Module 2 Section 5 - Transport Across Cell Membranes Flashcards
Define diffusion
Diffusion is the random net movement of particles from an area of higher concentration to an area of lower concentration, down the concentration gradient
Which way will molecules diffuse
Both ways, but net movement will be to area of lower concentration
When will diffusion stop
Diffusion continues until particles are evenly distributed throughout the liquid or gas
What is the concentration gradient
The path from an area of higher concentration to an area of lower concentration
How do particles diffuse
Down the concentration gradient
What type of process is diffusion
Passive process
What is a passive process
A process that requires no energy needed for it to happen
What type of molecules diffuse through cell membranes
Small, Polar molecules
Give example of small polar molecules
Oxygen, Carbon Dioxide
How do small polar molecules diffuse through cell membranes
Small polar molecules are able to diffuse easily through spaces between phospholipids
What is the diffusion of water molecules called
Osmosis
Is water small enough to diffuse
Yes, even though water is polar it can diffuse through plasma membranes
What affects the rate of diffusion
Steepness of Concentration gradient
Thickness of exchange surface
Surface area
Temperature
How does concentration gradient affect rate of diffusion
The steeper the concentration gradient the faster the rate of diffusion
How does the thickness of exchange surface affect rate of diffusion
The thinner the exchange surface, the faster the rate of diffusion
How does the surface area affect the rate of diffusion
The larger the surface area the faster the rate of diffusion
How does temperature affect the rate of diffusion
The warmer it is, the faster rate of diffusion because the particles have more kinetic energy
What does facilitated diffusion use to diffuse molecules
Carrier and channel proteins
What type of molecules use facilitated diffusion
Ions and polar molecules
Why can’t ions and polar molecules use simple diffusion
Because they can’t directly pass through the phospholipid bilayer of the cell membrane
How do ions and polar molecules diffuse
Through channel or carrier proteins
How do particles in facilitated diffusion move
Down the concentration gradient
What type of process is facilitated diffusion
Passive process
What do carrier proteins move
Large molecules into or out of the cell (down concentration gradient)
Describe the three steps a carrier proteins makes to diffuse substances
-Large molecule attaches to a carrier protein
-protein changes shape
-this releases the molecule on the opposite side of the membrane
What do channel proteins move
Charged particles
What do channel proteins form for charged particles to diffuse
They form pores
Different carrier proteins facilitate….
The diffusion of different molecules
Different channel proteins facilitate…
The diffusion of different charged particles
What is active transport
The movement of molecules or ions across a cell membrane from a region of lower concentration to higher concentration - against the concentration gradient
What type of process is active transport
Active process - it needs energy for the process to be completed
How do particles move in active transport
Against the concentration gradient
What does active transport involve
Carrier proteins
Active transport is very similar to facilitated diffusion but there is only one difference what is it
The only difference is that energy is used to move the solute against its concentration gradient
How do cells take in substances
Endocytosis
Why are substances taken into a cell by endocytosis
Because they are too large to be taken into a cell by carrier proteins
What happens when a substance undergoes endocytosis
-The cell surrounds the substance with a section of its plasma membrane
-The membrane pinches off to form a vesicles inside the cell containing the ingested substance
What type of process is endocytosis
Active process
How do cells secrete substances
Exocytosis
Substances produce by the cell are released by
Exocytosis
What are steps of Exocytosis
-Vesicle containing these substances pinch off the sacs of the Golgi apparatus and move towards plasma membrane
-the vesicles fuse with the plasma membrane and release their contents outside the cell
Something different happens to some substances in Exocytosis
Some substances e.g. membrane proteins, aren’t released outside the cell - instead they are are inserted straight into the plasma membrane
What type of process is Exocytosis
Active process
What is osmosis
The diffusion of water molecules across a partially permeable membrane down a water potential gradient.
What is meant by down the water potential gradient
The water molecules move from an area of higher water potential to an area of lower water potential
What is water potential
The potential of water molecules to diffuse out or into a solution
What has the highest water potential
Pure water
Cell are affected by…
The water potential of the surrounding solution
What happens to an animal cell in a hypotonic solution
Net movement of water molecules is into the cell. Cell bursts
What happens to an animal cell in an isotonic solution
Water molecules pass into and out of the cell in equal amounts. the cell stays the same
What happens to an animal cell in a hypertonic solution
Net movement of water molecules is out of the cell. the cell shrinks
What happens to a plant cell in a hypotonic solution
Net movement of water is into cell. Vacuole swell. The vacuole and cytoplasm push against the cell wall. The cell becomes turgid (swollen)
What happens to plant cell in an isotonic solution
Water molecules move into and out of the cell in equal amounts. the cell stays the same
What happens to a plant cell in a hypertonic solution
Net movement of water is out of the cell. The cell becomes flaccid (limp). The cytoplasm and the membrane pull away from the cell wall, the cell is plasmolysed
