrolytic enzymes; absent in most plant cells.
• Mitochondria = site of aerobic respiration; double membrane; own DNA.
• Chloroplasts = site of photosynthesis; found in plants and algae.
• Nuclear pores regulate transport between nucleus and cytoplasm.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Cytoskeleton (microtubules, etc.) is eukaryotic; prokaryotes have FtsZ, MreB, CreS homologs.
• Mature red blood cells lack a nucleus and organelles.
• Central vacuole in plant cells maintains turgor pressure.
• Peroxisomes break down fatty acids and detoxify H?O?.
• Endosymbiotic theory supported by organelle DNA, ribosomes, and double membranes.
• Gram-positive bacteria = thick peptidoglycan; Gram-negative = thin peptidoglycan + outer membrane.
• Animal cells lack cell walls and large vacuoles.
• Chloroplasts are not found in animal cells.
• Archaea are prokaryotes but differ from bacteria in membrane lipids and cell wall chemistry.
• Verify from standard textbook: exact ribosomal subunit sizes and gene content in mitochondria.