DORSAL 



CELLS AND TISSUES 53 



.Transverse plane 



ANTERIOR "^^ 



POSTERIOR 



VENTRAL 



Figure 3.17. Diagram to illustrate transverse, sagittal and frontal planes in a bi- 

 laterally symmetrical animal. 



Questions 



1. How would you define a cell? What is meant by the cell theory? 



2. Contrast the meaning of the term cell in the time of Robert Hooke, in the time of 

 Schieidcn and Schwann, and at present. 



3. How would you define a tissue? List and give the distinguishing characteristics of the 

 several types of animal tissues. 



4. Describe the parts of a typical animal cell and give the functions of each. 



5. Describe the methods that may be used to investigate the functioning of an ameba. 

 Of a mammalian liver cell. 



6. In a human cell undergoing mitosis, how many chromosomes are present in the 

 metaphase? In the anaphase? In the resting daughter cell? 



7. Outline briefly the events which occur in each stage of mitosis. Illustrate your discus- 

 sion with diagrams of mitosis in the cell of an animal with four pairs of chromosomes. 



8. What factors may regulate cell division? 



9. ^Vhat is tlie principle underlying histochemical studies of cell function? 



10. Differentiate clearly between diffusion, dialysis and osmosis. Of what biological im- 

 portance is the process of diffusion? 



11. In what ways do gases, liquids and solids differ? 



12. Define the term energy. Differentiate potential and kinetic energy. 



13. What is a semipermeable membrane? Give some examples of semipermeable mem- 

 branes in the hiunan body. 



14. How would you measure tiie osmotic pressure of the contents of a red blood cell? 



15. What kinds of tissue make up the human tongue, stomach, Uver, heart, eye? 



16. Compare the matrix present in bone, cartilage and fibrous connective tissue. 



17. How would you describe the position of a rhinoceros' tusks? Of a camel's hump? Of a 

 cobra's hood? 



Supplementary Reading 



The development of the cell theory is interestingly presented in Hall's A Source Book 

 in Afiimal Biology by means of long quotations from some of the original scientific papers. 

 Further discussion of the properties of cells and protoplasm will be found in General 

 Cytology by De Robertis, Nowinski and Saez. Maximow and Bloom's Textbook of Histol- 

 ogy is a detailed, technical discussion of the tissues of the human body. It contains many 

 fine illustrations, both at the light microscope and electron microscope level, of each 

 type of tissue. Our knowledge of cell structure obtained by electron microscope and x-ray 

 diffraction studies is summarized in The Fine Structure of Cells, the proceeduigs of a 

 Symposium held at Leiden, Holland, in 1954. 



