Exploring osmosis with carrots (Natasha Bunch)

TitleExploring osmosis with carrots and discovering the changing mass of carrots using  a Triple Beam Balance.

Principle(s) Investigated: 
Measuring Mass:
The ability to accurately measure the mass of an object is an important skill in the
science laboratory. The triple-beam balance is an instrument frequently used to measure the mass of objects.

BIG IDEAS about Passive Transport and Osmosis:
1. Molecules move into and out of cells along a concentration gradient, going from areas of high concentration to low concentration.
2. Cells have semi-permeable boundaries .
3. Molecules are constantly in motion.
4. The concentration of cells change with their changing environment.
5. Osmosis is the diffusion of water through a cell membrane and is an example of passive transport.


Standards : 

Seventh Grade Life Science

7.1.a  Students know cells function similarly in all living organisms.
7.7.a. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.
7.7.c Communicate the logical connection among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence.

Materials
  • One 200 mL beaker
  • Lab group brown baggie with supplies (LABELED WITH “O” for organic or “O” for non-organic (store)
    • salt (pre-measured in baggie) (store)
    • baby carrots (store)
    • labels (store)
    • sticks (store)
  • water (from sinks)
  • Two plastic cups (store)
  • triple beam balance
  • Scratch paper for each lab group (write names of lab partners and label each cup with solution contents)

Procedure

In this two day lab activity, students that are working in pairs will have an opportunity to see osmosis at work. They will use a triple beam balance to measure the mass of two carrots before immersing them into two different solutions for roughly a 24 hour period.  One carrot will be placed in a salt solution and the other will be placed in a plain water solution.

Students will be given two plastic cups that they will label to distinguish the salt solution carrot from the carrot in the plain water solution.  After 24 hours, the students will rinse and dry their carrots before measuring the mass of their carrots again.  The data that the students collect for both days will be recorded in their lab worksheets.


Student prior knowledge
    Before participating in this lab experiment, students know the basic concepts of passive transport and diffusion as the movement of a substance from an area of higher concentration to an area of lower concentration.

In order to be able to successfully find the mass of the carrots needed for this experiment, students had a lecture on the use of a triple beam balance and at least one other day of direct experience with the balance measuring the mass of other objects.

Explanation

This lab experiment investigates the movement of water into and out of cells. How water moves in and out of cells depends on the concentrations of dissolved chemicals, like salt and sugar, and how they compare inside and outside of the cells.  All cells are protected with a cell membrane that works as a barrier and controls the movement of different chemicals into and out of a cell.  When water moves across a cell’s membrane, it is called osmosis.  The direction of the movement of water across a cell’s membrane depends on the concentrations of dissolved chemicals, like salt and sugar, inside and outside of the cell.

After observing and recording the changing of the mass of the two carrots in different solutions over a 24 hour period, students will have a direct experience observing the affects of osmosis and the movement of water across a cell’s semi-permeable membrane.  They will observe a loss of mass and the movement of water out of a carrot by osmosis when it is in a salt solution where the higher concentration of water is inside the carrot compared to the lower concentration of water inside the salt solution.  Likewise, they will observe an increase in mass with the carrot that was in the plain water solution as the higher concentration of water was outside of the carrot, causing water to move into the vegetable.  

In this lab experiment, students will be able to relate the scientific concepts of diffusion and osmosis to real life situations and the environmental needs of plant and animal cells.  Students will understand the basic mechanics of passive transport and how it relates to the functioning of a cell’s membrane.  Individually, students will form a hypothesis related to this experiment and have an opportunity to test that hypothesis by collecting and recording data and then analyzing their information collected.


Let’s do the math:

1.) To calculate the mass for each of the carrots alone, you must subtract (-) the mass of the CUP from the TOTAL MASS for each item.  

(mass of carrot alone = total mass - mass of plastic cup)

2.) To calculate the % change in mass, you subtract (-) the initial (Day 1) mass from the final mass (After 24 hours) and then divide (÷) that by the initial mass.

[change in mass = (final mass - initial mass)/initial mass]

% change in mass = change in mass X 100

Record your results in the last column of the data table.   

SHOW YOUR MATH!!!!

ITEMS TO BE MEASURED

Day 1


Mass (g)

(TOTAL

MASS)

Day 1


Mass

(g)



Carrots

alone

After 24 Hours

Mass

(g)

(TOTAL

MASS)

After 24 Hours

Mass (g)

Carrots Alone


Change in Mass of Carrots

%

Change in Mass of Carrot

PLASTIC CUP

N/A

N/A

N/A

N/A

N/A

CARROT 1

(In Salt Solution)

CARROT 2

(In Water Solution)


Questions & Answers: 
Q: How does the process of osmosis relate to the functioning of plants?

A: Osmosis maintains an equilibrium between the outside and inside environment of plants.
Soil has a higher concentration of water than the inside of the roots of a plant.  Therefore, water  moves from soil to a region of low concentration and supplies the plant with needed water.  When the soil is dry, water moves out of the plant’s roots back into the soil having an adverse affect on the plant causing it to weaken and wilt.

Q: What might happen to a human’s red blood cells if they were immersed in a salt water solution?


A: Then the red blood cells would shrink as the result of osmosis and  the water moving from inside the cell to the surrounding salt water solution.


Q: Using your knowledge about diffusion and osmosis, why do you think it is effective to use salt as a means to kill snails and slugs?

A: Like many living creatures, snails and slugs are largely made up of water.  These creatures also have very permeable outer membranes.  When they are covered in salt or placed in a salt solution, the water from inside their cells moves out their bodies by osmosis and causes them to die.

Applications to Everyday Life: 
One vital process closely linked to osmosis is dialysis, which is critical to the survival of many victims of kidney diseases. Dialysis is the process by which an artificial kidney machine removes waste products from a patients' blood—performing the role of a healthy, normally functioning kidney. The openings in the dialyzing membrane are such that not only water, but salts and other waste dissolved in the blood, pass through to a surrounding tank of distilled water. The red blood cells, on the other hand, are too large to enter the dialyzing membrane, so they return to the patient's body.

Osmosis has several implications where medical care is concerned, particularly in the case of the storage of vitally important red blood cells. These are normally kept in a plasma solution which is isotonic to the cells when it contains specific proportions of salts and proteins. However, if red blood cells are placed in a hypotonic solution, or one with a lower solute concentration than in the cells themselves, this can be highly detrimental.

Read more: http://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol-2/Osmosis-Real-life-applications.html#ixzz1dx2PO9OH

Read more: http://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol-2/Osmosis-Real-life-applications.html#ixzz1dx23B87h

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made. 

YouTube Video

YouTube Video



ĉ
Norman Herr,
Nov 17, 2011, 3:59 AM
ĉ
Norman Herr,
Nov 17, 2011, 4:02 AM
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