biology paper 1

• Light microscopes : Cheap to make, allow you to see outlines of cells.
• Electron microscope : See finer details such as organelles due to higher resolution and greater resolving power.
• magnification = Image size/ object size
• prefixes

  milli= 1 x 10^-3

  micro= 1 x 10^-6

  nano= 1 x 10^-9

  pico= 1 x 10^-12
• Eukaryotic = plants and animal cells, contains a nucleus
• Prokaryotic = Bacteria cell, plasmid loop of DNA
• plants and animals:

  • Nucleus - DNA
  • Cell membrane- controls what enters and leaves the cell.
  • Cytoplasm- liquid,chemical reactions take place.
  • Mitochondria- respiration
  • Ribosome- Protein synthesis.
• Only in plant:

  • Cell wall- cellulose
  • Chloroplast- chlorophyll.
  • Vacuole - sap
• Enzymes are proteins, biological catalysts that break down molecules into shorter ones.
• Enzymes are specific, only break down substrates that fit their active site (lock and key). Substrate binds to enzyme active site- enzyme substrate complex.
• Activity(rate of reaction) increases with temperature until the enzyme denatures- same with too high or too low pH. Optimum- condition for max rate/activity.
• Enzyme Practical:

  1. Mix amylase and starch and start timer, remove few drops every 10 seconds and add to iodine.
  2. Turns black but will eventually stay orange showing starch is broken down.
  3. Record time for no starch to be detected( will remain orange).
  4. Repeat at different temperatures or with different pH buffer solutions added.
  5. Optimum pH is between 2 lowest times.
• Food test:

  Starch - turns iodine from orange to black

  Sugars- benedicts solution from blue to orange.

  protein- turns blurets reagent from blue to purple

  Lipids- cold ethanol to cloudy
• Diffusion- Movement of particles from an area of high concentration to low concentration, down a concentration gradient. Passive- no energy
• Osmosis-

  Diffusion of water across a semi-permeable membrane to balance the concentrations of solutions inside and outside a cell. Water must move as larger molecules cannot fit through the holes. Water moves in if concentration is higher outside.
• Rate of diffusion-

  Increased by increasing the difference n concentrations, surface area and temperature.
• Active Transport: The movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient. via carrier proteins.
• Mitosis: A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent cell
• Human cells have 23 pairs of chromosomes(Diploid). Gametes(eggs and sperm) have just 23 (Haploid). new diploid cells are made by mitosis for growth and repair.
• Process of mitosis:

  1. DNA duplicated (interphase), nucleus membrane dissolves (prophase).
  2. Two sets of chromosomes line up in middle (metaphase) pulled to opposite sides of cell (anaphase).
  3. Other organelles are duplicated, new membranes are formed around the two sets of chromosomes to make 2 nuclei. (telophase).
  4. The cell divides (cytokinesis), producing 2 genetically identical diploid cells.
• Cancer- damaged cells, divide uncontrollably.
• stem cells can differentiate or specialise to perform specific functions. They are found in animal embryos and plant meristems.
• Some stem cells made in bone marrow- specialise into blood cells.
• Embryo clones can be made of a person to harvest stem cells from. These can be used to treat conditions without them being rejected by patients body. Cloning can also be used to preserve species or produce crops with desired traits.
• CNS:

  Central nervous system (brain and spinal cord).
• PNS:

  Peripheral nervous system(all other nerves).
• Stimulus-receptor-sensory neurone- relay neurone- motor neurone -effector - response
• Electrical signal travels to spine through sensory and relay neurone. Signals travel through gap between these neurones(Synapse) by a neurotransmitter chemical. Once at spine the signal can go to brain to make a decision to act, Effect goes to arm via relay and motor neurone to move.
• Reflex Arc- Signal is much quicker. Glands are also effectors - they secrete chemicals.
• Practical for reaction times:

  1. Drop ruler between finger and thumb
  2. Measure distance fallen before caught, repeat, calculate mean. Independent variable- stimulant increases the neurotransmission. Depressant decreases neurotransmission.
• Meiosis- the process of cell division that produces four haploid gametes.
• Process of meiosis:

  1. Chromosomes in diploid are copied.
  2. similar chromosomes pair up and genes swapped between them.
  3. cell divides to make 2 diploid cells.
  4. these divide again to produce 4 haploid cells.
• Sexual reproduction- Offspring better adapted to environment
• Asexual reproduction- by mitosis the daughter cells will be identical, only one parent needed.
• DNA

  double helix polymer- stores genetic code. Bases made from sugar/phosphate. Bases= GCAT, every 3 bases code for amino acid.
• genotype- an organisms specific genetic code.
• phenotype- how this code is expressed in physical characteristics
• Inheritance-

  characteristics are determined by type and quantity of proteins synthesized. Some controlled by one gene, most by 2 or more.
• Alleles- different versions of a gene that code for different versions of a protein.
• Dominant allele - the allele that is expressed in the phenotype when the individual has two copies of that allele. 'B'