Science - Biology - General Biology - 2 Germination of seeds and
growth of plants (P8011200)
2.8 The function of the seed leaves
Experiment by: Phywe
Printed: Oct 8, 2013 10:40:50 AM
interTESS (Version 13.06 B200, Export 2000)
Task
Task
Do seed-leaves have any particular significance for the developing of a plant?
Examine the significance of the seed-leaves (cotyledons).
Use the space below for your own notes.
Logged in as a teacher you will find a button below for additional information.
-1-
Additional Information
The first two leaves of a young bean plant are particularly thick and fleshy. They are
called seed-leaves (cotyledons) and look quite different from the leaves that follow
later.
-2-
Material
Material
Material from "TESS advanced Biology basic set General Biology, BIO" (Order
No. 15296-88)
Position No.
Material
Order No. Quantity
64705-00
1
Glass beaker DURAN , tall, 600 ml
36006-00
1
3
Test tube rack f. 6 tubes, wood
37685-10
1
4
Test tube 160 x 16 mm
37656-03
(6)
5
Knife, stainless
33476-00
1
Cotton wool, white 200 g
31944-10
1
Petri dish, d = 100 mm
2
®
Consumables
Additional Material
Garden soil
Bean seeds
Material required for the experiment
-3-
Setup and Action
Setup and Action
Place about 15 beans in a 100 mm petri dish filled with water (Fig. 1) and let them swell for
one day.
Fig. 1
One day later, place the swollen seeds in a 600 ml glass beaker filled with garden soil (Fig. 2)
and water regularly.
Fig. 2
Within a few days the beans develop. As soon as the first small leaflets appear between the
seed-leaves, pick out six plants of roughly of the same size.
Carefully rinse the roots, which should also all be in about the same stage of development,
under the tab, to remove all soil.
With the aid of a little cotton wool insert each plant into a test tube so that the roots are
completely in the water (Fig. 3). The cotton wool, however, should not touch the water.
-4-
Fig. 3
Cut off both seed-leaves (cotyledons) from two of the germinated plants (two plants on the
right of Fig. 3), one seed-leaf from each of the other two (both plants in the middle of Fig. 3),
leave the seed-leaves intact on the other two plants (both plants on the left of Fig. 3) and place
the test tubes in a rack as shown in Fig. 3.
During the next days, observe the development of the six plants and note your observations
on the Results page.
-5-
Results
Results
Write down your observations on the development of the plants here.
How do the seed-leaves change? Do all plants develop in the same way?
As new leaves form, the seed-leaves shrink and wilt. Their colour turns yellow.
Eventually they fall off.
The plants develop more or less well depending on the amount of their seed-leaves.
The plants with both seed-leaves intact develop best, the plants without seed-leaves,
however, also grow, albeit much more slowly (Fig. 4).
-6-
Fig. 4
-7-
Evaluation
Evaluation
Question 1
How do the seed-leaves change?
The cotyledons are initially green and fleshy. Once the first true leaves have developed,
the seed leaves are thin, they shrink and begin to wilt. After some time, the withered
leaves fall off.
Question 2
Is there a relationship between the number of cotyledons and the growth of the plant?
-8-
In this experiment could be shown, that the bean sprouts with two cotyledons develop
best, while the bean sprouts without cotyledons developed much worse, the leaves
of those plants were much smaller than the leaves of the other sprouts.
The experiment shows that the cotyledons are significant for the growth of the young
plant.
Question 3
What do you think is the purpose of the seedleaves? (The answer of this question also explains
why the seedleaves are so thick and fleshy and why they change after germination).
The purpose of the cotyledons is the nutrient supply of the young plant.
The nutrients are stored as starch in the seed. During the germination of the seeds
water is absorbed, so that the starch can be converted into sugar (mono-or
disaccharides) by the help of the enzyme amylase (starch hydrolysis). As in the
cotyledons no photosynthesis takes place, the stored nutrients from the cotyledons
are of great importance for the growth of the young plant. When you cut off the
cotyledons, the young plant is suffering from a lack of nutrients, the plant grows very
slowly or withers. Only when the first true leaves are formed, the plant can form starch
independently by photosynthesis.
-9-
- 10 -