The answer is a. I learned about this in psychology.
Trait is an obvious, observable, and measurable trait; it is the expression of genes in an observable way. An example of a phenotypic trait is a specific hair color
The phospholipid bilayer has two hydrophilic surfaces: the extracellular and the intracellular surfaces. These two layers sandwiches a major layer of lipids or fat. Because of this nature of the lipid bilayer, water-soluble or <em>hydrophilic</em> hormones cannot enter the cell membrane. They have to rely on the mechanisms of receptors.
One can find transmembrane proteins embedded across the whole length of the lipid bilayer. One of the functions of these proteins is to serve as the link for hormones such as the ones given above. When the water-soluble hormones attach to one of these receptors, the receptor will be activated and send down a signal to the intracellular environment; these signals will then travel down towards their target site and eventually activate whatever it is the hormone was made for. One example of these transmembrane proteins are <em>G-coupled proteins; </em>examples of signals that cascade down the cell are cylic AMP and cyclic GMP.
4.3 Agricultural land. At present some 11 percent (1.5 billion ha) of the globe's land surface (13.4 billion ha) is used in crop production (arable land and land under permanent crops). This area represents slightly over a third (36 percent) of the land estimated to be to some degree suitable for crop production.
Answer:
The only reactants of the Krebs cycle proper are acetyl CoA and the four-carbon molecule, oxaloacetate.
