SB1 Key Concepts


SB1a Microscopes

  • Resolution - smallest distance between two points that can still be seen as two points.
  • Today's microscope -  magnify x1500 with resolutions of 0.0001mm.
  • Electron microscope, invented in 1930s, used beams of electrons to pass through a specimen to build an image. Magnify x2000000, with resolutions of 0.0000002mm
  • milli-, ÷1000 e.g. millimetres (mm). 
  • micro-, ÷1,000,000 e.g micrometres (μm)
  • nano-, ÷1,000,000,000 e.g. nanometres (nm)
  • pico-, ÷1, 000,000,000,000 e.g. picometres (pm)
  • To get from milli- to micro, ÷ 1000, from micro- to nano-, ÷1000 etc...
  • To get from pico- to nano- ,x1000, from nano- to micro, x 1000 etc...
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SB1b Plant and Animal Cells

  • Eukaryotic - cell with a nucleus.
  • Nucleus - controls cell and activities. Contains chromosomes/DNA.
  • Cytoplasm - contains dissolved nutrients and salts and structures called organells. Most chemical reactions occur.
  • Cell membrane - controls the movement of substances in and out of the cell.
  • Mitochondriarespiration occurs, most energy is released in respiration.
  • Ribosomes - Protein synthesis occurs.
  • Magnification - mesured size ÷ actual size / M = I ÷ O
  • Plant cells have additional structures:
  • Chloroplast - contains chlorophyll, which absorbs light for photosynthesis.
  • Cell wall - made of cellulose, supports and protects cell.
  • Vacuole - contains cell sap to keep the cell firm and rigid.
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SB1c Specialised Cells

  • Specialised cells - cells with a certain function (job).
  • Microvilli - cells that line the small intestine, that absorbs food molecules produced by digestion. Contain membranes with tiny folds that increase the surface area of the cell, so more area for molecules to absorb, quicker the absorbtion. 
  • Gametes - includes sperm and egg cells, haploid (contains one copy of 23 chromosomes) cells that fuse during sexual reproduction, so cell produced by fertilisation, embryo, has two copies.
  • Diploid - cell with two copies of 23 chromosomes. 
  • Egg cell - contains a haploid nucleus, jelly coat (hardens after fertilisation so only one sperm cell enters egg cell), cell membrane (fuses with sperm cell, also hardens) and cytoplasm (contains nutrients to supply egg with energy and materials for growth).
  • Sperm cell - contains acrosome (vacuole containg enzmes that break down substances in egg's jelly coat), nucleus, tail (swimming), mitochondria (arranged in spiral to release lots of energy to power tail) and membrane.
  • Cells line the oviduct to transport embryos, contain cilia (covered in cell membranes and contain strands of a substance that can contract and cause wavy movement).
  • Epithelial cells - cells that line structures in body.
  • Ciliated epithelial cells - epithelial cells with cilia.
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SB1d Inside Bacteria

  • Prokaryotic - cells that don't have nuclei.
  • Flagellum - move in a whip-like motion to move bacterium,(not all have this).
  • Chromosomal DNA - DNA found loose in the cytoplasm, controls most of cell's activities.
  • Plasmid DNA - smaller loops of DNA, controls a few of cell's activities
  • Slime coat - protection (not all have this).
  • Flexible cell wall - supports, notoutof cellulose.
  • Cytoplasm - contains ribosomes.
  • Standard form - figures from 1 to 10 multiplied by the power 10.
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SB1e Enzymes and Nutrition

  • Enzymes - proteins that function as biological catalysts (speed up a chemical reaction without being changed by the reaction). The substances that enzymes work on are called substrates and the substances produced are called products.
  • Digestive enzymes turn large molecules in food into smaller subunits, so it's small enough to be absorbed
  • Protein - made up of amino acids
  • Starch - made up of glucose molecules
  • Lipids-  made up of fatty acids and glycerol.
  • Synthesis - building larger molecules from their subunits.
  • Amylase - found in the saliva and small intestine, breaks down starch to sugars (e.g. maltose).
  • Catalase - most cells and mostly liver cells, breaks down hydrogen peroxide (made in cell reactions) into water and oxygen.
  • Starch synthase - plants, synthesis of starch from glucose.
  • DNA polymerase - nucleus, synthesis of DNA from its monomers 
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SB1f Testing Foods

  • Iodine Solution - changes from a yellow to a blue-black when in contact with starch.
  • Benedict's test - changes from blue to red when in contact with reducing sugars.
  • Biuret's test - changes from blue to purple when in contact with protein.
  • Emulsion lipid test - changes from colourless to milky white when in contact with lipids.
  • Calorimeter - measures the amount of energy in food by burning.
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SB1g Enzyme Action

  • Active site - the space where the substrate fits into an enzyme during a reaction. Different substrates have different 3D shapes so this explains why enzymes can only work with specific substrates. 
  • Lock-and-key model - Substrate collides with active site and becomes attached. Enzyme catalyses breakdown of substrate and products are released from active site. The enzyme is unchanged and can be reused.
  • Changes in pH or temperature can affect the active site. If the active site changes too much, the substrate cannot fit so the enzyme will not catalyse and has denatured.
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SP1h Enzyme Activity

  • Temperature - as temperature increases, molecules move faster increasing chance of substrates bumping into enzymes. However, if temperature gets too high, enzyme changes, becoming difficult for substrate to fit into active site 
  • pH - at pHs above and below the optimum, the shape is affected and enzyme doesn't work well.
  • Substrate concentration - at low conc" enzyme's active sites are empty, so rate of reaction slow. High conc", most enzymes contain substrates, so rate of reaction as fast as possible
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SB1i Transporting Substances

  • Diffusion - overall movement of particles from a high conc" to a low conc". Particles diffuse down a concentration gradient (difference between two conc"). The bigger the differece, steeper the gradient and faster the diffusion.
  • Osmosis - overall movement of water particles across a semi-permeable membrane from a dilute solution to a concentrated solution. Movement will stop when concentration is the same.
  • In osmsosis, tissues gain or lose mass. To calculate: ((final mass - initial mass) ÷ intial mass) x 100.
  • Active transport - transporting of particles across a cell membrane (from a region of low conc" to high conc") against the concentration gradient. This is carried out by transport proteins in cell membranes - they capture certain molecules and carry them across cell membrane. It is an active process so requires energy. 
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