4.3 Plant organs: stems

1. What was the difference in longitudinal growth between seedlings B and F?

1. What was the difference between the longest and the shortest seedling?

1. Describe the way in which a seedling's longitudinal growth occurs.

Assessment: Graph

Were you able to answer the questions?

[LO 2.3]

Assessment

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

• recalls meaningful information;
• categorises information;
• interprets information;

2.4 applies knowledge.

Memorandum

Plant organs: Stems

Activity

Assignment 1

• As you have indicated, the functions of the plant stem include bearing the leaves, flowers and eventually also the fruit, in such a way that they are exposed to sunlight, pollinating agents and fruit distributors respectively.
• In the case of large trees, the stem, in time, becomes the trunk, which is greatly thickened and strengthened with bark and other structures.
• Plant stems need to have channels for conducting the main products that have to be moved up and down. If you understand that water has to be conducted from the lowest tip of the roots to the highest tip of the uppemost leaf, you will realise that we need a conducting channel for such water and for mineral salts.
• The leaves produce starch and sugar, which have to be conducted to all the cells, even to those that are at the furthest tips of the roots, but cannot be conducted along the same channels as the water, because this would lead to confusion. The special channel for these nutrients is known as the PHLOEM.

• Further variations occur on the outer surfaces of stems.
• Herbaceous stems are green and fleshy, but woody stems are brown and hard.
• The annual monocotyledon usually has fleshy, green herbaceous stems and the perennial dicotyledon, e.g. a fruit tree, has hard, woody stems.
• As we are mentioning fruit trees – they are deciduous, which means that they lose their leaves in autumn.

• If you know that leaves are the most important part of the plant (and therefore of fruit trees) when it comes to respiration, and that deciduous trees are without leaves during winter, you might ask what they do about respiration. We should actually ask how gas exchange takes place.
• Examine the brown, woody twigs that you have collected. There is a good chance that you will notice fine white specks on these brown twigs. These are LENTICELS. Lenticels are pores (openings) that facilitate gas exchange during the wintry season.

Assignment 2

DIFFERENT PARTS ON THE TIP OF STEM

Terminal bud : end bud of a stem, where the growing tip is situated.

Apical meristem : growth tip tissue at the end tip.

Internodes: regions of the stem between nodes.

Nodes : region on stem where buds, leaves and lateral shoots will develop.

Leaf nodes : marks on stems where previous leaves have fallen off.

Axil: region in a node where bud growth will take place.

Scale leaves : Protective leaves for the terminal bud and other growth tips.

1. different types of twig – a green, herbaceous type and a brown, woody type.

Main functions of stems:

to carry leaves in such a way that photosynthesis can take place;

to carry flowers in such a way that they can be pollinated;

to carry fruit in such a way that they can be dispersed;

to conduct water and nutrients between leaves and the roots.

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. histogram have spaces inbetween

2. M – highest growth

3. approximately 6 mm

4. L and N

5. 8-7=1mm

6. 12-6= 6mm

7. cells divide – cells lengthen and differentiate = growth