66 he could see. amount ofdetail severely limited the Its crudelenses using this . first identifiedcells Figure 1.1 I. MainIdea explain those ideas. Summarize detailsthat further using theheadings as topics. As you read, make anoutline TAKING OTES eukaryotic cell prokaryotic cell VOCABULARY Unit 2: Cells Unit 2: > RE B. Supporting idea A. Supporting idea 3.1

2. Detail 1. Detail ADING TOOLBo


Cell Theory x technology—in thiscase, themicroscope. breakthroughs, thediscovery ofcells was aidedby thedevelopment ofnew before the1600s,peoplehadmanyotherideas aboutthebasisoflife. Like many smallest unitoflivingmatter that cancarryoutallprocesses required for . But a cell’s isclosely related to Today itsfunction. we know that cells are the You andallotherorganisms are madeofcells. Asyou saw ontheprevious page, Connect to Your World Key C . E arly led studies to development the of the

powerful withpowerful acompound microscope than with asingle lens. product of power magnifying the of each individual lens, is generally much more assisted by his father, Hans, usually gets credit for invention. this discovery. The Dutch maker eyeglass Janssen, Zacharias was who probably compoundthe microscope late inthe 1500swas an early step toward this lenses were not enough powerful to reveal individual cells. The invention of images to magnify used for lensesglass had been hundreds of years, early the cells areAlmost without all to small see too aid the of amicroscope. Although MAI MAI A compound microscope contains two or more lenses. Total magnification, the

tiny, hollow compartments tough outer bark of of tree. aspecies that He oak cork observed is made of his “animalcules” are pictured in organismssingle-celled swimming inadrop of pond water. Sketches of numerousof living first people the to he cells when observed describe Hooke’s compound crude microscope. In one became 1674,Leeuwenhoek of his research, his single-lens were much more than powerful was studying for methods new making lenses to examine cloth. As aresult looking only at and walls cell empty . microscope shown in In English 1665,the scientistHooke Robert three-lens the used compound Discovery ofCells shown cells he observed, in rooms found inamonastery, he gave so same the them name: cells. The oncept Prokaryotic cells lackanucleusandmost internal ofeukaryotic cells. Early studiesledto thedevelopment ofthecell theory. N ID N ID Around same the , Anton van aDutch Leeuwenhoek, tradesman, E E A AS

Cells are thebasicunitoflife. Figure 1.1 . The compartments reminded Hooke of small to examine slices thin of cork. Cork is the Figure 1.2 Figure 1.2 (bottom) (top), were dead. Hooke was .

©Science Museum London/HIP/The Image Works (tr )Library of Congress, Prints and Photographs Division [LC-USZ62-95187]; (cr) ©HIP/Art , New York; Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow ©The Granger Collection, New York Summarize FIGURE 1.3 the the of concepts first unifying the developed inbiology. The major principles of preexisting cells.early These contributors are shown in another scientist, German reported that cells come all from of part this Schwann’s was wrong. idea In 1855,, scientists studied process the of division, cell that realized they that cells form spontaneously by formation. free-cell As later conclusions. For example, Schwann stated inhis publication it had refined toover be years the as additional data to led new groundwork for biological all research that followed. However, made of cells and products. cell helped lay This the theory statement of theory, cell the concluding that living all things are made of cells. Shortly thereafter, in1839,he published first the studying.he had been Schwann concluded that all are similarities plant between structural the cells and the cells another scientist, German , wasby who struck are results the made of discussed cells. Schleiden of his work with microscopes to study plant . In 1838,he proposed that The scientist German Matthias compound used also Schleiden Cell Theory questions: Is living all made of cells? Where do cells come from? cells dividing.shapes, Scientists began to and observed ask important they examine even more . variety awide of cell observed They greater magnification. This combination of factors people led to century and ahalf, it sturdier, became easier to use, and capable of The is most cell the basic unit of life. • existing All cells are produced by other living cells. • organisms All are made of cells. • them. cells, andhenamed the firstto identify 1665 As people continued to improve microscope the over next the This accumulated research summarized theory, can cell inthe be one cell theory Hooke was H ook

E xplain the three major principles of cell theory in your own your words. in theory cell of principles major three the xplain e Contributors to Cell Theory are following: the greater detail. observed cells in Leeuwenhoek lenses,made better 1674 Lee u Because he wenho ek cells. plants are madeof the firstto note that 1838 S chl Schleiden was e Figure 1.3. id en

cells. things are madeof cluded that allliving 1839 sch Schwann con - wa nn in pondwater (bottom). life, whichhecalledanimalcules, observed anddrew microscopic (top). Incontrast, Leeuwenhoek the cell walls ofdead plantcells Figure 1.2 Chapter 3:Cell Structure andFunction other cells. cells come from proposed that all 1855 Hooke observed V Virchow ir W CHO 67 68 their role inhumandisease. their role intheecosystem, and their requirements to sustainlife, , whichdiscusses prokaryotes inViruses and You willlearn more about Prokaryotes Figure 1.4 nucleus tions: protozoan 3200 cytoplasm. (colored TEMs;magnifica- envelope separates DNA from the tozoan the (bottom), nuclear eukaryotic cells, suchasthispro- is suspendedinthecytoplasm. In such asthisbacterium (top), DNA 19,000 Unit 2: Cells Unit 2: CONNECT TO 3.1 2. 1. viRe ew 3 How do eukaryotic cell microscope help scientists form the How didimprovements inthe ) theory? In prokaryotic cells, Formative Assessment in prokaryotic and g 3 cells differ? ; bacterium bacterium ; cytoplasm

M ai n I d e structures of eukaryoticstructures cells. P as Summarize rokaryotic cells lack a nucleus and most internal

The variety offound types cell inliving things is staggering. Your alone body is based on internal their based structures: prokaryotic cells and cells. eukaryotic cytoplasm contains also as , nucleic acids, minerals, and . In of some types cells, the substancejellylike that contains dissolved molecular building blocks—such which stores genetic information. membrane. In many largest cells, the and most visible organelle is nucleus, the form distinctprocesses within acell. Most are surrounded by a a membrane that controls movement the of materials into and out of cell. the microscopic insizeand have similar building blocks. are They enclosed by also cells thatthe other make . up every In general, cells tend to be cells inyourthe share body many characteristics with one another and with as short, blocky skincells that cover and protect body. the Despite variety, this includeThey cells that long, nerve transmit thin information, sensory as well made of trillionsof cells of many different shapes, sizes, and functions. • • MAI As shown in Within membrane, the with cytoplasm. is acell filled Eukaryotic cells Prokaryotic cells membrane-bound organelles. do notihk) have anucleus or other organisms. are microscopic single-celled cytoplasm.in the Most prokaryotes Instead, cell’s the DNA is suspended cellular or organisms. single-celled information. may be multi- largest organelle, encloses genetic the bound organelles. The nucleus, the have anucleus and other membrane- N ID 4. 3. C

E thi ritical W similar to ? Compare the work ofearly scientists. Explain how thistechnique buildson human cells grown inpetridishes. Analyze A hat characteristics are shared by most cells? by most shared are characteristics hat Figure 1.4, kar (yoo- Today, scientists canstudy (pro-kar In what way are cells n organelles, cells can be separated cells can be into two broad categories ki -ee- n -ee- g aht

aht -ihk) -ihk) which are to per structures specialized - VISUAL VOCAB or othermembrane-bound organelles. other membrane-bound organelles. Eukaryotic cells Prokaryotic cells cytoplasm nucleus Premium Content 5. Medicine CONNECT TO or would notkill . brane. Explainwhyitwould pores inthenuclear mem- human cells by blocking Suppose a certain poison kills HMDScience.com Self-check Online Cytoplasm DNA have anucleusand do not have a nucleus organelle is a membrane cell


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