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My name is Poon Cheng Moh. I have been teaching biology in SMK(P) Raja Zarina, Port Klang for 26 years. I sincerely hope that this blog on SPM Biology will be useful to both teachers and students.

Friday, February 28, 2014


Estimating the number of beans in an opaque bag

Material : Kidney beans, opaque bag, specimen tube, marker pen

1.     About a beakerful of kidney beans is put in an opaque bag. (The kidney beans represent the population of animals.)
2.     An empty specimen tube is put into the bag filled with kidney beans and then taken out.  The kidney beans are placed in a petri dish and counted. (This represents the first capture).
3.     The beans are marked with a marker pen and the returned to the bag.
4.     The marked and the unmarked beans are mixed thoroughly by hand.
5.     An empty specimen tube is put into the bag again, filled with beans and then taken out.  One must not look into the bag when carrying out this step.  (This represent random recapturing).
6.     The kidney beans that have been scooped out are placed in a petri dish and counted. The number of beans that are found marked is noted. (This represent the number of animals found marked in the recapture).

The number of beans in the first scoop
The number of beans in the second scoop
The number of beans found marked in the second scoop
Therefore, an estimation of the number of beans in the bag
X x Y
Note: The accuracy of the method can be increased by
a)     taking out 2 scoops of beans each time instead of one
b)    repeating the experiment and finding the average of the results



1. The material used to mark the organism is important. Why?
    The substance used to mark the organism should not expose the
    organism to its predator, should not be poisonous, should not affect the
    activity of the organism, and yet not easily removed     

2. What is the estimated population size of beans in the bag?           

3. What is the actual population size of the beans?

4. Why is the estimated result different from the actual result?
     Estimation only whereas the second method is direct counting.

5. Why is direct counting difficult in real life situation?
     The organisms/animals move around, space/habitat is too big, you
     cannot capture them all, unlike the beans which are all in the bag.    

6. How can the accuracy of the data be improved?
·  Repeat the experiment and find the average of the results.
·   Mark a greater number of individuals.

7. State two assumptions made in this estimation method?
b.     The marked individuals can mix randomly in the population before the second sample is taken
c.      Marked and unmarked organisms in second sample are caught randomly
d.     The substance used to mark the organism should not be poisonous or affect the activity of the organism and yet not easily removed.
e.     The death rate and the birth rate are the same.
f.       The population to be estimated is stable/ the rate of the migration is equal to the rate of emigration of the organism. 
g.     There are no predators of the organism in the habitat to be studied.



1. A biologist originally marked 40 butterflies in Taman Bukit Cerakah, Shah Alam using tags. The marked butterflies were released back to where they were caught. After a week, the­ butterfly traps caught 200 butterflies. Of those 200, 80 were found to have tags. Based on this information, what is the estimated population size of the butterflies in Taman Bukit Cerakah?

2. A study of the garden snail population in a vegetable farm was carried out.  On the first trip, a total of 160 snail were caught, marked and released. A second trip was made after three days. There were 40 marked snails out of a total of 180 caught. Estimate the population of garden snails in the vegetable farm using the results obtained.

Sunday, February 16, 2014

Amali Book – Pg 4-6

Aim : To show the presence of xylem as a continous tube system to transport  water

Cross section of a balsam root

Cross section of a balsam stem

1.       Xylem tissue
2.       Yes
3.       The vascular tissues in the stem are arranged in a circle with the phloem tissue located in the outer layer.  In the root, the xylem tissues are found in the centre and are shaped like a star whereas the phloem tissues are between the radii of the xylem.
4.       A long tube filled with coloured water. This tube is the xylem tissue as it forms a continuos tube system to transport water.

The xylem tissues form a continous tube system from the root to the stem and leaves in transporting water in a plant.