Biology Paper 1

  • Created by: KateS03
  • Created on: 20-04-19 09:43
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    • 1. Cell Biology
      • cells
        • eukaryotic: complex, eukaryotic cells, e.g. plant & animal
        • prokaryotic: simple, single celled organism e.g. bacteria
        • plant & animal (subcellular structures): nucleus - genetic material controls cell, cytoplasm - gel-like with enzymes for chemical reactions, cell membrane - holds cell together & controls what goes in & out, mitochondria - aerobic respiration to transfer energy, ribosomes - proteins are made
        • plant (subcellular structures): cell wall - cellulose to support & strengthen, vacuole - cell sap of sugar & salts, chloroplasts - chlorophyll to photosynthesise,
        • bacteria - prokaryotes, cell membrane, wall & cytoplasm, with a DNA strand & DNA plasmids
      • microscopy
        • light microscope - light & lenses to form an image & magnify it, can see individual cells, large subcellular structures
        • electron microscope - electrons to form an image, higher magnification & resolution, see internal structures too
        • magnification = image size / real size
        • prepare the slide, set up the microscope correctly, & draw an observation
      • cell differentiation
        • differentiation is the process by which a cell changes to become specialised for its job
        • as they change, cells develop different subcellular structures and turn into different types of cells
        • differentiation often occurs as an organism develops, in mature animals they differentiate to repair & replace cells
        • sperm cells - reproduction, function to get DNA to the female DNA, long tail & streamlined to help it swim, lots of mitochondria giving energy, enzymes to digest cell membrane
        • nerve cells - rapid signalling, function to carry electrical signals, long & branched connections at their ends to connect to other nerves
        • muscle cells - contraction, function to contract quickly, long to be able to contract & lots of mitochondria to generate they energy needed
        • root hair cells - absorb water & minerals, function on the surface of plant root cells, big surface area to absorb
        • xylem cells - transporting substances, function to transport food & water around a plant, form tubes long & joined end to end, hollow
        • phloem cells - transporting substances, function to transport food & water around a plant, form tubes long & joined end to end, few subcellular structures so substances can flow
      • mitosis
        • body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle
        • when a cell divides, it is called mitosis, at the end of the cell cycles there are two new cells identical to the original cell, with the same number of chromosomes
        • growth & DNA replication: 1. in a cell that's not dividing, DNA is spread in long strings 2. before dividing, the cell grows & increases the amount of subcellular structures (mitochondria & ribosomes) 3. it duplicates it's DNA, it forms x-shaped chromosomes with each arm being a exact duplicate
        • mitosis: once DNA has been copied 4. the chromosomes line up at the centre of the cell & cell fibres pull them apart, the two arms go to opposite ends 5. membranes form around each chromosome, these become the nuclei of the cells 6. the cytoplasm & membrane divides, there is now two new identical daughter cells
      • culturing micro-organisms
        • bacteria are grown in a cultured medium with carbohydrates, minerals, proteins and vitamins they need to grow
        • contamination by unwanted micro-organisms will affect it and can result in the growth of pathogens
        • un-contaminated results: sterilise petri dish and inoculating loop to kill unwanted micro-organisms, tap on lid to stop air going in, upside down to stop condensation
        • antibiotic efficiency can be compared by the inhibition zones
      • chromosomes
        • the nucleus contains genetic material in the form of chromosomes
        • chromosomes are coiled up lengths of DNA molecules, each carries a large number of genes
        • body calls normally have two copies of each chromosomes - one from the mother and father, there are 23 pairs in a human cell
      • binary fission
        • prokaryotic cells replicate by binary fission: 1. circular DNA & plasmids replicate 2. cell gets bigger & DNA stands move to opposite 'poles' 3. cytoplasm begins to divide & new cell walls form 4. cytoplasm divides & two daughter cells are produced, there can be a variable number of plasmid copies
        • bacteria can divide very quickly if given the right conditions
        • the mean division time is the average amount of time for one bacteria cell to divide
      • osmosis
        • it is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
        • the molecules move in both ways because the molecules are moving randomly all the time, but as there is more on one side there is a steady net flow
      • diffusion
        • it is the gradual spreading out of particles from an area of higher concentration to an area of lower concentration - in solutions and gases
        • the bigger the concentration gradient, the faster the rate, a higher temperature will also give a faster rate because the particles have more energy
        • cell membranes hold the cell together and let stuff go in and out, but only small molecules can diffuse through, the larger the surface area of the membrane, the faster the diffusion rate because more particles can pass through
      • stem cells
        • differentiation is the process by which a cell changes to become specialised for its job
        • un-differentiated cells are stem cells can divide to produce more, they are in early human embryos and bone marrow (which can only turn into certain cells), they can be grown in labs to produce clones and made to differentiate to be used in medicine or research
        • stem cells from bone marrow can be transferred to replace faulty blood cells
        • embryonic stem cells could be used to replace faulty cells in sick people - insulin producing cells, nerve cells etc.
        • therapeutic cloning is when the embryo can be made to have to same genetic information as the patient so it would not be rejected but stem cells can be contaminated in a lab with a virus making them sicker
        • some people are against it: an embryo is a potential for human life, but some come from being unused in fertility clinics
        • in plants they are found in the meristems, these can be used to produce clones quickly and cheaply, they can be used to grow rare plants and plants with desired features, disease resistant
      • active transport
        • some substances need to be  absorbed against a concentration gradient from a lower to a higher concentration
        • the plant absorbs minerals from a very dilute solution against the concentration gradient, which is essential for growth but it needs energy from respiration to make it work
        • active transport is used in the gut when there is a lower concentration of nutrients in the gut but a higher concentration of nutrients in the blood
        • when there's a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood but if it is lower in the gut then active transport occurs to take glucose which can be transported to cells where it is used for respiration
      • exchange surfaces
        • cells can use diffusion to take in substances they need and get rid of waste products, how easy it is to exchange substances depends on the surface area to volume ratio
        • oxygen and carbon dioxide are transferred between cells, urea diffuses from cells into the blood plasma for removal by the kidneys
        • in single celled organisms gases and dissolved substances can diffuse directly into the cell across the membrane because they have a large surface area so enough can be exchanged at once
        • multicellular organisms need an exchange surface as the area to volume ratio isn't big enough
        • adaptions: thin membrane so there is a short distance to diffuse, large surface area so lots of substances can diffuse at once, lots of blood vessels to get stuff in and out of the blood quickly, gas exchange surfaces are often ventilated
      • exchanging substances
        • to transfer oxygen to the blood and remove carbon dioxide, the lungs contain alveoli they are specialised as they have: enormous surface area, moist lining for dissolving gases, thin walls, a good blood supply
        • in the small intestines, there are lots of villi, they increase the surface area so digested food is absorbed more quickly into the blood, they have a single layer of surface cells, and a good blood supply to assist absorbtion
        • carbon dioxide diffuses into  air spaces in the leaf, then  diffuse to where photo-synthesis happens, the under side of the leaf is an exchange surface, it is covered in holes called stomata, oxygen and water vapour diffuse out of the stomata
        • stomata care controlled by guard cells so they can close if too much water is being lost, the flat shape of the leaf increases the area of the exchange surface, the walls inside the leaf are another exchange surface
        • water containing oxygen enters the fish through the mouth and passes out through the gills, the oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses out
        • each gill has lots of thin plates called gill filaments which give a big surface area, they are covered in lamellae which increase the surface area more, they have blood capillaries to speed up diffusion, they have a thin surface layer of cells to minimise the distance

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