56 



ECOLOGY 



Part II 



Fig. 4.5. Common brown seaweeds that are great food producers. From left to 

 right, fan kelp, Laminaria: giant or vine kelp, Macrocystis; bladder wrack. Fucus; 

 ribbon kelp, Nereocystis. (Not drawn to scale.) Seaweeds constitute a large percent- 

 age of the basic food supply of the seas. On the rocks between the tides where they 

 abound they furnish food and holdfast for hosts of small animals. 



carbon dioxide. The chlorophyll occurs in chloroplasts usually rounded green 

 bodies in the tissues of leaf and stem. It is a complex protein, in higher plants 

 consisting of two pigments, a blue-green one, chlorophyll a {Cr.-Mi-Or.NiMg) 

 and the less abundant yellow-green, chlorophyll b (C55H7oOGN4Mg). The 

 chemical content of chlorophyll is in many ways similar to that of the hemo- 

 globin of blood except that iron occurs in the latter instead of magnesium. In 

 the higher plants chlorophyll is almost always associated with yellow pigments, 

 the carotenoids, and the various xanthophylls related to carotene. Their func- 

 tion is not wholly known; if they are concerned with photosynthesis they are 

 far less important than chlorophyll. Carotene and xanthophyll are much more 

 stable; the rich yellow autumn colors of birch and elm leaves are exultant 

 witnesses that these colors endure after chlorophyll has broken down. 



The Process. During photosynthesis the kinetic energy in light is changed 

 to the potential chemical energy of food. Carbon dioxide is mainly absorbed 

 from the atmosphere. It enters the leaf through the millions of pores or 

 stomata, diffuses through cell membranes in a dissolved state, and goes into 

 the chloroplasts (Fig. 4.8). Water enters chiefly through the roots. In the 

 presence of chlorophyll and with the aid of the energy of light, the carbon 



