Chap. 4 PLANTS PROVIDE FOR THEMSELVES AND THE ANIMALS 65 



male cells come in contact with the stigma and make their way down through 

 the stalk of the pistil to the ovary. Finally one of them reaches the ovule and 

 enters it. The subsequent fusion of the male and female cells within the ovule 

 is fertilization. These are the essentials of the journey of the male cell and its 

 union with the female, with many complexities omitted and numbers of irregu- 

 larities unmentioned. The fact remains that the behavior and function of the 

 primary sex cells are strikingly the same in plants and animals. 



Seed. The seed is an embryo plant which has developed from a fertilized 

 ovule. A fruit is a growth around one or more embryos (seeds) which protects 

 them and is a common means of their dispersal. 



Similarities of Plants and Animals 



1. Cells. Their basic material is protoplasm organized in cells. 



2. Food. Their main food and chief sources of energy are carbohydrates — 

 starches and sugars. Amino acids, the "building blocks" of proteins, are essen- 

 tial to them. Water is a vital need. 



3. Metabolism. The basic processes of respiration and of digestion and 

 assimilation are similar. Excess products of metabolism are mentioned below. 



In the respiration of plants and animals oxygen enters the cells and unites 

 with carbohydrates, fats, and lastly with proteins. Oxidation, i.e., chemical 

 burning occurs. Chemical energy is released as activity and heat. Carbon 

 dioxide and water are formed. 



During digestion food is changed to simpler chemical compounds. During 

 assimilation the digested food becomes part of a specific kind of protoplasm. 

 For example, food assimilated by the chromosomes in certain cells of an oak 

 tree acquires the characteristics of the appropriate substances in those chromo- 

 somes; food assimilated in the chromosomes of certain cells in a goat does 

 likewise. 



In both plants and animals, certain excess by-products may be stored. Ex- 

 amples of these are digitalis in foxgloves, opium in poppies, calcium carbonate 

 in earthworms. The use of these, if any, to the producing organisms is not 

 clearly understood. Certain other by-products may be used; carbon dioxide by 

 green plants in photosynthesis, and by animals in small amounts as a stimulus 

 to breathing and as a control of the force of the heartbeat. 



Differences between Plants and Animals 



1. Locomotion. The majority of plants do not move from place to place. 

 The majority of animals move about freely. 



2. Food. Green plants make carbohydrates by photosynthesis. Animals take 

 carbohydrates from plants. Plants are the chief makers of proteins which they 

 elaborate from amino acids. Animals take proteins from plants and other 

 animals. 



