Biology P5

[zeebujha]

I am not very good at bio P5. But I hope I will get some support from the readers to continue this thread. All I am going to do is start the thread. So, here it goes buddies:

A. How to calibrate an eyepiece graticule:

1. Use an eye piece lens that has been fitted with a graticule (lol)
2. Place the stage micrometer onto the microscope stage and focus using the low power objective lens so that the graticule scale becomes superimposed over the micrometer scale
3. Move the stage micrometer until the start or zero line of each scale is coincident
4. Look along the scale until another coincident point is found. Ideally, the point should be as furthest as well
5. The relationship between the two scales can now be calculated

B. Points to focus on while drawing plan diagrams (yes, you could be asked one of those in P5 as well but not directly from a slide as such)
1. NO SHADING. I think we all know this point well enough
2. NO CELLS in LOW POWER plan diagrams. CELLS NEED TO BE SHOWN in HIGH POWER plan diagrams

Also, when asked to give magnification, round it off to a whole number. x1000.755 should best be rounded off as x1000
3. Only outlines
4. ANNOTATIONS(Refers to describing the slide for example the xylem is stained red..........)
5. Always keep in mind the relative thicknesss of the various tissue layers being drawn.

 

[zeebujha]

For food tests: There is only one important point that I would like to make:
If the sample is a piece of food, then grind it WITH SOME WATER in a PESTLE and MORTAR to break up cells and release the cell contents.

These tests are SEMI-QUANTITATIVE as exact concentrations of chemicals cannot be known. Using known concentrations, we have to interpolate to get the required concentration

Also to use potato disc in enzyme-substrate reaction: It is best to first HOMOGENIZE the potato by adding a phosphate buffer of a given pH and then blending it for 45 second in a high speed blender. Then, filter through cheese cloth to remove large chunks. Use a paste rather than a thick piece would give better results.

 

[zeebujha]

10 vol H202 : It will produce 10cm3 of oxygen from every cm3 that decomposes. Likewise, 2cm3 10vol H2O2 will give 20cm3 of oxygen

Mass-volume %= Mass of solid solute in g per 100 ml of the resulting solution. Often used for solutions made from a solid solute dissolved in a liquid

Volume-volume %= Useful when a liquid-liquid solution is being prepared (and for gases as well). Volume of solute in ml per 100 ml

I don't know why ml is the preferred choice of volume here

 

[zeebujha]

Hydrogen peroxide less that 18 vol are low hazard. Solution at concentration 18-28 vol are irritant and any higher concentration is corrosive

At all times avoid contact of enzymes with EYES or SKIN. If you happen to come in contact, wash off immediately with plenty of water

 

[zeebujha]

How to use a colorimeter:
Determine the wavelength of light that the solution absorbs most strongly. This is simply the complimentary colour of visible colour of the solution
Use a color filter that filters out all but the complimentary color and set the wavelength of the colorimeter to the wavelength of the complimentary colour frequency
CALIBRATE the colorimeter. This involves referencing. A sample placed in a CUVETTE is used so that the same glass container with the same absorbtion is used all the the times to reduce the effect of the container. For calibration, use distilled water and set the abosrbance for that wavelength to be 0%. Alternatively, you could set the transmittance to 100%
Then place solutions of different known concentrations in the colorimeter one by one and record the corresponding absorbance/transmission
Then plot the graph of absorbance/transmittance on the Y axis against concentration of the solution on the X-axis
Now, you have a calibration curve
To find the concentration of the unknown solution, place solution in the colorimter and read the corresponding absorbance/ transmittance. Now, all you have got to do is find the corresponding value on the X-axis which gives the given value of transmittance/absorption on the Y-axis. The value on the X-axis is the measure of the concentration of the solution!

 

[zeebujha]

Practical details of how to prepare a slide of pollen grains and examine them using a microscope:
1. Brush the pollen grain using a brush and transfer it from the stamen to the slide
2. Use a suitable MOUNTANT such as water or glycerol. Iodine solution or methylene blue can also be used to stain the slide
3. A COVERGLASS should be placed in position, carefully, in order to avoid air bubbles being trapped in the preparation
4. Sliide should be placed on the STAGE of the microscope and use the focus knobs to bring the pollen grains into focus using the fine or the coarse knobs.

 

[zeebujha]

Investigation into where chloroplasts are found iin a leaf of a flowering plant:

(I) Preparing a microscopic slide of a sample of the leaf
- Let us use the leaf of a maize plant.
- Cut thin SECTION of the the leaf using a RAZOR/SCALPEL
- The mark scheme mentions something about "point of technique such as guard " but I do not understand what that means (Anyone who understands what that means- please clarify that)

-Use forceps to transfer the specimen to the slide or a mounting needle could be mused as well
- Add mountant such as water on the slide. However, stains such as iodine and methylene blue can be used as well as determined by:
In a wet mount slide, the specimen is simple held in a drop of water, covered with a coverslip - it is often used for living material (freshwater protozoa etc)
Some structures are difficult to see using a wet mount and stain is added to the specimen to show up structures like the nucleus. Stains enhance natural contrast

- Put cover glass on and be careful to avoid bubbles. For this, lower the glass slide with support at an angle
-The slide is then made clean and neat by blotting using a blotting paper

(II) Setting up and using the microscope:
- Place the glass slide on stage
- Put the clips on
- Illuminate using a light bulb or the microscope or a mirror. Diaphragm of the microscope is used for light control. Adjusting- the aperture of diaphragm helps adjust the width of the light beam so that we are only illuminating the part of the specimen that we are looking at. If we open it to maximum aperture, we have a lot of stray ligth from the light bulb and this decreases the contrast
-First focus using the low power objective lens
-Then shift to high power. Changing focus from low to high power is referred to as zooming
-In high power, do not turn the coarse focus knob (this determines the distance of the specimen from the objective lens. Only move the fine focus knob.

(III) Recording the observations:
- Drawing - Low power and high power plan diagrams
- High powe includes cells as well

 

[zeebujha]

Counting stomatal density:

Two ways:

1. Using epidermal strips:
Epidermal strips: The epidermis will peel from some leaves quite readily
- First cut the leaf. We can use our fingernails to catch hold of the leaf and peel off the epidermis, or we can use a sharp RAZOR BLADE (this sucker keeps turning up in microscopic slide preparation) . Mount the peel ini a drop of water on a microscope slide with a cover slip

CAUTION: EPIDERMAL STRIPS DO NOT REFER TO THE STRIPS OF A LEAF!!!!!!!!!!!!!!!!!!!!!!!!!!!

2. Nail Varnish impressions:
- Spread a thin layer of nail varnish on the leaf and LEAVE IT TO DRY
- Remove the layer of nail varnish by attaching a CLEAR STICKY TAPE to it
-Peel it off from the leaf and stick it to the slide
For repitition, be consistent about which part of the leaf to use for the leaves of the same plant
-View the epidermal impressions using a calibrated microscope fitted with an Eye Piece Graticule
-Calculate the area of the field of view using "(pi)r^2" when we have the measure of the true radius of the field of view
-Count the number of stomata impressions visible in each area of impression sampled

Now all you have to do is divide the number of stomata visible by the area of the field of view to get the stomatal density (i.e. no. of stomata visible per unit area of the leaf)

VOILA!!! You have the answer!!!! YEA!

 

[NIXORCollege]

Could you please post notes on the statistics? Like about t test and standard deviation and standard error
Thanks!

 

[zeebujha]

How to measure RQ:
Force your self to go through this piece of nightmare:

http://www.practicalbiology.org/areas/a ... 8,EXP.html

 

[zeebujha]

Could you please post notes on the statistics? Like about t test and standard deviation and standard error
Thanks!

I am thinking of doing that too but statistics is a total nightmare!!!!!!!!!!!

 

[zeebujha]

How to determine the RATE of oxygen uptake

Close the screw clip
Allow to stabilise
Note position of manometer fluid and start the clock
Note the position of the syringe at the point of starting
Read position of the fluid at fixed times and after each fixed time equalize the levels with the help of the syringe
Read off volume change in syringe
Divide the volume change by the fixed interval of time to find the rate of oxygen uptake
Do this for series of periods and plot of graph of oxygen uptake against time. The slope at anytime should give the rate of oxygen uptake at that time.

 

[zeebujha]

How to make alignate beads of algae:


(I) First why should we go through the trouble at all?
1. Algal balls make it easy to standardise the amount of photosynthetic tissue in any investigation, enabling semi-quantitative experiments to be undertaken.
2. The algae in the beads will stay alive for several months in a stoppered bottle of distilled water

How to do it

An awesome plus colorful note:

http://www.eurovolvox.org/Protocols/PDF ... UK_eng.pdf

 

[zeebujha]

Tit bits about photosynthesis experiments:
1. To measure light intensity, use light meter/ photo diode/LDR/photometer
2. Hydrogen carbonate is an irritant. So, use gloves and eye protection
3. Do not look directly into lamps
4. Do not touch the lamps while hot
150 W halogen lamps the best. They have a stand and handle to separate from the body of the lamp which makes them safer to handle. But they do produce heat, so we do need a heat filter for investigation.
Heat filter: Use a large erlemeyer (stupidly difficult to pronounce) flask with water in it. Works as a heat sink with the water absorbing the heat

 

[zeebujha]

Measuring transpiration rate using potometer:

http://en.wikipedia.org/wiki/Potometer


- Must cut the shoots under water at an angle. If air gets into the xylem vessel of the plant, it can form air locks that will prevent the plant taking up water and so reduce the measured rate of transpiration
- Potometers should be left for the leaves to dry. The experiment is not going to give any meaningful results until any excess water on the leaves has evaporated
- Adding food coloring to the water makes it easier to see the air bubble in the capillary tube

-Use of reservoir is to reset the air bubble to the end of the capillary tube. For this TAP of the water reservoir has to be opened
- Air bubble is introduced into the capillary tubing by lifting the whole potometer upwards. Leave the end of the capillary tube out of the water until an air bubble forms. Then put the end into a beaker of water
-WAIT FOR THE BUBBLE TO START MOVING AT A CONSTANT RATE AND THEN TAKE THE READINGS!!!!!!


CONTROLS:

Tempr: Increase in temperature increases the KE of water molecules. Move faster in the xylem. So, increase the rate of transpiration. Also, provides the latent heat of vaporisation so water evaporate faster
Pressure: Reduced air pressure leads to water evaporating faster and hence increased rate of evaporation lead to increased rate of transpiration
Limitations of the procedure:
- The potometer does not measure the rate of transpiration accurately due to the fact that not all of the water taken by the plant is used for transpiration (water may be used for photosynthesis or by the cells to maintain turgidity)

Safety:
-Some people find the sap from plants irritating to the skin
-Take care when cutting the plant shoot
-Take care when handling the glass potometer. It is easy to break the long glass tubes and cut or stab ourselves with broken ends. So, be prepared with first aid and for cuts from broken glass!!!!!!

 

[zeebujha]

http://www.thestudentroom.co.uk/wiki/Re ... xperiments

 

[NIXORCollege]

Could you please post notes on the statistics? Like about t test and standard deviation and standard error
Thanks!

I am thinking of doing that too but statistics is a total nightmare!!!!!!!!!!!

I know!! Please try to cover it. I am so bad at it :fool:

 

[kamranakmal6969]

10 vol H202 : It will produce 10cm3 of oxygen from every cm3 that decomposes. Likewise, 2cm3 10vol H2O2 will give 20cm3 of H2O2

You mean oxygen at the end rite?

 

[Newbie]

Hey Nixor college .... your name if you don't mind
I also study there

 

[NIXORCollege]

Hey Nixor college .... your name if you don't mind
I also study there

Haha who's your teacher?