Biology Unit 3

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Osmosis

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

  • tissue fluid surrounds cells in the body (water, oxygen, glucose ect)
  • water therefore moves into or out of the ccell to balance the concentrations
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Gas and Solute Exchange

  • substances move by diffusion, osmosis and active transport
  • diffusion and osmosis are from high concentration to low concentration, active transport works the other way against the concentration gradient

Exchange surfaces: thin, large surface area, lots of blood vessels (animals), ventilated (animals)

- exchanging substances gets more difficult in bigger and more complex animals

Leaf structure for diffusion:

  • underneath of leaf is an exchange surface covered in tiny holes (stomata) where carbon dioxide diffuses in and oxygen and water diffuse out
  • stomata size is controlled by guard cells to control water loss
  • flattened shape of the leaf increases surface area
  • walls inside the cells form an exchange surface
  • air spaces inside the leaf increase the surface area of the walls in the cells for substance exchange
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The Breathing System

  • the thorax is the top part of your body and is seperated from the abdomen (lower part) by the diaphragm
  • air that is breathed in goes through the trachea then splits into two tubes (bronchi) that go to each lung
  • bronchi split into progressively smaller tubes called bronchioles which end at small bags called alveoli where the gas exchange takes place

Breathing in - intercostal muscles and diaphragm contract, thorax volume increases which decreases pressure, drawing air in

Breathing out - intercostal muscles and diaphragm relax, thorax volume decreases which increases pressure, forcing air out

Artificial ventilators:

  • move air in and out of the lungs
  • was a giant case from neck to abdomen air was pumped into but could cause blood flow issues
  • now pump air into actual lungs, occassionally can cause alveoli to burst if lungs can't cope
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Diffusion Through Cell Membranes

Alveoli are specialised to maximise diffusion of oxygen and carbon dioxide into and out of the lungs by having: an enormous surface area, a moist lining (dissolving gases), very thin walls, good blood supply

Villi - cover the inside of the small intestine to increase surface area so food is absorbed faster into the blood

Specialised by having: a single layer of surface cells (thin), very good blood supply

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Active Transport

Root hair cells - cells on the surface of roots that stick out into the soil to maximise surface area for absorbing water and mineral ions from the soil

  • the concentration of water and minerals is usually higher in the root hair cell than the soil so active transport allows the plant to absorb water and minerals against the concentration gradient
  • active transport requires energy from respiration to work

In the gut:

  • sometimes there is a lower concentration of nutrients in the gut than there is in the blood
  • active transport therefore happens to still absorb the nutrients into the blood where they are needed which goes against the concentration gradient
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Water Flow Through Plants

Phloem tubes - transport food

  • made of columns of living cells that have holes in the ends to allow things to flow through
  • transport food substances (mainly dissolved sugars) made in the leaves to the growing regions and storage regions of the plant
  • transport goes in both directions

Xylem tubes - take water up

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

Transpiration stream - caused by evaporation and diffusion of water from inside the leaves, the slight shortage of water in the life causes more to be taken up from the roots by xylem to replace it. This happens continuously so therefore a transpiration stream is created.

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Circulatory System - The Heart

Humans have a double circulatory system (two circuits joined together) - one pumps deoxygenated blood to the lungs to be oxygenated then back to the heart, the other pumps oxygenated blood around the body to reach everything else which then becomes deoxygenated and is pumped back to the heart for the process to happen again

Heart - walls are mostly made of muscle tissue, it haves valves to prevent the flood flowing in the wrong direction (backwards)

  • blood flows into both atriums from the vena cava and the pulmonary vein
  • the atriums contract pushing the blood into the ventricles
  • the ventricles contract pushing 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 atriums fill again and the whole cycle starts over
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Circulatory System - Blood Vessels

Arteries :

  • carry the blood away from the heart
  • the walls are thick compared to the hole down the middle (the lumen)
  • contain thick layers of muscle to make them strong and elastic fibres to allow them to stretch and spring back which lets them cope with the high pressure of blood pumped from the heart

Capillaries:

  • are involved with the exchange of materials at the tissues
  • really tiny and carry blood really close to each cell for exchanging substances
  • permeable walls for diffusion (supply food and oxygen and remove carbon dioxide)
  • walls are one cell thick to increase the rate of diffusion

Veins:

  • carry blood to the heart (blood is at lower pressure so the walls aren't as thick)
  • bigger lumen helps the blood flow and has valves to keep blood flowing in the right direction
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Circulatory System - The Blood

Red blood cells - carry oxygen, have a concave shape for a larger surface area to absorb oxygen, don't have a nucleus allowing more room for oxygen, contain heamoglobin which combines in the lungs with oxygen to produce oxyhaemoglobin and in body tissues reverses to give heamoglobin and oxygen, releasing oxygen to cells

White blood cells - defend against disease, have a nucleus, consume pathogens (engulf), produce antibodies to fight them and produce antitoxins to counteract toxins

Platelets - help blood clot, small fragments of cells with no nucleus, stop blood pouring out and microorganisms getting in to cuts, lack of them can cause excessive brusing and bleeding

Plasma - liquid that carries everything in the blood (red blood cells, white blood cells, platelets, nutrients, carbon dioxide, urea, hormones, antibodies and antitoxins)

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Circulation Aids

Artificial blood - blood substitute that replaces the lost volume of blood if someone loses a lot to keep them alive which gives them time to produce more blood cells, if not they will need a blood transfusion

The heart (artificial parts) - artificial hearts are mechanical devices that are put into a person to pump their blood if their heart stops working, usually a temporary fix until a donor heart can be found but are sometimes a permanent fix

  •  main advantage is they are less likely to be rejected by the body's immune system as they are made from metals and plastics so the body doesn't recognise them as 'foreign'  and attack them the same way they do with living tissue
  • surgery to fit one can lead to bleeding and infection, they don't work as well as natural hearts, parts could wear out or the electrical motor could fail, blood doesn't flow through as smoothly which can cause blood clots and lead to strokes, the patient also has to take blood thinning drugs to make sure this doesn't happen which could cause problems if in an accident with bleeding
  • heart valves can be replaced with artificial ones which is less drastic but there can still be problems with blood clotting
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Circulation Aids 2

Stents:

  • keep arteries open
  • coronary heart disease is when arteries supplying blood to the heart get blocked by fatty deposits causing narrow arteries and restricted blood flow which can lead to a heart attack
  • stents and tubes are inserted into the arteries and keep them open making sure blood can flow through to the heart muscles to keep it beating
  • they lower the risk of heart attack in people with coronary heart disease but over time the artery can narrow again and scar tissue can grow
  • patient needs to take drugs to stop blood clotting on the stent
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Homeostasis

- maintenance of a constant internal environment

Things that need controlling: body temperature, water content, ion content, blood sugar level, carbon dioxide concentration, urea concentration

  • there is a thermoregulatory centre in the brain that acts as a personal thermostat, it contains receptors sensitive to blood temperature and recieves impulses from the skin about the skin temperature

Too hot - hairs like flat, sweat is produced by sweat glands and evaporates from skin removing heat, blood vessels dilate so more blood flows close to the surface of the skin making heat transfer from the blood to the environment easier

Too cold - hairs stand up to trap an insulating layer of air, no sweat is produced, blood vessels supplying skin capillaries constrict to close off the skin's blood supply, you shiver which needs respiration that releases energy to warm the body

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The Kidneys and Homeostasis

Removal of urea - proteins can't be stored by the body so they are converted into carbohydrates and fats (in the liver), urea is produced as a waste product of the reaction which is poisonous so it is released in the bloodstream, the kidneys filter it out of the blood and it is temporarily stored in the bladder as urine

Adjustment of ion content - if the ion or water content of the body is wrong the balance between then two will be upset meaning too little or too much water is drawn into cells by osmosis which can damage cells stopping them working as well, excess ions are removed by the kidneys (some ions are also lost in sweat)

Adjustment of water content - lost by urine, sweat and the air we breathe out, the water coming into the body has to be balanced against the water coming out the body (water balance is between liquids consumed, amount sweated out, amount secreted by the kidneys in the urine)

  • sports drinks replace lost water, sugar and ions
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Kidney Function

**nephrons are filtration units in the kidneys

Ultrafiltration - high pressure built up squeezes water, urea, ions and sugar out the blood and into the Bowman's capsule, membranes between the blood vessels and Bowman's capsule act like filters so big molecules like proteins and blood cells are not squeezed out they remain in the blood

Reabsorption - as the liquid flows along the nephron useful substances are reabsorbed back into the blood (sugar, sufficient ions, sufficient water) which happens as active transport

Releases of wastes - remaining substances continue out of the nephron, into the ureter and down to the bladder as urine

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Kidney Failure

- if the kidenys don't work properly then waste substances build up in the blood and you lose the ability to control ion and water levels

Dialysis machines - has to be done 3 times a week which takes 3-4 hours each time, the person's blood flows alongside a selectively permeable barrier surrounded by dialysis fluid, its permeable to ions and waste products but not big molecules, the fluid has the same concentration of dissolved ions and glucose as healthy blood so useful dissolved ions and glucose won't be lost from the blood only waste substances and excess ions and water, dialysis may cause blood clots or infections

Transplanted organs - the only current cure for kidney disease is a kidney transplant from a healthy kidney from an organ donor but the donor kidney can be rejected by the patient's immune system due to the foreign antigens

Precautions taken - a donor with a tissue type that closely matches the patient is chosen and the patient is treated with drugs that suppress the immune system so it won't attack the transplanted kidney

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Controlling Blood Glucose

Blood glucose level too high - insulin added by pancreas which makes the liver turn glucose into glycogen

Blood glucose level too low - glucagon is added by pancreas which makes the liver turn glucose into glycogen

Type 1 diabetes - pancreas produces little or no insulin

Controlling it:

  • limiting the intake of foods rich in simple carbohydrates
  • regular excercise
  • insulin therapy making sure glucose is removed from the blood quickly
  • insulin used to be sourced from pig and cow pancreases but now it is made by genetic engineering
  • can have a pancreas transplant  
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Human Impact on the Environment

  • world population is rapidly increasing (medicines and farming have increased this rate due to less people dying from disease and hunger)
  • increasing population puts pressure on the environment due to the resources we need to survive
  • raw materials are being used faster than they are replaced so at the moment we will run out one day
  • water - polluted by sewage and chemicals affecting plants and animals that rely on it
  • land - polliuted by chemicals for farming, nuclear waste underground and household waste in landfill
  • air - polluted by smokes and gases released into the air that cause pollution (global warming, global dimming, acid rain ect)

Reduce land for other species by: building, farming, dumping waste and quarrying

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Carbon Dioxide and the Greenhouse Effect

Natural carbon dioxide stores: oceans, lakes and ponds, green plants and peat bogs

Global warming:

  • gases naturally insulate the world to keep heat in otherwise it would be too cold
  • carbon dioxide and methane levels have been rising rapidly
  • the increasing amounts of the gases are gradually heating up the earth
  • this is called climate change which can cause other serious effects
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Deforestation and Destruction of Peat Bogs

Deforestation reasons - for timber as building material, to clear more land for farming (foods and fuels) and to produce paper

Deforestation problems:

  • more methane in the atmosphere - rice is grown in warm moist conditions where decomposers live and they produce methane also cattle produce methane so rearing them increases it
  • more carbon dioxide in the atmosphere - when trees are burnt and microorganisms feeding on dead wood releases it as a waste product of respiration
  • less carbon dioxide taken in - reduced photosynthesis
  • less biodiversity - causes many species to become extinct which also loses lots of oppurtunities as they could have been good for something we hadn't realised

Destroying peat bogs - partly rotted plants build up to form peat which carbon is stored in the plants within however the bogs are often drained and the peat dried and burnt releasing carbon dioxide, the decay of it as compost or in the dried up bog also releases it

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Climate Change

Consequences: rising sea levels (flooding), melting ice caps, more extreme weather, changes in animal distribution, reduced biodiversity due to species becoming extinct, changes in migration patterns

Weighing evidence - experiments/observations should be done over large areas and a long period of time to get more reliable and true results, if lots of scientists get the same result then it is more likely to be true hence why climate change is now starting to be taken much more seriously

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Biofuels

  • can be made by fermentation when yeast or bacteria break sugars down by anaerobic respiration
  • glucose                  ethanol + carbon dioxide + energy
  • ethanol distilled to remove any extra yeast and glucose

Biogas - anaerobic fermantation of waste material, 70% methane and 30% carbon dioxide, made in a simple fermenter called digester or generator, generator needs keeping at a constant temperature, two types batch and continuous, can't be stored as liquids so have to be used straight away (cooking, heating, lighting, turbines)

Fuel production - large scale generators are now being used in some countries, small scale ones can be used to provide energy for a small village or family, human waste, waste from keeping animals and food waste can be used to produce biogas, by products can also be used to fertilise crops and gardens

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Using Biogas Generators

Batch generators - make biogas in small batches, manually loaded up and by-products are cleared away after each session

Continuous generators - make biogas all the time, waste is constantly fed in, biogas is produced at a steady rate and they are more suited to large scale projects

Simple biogas generator - inlet for waste material to be put in, outlet for digested material to be removed through, outlet so gas can be piped to where it is needed

Factors to consider when designing one - cost, convenience, efficiency, position

  • biofuels are carbon neutral
  • burning the waste means methane isn't released into the atmosphere
  • raw material is cheap and readily available
  • digested material is a better fertiliser
  • acts as a waste disposal system
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Managing Food Production

Efficiency of food production improved by:

  • reducing the number of stages in the food chain - you can produce a lot more food for humans by growing crops than rearing animals but people do need a varied diet
  • restricting the energy lost by farm animals - kept close together so they are warm and can't move about much which saves them wasting energy on movement so the energy transfer is more efficient as they grow faster and on less food, it makes things cheaper
  • developing new food sources like mycoprotein - protein from fungi, used to make meat substitutes, grown in fermnters using glucose syrup as foods, it respires aerobically, fermenter is sterilised with heat, incoming nutrients are heat sterilised and air supply is filtered to stop other microorganisms getting in, it is harvested and purified
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Problems with Food Production and Distribution

Compromises and conflict in efficient food production - animal cruelty, crowded farm conditions are a favourable environment for the spread of disease, animals are given antibiotics to prevent disease which enter humans and can cause them to be less effective for humans, the animals need to be kept warm which uses power from fossil fuels,

- lots of food miles is bad because it is expensive and bad for the environment

Overfishing:

  • fish stocks are declining
  • ocean food chains will be affected

Fishing quotas - limits on number and size of fish that can be caught in certain areas

Net size - limits on mesh size to reduce the number of unwanted and discarded fish

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