The Effect of the Distance from the Light Source of

•To investigate the effect of the
distance from the light source of
Hydrilla verticillata on the rate of
• Alternative Hypothesis:
– There is a significant effect of the distance
from the light source of Hydrilla
verticillata on the rate of photosynthesis.
• Null Hypothesis:
– There is no significant effect of the
distance from the light source of Hydrilla
verticillata on the rate of photosynthesis.
(6) 15 cm Hydrilla verticillata
(3) 150 mL of water
(1) 1000 mL beaker
(3) 250 mL beaker
Light bulb (present in the laboratory)
Container with water
• Independent Variables
– Light intensity
– Distance from the light source (bulb and sunlight)
– Sunlight
• Dependent Variables
– Rate of photosynthesis (Number of bubbles)
– Range of flame in the match stick
• Controlled Variables
– Light bulb
– Volume of water
– Length of Hydrilla verticillata
1. The needed materials were prepared.
2. Six (6) 15 cm Hydrilla verticillata were cut
with the use of scissors in the container
with water to prevent from drying up.
3. Three beakers were filled by 150mL of
water and two Hydrilla verticillata each,
4. The beakers were then positioned on
their respective places:
– Control set-up was placed outside of the
laboratory for it to be lighted with sunlight.
–Set-up A was placed 10cm away from the
light bulb uplifted by a 1000mL beaker. (A
ruler was used to measure the distance.)
–Setup B was placed 25cm away from the light
source which is the light bulb inside the
laboratory. (A ruler was used to measure the
5. The 6 Hydrilla verticillata were allowed to equilibrate
for 3 minutes so that it can give enough time for the
plants to adapt to the new environment to have a
stable rate of photosynthesis.
6. After the time set for the adaptation of the plants,
the setups were then timed simultaneously for 20
7. The number of bubbles that appeared were
8. Lastly, the setups were illuminated with match
sticks to differentiate the abundance of oxygen
present in each beaker.
The students used the distance from the light source
as the focus of the experiment to identify which setup has
the greater and lesser rate of photosynthesis whether the
one that is nearer, farther or the one that is kept under
normal condition.
To determine the rate of photosynthesis, they count
the number of bubbles that appeared. The presence of
bubbles in the water represents the exchange of oxygen (byproduct) and carbon dioxide (needed gas in the process).
They also lighted a match in the beaker to visually
know and compare the presence of oxygen in each beaker.
Control Setup
Setup A
Setup B
5 – 10
10 – 15
15 – 20
Number of Bubbles
Control Setup
Setup A
Setup B
0 to 5
5 to 10
10 to 15
Number of Minutes
15 to 20
Based on the tabulated data, it can be
clearly observed that the three setups have
different number of bubbles in a certain time
although Setups A and B have equal number at
first but later on, the first one has drastically
increased in the number of bubbles in the
succeeding minutes.
Setup A had the greatest number of
bubble formation (144) followed by Setup B
(12) and Control Set-up (1), respectively.
Due to the students’ exemplary curiosity
level, they lighted a match stick inside the
beaker to identify which set-up has the most
number of oxygen. They linked this action to the
concept they learned in Chemistry, in which
Oxygen is an element necessary for combustion.
They thought that if the beaker will have the
greatest range of flame; oxygen is abundant in it
and the Hydrilla verticillata contained in that
beaker has the fastest rate of photosynthesis.
Lighting of the
match stick
With respect to the lighting of the match,
Setup A visually had the biggest flame, followed
by Setup B and Control setup, respectively.
The number of bubbles and the range of
flame produced the same rank and order with
regards to the rate of photosynthesis: Setup A,
Setup B and Control setup, correspondingly.
From the given data, the students learned
that it is the light intensity that caused Setup A
to have the fastest rate of photosynthesis and
slowest rate as for the control setup. As stated
by Bareja (2011), the nearer the distance of the
plant from the light source, the brighter light it
will have which means a stronger light intensity.
It is the reason why Setup A had the most
number of bubbles since it is the one closest to
the light source (10cm away from the bulb).
According to Manaker(1981), an increase in
the intensity of light will result to an increase in
the rate of photosynthesis and will likewise
reduce the number of hours that the plant must
receive every day. And so, they can produce more
food, release much oxygen and absorb more
carbon dioxide.
However, weak light intensities tend to
reduce plant growth, development and yield
because low amount of solar energy restricts the
rate of photosynthesis (Vergara 1978).
The students inferred that Hydrilla
verticillata under nearer distance from the
light source will have stronger light intensity
resulting to faster rate of photosynthesis in
contrast to those that are far from the light
source. Therefore, the alternative hypothesis is
accepted and the null one is rejected. Indeed,
there is a significant effect of the distance from
the light source of Hydrilla verticillata on the
rate of photosynthesis.
Manaker, GH. 1981. Interior Plantscapes:
Installation, Maintenance, and Management.
Englewood Cliffs, NJ: Prentice-Hall, Inc. 283 p.
VERGARA BS. 1978. Crop response to light
variations. In: Gupta US, ed. Crop Physiology. New
Delhi: Oxford & IB Publishing Co. p. 137-156.
Bareja, BG. What is Light Intensity, Effects on Plant
Growth(April 2011). Retrieved July 7, 2012 from

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