Practical 4 - Investigation of the digestion of starch agar using germinating seeds

Question 1

What are there large quantities of in the endosperm of seeds such as maize?

Answer 1

Starch

Question 2

Where is starch stored in seeds such as maize?

Answer 2

In the endosperm

Question 3

Where is starch stored in broad beans?

Answer 3

In the cotyledons

Question 4

What are there large quantities in the cotyledons of broad beans?

Answer 4

Starch

Question 5

Explain what happens during the germination of a seed

Answer 5

The starch is broken down by the enzyme amylase into maltose which is transported in the phloem to the growing points in the plumule and radical

Question 6

Which enzyme is starch broken by?

Answer 6

Amylase

Question 7

What does amylase break starch down into?

Answer 7

Maltose

Question 8

What is maltose transported in?

Answer 8

The phloem

Question 9

What is maltose transported in the phloem to?

Answer 9

The growing points in the plumule and radical

Question 10

Apparatus

Answer 10

Soaked maize seeds
Starch agar plates
White tile
Water bath
Scalpel
Iodine-potassium iodide solution
Boiling tube

Question 11

Method

Answer 11

Method
1. Cut the maize seed in half.
2. Place one half cut surface down onto the starch agar.
3. Place the other half of the maize seed into the boiling tube add water and place in a water bath at 80°C for 10 minutes. This will denature any enzymes present.
4. Place this half of the maize seed onto another starch agar plate cut surface down.
This will act as a control.
5. Incubate both plates at 25 °C overnight.
6. Remove the maize seeds and flood each plate with iodine-potassium iodide solution.
7. Observe and record any difference between the two plates.
8. Calculate the area of any ‘clear’ zone on the plates.

Question 12

Why do we place one half of the maize seed into a water bath?

Answer 12

Denatures enzymes = acts as a control

Question 13

Observations of the results

Answer 13

For the non-boiled seed, there is a lighter patch surrounding where the seed was in the iodine
This isn’t apparent on the seed that was boiled and there’s no clear gap in the iodine

Question 14

Area of the clear zone + why

Answer 14

pir^2
Approximately a circle

Question 15

Why is there no clear area in he iodine for the control?

Answer 15

Since he enzymes have denatured so there’s no digestion of starch

Question 16

Why is there a clear zone for the non-boiled seed?

Answer 16

Since enzymes have been released, which digest the starch

Question 17

How can we compare how different faces effect the germination of plants

Answer 17

By measuring the diameter of the clear zones in the starch

Question 18

What does flooding the plate with iodine do?

Answer 18

Makes it clear where the clear zones are where the enzymes have digested he starch/starch has been hydrolysed

Question 19

What do seeds release as they germinate?

Answer 19

Amylase

Question 20

What does amylase do to starch agar?

Answer 20

Digests it

Question 21

What does amylase digest?

Answer 21

Starch agar

Question 22

What digests starch agar?

Answer 22

Amylase

Question 23

What factors can we investigate that affect the germination of plants by comparing the diameter of different clear zones?

Answer 23

-use different varieties of seed (keep other variables the same)
-use different temperatures
-use different oxygen partial pressures
-initially soak the seeds for different times
-use different light intensities

Question 24

Why can we use different light intensities as a factor to compare germination in different plants in this practical?

Answer 24

Since some seeds need light to germinate