FOCUS Book Transport Systems in Plants

Beyond the Book

Transport systems in plants move water and nutrients. Conduct an experiment to test how leaves affect the movement of water in a plant. Use two plastic cups, water, food coloring, and four stalks of celery. Cut all the leaves off of two of the celery stalks, but keep the leaves intact on the two others. Place all four stalks of celery in cups filled with colored water.

After two days, observe all four celery stalks and record your observations. Did you notice any differences between the celery with leaves and the celery without leaves? What did this experiment tell you about the plant vascular system?

Use the Internet to research the history of vascular plants on Earth. How have plants changed over time?

Transport Systems in Plants


FOCUS Book

Imagine Earth without bushes or trees. Millions of years ago, the only plants were tiny and low to the ground, like the mosses of today. These were nonvascular plants—plants with no special system of tubes and tissues to move water and nutrients. A plant won’t grow taller if the upper part of the plant can’t get what it needs to survive.

Today, a vast variety of plants cover Earth! Vascular plants have tubes in their roots, stems, and leaves to move nutrients, food, and water. With this transport system, vascular plants, like giant redwood trees, can grow taller than 90 meters (300 ft.). That’s a long way to move water, food, and nutrients.

From Tiny to Tall

How do plant cells work together to move nutrients?

Systems and System Models

FOCUS Question



NONVASCULAR PLANTS

VASCULAR PLANT

liverwort

moss

giant redwood (sequoia) tree

The world's tallest tree is Hyperion, a tree in Redwood National Park in California. It’s approximately 116 meters (379 ft.) tall.

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Illustration Credits:pages 6 (top), 8, and 9 (top): © Q2A Media Inc.

2

You probably know the main parts of a plant. But do you know how they each move water, food, and nutrients throughout the plant?

RootsRoots not only anchor a plant in the ground; they pull water and nutrients from the soil. There are many tiny hairs on the roots, called root hairs, which help absorb water. One hair can’t absorb a lot, but think how much water thousands of hairs can absorb.

Roots also provide storage for the plant. Food is made in the leaves and flows down toward the roots. Plants use food to grow and maintain their tissues. They store extra food in their roots in the form of starch for times when they aren’t able to make new food.

LeavesLeaves differ greatly in size and shape. They can be single, simple leaves or clusters of small leaflets called compound leaves. Even the needles on a pine tree and the spines on a cactus are leaves.

Leaves gather sunlight and carbon dioxide from the air. They combine it with water to make sugars, the food for the plant. This process is called photosynthesis.

Veins in a leaf bring in water and minerals. The veins also send food from the leaf to other parts of the plant.

Tiny holes in the leaf let gases flow, letting carbon dioxide in and oxygen out. These holes are called stomata. Water exits stomata through the process of evaporation. This special kind of evaporation used by plants is called transpiration.

Flow Through Plant Parts

Water and nutrients move up from the roots. Sugars made in the leaves move down throughout the plant.

food (sugars)

water

leaf vein

stomata

Inside Living Things • Transport Systems in Plants 3 4

StemsThe stem holds the plant upright and connects the roots to branches and leaves. Within the stem of vascular plants are special tissues that transport substances throughout the plant.

The xylem (ZY-lum) moves water and minerals from the roots to the leaves. Xylem cells are long and thin. They die soon after they form, but their hard structure remains. Xylem cells form a pipeline from the roots to the stem or trunk. The pipeline splits off into branches and moves into every leaf.

The phloem (FLOW-um) carries food from the leaves to other parts of the plant. Phloem cells are long and connected to one another throughout the entire plant. Unlike xylem cells, phloem cells remain alive for the life of the plant. In trees, the phloem is the innermost part of the bark. It must not be damaged or the tree might die.

In some plants, the xylem and phloem are scattered throughout the plant in no particular order. In others, xylem and phloem are arranged in a ring around the edge.

vascular bundle

xylem

phloem

This section of a plant stem shows vascular bundles, which include the xylem (blue) and phloem (yel low).

A magnified cutaway view of a stem shows the xylem and phloem within a vascular bundle.

Like the tree trunk on page 2, a sunflower stem moves food and water throughout the plant.

phloem

stem

vascular bundle

INSIDE A STEM

xylem

When you observe tree rings, you are looking at the remains of old xylem tissue.


Water Is Sticky Getting to the TopCapillary action is important for vascular plants. In the xylem, there is always a column of water. Thanks to capillary action, that column of water is always moving up the plant.

Water evaporates from leaves during transpiration. Water molecules are able to stick together and cling to the sides of the xylem. As a water molecule evaporates from a leaf, another molecule moves up the vascular pipeline to replace it. In this way, transpiration pulls water up through the plant.

The xylem and phloem move water, nutrients, and food around plants. But unlike your body’s circulatory system, a tree has no pumps or muscles. How does water reach the highest branches? The answer can be explained using the properties of water.

Picture rolling a paper towel into a tube and sticking the end in water. Water will creep up the paper towel because water molecules stick and hold onto each other. Water also sticks to surfaces. Together, these two properties of water create capillary action that can move water through narrow spaces.

Cohesion makes the drops stick to the leaf. Adhesion makes water molecules stick to each other to form drops.

Water is taken up by the roots and pulled up the tree by capillary action.

Capillary action causes water to move into a paper towel.

cohesion

adhesion

TRANSPIRATION

Water evaporates from the leaves.


While the xylem only moves water up the plant, the phloem moves sap (sugary water and other nutrients) in all directions!

Sometimes, sap is moved down to the roots where it is stored. Root vegetables like yams, beets, and carrots are made from sugars that were moved to the roots via phloem cells and stored as starch.

In colder areas, some maple trees store sugar as starch to prepare for winter. In the spring, the starch is changed back into sugar. Then the sap rises up the tree trunk, which allows us to tap the trunk for maple syrup. Sugars are not only food for the tree, but may also be enjoyed by people!

Flowin’ Phloem

Tapping a maple tree for syrup

Sugar made in the leaves is moved throughout the plant by the phloem.

After reading the book, write your answers to these questions on separate paper.

1 What makes vascular plants different from nonvascular plants?

2 Why does every plant need stomata?

3 Where can you find phloem in a tree?A on the inside of the barkB deep inside the woodC on top of the bark

4 How is dipping a rolled-up paper towel into water similar to how a plant’s vascular system works? Describe how capillary action relates to both.

5 Describe what Earth would be like today if vascular plants had never developed. Use examples to support your answer.

How do plant cells work together to move nutrients? Explain the roles of xylem and phloem. Discuss how they are part of a system that moves water and nutrients through a plant.

FOCUS Question

Extra sugar is stored in the roots.


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FOCUS Book Transport Systems in Plants