Biology - B3

A brief summary of each topic within B3.

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Gas and Solute Exchange.


  • High Concentration to Low Concentration.
  • e.g.) When Bad smell spreads through a room.
  • e.g 2.) Dissolved particles diffuse through cell membranes.


  • Same as Diffusion, only happens in water through a partically permeable membrane.

Active Transport.

  • Only occurs when something diffuses against concentration gradient. (Low concentrationt to High concentration)

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Gas and Solute Exchange - Continued -

  • The Underneath of a leaf is called the exchange surface. Which is covered in Stomata (Little Holes). Carbon Dioxide, water and oxygen diffuse through these. 
  • If a plant is losing water faster than it is being replaced, then the stomata will close. This is why the stomata is important as without it, the plant would wilt. 
  • The Flattened shape increases the area of exchange.
  • And The walls of the cell have air spaces in which increase the chance of Carbon Dixoide getting into the cells. 


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Breathing In.

  • Intercostal Muscles and Diaghragm Contract.
  • Draws air in.

Breathing Out.

  • Intercostal Muscles and Diaghragm relax. 
  • Thorax volume decreases thus squeezing air out. 

Air travels down the trachea. 

Air splits of down the Bronchi (each one called a Bronchus).

Each Bronchus split off into Bronchioles. 

Bronchioles lead to alveoli

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Diffusion through Cell Membranes

Lungs transfer oxygen to the blood and remove Carbon Dioxdie. 

This is what Alveoli are for. 

They have:

  • Large Surface Area
  • Moist Lining
  • Thin Walls
  • Capious blood supply. 


Small intestine is covered in Villi.

They increase the surface area for digested food to be absorbed. 

They have a very good bloody supply and a single layer of surface cells. 

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Active Transport

Root Hair Cells. 

Big Surface area - Absorbs water and Mineral ions.

Concentration of minerals and water is higher in the root hair cell than in the soil. 

This is why the minerals go into the cell by Active Transport as it is against the concentration gradient. (From Low concentration to a high concentration)

Energy from respiration is needed for Active Transport.

Active transport also happens in Gut. 

Sometimes gut has lower concentration of nutrients than in the blood this is why active transport happens.

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Circulatory System.


Right Side of Heart.                                                                        Left side of heart.

De-oxygenated blood.                                                   Oxygenatenated blood.

Arteries - Carry blood Away (from heart) at high pressure.

Arteries usually split off into tiny capillaries which take blood to every cell.

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Very small hole through the middle. They're One cell thick - Easy for stuff to push through. Capillaries deliver food and oxygen and Take away Carbon Dioxide and Waste.


1.) White Blood Cells. 2.)Red Blood Cells. 3.)Plasma. 4.)Platelets. 

Plasma Carries - 

  • Hormones
  • Urea
  • Glucose and Amino Acids
  • Red and White Blood cells 
  • Antibodies and Antitoxins
  • Carbon Dioxide.

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(Muscle Cells use oxygen to release energy from glucose.) - Respiration contracts muscles. 

When the muscle activity increases, more oxygen and glucose is needed. Also carbon dioxide needs to be removed from the cells more quickly, this all means that blood must flow at a faster rate. 

This means - Breathing rate increases, Heart pumps more and Arteries Dilate

 Glycogen. - When glucose is used up...

  • Glucose is from food and some is stored as glycogen.
  • Each muscle has its own store of glycogen.
  • When Exercising vigorously, glucose is often used up so the body resorts to glycogen.
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Exercise (2)

Anaerobic Respiration - When Oxygen has been used up. 

  • Vigorous exercise means that muscles can't get enough oxygen, so muscles start doing anaerobic respiration, which is the break down of glucose without oxygen. Which produces lactic acid.
  • The problem with this is, when Lactic acid builds up, the muscles get painful. 

Anaerobic Respiration - Oxygen Debt.

  • If the body resorts to anaerobic respiration, when you stop exercising you will have oxygen debt which is where your body repays the oxygen your muscles didn't get while exercising. 
  • This is why you keep breathing hard after you stop exercising. It oxidises the lactic acid into harmless Carbon dioxide and water.
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High pressure builds up which squeezes:-

  • Water 
  • Urea
  • Ions
  • Sugar - out of blood into 'bowman's capsule.'
  • The membranes between the blood vessel and the bowman's capsule act as filters, so no large molecules like protein can get through (they stay in the blood).
  • The liquid flows along the Nephron and the useful substances are reabsorbed into the blood:-
  • Sugars (Active Transport)
  • Sufficient ions (Active Transport)
  • Sufficient Water.
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Kidney Failure.

If the kidneys don't work then there is a build up of waste in the body. This means the person loses the ability to control levels of ions and water in the body, this could result in death. 

  • Dialysis treatment filters the blood. - It has to be done regularly to keep levels of waste at a norm. 
  • Blood flows along a selectively permeable barrier, surrounded by dialysis fluid. 
  • The barrier is permeable to ions and waste substances (just like the membranes in the kidneys). Any excess ions and water diffuse across the barrier. 
  • It has to be done three times a week and takes 3-4 hours. 
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Kidney Failure (Little extra details)

Transplant organs.

  • Organ can be treated as a foreign body and get rejected.
  • Donor must have similar tissue type to patient.
  • Bone marrow is zapped with radiation to stop white blood cells from being produced and attacking the transplant organ.
  • Drugs are given to suppress the Immune system so it doesn't try to fight off the transplant organ. 
  • This means the patient CANNOT get ill as they will not be able to fight it off.
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Using Yeast.

Yeast is a single-celled fungus. It has:

  • Nucleus
  • Cell Wall
  • Cell Membrane
  • Vacuole
  • Cytoplasm

Yeast can respire without Oxygen.

Aerobic respiration of glucose with yeast:

Glucose ----> Ethanol + Carbon Dioxide + Energy.

Respiring with Oxygen.

Glucose + Oxygen ----> Ethanol + Carbon Dioxide + Energy. 

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Yeast - To make Bread and Beer.


  • Yeast converts sugar into Carbon Dioxide and Ethanol.
  • Carbon dioxide makes the bread rise. 
  • It expands and gets trapped in the dough, making it light


  • Beer is made from barley. The barely is allowed to germinate for a few days.
  • This gives time for the starch in the grains to be broken down, by enzymes, into sugar.
  • The grains are then dried in a kiln. (MALTING)
  • Malted grain is mashed up and water is added which makes a sugary solution which is then sieved. 
  • Hops are then added.
  • The solution is then fermented by yeast. The yeast turns the sugar into alcohol. 
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Microorganisms in Industry.

Microorganisms used to make many substances on a large scale:

  • Penicillin
  • Mycoprotein
  • Biogas + Ethanol

Microorganisms are grown on a large scale in large vessels called Fermenters.

  • Stirrers - To maintain the right temperature.
  • Air Supply - Provide oxygen for respiration.
  • Water Cooled Jacket - Removes heat.
  • Instruments - To monitor factors (pH/Temperature)
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Penny Eaton

Great notes! really helped me understand, thankyou!! :)


really useful :)


Very common Grammatical/ Spelling error:

Page 3/15:

"Air splits of down the Bronchi"

Instead of:


Sophie Courtier

It was a typing error rather than a spelling error..


these are so good sophie! the grammatical/spelling errors really don't bother me seeing as this is biology not english..

Sophie Courtier

Hahahaha Thankyou alice! :) 

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