All cells share four common core features: a plasma membrane, cytoplasm, genetic material, and ribosomes. The primary evolutionary distinction between prokaryotic and eukaryotic cells is the presence of a membrane-bound nucleus and specialized membrane-bound organelles in eukaryotes.
2. Organelle Structure and Function★★★☆☆⏱ 7 min
Eukaryotic organelles compartmentalize different cellular processes, allowing incompatible reactions to occur separately and increasing overall cellular efficiency. Almost all AP Bio exam questions for this topic ask to connect structure to function, so this link is critical to master.
3. Plant vs Animal Cell Differences★★☆☆☆⏱ 4 min
Both plant and animal cells are eukaryotic, but they have key structural differences adapted to their distinct lifestyles:
Plant cells have a rigid cellulose cell wall outside the plasma membrane for structural support
Plant cells contain chloroplasts, the site of photosynthesis
Mature plant cells have a large central vacuole for water storage and turgor pressure maintenance
Animal cells have centrioles (part of the centrosome for cell division) that are absent in most plants, and lysosomes that are rare in plant cells
4. Cell Size and Surface Area-to-Volume Ratio★★★★☆⏱ 6 min
Cell size is constrained by the surface area-to-volume ratio (SA/V). As a cell grows, its volume increases faster than its surface area. Since the plasma membrane exchanges nutrients and waste with the environment, a lower SA/V means less surface area to support the needs of the larger volume, making exchange inefficient.
\text{For a sphere: } SA = 4\pi r^2, V = \frac{4}{3}\pi r^3, \frac{SA}{V} = \frac{3}{r}
Common Pitfalls
Why: Ribosomes are non-membrane-bound, so they are present in all living cells
Why: Both organelles produce ATP, leading to mix-ups about their primary roles
Why: Total surface area is larger for big cells, but the ratio of surface area to volume decreases as size increases
Why: Cell walls are present in other groups, just made of different materials
Why: Many students only associate ribosomes with the rough ER