life cycle

mitosis

3.12 Amniotic fluid

understand how the developing embryo is protected by amniotic fluid
-in the uterus space there is a fluid called the amniotic fluid.
-the function is that it can protect the embryo- the fluid (largely water) cannot be compressed.
-when you try to squeeze the fluid it absorbs the pressure.
-any blows or force applied to the uterus wall, the amniotic fluid will absorb this pressure and prevent damage to the unborn child.
-another function is floating- this is because the bones cannot support the child yet as they are not calcified (hard) at that time.

if you want to experience the effect of absorbing the pressure
- if you are standing in the swimming pool and you try to kick out- your leg doesn't move very quickly and it is difficult to generate great force- example of how the fluid absorbs the force.

3.11 Placenta

describe the role of the placenta in the nutrition of the developing embryo.
-on one side of the wall of the uterus there is a placenta.
-when the child is in the uterus it is in a water filled environment (amniotic fluid) the child cannot digest, breathe or excrete.
-growing out of the developing embryo there is a placental structure (umbilical cord)
-the blood vessels inside the placenta are the child's blood vessels (arteries and veins)
-the placenta grows into the wall of the uterus.
-the mother continues to eat during pregnancy and in the bloodstream of the mother there will be glucose, amino acids, fats- these will travel through her bloodstream and into the wall of the uterus- these molecules will cross into the child's blood into the placenta- which are then taken into the child.
-the placenta has a large surface area- barrier from mother and child's blood is very thin.
-the child also produces molecules that exchanges into the maternal blood like carbon dioxide and urea.

3.9b Female Reproductive System

recall the structure of and function of the female reproductive system.
-ovary-meiosis occurs, production of eggs (female gametes)
-oviducts- carries the egg to the uterus. also the location where fertilisation takes place. (sperm cell meets egg cell)
-uterus- structure in the center, it is made out of muscle, stretches to accommodate pregnancy and it contracts during birth.
-lining of the uterus- develops the fertilized egg into the embryo and then the child. you can also see the development of the placenta here.
-uterus space- is where the sperm and egg cells move. where the embryo develops into the unborn child.
-cervix- entrance to the uterus. where sperm cells enter will make their way to the oviducts.
-vagina- collects sperm cells and allow them to pass through the cervix into the uterus.  

3.9a Male Reproductive System

recall the structure and the function of the male reproductive system
-bladder- stores urine.
-testis- there is 2 of them- carries out the process of meiosis that produces the gamete called a sperm cell.
-epididymis- stores sperm cells.
-vas deferens- carries the sperm cell to the penis during sexual stimulation. the tube pulses making the walls contract pushing the sperm cells into the penis.
-prostate- adds about 20-30% of the volume of the semen. it contains sugar and is alkali.
-seminal vesicles- produce sugar based secretion, also alkali. 70% of the semen in which the sperm cell can travel.

-when sperm cells are combined with the prostate and the seminal vesicle secretions we have semen- carried forward and down to the urethra (common tube which joins the left and right testes and the left and right vas deferens)

-urethra- takes semen down the penis and the exit for the urine which is stored in the bladder.
-penis- carries sperm cell into the vagina during sexual intercourse.

3.24c Mitosis 3

understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.

INTERPHASE

-in a microscope we would see the nucleus as a spherical structure- you would not see the chromosomes.

-DNA replication occurs.

PROPHASE

- the first sign which shows that a cell is entering the process of mitosis and cell division is when we see the break down of the nucleus membrane.

-the chromosomes become visible as a pair of chromatids- in pairs.

LATE PROPHASE

-the nucleus is gone.

-network of protein molecule- called spindle (each one is a fibre)- extend from pole of the cell to the other.

-the chromosomes pair (the pair of chromatids) will move towards the spindle and will join onto one of the spindle fibres.

METAPHASE

-pair of chromatids are attached to the spindle fibre.

-the chromosomes are in the middle- arranged across the equator of the cell.

ANAPHASE

-the spindle fibre shortens- the pair of chromatids are moving apart and they move to the pole of the cells.

-separation of the pair of the chromatids.

TELOPHASE

-end of mitosis.

-the nucleus begins to reform around the chromosomes at either end of the cell- will be the new nucleus of the new cell.

-the formation of 2 nuclei at opposite ends of the cell.

CYTOKINESIS

-cell split into two- not part of mitosis.

-cell begins to move inwards to divide cytoplasm in half- membrane fuse across equator to form the two cells.

-the new cells each contain a chromosome which is the same as the parental cell.

MITOSIS

P- appear

M-middle

A- apart

T- two