Biology Three A

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"OSMOSIS is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration."

Water moves into and out of cells by osmisis.

A partially permeable membrane is just a membrane with tiny holes in it, meaning tiny molecules can pass through it.

Water molecules actually pass both ways during Osmosis, because the molcules move randomly.

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Gas and Solute Exchange

Life processes need gasses or other dissolved substances so they can happen.

e.g. Photosynthesis needs Carbon Dioxide and water need to get into plant cells.

Waste substances also need to get out of cells so organisms can get rid of them.

These substances move to where they need to be by diffusion, osmosis and active transport.

In life processes, the gasses and dissolved substances have to move through some sort of exchange surface.

Exchange surfaces are adapted to be effective:

They are thin - so substances only have a short distance to diffuse.

They have a large surface area - so lots of a substance can diffuse at once,

They have lots of blood vessels - to get stuff into and out of the blood quickly

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The Breathing System

The lungs are in the thorax:

-The thorax is the top part of your body

-The thorax is separated from the abdomen by the diaphragm

-Air goes into the trachea which splits into two tubes called bronchi which split into progessively smaller tubes called bronchioles. These finally end at small bags called alveoli where gas exchange takes place.

Ventilation is breathing in and out:

-In: 1. Intercostal Muscles and diaphragm contract 2. Thorax volume increases 3. This decreases pressure, drawing air in.

-Out. 1.Intercostal Muscles and Diaphragm relax 2. Thorax Volume Decreases 3. This increases the pressure, so air is forced out.

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Diffusion Through Cell Membranes

Gas Exchange happens in the lungs

-The job of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it.

-To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place.

-The alveoli are specialised to maximise the diffusion of oxygen and COThey have:

-An enormous surface area (about 75m squared in humans)

-A moist lining for dissolving gasses

-Very thin walls

-A good blood supply

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mia is a ****

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