Biology 3

Life Processes and Microorganisms 

HideShow resource information

Gas and Solute Exchange (1)

  • Life processes need gases or other dissolved substances before they can happen e.g. Photosynthesis requires Carbon Dioxide
  • Waste Substances also need to be moved out of cells by:
  • Diffusion:
    • Particles move from a high area of concentration to a low area
    • Dissolved particles can diffuse in and out of cells via cell membranes 
  • Osmosis:
    • Only refers to water
    • Particles move across a partially permeable membrane 
    • From an area of high concentration to an area of low concentration
  • Active Transport:
    • The movement of substances against the concentration gradient
    • From an area of low concentration to an area of high concentration
  • Exchange Surfaces:
    • Are adapted to maximise effectiveness
    • They structure has to allow enough of the substances to pass through.
1 of 18

Gas and Solute Exchange (2)

The Structure of Leaves lets Gases Diffuse In and Out of Cells

  • C02 diffuses into the air spaces in the leaf then diffuses into cells where photosynthesis happens.
    • The leaf structure is adapted so this can happen easily
  • The underside of the leaf is an exchange surface and is covered in tiny holes called Stomata which the C02 diffuse through.
  • Water Vapour and Oxygen diffuse out through the Stomata.
  • The size of the Stomata is controlled by Guard Cells that close if the plant is losing to much water than can be replaced by the roots. 
    • Without them the plant would wilt.
  • The flattened shape of the leaf increases the area of the exchange surface so it is more effective. 
  • The walls of the cels inside the leaf form another exchange surface.
    • The air spaces inside the leaf increase the surface area so there is more chance for C02 to get into the cells.
2 of 18

The Breathing System

  • The Lungs
    • They are in the Thorax - the top part of your body.
    • They are separated from the lower part by the Diaphragm.
    • They are protected by the Ribcage.
    • The air you breathe in goes into the Trachea and splits into two tubes called Bronchi each one going to a lung.
    • Bronchi split progressively into smaller tubes called Bronchioles
    • The Bronchioles end at small bags called Alveoli where gas exchange takes place.
  • Breathing In
    • The Intercostal Muscles and Diaphragm contract (flatten out)
    • The Thorax increases in volume
    • This decreases the pressure drawing air in
    • The muscles between - ribs pull the Ribcage + Sternum up and out
  • Breathing Out
    • The Intercostal Muscles and Diaphragm relax (move up)
    • The Thorax decreases in volume and air is forced out.
    • The Ribcage + Sternum drop in and down.
3 of 18

Diffusion Through Cell Membranes

  • Gas Exchange happens in The Lungs
    • The Lungs Job is to transfer Oxygen to the Blood and remove water C02 from it.
    • To do this The Lungs contain million of air sacs called Alveoli where gas exchange takes place.
  • The Alveoli are specialised to maximise diffusion of Oxygen and C02:
    • They have an enormous surface area (75m squared in humans)
    • They have a moist lining for dissolving gases
    • They have very thin walls.
    • They have a ver large Blood Supply
  • The Villi are finer-like projections found inside the lining of the Small Intestine. They increase the surface area so digested food is absorbed more quickly into the blood.
    • They have a single layer of surface cells 
    • They have very good blood supply to assist quick absorption.
4 of 18

Active Transport

  • Root Hair Cells are specialised for absorbing water and minerals as they are cells on the surface of plant roots and grow into long hair that stick out go the soil which gives the plant a big surface area for absorbing stuff from the soil.
  • Root Hair Cells take in minerals using Active Transport:
    • The concentration of minerals is usually higher in the Root Hair Cell than the soil around it so diffusion doesn't work.
    • Active Transport allows the plant to absorb minerals against the concentration gradient which is essential for growth.
    • But Active Transport needs ENERGY from Respiration to make it work.
  • 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 is a higher concentration of Glucose and Amino Acids in the gut they diffuse naturally into the gut.
    • BUT when there is a lower concentration the concentration gradient is the wrong way so Active Transport is used.
5 of 18

The Circulatory System

  • The Heart is two pumps:
    • The right side pumps the deoxygenated blood to The Lungs to collect Oxygen and remove C02.
    • The left side pumps the oxygenated blood around the body.
  • Arteries carry blood away from The Heart at high pressure.
  • The Arteries split off into thousands of tiny Capillaries which take blood to every cell in the body.
  • The Veins then collect the used blood and carry it back to The Heart at low pressure.
  • The cycle starts over again. 


  • There are 4 chambers in The Heart. The top and bottom chambers are connected by valves.
  • Bloos arrives at the top chamber and leaves from the bottom chamber
  • To The Lungs = Pulmonary Artery, From The Lungs = Pulmonary Vein
  • To the body = The Aorta Artery
6 of 18


  • Capillaries
    • Use diffusion to deliver food and oxygen directly to the body tissues and take away C02 and other water materials
    • The walls are one cell thick = easy for stuff to pass in and out
  • Red Blood Cells
    • Carry O2 from Lungs to the body and C02 to from the body to Lungs.
    • Contain Haemoglobin + Oxygen = Oxyhaemoglobin
    • Have no nucleus and a concave shape to maximise surface area.
  • White Blood Cells
    • Fight Infections through: Antibodies, Antitoxins and Ingestion
    • Can move outside of the Blood Vessels + Made in Bone Marrow.
  • Plasma
    • Form the liquid part of the blood and transports stuff like hormones, blood cells, platelets, nutrients and glucose to all parts of the body.
  • Platelets
    • Make Blood Clots around cuts to prevent infection and stop bleeding.
7 of 18


  • Muscles are made from Muscle Cells which use oxygen to release energy from Glucose which is used to contract muscles.
  • An increase in muscle activity means a need for more Glucose and Oxygen.
  • It also means more C02 needs to be removed from the muscles cells which is done by increases the blood flow.
  • This is why physical activity:
    • Increases breathing make and you breathe more deeply 
    • Increase the speed at which your heart pumps
    • Dilates the arteries which supply blood to the muscles
  • Glycogen
    • Some glucose form food is stored as glycogen mainly in the liver but each muscles has its own store.
    • During vigorous exercise muscles use glucose rapidly and have to use their glycogen stores to provide more energy.
    • If exercise goes on for a while then the glycogen stores get used up
    • When the glycogen stores run low the muscles don't get the energy they need to keep contracting and so get tired.
8 of 18

Anaerobic Respiration

Glucose ---> ENERGY + Lactic Acid

  • It is when you do exercise without the presence of oxygen which leads to an incomplete breakdown of glucose which produces the mild poison lactic acid
  • Lactic Acid is not the best way to convert glucose into ENERGY because when lactic acid build up in muscles it can be very painful and makes the muscles tired.
  • Anaerobic Respiration doesn't release as much energy as Aerobic Respiration
  • An advantage is you can keep on using your muscles for a while longer.
  • Anaerobic Respiration leads to Oxygen Debt
    • It means you have to repay the oxygen that you didn't get to your muscles in time because your circulatory system couldn't keep up with the demand before.
    • It means you will be breathing hard after you stop yo oxidise the lactic acid to C02 and Water.
    • When high levels of C02 and Lactic Acid are detected in the blood by the brain the pulse and breathing rate stay high until they are gone.
9 of 18


Nephrons are the filtration units of the kidneys

  • 1) Ultrafiltration
    • High Pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's Capsule.
    • The membranes between the blood vessels and the Bowman's Capsule act like filters so big molecules like proteins and blood cells are not squeezed out and so stay in the blood.
  • 2) Reabsorption 
    • As the liquids flows along the nephron the useful substances are reabsorbed back into the blood:
      • All the sugar is reabsorbed using active transport
      • Sufficient Ions using active transport - excess ions are not 
      • Sufficient Water 
  • 3) Release of Waste
    • The remaining substances, including urea continue out of the nephron into the Ureter and down to the Bladder as Urine.
10 of 18

Kidney Failure

  • If The Kidneys don't work properly then waste substances build up in the blood and you are unable to control the levels of ions and water in your body which eventually results in death.
  • People with Kidney failure can be kept alive by having Dialysis Treatments where a machine takes the place of the kidneys:
    • Dialysis has to be done regularly to keep the concentration of dissolved substances in your body normal.
    • The persons blood flows along a selective permeable barrier surrounded by dialysis fluid which has the same concentration of of dissolved ions and glucose as healthy blood.
    • You have to have Dialysis Treatments 3 times a week for 3-4 hours.
  • Kidney Patients can also have Kidney Transplants from either an alive or dead donor.
    • This is currently the only cure available
    • The kidney can be rejected by the recipients immune system so the donor and recipient have to be closely matched.
    • Bone marrow has to be hit with radiation to prevent white blood cells from being produced and take Immunosupressive drugs.
11 of 18

Food and Drink from Microorganisms

  • People used to think that life could spontaneously generate from non-living material but evidence has shown that this isn't the case and supported:
    • The Biogenesis theory that says that things are created from other living organisms.
  • Louis Pasteur in 1859: Heated broth in 2 flasks which were left open to the air. One flask had a curved neck so bacteria and air would settle in the loop and no get to the broth. The broth with a curved neck stayed fresh proving that it was microbes and not air that caused it to go off.
  • Making Cheese
    • A culture of bacteria is added to milk which produces solid curds in it
    • The curds are separated to form the liquid Whey.
    • More bacteria is added and it is left to ripen.
  • Yoghurt Making
    • Milk is heat treated to kill of any bacteria then cooled before a starter culture of bacteria is added and the bacteria ferment in the Lactose Sugar present in milk to Lactic Acid.
    • The acid causes the milk to clot and solidify into yoghurt
    • Sterilised flavours are sometimes added.
12 of 18

Using Yeast

  • Yeast is a microorganism that is a single-celled fungus. A yeast cell has a nucleus, cytoplasm, a vacuole, a cell membrane surrounded by a cell wall.
  • Yeast can respire with or without oxygen:
    • Glucose ---> Ethanol + Carbon Dioxide + ENERGY
    • Glucose + Oxygen ---> Carbon Dioxide + Water + ENERGY
  • Yeast is used to make Bread:
    • The yeast in the bread dough converts sugars to Carbon Dioxide and some Ethanol but it is the Carbon Dioxide that makes the bread rise + as the bread expands it gets trapped in the dough making it lighter.
  • Yeast is used to make Beer:
    • The grain barley are allowed to germinate for a few days during which the starch in them is broken down into sugar by enzymes. The grains are then dried in a kiln = This process is called Malting.
    • The malted grain is mashed up and water is added to form a sugary solution and is sieved to remove the bits.
    • Hops are added to give it a bitter flavour.
    • The sugary solution is fermented by yeast turning the sugar into Alcohol
13 of 18

Microorganisms in Industry

  • Microorganisms are grown in fermenters (a container full of liquid culture medium which provide the right conditions for the microorganisms to grow and produce a useful product.) on a large scale.
    • Food is provided in the liquid culture medium.
    • Air is piped in to supply oxygen
    • The fermenters are cooled using water in water-cooled jackets 
    • Instruments monitor the pH level
    • Sterile conditions prevent contamination from other microorganisms
    • They are kept moving by a motorised stirrer which also helps maintain an even temperature.
  • Mycoprotein
    • Protein from Fungi and is a type of single-celled protein.
    • Used as a meat substitute for vegetarian meals e.g. Quorn
    • Grown in fermenters with glucose syrup as food 
    • Fungus respires aerobically so oxygen is supplied with ammonia
  • Penicillin - Discovered accidentally by Alexander Fleming in 1928
    • An antibiotic made by growing mould in a liquid culture medium containing sugar. Only starts to make penicillin after using most of the nutrients for growth.
14 of 18

Fuels from Microorganisms (1)

  • Fuels can be made by the fermentation of natural products and the waste products can often be used as well
  • Fermentation is when bacteria or yeast break sugars down by anaerobic respiration.
  • Ethanol 
    • Glucose ---> Ethanol + Carbon Dioxide + ENERGY
      • It is an anaerobic process
    • Sugar Cane Juices or Glucose from maize starch by carbohydrase
    • The Ethanol is distilled to separate it from the yeast and the remaining glucose before it is used.
  • Biogas
    • Is made by anaerobic fermentation of waste material
    • Usually 70% Methane and 30% Carbon Dioxide 
    • Lots of different microorganisms are used to produce Biogas
    • It is made in a simple fermenter called a digester to generator 
    • Biogas generators needs to be kept at a constant temperature
    • Biogas can't be stored as a liquid and needs to be used straight away
15 of 18

Fuels for Microorganisms (2)

  • Large-scale biogas generators are set up in a number of countries. 
  • Small-scale biogas generators are used to make enough gas for a village.
  • Human waste, waste form keeping pigs and food waste can be digested by bacteria to produce biogas. By-products are used to fertilise crops/gardens
  • Biogas Generators
    • Batch Generators - They are manually loaded with waste and make biogas in small batches and the by-products are cleared away at the end of each digesting session.
    • Continuous Generators - Waste is continuously fed in and biogas is being produced all the time at a steady rate. More suited to large scale biogas products.
    • All Biogas Generators have:
      • An inlet for waste material to be put in 
      • An outlet for the digested material to be removed through
      • An outlet so that the biogas can be piped to where it is needed
16 of 18

Fuels for Microorganisms (3)

  • When designing a generator you should consider:
    • Cost - Continuous gens are more expensive than Batch gens because the waste has to be mechanically pumped in 
    • Convenience - Batch gens are less convenient than continuous gens as they have to be continually loaded emptied and cleared
    • Efficiency - Gas is produced quickly at 35 degC so generators need to be insulated + gens shouldn't leak as gas will escape.
    • Position - The waste smells during delivery so gens should be placed away from homes + located close to a water source.
  • The Economic and Environmental Effects of Biofuels:
    • Biofuels are greener than fossil fusel as they are Carbon Neutral 
    • Biofuels don't produce sulphur dioxide which causes acid rain.
    • Burning Biogas means that Methane isn't released into the atmosphere and its a greenhouse gas. :{)
    • The raw material is cheep and easily available
    • Digested material is better fertiliser than undigested = better crops
    • Biogas Gens act as waste disposal systems - getting rid of waste that  otherwise caused disease and polluted water supplies
17 of 18

Using Microorganisms Safely

  • Microorganisms are grown on Agar Jelly in a Petri Dish.
    • Agar Jelly = Cultured Medium 
      • Poured hot into a s petri dish and set cold.
    • Microorganisms need nutrients which are added to the Agar Jelly:
      • Carbohydrates as an energy source
      • Mineral Ions
      • Supplementary Proteins and Vitamins
  • Equipment is sterilised to prevent contamination 
    • Unwanted microorganisms may = harmful things + cause disease.
    • Petri Dish and Growth medium must be sterilised before use
    • Inoculating loops used for transferring microorganisms to the growth medium are sterilised by passing them through a flame.
    • The Petri Dishes must have a lid to stop microorganisms in the air contaminating the culture and the lid is taped on.
  • The temperature must be kept low at 25 degrees C In school labs 
    • So harmful pathogens don't grow
    • In industry cultures are incubated at a higher temperature so they grow faster.
18 of 18


No comments have yet been made

Similar Biology resources:

See all Biology resources »