Protoplasm, the Cell, and the Organism - 29 



PLASTIC (CHLOROPLAST) 



CELL WALL 



NUCLEUS 



Fig. 2-14. Living cells in a leaf of a plant. 



Golgi Bodies. Golgi bodies are specialized 

 areas of cytoplasmic structure that are sel- 

 dom, if ever, found in plant cells; among 

 animal cells, the Golgi "apparatus" is par- 

 ticularly conspicuous in gland cells. Usually 

 the cell displays just one Golgi area, in the 

 vicinity of the nucleus, differentiated on the 

 basis of its susceptibility to staining with 

 neutral red and on the basis of its ultrastruc- 

 ture (Fig. 2-13). 



The Golgi body appears to be a specialized 

 part of the endoplasmic reticulum. Probably 

 it is concerned with the synthesis or elabora- 

 tion of secretional products, which differ ac- 

 cording to the particular kind of gland cell 

 observed. Ribosomal granules appear to be 

 absent from the boundary membranes of the 

 Golgi organelle (Fig. 2-13). 



Cytoplasmic Vacuoles. Vacuoles are of 

 various kinds. In general, each is a fluid- 

 filled vesicle with a definitive boundary mem- 

 brane. However, certain vacuoles may con- 

 tain one or more masses of solid material sus- 

 pended in the fluid content. 



Confractile Vacuoles. Contractile vacuoles 

 are characteristic of one-celled fresh-water 

 animals, such as Amoeba. In the amoeba (Fig. 



CEL MEMBRANE . 

 PSEUDOPODIUM _ 





CONTRACTILE VACUOLE 





:::> 



Fig. 2-15. Amoeba, a unicellular animal. 



2-15) the contractile vacuole appears as a 

 clear, round vesicle that gradually increases 

 in size. Reaching a maximum, the contractile 

 vacuole suddenly fades from view as it dis- 

 charges its contents to the exterior of the cell. 

 Apparently the contractile vacuole serves to 

 extract water from the cytoplasm and to 

 pump it outside the cell. This work must go 

 on constantly, since water keeps entering the 

 cell by osmosis (Chap. 6). Thus if the work 

 of the contractile vacuole is stopped, as it 

 may be by certain drugs, the amoeba begins 

 to swell and finally it may reach the bursting 

 point. 



