Final Lab Manual
Effect of Salinity on Plants (Experiments 1 and 2)BIO100A
This manual was adapted from Online BIO100A – Survey of Laboratory Manual Version 4.0 by Michael Maxwell and Omar Clay.
Instructions
Read A. Background.
Read B. Experiment Overview.
Complete Section 1 – Background of the Final Lab Report (“Report”).
Read C – Materials and Methods. Gather the materials you will need. Note that both experiments require multiple days, so plan accordingly.
Read D – Procedure. Follow the instructions to conduct the experiment.
As you proceed, record your results in Section 3 – Results in the Report.
Remember to take pictures as you proceed. Make sure that each picture includes a ID Card, a card with your name, the words “BIo100A, Midterm Lab,” the date, and your signature. Insert each picture in the appropriate location in the Midterm Lab Report (“Report”).
Analyze your results and complete Section 4 – Discussion in the Midterm Lab Report.
Materials Needed
Measuring cup
Measuring spoon
Water
Experiment 1
Red food coloring
Blue food coloring
Salt
Celery stalk
Experiment 2
Radish or other quick sprouting seeds (beans, lettuce, pepper)
Paper towels
Salt
Zip lock bags or saran wrap
Six cups
A. Background
Introduction
The abiotic (non-biological) features of an ecosystem (e.g., climate, soil quality, water availability) are important to understanding the biological community that comprises the biotic component of an ecosystem. Water availability is particularly important to all life.
Figure 1. About one percent of the world’s water is fresh groundwater.
Figure 2. The water cycle
Freshwater scarcity limits the range of many terrestrial species of plants and animals. Plants, like animals, have different tolerances to salt in their environment. All soils have some water-soluble salts, and essential plant nutrients are absorbed in this form. High salinity in the soil (the salt content) makes it more difficult for plants to extract water from the soil. Fresh water enters an ecosystem in the form of precipitation, a river or lake, or an underground aquifer (Figure 6.2). With human population growth, intensive agricultural practices, and urban water demand, water levels in many of the world’s aquifers are dropping. If fresh water is pumped out of an aquifer at a rate exceeding its natural recharge rate (from precipitation and underground water channels) salt water and other pollutants may intrude into the traditional aquifer basin. Saltwater encroachment is a growing problem in the aquifers of coastal communities.
Salty soil is also a problem that can arise in agriculture. As irrigation water is absorbed by plants and evaporated by the sun, salts are left behind. Over time, salt may accumulate such that the soil becomes too salty for many plants to grow. It is believed that the ancient population of Sumeria first thrived with its practice of irrigation, but over many generations began to suffer reduced crop yields due to the increasing salinity of the soil.
B. Experiment Overview
The goal of this experiment is to investigate the effects of salinity on plants. You will perform 2 experiments. Each is required. 2 pictures, each with an ID card, are required for each experiment.
In Experiment 1, you will investigate the effect of salinity on the ability of celery to transport water. You will place celery in low-salt or high-salt colored water for 6 hours to overnight and determine how well the celery transported the water to its top.
In Experiment 2, you will investigate the effect of salinity on seed germination. You will place radish seeds in environments with different salt contents and monitor them over five days. Each germinating environment will be a plastic-encased, water-soaked paper towel.
C – Materials
Measuring cup
Measuring spoon
Water
Experiment 1
Red food coloring
Blue food coloring
Salt
Celery stalk
Experiment 2
Radish or other quick sprouting seeds (beans, pepper)
Paper towels
Salt
Zip lock bags or saran wrap
Six cups
D – Procedure
Experiment 1Water Transport & Salinity
Obtain four cups and fill each cup with 400 ml of tap water. Use red dye to darkly stain two cups and use blue dye to darkly stain the other two cups. Be sure that each red cup gets the same amount of dye and that each blue cup gets the same amount of dye. Record the drops in each. Add a spoonful of salt into each cup.
Label one red dye cup and one blue dye cup with an S (high salt). Add 4 spoonfuls of salt to each of these cups. Stir the solutions thoroughly.
Obtain two similar stalks of celery, each with some leaves at the top. Cut a 1-cm piece (about one-half inch) off the bottom of each stalk. Keep the relative lengths of the two stalks as similar as possible.
Carefully, split the stalks up the middle about halfway. The stalks should each now have two “legs.” Be sure that the legs of each stock are similarly sized (i.e., the left leg and right leg are nearly the same length and width).
Figure 3. Celery activity. Left: cross-section of a celery talk. The dark green circles are clusters of vascular tissue. Right: picture of the celery stalk straddling the cups with the food coloring.
Place the red S cup and the blue S cup together. Gently place one “leg” of one stalk into the red S cup, and the other “leg” of the stock into the blue S cup. The celery should now be “straddling” the two S cups (Figure 3). Place the red non-S cup and blue non-S cup together and situate the legs of the other celery stalk into each cup (i.e., the celery “straddles” these two non-S cups).
Take a picture of your setup – the cups with the celery in them – and insert it in the Report under Experiment 1 Picture 1 – Setup.
Record the time at which you place each celery into the pairs of cups as “Start time” in Table 1 in the Report.
Let the celery sit in the cups for 6 hours, or until you can see color in the leaves of one of the stalks.
Record the time when you remove the stalks as “Stop time” in Table 1 in the Report.
Remove the celery from the cups (be sure to keep it clear which came from the high salt solution (S) and which came from the low salt (non-S) condition). Lay each stalk out flat. Examine the celery. Record your observations in the Report under Results/Experiment 1/#2.
Starting at the top, move down the stalk of each celery, making cross-sectional cuts. Stop when you first see evidence of dye. Measure how far up each stalk the red and blue dyes climbed (cm). Include the red dye in high salt conditions (S), the blue dye in high salt conditions (S), the red dye in low salt conditions (non-S), and the blue dye in low salt conditions (non-S).
Take a pic of your cut celery stalks and insert it in the Report under Experiment 1 Picture 2 – End.
Record your measurements in Table 2 of the Report.
Tear apart the celery stalk. Notice the feel of the vascular tissue, and how the food coloring lies within it.
Experiment 2 :The Effect of Salinity on Seed Germination
Prepare solutions of different salinity. Collect 6 clean cups and label them: “1/2”, “1/4”, “1/8”, “1/16”, “1/32”, and “0”.
Use a measuring spoon to add salt to 50 ml of water in a measuring cup (about ¼ cup). Add 1.5 tablespoons of table salt (sodium chloride). Stir the water while adding the salt. The solubility of sodium chloride is ~36 grams per 100 mL of fresh water at 25 C. After vigorously stirring the solution you should still be able to see some remaining salt crystals at the bottom of your solution. This indicates that you have reached the saturation point of salt in your water.
Pour off 40 ml of salt water into the cup labeled ‘1/2.” Do not pour the un-dissolved salt. The “1/2” cup will then contain your saturated saltwater solution.
Clean your measuring cup, and fill each of the remaining cups with 40 ml of plain water.
Add 40 ml of plain water to your salt solution in the “1/2” cup. You will then have 80 ml of a 50% saturated saline solution in the “1/2” cup.
Using your measuring cup as an intermediate, transfer 40 ml of the 50% saturated solution (“1/2” cup) to the cup labeled “1/4”. The “1/4” cup will then hold 80 ml of a 25% saturated saline solution.
Using your clean measuring cup as an intermediate, transfer 40 ml of the 25% saturated solution (“1/4” cup) to the cup labeled “1/8”. The “1/8” cup will then hold 80 ml of a 12.5% saturated saline solution.
Using your clean measuring cup as an intermediate, transfer 40 ml of the 12.5% saturated solution (“1/8” cup) to the cup labeled “1/16”. The “1/16” cup will then hold 80 ml of a 6.3% saturated saline solution.
Using your clean measuring cup as an intermediate, transfer 40 ml of the 6.3% saturated solution (“1/16” cup) to the cup labeled “1/32”. The “1/32” cup will then hold 80 ml of a 3.1% saturated saline solution. You have now prepared a pure water solution in cup “0” and a 3.1%, 6.3%, 12.5%, 25%, and a 50% saturated saline solution in cups “1/32”,”1/16”, “1/8”,”1/4”, and “1/2” respectively. See the diagram below.
Figure 4. Diagram of the serial salt solutions.
You have six solutions ranging in concentration from 0% to a 50% saturated saline solution. You can run this experiment using each solution as the basis for a germinating environment and following the instructions as they stand.
Prepare 2 additional cups with solutions that you choose. Examples include using water with additives such as sugar, alcohol, soda, or bleach, or even running two at the same salt concentration to get a sense of the uncertainty. You can also use the above protocol to test the effects of even smaller salt concentrations. Have fun!
Record your 2 additional cups in Table 3 of the Report.
Prepare for seed germination. Take three paper towels and cut them in half. Fold each half towel in half. These towels will be the seeds’ germinating environment.
Figure 5. Left: radish seeds laid out on a water-soaked paper towel. Right: a radish sprout.
Place a folded towel in each of the cups containing your salt solutions and possible alternatives. Make sure that each towel gets soaked with the solution and that you do not lose track of which one is in which condition. Label one corner of each towel with the corresponding solution (e.g., “1/2”, “1/4”, etc.).
Count out six piles of 15 or more radish seeds each. Make sure that each pile has the same number of seeds. If there are visible quality differences between seeds make sure that each pile has similar quality as well (e.g., discard cracked, broken, or discolored seeds).
Remove the soaked towels from the cups and lay the seeds from each pile out in each one of the towels (Figure 5). Be careful not to mix up which towel came from which cup. Record the initial date (Day 0) on which you first put the seeds in the towels in Table fin.2 in Lab Report 6. Spread the seeds over only one half of the towel so that you can fold the other half over the seeds. You may even want to add another fold.
Fold the towel up around the seeds in order to keep them wet, but you will also want to be able to unfold the towel to observe the germination process over the next four days. Wrap each wet towel with its seeds in saran wrap or in a sealed sandwich bag. This will ensure that the water in the towel does not evaporate away. Make sure that each towel and seed set is labeled to match the corresponding solution(e.g., “1/2”, “1/4”, etc.), perhaps by marking the plastic bag or wrap, or by placing a labeled piece of paper in the bag/wrap.
Take a picture of your setup and insert it in the Report under Experiment 2 Picture 2 – Setup.
Find a safe location where your seed sets can stay for the next four days. Make sure that each set is in identical condition. Monitor seed appearance and growth every day for the next four days. Unfold the wet towels carefully to avoid ripping the wet towel or fragile sprouts.
Every day, record the number of sprouts in each environment and anything else you observe about the seeds in Table 3 of the Report.
After4 days, take at least one picture of your results and insert it in the Report under Experiment 2 Picture 2 – End.