AQA Biology Unit 3 (B3)

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  • Created by: Triciaaa
  • Created on: 11-04-13 18:51

Dissolved Substances (B3.1.1)

Dissolved Substances

  • Osmosis - the net movement of water from a high water concentration to a low water concentration down a water concentration gradient through a partially permeable membrane
  • Diffusion - the net movement of molecules from a high concentration to a lowconcentration until the concentration is the same
  • Active Transport - the movement of substances from an area of low concentration to ahigh concentration using energy from respiration that fights against the concentration gradient.  
  • Soft drinks = sugar (energy release in exercise in muscles) water + ions (sweating e.g. Na ions) Rehydration is when we lose more ions than needed so cells dont work efficiently 
  • Exchanging materials most effective = good blood supply, large SA, thin, ventilation
  • Alveoli (lungs) large SA, thin walls of alveolus, bloody supply, ventilated 
  • Villi (intestine) large SA, thin walls, good blood supply (lots of mitochondria in microvilli)
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Gaseous Exchange (B3.1.2)

Gaseous Exchange

  • Thorax - upper part of the body (protected by the ribcage)
  • Abdomen - lower part of the body (by the diaphragm) 
  • Breathing system - 02 must diffuse INTO the bloodstream, Co2 must diffuse OUT
  • Ventilation - breathing in and out
  • Inspiration = intercostal muscles+diaphragm contract, thorax volume increases, pressure decreases, air is drawn in 
  • Expiration = intercostal muscles+diaphragm relax, thorax volume decreases, pressure increases, air forced out
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Exchange Systems in Plants (B3.1.3)

Exchange Systems in Plants

  • Water is absorbed by roots in the soil
  • Co2 enters leaves by diffusion 
  • Root hair cells have adaptations to obtain optimum amounts of minerals:
    - long hairs, stick to the soil
    - large SA, absorb water+ions
    - active transport (dilute solution in soil therefore it uses energy from respiration to work against the concentration gradient)
  • Stomata are located at the bottom of the plant (obtain Co2, release o2) 
  • Transpiration (plants lose water from the surface of their leaves continuously)
    - lost through stomata at the bottom of leaves
  • Conditions that increase rates of transpiration: hot, dry, windy
  • Stomata open - cells take in water, inflate, thin walls stretch, curves the cell, stoma opens
  • Stomata closed - guard cells lose water, deflate, cells no longer curvy, closes the stoma 
  • Plants close the stomata when transpiration rates increase because they're unable to absorb enough water from soil therefore have to replace the water lost)
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The Blood System (B3.2.1)

  • Circulatory system - transporting substances e.g. food and o2 around the body to cells
  • Double circulatory system involves...
    deoxygenated blood > lungs > oxygenated blood > heart > pumped around body 
  • Heart
    1. blood enters atria from the vena carva + pulmonary vein 
    2. atrium contracts pushing the blood to the ventricles
    3. ventricles contract forcing the blood to the pulmonary artery + aorta
    4. blood flows to organs, through arteries, returns to veins
    5. atria is full again, cycle continues
  • Arteries - thick walls, muscle+elastic tissue, when contracts-prevents blood flow
  • Veins - thin walls, blood flows at low pressure, prevents back flow by having valves
  • Capillaries - narrow thin walled blood vessels, diffusion rate is quick as its 1 cell thick
  • Stents - metal wire meshes, open up the artery, it collapses to a small diameter over a balloon catheter, once expanded, the catheter is removes
  • Heart valves - biological valves or mechanical valves (2 semicircular carbon leaflets that pivot on hinges (strong, lasts long but can damage RBC - increase blood clots
  • Artificial heart
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The Blood (B3.2.2)

  • Roles of the blood
    - provide needed materials to the cells in the body
    - remove waste materials
  • Blood is a tissue consisting of a fluid called plasma that has...
    - Red blood cells - transports o2, biconcave, no nucleus (more space for haemoglobin)
    - White blood cells - defence system against pathogens, antibodies engulf pathogens
    - Platelets - small fragments of cells, no nucleus, reduces blood loss by clotting
  • Plasma transports...
    - soluble products from small intestine to other organs e.g. sugars and amino acids
    - carbon dioxide from organs to lungs
    - urea from liver to the kidneys (formed by excess amino acids) 
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Transport Systems in Plants (B3.2.3)


  • xylem transports water and mineral ions from the roots to the stem + leaves
  • constant movement of this process is called transpiration stream
  • driven by evaporation of water
  • xylem vessels are dead = no content forming long tubes
  • thick rigid wall to prevent it from collapsing


  • carries dissolved sugars from the leaves to the rest of the plant e.g storage organs and growing regions
  • there are living tissues even though the sieve tube doesnt have a nucleus
  • companion cells = sugars transported by active transport
  • end walls have holes to make movement easy 
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Removal of Waste & Water Control (B3.3.1)

Homeostasis is the maintenance of a constant internal environment

There are 4 things a body needs at the right level:
1. Body temperature
2. Water & Ion content
4. Blood sugar 
There are 2 waste products
1. Carbon dioxide (product from respiration) removed by the lungs when we breathe out
2. Urea (waste product from excess amino acids) removed by kidneys, stored in bladder

Body Temperature

1. the thermoregulatory centre in the brain acts as a personal thermostat
2. it contains receptors that are senstive to blood temperature flowing through the brain
3. they receive impulses from the skin, giving info about the temperature

  • TOO COLD - hair erector muscles contracts, hair stand up, blood vessels constrict
  • TOO HOT - hair erector muscles relax, sweat glands produce sweat, blood vessels supplying the skin dilate so more blood flows to the surface (evaporation) 
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Removal of Waste & Water Control (B3.3.1) Part 2

Kidney Roles:
1. Remove urea from the blood
 - Proteins can't be stored therefore the amino acids convert to fats and carbohydrates
 - This process occurs in liver
 - Urea is released in the bloodstream (kidneys filter the blood and remove it) 
2. Adjustment of ions in the blood
 - Cells can be damaged if the balance between ions and water isn't right
 - Excess ions are removed by kidneys e.g. Na ions from too much salty food or sweat
3. Adjustment of water content of the blood 
 - lost in urine, sweat, air breathed out
Kidney failure = losing the ability to control levels of ions + water in the body 
Kidney dialysis (3x a week for 3hours that can cause blood clots or infections) 
- blood flows selectively permeable barrier surrounded by a dialysis fluid
- fluid = same conc. as dissolved ions and glucose (so they're not diffused out or lost) 
- waste substances diffused out 
Kidney transplant 
- kidneys with the same tissue type reduce chances of rejection (from the antibodies attacking antigens) 
-immunosuppresent drugs suppress the immune system but also cause other infections 

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Sugar Control (B3.3.3)

Blood glucose concentration

  • Most foods contain carbohydrates that is converted into glucose, into blood from gut
  • Metabollism of cells and exercise = remove glucose from blood
  • The pancreas is responsible for regulating the blood glucose levels using insulin & glucagon 
  • INSULIN = too much glucose > pancreas secretes insulin > lowers blood sugar conc > allows glucose to move from blood to cells > glucose converts to glycogen by liver
  • GLUCAGON = too little glucose > pancreas secretes glucagon > converts to glucose > liver turns glycogen into glucose to be released as energy 


  • Type 1 diabetes (produce very little or even no insulin) = patients unable to reduce blood glucose levels) 
  • Controlling levels of glucose:
    1. avoid carbohydrate rich foods
    2. inject insulin
    3. exercise
    4. pancreas transplant (but can reject the tissue) 
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Waste From Human Activity (B3.4.1)

Reasons for the rapid population growth:
1. Green evolution - agricultural advances > increase productivity > more food available
2. Industrial revolution - technology improvements > increase standards of living 
3. Advances in medicine - increase in research & development e.g. smallpox, malaria
4. Hygiene - more clean water > better sanitation > reduce disease transmission 

Impacts on growth
1. Loss of habitats 
2. Lack of raw materials 
3. Lots of waste 
- Water (sewage, toxic chemicals pollute lakes and oceans, also damages fertilisers) 
- Land (toxic chemicals for farming e.g. pesticides, nuclear and household waste)
- Air (smoke and gases e.g. sulfur dioxide causes acid rain 

Greenhouse effect and carbon dioxide
Removing Co2 = carbon sequestrian
1. photosynthesis (plants store carbon compounds that remove Co2) 
2. peat bogs (acidic and waterlogged areas that absorb Co2) 
3. oceans, lakes, ponds
4. carbonate rocks (creatures that absorb Co2 and buried at the bottom of the seabed) 

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Deforestation and Peat Bogs (B3.4.2)

Large Scale Deforestation
Why is there an increase in deforestation?
1. Timber (building materials) 
2. More land for crops e.g. food crops or biofuel crops (fuel derived from ethanol) 
3. More land for locals to live in (increase in population) 

Impacts on large scale deforestation?
1. More methane (increase in cattle and rice fields, more microorganisms decompose the material releasing methane) 
2. More carbon dioxide (microorganisms feed on dead wood, releasing co2 as respiration)
3. Less absorbtion of carbon dioxide (less trees, less photosynthesis)
4. Lack of biodiversity 

Peat Bogs
- Plants that live in bogs don't fully decay as it is too acidic and there's a lack of 02
- The partially dead material build up and store carbon rather than it being released
- Uses - compost for gardeners (but peat free compost is more beneficial as it reduces     the demand for peat) , cut up and dried to make fuels 


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Climate Change (B3.4.2)

Consequences of Global Warming:

  • Climate Change e.g. longer droughts 
  • Sea Level Rise water molecules expand
  • Reduction in Biodiversity
  • Changes in Migration Patterns more species migrate to norther parts where its warmer
  • Changes in Distribition of Species more widely distributed for warmer temperatures 

Collecting data 

  • Satellites are used to monitor snow&ice cover or sea surface temperatures 
  • Only useful with wide areas and a long enough time scare 
  • Helps governments make decisions 
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Biofuels (B3.4.3)

- produced from living plant material
- Ethanol can be produced by sugar and maize:
1. Extract the sugar cane to obtain the juice through fermentation by yeast - ANA. RESP)
2. Distill the fermentation products
3. Producing ethanol (+petrol = gasohol) 
1. Crush the maize to get glucose (using the carbohydrase enzyme that breaks down starch into glucose 
2. Ferment the glucose using yeast to break it down by anaerobic respiration 
3. Distill the fermenation products to separate yeast and remaining glucose 
4. Producing ethanol 

Benefits of Bioethanol: carbon neutral, no pollution (clean gases, only H20 + CO2) renewable, cheap raw mat, less dependant, cellulose can make more ethanol 
Costs of Bioethanol: carbon neutral? modifying cars, celluose can go to landfill, deforestation, demand for land, expensive process 

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Biofuels (B3.4.3) Part 2

Types of Biogas Generators
All generators have..
- inlet for waste material
- outlet for digested material (can be used as a fertiliser) 
- outlet for biogas 
1. Batch generators (small batches, manually load the waste) 
2. Continuous generators (large batches, waste is continuously fed in at steady rates) 

4 Facts to Consider
1. Cost 
2. Convienience
3. Efficiency
4. Position 

Economic and Environmental Effects  
cheap and readily available, saves drugery (dull work) for women 
carbon neutral
doesnt release methane or sig. amounts of sulfur dioxide > acid rain
good fertiliser
causes diseases and pollutes water supplies 

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Food Production (B3.4.4)

Food Chains
We can improve the efficiency of food production by..
1. Reduce the number of stages in the food chain (more biomass available at the end) 
2. Restrict the energy lost by farm animals e.g. reduce movement 
3. Develop new food sources e.g. mycoprotein 
Fish Stocks
- High demands for fish, fish stocks declining 
- Ocean food chains are affected (some species dissappear) 
- Aim to have sustainable food production: having enough food without using resources any faster than they are renewed
- Maintaining fish stocks: Fish Quotas, Net Sizes
- Mycoprotein is protein from fungi 
- Fusarium helps produce mycoprotein 
- Fungus is grown in fermenters using glucose syrup as food
- Fungus respires aerobically (02 supplied with ammonia and other minerals) 
- Fermenters are sterilised to prevent other microbes growing)
- Nutrients are heat sterlised, air supply is filtered
- Mycoprotein is then harvesterd and purified 

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Rianna Gokani


have you got any other resources like chem and phys

Aditya Karri


5/5 you given my mind a last minute boost for my exam. Thank You :D

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