ETV “Junior Secondary Science” Programme
Living Things and Air
Teachers’ Notes
Target Audience
Secondary 1 - 3
Duration
20 minutes
Production Aim
This programme is a teaching resource produced especially for enriching the
classroom teaching of the Syllabus for Science (Secondary 1 – 3) prepared by the
Curriculum Development Council (1998).
The content of the programme serves to illustrate the following parts of the
Syllabus:
“Unit 7: Living Things and Air
Topic 7.3 How does man obtain energy,
Topic 7.4 How do green plants obtain energy,
Topic 7.5 Gaseous exchange in animals and plants, and
Topic 7.6 Balance of carbon dioxide and oxygen in nature”
Key Points
1.
2.
3.
An explanation of the functions of respiration and photosynthesis.
An introduction to experiments on respiration and photosynthesis.
An explanation of the importance of photosynthesis in nature.
Content Outline
This programme is divisible into 5 parts as follows:
1. Breathing and Air
This segment demonstrates three experiments:
a. The percentages of oxygen and carbon dioxide in both inhaled air and exhaled
air are measured by means of an electronic apparatus. The result shows that the
exhaled air contains less oxygen and more carbon dioxide. This demonstrates
that breathing uses up oxygen and gives out carbon dioxide.
b. Air is blown into sodium hydroxide solution to absorb all the carbon dioxide
content. The carbon-dioxide-free air is then passed into a sealed plastic box
containing a rat. After a while, the air is passed into hydrogen carbonate
indicator to test for carbon dioxide. The indicator turns yellow indicating the
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c.
existence of large amount of carbon dioxide in the air. This demonstrates that
when animals breathe, they give out carbon dioxide.
Air is blown onto a mirror and the mirror became misty. A piece of blue cobalt
chloride paper placed onto the misty area turns pink indicating the substance on
the misty area is water. This demonstrates that exhaled air contains water.
2. Respiration of Animals
a.
b.
c.
This segment demonstrates another experiments. Two test tubes are connected
to both ends of a U-tube via rubber tubings. The two test tubes are then placed
into two thermos flasks respectively. One of the flasks contains a rat and the
other is kept empty as a control. At the beginning, the water mark inside both
tubes lie at the same level, indicating equal air pressure on both sides. Two
hours later, the water mark of the test tube in the empty thermos flask rises
while the other lowers showing that air pressure of the test tube in the thermos
flask with the rat has increased. This is probably due to a rise in temperature in
the flask, causing air in the test tube to expand. This demonstrates that heat
energy is released when the rat breathes.
An explanation of respiration follows. Breathing brings oxygen into the body of
a living thing. Oxygen is eventually brought into the cells. Chemical reactions
between oxygen and the food stored in the cells occur, releasing energy and
carbon dioxide. The energy is immediately used in metabolism. This process is
called respiration.
A piece of butter is burnt to heat up a small amount of water. During the
burning process a gas which turned lime water milky is released showing that
the gas was carbon dioxide. This demonstrates that burning and respiration are
similar in the way that both of them consume oxygen and give out energy and
carbon dioxide.
3. Respiration of Plants
This segment demonstrates three experiments:
a. Air is blown into sodium hydroxide solution to absorb all the carbon dioxide
content. The carbon-dioxide-free air is then passed into a sealed plastic box
containing a living green plant. The plastic box is covered up by a black box to
stop photosynthesis. After a while, the air is then passed into hydrogen
carbonate indicator to test for carbon dioxide. The indicator turns yellow
indicating the existence of large amount of carbon dioxide in the air. This
demonstrates that when plants respire, they give out carbon dioxide.
b. A capillary tube with a drop of red ink is inserted into a test tube containing
sodium hydroxide pellets and some germinating seeds. Another set-up is
assembled using boiled dead seeds as control. After a while, the red ink of the
set-up using germinating seeds drops indicating a decrease in the amount of air
inside the test tube. Meanwhile the ink drop in the control shows no change in
position. This demonstrates that plants respire to consume oxygen.
c. A thermometer is inserted into a thermos flask containing germinating seeds.
The thermos flask is then sealed and placed upside down. Another set-up is
assembled using dead seeds as control. After one day, an increase in
temperature for the flask containing germinating seeds is recorded while there
is no change in temperature for the control. This demonstrates that when plants
respire, they give out energy.
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4.
a.
b.
Photosynthesis
This segment demonstrates two experiments on photosynthesis:
Green water weed is placed under light and bubbles of gas produce. The
bubbles are collected in a test tube and tested by a glowing splint. The glowing
splint relights showing that the gas is oxygen. This demonstrates that plants
undergo photosynthesis to give out oxygen.
A green plant is placed in a dark chamber for several days so as to eliminate the
product of photosynthesis in the leaves. The plant is then taken out, and a part
of a leaf is covered with a piece of aluminum foil. The plant is then placed
under light for several hours to carry out photosynthesis. The leaf is then
removed and tested for starch using iodine solution. The uncovered part of the
leaf turns dark blue while the covered part shows the colour of the iodine
solution. This demonstrates that plants undergo photosynthesis to produce
starch.
5.
The importance of photosynthesis
a.
In nature, living things get their food from other animals or plants. For example,
vegetables in our meals come from plants, whereas beef and other meat come
from animals. However, cows feed on grass. Hence, people who eat beef
indirectly rely on plants. This example shows that, while a cow eats grass, a
man eats beef, which is the flesh of a cow. The energy fixed by grass through
photosynthesis is passed to the cow, the energy stored in the cow is eventually
passed to the man. This pathway of energy transfer is called the "food chain".
Animals breathe all the time, taking in the oxygen in air and releasing carbon
dioxide. Plants also respire all the time, consuming the oxygen in air and
releasing carbon dioxide. Burning also consumes oxygen and releases carbon
dioxide. However, the relative amount of oxygen and carbon dioxide in air
would not change. The reason is that green plants under sunlight undergo
photosynthesis while respiring, hence they consume the carbon dioxide in air
and release oxygen in return.
b.
Suggestions for Utilization
The teacher is advised to show the programme in one lesson. The teacher may spend
5 to 10 minutes at the beginning of each lesson to lead students to discuss with
reference to the Preparation before viewing the programme part of the Suggested
Activities. The teacher may then show the programme. After the show, the teacher
may spend another 10 to 15 minutes to discuss with students with a view to
consolidating the concepts and methods illustrated in the programme. The teacher is
advised to refer to the Activities after viewing the programme part of Suggested
Activities.
Suggested Activities
(The following activities are suggested for teacher’s reference only. The teacher
may wish to use the activities according to students’ abilities, the learning
environment of the class, and the teaching time available.)
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Preparation before viewing the programme
1. The teacher may ask students the following questions on living things and air
and let them think before watching the programme:
a. Where will oxygen go after being taken in the human body?
b. Why does a man breathe more rapidly during and after an exercise?
c. As animals breathe to take in oxygen and release carbon dioxide, will this
lead to increasing amount of carbon dioxide in air?
2. The teacher may then invite students to watch the programme carefully and find
out the answers themselves.
Activities after viewing the programme
1. The teacher may instruct students to carry out various experiments in the
programme so as to enhance their understanding on respiration and
photosynthesis. (Precaution: When conducting the experiment on burning butter,
the teacher should ensure that it is carried out in a well-ventilated area since it
will produce a rather fierce flame.) The teacher may also choose other kind of
food to carry out the experiment and compare the energy provided by different
kinds of food.
2. The teacher may ask students to record the menu for a certain meal and try to
draw the food chain on the sources of the related food.
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