1, name the part of the reproductive system in which fertilisation happens. 2, what is an embryo
3, where does the embryo develop into a foetus, and then a baby
4, why does the uterus lining start to grow thick and spongy, as an egg cell develops in an ovary
5, what happens to the uterus lining if the egg cell is not fertilised
6, how often does an egg cell leave an ovary, in an adult woman
7, how often does menstruation happen, in an adult woman

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Explanation:

1.fallopian tube

2.an unborn or unhatched offspring in the process of development, in particular a human offspring during the period from approximately the second to the eighth week after fertilization (after which it is usually termed a fetus)

3.First, the zygote becomes a solid ball of cells. Then it becomes a hollow ball of cells called a blastocyst. Inside the uterus, the blastocyst implants in the wall of the uterus, where it develops into an embryo attached to a placenta and surrounded by fluid-filled membranes.

4.Eggs live in ovaries, and the hormones that control your menstrual cycle cause a few eggs to mature every month. When your egg is mature, it means it's ready to be fertilized by a sperm cell. These hormones also make the lining of your uterus thick and spongy, which gets your body ready for pregnancy.

5.The fertilized egg attaches to the lining of the uterus. The placenta then develops. The placenta transfers nutrition and oxygen to the fetus from mother. If the egg does not become fertilized, the lining of the uterus (endometrium) is shed during menstruation.

6.The egg cell travels down the fallopian tube into the uterus. The moment the egg cell leaves the ovary is called ovulation. Once a girl has had her first monthly period, ovulation usually occurs once a month

7.The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens. The rise and fall of levels of hormones during the month control the menstrual cycle.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.