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Biology. Topic 1: microscopy. Magnification = image size/real size. M=I/A Light microscopes were invented in 1590s. they use light and lenses to form an image and magnify it. Allows us to see individual cells while it’s still alive. Electron microscopes were invented in 1930s. they use electrons to form an image giving them a larger magnification and higher resolution. They let us see smaller things in greater detail, but the specimen has to be cut open to use. Core practical: light microscope. 1) prepare the slide by adding a drop of water onto the slide and placing the onion layer in the slide. 2) use iodine to stain the onion and make it clear when looking through microscope. 3) clip the slide onto the stage with the lowest magnification. Use knob to raise the stage. 4) look down eyepiece and adjust knob to lower stage until image is clear. Topic 2: transport in cells. Core practical: effect of pH on enzymes. 1) Set up a Bunsen burner, heatproof mat, tripod and gauze. 2) Place a beaker of water on the gauze and adjust the flame to keep the water at about 35°C. 3) put two drops of iodine solution into each spot of a spotting tile. 4) Add 2 cm3 of amylase enzyme solution to a test tube. 5) Place 2 cm3 of starch solution into the same tube. 6) Finally add 1 cm3 of pH solution to the tube. This will keep the pH constant. 7) Mix the solution in the test tube and place it into the beaker of water on the Bunsen burner. 8) Use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile. 9)Repeat until the iodine solution stops turning black. Record the time this takes. Repeat with different pH solutions. Rate = 1000/time Core practical: food tests. Sugars: 1) place food sample into beaker and mix with benedicts solution. 2) place mixture into hot water for 5 mins.3) results will vary from blue to green to yellow to red from weak to strong. Starch: 1) mix food sample with iodine solution. 2) shake for 2 mins. 3) results change from orange to blue. Proteins: 1) mix food sample with hydroxide to make it alkaline. 2) add copper sulfate which is blue. 3) if mixture turns pink then it contains protein. Lipids: 1) mix ethanol with food sample 2) shake for 1 min until substance dissolves 3) pour into distilled water and cloudier means more fats. Energy in food = water mass x water temp change Energy per gram of food = food energy/food mass Transport in cells: Diffusion is the transport of particles from high to low concentration with the gradient through a partially permeable membrane. Osmosis is the movement of water from a high to low concentration with the gradient. Active transport is against the gradient from low to high concentrations. Core practical: effect of sugar on plants. 1) prepare sucrose solutions of different concentrations from pure water to very concentrated. 2) cut potatoes into similar sized cylinders and place into each concentration. 3) soak for 40 mins and then dry with paper towel. 4) weigh each potato to find out mass increase. Percentage change = mass change/initial change. Topic 3: cell division. Mitosis: 1) prophase – chromosomes get short and fat. Membrane around nucleus breaks down for chromosomes to move freely. 2) metaphase – chromosomes line up. 3) anaphase – spindle fibres pull chromosomes apart. Chromatids are pulled to opposite ends of cell. 4) telophase – membranes for each set of chromosomes form and split the cell into 2 daughter cells. Stem cells: Stem cells are cells that get turned into different cells while the foetus develops and can become anything. In adults, stem cells can only be found in bone marrow and can’t become anything. They are mainly used for repairing cell damage. Embryonic stem cells can be used to grow new cell tissue by extracting it from embryos before they need to use it during foetal development but ethical issues about unborn babies being killed make it hard to experiment on. People feel that embryos shouldn’t be used because they are unborn babies that could grow and have a life but since they haven’t been developed into a foetus, it could still be used. Plant stem cells, meristems, produce unspecialised cells which can form any plant cell but only work if the plant is still alive. Topic 4: nervous system. CNS: Sensory neurones carry impulses from receptors to CNS. Relay neurons carry impulses from receptors to motor neurons. Motor neurons carry impulses from CNS to effectors. Sensory neurons start with a receptor, impulses travel along dendron into the cell body across the axon and onto a receptor. Motor neurons start at dendrites and impulses travel along axon covered in myelin sheath into effectors. Relay neuron is the cell body with many axons branching off into dendrites. Reflex arc: 1) when receptors detect something, impulses are sent along sensory neurons to a relay neuron. 2) when impulse reaches a synapse between sensory and relay, neurotransmitter are released to carry on the message in chemical form. 3) same happens when impulse reaches relay and motor. 4) impulses travel along motor until it reaches an effector. If the effector is a muscle, it will contract and if it’s a gland it will secrete a hormone. Brain: Cerebellum is at the back and controls coordination & balance. Cerebrum is split into left and right hemispheres with the left controlling left side of the body and right controlling right side of the body. Medulla oblongata is at the base and controls unconscious activity like breathing. CT scanners ae used to x-ray the brain to check for brain damage. PET scanners need radioactive material in the patient which collects cells to act as a tracer to give detailed structure of brain. It can show areas that are underused or inactive. Eye: Cornea is transparent outer layer that refracts light. Lens refracts light onto retina and controlled by ciliary muscles and suspensory ligaments. Pupil is where the light enters. Iris controls how much the pupil contracts. Retina is at the back with rods and cones. Rods are light and cones are black and white. Optic nerve sends information about the image to the brain. When looking at close objects, the ciliary muscles contract and suspensory ligaments relax. Looking at long distances is the opposite. Long sight is due to the lens being incorrect and not refracting enough. convex lenses correct vision. Short sight is due to the lens refracting too much. Concave lenses correct vision. Meiosis: 1) cell duplicates genetic information and forms 2 armed chromosomes and arranges into pairs. 2) pairs line up in centre. 3) pairs are pulled apart, so each new cell has 1 copy of chromosome. Half of the fathers and half of the mothers genes are in each new cell. 4) in second division, chromosomes line up and are pulled apart. 5) 4 haploid daughter cells are formed as gametes with different genetic structures. Protein synthesis: 1) RNA polymerase binds to non-coding DNA and copies the complimentary base pairs and makes mRNA. 2) the mRNA leaves the nucleus and enters the ribosome where proteins are made. 3) amino acids are brought to ribosome by tRNA in an order that matches the base pairs. The T base is replaced with U instead. 4) amino acids join together by ribosome to form a polypeptide. The tRNA molecules move away again. Topic 5: genes. Alleles: Alleles are different versions of the same gene because we inherit half of DNA from both parents. For homozygous traits are where the allele is the same and heterozygous is when the alleles are different. The allele shown in the characteristic is the dominant gene and the other is recessive. The genotype is a combination of alleles which determine the phenotype. Gregor Mendel: Mendel did experiments with peas by breeding 2 desired traits to get offspring with that trait. He attempted with tall pea plants and cross bred with short ones to produce tall offspring. He bred 2 offspring plants to get most being tall but one short from the recessive short gene from original pair. The tall gene was the dominant, so more offspring were tall. Topic 6: evolution. Cavemen: Ardi was found in Ethiopia and is 4.4 million years old. Structure of feet meant she climbed trees with short arms and long legs like a monkey and her brain size was similar to chimpanzee. Walked upright and didn’t use hands to help walk. Lucy was found in Ethiopia 3.2 million years ago. She had arched feet for walking with normal sized arms and legs. Her brain was larger than Ardis and walked upright. Turkana boy was discovered in 1984 in Kenya dating back to 1.6 million years ago. Short arms and legs were human like, and brain was similar size to humans. Adapted to walking upright. Topic 7: genetics. Genetic engineering: 1) DNA is cut up with restriction enzyme leaving sticky ends. 2) restriction enzyme cuts the vector DNA open leaving sticky ends. 3) the sticky ends are stuck using ligase to produce recombinant DNA. 4) the cells are inserted back into the body.