Plant Transport and Responses
Plants have no heart, yet they move water from their roots all the way to their highest leaves, and they send food in the opposite direction. They also respond to their surroundings, bending toward light and growing roots downward. Understanding plant transport and responses explains how a still, silent organism stays alive and reacts to its world.
This lesson covers how plants transport materials and how they respond to stimuli.
Plants transport materials through two tissues: xylem carries water and minerals up from the roots, and phloem carries food made in the leaves to the rest of the plant. Plants also respond to stimuli through growth movements called tropisms, such as growing toward light.
How do plants transport water and food?
Plants have two transport tissues that run through roots, stems, and leaves. The xylem carries water and dissolved minerals in one direction: upward, from the roots to the leaves. The phloem carries the sugar made during photosynthesis from the leaves to wherever it is needed, including down to the roots. A helpful memory aid is that xylem moves water (both start with the flow up), while phloem moves food.
| Tissue | Carries | Direction |
|---|---|---|
| Xylem | Water and minerals | Roots to leaves (up) |
| Phloem | Food (sugar) | Leaves to rest of plant |
How does water get to the top of a tall tree?
Water rises largely through transpiration. As water evaporates from tiny pores in the leaves, it pulls the water column up behind it through the xylem, like sipping through a straw. Combined with water’s tendency to stick together, this steady pull can lift water dozens of meters without any pump.
How do plants respond to their environment?
Plants react to the world through tropisms, which are growth responses toward or away from a stimulus. In phototropism, a plant grows toward light. In gravitropism, roots grow downward with gravity while stems grow upward against it. These responses are slow because they happen through growth, not movement, but they let a rooted plant position itself for light, water, and support.
Watch: A Short Video Lesson
FuseSchool walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for plant transport questions
- Match the tissue: xylem carries water up, phloem carries food.
- Recall transpiration pulls water up from the leaves.
- For responses, identify the tropism and its stimulus.
- Phototropism is toward light; gravitropism responds to gravity.
- Remember plant responses happen through growth.
Practice questions
- Which tissue carries water from the roots to the leaves?
- Which tissue carries food made in the leaves?
- What is the process that pulls water up through a plant called?
- What is phototropism?
- Which way do roots grow in response to gravity?
- True or false: phloem carries water upward only.
Answers:
- The xylem.
- The phloem.
- Transpiration.
- A plant’s growth toward light.
- Downward, with gravity.
- False. Phloem carries food; xylem carries water upward.
Where this fits
Transport builds on plant structures and their jobs and delivers the water needed for photosynthesis. Plant responses connect to how living things react to their environment. Find all topics on the ASVAB General Science Learning Hub.
Recommended Prep Books
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