4.2 Plant organs: roots

[LO 1.2, 2.4]

Take a fresh plant with roots, rinse the roots to remove the soil and carefully examine the roots. Are you able to see the fine, hair-like growths at the tips of the roots? They will be particularly visible on bean plants that you germinate from seeds yourself. These structures are known as root hairs, or radical hairs.

What is the function of a root hair?

The following is an illustration of the tip of a root:

Assignment 3:

Explain what happens in each of the following regions:

Root hair region:

owing region:

Root tip:

Root hairs consist of special cells on the outer surface of the root right behind the growing region, which increase the surface of the root so that the maximum amount of water and mineral salts can be taken up from the soil.

Assignment 4:

Make a drawing showing the structure of a typical root hair. Provide your drawing with labels and a caption.

The root hair penetrates the small spaces between the particles of soil to suck up the moisture that is trapped between the soil particles. Then it is the function of the next plant organ, namely the plant stem, to conduct the moisture further.

Assessment: Root hairs

Were you able to draw the basic sketch?

[LO 1.2]

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

This is evident when the learner:

• conducts investigations and collects data;

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:

• categorises information;

2.4 applies knowledge.

Memorandum

PLANT ORGANS: ROOTS

Activity 1

Assignment 1

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

A typical plant consists of the PLANT ORGANS :

Root, stem, leaf and flower

Activity 2

Assignment 1

ROOT SYSTEMS

1. There are adventitious root systems and taproot systems.
2. Plants develop one or the other of these systems according to the type of plant that they are (There are two main types).
3. Plants that survive for more than one year, perennials, require deep root systems for finding water during dry seasons and to be anchored properly. You will realise that tall trees and large shrubs and bushes need such root systems. They belong to the group called DICOTYLEDONS . They develop from seeds that have two seed leaves or cotyledons, like the seed of the bean plant.
4. Other plants, like grasses and maize plants, annuals, live and grow for one season only and therefore do not need such deep root systems. They need wide-reaching, shallow root systems. These plants belong to the MONOCOTYLEDONS and develop from seeds that have one seed leaf, e.g. a maize kernel.

Assignment 2

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, the adventitious roots .

The life cycle of annuals is completed in a year – they do not need taproots – and they will therefore have an adventitious root system

Trees have a taproot system because they require to be anchored deeply and have to obtain water from deep below the ground.

As adventitious roots grow from stems, they will be of no value for trees that need deep anchoring.

Lateral roots only grow out of other roots.

Main functions of roots:

anchoring

uptake of water

uptake of mineral salts in solution

conducting water to the upper parts of the plant

When a root system is investigated, the following structure can be observed:

Assignment 3

Root hair region: region where root hairs develop

Cell lengthening region: region where cells lengthen and differentiate

Cell division region: where cells divide

Meristem: general region where cell division and cell lengthening occur

Root tip: Protects the sensitive foremost growth tip by keeping it slimy to prevent wear.

1. A root hair is a special cell on the outer surface of the root – immediately following the growth tip – that is specially enlarged to take up a maximal amount of water and salts from the soil.

The srtucture of the root hair is of importance in further studies in Biology.

Assignment 4

This is what we shall focus on next.

Root hair

1. The root hair penetrates the small spaces between the particles of soil to suck up all moisture that is trapped between the soil particles. Then it is the function of the next plant organ, namely the plant stem, to conduct the water.