Required practicals

• An optical microscope is used to view cells on a prepared microscope slide.
• The center of the microscope has a stage where the microscope slide is placed.
• The stage has clips to hold the slide in place.
• Below the stage, there is a lamp or a mirror used to reflect light up through the microscope slide.
• Above the stage, there are objective lenses with magnifications of four times, ten times, or forty times.
• The top of the microscope contains the eyepiece with a magnification of ten times.
• The microscope also has a coarse focusing dial and a fine focusing dial.
• To use the microscope, the slide is placed onto the stage and the lowest power objective lens is selected.
• The objective lens is positioned so it almost touches the microscope slide by slowly turning the coarse focusing dial.
• The fine focusing dial is used to bring the cells into a clear focus.
• The total magnification is calculated by multiplying the magnification of the eyepiece lens by the magnification of the objective lens.
• A higher power objective lens can be selected for a clearer view.
• Using an optical microscope, the nucleus, the cytoplasm, and the cell membrane can be seen in animal cells.
• Under the light microscope, the cell wall, the cytoplasm, the nucleus, and the vacuole can be seen in plant cells.
• Chloroplasts can also be seen under the light microscope in plant cells.
• A magnification scale is included in the drawing by measuring the diameter of the field of view in millimeters and showing this on a drawing using a scale bar.
• Osmosis is a diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
• When plants are placed in water, water moves into the cell by osmosis, causing the cell to expand.
• If a plant cell is placed into a concentrated solution, water moves out of the plant cell by osmosis, causing the cell to shrink.
• The plan used for investigating the effect of osmosis on plant tissue is a potato, but other vegetables such as beetroot or parsnip can also be used.
• The potato skin can affect osmosis, so it's important to peel the potato before using it for the experiment.
• A cork board is used to produce three cylinders of potato, all of the same diameter, using a scalpel to trim them to the same length.
• The length and mass of each cylinder are measured using a ruler and a balance.
• Each cylinder is placed into a test tube, filled with 10 centimeters cubed of an 0.5 molar sugar solution, 10 centimeters cubed of Nohr 22 5 molar sugar solution, and distilled water.
• The potato cylinders are left to simmer overnight to allow osmosis to take place.
• The potato cylinders are removed and gently rolled on paper towel to remove surface moisture.
• The length and mass of the potato cylinders are measured again, and the percentage change in length and mass is calculated using the equation: percentage change equals the change in value divided by the original value multiplied by 100.
• The chemical tests for carbohydrates, proteins, and lipids are required practicals that contain a lot of detail.
• The key things to learn for these tests are the chemicals used to test for each food group and the positive results.
• The potato cylinder with a starting mass of 1.5 6 grams increases by 0.25 grams, resulting in a percentage increase of plus 16.03 percent to two decimal places.
• All of the chemicals used in these tests are potentially hazardous, so safety goggles must be worn.
• The potato cylinder with a starting mass of 1 point 3 2 grams decreases by -0.19 grams, resulting in a percentage decrease of minus 14.39 percent to two decimal places.
• To test for carbohydrates, place two centimeters cubed of food solution into a test tube and add a few drops of iodine solution, which will turn blue black if starch is present.
• The graph of the percentage changes in mass or length against the concentration of the sugar solution shows that in water, the potato cylinder gains mass as water moves in by osmosis, while in concentrated sugar solution, the cylinder loses mass as water moves out by osmosis.
• To test for sugar such as glucose, add 10 drops of Benedict solution, a blue color, to two centimeters cubed of food solution, place the test tube containing the solutions into a beaker, and half fill the beaker with hot water from a kettle, leaving it for around 5 minutes.
• The line on the graph where the concentration outside the cell is the same as the concentration inside indicates no overall osmosis takes place.
• If sugars are present, the Benedict solution will change color, giving an approximate idea of the amount of sugar present but not the exact amount.
• To test for proteins, add two centimeters cubed of barley red solution, a blue color, to two centimeters cubed of food solution, and if protein is present, the barley red solution will change from blue to a purple or lilac color.
• To test for lipids or fats, grind food with distilled water using a mortar and pestle, add a few drops of distilled water and a few drops of ethanol to the food solution, and if lipids are present, a white cloudy emulsion forms.
• Ethanol, which is used in the lipid test, is highly flammable, so no naked flames should be present.