ASA

Chapter 3 Cellular Hierarchy

ALABAMA 7TH GRADE SCIENCE STANDARDS COVERED IN THIS CHAPTER INCLUDE:

3 Relate major tissues and organs of the skeletal, circulatory, reproductive, muscular, respiratory, nervous and digestive systems to their functions.

CELLULARHIERARCHY In Chapter 2, you learned aboutthe structureofplant and animalcells.How does this relate to actual plants and animals? As you may have already guessed, the microscopic differences between plant and animal cells translate into macroscopic (larger) differencesin organisms.This fact is explainedby the cellularhierarchy.As we will discover during this chapter, differences in cells mean differencesin larger structures like tissues or organs. You can think of it like the foundationaldifference between two different types of houses in a neighborhood — build a different foundation, get a differenthouse.

The cellular hierarchy starts with one cell and works its way to more complex Co In structuresthat eventually form the most complexofliving things: an organism.Take Co

CO 3. 1. Co a look at the cellular hierarchy flow diagram in Figure You should recognize 0? most of the words; they relate to systems within the human body. ui 0 1 D I- z0 0 Cellular Hierarchy

0.CO E Cells — Tissues —>Organs —>Organ systems —>Organism 00 .0 0 C CO 0 E © Figure 3.1 Cellular Flow Diagram

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33 Cellular Hierarchy CELLS Recall, multicellular organisms are composed of many cells that work together to carry out life processes. In multicellular organisms, cells group togetheranddividethe labor.Cellsin a multicellular organism are specialized to perform specific figure 3.2 functions. These specializationsusually cause the Figure 3.3 Red Blood Cells cells in a multicellularorganismto take on special Nerve Cell shapes.ExamineFigures3.2 and 3.3. These images show the differencesin external structuresof two differenttypes of cells. Figure 3.2 shows the round disk shape of red blood cells. This shape maximizes surface area, allowinglots of oxygenand carbondioxideto moveinto and out ofthe red bloodcells. Essentially,their disk shapeallowsred blood cellsto transportgasesefficiently.Figure 3.3 showsa nerve cell;you can see it has many long finger-likeextensions.This shape helps transmit information over long distances, throughout the entire human body. Thereare thousandsof examplesof cellularspecializationin plantsand animals.Some more examplesof cells are skin cells,liver cells,leaf cells and root cells.

TISSUES Cells group togetherto perform the same functionand are calledtissues. The human body is made up of four basic types of tissue: epithelial, connective, muscle and nervous. Epithelial tissue usually surrounds and protects the things beneath it. Epithelialcells can also filter,secreteand absorb substances.Some examplesinclude skin, ducts, glands and the outer layer of your eye called the sciera (the white part). Connective tissue connects and supports body parts. Cartilage and blood are two examplesofconnectivetissue.Muscletissue helpsmovethebody.Muscletissuemoves (0 (0 bones, digestiveorgansand the Co heart.Nervous tissue carriesmessagesfrom the body C? and environmentto the brain andback. LU

C) -J ORGANS I- Severaltypes of tissues grouptogether and form an organ. The brain, z0 0 heart, stomachand lungs are someexamplesof organs.Organsusually 0 perform a complex task. Figure 3.4 shows a four chambered human CC E 0 heart. This organ is made of specializedtissues that act as a pump to C) . 0 moveblood (and otherfluids)throughthe body.Cardiac muscle tissue 0 C contracts and causes the heart to beat. Nervous tissue in the heart CC Figure 3.4 Heart C.) C) receivessignalsfromthe brainto makethe heartbeat at the correctrate. E Epithelial tissue (called the pericardium) forms a protective sac around the heart. © Connective tissues formthevalvesofthe heart,preventingthebackflowofblood in the .C 0. heart’schambers.Not to mentionblood itself is a type of connectivetissue mentioned 0 C) earlierin this text.

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Chapter 3

ORGANSYSTEM An organ system is a group of organs working together for a particular function. Examples of organ systems are the digestive system, circulatory system and nervous system.The organ systems ofmulticellular organismswork togetherto carry out the life processes of the organism, with each system performing a specific function. All the organ systems combine to make up the organism.

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M tissue • . . -- Conecve -:s ::: ( clix CC)m13111C 4 to make tissues Tissues combine organs combine Organ systems tomakesmall tomakedigestive combine to make intestine organ organ system an organism

Figure 3.5 Cellular Hierarchy

As living things become more complex, their cells become more specialized, forming specifictypes oftissues and organs. z.==:===:: z:zz...z c c : :z : ._ z...... z..zzzz :c:zzz.zzz Activity Fill in the blanks in the tablebelow. . Cell Tissue Organ Organ System Lymphocyte Lymphfluid Spleen Co In Tendon Muscularsystem In C4 CO Redbloodcell Bone marrow Co Liver* Digestivesystem LU

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I- z0 BONUS: Complete the last row all on your own. 0 *Hjnt. Theliver is the largest gland in the human bodyand secretes manysubstances used in digestion. CO E 00 Activity 0 0 Use a sheet of paper to draw your own cellular hiearchy image similar to Figure 3.5.

CO :IBesure to show each level of organization from cell — tissue —> organ —> organ 0 E system —>organism. ©.

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