Why multicellular organisms need a ventilation system

Explain why multicellular organisms needs to develop a specialised exchange system and transport system, yet unicellular organisms do not Unicellular organisms have a large surface area to volume that is one cell thick, therefore they have a short diffusion distance and are metabolically inactive. Answered by Deepika K. Need help with Biology? One to one online tuition can be a great way to brush up on your Biology knowledge. Answered by Sophie S.

Answered by Alex L. Answered by Caroline W. The high levels of FSH and LH do not cause hyper-ovulation in women because the ovary becomes insensitive to FSH and the primary follicles have all degenerated or have all been used. Gender is determined by sex chromosomes. The chromosomes in females are XX and those in males are XY. Therefore, eggs carry an X chromosome, and a sperm carries either an X or a Y chromosome, as they separate during the first division of meiosis in males.

Half of the sperm carry X chromosome and half carry a Y chromosome, therefore the chances that the sperm, which fertilizes the egg, is carrying an X chromosome as opposed to a Y chromosome are the same.

Secondary sexual characteristics in males are the growth of pubic and armpit hair, growth of the larynx causing a deepening in voice, and building of muscles. In females, it is the growth of pubic hair, vagina, breasts, pelvis, fat deposits in thighs and buttocks, secretion of fluids in vagina, and the beginning of the menstrual cycle.

Another hormone, HCG, stimulates the maintenance of the corpus luteum and as a result, the production of progesterone. The levels of progesterone rise during pregnancy and inhibit FSH production.

Reducing the amount of embryos allowed to be transferred reduces the chance of having multiple births, which is beneficial as these types of births increase health risks for both the mother and the child, or children. Restricting the number of embryos allowed for transfer to two would prevent almost all multiple, especially triplet, births from occurring.

In older mothers, however, there is a lesser risk of multiple births; therefore, more embryos could be transferred to them. Copulation is the physical contact between the male and female reproductive structures that is needed for the sperms to move from the male to the female but does not necessarily result in fertilization due to the use of a contraceptive or being infertile. Fertilization is the fusion of the male and female nuclei to produce the zygote. Fertilization occurs, resulting in mitotic divisions or cleavage divisions which lead to the formation of a ball of cells called the morula.

The morula reaches the uterus about 4 days after fertilization. Slightly unequal divisions continue until the 7th day, causing a fluid filled spaced in the middle of the morula to form. This is the blastocyst. The outer cells of the blastocyst are called trophoblast and will imbed itself in the endometrium. Outline the process of birth and its hormonal control, including progesterone and oxytocin. Labor, delivery, and afterbirth mark the three stages of birth.

Labor is marked by contractions of the uterus, it is stimulated by a hormone called oxytocin, which is released as levels of progesterone decrease by the pituitary gland. Oxytocin causes dilation of the cervix. The most powerful contractions are during the next stage, delivery. Placenta, along with other fluids and blood come out after the baby.

This placenta that comes out marks the afterbirth. Labor and delivery are controlled by the actions of oxytocin, progesterone, and estrogen. Describe four methods of family planning and contraception. Some people believe it is unethical to abort a baby, that is to kill a fetus that was formed after fertilization.

Other people think it is the right of the woman carrying the fetus to decide what to do with it. Ethical considerations on the use of contraceptives may include: considerations about overpopulation, considerations about the future of the child ren , religious considerations. Some religions teach that it is wrong to interfere with natural processes such as reproduction.

Amniocentesis is where some amniotic fluid from the amniotic sac is drawn by a syringe through the abdomen of the mother. The cells are then grown on a tissue culture to be studied to create a karyotype and are then studied to find out if there are any abnormalties. From Wikibooks, open books for an open world. Category : Book:IB Biology. Namespaces Book Discussion.