Biology - how light intensity affects the rate of Essay

This essay has a total of 2115 words and 11 pages.

biology - how light intensity affects the rate of photosynthesis

Biology Coursework ¡V Does The Light Intensity
Affect the Rate of Photosynthesis

The Investigation

In this experiment I will investigate the affect in which the light intensity will have on
a plants photosynthesis process. This will be done by measuring the bubbles of oxygen and
having a bulb for the light intensity variable.


The input variable which will be used in this investigation will be the light intensity
(this will be a 100Watt bulb being moved closer and further away from the plant). The
outcome variable which will change as a result of this experiment will be the amount of
oxygen made in the experiment due to the amount of light intensity increases (causing the
plant to photosynthesise more).


I predict that as the input variable, the light intensity increases (the light moved
towards the plant) the outcome variable, the amount of oxygen, produced from
photosynthesis will be larger.

Plants can absorb and use light energy because they have a green pigment, chlorophyll,
contained in the chloroplasts in some of their cells. Chlorophyll allows the energy in
sunlight to drive chemical reactions. Chloroplasts act as a energy transducers, converting
light energy into chemical energy. So as the plant has more light the chlorophyll inside
the chloroplasts can react faster absorbing in more light for food and energy.

The equation for photosynthesis can help to predict the outcome of the investigation.

Light Energy
Carbon Dioxide Water --------------,³ Glucose Oxygen

This shows that there could be three variables in this experiment, carbon dioxide, water
and light energy. So in our case the variable light energy (light intensity) will be used.
The equation also shows that if there is more light energy then more glucose and oxygen
will be produced.

I also predict that as the light is moved closer to the plant there will be more bubbles
(oxygen) produced due to the increase of photosynthesis speed explained above. So in
conclusion I predict that the more light intensity there is on the plant the faster the
rate of photosynthesis there will be.

Fair Testing

The fair testing will be carefully checked so the results do not come out to be void. The
light intensity will be changed for it is the only variable used in the experiment. Though
the temperature, watt of the bulb, amount of water, size of the plant and position of the
clamp and stand. The preliminary experiment I did has helped me to decide in which
conditions/measurement I will use. The reason in which I will keep the other variables the
same is because if increased they would increase the rate of photosynthesis making the
experiment pointless and a waste of time. Also if they decrease then it will be likely
that the rate of photosynthesis will decrease as well. Me and my partner in this
experiment decided that we will set the timer to start after sixty seconds in which the
light has been turned on, we chose this because the photosynthesis rate will have been
rising and be at a steady rate to take the amount of bubble recording after one minute. We
will be doing each light intensity test three times to get an average (for our graphs).


The apparatus I will be using are:
Clamp Stands
Test Tube
100Watt Bulb and Light
Plastic Screen
Automatic Counter
1 Metre Ruler
Light Meter

Preliminary experiment

The preliminary experiment was done to find out what range of values I will use and
details of the measuring instruments. I decided that the amount of water will fill the
test tube, the light intensity readings will be at 100cm, 75cm, 50cm and 25cm on the metre
ruler, the stop watch will be turned on after 60 seconds of the light been on and the
results will be taken three times and put into a results table. The results my partner and
I ended up with where:

100Cm between light and plant = 6 bubbles
25Cm between light and plant = 12 bubbles
I will be measuring the light intensity with a light meter at each of the distances. When
I do this, I will then find the light intensity by dividing the number which came up on
the light meter into 1; this will be the light intensity. During the preliminary
experiment I did not come up against any noticeable problems so no solutions where needed.


The plan or method I will be using will start of by placing a plant in a test tube filled
with water. This test tube will then be held by a clamp stand and around 100 cm¡¦s
across from the clamp stand there will be a lamp with a 100 watt bulb in it. The 100 cm
ruler will be placed between the clamp stand and lamp so you know how far to move the lamp
after you record the bubbles for each light intensity. The light intensity will by using
the light meter to record the readings at 100cm75cm, 50cm and 25cms, then dividing the
number which comes up on the light meter into one and the way they will be recorded are as

1) Turn on lamp for 1min
2) Start stop watch after 1min of the light being on
Continues for 6 more pages >>