What are some mechanisms of developmental symbiosis?

What are some mechanisms of developmental symbiosis?
Identify an example of symbiosis.
Is your example obligate or facultative?
Which of the 7 developmental questions does this topic involve?
How is the evidence evaluated
Your answer to the above questions should be written as cohesive essay that is 5000-7000 words.

Below are the 7 questions of developmental biology:

Put another way, there are two fundamental questions in developmental biology. How does the fertilized egg give rise to the adult body? And, how does that adult body produce yet another body? These huge questions can be subdivided into several categories of questions scrutinized by developmental biologists:

? The question of differentiation A single cell, the fertilized egg, gives rise to hundreds of different cell types?muscle cells, epidermal cells, neurons, lens cells, lymphocytes, blood cells, fat cells, and so on. This generation of cel- lular diversity is called differentiation . Since every cell of the body (with very few exceptions) contains the same set of genes, how can this identical set of genetic instructions produce different types of cells? How can a single fertil- ized egg cell generate so many different cell types?

? The question of morphogenesis How can the cells in our body organize into functional structures? Our differentiated cells are not randomly distrib- uted. Rather, they are organized into intricate tissues and organs. During development, cells divide, migrate, and die; tissues fold and separate. Our” “fingers are always at the tips of our hands, never in the middle; our eyes are always in our heads, not in our toes or gut. This creation of ordered form is called morphogenesis , and it involves coordinating cell growth, cell migra- tion, and cell death.

? The question of growth If each cell in our face were to undergo just one more cell division, we would be considered horribly malformed. If each cell in our arms underwent just one more round of cell division, we could tie our shoelaces without bending over. How do our cells know when to stop divid- ing? Our arms are generally the same size on both sides of the body. How is cell division so tightly regulated?

? The question of reproduction The sperm and egg are highly specialized cells, and only they can transmit the instructions for making an organism from one generation to the next. How are these germ cells set apart, and what are the instructions in the nucleus and cytoplasm that allow them to form the next generation?

? The question of regeneration Some organisms can regenerate every part of their bodies. Some salamanders regenerate their eyes and their legs, while many reptiles can regenerate their tails. While mammals are generally poor at regeneration, there are some cells in our bodies? stem cells ?that are able to form new structures even in adults. How do stem cells retain this capacity, and can we harness it to cure debilitating diseases?

? The question of environmental integration The development of many (perhaps all) organisms is influenced by cues from the environment that sur- rounds the embryo or larva. The sex of many species of turtles, for instance, depends on the temperature the embryo experiences while in the egg. The formation of the reproductive system in some insects depends on bacteria that are transmitted inside the egg. Moreover, certain chemicals in the environment can disrupt normal development, causing malformations in the adult. How is the development of an organism integrated into the larger context of its habitat?