вторник, 22 октября 2019 г.

Sexual reproduction


Vocabulary list
zygote - a single cell that develops into a person or animal, formed by the joining together of a male and a female gamete (= a cell that is provided by each parent)
blastula - a hollow sphere of cells
 
Animals that reproduce sexually begin life as a zygote. The zygote undergoes a series of divisions to form a blastula, a hollow ball of cells. The blastula folds in on itself, forming a single opening called a blastopore. The blastopore leads to a central tube that becomes the digestive tract. A protostome is an animal whose mouth is formed from the blastopore. A deuterstome is an animal whose anus is formed from the blastopore. The anus is the opening through which wastes leave the digestive tract.
During early development, the cells of most animal embryos differentiate into three layers, called germ layers. The endoderm is the innermost germ layer. The mesoderm is the middle germ layer. And the ectoderm is the outermost germ layer. 
  
Answer the questions:
What is the first stage  of a living being that starts his life as a result of sexual activity?
How is digestive tract formed?
Can you name three germ layers?

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