Thinking with Data: Science Part 4
How Does Salinity Affect the Growth of Plants?
An Experiment
Research Question: Does salt water affect plant growth?
Materials:
 seed packet (9-15 seeds)
 3 plastic containers
 3 peat pellets
 3 - 20 oz plastic bottles with caps
 Permanent pens to label with
 Table salt
 ¼ teaspoon, ½ teaspoon, ¼ cup measures
 Ruler with mm markings
Procedure:
Day 1: Preparing the peat pellets
1) Label each bottle as follows “no salt”, “ ¼ tsp salt”, and “ ½ tsp salt”. Fill each bottle almost to
the top with warm (but not hot) water. Add ¼ teaspoon of salt to the “ ¼ tsp salt” bottle, then
close the cap tightly and shake to combine the salt with the water. Add ½ teaspoon of salt to
the “ ½ tsp salt” bottle, then cap and shake to combine. Leave the “no salt” bottle of water
without salt.
2) Prepare 3 containers by labeling each (no salt, ¼ tsp. salt, ½
tsp. salt). Set one peat pellet in each container.
3) Add ¼ cup of the corresponding water (from your bottles) to
the bottom of the container. DO NOT POUR DIRECTLY ON TO
PEAT PELLET. The peat pellets will slowly absorb the water.
4) Put the container away in a non-sunny location until tomorrow.
5) Close your bottles and keep in a non-sunny location. You will use this water to water your
plants for the duration of the experiment.
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6) Tomorrow the peat pellets will have soaked up the water
and be about 1 inch tall.
Day 2: Planting the seeds
7) Pull away the fine netting to expose the top of the pellet.
Separate seeds into three equal parts- you will plant the same
number of seeds in each pellet.
8) Use a pencil to poke holes for the seeds in the top of the
peat pellets- the holes should be deep enough for the seed to
fit.
9) Push the seeds into the holes.
10) Use your fingers to cover the seeds with the surrounding
peat.
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11) Place the containers (with peat pellets in them) in a sunny
location. Be sure all containers get equal light and heat.
12) Water your containers twice a week when your teacher tells you. Add ¼ cup of the
corresponding water (from your bottles) to the bottom of the container. It is important that all
plants be given equal amounts of water!
13) Record plant growth twice a week and record your findings in the table. Be sure to include
the extra measurement your group decided to use.
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Data Collection:
Type of seed: _____________________________
Water
Date
# of
sprouts
Average
height
(mm)
Water + ¼ tsp Salt
# of
sprouts
Average
height
(mm)
Water + ½ tsp Salt
# of
sprouts
Average
height
(mm)
Reporting:
In four weeks, your group will report on the results of your experiment. Each student will turn in
a lab report.
Use the Salinity Experiment Reporting Template to help you structure your report.
Your group will also do an oral presentation. The presentation should take no more than 5
minutes. It should focus on:



the type of seeds used in the experiment
comparisons you found between the growth of plants in the three salinity conditions (you
will use the computer to project Excel graphs of your data)
whether or not salt affected the growth of your plants
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