AP - Biology:: Cell Structure and Function

What is CELL THEORY, one of the foundational principles of biology?

- **A)** A theory describing only the structure of plant cells, with no application to animal cells
- **B)** The idea that only some living organisms are made of cells, while others are not composed of cells at all
- **C)** The idea that ALL living organisms are composed of one or more cells, the cell is the basic unit of structure/function in organisms, and all cells arise from PRE-EXISTING cells
- **D)** Cell theory states that cells can spontaneously generate from non-living matter with no need for a pre-existing cell

What is the fundamental difference between a PROKARYOTIC cell and a EUKARYOTIC cell?

- **A)** A eukaryotic cell always lacks a nucleus, while a prokaryotic cell always has one (the reverse of the truth)
- **B)** A prokaryotic cell LACKS a membrane-bound NUCLEUS (and generally lacks other membrane-bound organelles), while a eukaryotic cell HAS a true, membrane-bound nucleus (and typically other membrane-bound organelles)
- **C)** Prokaryotic cells are always significantly LARGER than eukaryotic cells
- **D)** Prokaryotic and eukaryotic cells are always exactly identical in every structural respect

What is the CELL MEMBRANE (plasma membrane)'s primary function?

- **A)** The cell membrane's only function is providing rigid structural support, identical to a plant cell wall
- **B)** Forming a SELECTIVELY PERMEABLE barrier that separates the cell's internal contents from its external environment, while regulating what substances enter or exit the cell
- **C)** The cell membrane completely prevents ANY substance from ever entering or exiting the cell
- **D)** The cell membrane's function is unrelated to controlling what enters or exits a cell

What does the FLUID MOSAIC MODEL describe about the structure of the cell membrane?

- **A)** The fluid mosaic model describes the membrane as containing no proteins at all, only phospholipids
- **B)** The membrane consists of a phospholipid bilayer with various PROTEINS and other molecules EMBEDDED within it, and both the phospholipids and many proteins can move somewhat FREELY within the membrane's plane, giving it a fluid, dynamic quality rather than a rigid, fixed structure
- **C)** This model applies only to plant cell walls, never to cell membranes
- **D)** The cell membrane is a completely RIGID, unmoving structure with no fluidity whatsoever

What is the difference between INTEGRAL (transmembrane) membrane proteins and PERIPHERAL membrane proteins?

- **A)** Only peripheral proteins are ever found in a real cell membrane; integral proteins do not actually exist
- **B)** Integral and peripheral proteins are always exactly identical in their location and structure
- **C)** Peripheral proteins always span completely through the membrane, while integral proteins never do (the reverse of the truth)
- **D)** INTEGRAL proteins are embedded WITHIN (often spanning all the way through) the membrane, while PERIPHERAL proteins are attached to the membrane's SURFACE without actually being embedded inside it

What is PASSIVE TRANSPORT across a cell membrane, and why is it called 'passive'?

- **A)** This term describes a process that never actually moves any substance across a membrane
- **B)** Movement of substances ACROSS the membrane WITHOUT requiring the cell to expend energy (ATP), typically moving substances DOWN their concentration gradient (from higher to lower concentration)
- **C)** Passive transport always moves substances AGAINST their concentration gradient, from low to high concentration
- **D)** Passive transport always REQUIRES the cell to actively expend energy (ATP) to move substances

What is DIFFUSION, as a specific type of passive transport?

- **A)** Diffusion always moves particles from LOW to HIGH concentration, requiring active energy input
- **B)** Diffusion can only ever occur across a cell membrane, never in open space
- **C)** A synonym for active transport
- **D)** The net movement of particles from an area of HIGHER concentration to an area of LOWER concentration, occurring spontaneously due to random particle motion, without requiring any cellular energy

What is OSMOSIS, specifically?

- **A)** The diffusion of any solute EXCEPT water across a membrane
- **B)** A synonym for active transport requiring ATP
- **C)** Osmosis refers only to the movement of proteins across a membrane
- **D)** The diffusion of WATER specifically, across a selectively permeable membrane, from an area of HIGHER water concentration (lower solute concentration) to an area of LOWER water concentration (higher solute concentration)