Diffusion Osmosis And Active Transport 75y44

HUMAN AND SOCIAL BIOLOGY 10CMH DIFFUSION ,OSMOSIS AND ACTIVE TRANSPORT

Movement of Substances  Cells

need to move different substances into and out of the cell in order to function properly.

 Diffusion

,osmosis and active transport are two processes by which this takes place

Diffusion  The

movement of molecules from a region where they are in higher concentration to a region where they are in lower concentration.

 All

substances are made of particles.

 In

gases and liquids these particles move around randomly.

 Diffusion

take place when particles are not evenly distributed.

 Eventually

the particles will spread out evenly (equilibrium is reached).

 The

particles move along a concentration gradient.

 The

bigger the difference in concentration between two regions, the steeper the concentration gradient.

 Diffusion

takes place more quickly when there is a steeper concentration gradient.

Diffusion and cell membrane Substances

into and out of a cell through a cell membrane. The

cell membrane is a barrier with tiny pores or holes in it.

Small

molecules, such as oxygen ,carbon dioxide, water and glucose, are able to diffuse through.

Large

molecules, such as starch and proteins cannot.

 Cell

membrane is called partially permeable, as it allow only some substances to through.

Diffusion In Human Body  After

breathing in, oxygen diffuses into the small blood vessels of the lungs.

 Carbon

will diffuses from blood vessels to the air sacs in the lungs.

 Digested

food also es from the small intestines into the blood capillaries by diffusion.

Concentration Gradient  This

is when there is a place of high concentration and a place of low concentration.

 Diffusion

allows substances to move from a place of high concentration to a place of lower concentration (down a concentration gradient).

 Until

an equilibrium is reached.

Adaptations That Speed up Diffusion Diffusion distance are short  Membranes in the lungs are very thin for example.  Hence

oxygen and carbon dioxide can diffuse between the blood and air sacs.

Concentration Gradients Are Maintained  Glucose molecules that cross from the gut into the blood are quickly removed by circulating blood.  Hence

there will always be a concentration gradient.

Diffusion Surfaces Are Large  The surface area of the air sacs in the lungs are large because of the millions of air sacs which are present.

Osmosis Osmosis is a special case of diffusion. Osmosis

involve the movement of water through a partially permeable membrane. This

means that only some substances can through the membrane. Small

molecules, such as water, can through but larger molecules cannot.



Osmosis is water moving from a region where its concentration is high (in a dilute solution) to where its concentration is low (to a more concentrated solution).

Cell in Water  When

you place a cell in water, water will enter the cell by osmosis.

 The

cell will become turgid or stiff.

 Animal

cells will swell up and burst if too much water enter the cell.

 The

strong cell wall stop plant cells from bursting when water enters them.

Cells in a Concentrated Solution  Water will leaves the cell by osmosis. 

Animal cell will shrink



In plant cell, the strong cell wall will stay the same.



The inside of the cell shrinks away from the cell wall.



Cell is plasmolysed.

Active Transport  The movement of a substance across a cell membrane, against concentration gradient, with the use of energy provided by the cell.  At

times the cell needs something that is present in low concentration outside of the cell.



There are special molecules in the cell membrane that can grab glucose molecules in the cell membranes.

They drag them through the cell membrane and into the cell.  This uses up energy.  The energy is provided by respiration in the cell. 