Food Uptake And Utilization

midgut. For most neutral amino acids, a symport system operates; that is, active transport of 503

the amino acid occurs concurrently with movement of a cation, especially K+. Some amino acids, however, are transported in the absence of cations (the uniport system). Within the midgut, there are regional differences in uptake ability; for example, in larvae of Manduca sexta the symport system for leucine and proline is concentrated in the posterior midgut (Wolfersberger, 1996).

Another mechanism that may facilitate their absorption, is to convert amino acids to a more complex storage molecule. For example, when certain amino acids were fed to starved Aedes, glycogen rapidly appeared in some of the cells of the midgut and ceca. However, it is not known whether the glycogen was formed directly from these amino acids.

Early histochemical studies demonstrated that droplets of lipid are present in the epithelial cells of the crop and gave support to the idea that the crop was the site of lipid absorption. Though, as noted above, a few reports indicate that certain lipoidal molecules can penetrate the crop wall, Treherne's work, again involving labeled compounds, showed that, in Schistocerca, absorption of lipid occurs not across the crop wall but via the anterior midgut and ceca. In other insects the occurrence of lipophilic cells in the middle and posterior regions of the midgut suggests that these may be sites of lipid absorption. Absorption of lipids is again a passive process and is relatively slow compared to sugars and amino acids; its rate is, however, increased by the esterification of the absorbed materials in di-and triglycerides and other complex lipids in the midgut epithelium, a process analogous to the situation in vertebrates.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment