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Natural sciences

Grade 9

Plants: structure, including genetics

Module 27

Plant organs: roots

Plants live and grow unobtrusively and we are often unaware of the marvels that are hidden within them. We need to take a closer look to understand how miraculously they function.

A plant consists basically of four kinds of organs: roots , stems , leaves and flowers.

Activity 1:

to identify the organs of a plant

[LO 2.2]

Assignment 1:

Complete the tables by supplying the missing information about the different organs.

Plant organ
Root
Stem
Leave
Flower
Above ground/Underground
Main function

Activity: 2

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

[lo 1.2, 2.4]

Plant roots

Assignment 1:

Go to the garden or the school playing fields and collect one small example of each of four kinds of common plants. Choose weeds, if possible. Ensure that you remove the plant with its root system intact. Rinse off any soil and arrange the plants on a sheet of clean paper.

Do you observe any noticeable differences with regard to the root system?

If you are lucky your plant samples will have two different kinds of root system. Sketch the two main types of root system. Your educator will provide the necessary guidance.

The TWO types of root system are known as the ADVENTITIOUS ROOT SYSTEM and the TAP ROOT SYSTEM .

Plants that have a taproot system have a main root that grows deep into the soil. Most of the plants that survive for more than a year (perennials) have a taproot system. This type of root system can reach water that is far below the soil surface and can anchor the plant. High trees and shrubs and bushes need such root systems. They belong to the group DICOTYLEDONS . They develop from seeds that have two seed leaves or cotyledons, like the seed of the bean plant. Many dicotyledonous plants, of course, are also annuals, but they do have taproot systems.

Monocotyledons, e.g. grasses and maize plants, are annuals. As they grow for one season only, they do not need very deep root systems. They actually need a wide, shallow root system to absorb all the moisture that might reach the soil. MONOCOTYLEDONOUS plants have adventitious root systems and develop from seeds that have one cotyledon, e.g. a maize kernel.

A taproot system consists of one main root, the taproot, and lateral roots that grow from it.

An adventitious root system consists of equally sized roots that grow from the base of the stem and are called adventitious roots . These roots are not branched.

Assignment 2:

Provide the correct labels for the sketches of the two types of root systems.

1. Which type of root system would you find with petunias, which are annuals?

2. Why do petunias develop this type of root system?

3. Which type of root system would an oak tree have?

4. Why would a tree need this type of root system?

5. Do trees have adventitious roots? Provide an explanation for this.

6. Can lateral roots develop from adventitious roots? Explain your answer.

7. Explain the main functions of roots.

Assessment of Root systems

Were you able to distinguish different types of roots and apply your knowledge?

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Source:  OpenStax, Natural sciences grade 9. OpenStax CNX. Sep 15, 2009 Download for free at http://cnx.org/content/col11069/1.1
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