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Section 1 |_ Organization of Life

multicellular population community ecosystem

tissue organ organ system organism unicellular

Wlui£YouMDo> • Explain how life is organized,

from a single cell to an ecosystem.

• Describe the difference between unicellular organisms and multicellular organisms.

Figure 1 The first cell of a chicken is one of the largest cells in the world.

Imagine that y o u are going on a t r ip to Mars. I n your suit­case, you should pack everything y o u w i l l need i n order to survive. W hat w o u l d y o u pack? To start, y o u ' d need food, oxygen, and water. A n d that's just the beginning. You w o u l d probably need a pretty big suitcase, w o u l d n ' t you? Actually, you have all of these items inside your body's cells. A cell is smaller than the period at the end of this sentence, yet a sin­gle cell has all the items necessary to carry out life's activities.

Every l i v i n g t h i n g has at least one cell. Many l i v i n g things exist as a single cell, whi le others have tr i l l ions of cells. To get an idea of what a l i v i n g t h i n g w i t h nearly 100 t r i l l i o n cells looks like, just look i n the mirror !

Cells: Starting Out Small Most cells are too small to be seen w i t h o u t a microscope, but y o u m i g h t have one of the world's largest cells i n your refrig­erator. To f i n d out w h a t T t is, see Figure 1. The first cell of a chicken is yel low w i t h a t i n y whi te dot i n i t , and i t is sur­rounded by clear, jellylike f l u i d called egg whi te . The whi te dot divides over and over again to f o r m a chick. The yellow yolk ( from the first cell) and the egg whi te provide nutrients for the developing chick's cells. Like a chicken, y o u too began as a single egg cell. Look at Figure 2 to see some of the early stages of your development.

Not all of your cells look or act the same. You have about 200 different kinds of cells, and each type is specialized to do a particular job. Some are bone cells, some are b lood cells, and others are skin cells. W h e n someone looks at all of those cells together, they see you.

Figure 2 You began as a single cell. But after many cell divisions, you are now made of about WO trillion cells.

24 hours 40 hours 6 days 4 months

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Tissues: Cells Working in Teams W h e n y o u look closely at your clothes, y o u can see that threads have been grouped together (woven) to make c loth that has a funct ion . I n the same way, cells are grouped together to make a tissue that has a funct ion . A tissue is a group of cells that work together to perform a specific job i n the body. The material around and between the cells is also part of the tissue. Some examples of tissues i n your body are shown i n Figure 3.

Organs: Teams Working Together W h e n t w o or more tissues work together to per­f o r m a specific job, the group of tissues is called an organ. Some examples of organs are your stomach, intestines, heart, lungs, and skin. That's r ight ; even your skin is an organ because i t contains different kinds of tissues. To get a closer look, see Figure 4.

Plants also have different kinds of tissues that work together. A leaf is a plant organ that contains tissue that traps l ight energy to make food. Other examples of plant organs are stems and roots.

Figure 4 The skin is the body's largest organ. An average-sized person's skin has a mass of about 4.5 kg.

Muscle

Figure 3 Blood, fat, and muscle cells are just a few of the many cells that make tissues in your body.

m F O O J J

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The part of the skin, hair, and nails that you can see is dead tissue! Isn't it strange to think that we put so much effort into making sure our dead cells look nice?

Cells: The Basic Units of Life 57

t \ Chemistry C O N N E C T I O N

On the surface of every person's cells are special proteins that act like identification cards. When a person gets an organ transplant, the cells of the new organ must have most of the same "ID cards" as the person's cells. If too many are different, the person's body will try to reject the new organ.

— A c t i v i t y -A school system's job is to educate students at all levels. The different schools (el­ementary, middle, and high school) are like the different organs within an organ sys­tem. Groups of teachers at each school work together to teach a specific grade level. If each group of teachers can be thought of as tissue, what would that make each indi­vidual teacher? What other examples can you use to represent the parts of an organ system? Explain your answer.

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Organ Systems: A Great Combination Organs work together i n groups to perform particular jobs. These groups are called organ systems. Each system has a specific job to do i n the body. For example, your digestive system's job is to break d o w n food i n t o very small particles so i t can be used by all of your body's cells. Your nervous system's job is to transmit i n f o r m a t i o n back and f o r t h between your brain and the other parts of your body. Organ systems i n plants include leaf systems, root systems, and stem systems.

Your body has several organ systems. The digestive system is shown i n Figure 5. Each organ i n the digestive system has a job to do. A particular organ is able to do its job because of the different tissues w i t h i n i t .

The organs i n an organ system depend o n each other. If any part of the system fails, the whole system is affected. A n d failure of one organ system can affect other organ sys­tems. Just t h i n k of what w o u l d happen if your digestive system stopped converting food to energy. None of the other organ systems w o u l d have energy to funct ion .

Figure 5 The digestive system is one of the 17 main organ systems. It is made of different organs, which in turn are made of different tissues.

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Organisms: Independent Living A n y t h i n g that can live o n its o w n is called an organism. A l l organisms are made up of at least one cell. I f a single cell is l i v i n g o n its o w n , i t is called a unicellular organism. Most unicellular organisms are so small that you need to use a microscope to see them. Some different kinds of unicellular organisms are shown i n Figure 6.

You are a multicellular organism. This means that y o u can exist on ly as a group of cells and that most of your cells can survive only i f they remain a part of your body. W h e n y o u fall d o w n o n a sidewalk and scrape your knee, the cells y o u leave behind o n the sidewalk are not able to live o n their o w n . Figure 7 shows how your cells work together to make a multicellular organism.

Figure 6 Unicellular organisms come in a wide variety of shapes and sizes.

Organism

Heart Heart muscle cell

Tissue

Heart muscle tissue

Made of many organ systems

HESS

Figure 7 Multicellular organisms are made of many cells that work together in tissues and organs.

The Big Picture A l t h o u g h unicellular organisms and multicel lular organisms can live o n their o w n , they usually do not live alone. Organisms interact w i t h each other i n many different ways.

Populations A group of organisms that are of the same k i n d and that live i n the same area make up a population. A l l of the ladybird beetles l i v i n g i n the forest shown i n Figure 8 make up the ladybird bee­tle populat ion of that forest. AH of the red oak trees make up the forest's red oak populat ion. Figure 8 A population is made up of all of

the individuals of the same kind that live in the same area.

Cells: The Basic Units of Life 59

Figure 9 The fox, flowers, and trees are all part of a forest community.

Communities ^ Two or more different popula­tions l i v i n g i n the same area make up a community. The populations of foxes, oak trees, lizards, flowers, and other organisms i n a forest are all part of a forest community , as shown i n Figure 9. Your h o m e t o w n is a c o m m u n i t y that includes all of the people, dogs, cats, and other organisms l i v i n g there.

Ecosystems *iThe c o m m u n i t y and all of the n o n l i v i n g things that affect i t , such as water, soil, rocks, temperature, and l ight , make up an ecosystem, M Ecosystems on land are called terrestrial ecosystems, and they include forests, deserts, prairies, and your o w n backyard. Ecosystems i n water are called aquatic ecosystems, and they include rivers, ponds, lakes, oceans, and even aquariums. The c o m m u n i t y i n Figure 9 lives i n a terrestrial ecosystem.

REVIEW

internetconnect

5Cli INKS,

TOPIC: Organization of Life & Populations, Communities, and Ecosystems

GO TO: www.scilinks.org sc/LINKS NUMBER: HSTL055, HSTL060

, Complete the f o l l o w i n g sentence: Cells are related to ? i n the same way that J_ are related to organ systems.

, How do the cells of unicellular organisms differ f r o m the cells of multicellular organisms?

, Applying Concepts Use the picture of an aquarium below to answer the f o l l o w i n g questions:

a. How many different kinds of organisms are visible?

b . How many populations are visible?

c. How many communities are visible? ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

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