Biology

B3 revision notes

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  • Created by: camber
  • Created on: 06-04-09 08:59

Gas exchange

· Life processes need gases or dissolved substances and waste substances need to be gotten rid of

· They move to where they need to be through:

o Diffusion: passive movement of particles in a gas or liquid from a region of high concentration to a region of low concentration

o Osmosis: water moving from through a partially permeable membrane from an area of high water concentration to an area of low water concentration

o Active transport: movement of particles through a membrane from a low concentration to a high concentration that requires energy from respiration

· Gas exchange surfaces are adapted to maximise effectiveness

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Gas exchange in plants

Gas exchange in plants – leafs are structured to be adapted for easy gas exchange

· Carbon dioxide diffuses into the leaf through the stomata: the leaf has a large flat surface area so the stomata can absorb a lot of carbon dioxide

· Air spaces inside leaf increase area of surface for carbon dioxide to get into the cells

· Water vapour and waste product of photosynthesis, oxygen, diffuse out the stomata

· Water vapour escapes by diffusion because there’s a lot of water inside the leaf and less outside. This diffusion is called transpiration and quickest in hot, dry, windy conditions.

· Size of stoma is controlled by guard cells and if a plant needs to reduce the amount of water being lost through transpiration the guard cells make the stoma narrower to stop water loss.

· If plant loses water faster then it is being replaced the roots it will wilt because water is needed to keep a plant turgid

· Plant needs water for solvent for minerals, photosynthesis and keep the plant cool on a hot day by allowing water to evaporate

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Breathing system

· Air you breathe in goes through the:

1. trachea

2. splits into two tubes that go into each lung called bronchi

3. split into smaller tubes called bronchioles

4. end at small bags called alveoli where gas exchange takes place

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• The alveoli maximise diffusion of oxygen and car

o Large surface area

o Moist lining to dissolve gases

o Thin walls

o Close to tiny blood vessels to diffuse easily

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Alveoli

· Deoxygenated blood (blood with carbon dioxide) enters the blood vessels and oxygen diffuses into the blood because there is a higher concentration of oxygen in the alveoli than the blood and the red blood cells pick up the oxygen

· Carbon dioxide diffuses out the blood because there is a higher concentration of carbon dioxide in the blood so ends up with oxygenated blood needed for respiration

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Breathing in:

o the intercostal muscles and the diaphragm contract

o causing the diaphragm to flatten

o rid cage and sternum to move up and out

o thorax volume increase

o causing pressure to increase

o and air forced out the lungs

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Breathing out:

o the intercostal muscles and diaphragm relax

o causing ribcage and sternum to move down and in

o volume of thorax decreases

o pressure decreases

o air is drawn in the lungs

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Villi

· Small intestine has millions of tiny projections called villi that uses diffusion and active transport to absorb products of digestion into the bloodstream

· Adaptations:

o They increase surface area so food can be absorbed more quickly into the blood

o Single cell thick wall to enable diffusion to happen quickly and enter the blood

o Good supply of blood capillaries to increase surface area so quantity of food absorbed per unit time is large

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