LIGHT AND PLANT GROWTH
Amber Webb
Grade 4
South George Town Primary School
Abstract
In this investigation I tested what happens to plant growth when plants get limited amounts of light. I planted 12 bean seeds with same controls in tubes with different amounts of light. I measured the growth of the plants daily. The results were the opposite of my prediction.
Topic
How light effects plant growth.
Background
In my family gardening is a big thing. We have animals and grow our own food. We have lots of land and plants surrounding our house. I have always wanted to know how plants grow. I knew sunlight was a big part of it. I found out that sunlight is essential for plant photosynthesis – the process through which plants use water and carbon dioxide to create their food, grow and release excess oxygen into the air( because this year’s TSTS theme is Light, I decided to do an investigation to find out how light effects plant growth.
Question
When I change the amount of light a plant gets what happens to its rate of growth?
Hypotheses
If we limit the amount of light a plant gets it will not grow as well as a plant that getsmore light.
Materials
36 butter bean seeds
12 small pots
4 ice-cream containers
Potting mix
Black card
Foil
A ruler
Variables:
Controlled
Location
Soil
Water
Depth of seed in soil
Same type of seed
Tubes same size
Pots same size
Independent
The amount of holes in the tubes
Dependent variable
The growth of the plants
Procedure
- Plant 3 seeds the same depth in each pot, water in (same amount). Put three pots in each of the 4 ice-cream containers, label pots from A-L.
2. Make4 tubes - one with 0 holes, one with 10 holes, one with 15 holes and one with 20 holes.
- Cover tubes with a lid made from foil.
- Cover each ice-cream container with a tube and put in windowsill to get light.
- Water the plants with the same amount of water (when needed, ongoing).
- Remove tubes to observe and measure the growth of the plants daily for 3 weeks.
Results
Average Daily Growth (cm)
day / 0 holes / 10 holes / 15 holes / 20 holes11 / 0 / 0 / 0 / 0
12 / 0.05 / 1 / 0 / 0
13 / 1.5 / 2.6 / 1.2 / 0.9
14 / 2.3 / 4.1 / 3 / 2.8
15 / 2.5 / 6.9 / 5.4 / 2.25
16 / 2.7 / 8.9 / 7 / 3
17 / 3.1 / 13.4 / 8.9 / 3.7
18 / 3.3 / 14.6 / 9.9 / 4.7
19 / 4 / 16.9 / 11.5 / 6.8
20 / 4.7 / 19.4 / 16.6 / 8.85
21 / 5.9 / 20.4 / 19.9 / 11
22 / 7.9 / 24 / 21 / 12.4
23 / 10.2 / 26.1 / 21.8 / 22.2
24 / 11.25 / 27 / 22.5 / 23.5
25 / 12 / 28.25 / 21.5 / 24.5
26 / 13.1 / 28 / 21.2 / 25.1
27 / 15 / 28.6 / 22 / 25.5
28 / 15.6 / 28.6 / 25.6 / 25.5
29 / 18.5 / 28.6 / 25.7 / 26.2
30 / 20.1 / 29.2 / 26.6 / 26.1
31 / 20.6 / 29.6 / 28.4 / 26.5
32 / 21.25 / 29.7 / 28.5 / 27.1
Discussion
The plants with 10 holes (orange line) grew the most and the fastest.
The plants with 0 holes (blue line) grew the least.
The pots with 20 holes made a big jump at days 12-13 because (as with all the sample groups) one seed didn’t germinate (leaving only two samples in each group). One germinated nine days late which meant we only got data for the last 11 days from a single sample.
The results were different to my prediction. The plants with 0 holes grew the least (as predicted) but the plants with 20 holes didn’t grow the most.
I think that theplants with 0 holes were affected by heat as the soil dried out quicker than the other samples. I think this is because the covering tube had no holes to let the heat out.
My teacher and I did some research on why plants with reduced light grow fast. We found out about etiolation. Etiolation is when plants don’t get enough light so they try to get more light by stretching taller. This causes them to have longer stems but fewer leaves. This explanation matches my observations (see photo below).
Photo showing etiolation