Testing for starch in leaves

Question 1

What is diffusion?

Answer 1

Diffusion refers to the random movement of particles from a region of high concentration to a region of low concentration.

Question 2

What is osmosis?

Answer 2

Osmosis refers to the movement of solvent molecules fro a region of high concentration to a region of low concentration using a semi-permeable membrane.

Question 3

What is a hazard? What is a risk?

Answer 3

Hazard - something (chemical, physical or biological) which can cause damage
Risk - quantifies the severity of the damage caused by the hazard

Question 4

How can we test for starch?

Answer 4

Starch is a carbohydrate.
When you add iodine solution, it forms a blue black compound

Question 5

Identify the reagent and the sample in the test for starch.

Answer 5

Reagent - Iodine solution
Sample - Starch

Question 6

Explain the procedure of the test for starch in leaves?

Answer 6

1. Boil the leaf in hot water (85°-90°) for 1 minute
2. Add ethanol to a test tube, place the leaf in the test tube an boil it for 4-5 minutes (temp should be 85°-90°)
3. Rinse the leaf
4. Put it on a petri dish and add iodine solution (maximum 5 drops)
5. Observe

Question 7

Why do we boil the leaf?

Answer 7

1. It will kill the leaf
2. Disrupts the cell membrane and softens the cuticle
3. This allows the iodine solution to penetrate

Question 8

What is the observation?

Answer 8

When iodine solution was added to the bleached leaf, a blue black compound formed on the leaf. This indicates the presence of starch in the leaf as starch reacts with iodine to form a blue black compound

(talk about how dark the compound is and how that relates to amount of starch)

Question 9

Why do plants form starch?

Answer 9

1. It is insoluble in water, and hence osmotic balance is maintained
2. It forms a bigger molecule so it saves space (as many small molecules of glucose form one starch molecule)