B3 Gateway

  • Created by: allie_99
  • Created on: 09-04-15 14:36

Animal and Plant Cells

  • ribosome in animal cells where proteins are synthesised. They are found in the cytoplasm
  • mitochondria are where most of the reactions involving respiration take place, so cells that need a lot of energy contain many mitochondria e.g. liver cells (energy demanding matabolic reactions) and muscle cells (energy to contract)
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Bacteria Cell

smaller and simpler than plant and animal cells

bacteria dont have "true" nucleus - they have a singular strand of DNA that floats freely in cytoplasm

Bacteria dont have chloroplasts or mitochondria

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  • chromosomes are long molecules of coiled DNA
  • double helix structure - each strand is made up of small groups called "nucleotides"
  • each nucleotide contains a small molecule called a "base"
  • only 4 types of base, A C G T
    • A always pairs with T
    • C always pairs with
  • Watson and Crick were first to model DNA (1953)
    • used X-ray data showing double helix form and other data showing bases occured in pairs
      • wern't widely accepted at first, other scientists had to repeat the work to make sure it is reliable
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Replicating DNA

  • DNA copies itself every time a cell divides, so each new cell has full amount of DNA
    • double helix "unzips" to form two single strands
    • new nucelotides (floating freely in nucleus) join on using complementary base-pairing (A & T and C & G)
    • this makes an exact copy of the DNA on the other strand
    • results in 2 double stranded molecules of DNA that are identical to the original molecule of DNA
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Protein Synthesis

  • DNA controls the production of proteins
  • section of DNA that codes for a particular protein is called a gene
  • proteins are made up of chains of molecules called amino acids
    • each protein has its own number and order of amino acids
    • gives protein a different shape so have different functions
  • the order of bases in a gene deciees order of amino acids in protein
  • each amino acid is coded for by a sequence of 3 bases in the gene
  • the amino acids join to make proteins, following the order of the bases in the gene
  • each gene contains different sequences of bases - this allows it to code for a unique protein
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Protein Synthesis (cont.)

  • Ribosomes are the site of protein synthesis and are found in the cytoplasm but DNA is found in the nucleus
  • messenger RNA (mRNA) carries the genetic code needed to make a particular protein from the DNA to the ribosomes
    • single stranded molecule which is a copy of one strand of DNA (copy of a gene)
    • mRNA goes to a ribosome telling it how the amino acids are assembled to proteins
    • e.g. amino acids which you get from eating and digesting protein in food are assembled into long chains
    • the sequence of amino acids in protein governs how the protein will fold into a particular shape
      • mRNA from DNA is called transcription
      • Proteins from mRNA is called translation
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DNA Controls Protein Production

proteins produced in a cell affect how it functions

  • different types of cell have different functions as they are made of different proteins
  • only make certain proteins as only some of the full set of genes is used in any one cell
    • some genes are "switched off" so the proteins they code arent produced
    • the genes that are "on" determin the function of the cell
      • e.g. muscle cell only genes that code for muscle cell proteins are on. genes that code for bone, nerve or skin cells are off
      • allows muscle to function as a muscle
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Functions Of Proteins

  • Collagen
    • makes up skin, bones, cartilage, tendons, ligaments, walls of blood vessels
    • collagen is a structural protein (as it makes up some of the structure of your body)
  • Insulin
    • protein hormone made in pancreas
    • travels in blood stream to target organs, muscle and liver
    • regulates blood sugar levels
      • type 1 diabetics have to inject insulin
  • Haemoglobin
    • in red blood cells
    • carries oxygen from lungs to your respiring cells
    • carrier protein
  • Enzymes
    • catalysts that control chemical reactions in cells and in yur digestive tract (gut)
  • other proteins - anitbodies, channels in cell membranes and receptors for hormones on membranes of target cells
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  • speed up rections in living cells (e.g. photosynthesis, respiration, protein synthesis)
  • can be used to catalyse the same type of reaction many times
  • enzymes are a particular shape, the active site is very important
    • substrate molecules (substances involved in the chemical reaction) fit into the active site
    • this brings them togther to form a bond
    • this makes a larger molecule
      • sometimes a substrate molecule fits into the active site
      • a bond breaks
      • two smaller products are made
  • only one particular substrate can fit into an enzymes active site (like a lock and key) so each enzyme is specific for its substrate molecules

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Enzymes (cont.)

  • low tempertures
  • enzymes and substrate molecules have less energy. do not move very fast so they do not collide often. rate of reaction is therefore low
  • high temperatures
  • as temparature increases, the enzyme and substrate molecules move quicker so collide more often so rate of reaction is high
    • if temperature is too high:
      • shape of enzyme active site changes
      • substrate molecule cannot fit into the active site
      • rate of reaction slows and eventually stops
    • once the active site changes, it cannot go back to original shape. the enzyme is denatured
    • Q10 values show how the rate of reaction changes with temperature
    • Q10 = rate at higher temperature ÷ rate at lower temperature
  • pH
  • each type of enzyme works at different pH's. if the pH changes then:
    • shape of active site changes, substrate molecules cannot fit into it so the enzyme has been denatures
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  • a mutation is a change in the DNA base sequence (caused by: chemicals (tar in tobacco smoke) or ionising radiation (x-rays or UV light))
    • if a mutation occurs in a gene, it could stop the production of the protein the gene normally codes for or make a different protein for
  • some mutations are harmful, causing
    • cells to keep dividing (cancer)
    • particular enzyme to not work, causing serious illness
    • different shaped haemoglobin molecules (sickle cell anaemia)
      • gene mutation that causes protein channel in a cell membrans lining in the airways to be different and not function causes cystic fibrosis
  • some mutations are useful
    • pale skin is caused by mutations to genes that control skin colour.
    • not useful in hot regions as skin has less protection against sunlight.
    • however is useful for low temperature regions as allows skin to make vitain D as weaker sunlight can penetrate their paler skin.
    • Early humans with this mutation could like in temperature regions without getting rickets
  • some mutations are neutral (roll you tongue, free/attached ear lobes)
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Multiplying Cells

  • advantages of being multicelled:
    • organisms can be larger so travel further, top of food chain, gain nutrients in different ways
    • different types of cells that do different jobs e.g. reacting to light in the eyes
    • can be more complex - adapted specifically to their environment
  • multcellular means organisms have specialised organ systems:
    • system to communicate between different cells e.g. nervous system
    • system to supply cells with nutrients they need e.g. circulatory system
    • system that controls the exchange of substances with environment e.g. respiratory system

In mammals, body cells are diploid.

  • They contain chromosomes in matching pairs.
  • The chromosomes need to be copied so that new cells can be produced for:
    • Growth
    • Repair to damaged tissue
    • Replacement of worn out cells
    • Asexual reproduction (which involves only one parent)
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  • when a cell reproduces itself by splitting to form two identical offspring
    • each chromosome makes a copy of itself
    • they then line up across the centre of the cell
    • each double chromosome splits into two identical copies
    • each copy moves to opposite ends of cell
    • two new nuclei form each with a full set of chromosomes
    • cell divides into two geneticaly identical cells

asexual production uses mitosis. the cell produced by mitosis are genetically identical to the parent cell. they have the same alleles (versions of genes) as the parent

  • in mature animals cell division is restricted to replacement of cells and repair of tissues. THEY DO NOT CONTINUE TO GROW.
  • mature plants still have areas (roots, shoot tips) where they can grow. the new cells made in these areas, by mitosis, can become different and specialise into many different types of plant cell
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Meiosis is another type of cell division

  • before the cell divides, copies of genetic info are made so each chromosome has an exact copy of itself
  • in meiosis the cell divides twice forming 4 gametes
  • in the first division the chromosomes pair up in their matched pairs
  • they line up along the centre of the cell
  • members of each pair split and go to opposite ends of the cell
  • these two new cells divide again
  • double chromosomes split up and go to opposite ends
  • four cells, genetically different from each other and from the parent cell and with only half the number of chromosomes of the parent cell are produced
    • gametes are made by meiosis and are sex cells that are involved in sexual reproduction - egg cells are made in ovaries and sperm cells made in testes. 
    • body cells are diploid (two copies of each chromosome in the nucleus one from mum other from dad)
    • gametes are haploid, only have one copy of each chromosome so when egg and sperm combine they will have the diploid number of chromosomes
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Diagram of Meiosis and Mitosis


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Fertilisation and Adaptation


  • male and female gametes combine to form diploid cells. this cell is called a zygote
  • characteristics of zygote are controlled by combination of genes on its chromosome 
  • since zygote will have inherited chromosomes from parents, it will show features of both but wont be exactly like either 

Sperm cells are adapted to its funtion:

  • small and have long tails - swim to the egg
  • a lot of mitochondria - lots of energy needed to swim the distance
  • acrosome at the front of the 'head' which release enzymes - digest their way through the membrane of the egg cell
  • large numbers - increases chance that one will find egg
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  • Animals
  • animals grow until they reach a finite size (full growth) and then stop growing
  • in animals growth happens by cell division. Four main growth stages in humans:
    • infancy - rapid following birth 
    • childhood - slows to steady rate
    • adolescence - puberty causes rapid growth
    • adulthood - growth rate falls to 0
  • Plants
  • plants grow continuously - even old trees will keep growing branches
  • in plants growth in height is due to cell enlargement (elongation)
  • growth by cell division usually just happens in areas of the plant called meristems (tips and roots of shoots 
    • meristems contain stem cells throughout their lives. these stem cells:
    • are un differentiated
    • have very thin walls
    • have small vacuoles
    • are packed closely together
    • are small and do not contain chloroplasts
    • can divide making new cells that differentiate
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Stem Cells

  • differntiation is the process by which a cell changes to become a specialised cell. in most animal cells, this ability is lost at an early stage.
  • some cells are UNDIFFERENTIATED. so they can develop into different types of cell/tissue/organs. these are called STEM CELLS
  • stem cells are found in early embryos.
  • adults also have stem cells but are only found in certain places like bone marrow (these arent as versatile as embryonic stem cells - they cant turn into any cell type at all only certin types

Stem cells may be able to cure many disorders like blood disorders (sickle cell anaemia and leukaemia with a bone marrow transplant). Scientists is devloping ways of using stem cells to treat Parkinsons disease, grow tissues or organs, repair spinal cord injuries, treat type 1 diabetes. 

  • use of emryonic stem cells raise ethical issues as the spare emryos used could have developed into people. 
  • but without stem cell research these embryos would still be discarded
  • there are now "stocks" of stem cells that scientists use for research. USA doesnt fund to make new stocks but in UK its allowed as long as they stick to strict guidelines
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More on Growth

Growth can be measured as an increase in:

  • Height - easy to measure - doesnt tell you about width, diameter, number of branches, etc.
  • Wet mass - easy to measure - very changeable (plants will be heavier if its recently rained. animals will be heavier with a full bladder or if just eaten)
  • Dry mass - not affected by amount of water in a plant/animal or how much that has been eaten - have to kill organism to work it out (leads to ethical issues e,g, dry mass of a person)
    • dry mass is the best measure in plants and animals - tells you the size of whole organism

organisms dont grow evenly

  • brain grows faster then body just after birth as otherwise heads would be too large to pass through birth canal
  • adolescence means reproductive organs grow a lot as you become an adult
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  • process of releasing energy from glucose
  • needed for protein synthesis, muscle contraction, control of body temprespiratory quotient - RQ = carbon dioxide produced ÷ oxygen used
    • aerobic respiration needs plenty of oxygen <-- use this most of the time
    • Glucose + oxygen --> carbon dioxide + water
    • C6H12O6 + 6O2--> 6CO2 + 6H2O
  • For aerobic respiration using glucose, RQ = 1. if greater then 1, it is anaerobic respirationrespiration takes place in mitochondria. Liver cells carry out many reactions so they need lots of ATP (energy) and have lots of mitochondria to supply this. 
    • anaerobic respiration does not use oxygen at all
    • happens during excercise
    • Glucose --> lactic acid (+energy)
    • after you stop excercising you'll have an oxygen debt as you will need extre oxygen to break down the lactic acid and to allow aerobic respiration to begin again. 
    • lactic acid is carried to the liver to be broken down so your heart rate has to stay high
  • muscle cells also have mitochondria as they need a lot of ATP for contraction
  • The metabolic rate is the rate at which energy is used by the body. Since aerobic respiration needs oxygen, the rate of oxygen consumption can be used as an estimate of metabolic rate.
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Respiration (cont.)

enzymes and respiration

  • reactions in respiration are controlled by enzymesw.
  • rate of respiration is influenced by temp and pH


  • when people warm up before excercise their muscles warm up and respiration reactions happen quicker.
  • when they start excercising hard, respiration is faster and can release more energy


  • increased lactic acid from anaerobic respiration lowers pH.
  • this reduces enzyme activity so reduces rate of respirtation.
  • muscles get fatigued - this is painful and your muscles stop contracting
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Functions of the Blood

  • Plasma - pale yellow liquid which carries anything that needs transporting round the body
    • water and digested food products (glucose, amino acids from gut to body cells)
    • waste substances like carbon dioxide from body cells to lungs and Urea from liver to kidneys (removed in urine)
    • hormones - act like chemical messengers
    • antibodies - proteins involved in the body's immune response
  • Red Blood Cells - carry oxygen from lungs to all cells in the body
    • small and flexible- lets blood cells pass through narrow capillaries
    • flat disc shape - large surface area allowing rapid diffusion of oxygen
    • contains haemoglobin - absorbs O2 in the lungs and releases oxygen in the rest of body
    • no nucleus - increase amount of space for haemoglobin
  • White blood cells - protect against disease
  • Platelets - used in blood clotting and stops bacteria entering wound
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Blood Vessels


  • carries blood away from heart at high pressure
    • thick, elastic muscular walls to withstand pressure and to exert force (pulse)


  • allow exchange of materials between blood and tissues
    • thin permeable walls
      • glucose and oxygen pass by diffusion from this plasma into cells (for respiration)
      • amino acids pass into cells so made into proteins cell needs
      • CO2 and lactic acid pass from respiring cells into plasma


  • return low pressure blood to heart
    • large diameter to offer least flow resistance and valves to prevent back flow.
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The Heart

  • mammals have a double circulatory system meaning the blood is pumped twice by heart
  • You need to be able to identify these parts, and where they are:
    • Atria (left and right)
    • Ventricles (left and right)
    • Semilunar, tricuspid and bicuspid valves
  • The four main blood vessels of the heart:
    • Vena cava
    • Pulmonary artery
    • Pulmonary vein
    • Aorta 
  • the left and right atria recieve blood from veins.
  • the left and right ventricles pump blood to arteries.
  • the valves prevent backflow right side of the heart pumps blood to the lungs
  • right ventricle has thinner wall and generates less pressure so lungs arent damaged
  • left side of heart pumps blood to rest of body, including head
  • left ventricle wall is thick and muscular so it generates high pressure getting fast delivery of O2 to body tissues and taking away waste quickly
  • at the same time, blood at lower pressures is pumped into pulmonary arteries to travel shorter distance to lungs
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Diagram of Double system and Heart

deoxygenated blood travels from the head and the liver and the rest of the body, to the heart, and from the heart to the lungs. Oxygenated blood travels from the lungs to the heart, and from the heart to everywhere else.  (http://www.bbc.co.uk/staticarchive/04271685df038d771ccc21d7a0759d3b68d11e4f.gif)(http://www.bbc.co.uk/staticarchive/f55714112a7e235b72badb579fbf299df173efd4.gif)

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Selective Breeding Plants

  • when humans artificially select plants/animals that are going to breed and have genes how we want them. we want plants to have the best features as we need varieties of crops that:
    • have high yield
    • resistant to diseases that cause health problems within a species
    • do not bend/break stalks in wind
    • resistant to drought/flooding/frost
    • taste good
    • long shelf lives
    • contain desired nutrients
  • a selective breeding programme can take up to 20 years
    • Decide which characteristics are important
    • Choose parents that show these characteristics
    • Cross bred - pollen from one parent plant is placed on female part of other parent plant
    • Offspring that have inherited both characteristices are selected and bred again
    • seeds are collected and grown
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Selective Breeding Animals

  1. Decide which characteristics are important
  2. Choose parents that show these characteristics
  3. Select the best offspring from parents to breed the next generation
  4. Repeat the process continuously
  • this produces breeds of animals that:
    • have more muscle, less far for lean meat
    • produce higher milk yields
    • lay more eggs
    • reach maturity quicker
    • have better/more wool
    • can run faster (race horses/greyhound dogs)
  • HOWEVER in this breeding process, inbreeding may reduce gene pool which could lead to:
    • accumulation of harmful recessive characteristics
    • reduction in variation
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Genetic Engineering

  • 3 stages to genetic engineering:
    • gene responsible for producing desired characteristic is selected & cut from DNA using enzymes, and isolated
    • useful gene is inserted in DNA of another organism
    • organism then replicates and soon there are lots of similar organisms producing same thing
  • 3 examples of genetic engineering:
    • populations that rely heavily on rice have vitamin A deficiency as rice does not contain much of this - take gene that controls the beta-carotene production from carrot plants and put it into rice plants. humans can change this gene into vitamin A
    • gene for human insulin production has been put into bacteria - then cultured in a fermenter and the gene is then extracted from the medium as they produce it
    • some plants are resistant to herbicides, frost and disease - cut out gene responsible and stick it to useful plants such as crops
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Genetic Engineering

  • advantage - produce organisms with new and useful features very quickly
  • disadvantage - inserted gene may have unexpected harmful effects
    • genes are often inserted in bacteria so they produce useful products. if bacteria mutatesand became pathogenic the foreign genes may make them harmful and unpredictable
    • engineered DNA "escaping" - e.g. weeds gaining rogue genes from crops that had genes for herbicide resistance

moral and ethical issues

  • wrong to genetically engineer other organisms for human benefit - problem in engineering of animals, especially if animals suffer
  • worry we wont stop at engineering plants/animals. in the future, we may engineer our children - and those who cannot afford it may become the 'genetic underclass'
  • evolutionary consequences of genetic engineering are unknown, so some think its irresponsible to carry on when were unsure of impact on future generations
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Gene Therapy

involves altering a person's genes in an attempt to cure geneic disorders. there are 2 types

  • changing gene in a body cell most affected by the disorder
    • cystic fibrosis affects lungs - target the cells lining lungs. wouldnt affect gametes though sp any offspring could still inherit disease
  • changing genes in the gametes - every cell of any offspring produced from these will be affected by the therapy and offspring wont suffer the disease (currently illegal)

!controvercial involving gametes!

  • may have unexpected consequences which cause new set of problems which will be inherited by all future generations
  • fears that this kind of therapy could lead to "designer babies" - parents choose genes they want for their child (e.g.eye colour)
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Cloning Plants

  • clones are genetically identical organisms
  • Produce by asexual reproduction
    • Spider plants grow new plants, called plantlets, on their stems
    • Potato plants produce tubers (the part we eat), which can grow new roots and shoots
    • Strawberry plants grow stems called runners, which have plantlets on them
  • Advantages - Cloning allows growers to mass produce plants that may be difficult to grow from seed. All the plants are genetically identical, - you can be sure of their characteristics.
  • Disadvantages- the lack of genetic variation means that if the plants become exposed to disease or to changes in environmental conditions, all of them will be affected.
  • Method:
    • Choosing a plant that has the desired characteristics
    • Removing a large number of small pieces of plant tissue
    • Using aseptic (sterile) technique – keeping everything sterile
    • Using a suitable growth medium and warm, moist conditions
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Cloning Animals

  • Dolly the Sheep (first successful mammal clone) how it worked:
    • nucleus of sheeps egg cell removed - leaving it without any genetic info
    • another nucleus was inserted in its place (diploid nucleus from an udder cell of the sheep being cloned containing all genetic info)
    • electric shock to cell so divided by mitosis (as if normal fertilised egg cell)
    • dividing cell (embryo now) implanted into uterus of surrogate mum to develop until birth date


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Uses and Risks of Cloning Animals

  • Benefits
    • allows mass production of animals with desired characteristics
      • ones that produce medicines in milk, engineered and cloned - transfer human genes that produce things like blood clotting agent factor VIII (treating haemophilia)
      • e.g. pigs have organs suitable for transplantation into humans which can be developed though genetic engineering then cloned - ensure constant supply of organs for transplant as human donor have short supply (issues - viruses could be passed from animals to humans)
    • Human embryos produced by cloning adult body cells - embryo supplies stem cells for stem cell therapy. these cells would have same genetic info as patient reducing risk of rejection
  • Risks
    • evidence that cloned animals may not be as healthy
    • cloning is new science and it may have consequences that were unaware of
  • Ethical issues with human clones - surrogate pregnancies with high miscarriage and stillbirth rates; clones of other mammals often are unhelthy and die prematurely; psychological damage by knowledge that its just a clone of another human
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