5 3 the building blocks of organisms (life sciences)

California Leveled Science Readers (Grade 5) Content leveled readers teach science concepts, vocabulary, and reading skills – at each student’s reading level – and allow students to read and explore the wonders of nonfiction. Leveled science readers deliver science content to help address the individual needs of all students. They reinforce reading skills and strategies while promoting science understanding. Each grade 5 science reader is a richly illustrated, selfcontained little book with 10 to 14 double pages. BELOW 5.1 Building Blocks of Matter (Physical Sciences) 5.2 Changes in Matter (Physical Sciences) 5.3 Basic Structures of Organisms (Life Sciences) 5.4 MISSING 5.5 Water on Earth (Earth Sciences) 5.6 Weather (Earth Sciences) 5.7 The Solar System (Earth Sciences) ON 5.1 Understanding Matter (Physical Sciences) 5.2 How Matter Changes (Physical Sciences) 5.3 The Building Blocks of Organisms (Life Sciences) 5.4 Systems of the Human Body (Life Sciences) 5.5 Earths Hydrosphere (Earth Sciences) 5.6 How Weather Works (Earth Sciences) 5.7 Earths Solar System (Earth Sciences) ADVANCED 5.1 Atoms (Physical Sciences) 5.2 Acids and Bases at Work (Physical Sciences) 5.3 MISSING 5.4 MISSING 5.5 MISSING 5.6 Hurricanes (Earth Sciences) 5.7 The Red Planet (Earth Sciences)

Genre Comprehension Skill Text Features Science Content

• Diagrams

• Labels

• Glossary

Structures of Living Things

Scott Foresman Science 5.3

Standards Preview Standard Set 2 Life Sciences

2 Plants and animals have structures for

respiration, digestion, waste disposal,

and transport of materials As a basis

for understanding this concept:

2.a Students know many multicellular

organisms have specialized structures

to support the transport of materials.

2.e Students know how sugar, water,

and minerals are transported in a vascular plant.

2.f Students know plants use carbon

dioxide (CO2) and energy from sunlight

to build molecules of sugar and release oxygen.

2.g Students know plant and animal

cells break down sugar to obtain energy, a process resulting in carbon dioxide (CO2) and water (respiration).

ISBN 0-328-23570-9

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by Lillian Duggan

Life Sciences

cellular respiration

chlorophyll

chloroplast

organ

phloem

photosynthesis

tissue

vacuole

vascular

xylem

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Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

1 Ken Wagner/Visuals Unlimited; 3 (Inset) David Bassett/Photo Researchers, Inc., (Bkgd) Dr Neal Scolding/Photo

Researchers, Inc.; 14 Michael Gadomski/Animals Animals/Earth Scenes; 15 (T) Biodisc/Visuals Unlimited, (B) Ken

Wagner/Visuals Unlimited; 19 Michael Bisceglie/Animals Animals/Earth Scenes.

ISBN: 0-328-23570-9

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1 2 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06

by Lillian Duggan

What are multicellular

organisms made of?

Plants and animals are made up of cells Cells are living parts

that have the same needs as the plants and animals they make

up The smaller parts inside cells carry out specialized jobs so

that cells can meet their needs

The Jobs of Cells

The basic building blocks of all living things are cells Cells

are the tiniest living parts of plants and animals Some living

things are made up of only one cell Multicellular organisms can

be made up of trillions of cells

Cells are extremely small You have to look through a

microscope to see most cells One drop of blood has millions

of red blood cells

Like all living things, cells have basic needs for survival

They take in food to use for growth and to repair broken parts

They also release wastes Like you, cells sense changes in their

environment and respond to these changes Most cells do

not move, but all cells have parts that move They can even

communicate and work with other cells to get jobs done

Cells also need energy to grow, move, and make new cells

To get energy, most cells use cellular respiration In cellular

respiration, oxygen and food are combined to get energy

3

These are brain cells called neurons Trillions of neurons work together to help your body to function.

Cell Parts

There are many different types of cells, but all cells have

some parts in common Some cell parts perform the same jobs as

the structures of your body For example, some cell parts form a

protective covering, just like your skin Other cell parts control what

happens in the cell, provide support, and store food and wastes

The diagram below shows the parts of an animal cell The

cell membrane goes around the outside of the cell It holds the

cell together and controls what materials go in and out Sugar,

water, and oxygen are allowed to enter the cell The vacuole

stores water and nutrients It may also help the cell digest food

Wastes such as carbon dioxide leave the cell

Plant cells contain all of the parts that animal cells have

They also have chloroplasts and cell walls, which animal cells

do not have

Animal Cell

Cell membrane

Cytoplasm

fl uid containing

cell parts

Ribosome

begins the process

of making proteins

Nucleus

directs the cell’s activities and stores information

Mitochondria

change chemical energy

of food into a form that the cell can use

5

Cell Size and Shape

All cells must stay a certain size If a cell grows too big, important materials such as oxygen won’t be able to reach all the parts of the cell fast enough to keep the cell alive On the other hand, if a cell is too small, it can’t contain all of its parts

The shape of cells is also important Some cells have special shapes that fi t the job they do Many cells even have special structures that help them to do their work

Vacuole

stores water and nutrients

Plant Cell

Chloroplast and chlorophyll

Chloroplasts contain chlorophyll, allowing the plant to make food.

Cell wall

gives the cell extra support

Cell Tissue

6

From Cells to Tissues

Cells usually do not do their jobs alone Instead, they work

with other cells in tissues A tissue is a group of the same kind

of cells that work together to do the same job Bundles of nerve

cells make up nerve tissue, just like bundles of muscle cells make

up muscle tissue Skin is a tissue made up of a group of skin cells

Plants have tissues too

From Tissues to Organs

Different types of tissues combine to form organs An

organ is a group of different tissues that join together into one

structure Organs such as your heart, lungs, ears, and kidneys

perform important jobs in your body Many animals have similar

tissues and organs Plants also have organs, including stems,

roots, leaves, and fl owers

These pictures show a

heart muscle cell, heart

muscle tissue, the heart

organ, and the circulatory

system in a person.

Here we see a cell, tissue,

leaves, and the entire

California oak tree

System Organ

7

From Organs to Organ Systems

Just as cells and tissues work together, so do organs An organ system is a group of organs that work together to carry out a life process Organ systems are important to living things

For example, the nerves, spinal cord, and brain work together

to process information Blood cells, blood vessels, and the heart form the circulatory system Look below to see how tissues and organs compare between a human and a plant

Getting Food and Oxygen

In order to stay alive, cells must be able to get food and

oxygen, and get rid of wastes Multicellular organisms use

different organ systems to carry out these tasks

Look at the picture of the digestive system of a rabbit The

job of the digestive system is to take in food and break it down

into a form that body cells can use The substances in food that

cells take in are called nutrients

This picture shows the organs in the rabbit’s digestive system.

Stomach

Small intestine

Large intestine Esophagus

Mouth

9

Transporting Nutrients and Wastes

Nutrients can only be used by cells if they are transported

to the cells This job is done by the blood Blood is a tissue in the circulatory system It also carries sugar and oxygen to cells

Another role of blood is to carry wastes away from cells

Look at the picture of the circulatory system of a fi sh The heart and blood vessels are organs in the fi sh’s circulatory system The gills are part of the respiratory system The fi sh absorbs oxygen through its gills Then the oxygen is carried by the blood to all of the fi sh’s cells The blood also picks up wastes made by the cells One waste is carbon dioxide It is carried

to the gills, which let it out Other waste is removed by the excretory system

The circulatory system

of a fi sh supplies food and oxygen to all of the fi sh’s cells.

How do materials

move through plants?

Two of the major organs of plants are stems and roots Their

special structures allow them to perform important jobs

Stems and Leaves

Stems are plant organs that support,

or hold, other plant organs These organs

include leaves, fruit, and fl owers Leaves

take in sunlight to make food Some stems

hold leaves high so that they can receive

more sunlight Leaves held lower to the

ground might be more shaded

The Vascular System

Like animals, plants need a system

to transport materials Many plants use

a vascular system A vascular system

is a system of tubes that transport

materials such as water and minerals

Plants that use a vascular system are

called vascular plants The roots, stems, and

leaves of vascular plants contain vascular tissue

called xylem and phloem

Xylem

Phloem

11

Xylem tubes carry materials from the plant’s roots to its

leaves Plant roots soak up water from the soil The water contains minerals that plants need These minerals are important for plant processes such as photosynthesis

Phloem tubes carry sugar away from the leaves The sugar

is dissolved in water and gets carried by the phloem to the roots

Phloem in trees is located under the bark The growth of new phloem cells causes the old, dead phloem cells to be pushed outward The old phloem makes up the bark, which protects the new phloem

Trees and shrubs have woody stems Woody stems have a lot more xylem tissue than non-woody stems

Plants such as sunfl owers and pea plants (left) have non-woody stems They have less xylem tissue.

Cross-section of a woody stem

Cross-section of a non-woody stem

More About Vascular Plants

As you know, many plants have a vascular system for

transporting materials To get the energy they need, plants break

down sugar This sugar is what plants use for food Plants make

this food in their leaves Once the sugar is broken down, it is

transported from the leaves to the rest of the plant Remember

the phloem? This system of tubes is what transports the sugar all

over the plant

Plants use water to make food The roots of a plant get water

by absorbing it from the soil Then the water and dissolved

minerals travel from the soil to the rest of the plant through

the xylem

You can see the vascular system at work in a simple

experiment If you’ve eaten celery, you’ve eaten a stem A leaf

stem attaches a plant’s leaves to its stem Celery is a stem that

can show how xylem works In this experiment, a stalk of celery

is placed in a cup containing water mixed with food coloring

The food coloring represents minerals dissolved in the water

While the celery sits, water evaporates from its leaves Then

the colored water from the cup begins to move up the stalk to

replace the evaporated water

The picture of the soaked celery shows that the red food

coloring moved up the stalk through the xylem You can see

a single xylem cell from a cross-section of the celery under

a microscope

As the colored water moves up the leaf stem, you can see it turn the xylem cells red.

13

This is a microscopic view

of a single xylem cell.

Types of Roots

Like stems, roots are a type of plant organ Roots grow

underground, holding the plant fi rmly in the ground as it grows

There are different kinds of root systems Two of the main

types are taproots and fi brous roots A taproot is a large root

that grows straight down into the ground Small roots may grow

from the main taproot But the taproot will remain the largest

root structure as the plant grows Carrots, beets, turnips, and

radishes are all taproots

Fibrous root systems have many roots growing in all

directions Fibrous roots are much thinner than taproots, and

they divide into smaller and smaller roots They look like an

upside-down version of the branches on a tree

Roots have special tissues near their tips that help them to

grow longer The cells that make up these tissues divide quickly,

forming new cells The new cells push the root tips farther into the ground as they grow

This is the fi brous root system of a cosmos.

Root Functions

Roots have several important jobs Some roots store food

Roots also anchor a plant in the soil and absorb water from the soil Nutrients dissolved in water help the plant grow, stay healthy, and reproduce

Xylem and phloem cells form tubes in the cross-section of this soybean root.

Soybean roots

How Cells Get and

Use Energy

A plant’s leaves make sugar This sugar contains energy the

plant can use for life functions Cells break down the sugar to

release its energy

Making Sugar

Plant leaves contain chlorophyll

Chlorophyll is a green substance that

traps energy from the Sun and allows

plants to make their own food

Plant cells contain structures called

chloroplasts Chloroplasts store

chlorophyll Animal cells do not have

chloroplasts or chlorophyll They cannot

make their own food

Plants make a sugar, glucose, in a

process called photosynthesis During

photosynthesis, a plant uses water, light

energy from the Sun, and carbon dioxide

from the air When the carbon dioxide

and water are combined, the plant makes

sugar and oxygen Sugar is a source of

energy for the plant and for organisms

that eat the plant

This chloroplast contains chlorophyll Inside the chloroplast

is a large light-colored structure

This structure holds starch, which was made from sugar.

A thin layer of cells on the top and bottom of the leaf allows sunlight

to pass into the middle

of the leaf

17

Chlorophyll must be present for photosynthesis to take place The following equation represents the process of photosynthesis:

6CO2 + 6H2O C6H12O6 + 6O2

During photosynthesis, plants take in carbon dioxide and release oxygen Without the oxygen made by plants, most organisms would not be able to survive

Most leaves exchange water vapor, carbon dioxide, and oxygen through tiny openings on the bottom

The leaf bottom is protected from the Sun, so it is cooler than the top Therefore, less water is lost.

Because these cells are spread apart, carbon dioxide can move easily through the leaf.

This is the vein of a leaf The xylem and phloem are found here.

Tall, thin cells in the middle of the leaf contain chloroplasts They absorb sunlight, so that photosynthesis can take place.

Some leaves have waxy coverings

to help prevent water loss.

carbon dioxide + water light energy sugar + oxygen

chlorophyll

Getting Energy from Food

Sometimes plants make more sugar than they need Any

extra sugar is stored in the plant as other kinds of sugars or

starches When the plant needs more energy, it must break

down this extra food to release the energy

The process by which cells break down sugar to release

energy is called cellular respiration Respiration is a word

people may use to mean breathing air through the lungs But

cellular respiration is different from breathing

During cellular respiration, sugar starts to be broken down

in the mitochondria The result is the creation of carbon dioxide

and water, and the release of energy The following equation

shows the process of cellular respiration:

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

Sugar + oxygen carbon dioxide + water + energy

Sugar

Water

Energy

O xygen

19

The Carbon Dioxide-Oxygen Cycle

You may have noticed that the equations for photosynthesis and cellular respiration are very similar They look like the reverse of each other The sugar and oxygen that are made during photosynthesis are combined during cellular respiration

The two processes form a cycle The cycle is called the carbon dioxide-oxygen cycle

The carbon dioxide-oxygen cycle involves both plants and animals Plants take in oxygen and carbon dioxide through their leaves Animals breathe in oxygen from the air Both plants and animals use oxygen during respiration to make energy from food Their cells release carbon dioxide In animals, the released carbon dioxide enters the blood and is transported to the lungs

Plants use energy to change water and carbon dioxide into more food and oxygen during photosynthesis The carbon dioxide-oxygen cycle helps living things get the dioxide-oxygen and carbon dioxide they need to live

The carbon dioxide-oxygen cycle makes sure that plants and animals have the oxygen and carbon dioxide they need.