2: The Cell as the Basic Unit of Life - Practical Flashcards
2.1: Observation with a light microscope
What is the purpose of adjusting the disphragm?
To allow entry of a suitable amount of light.
A dim image may result if there is insufficient light while a faint image may result if the light is too bright.
2.1: Observation with a light microscope
When using the high-power objective for observation, why should we not focus with the coarse adjustment knob? (2)
The coarse adjustment knob leads to a larger degree of movement of the stage (or the body tube).
The movement controlled by the coarse adjustment knob may damage the objective or the slide
because the distance between the objective and the slide is very small.
2.1: Observation with a light microscope
Draw a labelled diagram to show onion epidermal cells under a light microscope with 150x magnification.
2.2: Preparing and observing a temporary mount of ox corneal cells
Which staining solution is used in preparing the temporary mount?
Methylene blue solution
2.2: Preparing and observing a temporary mount of ox corneal cells
What is the purpose of adding methylene blue solution to the area touched by the ox eye on the slide?
To stain the nuclei blue,
and act as a mounting medium.
2.2: Preparing and observing a temporary mount of ox corneal cells
List 4 reasons why a cover slip is put over the cells for observstion with a microscope. (4)
To flatten the specimen so that they can be seen clearly in one plane of focus for the objective lens.
To prevent the objective lens from getting dirty by touching the specimen or the mounting medium.
To prevent the specimen from drying out by evaporation.
To protect the specimen from being damaged.
2.2: Preparing and observing a temporary mount of ox corneal cells
What sub-cellular structures can be seen in an aminal cell with a light microscope?
Cell membrane, cytoplasm, nucleus
2.3: Preparing and observing a temporary mount of plant cells
What is the staining solution added to the onion epidermis?
Iodine solution
2.3: Preparing and observing a temporary mount of plant cells
Why are the onion epidermis and banana tissues stained, while the Hydrilla leaf is not? (2)
Hydrilla leaf cells have pigments (chlorophyll) which can be observed clearly under a microscope.
Onion epidermal cells and banana cells do not have pigments. They need to be stained with iodine solution before observation.
2.3: Preparing and observing a temporary mount of plant cells
Why is the banana tissue stirred with the toothpick before observation?
To spread out the cells so that light can pass through them.
2.3: Preparing and observing a temporary mount of plant cells
What sub-cellular structures can be seen in a plant cell with a light microscope?
Cell wall, cell membrane, nucleus, cytoplasm, chloroplast and granules.
2.3: Preparing and observing a temporary mount of plant cells
Explain if all plant cells observed are green in colour.
No, because not all of them contain chloroplasts or chlorophyll. Only those with chloroplasts are green.
