CELLS

cell: the basic unit of structure inliving things

AIM I What are ce lls?

The G reat Pyramids

special job to dJu. 111415s:' part : ork together to keep the cell

Buildings are put together with bricks. Birds build their nestswith grass and twigs. l verything is made up of smallerParts. ... EVEN YOU

Livia; things are made up of small parts called cells. Thecell is the basic unit of structure in all living things. Because allliving things are made up of cells, cells are often called thebuilding blocks of life."

Some organisms, like bacteria, are made up of only onecell. Larger organisms have many more cells. A person, for ex-ample, is made up of trillions of cells. Can you imagine howmany cells a whale must have?

Cells come in many sizes. Most are microscopic )my kruhSKOP ikj. Some cells, however, can be seen easily. For example,a chicken's egg is a single cell. Do you need a microscope to seea chicken's egg?

Cells also come in many shapes. For example, a musclecell has a different shape than a nerve cell. Skin cells have adifferent shape than fat cells.

As you see, there are many differences among cells. Butcells also have many things in common. For example, all cellsare made up of a living material called protoplasm (PRO tubplaz urn). Protoplasm is mostly water. But protoplasm also con-tains dissolved salts and many organic (carbon) compounds.The term organic means "life.,,

A cell is a living thing. It carries out all the life functions.For example, a cell takes in nutrients and oxygen. It gives offw,wros(e products. Cells use and release energy.

takesplace inside a + Ol?. il nd, cells d1 so reproduce.

Culls are ra2aat"h' 1.11:8 of m any parts. UaCI'l cel l part has a

Inoctioning propi.-rly,

im, ycui will learn about sore of these cell parts.You w6'11 also learn how aniral al cells are different from plant (oils.

F igu

shows seven cell parts . These parts are found in almos t every K€xk.irr rxl cell. Thename of each cell part is listed below,

ell membrane (ELL %MFbrand l

m t.cr .hckrt ;tia (rny tub KON dregrah)

tai (S

tulr pl : r.tx'r:r

• rttu"Ieos (NEW klee trs)

• nuclear (NEW klee ar) membrane

n ribosomes (.Y )till soarnkr

endoplasm c reticulum (EN deliplaz ra ik rill TIK yoo lu n)

Each cell part is described below the diagram. As you read each description,n identify the cell part in the diagram, then

Figure A A typical animal cell.

CE I, IF:MBB RANF A thin covering that surrounds the cell. The cell.membrane a) protects the cell,

b) helps give the cell its shape,c) allows materials to enter and

leave the cell, and

d) helps keep the cell material to gether.

A thin covering that surrounds the nucleus. The nuclearmembrane controls the passage of materials into and out ofthe nucleus. It also gives the nucleus its shape.

Mitr::hondria are rod-shaped. They are the "power houses"of the cell. Mitochondria store and release the ener;yT thecell needs to carry out the life functions.

A network of channels. The endoplasmic reticulum is like aseries of "roadways." They are used for moving materialswithin the cell.

Tiny grainlike structures. The ribosomes make and storeprotein. Most ribosomes are found on the endoplasmic re-ticulum. Some, however, move freely within the cytoplasm.

Answer the following questions about cells.

8.

The parts of the cell that you have labeled are all made up of "living" material,What is the living material of the cell called?

9.

Where do most of the life functions take place within a cell?

10. a) Does each part of the cell work alone?

b) Explain you answer.

WORD ABOUT PLANT CELLS

Plant cells and animal cells are similar. But they are not exactly the same.

Plant cells have two parts that animal cells do not have. These parts are: a cell walland chloroplasts.

The d: eli wall surrou nds the cell membrane of the pla:c::c 11 wail i s made of ;an

g

onf

iv .i+̂

ng Yraat erial called ^.iAlulose.>C

The cellgives a plant its stiffness. It helps a plant to st.,ind erect.

-;laloroplasts are sprea d throughout the cytoplasrri of plant cells. The

cc,hloropfasts contain a green substance called chlorophyll. Greenplants need chlorophyll (along with carbon dioxide and light en-ergy) to make the ir own food. Ghloa•otahy-il is found mostly in leafells.

NUCLEAR MFMBR A 1E

MI " ONDI UA

ENDOPL%SM ICI lgTICULi..;It

RIBOSOMIES

Substances must be able to get into and out of a cell in order for the cell to do itsjob. The passage of these materials takes place thruu11 boss," controls the passage of these mater

membrane has tiny holes. Liquids carrying dissolved substances passthrough these holes in it process called osmosis jahs :' IOH sisJ. Osmosis i"chaosr." It allows univ certain substances to move into the ce ll. And only,stances a stay move out of the cell. For example, dissolved nutrients and oxygen can move

only into the cell. Dissolved wastes, such as carbon dioxide, can move only )tit of thecell.

What might happen if the amounts of sub-stances entering and leaving the cell were

not controlled? It depends.... The cellmight a) swell or

b) shrink, or

c) become poisoned.

I. Think about each of the following possibilities. Write youranswer in the space provided.

What might happen if:

1.

too much liquid moved into a cell?

2.

too much liquid moved out of a cell?

3.

too little liquid moves into a cell?

4.too much liquid moves out of a cell?

5,

too little waste moves out of a cell?

,v,as>te :m

llat kinds tit i)Iat +-'r)+ils if ai, O :! i.ell,,

E k(1d; tii

'...!'.ail F)ee(.ls

h)

.LS C t

he letter of he correct Baas

What kin

a)

liter a ceii

cell needs

sidts

cellserect

shapesize-

nucleusOsmosis

f(X)'d-IIIakijI8eater

chloroplasts

cell walllife functionorgann compoun dprotoplasm

. \

.ir o r

1. The "building blocks" of living things are

2. Cells vary in

and

3. A cell carries out every

4. The living material of a cell is called

Pro Moser, and

Two cell parts that are found only i n plant cells are a

and

7. Chloroplasts are needed for

in plants.

8. The cell wall helps a plant stand

9. Substances move into and out of a cell through a process called

10. The passage of substances into and out of a cell takes place through the

On a separate piece of paper, draw a plc`rc>m rmemory. Be sure to include and labe

iY iYA,r

A C.n

• mitochondr is reticulunear rnembrai

f

WHAT 1S A CELL

cell: the basic unit of structure inliving things

cell membrane: the thin outercovering of a cell

nucleus: the part of a cell that con-trols the cell

nuclear membrane: the thin outercovering of the nucleus

cytop lasm : the jelly-like sub-stance inside a cell between thenucleus f. rid the cell membrane

protoplasm: the living material ofa cell

The invention of the microscope made many importantscoveries possible. One of these discoveries was made by theish scientist Robert Hooke in 1665. Hooke discovered thativing things are made up of even smaller livin g parts. He

called these living parts cells.

lying things are made up of cells. Some organisms,like large plants and animals, are made up of billions of cells.Others, like bacteria, are made up of only one cell.Cells are living things. All of the life functions are carriedout by every cell.

The cell itself is made up of smaller parts. These partsinclude the cell membrane [YMEM btane], the nucleus [Ni81Vklee us[, the nuclear [NEW flee ar] membrane, and the cyto-plasm [SY toh plat urn]. All of these parts are made up of aliving substance called protoplasm [PRO tuh plat urn[.Plant and animal cells are not exactl alike. Plant cellshave some parts that animal cells do not have. These parts arethe cell wall and the chloroplasts [KLOR uh plasts].

CELL MEMBRANE The cell membrane is like a thin skin thatcovers the cell. It protects the cell and gives it its shape.The cell membrane has tiny holes in it. Materials enterand leave the cell through these tiny holes.NUCLEUS The nucleus is inside the cell. It controls every-thing that happens in the cell. The nucleus is like the"boss" of the cell. The nucleus is usually near the centerof a cell.

NUCLEAR MEMBRANE The nuclear membrane surroundsthe nucleus. It controls the passage of materials into andout of the nucleus.

CYTOPLASM The cytoplasm is a jelly-like substance locatedbetween the nucleus and the cell membrane. It fills mostof the inside of the cell. Like the cell membrane, the cyto-plasrn helps give a cell its shape. Most of the life f lrnc-tcjns take Place in the cytoplasm.

44

"D THE PARTS

The illustration on the right shows

an animal cell. Four parts of this animalcell are shown . `rl ey are: the nucleus, thecell membrane, the nuclear membrane,and the cytoplasm.

Find each part of the cell in the pic-ture. Write the nave of each part on thecorrect line.

Are these parts also found in plant

cells?

PARTS OF AN ANIMAL CELL

WHAT Do Look at each picture. Then answer the questions.THE

PICTURESSHOW?

The cell membrane has tiny holes in it.Materials needed for the life functions enterthe cell through these holes; wastematerials leave.

1. What needed materials enter the cell

through the cell membrane?

2. What waste materials leave the cell

through the cell membrane?

0 , .

oxygen anddigested food

o

cell membrane

t

carbondiox de

andother

wastesOUT

A bird's egg is made up of only one cell. Abird's egg has a hard shell that covers thecell membrane.

3. Do you need a microscope to gee this

cell?

4, What extra part does a bird's egghat most other cells do not

have?

PECtAL KIND OF C EIJ,

4S

ARE PLANT CELLS DII~ F ERENN IMAL C

Plant cells and animal cells are not exactly alike. Plant cells have certain parts thatanimal culls do not have. These parts include a cell wall and c hioroplasts.

• The cellthe entire plant cell.

outside the cell riser plant cell. It surrounds

The cell w all is made of a nonliving material called cellulose [S ELL yuh loasj. Theis more rigid (stiff) than the cell membrane. It gives a plant cell its stiffness, It-es it its shape.

n Chloroplasts are found in the cytoplasm of a plant cell. Chloroplasts contain

agreen substance called chlorophyll {KLOR uh fillJ.

Chlorophyll is needed by green plants for food-making, The food-making processof green plants is called photosynthesis [fo tuh SIN thuh sis . Most chlorophyll is foundin the leaf cells of green plants.

Plants can make their own food. Animals cannot. Animal cells do not containchlorophyll.

1. Does photosynthesis take place in animals?

2. Why?

MORE ABOUT PLANT CELLS

The picture on the right shows a plant

1. Find each part of the plant cell in thecell. The parts of the plant cell that are

picture. Write the name of the part onshown in the picture are listed below.

the correct line in the picture. One ofthe parts has been labeled for you.cell membrane

nucleuschloroplastsx:ytoplasruu

f

'taw, answe r the questions about plant cells.

1. What is found inside of the chioroplasts?

2. '}Vhdt is this

Answer the following c

1.

and animal culls.

animt7aI c calls do not have?

al used for?

ahoc

s I

. _ and

2. Wheat is the cell ",all madprotoplasm, cellulose

3. Is cellulose living material?

ties, 110

4. What is the cell membrane made of?

protoplasm, c lluInse

5. Is protoplasm living material?yes, no

6. Where are the chloroplasts located?in the nucleus, in the cytoplasm

7. Wha t substance is found inside the chloroplasts?

protoplasm, chlorophyllS. What is the substance inside the chloroplasts used for?

food-making, excretion9. Can animals make their own food?

yes, no

10. Why can' t animals make their own food?

Match the two lists. Write the correct letter on the line next toeach number.

chlcaroplasts and cell

a) parts of all cells"v,all

h) food-making process of plants

c) found only in plant cells

d) nnnlivin ,g material of the coil sill

e) any living m aterial of the cell

i hoto.;v

ott(;leus, maclear meinr^i ntnlrrane,no, ('61

^ .l^^lli,.ltiflt

f

i'It I, 4(t'i t'.

:)1PLETING Complete the sentences with the words below. Three words willSENTENCES be used twice.

chlorophyll

cell membrane

life functionsliving

cellulose

cell wallchloroplasts

cytoplasm

nuclear membranernocleus

waste products

1. The parts that all plant and animal cells have are the

the

the

, and the

2. A plant cell has two parts that animal cells do not have. They are the

and the

3. Cells are

things. All of the

are carried out inevery cell.

4. The

is the control center of the cell.

5. Materials needed for the life functions enter the cell throu the

6. leave the cell through the cell membrane.

7. The cell wall of a plant cell is made of a nonliving substance called

8. The special cell parts needed for food-making in plants are the

9. Chloroplasts contain a green substance called

WORD Unscramble each of the following to forma word or term that youSCRAMBLE have read in this aim. Write your word in the spaces below.

t,CoT`\lYc

_SA',fPLOTRO'

Look at each picture. Answer the questions next to each pictu

What holds up a person?

2. What holds up a plant? --

3. What is taking place in this picture?

4. In what part of a plant is food made?

l' 1 'E' (? ( Write T on the line next to the number if the sentence is true.Write F if the sentence is false.

ck has cells.

,Most of a cell is the nucleus.

ly the ruckus of it cell is protoplasm.

The cell membrane has holes,

Most cells sire microscopic in size.

t'huit ^_ c2 il "3 , â t;! ,3u mn it t Ods ir(.' t ( :

it)

REACC IN(.

without looking back, try to draw a picture of an animal cell. Label the nucleus, thenuclear membrane, the cell membrane, and the c°toplasm.

2. Now try to draw a picture of a plant cell. Label the nucleus, the nuclear membrane,the cell membrane, the cell wall, the cytoplasm, and the chloroplasts.

s.L'hat do you think would happen i f c vaste products could not leave a cell?

t:t