🎯Diagnostic: Test Your Starting Level24 questions (~2 per section). No prior reading required - see what you already know.
Aim to answer every question before checking. Missed questions point you to the sections you need most.
1. (1.1) "All cells arise from preexisting cells" - this tenet of cell theory was proposed by:
B. Virchow added "omnis cellula e cellula" (all cells from cells) to the earlier Schleiden-Schwann framework, completing classical cell theory and ruling out spontaneous generation of cells.
2. (1.1) Which statement belongs to modern cell theory?
A. The three classical tenets: (1) all living things are made of cells, (2) cells are the basic unit of life, (3) cells arise only from other cells. Viruses are excluded because they cannot self-replicate outside a host.
3. (1.2) Which feature is present in eukaryotes but ABSENT in prokaryotes?
C. The defining difference: eukaryotes have a true nucleus enclosed by a double membrane. Prokaryotes keep their single circular chromosome in a nucleoid region with no envelope.
4. (1.2) Prokaryotic ribosomes are:
D. Bacteria and archaea have 70S ribosomes (50S large + 30S small). Eukaryotes have 80S. Sedimentation values are not additive because they depend on shape and mass. Many antibiotics target the 70S ribosome selectively.
5. (1.3) The fluid mosaic model describes the plasma membrane as:
B. Singer and Nicolson (1972): the bilayer behaves as a 2D fluid in which proteins (integral and peripheral) diffuse laterally. The mosaic is the mix of proteins, lipids, and cholesterol.
6. (1.3) Cholesterol in animal cell membranes:
C. Cholesterol is a fluidity buffer: at high temperature it restricts phospholipid motion (making the membrane less fluid); at low temperature it prevents tight packing (keeping the membrane from freezing).
7. (1.3) The hydrophilic head groups of membrane phospholipids face:
A. Phospholipids are amphipathic; the bilayer orients heads outward toward water on both sides and tucks hydrophobic tails inside. Swapping this arrangement (answer D) would be thermodynamically unstable in an aqueous cell.
8. (1.4) Rough ER is distinguished from smooth ER by:
D. The "rough" appearance comes from ribosomes bound to the cytosolic face, translating secretory and membrane proteins directly into the ER lumen. Smooth ER (no ribosomes) handles lipid synthesis and detoxification.
9. (1.4) The primary function of the Golgi apparatus is:
C. The Golgi is the cell's post office: it receives vesicles from the ER at the cis face, glycosylates / modifies proteins through its stacks, and sorts/ships them from the trans face to their final destinations.
10. (1.4) Lysosomes are characterized by:
B. V-ATPases pump H⁺ into the lumen (pH ~4.5-5), which is the pH optimum for lysosomal acid hydrolases that break down proteins, lipids, nucleic acids, and carbohydrates.
11. (1.5) Mitochondrial DNA and the citric-acid-cycle enzymes are located in the:
D. The matrix is the innermost aqueous compartment. It houses mtDNA, mitochondrial ribosomes, and the TCA-cycle enzymes. The electron transport chain sits in the inner membrane.
12. (1.5) The proton gradient driving ATP synthesis is built across the:
A. ETC complexes I, III, and IV pump H⁺ from matrix to intermembrane space, creating a proton-motive force across the inner membrane. ATP synthase then lets H⁺ flow back, coupling that flow to ATP synthesis.
13. (1.6) Microtubules are assembled from:
B. 13 protofilaments of αβ-tubulin dimers form the hollow 25 nm microtubule. Microtubules track vesicles via kinesin/dynein and build the mitotic spindle. Actin makes thin microfilaments; keratins are intermediate filaments.
14. (1.6) A primary role of intermediate filaments is:
C. Intermediate filaments (keratins, vimentin, lamins, neurofilaments) are rope-like and tension-resistant. They anchor the nucleus, maintain cell shape, and hold tissues together at desmosomes.
15. (1.7) Which junction creates a watertight seal between adjacent epithelial cells?
A. Tight junctions (zonula occludens) fuse adjacent plasma membranes with claudin/occludin strands, blocking the paracellular pathway. They are critical in the gut lining and blood-brain barrier.
16. (1.7) Gap junctions function in:
D. Aligned connexons form aqueous channels that let ions and small molecules (< ~1 kDa) pass directly between cells. This electrical coupling is how cardiac muscle cells synchronize contraction.
17. (1.8) The four primary tissue types in animals are:
A. Every tissue in the body falls into one of these four categories. B lists muscle subtypes, and D lists connective-tissue subtypes.
18. (1.8) Connective tissue is distinguished by:
B. Connective tissue's signature is sparse cells (fibroblasts, chondrocytes, etc.) in a large ECM of collagen, elastin, and ground substance. Epithelium, in contrast, is cell-dense with minimal ECM.
19. (1.9) A virus is best described as:
D. Viruses are acellular: genome (DNA or RNA) + capsid ± envelope. They can only replicate by hijacking a host cell's machinery, which is why they sit outside the classical cell theory.
20. (1.9) HIV and other retroviruses require which enzyme for replication?
C. Retroviruses carry an RNA genome plus reverse transcriptase, which converts viral RNA into double-stranded DNA that is then integrated into the host genome by integrase.
21. (1.10) Passive transport across a membrane:
A. Passive transport (simple diffusion, facilitated diffusion via channels or carriers, osmosis) is thermodynamically downhill and needs no ATP. Active transport goes uphill and requires energy input.
22. (1.10) Per ATP hydrolyzed, the Na⁺/K⁺ pump transports:
D. The pump exchanges 3 Na⁺ (out) for 2 K⁺ (in) per ATP, making it electrogenic (net +1 charge leaves the cell each cycle). This drives the resting membrane potential and establishes gradients for secondary active transport.
23. (1.11) The bacterial cell wall is composed primarily of:
B. Peptidoglycan is a mesh of NAG-NAM sugar strands cross-linked by short peptides. Penicillin inhibits the transpeptidase that forms the cross-links, weakening the wall and lysing the cell.
24. (1.11) Bacterial conjugation transfers genetic material via:
C. The F⁺ donor extends a sex pilus, draws in the F⁻ recipient, and transfers a copy of its F plasmid through a conjugation bridge. Transformation (D) and transduction (A) are the other two bacterial gene-transfer mechanisms.
Previous Attempts
Every organ in your body, every tissue, every function that keeps you alive right now - it all comes back to cells. Your heart is not some magic pump. It’s billions of specialized cells, coordinating contractions through electrical signals passed from one cell to the next.
Your immune system is not an abstract shield - it is individual white blood cells hunting down invaders, engulfing them, and destroying them with acid-filled sacs.
Understanding the cell is not just “Chapter 1 material.” It is the foundation of everything else in biology and biochemistry. If you truly grasp how a cell works, MCAT passages about disease, drugs, and experimental techniques become dramatically easier to decode.
The Cell is a City
Before we dive into the technical details, let’s build a mental model you can carry through this entire book. A cell is a tiny city. Every city needs a government, workers, factories, a post office, a power grid, a recycling center, and a wall with guarded gates. A cell has all of these.
The nucleus is city hall - it holds the master blueprints (DNA) and makes all the executive decisions about what gets built and when. Ribosomes are the construction workers - they read copies of the blueprints (mRNA) and build the products (proteins). The endoplasmic reticulum is the factory floor - the rough ER has workers attached (ribosomes on its surface), while the smooth ER manufactures lipids and detoxifies chemicals.
The Golgi apparatus is the post office - it receives packages from the factory, labels them with the correct address, and ships them to their final destination. Lysosomes are the recycling center and demolition crew, breaking down waste and worn-out parts. Mitochondria are the power plants, generating the energy (ATP) that keeps the whole city running.
And the cell membrane? It is the city wall with guarded gates - controlling exactly who gets in and who stays out.
