. [ I n s t r u c t i o n a l S t r a t e g i e s D e a l i n g ] .
. [ W i t h S t u d e n t s ' M i s c o n c e p t i o n s ] .

By Mr. Yip Din-yan
Department of Curriculum and Instruction, Faculty of Education, the Chinese University of Hong Kong

1.    Excretory wastes

Questions for the interview:
You consider that ...... why do you think so?  How would you distinguish between 'excretion' and 'egestion'?  Name 2 other substances excreted from the body.

Students' misconceptions: Egestion is   aspecial mode of excretion; faeces is an excretory waste; waste substances include sweat, urine, bile, saliva; CO2 is not an excretory waste.

Causes of misconceptions
Considering the teaching sequence:
Definition of excretion - How? When? Conception of characteristics of living organisms

1.    Lack of prerequisite knowledge
2.    Using everyday language in a scientific context
       Students' preconceptions on the meaning of 'wastes': excretion = egestion.
       How to convince students of the problem of their informal preconception?
       e.g. examples, analogy, cognitive conflict.
3.    Compartmentalisation of concepts
       Textbook-based approach: Individual topics are presented in isolation with little integration.
       Need to establish meaningful relationships between nutrition, gas exchange and excretion.

2.    Food for seed germination

Students' misconceptions:
The edible part of the apple, the receptable, provides food for seed germination.

Causes of misconceptions:

The teaching sequence:
Structure & function of the flower: a list of vocabularies WB00678_.gif (615 bytes) Examination of a local flower WB00678_.gif (615 bytes) Process of pollination & fertilisation, with terms like funicle, integuments, micropyle, meiosis WB00678_.gif (615 bytes) Differences between insect- & wind-pollinated flowers WB00678_.gif (615 bytes) Process of fertilisation & fate of floral parts WB00678_.gif (615 bytes) Functions of the fruit & mechanism of seed dispersal WB00678_.gif (615 bytes) Structure of sed & functions of testa, micropyle, cotyledons, plumule & radicle WB00678_.gif (615 bytes) Factors affecting seed germination & investigations.

1.    Too many termis & dry facts WB00678_.gif (615 bytes) rote learning with little understanding.
       Not appealing to students' experiences & interest.
       Little integration between different processes.
2.    Lack of prerequisite knowledge
3.    Students' preconceptions: The receptacle is fleshy & edible; seeds are dry and hard.

3.    A teaching strategy based on the constructivist principle:

Further examples to prevent comparmentalisation of concepts:

In bright light, the leaf performs photosynthesis.   Since water is used in the process of photosynthesis, the rate of the water loss from the plant rises with increase in light intensity.

Excess carbohydrate is converted into glycogen which is stored in the liver and muscles.  It leads to an increase in body weight.

Fat is digested into fatty acid and glycerol which are stored under the skin.

4.    Causes of misconceptions - a summary

Students' factor:

    • Lack of prerequisite knowledge
    • Informal preconceptions
    • Motivation & interest

Teachers' factor:

    • Emphasis on excessive details WB00678_.gif (615 bytes) rote memory vs. understanding
    • Compartmentalisation of concepts
    • Inadequate subject knowledge

5.    Appendix

  1. Item assessing the concept of excretion
    Which of the following is an excretory process?

    A.   exhalation                                        (43.4%)
    B.   removal of undigested wastes      (40.7%)
    C.   release of saliva                              (10.0%)
    D.   vomiting                                            (5.9%)
  1. Item assessing the concept of seed germination
    2. The diagram below shows the vertical section of an apple:

    misconception1.gif (4686 bytes)

    Which of the following structures contain(s) stored food for seed germination?

    A.   1 only                    (28.2%)
    B.   2 only                    (54.5%)
    C.   1 and 2 only         (7.7%)
    D.   1, 2 and 3             (9.6%)