Tryptophan self-controls its synthesis. If we have a large amount of tryptophan in the sense that it exceeds, tryptophan would act as a co-repressor which prevents synthesis of more enzymes for its production. Hope this answers the question.
Natural selection. The trait that is unfavorable to the baby giraffe's survival will cause the death of giraffes with that specific gene that is responsible for a short neck vs a long neck. Natural selection causes traits that help the survival of the species will be carried throughout generations while unfavorable traits will be lost.
The correct answer is that mammals use a closed, double loop , four chambered heart as a circulatory system of the body.
The circulatory system of mammals is closed system that consists of four chambers, two articles and two ventricles. The deoxygenated blood comes into the heart from one loop and the oxygenated blood from other loop from the heart is circulated to the whole body. This is called as double circulation.
