Houghton mifflin boston 2 Program Authors William Badders



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Conclusion

1. Analyze Data Were the same structures visible on the outside and inside of the flower? Explain.

2. Infer Why do you think plant scientists study the insides as well as the outsides of plants?

STEP 1

Drawing of Outer Structures

Drawing of Inside Structures

[Image: STEP 2.]

[Image: STEP 4.]

***

Investigate More! Design an Experiment

Plant seeds of field mustard plants or other fast-growing plants. Provide the plants light, water, and warmth. Observe and record the stages of their life cycle.

***

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* VOCABULARY

angiosperms p. A70

gymnosperms p. A69

pollination p. A69

spores p. A68

* READING SKILL

Compare and Contrast

Draw a Venn diagram to show how two types of plants are alike and different.

[Image: A Venn diagram.]

Plant Reproduction

MAIN IDEA Plants reproduce using spores or seeds. They are dispersed in different ways.

Seedless Plants and Conifers

A plant's pattern of generation, growth, and reproduction is known as its life cycle. Scientists classify plants into two major groups according to their life cycles. One group is the seed plants, which reproduce with seeds. The second group is the seedless plants, which reproduce with spores or other structures.



Fern Life Cycle

Sporangia

Spores are produced in sporangia on the undersides of fronds

Spores

The wind scatters mature spores from the sporangia.

Gametophytes

Some spores grow into structures that produce gametes, or male and female cells.

Fern

The zygote will grow into a mature fern.

Male and female cells join to form the zygote, a process called fertilization. A new plant begins.

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One common seedless plant is the fern. Ferns grow throughout the United States, but they grow best in warm, moist climates such as in tropical rain forests. Let's take a close look at its life cycle.

Most large plants are seed plants. Scientists further divide the seed plants into two large groups.

Plants with seeds that are not covered by a protective fruit are called gymnosperms, which means "naked seeds." Conifers, such as pine, spruce, cedar, and redwood trees, are the most common of the gymnosperms. The seeds of these conifers develop inside cones.

Conifers produce both male and female cones. Male cones are smaller. They are often located near the tips of the branches. Female cones are generally larger. Some types of conifers produce both male and female cones on the same plant. Other types of conifers have male and female plants that each produce only one type of cone.

Male cones produce pollen. Pollen is reproductive material that contains male gametes, or sperm cells. Female cones, called seed cones, contain ovules. Ovules contain female gametes, or eggs.

In the spring, pollen cones release millions of tiny pollen grains into the wind. Many pollen grains fall to the ground or land on water. But some are blown onto seed cones. Any process that delivers pollen to eggs is an example of pollination, With conifers, the wind or air is the agent of pollination.

Once the pollen grain lands on a seed cone, it releases sperm cells. These sperm cells can fertilize the ovules. This forms a new zygote, which can divide and develop into seeds. When the seeds mature, they are released from the cone. If the conditions are right, a seed will develop into a new conifer.

***


COMPARE AND CONTRAST

How are ferns different from conifers?

[Image: Pine cones produce pollen (in the male cones) and ovules (in the female cones). Seeds develop in the female cone .]



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Flower Life Cycle

Fruits

Fruits are mature plant ovaries, which expand to protect and nourish seeds.

Fertilization

Fertilization takes place inside the ovary, when a male gamete from the pollen joins a female gamete in the ovary.

Germination

Germination occurs when a seed sprouts into a new plant.

Flowering Plants

The second large group of seed plants are the angiosperms. An angiosperm produces seeds within a protective covering. Angiosperms are also called flowering plants because they store seeds inside flowers and fruits. The flowering plants make up the largest group of plants in the world. In fact, nine out of ten plant species are flowering plants.

Flowers are the reproductive organs of angiosperms. They have many parts, and each has a purpose related to reproduction.

The male reproductive organ is called a stamen. Two parts make up the stamen: a thin filament, or stalk, and a rounded anther. The anther produces pollen, or male gametes.

The female reproductive organ of a flower is called the pistil. Pistils are found in the center of a flower. Three parts make up the pistil: the stigma, the style, and the ovary. The stigma is the sticky tip of the pistil. The style connects the stigma to the ovary. The ovary contains one or more ovules.

Keep in mind that not all flowering plants are identical. Some flowering plants make both male and female reproductive organs in the same flower. In other plants, they are made in different flowers.



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Flowers

Flowers contain the reproductive parts of the plant.

Pollination

Pollen from the male anther reaches the female stigma.

The colorful, leaflike structures of a flower are called petals. Flower petals surround and protect the male and female reproductive organs. They also play an important role in pollination, as you will find out soon.

In flowering plants, pollination occurs soon after a grain of pollen lands on the sticky stigma. If the pollen is from the right type of plant, the pollen produces a tube that grows through the style and into the ovule. A sperm cell is released from the tube to fertilize the egg cell in the ovule. The resulting zygote develops into a seed that may eventually become a new plant.

As the seed develops, the ovary changes to become a fruit. The fruit protects and nourishes the seeds. Fruits also attract animals that help spread the seeds.

The fruits you eat are mature ovaries that surround the seeds inside. These fruits include apples, oranges, cherries, and berries. They also include some foods you may not think of as fruits, such as tomatoes, peppers, and cucumbers.

***


COMPARE AND CONTRAST

How do angiosperms differ from gymnosperms?

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Pollination

Pollen can be dispersed in many ways. Here are some examples.



Self-pollination In some plants pollen can move directly from the male parts to the female parts. In peas and beans, for example, a single flower contains both parts.

Wind Some plants release pollen into the wind. These plants usually produce large amounts of pollen because much of it will be wasted on the ground or in water.

Plants that depend on the wind often have structures that expose the pollen to the air. For example, some plants have very long stamens that reach into the open air. They also may have stigma with feathery arms that catch pollen from the air.

Corn is one example of a wind-pollinated plant. Male parts are located near the top of the plant, where the wind can catch the pollen. Female parts are located farther down the plant.

[Image: Honeybees have thick leg hairs that pollen clings to.]

[Image: Hummingbirds have long, thin beaks that allow them to reach the nectar inside narrow flowers.]

Water Some plants live in water and use water to carry pollen. The pollen grains float from male parts to female parts. Sea grasses use this method of pollination.

Animals Flowers that have bright colors or strong fragrances are usually pollinated by animals. The colors and scents attract animals that come to feed on a sugary nectar that the flower produces.

As the animals gather nectar, pollen becomes stuck on their bodies. The pollen is deposited in different flowers as the animals move among them. Hummingbirds, bats, bees, and butterflies all pollinate flowers in this way.

Farmers who grow fruits often raise bees as well. Bees help pollinate the trees and they make honey.

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Seed Dispersal

Like pollen, plant seeds are also dispersed by different means.



Wind Have you watched the feathery seeds of a dandelion float through the wind? Dandelions, orchids, and other plants have small, light seeds that winds easily carry. The seeds of black maple trees are covered by thin, dry fruits that act as propellers.

Water Some plant seeds and fruits are spread by water. These fruits and seeds contain air chambers that help them to float. The large fruits of the coconut palm, for example, can float great distances on ocean currents. This is why coconut palms often grow on small tropical islands.

Animals If you have ever had a burr stuck on your clothing, you may have helped to disperse plant seeds. Burrs are fruits that stick to the fur of animals. As an animal moves around, it spreads the seeds to new locations.

[Image: Seed dispersal can depend on wind, but animals are also efficient at spreading seeds. ]

[Image: Do you see the burrs on this dog? Each burr holds seeds. The dog helps spread them away from the parent plants .]

Many animals are attracted to the sweet taste of many fruits. As the animal eats the fruit, it may disturb some of the seeds. The seeds drop to the ground where they may grow into new plants.

Animals can also help spread seeds by eating fruits. Some seeds pass through an animal intact, and thus become part of its waste. Fruit-eating birds often spread plant seeds in this way.

***


COMPARE AND CONTRAST

What are different ways that pollen and seeds are dispersed?

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Plant Structure

Flowers

Fruits and Seeds

Grasses

Avocado

Sunflower

Orange

Corn

Strawberry

Variety in Flowering Plants

Angiosperms grow in most places on Earth. A few species even live in ocean water. Angiosperms around the world have developed an amazing variety of structures to help them reproduce in their environments.

Flowers exist in many different sizes, shapes, and colors. Water lilies have some of the largest flowers. Clover, sedges, and grasses have some of the smallest. The most common flower colors are red, yellow, white, and blue.

Fruits also exist in many sizes, from tiny berries to large coconuts. Fruits grow around different kinds and numbers of seeds. Pomegranates have many tiny seeds. A grape or apple might have two or three seeds. A cherry or avocado has only one seed.

People have learned to take advantage of this variety in flowers, fruits, and seeds. Humans eat not only seeds and plants, but also flowers. Cauliflower and broccoli are examples of flowers that people eat.

Farmers plant seeds at the start of each growing season. The ability to grow crops from seeds has helped humans thrive and flourish for thousands of years.

***

COMPARE AND CONTRAST

How do people take advantage of the variety in flowers, fruits, and seeds?

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Lesson Wrap-Up Visual Summary

Seedless Plants

Gymnosperms

Angiosperms

reproduce by

reproduce by

reproduce by

Sporangia

Cones

Flowers

spores

seeds

seeds

Wind or water

Wind

Wind, Water, Animals

LINKS for Home and School

MATH Make a Scale Drawing Suppose a beekeeper has 180 acres of clover and 9 honeybee hives. How many acres must each hive pollinate in order for the clover to reproduce? Make a scale drawing of the farmer's land, showing the location of each hive and the size of the plot of land it is on.

TECHNOLOGY Make a Poster

Research ways that farmers depend on insects to help in crop pollination and reproduction. Make a poster that features one kind of insect. Show how it helps farmers.



Review

1 MAIN IDEA What are the most numerous types of plants?

2 VOCABULARY Write a sentence or short paragraph using the terms gymnosperms and angiosperms.

3 READING SKILL: Compare and Contrast What do sporangia, cones, and flowers have in common? How are they different?

4 CRITICAL THINKING: Apply

Explain why many gardeners plant flowers that attract bees and butterflies.



5 INQUIRY SKILL: Analyze

Data Give three reasons why angiosperms are the most successful plants on Earth.

***


TEST PREP

All flowering plants produce seeds and



A. fruits.

B. other edible parts.

C. brightly colored petals.

D. sporangia.

***


Technology

Visit www.eduplace.com/scp/ to find out more about plant reproduction.

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Stuck On You

Is It a giant worm from outer space?

An undersea creature? No, you're looking at a magnified burr--a tiny seed with hooks. Many plants depend on wind and water to scatter their seeds. Others rely on animals to leave them in droppings. But burrs are hitchhikers. They travel by hooking themselves onto animals' fur--and people's clothing!

Through a microscope, you can see a strong resemblance between a burr and a strip of the hooked fastener called VelcroTM. This is no coincidence. Inventor George de Mestral got the idea for the tiny hooks of VelcroTM from studying the clingy burrs that he plucked from his dog's fur.

Grab a ride! Some plant species, like cockle burrs, have literally hitchhiked across North America and Europe.

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Super cling! Burrs cling tight, and so does Velcro TM . A piece of Velcro TM the size of two hands can support the weight of a small car!

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Chapter 2 Review and Test Prep Vocabulary

1. The green pigment in plants is called_

2. The process by which plants use solar energy to make food

is_


3. Openings called _let air and water in and out of leaves.

4. A_ has vessels to carry water, minerals, and nutrients.

5 . Tissues known as _transport water from a plant's roots to its leaves.

6 . The plant tissues that transport nutrients away from the leaves are_

7. The process of_ takes place when liquid water from a plant's leaves changes to water vapor.

8 . Seedless plants reproduce by releasing_

9. The process of delivering pollen to eggs is called_

10. _are plants that produce seeds with a protective covering



angiosperms A70

chlorophyll A51

chloroplast A51

gymnosperm A69

nonvascular plant A62

phloem A63

photosynthesis A50

pollination A69

spores A68

stomata A52

transpiration A64

vascular plant A63

xylem A63

***


Test Prep

Write the letter of the best answer choice.

11. Chlorophyll has the ability to_

A. transport carbohydrates

B. protect the cell from the Sun

C. absorb light energy

D. build cell walls

12. People rely on photosynthesis in plants for food and_



A. oxygen

B. carbon dioxide

C. chlorophyll

D. minerals

13. Some nonvascular plants have the ability to_



A. transport water and minerals through vessels

B. help control moisture in their environments

C. develop strong stems and leaves

D. produce xylem and phloem

14. Angiosperms produce their gametes inside_



A. flowers

B. sporangia

C. cones

D. stems

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15. Synthesize Identify at least two functions for each of these plant parts.

A. [Image: A plant.]

B. [Image: A plant.]

C. [Image: A plant.]



16. Experiment Describe an experiment that would help show which plants attract butterflies. Propose an hypothesis about whether butterflies are attracted to a specific color or shape of flower.

Map the Concept

The chart shows three processes. Place each word or term in the correct column. Some words go in more than one category.



chloroplasts

fruit

gametes

germination

oxygen

solar energy

stomata

cohesion

evaporation

water

fertilization

root pressure

Photosynthesis

Upward Movement

Reproduction














































***

Critical Thinking

17. Applying Why do moss plants grow best in damp places, such as the floor of a forest? Would mosses grow well in dry, sandy soil? Explain.

18. Analyzing List three different ways that seeds are spread from place to place, and include one example of each. Why is seed dispersal important to plants? Why is it important to humans?

19. Synthesizing A perfect flower has both male and female parts. An imperfect flower has either male or female parts, but not both. How would a plant that makes imperfect flowers be able to reproduce?

20. Experimenting A student mixes a few drops of food coloring in a glass of water. She places a stalk of celery in the glass, and observes the colored water climb slowly up the stalk's tissues. What does this show about the way water travels through a plant?

Performance Assessment Diagram a Plant

Draw and label a diagram that shows the major parts of a flowering plant. Then draw the same diagram, but write labels to show functions instead of names of parts.



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Chapter 3 Traits of Living Things

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Lesson Preview

Lesson 1

This flamingo was born with some traits and it acquired others. What determines traits?

Read about it in Lesson 1.

Lesson 2

Certain traits help organisms to survive. Why are some traits more common than others?

Read about them in Lesson 2.

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Lesson 1 How Are Traits Inherited? Why It Matters...

A trait is a physical or behavioral characteristic of an organism. Every person has a unique combination of traits. You have a set of traits that belongs to you alone. You also have traits you have acquired from interacting with your environment.



PREPARE TO INVESTIGATE Inquiry Skill

Analyze Data When you analyze data, you look for patterns in information you have collected.

Materials

* index cards

* pencils

***


Science and Math Toolbox

For step 3, review Making a Chart to Organize Data on page H11.

***

[Image: A boy.]



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Trait Tabulation Procedure

1 Collaborate Work in a small group. Your team will get a letter. Assign a number to each person in your group. For example, your group letter might be C and your number might be 5, or C5.

2 Observe Copy the chart shown at right onto an index card. Write your number-letter code, not your name, on your card. Answer the questions in the chart.

3 Collaborate Collect your team's cards and exchange them with the cards from another team. Then work with your team to count the number of people with each trait. Work in the same way with each of the other teams.

4 Record Data Tally the results for everyone in the class. Prepare a circle graph, bar graph, or appropriate chart of your choice to show the data.

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