Chapter 7.4, Problem 3MI

Summary Introduction

To fill:

The correct term in the in the left column for each definition.

Introduction:

The movement of substances across the cell membrane is called cell transport. Cell membrane is a selectively permeable membrane. It has control over what molecules or ions can enter or leave the cell. There are various ways through which membrane transport occur.

Answer to Problem 3MI

Term	Definition
Diffusion	net movement of particles from an area where there are many particles of the substance to an area where there are fewer
Dynamic equilibrium	condition in which there is continuous movement but no overall change in concentration
Facilitated diffusion	form of transport that uses transport proteins to move other ions and small molecules across the plasma membrane
Osmosis	diffusion of water across a selectively permeable membrane
Isotonic solution	solution in which the inside of the cell and the solution it is in have the same concentration of water and solutes
Hypotonic solution	solution that has a lower concentration of solutes in the cell
Hypertonic solution	solution that has a higher concentration of solutes in the cell
Active transport	Using energy to move substances from a region of lower concentration to a region of higher concentration
Endocytosis	process by which the plasma membrane surrounds a substance inside the cell and moves it inside the cell
Exocytosis	process by which the plasma membrane surrounds a substance outside the cell and moves it outside the cell

Explanation of Solution

Cellular transport is the movement of substances across the plasma or cell membrane either into or out of the cell. There are four main ways through which molecules can pass through the plasma membrane. The first way is diffusion that does not require energy. Diffusion may be passive diffusion and osmosis. No assistance by transport is necessary for simple diffusion. But facilitated diffusion involves the assistance of transport proteins. The third way is the active transport which requires the use of cell energy to pull in or pump out certain molecules and ions. The fourth way is through vesicle transport, in which large molecules are moved across the membrane in bubble-like sacks that are made from pieces of the membrane. Vesicular transport includes exocytosis and endocytosis. The relative concentration of solutes dissolved in solution which determine the direction and extent of diffusion is called tonicity. If the fluid outside the cell has a higher osmolarity than the cell’s cytoplasm, it is said to be hypertonic and if the fluid outside the cell has a lower osmolarity than the cell’s cytoplasm, it is said to be hypotonic. If the osmolarity equal on both sides then it is said to be isotonic.