biology (powerpoint)

• Making a slide e.g. onion cells

  1. Place a thin section of the specimen onto slide

  2. Add a stain e.g. Iodine

  3. Gently lower cover slip
• Examining under a microscope

  1. Switch on the light source and place your slide on the stage

  2. Use the lowest objective lens and turn the focusing wheel slowly until you can see a clear image

  3. Increase the magnification by changing the objective lens and re-focus
• Magnification


  The size of the image compared to the real size of the object
• Worked example 1


  • A magnified animal cell structure has a diameter of 6 mm, the actual diameter of the structure is 0.15mm, calculate how many times the structure has been magnified
• You may need to write your answers in standard form
• 8 Practicals. A quick Recap.
• pH and enzymes


  1. Took a sample every 20 sec

  2. Time taken for enzyme to work

  3. SPOTTING TILE!
• Enzymes


  • Made of proteins and are biological catalysts that increase the rate of chemical reactions without being used up
  • The shape of the active site of the enzyme is specific for each substrate
• If the shape of the active site becomes altered by the wrong conditions e.g. high temp, wrong pH: the enzyme will no longer work. It is denatured.
• Rate of enzyme activity

  Inversely proportional to the time to react
• Digestive enzymes


  • Carbohydrase (amylase) - breaks down carbohydrates into simple sugars
  • Protease - breaks down proteins into amino acids
  • Lipase - breaks down fats and oils into fatty acids and glycerol
• Enzymes control the synthesis and breakdown of chemicals in the body
• Pepsin works in the stomach where it is acidic due to the HCl. Its optimum pH is 1-2.
• Body temp. is 37°C so this is optimum for enzymes
• Mitosis


  • Cells divide during growth (number of cells need to increase) and repair (to replace damaged cells)
  • Each new cell is genetically identical to the parent cell
  • In humans this is 46 (23 pairs)
• Stages of mitosis


  1. Interphase - DNA replication, cell parts replicate

  2. Prophase - Preparing

  3. Metaphase - Middle

  4. Anaphase - Away

  5. Telophase - Two

  6. Cytokinesis - Cell splits into two
• A mutation might cause the cells to start dividing uncontrollably, this can result in the formation of a tumour which can lead to cancer (not all tumours are cancerous)
• Growth


  • Increase in size or mass
  • In young animals by rapid cell division all over the body
  • In plants by cell division at the root and shoot tips, and cell elongation throughout the plant's life
• Cell differentiation


  • Most animal cells differentiate in early development, plant cells can differentiate throughout their life cycle
  • Cell changes to become specialised, forming different sub-cellular structures
• Stem cells


  • Undifferentiated cells within an organism
  • In plants, found in meristems which can be used to produce clones quickly and economically
• Sexual reproduction


  Involves the joining of male and female gametes, mixing of genetic information, resulting in unique offspring
• Asexual reproduction


  Involves only one parent, no fusion of gametes, all offspring are genetically identical (clones)
• Meiosis


  • The process a cell goes through to produce gametes (sex cells)
  • Results in 4 genetically different daughter cells, each with half the number of chromosomes
• Genetics - Meiosis


  • Meiosis results in haploid cells (23 chromosomes)
  • Fusion of male and female gametes during fertilisation restores the normal diploid number (46 chromosomes) in the zygote
• DNA structure


  Genetic material in the nucleus, a polymer made from two strands in a double helix

  DNA is made from nucleotides, each with a phosphate, sugar, and one of 4 bases that pair up (A-T, C-G)
• DNA and the genome

  DNA is arranged in chromosomes, the genome is the entire DNA of an organism

  Human body cells have 23 pairs of chromosomes, each gene codes for a sequence of amino acids to make a specific protein
• Extracting DNA from fruit

  Crush and grind fruit to break down cell membranes

  Add detergent, salt and water to further break down cell and nuclear membranes

  Filter the mixture

  Add ice cold ethanol to precipitate out the DNA
• Evolution


  Change in the inherited characteristics of a population over time, through the process of natural selection

  Variation in a population gives some individuals an advantage, which may result in a new species being formed
• DNA


  Double Helix - coils around each other making a spiral ladder
• Nucleotides


  Repeating monomers that DNA is made from
• Components of a nucleotide

  • Phosphate group
  • Pentose sugar
  • Base
• There are 4 bases in DNA
• DNA base pairing


  1. T and C-G (Apples in the Tree, Cars in the Garage)
• DNA base pairs


  Joined by weak H bonds
• Chromosomes


  Structures DNA is arranged in inside a cell's nucleus
• Genome


  The entire DNA of an organism
• In human body cells the chromosomes are normally found in pairs, with 23 pairs per cell
• Gene


  A small section on a chromosome that codes for a particular sequence of amino acids to make a specific protein
• Extracting DNA from fruit

  1. Crush and grind fruit to breakdown cell membranes

  2. Add detergent and salt and water to further break down cell and nuclear membranes and expose DNA

  3. Filter the mixture

  4. Add ice cold ethanol to precipitate out the DNA
• Evolution


  A change in the inherited characteristics of a population over time