What are three substances that the embryo needs to grow and one substance it needs to excrete

Development of the fetus  to grow

oxygen for respiration. nutrients (food and water)

The developing fetus also needs its waste substances removing. The fetus is protected by the uterus and the amniotic fluid , a liquid contained in a bag called the amnion.

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hey there!

so, when you eat, your teeth chew and grind food into smaller pieces. this is mechanical digestion. then reactions aided by digestive enzymes break down large food molecules into smaller molecules. this is chemical digestion. the two processes change the food into simpler substances that can be used by the body for raw materials and energy.

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tobey

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."