Specific objectives
By the end of the topic, I should be able to:
- Define transport.
- State necessity of transport in plants and animals.
- Relate function of the root hair, xylem and phloem to their functions.
- Explain the uptake of water and mineral salts from the roots.
- Differentiate between transpiration and guttation.
- State the significance of transpiration.
Meaning and importance of transport systems
Transport system in plants and animals involve movement of soluble and insoluble materials form one part of the living organisms to another.
All living organisms are made up of cells. In order to stay alive, these cells take up useful substances from their environment. They also produce and release metabolic waste substances.
- Name some useful substances, cells acquire from their environment.
- Name metabolic waste substances released by cells.
In Form 1, you learnt about the relationship between surface area and volume of an organism and how these affect diffusion. We shall review this concept using Activity 1.1 below.
Requirements
Potato, razor blade, ruler, iodine solution, 150 ml beaker and a stop watch or any other means of timing.
Procedure
1. Make a table similar to the one shown below and complete it.
2. Measure and cut potato cubes with the dimensions shown in the table.
Table 1.1: Results
Potato cube | Dimension of potato cube | Surface area (cm2) | Volume (cm3) | SA: Volume ratio |
A | 1 cm | |||
B | 2 cm |
- Note their sizes carefully.
- Which cube has a larger surface area to volume ratio?
3. Soak the two cubes in enough iodine solution and leave them for 10 minutes.
4. Remove the cubes and slice them into halves.
- Note the colour change of the iodine solution.
- Why does the iodine change its colour?
- Note the colour change in the two cubes.
- Which potato cube changed colour the most?
5. Assume that the potato cubes represent living organisms. Use the results obtained from the experiment to explain what happens to the surface area to volume ratio as the size of the organism increases.
Discussion
The rate of diffusion of the iodine molecules is faster in the smaller cube which has a larger surface area to volume ratio than the bigger cube.
Necessity of transport system
Most single-celled organisms are very small. They have a large surface area compared to their volume. In these organisms, substances rapidly get in and out of the cell by simple diffusion to meet the cell requirements.
The multicellular organisms are usually big and hence have a small surface area compared to their volume. In addition, many of their cells are far from the outside environment which is a source of oxygen and nutrients or into which they release metabolic waste substances, which can be harmful if left to accumulate in the cells. These organisms therefore need a special transport system to efficiently move substances into and from the cells.
A transport system in living organisms is made up of specialised tissues and organ systems. The type of transport system contained in an organism depends on its complexity and whether it is a plant or an animal.
Transport in plants
The substances that need to be transported in plants are:
- Water used in photosynthesis.
- Mineral salts important in various metabolic processes.
- Organic substances produced mainly by photosynthesis.
In plants, the transport system consists of two types of tissues namely phloem and xylem. These tissues are found in the root, the stem and the leaves. Phloem tissues transport food substances such as sucrose and amino acids from the leaves to other plant tissues where they are used or converted into storage forms.
The xylem tissues transport water and mineral salts absorbed by the roots to different parts of the plant.
- Where are the photosynthetic cells located in a plant?
- How do water and mineral salts reach the photosynthetic cells?
- Where do plants obtain water and mineral salts from?
- State how the products of photosynthesis are distributed to other parts of a plant.
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