Purpose: Observe the process of osmosis in plants and relate to biotic elements of the
oceans.
Background:
Water is a critical element of the body, and adequate hydration is a must to allow the body to function. Up to
75% of the body's weight is made up of water. Most of the water is found within the cells of the body
(intracellular space). The rest is found in what is referred to as the extracellular space, which consists of the
blood vessels (intravascular space) and the spaces between cells (interstitial space).
Dehydration occurs when the amount of water leaving the body is greater than the amount being taken in.
The body is very dynamic and always changing. This is especially true with water in the body. We lose water
routinely when we: breathe, sweat, or urinate. In a normal day, a person has to drink a significant amount of
water to replace this routine loss. The body lives within a very narrow range of normal parameters, and signs
and symptoms of dehydration will occur quickly if the water is not replenished. Complications from dehydration
include crams, vomiting, nausea, heart palpitations, kidney failure, coma, and shock.
Water molecules move across membranes through a process called osmosis. Water moves across a a
membrane to higher levels of salt concentration to reach equilibrium. Animals and plants that live in the ocean
usually have a high salt content within their cells in order to avoid dehydration. On the other hand animals and
plant that are not adapted to salt water may have a low salt content, and thus become dehydrated when placed
in salt water.
Question:
Why can’t many land and freshwater plants live in the ocean?
Why can’t many saltwater plants live in fresh water?
There are freshwater fish and saltwater fish, and few of them can live in both environments: why is this so?
Procedures:
Day 1
1. Mix a strong salt water solution in a beaker with 100 ml of water (If the solution is 10% salt…, how
much salt should you add to 100 ml of water?( _______________)
2. Fill a second beaker with 100 ml fresh water
3. Gather two pealed pieces of carrot and two pieces of celery.
4. Test the crispness of your vegetables by trying to bend them.
5. Weigh each vegetable and record in the table on the following page.
6. Place vegetables in beakers and observe next class. Write a hypothesis.
Identify the following elements of this experiment:
Independent Variable:___________________________________
Dependent Variable: ____________________________________
Control Group: _________________________________________
Constants (3-5): _________________________________________________________________________
Hypothesis (in Salt Water): ___________________________________________________________________________
Rationale:
Hypothesis (in Fresh Water): _________________________________________________________________________
_Rationale:________________________________________________________________________________________
Day 2
1. Again test the flexibility and weight of each vegetable. Record in chart.
2. Extension – place vegetables from salt water back in to the fresh water. Observe at the end of the
class period. Is there a change?
Data Chart Carrot:
Solution:
Day 1 Description
Day 1
Weight
in grams
Day 2
Description
Day 2
Weight
in grams
Difference
in weight
Gain or
Lose H20
Day 1
Weight
in grams
Day 2
Description
Day 2
Weight
in grams
Difference
in weight
Gain or
Lose H20
Salt Water
Fresh Water
Data Chart Celery:
Solution
Salt Water
Fresh Water
Day 1 Description
Class Data -Carrot
Group:
1
Salt
Water:
Difference
in weight
Fresh
Water:
Difference
in weight
2
3
4
5
6
7
8
2
3
4
5
6
7
8
9
Average
Class Data –Celery
Group:
1
Salt
Water:
Difference
in weight
Fresh
Water:
Difference
in weight
Graph class averages on the graph paper on the next page.
Describe the overall observed changes from day 1 to day 2:
How do animals and plants in the ocean avoid dehydration?
What would happen if you placed a freshwater plant in an ocean environment?
9
Average
My conclusion is that molecules of water diffuse from an area of ________ concentration to an area of
_______ concentration. When the vegetables soaked in salt water, the water traveled from the
____________ into the __________; the vegetables mass __________ by __________ g. The reverse
happened when the vegetables were soaked in fresh water. In that case, the water flowed from the
_________ into the _____________; the vegetable’s mass ___________ by _________g. Hence, the water
tends to leave the inside of the organism, unless it has a __________ salt level than its environment.
Graph – don’t forget title, axis values, axis titles, and the bar graph!