Session 2 - Artificial Selection in Brassica rapa (2/4); Microscopy and Mitosis Flashcards
What should be distinguished from the first true leaves of the plant?
The cotyledons (“seed leaves”)–these are more square, two lobed and rather thick.
What is the petiole?
The petiole is the stalk connecting the leaf to the stem. It begins at the junction to the main stem–the junction often has a slight ridge and is brown/red-ish in color. It ends at the point (at the leaf end) at which the first leaf vein intersects it.
What happens in pollination?
Pollen from the anther of a flower is tranferred to the sigma of another (cross-pollination) (normally done by bees)
How did we cross-pollinate the flowers?
By using bee sticks (made from glued bee thorax + toothpick). The thorax is the body segment to which the wings are attached. Remove head, abdomen and legs.
In the microscope, what illuminates the object being studied?
lamp
What does the lamp have integrated in it?
an (integral) filter holder that accomodates standard microscopic filters
What is used to limit the amount of light entering the condenser?
field diaphragm ring
What does the condenser do?
It focuses light onto a small area in the plane of the specimen by means of the condenser focus knob.
Why would the aperture selector be rotated?
To choose between different apertures appropriate for bright-field, phase-contrast, dark-field microscopy.
For the purposes of the experiment it should be set to “O” for bright-field microscopy.
What is the aperture diaphragm adjustment and what should it not be used for?
It controls the amount of light entering the objective lens under the bright-field illumination; it should not be used to control the brightness of the field. Too much light will decrease contrast, too little will decrease resolving power.
What does the stage do?
It holds the slide (specimen) in place under the objectives. It has a Vernier scale to allow you to retrieve the location of an interesting object.
Slides are clipped into what that rests on the stage?
specimen holder
Where and what do the stage manipulation controls do?
They are located beneath the right-rear corner of the stage. They are two knobs that are rotated to move the specimen left/right, back/forward on the stage
What are concentrically arranged and used for focusing the specimen?
The coarse and fine focus knobs
What actually magnifies and focuses an image of the specimen?
The objective and ocular lenses; the objectives are located on a revolving nosepiece with click-stop centering positions
How do you customize the microscope for your own pupil-to-pupil distance?
Use the interpupillary distance adjustment
What can be adjusted on the ocular lenses to ensure that the images reaching both eyes are properly focused?
diopter ring
What shaped cells (in the onion) should one be looking for, for mitotic activity?
Look for short square cells; elongated cells will not be dividing.
What were the onion roots soaked in before staining?
A vial of 18% HCl for 4 minutes, then a vial of Carnoy fluid for 4 minutes
What part of the onion root was stained, and what was it stained with?
The root tip; the stains used were fuchsin and toluidine. After staining, the tips were rinsed by adding and blotting away a drop of distilled water with a Kimwipe. Then cover the root tip with a drop of water and place the coverslip onto it
What is the purpose of the soaking in HCl and Carnoy fluid?
HCl makes the cell permeable and Carnoy fluid fixates the cells in their stage
How does gamma radiation affect DNA?
It breaks the phosphodiester linkages in the DNA (effectively breaking the strand in some cases); spindle fibers would then be less able to attach to centromeres and uneven distribution of chromosomes would occur. Cell death is even possible.
How does colchicine affect the cell?
It inhibits spindle fiber formation, effectively arresting the cell in prophase (preventing it from progressing into metaphase)
What part of the onion root tip should be observed?
The zone of cell DIVISION–not the zone of cell differentiation or the zone of elongation
