Life Processes in Plants · Lesson 4 of 6
Moving Water, Minerals, and Food Through Plants
“Follow the pathways that supply leaves with water and distribute the food they make.”
• Explain how roots supply water and dissolved minerals. • Interpret the coloured-water twig investigation. • Describe the role of xylem in water and mineral transport. • Describe the role of phloem in food transport. • Connect food production in leaves with use and storage in other plant parts.
A leaf needs supplies from the roots
A plant’s roots may be in the soil while its leaves are far above them. Photosynthesis in those leaves requires water, so the plant needs a route that connects the two. It also needs to supply other growing parts with water and dissolved minerals.
Roots take up water and minerals present in the soil. Minerals are important nutrients for growth. When a mineral is dissolved in water, it can move with that water through the plant. The plant therefore needs transport inside its body, even though it does not walk from place to place.
Think of transport as connecting where a material enters or is made with where it is needed. Roots obtain water; leaves make much of the food; roots, stems, flowers, and seeds may all need supplies. One pathway alone cannot explain all of these movements because water and manufactured food have different starting points.
Making water’s route visible
Water itself is difficult to see inside a stem. Adding a coloured substance to water makes its movement easier to follow. A plain-water comparison helps us recognise which visible changes are associated with the coloured water.
Fill about one-third of each of two glass tumblers with water and label them A and B. Add a few drops of red ink to B. Select similar tender plant twigs, preferably with white flowers, such as white sadabahar or balsam. Cut each stem obliquely at its base while it is under water, then place one twig in each tumbler.
Observe the twigs the next day. The twig in coloured water can show red colour in its stem, leaves, and flowers. The plain-water twig supplies a comparison for their ordinary appearance. Cutting the upper stem above the immersed part and observing the cut end with a magnifying glass reveals the coloured route inside the stem.
The visible staining does not mean that the entire twig is a hollow drinking straw. Water moves through thin, tube-like structures called xylem. The coloured-water result makes this internal pathway easier to recognise.
The plant’s transport tissue that carries water and dissolved minerals from roots to the stem, leaves, and other parts.
Problem
A white flower becomes pink after its cut stem has stood in coloured water. What does this suggest?
- 1.The flower was not dipped directly into the coloured water; the stem base was.
- 2.The colour must have reached the flower through a route inside the twig.
- 3.The observation supports water transport from the cut stem toward upper parts through xylem. Compare it with the plain-water twig to interpret the change.
The twig experiment uses a cut stem rather than an intact rooted plant. Its evidence reveals internal water transport, while in an intact plant roots supply that pathway. Distinguishing the setup from the full plant prevents us from imagining that ordinary plants need their stems cut to obtain water.
Distributing food from the leaves
Water transport explains how one raw material reaches the leaf. It does not explain how the food made in the leaf reaches roots or developing seeds. Plants have another set of thin transport structures for distributing that food.
The plant’s transport tissue that carries food from places where it is made, such as leaves, to other parts where it is used or stored.
A leaf can make food by photosynthesis, while a root beneath the soil may receive little or no light. The root can still grow because it receives food transported from food-making parts. Phloem connects food production with the needs of other plant parts.
| Feature | Xylem | Phloem |
|---|---|---|
| Material carried | Water and dissolved minerals | Food made by the plant |
| Starting point emphasised here | Roots in an intact plant | Leaves and other food-making parts |
| What the pathway supplies | Water and minerals to plant parts | Food to parts that use or store it |
| Evidence or connection | Coloured water moving through a twig | Food made in leaves reaching other plant parts |
Soil minerals support plant growth, but they are not the glucose made during photosynthesis. Roots obtain water and minerals; chlorophyll-containing parts make food; phloem distributes that food. Calling soil the plant’s complete food supply hides these different roles.
Problem
How can an underground root grow when it is not exposed to sunlight?
- 1.The root can take up water and minerals, but it is not the main light-exposed food-making site.
- 2.Leaves make food using photosynthesis, and phloem transports some of that food to the root.
- 3.The root can use transported food for its needs. A plant organ need not make all of the food that it uses.
Transport links use with storage
A plant does not always use every supply of food immediately. Some food can be stored in parts such as roots and seeds. Storage gives the plant a reserve that can be used later, while transport allows food made in one place to reach another place.
This connects three ideas that should be kept distinct: production, transport, and storage. Leaves are usually the main production sites. Phloem distributes food. Storage parts retain food reserves. None of these roles replaces respiration, which explains how food is used to release energy.
Problem
Describe the pathways involved when soil water helps a leaf make food that is later stored in a seed.
- 1.Roots take up water containing dissolved minerals from the soil.
- 2.Xylem carries water to the leaves, where water is one input for photosynthesis.
- 3.The plant makes food in the leaves and distributes food through phloem to other parts, including developing seeds where reserves may be stored.
Quiz
Which tissue carries water and dissolved minerals from roots?
Which material is transported through phloem?
Why is a plain-water twig included in the red-water investigation?
A twig’s upper cut end shows stained pathways after standing in coloured water. What is supported?
Which statement correctly connects production and transport?
Why can food be found in a seed even though a leaf made it?
Practice Problems
- Explain why water transport is necessary even when the roots already have water.
- Describe the coloured-water twig investigation, its comparison, and what the upper cut stem shows.
- Compare xylem and phloem in a table using the materials they carry and the roles they perform.
- Explain how a root can receive food without being exposed to light.
- Trace a connected route from soil water to a leaf and then from food production to storage in another plant part.
- A learner calls soil minerals the same thing as food made in a leaf. Explain how the two roles differ.
Key Takeaways
• Roots take up water and dissolved minerals from soil. • Xylem carries water and minerals to plant parts, including leaves. • Coloured water helps reveal the water pathway in a twig. • Phloem distributes food made in leaves to other parts. • Food can be used or stored after transport; production, transport, and storage are different roles.