<span>Molecular clock is a scale which uses a technique whereby evolutionary time for different life forms is deduced from the mutation rate of biomolecules. Biomolecular data used for calculations in order to come up with the prehistoric time scale normally uses nucleotide sequences for DNA or amino acid sequences for proteins.
Hence, in order to develop a molecular clock, one would need: a sequence of molecules, the rate at which changes occur in a type of molecule and how much total change has occurred in a type of molecule from different species.</span>
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Because having 3 eyes or 6 does isnt harmful but having 3 arms or legs you could get seriously hurt or lose the limb and bleed out.
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Responding to stimuli / the environment
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The placenta is the temporary association of fetus and maternal tissue. It is meant for nutrition and transport of different substances.
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The placenta is a temporary association of fetal and maternal tissues. The placenta is formed from the trophoblast of the blastula. These trophoblasts form chorionic villi which later forms the placenta. The chorion and allantois also take part in the formation of the placenta. Hence, the human placenta is known as the chorioallantoic placenta. The process of formation of the placenta is known as placentation.
The placenta has several functions but the major function is to provide nutrition to the fetus. The developing fetus gets nutrition from the mother's body by the placenta. The placenta provided with blood vessels which help in the transportation of different substances. It also helps in gas exchange between the mother and baby. Thus it plays a vital role in fetal respiration. The metabolic wastes diffuse through the placenta. Placenta also stores fat, glycogen, which participates in protein metabolism.
