GCSE AQA Biology Unit 2

Life Processes,

Enzymes and Homeostasis,




Animal and Plant Cells:

  • Nucleus = contains genetic material e.g. brain
  • Cytoplasn = gel-like substance where chemical reaction take place
  • Cell Membrane = holds cell together controls what goes in and out
  • Mitochondria = reactions for respiration take place, releases energy
  • Ribosomes = where protein synthesis takes place

Plant Cells:

  • Rigid Cell Wall = supports and strengthes, made of cellulose
  • Permanent Vacuole = contains cell sap, weak solution of sugar and salts
  • Chloroplasts = Photosyntesis occurs, contian green substance chlorophyll
  • Cells,Tissue, Organ System 
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Specialised Cells

  • 1) Palisade Leaf Cell 
    • Packed with chloroplasts near the top - nearer to light
    • Tall so lots of surface area for absobing C02
    • Thin pack loads at the top of the leaf
  • 2) Guard Cells
    • Special kidney shape that opens and closes the stoma
    • Thin outer wall + thick inner wall makes opening and closing work
    • sensitive to light so close at night
  • 3) Red Blood Cells
    • Concave shape = big surface area for absorbing oxygen
    • Packed with haemoglobin (pigment abosrbs oxygen)
    • No nucleaus = more room for haemoglobin
  • 4) Sperm and Egg Cells 
    • Egg = Huge food reserves to feed the embryo
      • When sperm fused membrane changes so no more get in 
    • Sperm = Long tail + stream lined head + lots of mitochondria 
      • Carrys enzymes to digest through the eggs membrane
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Diffusion is the passive movement of particles from an are of high concentration to an area of low concentration.

  • Happens in both liquids and gases
  • The bigger the difference of concentration the faster the diffusion rate

Cell Membranes:

  • Hold cell together and let particels in and out
  • Only small particles can diffuse through - Glucose, Amnio Acids, Water, Oxygen. Big molecules can't - Starch, Proteins.
  • Rate of dissusion depends on:
    • Distance - Not far to move = faster
    • Concentration Difference - Big differnce = faster
    • Surface Area - more surface area = faster
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Osmosis in the movement of water particels across a partially permemable membrane from a region of high water concentration to a region of low water concnetration.

  • A type of diffusion - passive movement of water particles
  • Partially Permable Membrane = only tiny molecules like water can pass
  • Water passes both ways through membrane as it is a random movement
  • A strong sugar solution gets more dilute (acts like trying to even up)
  • If there are more water molescules on one side the net movement is to the region of fewer molecules e.g. into the stonger sugar solution

Water, Osmosis and Cells:

  • Tissue Fluid = water, oxygen and glucose has a differnece concentration to the fluid inside cells so water move into or out of a cell by osmois.
  • Cell short of water = concnetrated Tissue Fluid - more dilute so water will more into cell by osmosis and vice versa.
  • Potato Cylinder Test
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Carbon Dioxide + Water (Sunlight) --> Glucose + Oxygen

  • Photosynthesis = Process produces food (glucose) for plants
  • Takes place in leaves of all green plants
  • Happens inside chloroplasts which contain chlorophyll that absorb sunlight
  • Water reaches chloroplasts through leaf veins and CO2 diffuses into leaf
  • Four things needed for photosynthesis:
    • Light - from the sun
    • Chlorophyll  - green substance found in chloroplasts
    • Carbon Dioxide  - diffuses from the air into leaf
    • Water - from soil up roots and stem into leaf
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The Rate of Photosynthesis - Limiting Factors

  • 1) Not enough Light:
    • Light provides energy for photosynthesis 
    • Increased light = increased rate up to a point
    • In a lab experiment = moving a lamp closer, further away ect.
  • 2) Too little Carbon Dioxide:
    • Raw material needed for photosynthesis
    • Increased amount of CO2 = increased rate up to a point
    • In lab experiment = dissolve sodium hydrogen-carbonate = CO2
  • 3) Temperature has to be just right:
    • The temp affects the enzymes needed for photosynthesis
    • Plant too hot - enzymes are denatured about 45
    • Too Cold - work slowly
    • In a lab experiment use a water bath to control temp
  • Artificially Create Ideal Conditions:
    • Green house - Trap suns heat + Keeps pests and diseases out
    • Artificial Light - Photosynthesis can happen at night
    • C02 = Paraffin heater produces Co2 as a by-product
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How Plants use Glucose

  • 1) Respiration:
    • Plants make glucose in leaves which can then be used fro respiration which releases energy which enables glucose to be produces into other substances.
  • 2) Making Fruits:
    • Glucose + Fructose = Sucrose
  • 3) Making Cell Walls:
    • Glucose is converted into cellulose
  • 4) Making Proteins:
    • Glucose + Nitrates = amino acids which are then made into proteins
  • 5) Stored in Seeds:
    • Turned into lipids (fats and oils) e.g sunflower seeds = a lot of oil which we use for cooking oil. Seeds also store starch.
  • 6) Stored as Starch:
    • Glucose turned into starch and stores in roots for winter. Starch is insoluble - doesn't bloat storage cells by osmosis (glucose would)
    • Potatoes, Carrots ect.
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Minerals for Healthy Growth

  • 1) Nitrates 
    • Needed to make amino acids which then make proteins
    • Without it plants show stunted growth 
  • 2) Magnesium
    • Needed to make chlorophyll (green pigment) for Photosynthesis
    • Without it leaves turn yellow
  • Potassium and Phosphates are needed for making DNA and cell membranes and for helping enzymes involved in photosynthesis and respiration to work properly
  • Deficiencies can be caused by monoculture:
    • When one type of crops grown in the same fields year after year.
    • Plants of the same crop need the same minerals so the soil becomes deficient in the minerals the plant needs.
    • Deficiency = poor growth + reduced yield
    • Fertiliser can replenish the depleted materials
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Pyramids of Number and Biomass

  • There is less energy and less biomass every time you move up a tropic level in a food chain.
  • There is usually fewer organisms as well but not always as one fox could have 500 fleas feeding on it so it is better to use a pyramid of biomass than a pyramid of numbers.
  • Each bar on a pyramid of biomass shows the mass (how much the organisms weigh) of living material at each stage of the food chain.
  • Pyramids of biomass are always the right shape (unlike number pyramids)
  • Bar along the bottom = producer Next bar = Primary consumer and so on.
  •  A tree can have lots of aphids on it but the tree still has a larger biomass even though there is only one of it.
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Energy Transfer and Decay

  • Energy from the sun is the source of nearly all life on earth.
  • Represented in Sankey Diagrams 
  • Energy is loss in waste:
    • Faeces and Urine:
    • Animals can digest all the food that they eat.
  • Energy loss due to movement:
    • More it moves about so more energy is taken from its food
    • Muscle contraction produces heat
  • Energy loss in trying in keeping a constant body temperature:
    • Warm-blooded animals have to keep a constant body temperature which is normally higher than their surroundings this uses up energy
    • Cold-blooded animals don't have this problem.
  • Decay:
    • The elements that plants take from the soil are returned when they die because the materials decay when when they are broken down by micro-organisms.
    • They work best in warm, moist conditions with plenty of oxygen.
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Managing Food Production - Efficiency and Ethics

  • 1) Reduce the number of stages in a food chain:
    • lots more food can be produced by growing crops instead of animals
    • only 10% of beef cattle is useful meat for people to eat
    • However some land is unsuitable for growing crops and people need a varied diet.
  • 2) Restrict energy lost by farm animals:
    • Intensive or battery farming keeps animals like chickens and pigs close together, warm and without space to move around.
    • They don't waste any energy in movement which stops them giving out heat they also don't have to keep themselves warm.
    • The transfer of energy from feed to animal is more efficient do they grow faster with less feed.
  • Crowed Conditions = Spread of diseases
  • Prevent diseases using antibiotics = Immune Microbes
  • Carefully controlled environment = Use of fossil fuels
  • Unnatural uncomfortable conditions are cruel =  demand for organic meat
  • Feeding animals fish = Fish stocks are getting low
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The Carbon Cycle

  • Everything is powered by photosynthesis
  • CO2 returned when plants respire
  • Plants are eaten and carbon becomes part of the food chain
  • CO2 returned to the atmosphere when plants respire
  • Plants and animals die or produce waste micro-organisms feed on remains they respire releasing co2 into the atmosphere
  • Carbon dioxide is released into the atmosphere when fossil fuels are burnt.
  • Carbon is constantly being cycled from the air, through food chains and eventually back into the air again.
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The Carbon Cycle Diagram

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Biological Catalysts - Enzymes

A catalyst is a substance which increases the speed of a reaction without being changed or used up in the reaction.

  • Reactions need to be controlled to get the right amount of substance
  • Enzymes act as biological catalysts
  • Enzymes are made out of chains of amino acids (proteins) which are folded into a unique shape enzymes to do their job.
  • Every enzyme has a unique shape that usually only catalyses one reaction
  • They need the right temperature an pH.
  • As you increase the temperature the rate of the reaction increases as first but if it get too hot then the bonds holding it together break and it becomes denatured.
    • Enzymes in the human body work best at 37 (degrees)
  • If the pH is too high or low then it interferes with the bonds.
    • Each enzyme has an optimum pH e.g. Pepsin = pH 2 
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Enzymes and Respiration

  • Enzymes used to synthesise molecules like amino acids - that you don't get from your diet. They catalyse protein synthesis by joining amino acids  which could be enzymes.

Respiration is the process of releasing energy from glucose which goes on in every cell. (Not breathing in and out)

  • Aerobic Respiration needs plenty of oxygen and happens in the mitochondria.
  • Glucose + Oxygen ---> Carbon Dioxide + Water + ENERGY
  • Uses of Respiration:
    • To build larger molecules from smaller ones
    • In animals to allow muscles to contract  for movement
    • In mammals to keep their body temperature constant
    • In plants to build sugars, nitrates and other amino acid which are then built up into proteins.
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Enzymes and Digestion

  • Digestive enzymes break down big molecules into smaller ones: 
  • Amylase:
  • Catalyses: Carbohydrates e.g.starch into simple sugars
  • Made: The Salivary gland, The Pancreas, The Small Intestine 
  • Works: The Mouth, The Small Intestine
  • Protease:
  • Catalyses: Proteins breaking them down into amino acids
  • Made: The Stomach, The Pancreas, The Small Intestine
  • Works: The Stomach, The Small Intestine
  • Lipase:
  • Catalyses: Lipids e.g. fats and oils
  • Made: The Pancreas, The Small Intestine 
  • Works: The Small Intestine
  • Bile: 
  • Made: Liver   Stored: Gall Bladder 
  • Works: The Small Intestine
  • Neutralises the stomach acids in prep for SI and emulsifies fats - Alkaline 
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The Digestive System

  • The Salivary Gland = Produces amylase enzyme in the saliva.
  • Epiglottis = Closes trachea when swallowing
  • Gullet (Oesophagus) = Takes food from the mouth to the stomach
  • Bolus = Food
  • Stomach = Pummels Food with muscular inner walls, produces Pepsin (protease) enzyme. Produces Hydrochloric to kill bacteria and the right pH.
  • Pyloric sphincter = Lets food in and out of the stomach
  • Liver = Produces Bile
  • Gall Bladder = Stores Bile
  • Vial Duct = Takes Biles from the gall bladder to the small intestine
  • Pancreas = Produces protease, amylase and lipase. Release into SI
  • Small Intestine = Produces Protease, Amylase and Lipase, where food is absorbed out of the digestive system and into the body
  • Large Intestine =  Where excess water is absorbed from food
  • Rectum = Where the faeces (indigestible food) are stored before 
  • Anus = Goodbye faeces
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Uses of Enzymes

  • In Biological Detergents
    • Proteases and Lipase's
    • Attack animal and plant matter - ideal for removing stains
  • To Change Foods:
    • Proteins in baby-food are pre-digested by proteases
    • Carbohydrases change: Starch syrup to sugar syrup (yum)
    • Glucose Syrup changed into Fructose syrup -sweeter so you use less of it for slimming diets.
  • Industry:
    • Speed up reaction without high temps and pressures
    • Advantages:
      • Specific - only catalyse the reaction you want
      • Low temp = low cost + saves energy
      • Biodegradable = less environmental pollution 
    • Disadvantages:
      • Some people have allergies
      • Denatured by a very small increase in temperature or pH 
      • Contamination with other substances can affect the reaction
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Homoeostasis is the maintenance of a constant internal environment.

  • 1) Body Temperature:
    • The Thermoregulatory Centre in the brain contains receptors sensitive to the temp of the blood flowing in the brain.
    • Receives impulses from the skin about the skin temp
    • Too hot - Hairs lie flat, Sweat produced, Blood vessels dilate
    • Too Cold - Hair stand, No sweat, Blood vessels constrict, Shiver
  • 2) Water Content:
    • Too much or too little water moving in an out of cells damage them
  • 3) Ion Content
  • 4) Blood Sugar Levels:
    • Need to stay within certain limits e.g. diabetes
  • 5) Carbon Dioxide:
    • The toxic product of respiration.
    • Removed from lungs when you breathe out.
  • 6) Urea: 
    • Waste product from excess amino acids
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The Kidneys and Homeostasis

  • The Kidneys:
    • Remove Urea
      • Waste product made of excess amino acids.
      • Produced in the Liver.
      • Remove by Kidneys
      • Excreted from the body on urine
    • Adjust the Ions in the blood:
      • Ions are taken into your body through food e.g. sodium
      • If the ion content in the body is wrong too little to much water could be drawn into cells by osmosis - damages cells
      • Removed by kidneys or lost through sweat
    • Adjust the water content in the blood:
      • Water is taken into your body through food and drink.
      • Taken out - Urine, Sweat and breathing out water vapour
      • Water balance is between - Liquid consumed, Amount sweated out, Amount excreted by kidneys in urine.
      • Cold day - no sweat = more urine pale and dilute
      • Hot day - sweat = Less urine dark and concentrated
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Controlling Blood Sugar

  • Eating Carbohydrates puts glucose into the blood from the gut.
  • Metabolism reaction and exercise removes glucose from the blood.
  • Glucose levels must be kept steady - change is monitored by the pancreas
  • Blood Glucose Level too high - Insulin added
  • Blood Glucose Level too low - Insulin is not added
  • Type 1 Diabetes - Pancreas doesn't make enough insulin
    • Result: If blood sugar levels rise too high they can be fatal.
    • Controlled:
      •  Avoiding foods rich in carbohydrates and exercising after eating.
      • Injecting Insulin into the blood at mealtimes (must eat sensibly after after injecting otherwise blood sugar could drop too low)
    • The amount of insulin injected depends the persons diet and how active they are.
    • Diabetics can check their blood sugar using a glucose-monitoring device - A hand-held machine takes a drop of blood from their finger to check.
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Insulin and Diabetes

  • Banting and Best:
    • Remove the pancreas from dogs who became diabetic which could be proven by their sugar urine.
    • They Isolated Insulin:
    • 1) tied string around a dogs pancreas - a lot of organ wasted away except the bit that made hormones.
    • 2) Removed pancreas from dog and obtained an extract of it.
    • 3) Injected extract into diabetic dogs and observed BSL
    • 4) After injection BSL fell - the pancreatic extract caused a temporary decrease in BSL
    • 5) Isolated substance in the pancreatic extract it was INSULIN.
  • Since the 1980's Human Insulin has been mass produced using genetic engineering. Before that it was extracted from pigs and cows.
  • Slow, Intermediate and fast acting insulin make you BSL easier to control
  • Pancreatic Transplants:
  • Body can reject organ = costly drug - serious side effects
  • OR transplant the cells that produce insulin.
  • OR artificial pancreas using stem cells
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  • Nucleus, Chromosome, Gene, DNA
  • Chromosomes
  • DNA (= Deoxyribose Nucleic Acid) contains instruction to put an organism together and make it work.
  • Found in the nucleus of really long molecules called chromosomes
  • Genes
  • A Gene is a section of DNA - instructions to make a specific protein 
  • Make proteins by stringing amino acids together in a particular order
  • Only 20 amino acids are used but = thousands of different proteins
  • Genes tell cells what order to put amino acids in
  • DNAdetermins what proteins cellls produce which = what cell it is
  • DNA Fingerprinting
  • Cut up a persons DNA into sections + look at the pattern of their DNA from this you can identify them as DNA is unique (Identical twins)
  • 1) Forensic Science - Tests DNA from a crime scene to find a suspect
  • 2) Paternity Tests - Which man in the father of my child? DNA comparison.
  • Some want a gentic database of everyone in the country = Invasion of privacy + errors and false positive could occur if data misinterpreted.
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Cell Division - Mitosis

Mitosis is when a cell reproduces itself by splitting to form two identical offspring.

  • Humans have 23 pairs of chromosomes in a body cell.
  • It divides it makes identical cells to the origional still with 23 Chromosomes.
  • Known as 'Copying Division'
  • Used to grow or to replace cells that have been damages.
  • 1) The cell duplicates its DNA (forms an X-shaped chromosome) 
  • 2) Chromsomes line up, cell fibres pull them apart to oppoiste ends of cell  (each chromosome arm will go to different ends)
  • 3) Membranes form around each set - these become the nuclei of the two new cells 
  • 4) The cytoplasm divides  
  • Asexual Reproduction uses Mitosis
    • Offspring have the same DNA as parents - No Viration
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Cell Division - Meiosis

Meiosis produces cell which have half the normal number of chromosomes.

  • During Sexual Reproduction two gametes combine to from a new individual
  • Gametes only have one copy of each chromosome.
  • Body Cell = 46 Single chromosomes + Sex Cell = 23 Single chromosomes 
  • 1) Cell duplicates its DNA (each arm is an exact copy of the other)
  • 2) Chromosomes line up in the centre of cell (FIRST DIVISION)
  • 3) Pairs are pulled apart - some of each parents is in the new cell
  • Each new cell has a mixture = Variation which is a huge advantage.
  • 4) Chromosomes line up again and the arms are pulled apart (SECOND DIVISION)
  • 5) You get 4 gametes each with only a single set of chromosomes
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Stem Cells

  • Most cells in your body are specalised for a particular job
  • Differentation is the process of a cell changeing to become specalised
  • In animal cells that ability to differentate is lost at an earlt stage
  • Lots of plant cells don't lose this ability
  • Undifferentated cells are called Stem Cells - can become any type of cell
  • Can be found in human embryos or in the bone marrow of adults (>versitile)
  • Adult stem cells can already be used to cure blood diseased - bone marrow transplants
  • Scientist can extract stem cells from human embryos and grow them
  • Replace faulty cells in sick people e.g. Paralysed by spinal injury ect..
  • Working on - controlling differentation by changing enviroment - more research needed
  • For and Against Stem Cell Research:
    • Human embryos are a potential human life so shouldnt be used
    • Suffering people are more important than embryos
    • Embryos from fertility clinics would be destroyed if not used in research.
    • Should develop other sources without using embryos.
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X and Y Chromosomes

  • 23rd pair of chromosomes control you gender.
  • Men = XY
  • Women = **
  • There is a 50% chance that each sperm cells gets an X and a 50% chance it has a Y
  • The Gender of a child is determined by the male gamete (is it X or Y)
  • The probabilty of getting a boy or a girl can be show with a genetic diagram.
  • 50:50 or 50% Chance
  • There are 2 types of diagram: Square (boxes) and Spider (lines)
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Examples of Genetic Diagram's

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The Work of Mendel

  • Mendel = Austrian Monk trained in mathematics and natural history
  • He notice that in the monastry's garden charactistics of plants were passes on from one generation to the next. - using Pea Plants
  • His research was published in 1866 = foundation of modern genetics.
  • 'Mendel had showed that the height charactistics in pea plants wea determined by seperatly inherited 'hereditary units' passes on from each parent. The ratios of tall anf dwarf plants in the offspring showed that the unit for tall plants: T was dominant over the unit for dwarf plants: t.
  • Medel reached 3 important conclusions:
    • Characterists of plants are determined in 'hereditary units'
    • Heredirty units are passes from both parents, one unit from each
    • Hereditary units can be dominant or recessive.
  • Hereditart units are Genes
  • Nobody at the time knew anything about genes or DNA so the signifigance of his work was not realised until after his death and the invention of microscopes.
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More Genetic Diagrams

  • Alleles are different versions of the same gene.
  • You usually have two copies of the same gene.
  • If there different alleles only one can be expressed in the organism
  • In genetic diagrams letters represent genes.
  • Dominant alleles are always shown using a CAPITAL LETTER. e.g.B
  • Recessive alleles are allways shown with a lower case letter e.g.b
  • For an organsim to display recessive charactistics both alleles must be recessive. If one is dominant and the other recessive the dominant wins!
  • In a genetic diagram there are 4 possible outcomes
  • Ratios are used to show the probality of a gentic diagram's outcome
  • Homozygous Cross - Homosexual's like the same sex
    • Apair of alleles that produce a cahractistic that are the same e.g. HH or hh
  • Hetrozygous - Hetrosexual's like the opposite sex
    • A pair of alleles that produce a charactistic that are different e,g Hh
  • Pheontype = The physical expression of the alleles e.g the colour of a flower
  • Genotype = A description of a pair of alleles present for a charactistic.
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Genetic Disorders

  • Cystic Fibrosis:
    • Caused by a recessive allele (carried by about 1 in 30 people)
    • If you have only 1 recessive you are a carrier
    • In order to have it both parents must be suffers or carriers
    • Both parents are carriers there is a 1 in 4 chance of a child having it.
  • Huntingtons Disease:
    • Caused by a dominant allele - can be inherited if only 1 parents has it
    • Carrier is a suffer - symptoms dont appear unitl after 40 years old - so they may have already passes on disorder to children
    • 50% chance of passing to children if one parents suffers it
  • Embryo Screening:
    • Against:
      • Rejected embyos are destroyed - could have been humans
      • Implies genetic problems are undesirable - creates predjuice
    • For:
      • Stop people suffering
      • Save's the government a lot money in treating disorders
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thank you

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