Houghton mifflin boston 2 Program Authors William Badders

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Nervous System

Have you ever used your big toe to test the temperature of bath water? In such a case, the toe sends a message up to the brain. The brain interprets the message, then sends a new message to muscles in the arms and hands to adjust the hot or cold water tap!

Your nervous system takes actions like this all the time. It receives and processes information, and it controls how the body reacts and moves.

The nervous system is made of specialized cells called neurons. Neurons receive and send information in the form of electrical impulses. In some ways, neurons act like electric wires, although the impulse they carry are very different from electricity.

The brain is the central organ of the nervous system. The human brain is composed of more than 100 billion neurons! Individually, those neurons do very little. Yet working together, they allow your brain to think, remember, learn, interpret information from the senses, and control movement of your body.

Extending down from the brain is a thick cord of nerve cells called the spinal cord. Nerves fan out from this cord to the rest of the body. The spinal cord is protected by a thick series of bones called vertebrae. These bones make up your backbone.



What are the important functions of the human brain?

Nervous Systems

[Image: Grasshopper .]

[Image: Earthworm .]



[Image: The Nervous System.]



[Image: The Muscular and Skeletal Systems.]

Muscular and Skeletal Systems

The muscular system of the human body has three types of muscle tissue:

Smooth Smooth muscles look smooth under a microscope. They are also called involuntary muscles because they contract without your conscious control. Smooth muscles control breathing, blood pressure, and movements in the digestive system.

Cardiac Cardiac muscle is found only in the heart, where it makes the heart beat. Like smooth muscle, cardiac muscle is involuntary.

Skeletal Skeletal muscles, also called voluntary muscles, are attached to the bones. They pull on bones and move them. Skeletal muscles also help shape the body and protect its internal organs.

Bones are held together by stringy tissues called ligaments, and they are attached to muscles by tough tissues called tendons. Bones, ligaments, and tendons make up the skeletal system.

The skeletal system provides shape and support, protects tissues and organs, and lets the body move. In addition, blood cells are made inside many bones.

Vertebrates have an internal skeleton and a backbone. Many invertebrates have hard external skeletons called exoskeletons.

[Image: A hard exoskeleton covers this ghost crab.]



Endocrine and Excretory Systems

The rush of energy you feel when you are frightened or excited is produced by the endocrine system. The endocrine system consists of glands. A gland is an organ that sends chemical messengers called hormones to other parts of the body.

Hormones affect the activity of cells far from where they are produced. They diffuse into the blood and are carried to where they are needed. The body produces many types of hormones. Each one acts on a specific type of cell.

Endocrine glands are located throughout the body. The thyroid gland, which is located in the neck region, controls the body's metabolism, or how cells provide energy. The adrenal glands, which are located above each kidney, are involved in the body's reaction to dangerous or frightening situations. And the pancreas, which is in the abdomen, maintains blood sugar levels.

The excretory system is responsible for removing wastes from the body and maintaining the body's water balance. Recall that undigested food is removed from the large intestine. It is the excretory system that takes over from the digestive system and flushes the waste from the digestive tract.

The kidneys are another important part of the excretory system. They are bean-shaped organs located near the middle of the back. As blood passes through the kidneys, waste and excess water are filtered out of it. They then travel from the kidneys to the bladder and then out of the body.

The excretory system plays a very important role. Without it, wastes would quickly poison the body.



What is the role of the excretory system?

[Image: The Endocrine and Excretory Systems .]

Excretory System

The excretory system is responsible for ridding the body of waste.



Other Systems

The human body contains other organ systems as well. For example, the lymphatic system circulates a fluid called lymph. This helps keep tissues free of excess fluid.

The integumentary system includes the skin, fingernails and hair. The skin has inner and outer layers of specialized tissues.

The immune system defends the body from bacteria and other disease-causing agents. It produces antibodies and distributes them through the blood. Antibodies are proteins that help fight disease.

All body systems work together in many ways. When you exercise, for example, your nerves and muscles work together to move your skeletal system. Nerves also increase your heart rate and slow your digestion, while a hormone helps move sugar into your blood. Usually, all of this happens without you even realizing it. The body is an amazing machine!

[Image: Doctors use x-ray images to view some organs.]

Keeping Healthy

You can follow many simple steps to stay healthy. To kill harmful bacteria, wash your hands often. Always cover your mouth and nose when coughing and sneezing. This will help stop the spread of harmful microorganisms.

Eating fresh foods that are rich in vitamins gives cells the nutrients they need. Refusing to smoke or take drugs keeps cells strong so that they can resist infection. Exercising keeps muscles flexible. Exercise also helps you breathe more deeply and your body work efficiently.



What is the function of antibodies?

Types of Doctors




* cares for young people


* cares for the skin


* cares for bones, joints, and their related muscles


* cares for the eyes



Lesson Wrap-Up

[Image: Visual Summary.]

Circulatory System

Digestive System

Muscular System

Endocrine System

Respiratory System

Nervous System

Excretory System

Skeletal System

LINKS for Home and School

MATH Make a Graph Research the average body length of horses, cats, and humans. Make a bar graph to compare body lengths to the lengths of the small intestine, listed on p. A36.

HEALTH Write a Report Research one of the human organ systems covered in this lesson. Write a report on common diseases that affect the system. Share your findings with the class.


1 MAIN IDEA What processes take place in the capillaries?

2 VOCABULARY Write a sentence or short paragraph using the terms tissue and organ.

3 READING SKILLS: Main Idea and Details Choose two human body organ systems. Describe the main function of each.


Apply How are vertebrates and invertebrates different from each other?


Ask Questions Give examples of questions that scientists might ask about a cell, a tissue, an organ, an organ system, and an organism.



A major organ of the nervous system is the

A. stomach.

B. brain.

C. kidney.

D. lung.



Visit www.eduplace.com/scp/ to find out more about cell organization.



EXTREME Science Cells in Glass Houses

Did you brush your teeth with fossils today? If you used toothpaste, you probably did! Fossil diatoms, ancestors of the diatoms shown here, are used in many types of toothpaste. They provide the fine grit that helps scrub and polish your teeth. But there's much more to diatoms than toothpaste!

Diatoms are an important part of Earth's ecosystem. They create much of Earth's oxygen and are the foundation of the ocean's food chain. The diatom is also one of the greatest architects in the world. These single-celled organisms build amazingly beautiful structures out of silica, which is the main ingredient of glass.



Based on their symmetry, diatoms are classified into two Orders.

[Image: One consists of diatoms that have radial symmetry.]

[Image: The other is made up of diatoms that have bilateral symmetry.]

Diatoms are tiny. One hundred would fit across the head of a pin!



Chapter 1 Review and Test Prep Vocabulary

1. Examples of a(n)_include the skeletal system, respiratory

system, and circulatory system.

2. A(n)_is made up of a group of related cells that work together to perform a function.

3. In many cells, genetic information is stored in the_

4. Water diffuses through the cell membrane by a process called_

5. Structures called _move a paramecium much as propellers move a boat.

6. Animals and plants are classified in separate_

7 . Single-celled organisms with nuclei are most likely_

8. Mushrooms and other_ get their energy by decaying dead


9. Unlike other_, ribosomes are not surrounded by membranes.

10. A group of related tissues that work together form a(n)_

cell A6

cilia A16

diffusion A17

flagellum A17

fungi A26

kingdoms A24

nucleus A8

organ A33

organelles A8

organ system A33

osmosis A17

protists A25

tissue A33


Test Prep

Write the letter of the best answer choice.

11. According to the cell theory, cells are the_

A. same in plants and animals

B. largest parts of the body

C. smallest units of life

D. smallest particles on Earth

12. The kidneys and the bladder form part of an important_

A. level of organization

B. organ system

C. cellular structure

D. kingdom

13. Protists are usually single-celled and are always_

A. specialized

B. like animals in structure

C. prokaryotic

D. eukaryotic

14. Oxygen from the air you breathe is transferred to blood in the_

A. alveoli of the lungs

B. nose and nasal passages

C. heart

D. bone marrow




15. Classify Into which kingdoms would you classify each of these organisms? Give a reason for your classification.

A. [Image: An organism.]

B. [Image: An organism.]

16. Infer Describe how a disease of the circulatory system could harm another system of the body. Give examples of different kinds of damage.

Map the Concept

The chart shows four categories. Place each word or term within a category.









smooth muscle



Critical Thinking

17. Evaluating Suppose someone discovers a new form of bacteria that eats plastic. What might be the good and bad effects of this discovery?

18. Analyzing What other body systems does the circulatory system affect? Describe the role of the circulatory system in the body.

19. Synthesizing What are four characteristics that scientists can use to compare organisms? List specific examples of organisms that have these characteristics.

20. Applying Smoking damages the respiratory system, sometimes by thickening the walls of alveoli. What health problems would a smoker experience as a result?

Performance Assessment

Diagram Levels of Organization

Draw a diagram that shows the relationship among cells, tissues, organs, and organ systems in an organism.




organ system



Chapter 2 Plant Systems



Lesson Preview

Lesson 1

Tiny structures inside these plant cells use energy from the Sun to make food. How do they do it?

Read about it in Lesson 1.

Lesson 2

Plants defy gravity by making water go up. How do plants move water up stems?

Read about it in Lesson 2.

Lesson 3

Wild animals and even family pets can help plants to grow. How do animals help plants?

Read about it in Lesson 3.



Lesson 1 How Do Plants Produce Food? Why It Matters...

Almost all living things need plants to survive. Plants make food and give off oxygen. Animals, including people, eat food and breathe oxygen. The process through which plants use energy from the Sun to make food makes life as you know it possible.


Experiment When you conduct an experiment, you plan and carry out an investigation to test a hypothesis.


* geranium plant with at least 4 leaves

* squares of cotton cloth (10 cm x 10 cm)


Science and Math Toolbox

For step 1, review Making a Chart to Organize Data on page H11.




Keeping Green Procedure

1 Collaborate Work in a small group. In your Science Notebook, draw a chart like the one shown. Use the chart to help you test this hypothesis: Plant leaves need sunlight to stay green.

2 Experiment Place your plant in a sunny window or plant it outside in a sunny, sheltered spot. Use the cloth squares to cover at least three leaves. Leave at least one leaf uncovered to serve as a control.

3 Predict How do you think the different leaves will change over time? Record your prediction.

4 Record Data Check the plant every day and give it water if the soil is dry. Every two days, remove the cover from one or more leaves. Record your observations, then cover the leaves again.

5 Analyze Data Discuss the differences that you observed and recorded. Compare the effects of blocking sunlight for two days, four days, and six days.


1. Use Variables What was the variable in this investigation? How did you change it? What was the control?

2. Analyze Data Review the hypothesis and your prediction. Did you find evidence to support the hypothesis? Explain why or why not.



Uncovered Leaves

Covered leaves

2 days

4 days

6 days

[Image: STEP 2.]

[Image: STEP 4.]


Investigate More! Design an Experiment

Plan and conduct an experiment on plants that tests another variable, such as water or soil quality. Describe the control in your experiment.




chlorophyll p. A51

chloroplast p. A51

photosynthesis p. A50

stomata p. A52


Sequence Use a chart to show the sequence of steps in photosynthesis.

[Image: A chart.]

Producing Food

MAIN IDEA Plants use energy from the Sun to make food. They combine carbon dioxide and water to make sugar, and release oxygen in the process.


You are constantly using energy to conduct all of your life processes. You need energy to breathe, eat, move, think, and even sleep.

The energy you use ultimately comes from the Sun. Recall from Chapter 1 that plants transform the energy of sunlight into chemical energy stored in food. Plants, along with some protists and bacteria, accomplish this through a process called photosynthesis.

During photosynthesis, plants combine water and carbon dioxide into compounds called sugars. They release oxygen in the process.

[Image: A vine called kudzu can grow very quickly. Like almost all other plants, it uses photosynthesis to make food .]



[Image: Plant cells contain organelles called chloroplasts. Inside them, light energy is changed to chemical energy.]

Sugars are a plant's food. The plant stores sugars in its tissues and breaks them down when it needs energy. When an animal eats the plant, it can use the stored sugars. And when a larger animal eats the plant-eater, it too obtains energy originally stored in plants. In this way, all animals depend on plants for energy.

In Chapter 1 you learned that photosynthesis takes place in organelles called chloroplasts. The number of chloroplasts in a cell depends on the organism. Some tiny algae cells have only one chloroplast, while the cells in the leaves of a tree may each contain more than fifty.

Most chloroplasts have the same basic structure. Each is surrounded by two membranes. Another system of membranes courses through the interior of the chloroplast. These membranes look like flat sacs arranged in stacks called grana.

Inside the membranes are a variety of pigments. A pigment is a substance that absorbs light. The most important pigment in a chloroplast is chlorophyll.

[Image : Inside a chloroplast, stacks of membranes called grana contain chlorophyll, which absorbs sunlight.]

Chlorophyll absorbs most colors of light, but not green. This means that when sunlight hits chlorophyll, green light is reflected to your eye. This is why plant parts that contain large amounts of chlorophyll look green.

How does photosynthesis work? When light strikes chlorophyll, the energy is used to split apart water molecules into hydrogen and oxygen. Later, during a series of chemical reactions, the hydrogen joins with carbon from carbon dioxide to form sugars. The oxygen gas is released.

Photosynthesis is a unique process, and it's hard to imagine life on Earth without it. The next time you look at a tall tree or other plant, remember that almost all of its matter came from only water and carbon dioxide.



What happens during the process of photosynthesis?



Plant Leaves

In almost all plants, leaves hold most of the plants' chloroplasts. You can think of leaves as the food factory for a plant.

Plant leaves come in many different shapes and sizes. They can be round or heart-shaped. They can be smooth or have jagged edges.

The broad, flat portion of a leaf is called the blade. Scientists group leaves by the structure of the blade. A simple leaf has a blade that is one piece. Oak trees and apple trees have simple leaves. A compound leaf has a blade that is divided into parts. Rose bushes and palm trees have compound leaves.

Leaves are made of different tissues. The outer layer is called the epidermis. The cells in this tissue have a waterproof coating that prevents water loss.

Remember that a plant needs to exchange gases with its environment. Small openings in the epidermis allow oxygen and carbon dioxide to enter or leave the cells. They also allow water vapor to leave. These openings are called stomata, and are scattered about the underside of the leaf. The word stomata comes from the Greek word stoma, which means mouth. You can see from the picture that stomata look like small mouths.

Specialized structures that act like gates control the opening and closing of the stomata. When they open, carbon dioxide enters the leaf while oxygen and water vapor exit.


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