Chapter 5: Cell Membrane

Facilitated Diffusion

Material passes through transmembrane protein channel

The membrane potential of a cell favors the:

Movement of cations into the cell

Diffusion

Natural movement from an area of high concentration to a low concentration

A single layer of phospholipid molecules coats the water in a beaker. What part of the molecules will face the air?

The hydrocarbon tails (hydrophobic)

The fluid mosaic model describes biological membranes as consisting of:

A lipid bilayer with proteins coating the outside of this hydrophobic structure

Description of an integral, transmembrane protein

A middle region composed of alpha-helical stretches of hydrophobic amino acids, with hydrophilic regions at both ends of the protein

A plant cell placed in a hypotonic environment will:

Become turgid

Osmosis

Diffusion of water through membrane; solutes DO NOT move

A cell is manufacturing receptor proteins for cholesterol. How would those proteins be oriented in the following membranes before they reach the plasma membrane?

Facing inside the ER lumen and inside the transport vesicle

The fluidity of membranes in a plant in cold weather can be maintained by:

Increasing the number of phospholipids with unsaturated hydrocarbon tails

The extracellular fluids that surround the cells of a multicellular animal must be ... to the cells.

Isotonic

You observe plant cells under a microscope that have just been placed in an unknown solution. First the cells plasmolyze; after a few minutes, the plasmolysis reverses and the cells appear normal. What would you conclude about the unknown solute?

It is hypertonic to the plant cells, but its solute can cross the plant cell membrane

LDLs (low-density lipoproteins) enter animal cells by:

Receptor-mediated endocytosis

A freshwater Paramecium is placed in salt water. Which of the following events would occur?

Shriveling of the cell

The proton pump in plant cells is the functional equivalent of an animal cell's:

Sodium-Potassium Pump

Support for the fluid mosaic model of membrane structure comes from:

The free-fracture technique of electron microscopy The movement of proteins in hybrid cells The amphipathic nature of membrane proteins

Exocytosis involves:

The fusion of a vesicle with the plasma membrane A mechanism to transport carbohydrates to the outside of plant cells during the formation of cell walls A mechanism to rejuvenate the plasma membrane A means of exporting large molecules

Pinocytosis involves:

The pinching in of the plasma membrane around small droplets of external fluid

Watering a houseplant with too concentrated a solution of fertilizer can result in wilting because:

The soil solution becomes hypertonic, causing the cells to lose water

Carrier molecules involved in facilitated diffusion

They increase the speed of transport across a membrane They can have specific binding sites for the molecules they transport They can undergo a conformational change upon binding of solute They can be inhibited by molecules that resemble the solute to which they normally bind

Cotransport can involve:

Transport of one solute against its concentration gradient in tandem with another that is diffusion down its concentration gradient

Facilitated diffusion across a cellular membrane requires ... and moves a solute ... its concentration gradient.

Transport proteins ... down

Osmosis

Water moves from a hypotonic to a hypertonic solution Solute molecules bind to water and decrease the water available to move It increases the entropy in a system There is no net osmosis between isotonic solutions

Glycolipids and glycoproteins are important for:

cell-cell recognition (cell identity markers)

Ions diffuse across membranes down their:

electrochemical gradient