Download Lesson 3 How Do Plants Meet Their Needs? Fast Fact Sprouting

Lesson 3
How Do Plants Meet Their Needs?
Fast Fact
Sprouting Seeds Like most plants, cacti grow from seeds. Cactus seeds have adaptations that
allow them to grow in harsh desert climates. During hot, dry periods, the seeds are
dormant, or inactive. When it rains, a protein in the seed attracts water, improving the
chance that the seed will grow into a new plant. In the Investigate, you will observe how
seeds of other plants germinate.
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Germinating Seeds
Materials
 5 clear plastic cups
 masking tape
 water
 paper towels
 permanent marker
 shoe box with lid
 20 bean seeds
 measuring cup
Procedure
1. Line each cup with a folded paper towel. Then fill the cups with crumpled paper towels.
2. Between the paper lining and the side of each cup, place four bean seeds.
3. Use masking tape and a marker to label the cups A, B, C, D, and E. For each cup, follow
the directions next to its letter.
A. Drip water into the cup until the towels are moist. Place the cup in the shoe box. Close
the lid. Add water daily as needed to keep the towels moist.
B. Fill the cup with water.
C. Add no water.
D. Moisten the towels as for A. Keep them moist. E. Moisten the towels as for A. Keep
them moist.
4. Place cups A, B, C, and D in a warm place (not in direct sunlight). Place cup E in a
refrigerator. Observe the cups daily. Record your observations.
Draw Conclusions
1. In which cups did you observe the seeds sprouting? In which were they sprouting the best?
2. Inquiry Skills From your observations, draw conclusions about what seeds need in order to
germinate, or begin to grow.
Investigate Further
You controlled a number of variables in this investigation. What variables did you test?
Choose one variable, and design a simple investigation to test it.
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Reading in Science
VOCABULARY
stomata p. 51
vascular plant p. 52
xylem p. 52
phloem p. 52
transpiration p. 52
nonvascular plant p. 54
SCIENCE CONCEPTS
 what the needs of plants are
 how plants make and store food
READING FOCUS SKILL
MAIN IDEA AND DETAILS Look for ways plants meet their needs.
How Plants Meet Their Needs
Look around you. You see plants wherever you look—in your house, in your yard, on the
way to school, in so many places. Do you realize that life on Earth could not exist as we
know it if there were no plants? Why is that true? Plants supply the oxygen that most
organisms need to stay alive. They also supply food for many organisms, either directly or
indirectly.
Plants grow almost everywhere on Earth, from arid deserts to the marshy Everglades to the
Arctic Circle. In the Investigate, you found that seeds need certain conditions in order to
germinate. How, then, do seeds in harsh climates sprout and their seedlings grow? The
answer is that they are adapted to get what they need from their surroundings. To be
adapted means that the species has changed over time to be suited to get its needs met
where it lives.
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Seeds need water and air to germinate. When the conditions are right, the seed absorbs water.
The seed coat swells and splits open, and the tiny seedling inside emerges. A little root
begins to grow downward, and a shoot begins to grow upward. This growth takes place at
the tips of the root and shoot. In some plants, branches may grow from side buds as well.
As with the roots and shoots, the tips of the side branches grow. The branches produce
leaves and more side buds, from which new branches grow.
The new plant needs five things to stay healthy—water, light, carbon dioxide, oxygen, and
nutrients. These materials are used to carry out all the life processes that take place in the
plant's cells.
Plants are among the living things that make their own food by photosynthesis. This process
requires water, carbon dioxide, and sunlight. Water is absorbed from the soil by the roots.
Carbon dioxide enters the plant through stomata, tiny openings in the leaves. Sunlight is
also taken in by the leaves. The green pigment chlorophyll, found in the leaves'
chloroplasts, captures the sun's energy. This energy is then used to change carbon dioxide
and water to sugar and oxygen. The sugar (glucose) is stored in the plant, and oxygen is
released into the air.
Once the sugar is made, plants can use some of the oxygen to release the chemical energy that
is stored in the sugar. In a process called respiration, oxygen combines with the sugar to
produce energy, carbon dioxide, and water. The energy is used to carry out life processes
within the plant cells.
* MAIN IDEA AND DETAILS How do plants
Focus
Skill get the materials they need?
---see pictures pg.50
In most plants, tiny root hairs absorb water and nutrients, such as nitrogen, phosphorus,
and sulfur, from the soil.
The seedling grows where plant cells divide rapidly. This is most often at the tip of the
root and the tip of the shoot.
The root tip—also shown in the micrograph above—is a dome- shaped zone where cells
divide rapidly.
A The tiny plant grows taller as the cells at its tip divide and grow longer.
---see pictures pg51
Photosynthesis
Plant cells contain chloroplasts. These structures are green because they contain the
pigment chlorophyll.
Chlorophyll captures the sun's energy, which is used to combine carbon dioxide and
water to make sugar. Plant cells use sugar for energy to carry out their life processes.
Gases, such as carbon dioxide and oxygen, can enter and leave the leaf through pores
called stomata. During a process called transpiration, water, too, is released through
the stomata.
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Vascular Plants
All of the cells in a plant have the same basic needs. They need water, nutrients, and food. The
water and nutrients absorbed by a plant's roots are carried throughout the plant. The food,
in the form of sugar, made in the plant's leaves is delivered to each cell, too. In many
plants, these materials are transported by specialized tissues. Plants that have transport
tissues for carrying water, nutrients, and sugar to plant cells are called vascular plants.
The tree shown on these pages is a vascular plant.
Because they have transport tissues, many vascular plants can become very large. The transport
tissues form a system of tubes that extends from the roots to all parts of the plant. These
tubes are made up of two kinds of tissue. Xylem tissue carries water and nutrients from the
roots to the leaves. Phloem tissue carries sugar from the leaves to other cells of the plant.
Sugar that is not immediately needed for energy is stored in different parts of the plant.
What causes water to move through xylem tissue? You can model the process of water and
nutrient transport by sipping water through a straw. The straw represents the xylem. The
movement of water into your mouth represents transpiration, the loss of water from a
plant through the stomata.
In a vascular plant, transpiration causes negative pressure—or suction—that draws water
upward through the xylem. Put very simply, transpiration pulls water and minerals upward
through the plant.
---see pictures
Xylem tissue forms continuous, hollow tubes. These tubes reach from the roots all the way
up the trunk and through the branches to the leaves.
Some plants, like the trees shown here, have woody stems that grow thicker each year as
new xylem and phloem form. The rings of xylem at the center are the oldest. These
tubes no longer carry water, but their strong walls continue to support the tree.
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How does sugar move through phloem? Positive pressure is responsible for the flow of
materials in phloem. When a solution is more concentrated in one area, water flows into
the area and dilutes it. The sugar solution in phloem is concentrated. It draws water from
neighboring xylem into the phloem. The added water increases pressure, causing the sugar
in the phloem to move through adjoining cells toward the areas where it is needed.
Some of the sugar is stored. Much of the sugar moves through the phloem to the root tips and
stem buds. There, it provides the energy for cell division and growth.
MAIN IDEA AND DETAILS What causes the movement of materials through xylem and
phloem?
Insta-Lab
Make a Model
Use a plastic knife to trim the end from a stalk of celery. Examine the cut ends of the celery.
Use a hand lens to identify the xylem and phloem. Draw a diagram to show the vascular
tissues. Label the parts of the diagram and the materials they transport.
---see pictures
From the roots, water and nutrients move upward through the xylem.
Phloem carries sugar made in the leaves to all parts of the plant. Some of the sugar is
converted to the energy needed for life processes. The rest is stored.
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Nonvascular Plants
Some plants, such as mosses, liverworts, and hornworts, do not have xylem and phloem tissues.
Plants that lack tissues that transport water, nutrients, and sugar are called nonvascular
plants.
Nonvascular plants are different from vascular plants in several ways. Because they do not
have tissues to carry the materials that cells need to stay healthy, they don't grow very
large. These plants don't have true roots to absorb water. Instead, each cell absorbs the
water and nutrients it needs directly from the soil or air. Because they live very close
together, the cells of these plants may also get materials they need from neighboring plant
cells.
Nonvascular plants are anchored in the soil by long cells that look like roots. These structures
are called rhizoids.
Many nonvascular plants thrive in moist, shady places such as forests and swamps. There, they
can get enough water to meet their needs. These plants require water for sexual
reproduction. The male sex cells must swim through water to get to the female sex cell to
fertilize it.
Nonvascular plants have structures that function like leaves, stems, and roots, but they are less
complex than those in vascular plants. Like vascular plants, the leaflike parts of mosses
and liverworts contain chlorophyll and produce food for the plant.
MAIN IDEA AND DETAILS Why do nonvascular plants remain small?
---see pictures
Some moss plants can grow by vegetative, or asexual, reproduction. When a leaf is broken
off, a whole new plant can grow from it.
If you carefully observe this plant, you can see parts that look like capsules on stalks.
These form after male cells fertilize female cells. When conditions are right, the
capsules open and a fine dust of spores is released.
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1. MAIN IDEA AND DETAILS Draw and complete this graphic organizer.
---see organizer
2. SUMMARIZE Use the information in the graphic organizer to describe the differences
between vascular plants and nonvascular plants.
3. DRAW CONCLUSIONS Why is photosynthesis important to animals?
4. VOCABULARY Write a short paragraph that uses each of the vocabulary words in this
lesson.
Test Prep
5. Critical Thinking Compare the steps in photosynthesis with the steps that take place when
plants use sugar for energy.
6. Which part of a tree makes food for the whole plant?
A. leaves
B. phloem
C. roots
D. xylem
Writing
Descriptive Writing
A travelogue is a description of a person's travels. Write a fantasy travelogue to describe the
travels of sugar through phloem. Be creative! Describe the places the sugar visits and what
it sees and does in each place.
Math
Calculate Percentages
Germination rate tells the percent of seeds that sprout. If 75 out of 100 seeds sprout, the
germination rate is 75 percent. Calculate the following rates as percents: 10 out of 25; 28
out of 50; 36 out of 50; and 64 out of 100.
Social Studies
Research
Peat moss is an important energy source in many parts of the world. Use Internet resources to
learn about peat moss and its importance in nineteenth-century Scotland. Share your
findings with the class.
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