Biology Unit 3 AQA (2014 specification used)

  • Created by: sahar
  • Created on: 08-05-14 18:07


Unit B3.1 Movement of molecules in and out of cells:

·         Cells, tissues and organs in plants and animals are adapted to take up and get rid of dissolved substances.

·         Different conditions can affect’s the rate of transfer.

·         Energy is needed at times to allow transfer to take place-Active transport (movement of molecules against concentration gradient- low to high concentration).

Unit B3.1.1 Dissolved substances:

·     Dissolved substances move by diffusion and by active transport.

·     WATER moves across boundaries by OSMOSIS.

OSMOSIS: Diffusion of water from a dilute (high concentration of water molecules) to more concentrated solution through a partially permeable membrane; that allows the passage of water molecules.

·  Water surrounding cells contain dissolved molecules; sugar, oxygen and proteins which the cells needs to survive.

·  If cells are short of water- water diffuses into the cell through partially permeable membrane.

·  If too much water (dilute) – water diffuses out of the cell


Sports drinks: contain-

·  Water; to replace water lost during activity-sweating.

·  Sugar; to replace the sugar used in energy release during activity.

·  Ions; to replace the ions lost during activity-sweating.

-If the WATER & IONS are not replaced this can cause an in balance in the body causing cells to not work as efficiently.

Active transport:

·  Substances are absorbed against a concentration gradient; the energy for this is obtained from respiration- this process called ACTIVE TRANSPORT; which enables cells to absorb ions from very dilute solutions.

Organ systems are specialised for exchanging materials by having:

·         Large surface area.

·         Thin membrane/cell wall to provide short diffusion path.

·         ANIMALS- efficient blood supply

·         ANIMALS- gas exchange-being ventilated.

It is essential for exchange in gas and solutes to occur effectively in humans and other organisms. The size of an organism’s cause’s difficulty for gas exchange as the distance where exchange occurs is further away.


·         The surface area of lungs is increased by alveoli’s.

·         The surface area of the small intestines is increased by the villi which have micro villi- provides a large surface area with a lot of capillaries to absorb products of digestion by diffusion and active transport.


Unit B3.1.2 Gaseous exchange:

·         The lungs are in the upper part of the body (thorax).

·         Protected by the ribcage; preventing damage to lungs.

·         Separated from the lower part of the body (abdomen) by the diaphragm.

·         Each lung gets good supply of oxygen due to the splitting of bronchus into two.

The breathing system takes in & out air of the body so that oxygen can diffuse into the blood &carbon dioxide out of the blood.

The alveoli allow the diffusion of oxygen and carbon dioxide. Oxygen is supplied into the red blood cells by the lining of the capillaries via diffusion


Artificial ventilators:


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