Life Processes

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

  • A partially membrane is just one with very small holes in it. So small that only tiny molecules like water can pass through them and bigger molecules like sucrose can not
  • The water particles molecules pass both ways through the membrane during osmosis. This happens because water particles move about randomly all the time
  • But because there are more water molecules on one side than the other, there's a steady net flow of water into the region with fewer water molecules
  • This means that solutions such as strong sugar solutions get more dilute. The water acts like it's trying to even up the concentration either side of the membrane
  • Osmosis is a type of diffusion- passive movement of particles from an area of high water concentration to an area of low water concentration 
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Water moves in and out of cells by Osmosis

  • Tissue fluid surrounds the cells in the body- it's basically just water with oxygen, glucose and stuff dissolved in it. It's squeezed out of blood capillaries to supply the cells with everything they need.
  • The tissue fluid will normally have a different concentration to the fluid inside the cell. This means that water will either move into the cell from the tissue fluid or out of the cell by Osmosis
  • If a cell is short of water, the solution inside it will become quite concentrated. This usually means the solution outside is more dilute and so water will move into the cell by osmosis
  • If a cell has lots of water, the solution inside will be more dilute, and water will be drawn out of the cell and into the fluid outside by osmosis
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Experiment to show osmosis works

  • Firstly cut up potato into identical cylinders 
  • Get some beakers and with different sugar solutions in them, one should be pure water and the others should be very concentrated sugar solution and you can have a few others with concentrations in between
  • Then measure the length of the cylinders and leave one in each of the beakers for half an hour
  • Then take them out and measure them again
  • If the chips are longer they have taken in water via osmosis
  • If they are shorter they have had water drawn out


  • Independent- Concentration of sugar solution
  • Dependent- Chip length
  • Things which should be the same- Volume of solution, temperature, time, type of sugar used 
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Substances move by diffusion types of diffusion

  • Life processes need gases or other dissolved substances before they can happen
  • For example, for photosynthesis to happen, carbon dioxide and water have to get into plant and for respiration to take place glucose and oxygen both have to get inside cells.
  • Waste substances also need to move out of the cells so that the organism can get rid of them
  • Diffusion is where particles move from a high concentration to an area of low concentration
  • Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to an area of low water concentration
  • Active transport moves substances from a low concentration to a high concentration 

Exchange surface are adapted to maximise effectiveness:

  • They are thin so substances only have a short distance to diffuse
  • They have a large surface area so lots of substances can diffuse at once
  • exchange surfaces in animals have lots of blood vessels to get stuff in and out of the blood quickly
  • Gas exchange surfaces in animals are often ventilated too- air moves in and out

Exchange substances gets more difficult in bigger and more complex organisms- the place where the substances are needed ends up being along way away from exchange surfaces

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Gases in leaves

  • Carbon dioxide diffuses into air spaces within the leaf, then it diffuses into cells where photosynthesis happens. The leaf's structure is adapted so that it can happen easily
  • The underneath of the leaf is an exchange surface. It's covered in little holes called stomata which the carbon dioxide diffuses through
  • Oxygen and water vapour also diffuse out through the stomata.
  • the size of the stomata are controlled by guard cells. These close if the plant is losing water faster than it is being replaced by the roots. without these guard cells the pant would wilt
  • The flattened shape of the leaf increases the area of this exchange surface so that it's more effective
  • The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increases the area of this surface so there's more chance for carbon dioxide to get into the cells

The water evaporates from the cells inside the leaf. Then it escapes by diffusion because there is lots of it inside the leaf and less of it in the air outside. Evaporation is quickest in hot, dry and windy conditions.

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Breathing System

  • The lungs are in the thorax
  • The thorax is the top part of your body
  • It's separated from the lower part of the body by the diaphragm
  • The lunges are like big pink sponges and are protected by the ribcage
  • The air that we breath in goes through the trachea. This splits into two tubes called bronchi one going in each lung
  • The bronchi split progressively smaller tubes called bronchioles
  • The bronchioles end at small bags called alveoli where gas exchange takes place 

Breathing in

  • Intercostal muscles and diaphragm
  • Thorax volume increases
  • This decreases the pressure drawing in air

Breathing out

  • Intercostal muscles and diaphragm relax
  • Thorax volume decreases
  • This increases the pressure so air is forced out
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Artificial ventilators

Artificial ventilators help people to breath

  • Ventilators are machines that move air into or out of the lungs. They help people who can't breath by themselves
  • They used to be a giant case from the neck to the abdomen with only the patients head poking out. Air was pumped out of the case pressure dropped the lungs expanded and so air was drawn into the lungs. Air pumped into the case and had the opposite effect forcing air out of the lungs. However they could interfere with blood flow to the lower body
  • Nowadays, most ventilators work by pumping air into the lungs. This expands the ribcage- when they stop pumping, the ribcage relaxes and pushes air back out of the lungs. This doesn't interfere with blood flow, but it can occasionally cause damage (e.g damage alveoli) if the lungs can't cope with the artificial air flow
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Diffusion happen in the lungs

Gas exchange happens in the lungs

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

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

3) The alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide. They have:

  • An enormous surface area 
  • a moist lining for dissolving gases
  • very thin walls
  • a good blood supply

The villi provide a really big surface area

  • The inside of the small intestine is covered in millions and millions of these tiny little projections called villi
  • They increase the surface area in a big way so that digested food is absorbed much more quickly into the blood
  • They have a single layer of surface cells and a very good supply to assist quick absorption
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Active transport

Sometimes substances need to be absorbed against a concentration gradient i.e from a low concentration to a high concentration.

We need active transport to stop us starving

Active transport 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

  • When there's a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood 
  • BUT- sometimes there's a lower concentration of nutrients in the gut than there is in the blood
  • This means the concentration gradient is wrong
  • This requires active transport which uses energy from respiration
  • Active transport allows nutrients to be taken into the blood, despite the fact the concentration gradient is wrong
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Root Hair Cells- Active transport

Root hair cells are specialised to absorb water and minerals

  • The cells on the surface of the plant roots grow into long hairs which stick out into the soil
  • This gives the plant a big surface area for absorbing water and mineral ions from the soil
  • Most of the water and mineral ions that get into the plant are absorbed by root hair cells

Root hairs take in minerals using active transport

  • The concentration of minerals is normally higher in the root hair than the soil around it
  • So normal diffusion doesn't explain how minerals are taken up into the root hair cell
  • They should go the other way if they followed the rules of diffusion
  • The answer is active transport
  • Active transport allows the plant to absorb minerals from a very dilute solution, against a concentration gradient. This is essential for its growth. But active transport needs energy from respiration to make it work
  • Active transport also happens in humans, for example in taking in  glucose from the gut and from kidney tubules
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Water flow through plants

Phloem tubes transport food:

  • Made of columns of living cells with small holes in the ends to allow stuff to flow through
  • They transport food substances (mainly dissolved sugars) made in leaves to growing regions like new shoots and storage organs (e.g root tubers) of the plant 
  • The transport goes in both directions

Xylem tubes take water up:

  • Made of dead cells joined end to end with no end walls between them and the hole down the middle
  • They carry water and minerals from the roots to the stem and leaves in the transpiration stream
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Transpiration is the loss of water from a plant

  • Transpiration is caused by evaporation and diffusion of water from the inside of leaves
  • This creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through xylem vessels to replace it 
  • This in turn means more water is drawn up from the roots and so there's a constant transpiration stream of water through the plant
  • Transpiration is just a side-effect of the way leaves are adapted to photosynthesis. They have to have stomata in them so that gases can be exchanged easily. Because there's more water inside the plant than in the air outside, the water escapes from the leaves through the stomata 
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Circulatory system

Its main function is to get food and oxygen to every cell in the body. As well as being a delivery service, it's also a waste collection service- it carries waste products like carbon dioxide and urea to where they can be removed from the body.

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. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped out to the lungs again
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The heart contracts to pump blood around the body

  • The heart is a pumping organ taht keeps blood pumping around the body. The walls of the heart are mostly made of muscle tissue
  • The heart has valves to make sure that blood goes in the right direction- they prevent it flowing backward

 This is how the heart uses its four chambers to pump blood around:

  • Blood flows into the two atria from the vena cava and the pulmonary vein
  • The atria contract, pushing the blood into ventricles
  • The ventricles contract, forcing the blood into the pulmonary artery and the aorta, and out of the heart
  • The blood then flows to the organs through arteries, and returns through veins
  • The atria fill again and the whole cycle starts over
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Types of blood vessels


These carry the blood away from the heart


These are involved in the exchange of materials at the tissues


These carry the blood to the heart

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Blood vessels

Arteries carry blood under pressure

  • The heart pumps the blood out at high pressure so the artery walls are strong and elastic
  • The walls are thick compared to the size of the hole down the middle the lumen
  • They contain thick layers of muscle to make them strong, and elastic fibres to allow them to stretch and spring back

Veins take blood back to the heart

  • Capillaries eventually join up to form veins
  • The blood is at lower pressure in the veins so the walls don't need to be as thick as artery walls
  • They have a bigger lumen than arteries to help the blood flow despite the lower pressure
  • They also have valves to help keep blood flowing in the right direction


Arteries branch into capillaries. Capillaries are really tiny- too small to see. They carry blood really close to each cell in the body to exchange substances with them. They have permeable walls, so substances can diffuse in and out. They supply food and oxygen and take away waste like carbon dioxide. Their walls are usually one cell thick. This increases the rate of diffusion by decreasing the distance over which it occurs

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The blood- cells

Red blood cells carry oxygen

  • The job of red blood cells is to carry oxygen from the lungs to all the cells in the body
  • They have a doughnut shape to give a large surface area for absorbing oxygen
  • They don't have a nucleus- this allows more room to carry oxygen
  • They contain a red pigment called haemoglobin
  • In the lungs, haemoglobin combines with oxygen to become oxyhaemoglobin. In body tissues, the reverse happens- oxyhaemoglobin splits into haemoglobin and oxygen, to release oxygen to the cells

White blood cells defend against disease

  • They can change shape to gobble up unwelcome micro-organisms
  • They produce antibodies to fight micro-organisms, as well as anti-toxins to neutralise any toxins produced by micro-organisms
  • Unlike red blood cells, they do have a nucleus
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Platelets and plasma

Platelets help blood clot

  • These are small fragments of cells
  • Have no nucleus
  • They help the blood to clot at a wound, to stop all of your blood pouring out and to stop micro-organisms getting in
  • Lack of platelets can cause excessive bleeding and bruising

Plasma is the liquid that carries everything in blood

This is a pale straw-coloured liquid which carries just about everything:

  • Red and white blood cells and platelets
  • Nutrients like glucose and amino acids. These are the soluble products of digestion which are absorbed from the gut and taken to the cells of the body
  • Carbon dioxide from the organs to the lungs
  • Urea from the liver to the kidneys
  • Hormones 
  • Antibodies and antitoxins produced by white blood cells
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Artificial blood

Artificial blood can keep you alive in an emergency

  • When someone loses a lot of blood, e.g in an accident, their heart can still pump the remaining red blood cells around as long as the volume of the blood can be topped up
  • Artificial blood is a blood substitute, e.g a salt solution, which is used to replace the lost volume of blood. It's safe (if no air bubbles get into the blood) and can keep people alive even if they lose 2/3 of their blood cells. This may give the patient enough time to produce new blood cells. If not, the patient will need a blood transfusion
  • Ideally, an artificial blood product would replace the function of the red blood cells, so that there's no need fro a blood transfusion. These are being developed but currently have problems with side-effects

Stents keep arteries open

  • Coronary heart disease is when the arteries that supply the blood to the muscle of the heart get blocked by fatty deposits. This causes arteries to become narrow and blood flow is restricted- can cause heart attack
  • Stents are tubes that are inserted inside arteries. They keep them open, making sure blood can pass through to the heart muscles. This keeps the person's heart beating
  • Stents are a way of lowering the risk of a heart attack in people with coronary heart disease
  • But over time, the artery can narrow again as stents can irrtate the artery and mke scar tissue grow. The patient also has to take drugs to stop blood clotting on the stent
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The heart can be repaired with artificial parts

  • Artificial hearts are mechanical devices that are out into a person to pump blood if their own heart fails. They're usually used as a temporary fix, to keep a person alive until a donor heart can be found. In some cases they're used as a permanent fix, which reduces the need for a donor heart
  • The main advantage of artificial hearts is that they're not rejected by the body's immune system. This is because they're made from metals or plastics, so the body doesn't recognise them as 'foreign' and attack in the same way as it does with living tissue
  • But surgery to fit an artificial heart can lead to bleeding and infection. Also, artificial hearts don't work as well as healthy natural ones- parts of the heart could wear out or the electrical motor could fail. Also blood doesn't flow through artificial hearts as smoothly, which can cause blood clots and lead to strokes. The patient has to take drugs to thin their blood and make sure this doesn't happen, which can cause problems with breeding if they're hurt in an accident
  • If it's just the heart valves which are defective, they can be replaced by mechanical valves 
  • Replacing a valve is a much less drastic procedure than a whole heart transplant. But fitting artificial valves is still major surgery and can still cause problems with blood clots.
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Homeostasis is the maintenance of a constant internal environment

There are six main things which need to be controlled 

  • The body temperature can't get too hot or cold
  • Water content must not get too high or low, or too much water could move into or out of cells and damage them.
  • If the ion content of the body is wrong, the same thing could happen as above
  • The blood sugar levels need to stay within certain limits
  • Carbon dioxide is a product of respiration. It's toxic in high quantities so it's got to be removed. It leaves the body by the lungs when you breath out
  • Urea is a waste product made from excess amino acids.
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Body temperature

  • All enzymes work best at a certain temperature. The enzymes within the human body work best at about 37 degrees. If the body gets too hot or cold, the enzymes won't work properly and some really important reactions could be disrupted. In extremes cases, this could lead to death
  • There is a thermoregulatory gland in the brain which acts as your own personal thermostat
  • It contains receptors that are sensitive to the temperature of the blood flowing through the brain
  • The thermoregulatory centre also ecieves impulses from the skin, giving info about skin temperature
  • If you're getting too hot or cold, your body can try to cool you down or warm you up:
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Kidneys- Removal of urea

  • Proteins can't be stored in the body - so any excess amino acids are converted into fats and carbohydrates which can be stored
  • This process occurs in the liver. Urea is produced as a waste product from the reactions
  • Urea is poisonous. It's released into the bloodstream by the liver, the kidneys then filter it out of the blood. It is then temporarily stored in the bladder in Urine and excreted from the body
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Kidneys- Three main jobs

Removal of Urea

  • Proteins can't be stored in the body - so any excess amino acids are converted into fats and carbohydrates which can be stored
  • This process occurs in the liver. Urea is produced as a waste product from the reactions
  • Urea is poisonous. It's released into the bloodstream 

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