1

Things that you find inside the cell, don’t always stay inside the cell, and sometimes things you find outside a cell, you really don’t want inside the cell, so the methods of controlling what comes in and what comes out is as important in your cells as it is in a trendy nightclub. We’re going to look at three experiments that tell us a little about these transport methods.

OneYou need...

About 20 cm3 thick starch solutionWarm waterIodine (dissolved in KI)Medium sized (200–300 cm3)

beakerClear plastic bag (the thin ones used

for vegetables at the supermarket work well)Safety: view information sheet for iodineProcedure1 Cut a section from the plastic bag. You need the largest roughly square

sheet possible but with no ventilation holes. If there are no holes in the bag the complete bag can be used.2 Spread the plastic over the top of a beaker or your cupped hand and pour the starch solution into the centre of the plastic. Hold the sides of the plastic up and twist them together to make a closed bag. Tie a knot in the bag or use a rubber band to tightly seal the bag of starch solution.3 Half fill the beaker with warm water. Add enough iodine to make a light yellowy brown solution.4 Place the plastic bag of starch solution into the iodine and observe for about 15 minutes

Questions to answerDescribe and explain the changes you saw. Why did we use warm water?

Knowledge is not simply another commodity. On the contrary. Knowledge is never used up. It increases by diffusion and grows by dispersion.

Daniel J. Boorstin

Methods of Transport within and between cellsthree investigations

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Iodine What colour is iodine? What does it react with? What colour will it turn?

2

What is different about the cells of a grape to the cells in your own body? Will they cope better with more water or less well? What is different about the skin of a grape to the inside of a grape?

You need4 grapes of similar size50 cm3 water50 cm3 strong sugar solution2 small beakers

SafetyWrite a safety risk assessment for this

practical

Procedure1 Pour approximately 50 cm3 of strong sugar solution into a small beaker.2 Pour approximately 50 cm3 of water into another small beaker.3 Label the beakers clearly.4 Peel two of the grapes and add one peeled and one un-peeled grape to each beaker.

5 Leave for at least 24 hours. Then observe and feel the fruit

QuestionsWrite a description and explanation of the changes or lack of changes in your pieces of fruit

What limits the change in size ofa. The unpeeled fruit?b. The peeled fruit

two

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3

You need

2 thin slices of potato (about 0.5 cm wide)

2 thin slices of cucumber (about 0.5 cm wide)

WaterSaturated salt solution2 Petri dishes

Safety:Write a risk assessment for this investigation

Procedure1 Place a slice of cucumber and a slice of potato in each Petri dish.

2 Fill one Petri dish with water and the other with saturated salt solution, being careful to cover the slices and making a note of which is which.

3 Remove and examine the slices after 10 minutes.

QuestionDescribe and explain the changes

Homeworkone

Create a template for all practical investigations that you can use throughout the year

two

Make sure all of the questions on this sheet have been thoughtfully answered - including all risk assessments for the investigations carried out (remember the format 1. Risk 2. What could happen 3. How would you prevent this?)

three

What would happen to blood if you placed it in a hypertonic or hypotonic solution? illustrate your answer. If you did the same to an onion cell would you expect to see the same? What is different about the two cells. Again, illustrate your answer.

Due: October 6th 5pm

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Cucumber Are cucumbers water based? How could you find out? what observations can you make about cucumbers? Can you eat them without dribbling?