biology unit 3 revision

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  • Created by: tom
  • Created on: 09-04-13 19:59


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


v  Water moves in and out of cells by osmosis


v  Tissue fluid surrounds the cells in the body.


v  Tissue fluid will have a different concentration to the fluid inside a cell.

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Gas and solute exchange

v  Substances move by diffusion osmosis and active transport.

v  For photosynthesis to happen carbon dioxide and water have to get into plant cells, and for respiration to take place glucose and oxygen both have to get inside cells.

v  The structure of leaves lets gases diffuse in and out of cells.

v  Carbon dioxide diffuses into the air spaces within the leaf then it diffuses to where the photosynthesis happens.

v  Water vapour evaporates from the cells inside the leaf, and then it escapes by diffusion because there is a lot of air inside the leaf and less of it in the air outside.

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The breathing system

v  The lungs are in the thorax which is in the top part of your body.

v  Ventilation is breathing in and breathing out.

v  Artificial ventilators can help people breath in and out. They are machines that move air in and out of the lungs.

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Diffusion through cell membranes

v  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.

v  The alveoli are specialized to maximise the diffusion of oxygen and carbon dioxide. They have huge surface area, moist lining for dissolving gases, very thin walls and a good supply of blood.

v  The villi provide a really big surface area. It has a single layer of surface cells and a very good supply to assist quick absorption.


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Active transport

v  Root hairs are specialised for absorbing water and minerals

v  Root hairs take in minerals using active transport

v  We need active transport to stop us starving, because it is used in the gut when there is a low concentration of nutrients in the gut but a high concentration of nutrients in the blood.

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Water flow through plants

v  Phloem tubes transport food made in the leaves to growing regions.

v  Xylem tubes take water up, it is made from dead cells joined end to and with no end walls between them and a hole down the middle. They carry water and minerals from the roots and to the stem and leaves in the transpiration stream.

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Circulatory system – the heart

v  Humans have a double circulatory system –two circuits joined together.  The first one pumps deoxygenated blood to the lungs to take in oxygen. The second one pumps oxygenated blood around all other organs of the body.

v  The heart contacts to pump blood around the body.

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Circulatory system – blood

v  Red blood cells carry oxygen

v  White blood cells defend against disease

v  Platelets help blood clot which heals wounds and cuts.

v  Plasma is the liquid that carries everything in the blood – antibodies and antitoxins produced by the white blood cells.

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Circulatory system – blood vessels

v  Blood vessels are designed for their function

v  Three different types of blood vessels – arteries, capillaries and veins.

v  Arteries carry blood under pressure

v  Capillaries are really small

v  Veins take blood back to the heart.

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Circulation aids

v  Artificial blood can keep you alive in an emergency

v  The heart can be repaired with artificial parts

v  Stents keep arteries open

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v  Homeostasis is the maintenance of constant interval environment.

v  Body temperature must be carefully controlled

v  When your too hot – hairs lie flat, sweat is produced

v  When your too cold – hair stands up to trap an insulating layer of air, no sweat is produced


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Kidney failure

v  The kidneys remove waste from the blood; if they stop working then you can’t control the levels of ions in your blood.

v  Dialysis machines filter the blood

v  Transplanted organs can be rejected by the body

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Kidney failure

v  The kidneys remove waste from the blood; if they stop working then you can’t control the levels of ions in your blood.

v  Dialysis machines filter the blood

v  Transplanted organs can be rejected by the body

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Controlling blood glucose

v  Insulin and glucagon control blood glucose level


Blood glucose level too high = insulin is added

Blood glucose too low = glucagon is added


v  Type 1 diabetes is cause by a lack of insulin

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Human impact on the environment

v  There are over six billion people in the world which are using up a lot of resources.

v  We produce more waste which increases more and more pollution.

v  More people means less land for plants and other animals to live.

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Carbon dioxide and the greenhouse effect

v  Carbon dioxide is removed from the air and stored in various places.

v  It is stored in places such as oceans and lakes, green plants, and peat bogs.

v  Carbon dioxide and methane trap heat from the sun

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Deforestation and peat bogs

v  Deforestation means chopping down trees

v  Deforestation leads to four main problems

-          More methane in the atmosphere

-          More carbon dioxide in the atmosphere

-          Less carbon dioxide taken in

-          Less biodiversity


v  Destroying peat bogs adds more co2 to the atmosphere

v  Bogs are areas of acidic and waterlogged plants.

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v  Fuels can be made by fermentation

v  Ethanol is made by anaerobic fermentation of sugar

v  Glucose à ethanol + carbon dioxide + energy

v  Biogas is made by anaerobic fermentation of waste material

v  Fuel production can happen on a large or small scale

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