bio 3

Why are cell membranes semi-permeable?

Cell membranes are semipermeable, which means molecules can move through them. This is pretty important for cells to survive. Osmosis is where solvent molecules (usually water) move from one side of a cell membrane to the other.

Osmosis

Diffusion of water through a selectively permeable membrane

active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference

hypotonic

Having a lower concentration of solute than another solution

What types of particles do not diffuse through membranes wells?

The membrane is selectively permeable because substances do not cross it indiscriminately. Some molecules, such as hydrocarbons and oxygen can cross the membrane. Many large molecules (such as glucose and other sugars) cannot.

process of exocytosis

When particles are too big to exit though protein channels, the membrane surrounding the material fuses with the cell membrane changes shape.

facilitated transport

a process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins

Hypertonic

high solute, low water

Why cell membranes are selectively permeable.

it only lets certain things in and out. The structure of the phospholipid bilayer prevents random things from drifting through the membrane, and proteins act like doors, letting the right stuff in and out.

Hypotonic

low soute, high water

Describe the structure of the plasma (cell) membrane.

phospholipid bilayer arranged back-to-back.

Passive transport

the movement of substances across a cell membrane without the use of energy by the cell

processes of endocytosis

the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell.

hypertonic

when comparing two solutions, the solution with the greater concentration of solutes

isotonic

when the concentration of two solutions is the same