Cell Theory
State the three main principles of cell theory
All living organisms are composed of cells; cells are the smallest unit of life; all cells come from pre-existing cells.
Label two membrane-bound organelles found in eukaryotic cells.
Examples: Nucleus, mitochondrion, rough ER, Golgi apparatus, lysosome, chloroplast.
State the main components of a phospholipid bilayer.
Phospholipids, proteins, cholesterol, glycoproteins, glycolipids.
State the unit used to measure most cells.
Micrometers (µm).
State one example of a specialized cell and its function.
Example: Red blood cell – transports oxygen using haemoglobin.
Outline two exceptions to the cell theory.
Examples: Giant algae (large single cell), striated muscle fibers (multinucleated), aseptate fungal hyphae (continuous cytoplasm), viruses (non-cellular).
State one function for each of the following: mitochondrion, ribosome.
Mitochondrion – ATP production; Ribosome – protein synthesis.
Outline the difference between diffusion and active transport.
Diffusion: passive, along concentration gradient, no ATP. Active transport: requires energy (ATP), against concentration gradient.
Outline one advantage of electron microscopes over light microscopes.
Higher resolution and magnification → can view ultrastructure like ribosomes or membranes
Outline how vesicles are used for transport within cells.
Form at ER → carry proteins to Golgi → modified and packaged → vesicles fuse with membrane for exocytosis.
Explain how one named example challenges a principle of cell theory.
E.g. Giant algae challenges the principle that cells are small and simple because it is large and complex but still a single cell.
Compare the structure of prokaryotic and eukaryotic cells.
Prokaryotic: no nucleus, circular DNA, no membrane-bound organelles, smaller (70S) ribosomes. Eukaryotic: nucleus, linear DNA, membrane-bound organelles, larger (80S) ribosomes.
Explain the fluid mosaic model of membrane structure.
Phospholipid bilayer with hydrophilic heads and hydrophobic tails; proteins embedded (integral/peripheral); fluid because components move laterally.
Calculate the actual size of a cell if its image is 5 mm and the magnification is ×1000.
Actual size = image size / magnification = 5 mm / 1000 = 0.005 mm = 5 µm.
Explain the role of cholesterol in the plasma membrane.
Regulates fluidity, prevents membrane from becoming too rigid or too permeable, stabilizes structure.
Compare the cell theory with one exception and discuss how the theory remains valid.
Despite exceptions, the cell theory still applies to the vast majority of life forms and provides a unifying framework. Exceptions highlight diversity rather than invalidate the theory.
Explain how the structure of the rough ER and Golgi apparatus are related to their function.
Rough ER: flattened cisternae with ribosomes — protein synthesis and transport. Golgi: modifies, sorts, and packages proteins into vesicles for secretion.
Describe how facilitated diffusion differs from simple diffusion.
Facilitated diffusion uses membrane proteins (channels/carriers) to move substances down a concentration gradient; simple diffusion is direct movement through the bilayer.
Compare transmission and scanning electron microscopes.
TEM: passes electrons through thin section, 2D, higher resolution. SEM: scans surface, 3D image, lower resolution.
Analyse how evidence from Pasteur’s experiment supports the cell theory.
Sterilized broth remained free of microbes until exposed to air → disproved spontaneous generation → supports that cells come from pre-existing cells.
Evaluate the statement: “All living things are made of cells” using evidence from both supporting examples and exceptions.
Students must refer to evidence (e.g., all multicellular organisms, unicellular protists) and exceptions (e.g., viruses, muscle fibers) and conclude that the theory is broadly valid but not universal.
Discuss how compartmentalization benefits eukaryotic cells.
Increases efficiency of metabolic processes, isolates harmful reactions, allows specialized environments, supports complex functions.
Predict and explain what would happen to an animal cell placed in a hypertonic solution.
Water leaves cell via osmosis; cell shrinks and may undergo crenation due to lower water potential outside the cell.
Explain how surface area to volume ratio limits cell size.
As cell size increases, SA:V decreases → reduced diffusion efficiency for nutrients/wastes → limits growth and necessitates division or adaptations.
Evaluate the importance of membrane transport in maintaining homeostasis.
Transport maintains ion gradients, removes waste, enables nutrient uptake — essential for enzyme function, signaling, osmotic balance, and cell survival.