Question 7
Materials: eye protection such as safety goggles, dropper, water, pair of forceps (tweezers), piece of onion, glass slide, iodine solution, coverslip, mounted needle, filter paper, microscope.
1 Squeeze the bulb of the dropper very gently and then dip it in the water. Release the bulb to allow a small amount of water to enter the dropper. Now place the dropper over the centre of a glass slide, and gently squeeze the bulb to add a drop of water to the slide.
2 Using a pair of forceps, gently peel back a single layer of onion tissue (epidermis) from the onion. The layer should be almost see-through. Spread a small piece of the onion epidermis into the water on the glass slide.
3 Use the dropper to add one or two drops of iodine solution to the onion epidermis. This will stain some parts of the cell, making them easier to see.
4 Place one end of a coverslip against the slide. Support the other end with a mounted needle.
5 Lower the other end of the coverslip gently, using the mounted needle. This will prevent air bubbles from being trapped under the coverslip.
6 Carefully soak up any excess liquid using filter paper.
7 Put the lowest power objective lens of a microscope in place. Use the coarse adjustment wheel to move the lens as far away from the stage as possible. Place the slide on the stage of the microscope. Secure it with the stage clips.
8 Observe the cells by looking through the eyepiece of the microscope.
a Find the onion cells using the low-power objective lens. Turn the coarse adjustment wheel to bring the image into focus.
b Rotate the lenses so that a higher-power objective lens is now above the slide. Then use the fine adjustment wheel to bring the image into focus.
Caution: Handle the glass slide and coverslip with care as they can break easily. Handle mounted needles with extreme care and only leave them in a place where you and others can see them. Iodine solution is harmful to skin and is dangerous to the eyes. It stains the skin and clothing readily. Wear eye protection such as safety goggles, and do not touch the solution. Use it very carefully. Turn the adjustment wheel slowly. Check from the side so that the objective lens does not hit the glass slide.
Figure labels: mounted needle; coverslip; onion epidermis; glass slide; filter paper; iodine solution.
9 Draw one onion cell. Label the cell parts that you can observe. Make sure you include the edges of the cells around it. Record the magnification of the microscope.
1 Squeeze the bulb of the dropper very gently and then dip it in the water. Release the bulb to allow a small amount of water to enter the dropper. Now place the dropper over the centre of a glass slide, and gently squeeze the bulb to add a drop of water to the slide.
2 Using a pair of forceps, gently peel back a single layer of onion tissue (epidermis) from the onion. The layer should be almost see-through. Spread a small piece of the onion epidermis into the water on the glass slide.
3 Use the dropper to add one or two drops of iodine solution to the onion epidermis. This will stain some parts of the cell, making them easier to see.
4 Place one end of a coverslip against the slide. Support the other end with a mounted needle.
5 Lower the other end of the coverslip gently, using the mounted needle. This will prevent air bubbles from being trapped under the coverslip.
6 Carefully soak up any excess liquid using filter paper.
7 Put the lowest power objective lens of a microscope in place. Use the coarse adjustment wheel to move the lens as far away from the stage as possible. Place the slide on the stage of the microscope. Secure it with the stage clips.
8 Observe the cells by looking through the eyepiece of the microscope.
a Find the onion cells using the low-power objective lens. Turn the coarse adjustment wheel to bring the image into focus.
b Rotate the lenses so that a higher-power objective lens is now above the slide. Then use the fine adjustment wheel to bring the image into focus.
Caution: Handle the glass slide and coverslip with care as they can break easily. Handle mounted needles with extreme care and only leave them in a place where you and others can see them. Iodine solution is harmful to skin and is dangerous to the eyes. It stains the skin and clothing readily. Wear eye protection such as safety goggles, and do not touch the solution. Use it very carefully. Turn the adjustment wheel slowly. Check from the side so that the objective lens does not hit the glass slide.
Figure labels: mounted needle; coverslip; onion epidermis; glass slide; filter paper; iodine solution.
9 Draw one onion cell. Label the cell parts that you can observe. Make sure you include the edges of the cells around it. Record the magnification of the microscope.
