TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Biology Practicals - how to carry out some experiments
Using a simple respirometer
This ones hard to describe without the image...
- pour 5cm^3 of potassium hydroxide solution into each tube of respirometer
- fill the plastic or metal cage with germinating seeds. Place in one vessel making sure that seeds don't come in contact with potassium hydroxide solution.
- add to other tube, a volume of water eq. to the volume of seeds
- draw Brodie's fluid into manometer tube (the center tube thing) so it comes halfway up the scale on either side
- remove the syringe + screw clip
- stand respirometer in water bath at 20 degrees with manometer outside the water bath
- leave at least 5 mins to equilibriate then adjust position of syringe so its at a set level
- record positions and level of manometer at set intervals
- repeat with 30 and 40degrees
- once completed, record mass of living material
Results=- plot graph of manometer readings against time for each set of results at a particular temp. Use this for analysis
Demonstration and measurement of transpiration
Image
- cut leafy shoot from a round, woody stem + immediately place cut end in container of water
- in lab, make second cut to remove about 5cm of bottom of shoot. (helps to avoid air bubbles entering xylem vessels)
- assemble a POTOMETER in sink full of water. Stick shoot in rubber bung. Then remove last 3cm of bark from shoot to prevent phloem sap from blocking xylem.
- introduce an air bubble into end of capillary tube by lifting tube out of the water its end was in. Blot end carefully with paper towel + replace tube in water when air bubble 3-6mm long has entered capillary tube.
- when bubble moving at steady rate, record the movement along the scale at regular time intervals.
Results= tabulate results showing times + position of bubble along the scale. Plot graph to show position (vertical axis) vs time (horizontal)
Stomatal Counts
- paint a small area of nail-varnish (clear) on lower epidermis of leaf.
- when dry, cover nail-varnish film with clear adhesive tape + press gently so sticks
- peel off tape + transfer onto a clean microscope slide
- examine the impression with a microscope.
- count # of stomata in field of view. Count at least 3 different ones and find mean. (average).
- use a stage micrometer to find diameter of field of view then use the formula Area= (pi)r^2 to find area of stage of view.
- Calculate # per mm by dividing number in view by size of stage area.
Examination of stained blood films and the identification of cells
- only involves getting a pre-made slide of stained blood and comparing to see what blood cells they are- we often get images within our exams telling us to identify different white blood cells (neutrophils, eosinophils, lymphocytes and monocytes particularly)
Erythroctes (red blood cells)- biconcave shape, appear circular with lighter centres. Outnumber white blood cells 600 to 1.
Neutrophils - 70% of all w.b.c.- irregular lobed nucleus, usually staining blue or purple. Fine granules in cytoplasm.
Lymphocytes - relatively large, round nucleus with clear cytoplasm. In smaller lymphocytes the nucleus takes up most of cell.
Monocytes - largest of all w.b.c. horseshaped/indented nucleus. Cytoplasm usually appears pale blue colour or clear.
Eosinophils - large, red-stained granules in cytoplasm, lobed nucleus (usually 2 lobes)
Basophils - rare (less than 1% of w.b.c.). Typically dark stained granules in cytoplasm + lobed nucleus.
Factors affecting growth of pollen grains
- place 1 drop of sucrose solution in center of coverslip + dust small amount of pollen onto solution.
- carefully invert coverslip onto ring of plasticine- forming a hanging drop preparation
- leave at a temp of 20-25 degrees for 1-2hrs then examine under microscope
- count total # of pollen grains visible in field of view + number which have germinated (have pollen tubes).
Results- record in a table showing % of pollen grains that have germinated in each solution. Plot graph showing relationship between % germination of pollen grains and diff. concs of sucrose.
Observations on preparations of an insect testis squash
- set up microscope + place slide on tage
- focus lens on different magnifications
Results= you should be able to see chromosomes clearly and distinguish its stage of meiosis. Possible to also see bivalents (pairs of homologous chromosomes) and chiasmata.
Comments
These notes were originally written by cclose in this post on TSR Forums.
