Cell Theory & Types of Cells
What is the basic unit of structure and function in all living things?
the cell!
Which organelle is the “control center” of the cell?
the nucleus
What does it mean for the cell membrane to be semi-permeable?
It allows some substances to pass while blocking others.
What are the three phases of Interphase?
G1 (growth), S (DNA replication), G2 (prep for division).
Define homeostasis.
Maintaining a stable internal environment despite external changes.
Define unicellular and multicellular organisms and give an example of each.
Unicellular = one cell (example: bacteria); Multicellular = many specialized cells (example: humans).
What organelle is the site of protein synthesis?
ribosomes
What is the main structure of the plasma membrane called, and what is it made of?
The phospholipid bilayer, made of phospholipids with hydrophilic heads and hydrophobic tails.
In which phase of mitosis do chromosomes line up at the center of the cell?
metaphase
What are the four parts of a feedback loop?
Stimulus, sensor, control center, effector.
Give one major difference between prokaryotic and eukaryotic cells.
Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have both.
How does the Rough ER differ from the Smooth ER?
Rough ER has ribosomes and makes proteins; Smooth ER has no ribosomes and makes lipids/detoxifies.
What is the difference between passive and active transport? Give an example of each.
Passive = no energy, moves down concentration gradient (example: diffusion); Active = requires energy, moves against gradient (example: sodium-potassium pump).
What is the purpose of checkpoints in the cell cycle?
Ensure the cell is ready to divide, DNA is copied correctly, and chromosomes attach properly.
Compare positive and negative feedback with an example of each.
Negative = stabilizes system (example: insulin regulating blood sugar); Positive = amplifies change (example: contractions during childbirth)
What are the three main principles of the Cell Theory?
All living things are made of cells; the cell is the basic unit of structure and function; all cells come from preexisting cells.
Which organelles are unique to plant cells, and what are their main functions?
Chloroplasts (photosynthesis), central vacuole (storage/support), and cell wall (structure/protection).
Define diffusion and osmosis. How are they similar and different?
Diffusion = movement of molecules from high to low concentration; Osmosis = diffusion of water across a membrane; both are passive, but osmosis involves only water.
Compare aerobic and anaerobic respiration in terms of oxygen use and ATP yield.
Aerobic requires oxygen, produces lots of ATP; anaerobic does not require oxygen, produces less ATP.
How do bacteria reproduce?
Mainly by binary fission (asexual cell division).
Expanded Cell Theory states three additional principles. Name two of them.
Cells carry genetic material; all cells are similar in chemical composition; energy flow occurs within cells.
Trace the pathway of a protein from instructions in the DNA to delivery out of the cell
DNA in nucleus → ribosomes (protein synthesis) → rough ER (fold/modify) → Golgi apparatus (package/ship) → vesicles → cell membrane (export)
Explain the Fluid Mosaic Model and why membrane fluidity is important.
The membrane is a flexible, moving mosaic of phospholipids and proteins; fluidity allows transport, communication, and enzyme activity.
Explain how ATP is like a “rechargeable battery” for the cell.
Energy is stored in phosphate bonds; breaking releases energy, and bonds can be re-formed to recharge.
Compare the lytic and lysogenic viral cycles.
Lytic = virus replicates and destroys host cell; Lysogenic = virus DNA integrates and lies dormant, later may enter lytic.