62 - The Cell 



HAPLOID 



DIPLOID 



AMOEBA 



GREEN 

 ALGA 



HIGHER 

 PLANT 



HIGHER 

 ANIMAL 



Fig. 3-20. Diagrams illustrating the relations of the haploid and diploid stages in various types of life cycles 

 (see text). In each figure the single line represents the haploid, the double line the diploid condition. The 

 direction of the arrows indicates the succession of generations. F, fertilization; M, meiosis. 



lour from the spore mother cells in the 

 spore capsule. Consequently the spores are 

 always haploid. Each haploid spore invari- 

 ably gives rise to a haploid form of the plant, 

 which eventually will reproduce by gametes. 

 Thus the haploid sexual generation in higher 

 plants is called the gametophyte. Finally 

 when fertilization again takes place, the hap- 

 loid gamete nuclei fuse, and the diploid con- 



dition of the succeeding sporophvte genera- 

 tion is restored. 



The early evolution of reproductive struc- 

 tures among plants and animals appears to 

 have occurred by trial and error. A variety 

 of methods first appeared among primitive 

 organisms, but only a few were successful 

 enough to be passed on to higher plants and 

 animals. 



1. Explain three important differences and 

 three important similarities between mitosis 

 and meiosis. 



2. What is //mitosis? Why is amitosis not re- 

 garded as a normal kind of cell dhision? 



3. In proper sequence list the events that occur 

 during the prophase of mitosis: (a) in a plant 

 cell; (b) in an animal cell. 



4. How does the prophase of the first meiotic 

 division differ from the prophase of mitosis? 



5. How are metaphases and anaphases dis- 

 tinguished from the other stages ol mitosis? 



6. In mitosis, what invariable rule determines 

 the movements ol the members of each pair 

 ol daughter chromosomes (the two chromo- 

 somes formed by the division of each parent 

 chromosome)? 



7. What importance is attached to the fact that 

 each chromosome divides lengthwise, rather 

 than crosswise? 



8. Specify two ways in which the telophases of 

 plant and animal cells are: (a) different; and 

 (b) similar. 



TEST QUESTIONS 



9 



10. 

 11. 



14. 



15. 



Assuming that the chromosomes were dis- 

 tinctly visible, how would you decide whether 

 a given cell were haploid or diploid? 

 Explain the term homologous chromosomes. 

 Is it true that any species of plant or animal 

 can be identified by studying the chromo- 

 somes of one of its cells? Explain your answer 

 carefully. 



In man. most of the cells are formed b\ 

 mitosis, but some are produced by meiosis. 

 Explain this statement more specifically. 

 Identify each of the following terms: (a) 

 spireme chromosomes: (I)) spermatogonia: 



(c) primar\ spermatocytes: (d) synapsis: (e) 

 tetrads; (f) secondary spermatocytes; (g) diads: 

 (h) spermatids: (i) sperm. 



In each case specif) the distinguishing fea- 

 tures and cite a specific example: (a) asexual 

 reproduction: (b) binary fission; (c) budding: 



(d) sporulation; (e) zoospores. 



Carefully define each term and in each case 

 cite three specific examples: (a) a gamete 

 cell: (b) the zygote; (c) fertilization. 



