STEM Readiness: Physics Readiness - Kinematics: 1D Kinematics - SUVAT Equations, Choosing the Right Equation

Must?Know

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• 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 but may have pseudopeptidoglycan or other polymers.
• Plant cell walls are composed of cellulose; fungal cell walls are made of chitin; animal cells lack a cell wall.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotic cells contain membrane-bound organelles: nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and (in plants) chloroplasts.
• Prokaryotes lack membrane-bound organelles; metabolic functions occur in the cytoplasm or at the plasma membrane.
• Bacteria (e.g., Escherichia coli) and archaea (e.g., Methanogens) are prokaryotes; animals, plants, fungi, and protists are eukaryotes.
• Mycoplasma species are bacteria that lack a cell wall, making them resistant to antibiotics like penicillin.
• Human red blood cells lack a nucleus and most organelles, maximizing space for hemoglobin.
• Endosymbiotic theory posits that mitochondria evolved from aerobic bacteria and chloroplasts from cyanobacteria engulfed by ancestral eukaryotic cells.
• Evidence for endosymbiosis includes: mitochondria and chloroplasts have their own circular DNA, 70S ribosomes, and double membranes.
• Nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport between nucleus and cytoplasm.
• Nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome subunit assembly.
• Rough endoplasmic reticulum (RER) has ribosomes attached and synthesizes proteins for secretion or membranes.
• Smooth endoplasmic reticulum (SER) lacks ribosomes and functions in lipid synthesis, detoxification, and calcium storage.
• 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; present in animal cells, rare in plants.
• Peroxisomes contain oxidative enzymes (e.g., catalase) that break down fatty acids and detoxify hydrogen peroxide.
• Mitochondria are the site of aerobic respiration; produce ATP via electron transport chain and chemiosmosis.
• Chloroplasts (in plants and algae) perform photosynthesis; contain thylakoids with chlorophyll and produce glucose.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologs (e.g., FtsZ) but no true cytoskeleton.
• Flagella differ structurally: prokaryotic flagella are made of flagellin and rotate; eukaryotic flagella are made of microtubules (9+2 arrangement) and undulate.

Difficulty Level

Intermediate – requires precise differentiation of structures, components, and exceptions commonly tested in first-year biology exams.

Common Traps

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (other polymers) have different wall compositions.
• Trap: Ribosome size correlates with organism complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, like prokaryotes, due to endosymbiotic origin.
• Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes (e.g., cyanobacteria) have internal membrane systems like thylakoids for photosynthesis.
• Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes (outer and inner).
• Trap: Eukaryotes evolved from prokaryotes – Fact: Eukaryotes and archaea share a more recent common ancestor; eukaryotes did not directly descend from modern prokaryotes.

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 only found in eukaryotic cells.

Question: A cell is observed to contain peptidoglycan in its cell wall and lacks a nucleus. It most likely belongs to which domain?
A) Eukarya
B) Archaea
C) Bacteria
D) Protista
Answer: C
Explanation: Peptidoglycan is a defining feature of bacterial cell walls.
Why the top distractor is wrong: B (Archaea) lack peptidoglycan, though they may have similar structural polymers.

Question: Which structure is present in plant cells but absent in animal cells?
A) Lysosome
B) Mitochondrion
C) Chloroplast
D) Golgi apparatus
Answer: C
Explanation: Chloroplasts are organelles for photosynthesis and are found only in plants and algae.
Why the top distractor is wrong: A (lysosomes) are common in animal cells and occasionally found in plant vacuoles, but not a defining feature.

Question: Mitochondria are thought to have evolved from free-living prokaryotes due to all of the following EXCEPT:
A) They contain circular DNA
B) They have 80S ribosomes
C) They reproduce by binary fission
D) They have double membranes
Answer: B
Explanation: Mitochondria have 70S ribosomes, not 80S, supporting prokaryotic origin.
Why the top distractor is wrong: A is correct evidence—circular DNA is typical of prokaryotes.

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: The nucleolus is best described as the site of:
A) DNA replication
B) ATP synthesis
C) Ribosomal RNA synthesis
D) Protein degradation
Answer: C
Explanation: The nucleolus synthesizes rRNA and assembles ribosomal subunits.
Why the top distractor is wrong: A (DNA replication) occurs throughout the nucleus, not specifically in the nucleolus.

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

Last?Minute Revision

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes have no nucleus; DNA in nucleoid.
• Eukaryotes have membrane-bound nucleus with nuclear pores.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacterial cell wall contains peptidoglycan; archaea do not.
• Plant cell wall = cellulose; fungal = chitin; animal cells = no cell wall.
• Mycoplasma has no cell wall – smallest known cells.
• Human red blood cells lack a nucleus and mitochondria.
• Both cell types have phospholipid bilayer plasma membrane.
• Eukaryotes have internal membranes (ER, Golgi, etc.); prokaryotes generally do not.
• Rough ER has ribosomes; smooth ER does not.
• RER synthesizes proteins; SER synthesizes lipids and detoxifies.
• Golgi apparatus: modifies, sorts, packages proteins.
• Lysosomes contain hydrolytic enzymes; active at acidic pH.
• Peroxisomes break down fatty acids and neutralize H?O?.
• Mitochondria produce ATP via aerobic respiration.
• Chloroplasts perform photosynthesis; contain thylakoids and grana.
• Nuclear envelope is a double membrane with nuclear pores.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Cytoskeleton: microtubules, microfilaments, intermediate filaments – eukaryote-specific.
• Prokaryotic flagellum = flagellin, rotates; eukaryotic = 9+2 microtubules, bends.
• Endosymbiotic theory: mitochondria from aerobic bacteria, chloroplasts from cyanobacteria.
• Some prokaryotes (e.g., cyanobacteria) have internal membranes for photosynthesis.
• Eukaryotes are more closely related to archaea than to bacteria.