92 



THE ORGANISM: 



PLANT CELL 



• •♦ 





plastld 

 cell wa 1 1 

 vacuole 



nucleus 

 cytoplasm 

 cell membrane 



ANIMAL CELL 



centrosome 



nucleus 

 cytoplasm 

 cell membrane 



Figure 6.8 Comparison of a plant and an animal cell, highly 

 schematized. 



the site of photosynthesis (they usually contain chlo- 

 rophyll) and food storage. Vacuoles may be related 

 to cell gas and water functions. 



TISSUES 



Cells that have essentially the same structure and 

 function when organized into a single unit are a tis- 

 sue. Because tissues are found only in multicellular 

 organisms and such plants and animals are quite un- 

 like one another, plant and animal tissues are classi- 

 fied differently. 



Plant tissues are of two types, growing and perma- 

 nent (Figure 6.9). Growing tissues contribute to the 

 development of increased size and new structures. 

 Permanent tissues are further subdivided into two 

 groups. The simple permanent tissues are composed 

 largely of a single kind of cell. These tissues are of 

 approximately five kinds that function in protection, 

 support, and/or nutrition of plants. The complex 

 permanent tissues, .v^y/crd and phloem, are arrangements 



bundle sheath 



spongy 



epidermis 



Figure 6.9 A vascular plant leaf, an organ, and some of its tissues. 

 Palisade, spongy, and bundle sheaths are different tissues modified 

 from the simple permanent tissue type called parenchyma. Epidermis is 

 a simple permanent tissue. Xylem and phloem are the complex per- 

 manent tissues forming the framework of the vessels of vascular plants. 

 The rectangle on the cut leaf blade indicates the site of the leaf 

 cross- section. 



of several kinds of cells. Together xylem and phloem 

 form the vascular bundles which function in transporta- 

 tion of materials dissolved in water, but they are 

 found together only in the vascular plants, the Tra- 

 cheophyta. The only permanent tissues found outside 

 the Tracheophyta are phloemlike and are in the 

 brown algae. Xylem and phloem are both supportive 

 tissues; xylem conducts water and dissolved material 

 mostly upward and phloem conducts nutrients chiefly 

 downward. 



Animal tissues are also of two major types, repro- 

 ductive and body. The reproductive tissues form the 

 reproductive cells, or gametes. The body tissues are 

 epithelial, or covering; connective, or supporting; 

 muscular, or contracting; and nervous, or coordinat- 

 ing. 



ORGANS 



An organ is a group of tissues that performs a par- 

 ticular function. Organs in plants tend to be simpler 

 structurally and of fewer kinds than those in animals. 

 Fully developed plant organs are found only in the 

 Subkindom Embryophyta, the embryo plants. These 

 plants have true organs of four kinds: roots, stems, 

 leaves, and reproductive organs (often grouped into 

 flowers or cones). The functions of roots include 

 anchorage and support of plants, absorption of water 

 and dissolved nutrients from the soil, conduction of 



