4.3 Plant organs: stems

Natural science

Grade 9

Plants

Module 27

Plant organs: stems

Activity:

To determine how the structure of a plant stem is related to the functions that it performs

[lo 2.1, 2.2, 2.3, 2.4]

The functions of the plant stem include bearing the leaves, flowers and fruit in such a way that they are exposed to sunlight, pollinating agents and fruit distributors.

In the case of large trees, the stem, in time, becomes the trunk, which is greatly thickened and strengthened. The organs that are above ground cannot live without water. As water is obtained from the soil, it has to be conducted upwards. The conducting channels for water and mineral salts are formed by lengthened, dead cells, which form the wood of the plant. The botanical name for wood is xylem . The nutrients have to be conducted to the rest of the plant, including the roots. A system of living, lengthened cells forms the bark of the tree. The botanical name for bark is phloem .

Leaves, in their turn, manufacture starch and sugar.

Assignment 1:

Collect a few twigs and stems from different plants. Place these on the desk and examine them for differences.

Divide your specimens into two groups: brown, woody types and green herbaceous types.

1. Why do these differ?

This depends on the type of plant.

1. What kind of stem would an annual, monocotyledonous plant have?

1. What kind of stem would a perennial dicotyledon, e.g. a fruit tree, have?

Fruit trees are deciduous.

1. What does this mean?

1. Leaves make it possible for a plant to "breathe". What happens in the case of deciduous trees that lose their leaves during the winter? How do they "breathe"? (They do not really breathe, of course. We should ask how gas exchange takes place.)

Take a look at the brown, woody twigs that you have collected. There is a fair chance that you will notice white specks on the brown twigs. These are LENTICELS. Lenticels are pores (openings) that facilitate gas exchange during winter.

Assessment: Study of stems

Were you able to recall information that enabled you to distinguish what you needed to know?

[LO 2.1]

Assignment 2:

1. Draw an example of two different types of twig – a green, herbaceous type and a brown, woody type.

2. Your educator will assist you with the descriptions of the following concepts. They are related to structures found on stems.

Terminal bud:

Apical meristem:

Internodes:

Nodes:

Leaf nodes:

Axil:

Scale leaves:

3. Refer to the above list (at no. 2) to provide labels for the illustrations in no. 1.

4. Make your own deduction: What are the main functions of stems?

Assessment: Sketches and Questions

Were you able to indicate the differences and the structure?

[LO 2.2; LO 2.3]

Assignment 3:

The following column graph shows the longitudinal growth of six different sunflower seedlings (A, B, C, D, E, F) during the first week after germination.

1. What is the difference between a column graph and a histogram?

1. Which of the seedlings experienced the most favourable conditions for growth? Provide a reason for your answer.

1. What height did seedling A attain in the first week?

1. Which two seedlings displayed equal longitudinal growth?