BIOLOGICAL DRAWING OF BANANA (CROSS SECTION)

In the past practical papers, there used to be a question asking candidates to draw a cross section (or transverse section) of a banana. The following figures should help.

Real Specimen

Biological Drawing of a Cross Section of a Banana
NOTE:
During that time, food tests were also conducted on the banana slice. What type of food nutrients do you think are present in it?

ONION BULB

DO YOU KNOW THAT AN ONION BULB ACTUALLY CONSISTS OF LEAVES (SCALE LEAVES)?

DO YOU KNOW THAT AN ONION PLANT IS AN EXAMPLE OF A MONOCOT?
NOTE: BE AWARE THAT THERE MAY BE QUESTIONS IN THE PRACTICAL PAPER ASKING YOU TO MAKE A FULLY LABELLED DRAWING OF AN ONION BULB. NOTE THE LEAVES AND THE STEM TISSUE.
FOOD TEST MAY ALSO BE ASKED AND DO NOT BE SURPRISE THAT AN ONION BULB CONTAINS REDUCING SUGAR!!! (NOTE: WHEN COOKING ONION, THE DARK BROWN CARAMEL IS ACTUALLY THE SUGAR!!!)


The following figure shows how an onion bulb is to be drawn (Longitudinal Section!!!)

MONOCOTS VERSUS DICOTS

Monocotyledonous plants and dicotyledonous plants are different in many ways. Knowing their differences is very important in your practical paper. The following figure shows five ways in which they are different:

They are different in terms of:

• The number of cotyledons in their seeds - A monocot has one cotyledon in their seeds whereas a dicot has two cotyeldons in their seeds.
• The arrangement of the veins in their leaves - The veins in the leaves of a monocot are usually parallel whereas those in the leaves of a dicot are netlike or branching (reticulated venation).
• The arrangement of the vascular bundles in their stems - In a monocot, the vascular bundles are usually randomly arranged whereas in a dicot, they are arranged in ring.
• The root systems - A monocot has fibrous root system whereas a dicot has a tap root system.
• The number of flower parts - The flower parts in a monocot are usually in a multiple of three whereas those in a dicot are in a multiple of four or five.
• The stomata in the leaves of a dicot leaf are mostly found on the lower surface of the leaf whereas those in the leaves of a monocot are evenly distributed on the lower and upper surfaces of the leaves.
  

HALF FLOWER

To draw a flower is not an easy task for a Biology student. But with lots of practice, I am sure you can master it. You don't have to be an artist! What the examiner looks for is the details and accuracy of your drawing. Remember, drawing is a way your POWER OF OBSERVATION is tested.

IODINE TEST, BENEDICT TEST, BIURET TEST, ALCOHOL TEST AND SULPHUR TEST

In 'O' Biology practical examination, you are required to know Iodine test, Benedict test, Biuret test, Alcohol test and Sulphur test. All or some of these tests are usually used for testing for the presence of food type in a given food sample or specimen and also for testing for the presence of certain materials in a given urine sample. Usually after testing and confirming the presence of these materials in the urine sample, diseases or organ failures can be detected.

A. IODINE TEST (TO DETECT FOR THE PRESENCE OF STARCH)
PROCEDURES

• Place sample in a test tube.
• Dissolve sample in water.
• Add a few drops (or 3 to 5 cc) of Iodine solution into the test tube.
• Observe.
  

EXPECTED OBSERVATION AND CONCLUSION

• If brown Iodine solution changed to blue-black (OBSERVATION), starch is present (CONCLUSION).
• If brown Iodine solution remains unchanged (OBSERVATION), starch is absent (CONCLUSION).
  

B. BENEDICT TEST (TO DETECT FOR THE PRESENCE OF REDUCING SUGAR)
PROCEDURES

• Place the food sample or urine sample in a test tube.
• Add a few drops (or 3 to 5 cc) of Benedict solution into the food sample or urine sample.
• Place the test tube in a water bath for not more than five minutes.
• Observe.
  

EXPECTED OBSERVATION AND CONCLUSION

• If the blue Benedict solution changed to brick-red (or brown/yellow/orange) (OBSERVATION), reducing sugar is present (CONCLUSION).
• If the blue Benedict solution remains unchanged (OBSERVATION), reducing sugar is absent (CONCLUSION).
• Note: For urine test, the presence of reducing sugar in the urine sample indicates that the person is a Diabetic patient.
  

C. BIURET TEST (TO DETECT FOR THE PRESENCE OF PROTEIN)
PROCEDURES

• Place the food sample or urine sample in a test tube.
• Add a few drops (or 3 to 5 cc) of Biuret reagent in the test tube containing the food sample or urine sample.
• Observe.
  

EXPECTED OBSERVATION AND CONCLUSION

• If the blue Biuret reagent changed to purple/violet (OBSERVATION), protein is present (CONCLUSION).
• If the blue Biuret reagent remains unchanged (OBSERVATION), protein is absent (CONCLUSION).
• Note: For urine test, the presence of protein in the urine sample indicates that the person suffers from kidney failure.
  

D. ALCOHOL TEST (TO DETECT FOR THE PRESENCE OF FATS OR OIL)
PROCEDURES

• Place the dissolved food sample in a test tube.
• Add equal amount of alcohol into the food sample.
• Shake the content of the test tube and leave it to stand or leave it aside for a few minutes.
• Prepare another test tube containing water.
• Pour in the upper layer of the content in the first test tube into the test tube containing water.
• Observe.
  

EXPECTED OBSERVATION AND CONCLUSION

• If a white emulsion is formed (OBSERVATION), fats or oil is present (CONCLUSION).
• If no white emulsion is formed (OBSERVATION), fats or oil is absent (CONCLUSION).
  

E. SULPHUR TEST (TO DETECT FOR THE PRESENCE OF BILE)
PROCEDURES

• Place the urine sample to be tested in a test tube.
• Place a spatula-full of sulphur into the test tube containing the urine sample.
• Observe (DO NOT SHAKE).

EXPECTED OBSERVATION AND CONCLUSION

• If sulphur sinks (OBSERVATION), bile is present (CONCLUSION).
• If sulphur floats (OBSERVATION), bile is absent (CONCLUSION).
• Note: The presence of bile in the urine sample further indicates that the person suffers from liver damage.
  

NOTES:

• If sample or specimen given is in solid form, chop and crush the sample or specimen finely (This is to increase the surface area so that reaction, if any can take place faster)
• Amount of sample to be tested and the amount of test reagents to be used must be stated clearly.
  
• State the colour clearly in your observation and make sure to state the name of the reagent when describing you observation (Always ask your self: What is it that change colour? Remember, the one having colour is usually the reagent so it is only right that you mention the name of the reagent in your observation)
• For the Benedict test, make sure that your water in the water bath is already boiling before carrying out the test and make sure that you only place the test tube containing the sample or specimen for not more than five minutes (Remember!!! if the sample or specimen happened to contain starch and you are boiling your sample or specimen for more than five minutes, the starch may be hydrolysed or broken down into reducing sugar. This may give you the result that you should not get)
• Iodine test is very simple. If you are given sample in powder or solid form, you simply can place the sample on a white tile without dissolving it in water and then place a few drops of Iodine solution on to it.
• Benedict test is usually time consuming since it requires you to boil the sample or specimen in a water bath. So, manage you time wisely. While waiting, you can always proceed to other tests.
• Iodine test is usually used for detecting starch in food sample.
• Benedict test is usually used for detecting reducing sugar in food sample and urine sample.
• Biuret test is usually used for detecting protein in food sample and urine sample.
• Alcohol test is usually used for detecting fats or oil in food sample.
• Sulphur test is usually used for detecting for the presence of bile in urine sample.
  

BIOLOGICAL DRAWING

Many students taking Biology are intimidated by "Biological Drawing" and many take this lightly. Actually, to do a Biological drawing one does not have to be an artist. You are not expected to produce a masterpiece. What important here is to draw a given specimen as accurately as possible. Whether you like it or not, you will have to do it one way or another. You as a Biology student, cannot escape from it. It is always asked in the practical paper of the 'O' level examination.

Why is Biological drawing important?
You may sometimes think that Biological drawing is ridiculous but actually it is training and testing your power of observation. Having a strong power of observation is one characteristic that a future scientist must have. It helps you to be more pertinent in your future work. For example, if you want to be a forensic scientist, having a strong power of observation is very important in solving a problem.

DRAWING TECHNIQUES:

• Draw what you see, do not draw what you imagine or what you have seen and remember from books.
• Your drawing is two-dimensional only, not three dimensional.
• You must have with you a sharp 2B pencil and a high quality eraser (Remember: neatness and cleanliness count!!!).
• Do not shade your drawing. Coloring is totally forbidden!
• Your drawing should be large covering at least 75% of the given drawing space.
• Drawing line must be continuous and not fuzzy.
• Mind your proportion. For example, if you are asked to draw a fruit, the size of the seed(s) must be in the right proportion as that of the whole fruit.
• Your drawing must have a suitable title. Example: Transverse Section of Fruit W1 (X2.3).
• Labeling (in pencil) is preferably on one side of your drawing. Criss-crossing is not allowed when labeling.
• Determine the magnification of your drawing by dividing the length of your drawing with the length of your specimen. Your magnification should have a multiplication sign before the value (for example: X2.3) and there should not be any units placed after your magnification value.
• Draw a line on your drawing to show where you were taking your measurement.

Examples of well drawn specimen (Mind you, labeling and lines to show where measurements for calculating the magnification are not shown in the following drawings)
The following are examples of Biological drawings which deserve high credit (Remember: Your drawings should be clear and show that you really draw what you observed)