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How do plants transport water and minerals?

Class 7 ScienceNCERT chapter: Life Processes in Plantsइसे हिंदी में पढ़ें

Exam-ready answer

Plants absorb water and dissolved minerals from the soil through root hairs. These are carried upward from the roots through the stem to the leaves by a vascular tissue called xylem, made of long pipe-like tubes. Evaporation of water from the leaves, called transpiration, creates a pull that helps lift the water. Food made in leaves is carried by phloem.

Explanation

Roots anchor the plant and absorb water from the soil. Near their tips, roots have many thin root hairs that greatly increase the area in contact with the soil. Water, along with minerals dissolved in it, such as compounds of nitrogen, phosphorus and potassium, enters the root hairs and moves inward to the centre of the root.

Through the centre of the root, the stem and the veins of leaves runs the xylem, a set of long tube-like cells joined end to end, like a continuous water pipe. Xylem carries water and minerals in one direction, upward from the roots to every leaf. The other vascular tissue, phloem, carries food prepared in the leaves to all parts of the plant, including roots and fruits.

In a simple activity, a white flower or a balsam twig is kept in water coloured with red ink. After a few hours, red streaks appear in the stem and veins, showing the path of water through the xylem. Water keeps moving up because leaves keep losing water vapour by transpiration; this creates a suction pull that draws the column of water up from the roots.

Points to remember

  1. Root hairs absorb water and dissolved minerals from the soil.
  2. Xylem: vascular tissue that carries water and minerals from the roots to the leaves.
  3. Phloem: vascular tissue that carries food from the leaves to other parts of the plant.
  4. Xylem and phloem together form the vascular tissue, the plant's system of pipes.
  5. Transpiration from leaves creates a suction pull that helps water rise even in tall trees.

Exam tip

Draw a simple plant with arrows: water and minerals moving up through xylem and food moving through phloem. Write the functions of xylem and phloem on two separate lines so the examiner sees the contrast clearly.

Questions students also ask

What is the difference between xylem and phloem?
Xylem carries water and minerals upward from the roots to the leaves. Phloem carries food, made in the leaves by photosynthesis, to all parts of the plant, both upward and downward. Both are vascular tissues.
Why do plants need minerals?
Minerals such as nitrogen, phosphorus and potassium are needed to make proteins and other substances for healthy growth. Plants take them from the soil as a solution in water, which is why manure and fertilisers are added to fields.
How does coloured water show the path of water in a plant?
When a cut twig or a white flower stands in water mixed with red ink, the coloured water rises through the xylem. A thin cross-section of the stem then shows red spots or streaks that mark the tubes carrying water.

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