OCR A LEVEL BIOLOGY MODULE 2 : FOUNDATIONS IN BIOLOGY REVISION NOTES For 2015 onwards specification Miss T Banda
All living things are primarily made from 4 key elements: Carbon (C) Hydrogen (H) Oxygen (O) Nitrogen (N) Other elements that play important roles in the biochemistry of cells are: Phosphorus (P) Sulfur (S) Not as important Iron (Fe), Sodium (Na), Potassium (K) and Calcium (Ca). Carbon Hydrogen Oxygen Nitrogen Carbon Atoms can form four bonds with other atoms. Hydrogen Atoms can form one bond with other atoms. Oxygen Atoms can form two bonds with other atoms. Nitrogen Atoms can form three bonds with other atoms. IONS. An atom or molecule in which the number of protons is not the same as the number of protons is called an ion. CATION = When a molecule or atom loses and electron and becomes charged. ANION = When a molecule or atom gains an electron and becomes charged. CATION NECESSARY FOR: ANION NECESSARY FOR: SODIUM ION [NA + ] POTASSIUM ION [K + ] HYDROGEN ION [H + ] AMMONIUM ION [NH 4 + ] CALCIUM ION [CA 2+ ] KIDNEY FUNCTION STOMAL OPENING PH DETERMINATION PRODUCTION OF NITRATE IONS MUSCLE CONTRACTION NITRATE ION [NO 3 - ] HYDROGEN CARBONATE ION [HCO 3 - ] CHLORIDE ION [CL - ] PHOSPHATE ION [PO 4 3- ] HYDROXIDE ION [OH - ] AMINO ACIDS AND PROTEINS IN PLANTS MAINTAINS BLOOD PH BALANCE + CHARGE OF NA AND K IONS PLASMA MEMBRANE, NUCLEIC ACIDS, BONES PH DETERMINATION, CATALYSIS OF REACTIONS SUMMARY OF BIOLOGICAL MOLECULES. Some of elements present in the key biological molecules are: Carbohydrates Carbon, Hydrogen, Oxygen) C x (H 2 O) x Lipids Carbon, Hydrogen, Oxygen. Proteins Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur. Nucleic Acids Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus.
Sample Preparation. There are 3 types of Sample Preparation for Light Microscopy. 1. DRY MOUNT Specimen cut into thin slice (sectioning), Specimen placed on centre of slide and put a cover slip on top. 2. WET MOUNT Specimen is suspended in liquid. Place a cover slip on at an angle, to keep liquid under cover slip. 3. SMEAR SLIDES Use the edge of a slide to smear the sample, creating a thin, even coat. Place a cover slip over. Staining Staining is used because some cells let a lot of light through, so there is not enough contrast to see the cells. Stains increase the contrast and allow components to become visible. Staining is sometimes required in light microscopy, some stain the components of the cell, or stain the outside to stand out against the background. The two types are: GRAM STAIN TECHNIQUE Gram Positive bacteria will, when stained with iodine or crystal violet, show up blue/purple under a microscope. Gram Negative bacteria, when stained, lose the original stain so are counterstained. They then appear red/pink under the microscope. ACID-FAST TECHNIQUE Cells are dyed, and washed with acid. Mycobacterium are not affected and appear bright red under a microscope. Other bacteria lose the stain and are exposed to methylene blue, with stains blue.
In Electron Microscopy, a beam of electrons with a short wavelength is used to illuminate the specimen. The small wavelength allow more detail of the cell s ULTRASTRUCTURE to be seen. They can produce images with magnification sup to 500 000x and still have a clear resolution. The disadvantages of Electron Microscopy is that the equipment is expensive, can only produce images in controlled environments and the electrons can sometimes damage the specimen. TRANSIMSSION ELECTRON MICROSCOPE (TEM) In a TEM, a focused beam of electrons is transmitted through a specimen. The electrons can be absorbed, scattered or pass through the specimen. The electrons that reach the fluorescent film at the end of the TEM create the image. The dark areas means there is more absorption, while the lighter areas absorb less. Resolution = 0.5nm Magnification = 500 000x SCANNING ELECTRON MICROSCOPE (SEM) In a SEM, a concentrated beam of electrons is pass across the surface of the specimen. The electrons are scattered by the specimen and these electrons create the image. The scattered electrons are detected by appropriate detectors and the micrograph is produced. SEMs create 3D micrographs giving us information on their appearance. Resolution = 10nm Magnification = 100 000x DIFFERENCES BETWEEN TEM AND SEM TEMs have a higher resolution and magnification than SEMs. TEMs are only ever black and white, but SEMS can be in colour. TEMs produce 2D images, SEMs produce 3D images. TEMs only allow a small area to be analysed. SEMs allow a much larger area.
Magnification = How many times larger the image is than the actual size of the object being viewed. To calculate magnification it is MAG = IMAGE SIZE / ACTUAL SIZE This formula can be manipulated to find the image size and the actual size. REMEMBER I.A.M Cover the one that you want to find out and you can get the equation. RESOLUTION = the ability to see individual objects as separate entities. With light microscopes, the structures are very close together, so the light beams can cross over and we can no longer see them individually. Resolution can be increased by using electron beams. Their wavelength is shorter, so the individual beams won t overlap and we can see at a much higher magnification, with a high resolution. USING A GRATICULE TO CALIBRATE A MICROSCOPE Every microscope has to be calibrated with an eyepiece graticule, because the magnification stated differs from microscope to microscope. Each objective lens needs to be calibrated. A stage micrometer which has an accurate scale in micrometres. The eyepiece graticule and stage micrometer will need to line up to calibrate a lens. 1. Put the Stage Micrometer and Eyepiece Graticule in place 2. Get the scale of the micrometer in clear focus 3. Align the micrometer scale with the eyepiece scale, take a reading. 4. 100 small divisions are 1mm, so 1 division is 10um. 5. Work out the magnification of the lens. 6. Replace the stage micrometer with a specimen and measure using the eyepiece graticule.
Cellular Structure Prokaryotic Unicellular, very basic structure. 0.1-10 um in size Eukaryotic Can be Multicellular, more complicated internal structure. 10-100um in size. DNA Prokaryotic Only 1 DNA molecule, a chromosome, supercoiled. Floats in Cytoplasm. No Nucleus. Eukaryotic Multiple chromosomes, wrapped around proteins called histones. Packages into Chromatin, found in the Nucleus. Organelles Prokaryotic - Non membrane-bound. Eukaryotic Both non membrane-bound and membrane-bound, compartmentalises the cell. Ribosomes Prokaryotic Smaller: 70S. Eukaryotic Larger: 80S. Larger due to their involvement in making more complex proteins. Cell Wall Prokaryotic YES made of Peptidoglycan. Eukaryotic YES Plant Cells made of Cellulose, NO Animal Cells and YES Fungi made of Chitin.