I have got this assignment that needs to be in tomorrow...
Explain and analyse, with the aid of diagrams, the role of hormones in human ovulation and sperm production and compare the means by which cell division takes place to produce gametes and non-gamete cells.
I have explained (don't know about analysed) with aid of diagrams the hormones in human ovulation and sperm production but I don't undertsand the next bit - somebody PLEASE help me! LOL
Whoa freaky i've just come in, made a coffee and sat down on the settee, noticing my son had left his GCSE Biology on the settee.....tutting thinking well I suppose i'll put this away shall I? LOL
Thanks so much Bev... I rang my dad and he was confused too! LOL - I think what you have said is right and I need to compare mitosis (non-gamete cells) with mieosis (gamete cells)?
OMG there are some real braniacs on here did'nt have a clue what you were talking about you pair of know it alls lol now you make me feel stupid, :~D :~D 98) 98) 98)
I'm really scared I am doing it wrong. This is what I have done so far...
Explain and analyse, with the aid of diagrams, the role of hormones in human ovulation and sperm production and compare the means by which cell division takes place to produce gametes and non-gamete cells.
In this assignment I intend to explain and analyse, with the aid of diagrams, the role of hormones in human ovulation and sperm production and compare the means by which cell division takes place to produce gametes and non-gamete cells. Firstly I will be explaining about the menstrual cycle and the role of hormones in human ovulation and sperm production. I will then go on to compare the means by which cell division takes place to produce gametes and non-gamete cells.
Ovulation is part of the menstrual cycle which goes through a regular series of changes. This takes part in female reproductive system between the ages of 10 and 17. Each month, an egg (ovum) is released from one of the ovaries and makes its way along the fallopian tube towards the uterus. It takes about seven days for the ovum to get from the ovaries to the uterus. This happens because it prepares the body for fertilisation and pregnancy.
The menstrual cycle on average takes 28 days to complete and is controlled by hormones from the hypothalamus, pituitary gland and ovaries. Four stages occurs to the uterus lining during the menstrual cycle: Menstruation – The uterus lining comes away from the wall and is removed from the body in a flow of blood. Repair Phase – The uterus wall builds up a new lining. An egg completes its development and is released about day 14 (ovulation). Receptive Phase – The uterus is ready to be able to receive a fertilized egg. If the egg has been fertilized, it will embed itself into the lining of uterus wall and pregnancy will begin. Pre-menstrual Phase – The lining of the uterus will start to break down again if the egg is not fertilized.
The “menstrual clock†is controlled by the hypothalamus which can be found in the brain. Information is received about conditions in all parts of the body both the blood as it flows through the brain and the nervous system. The hypothalamus releases hormones when the conditions are right. F.S.H. (Follicle Stimulating Hormones) is synthesized and secreted by gonadotropes in the anterior pituitary gland. (http://en.wikipedia.org/wiki/Follicle-stimulating_hormone) F.S.H. operates with L.H (Luteinising hormone) to encourage the development of the small follicles in the ovaries. The production of the ovarian hormone oestrogen is also stimulated by the Follicle Stimulating Hormones. F.S.H. works with L.H. to regulate the activity of the sex organs in men and women. The Liteinising Hormone (L.H) also comes from the pituitary gland and stimulates ovulation and the development of the Corpus Luteum. Oestrogen causes the lining of the uterus to thicken. It also helps stimulate the growth of the egg within the follicle. Oestrogen is mainly responsible for the changes which occur in young women around puberty. Progesterone is produced mainly by the corpus luteum in the ovary following ovulation. It prepares the lining of the uterus to accept a fertilised egg so that the egg can develop. Progesterone also prevents the release of any further eggs until the pregnancy is terminated.
There are two phases which occur in the ovary and in the uterus. The Follicular Phase and the Luteal Phase. In the ovary, the follicular phase is when during the first 14 days of the cycle it FSH and LH initiates the growth and maturation of an ovum and the secretion of oestrogen by the ovary. The LH in the follicle causes the thecal cells to secrete testosterone. Enzymes are activated by the FSH in the granular cells which change it to oestrogen. During the follicular phase, the level of oestrogen rises in the blood supply. There is a positive feedback effect by the oestrogen that there is a surge in LH and FSH production by anterior pituitary. This occurs on day 14 and is the reason for ovulation. High concentration levels of LH is responsible for the enzymes splitting the ovary wall causing ovulation to happen. The Luteal Phase is the next event after ovulation. The Corpus Luteum begins to secrete the hormone progesterone as well as oestrogen. An opposite effect (negative feedback) occurs on the hypothalamus by the presence in the blood stream of oestrogen and progesterone to that of oestrogen alone. Further secretion of releasing cause a drastic drop of levels of LH and FSH. Whilst the corpus luteum continues to secrete progesterone, no further follicular development is possible. The corpus lutem degenerates about the 10th day after ovulation if the egg is not fertilised and the cycle may be repeated.
Events in the uterus during the follicular phase cause the levels of oestrogen to rise which stimulates the layer of smooth muscle (myometrium) to develop. There is also the growth of the glandular epithelial lining of the uterus (entometrium) for it to be prepared to receive a developing embryo. In the luteal phase (after ovulation), the glandular epithelium becomes enlarged by the progesterone for it to synthesise and store the food glycogen. During the last few days of the 28-day cycle, if pregnancy does not occur the levels of progesterone and oestrogen cause the myometrium and entometrium to shrink. As a result of this shrinkage, a woman loses up to 50cm3 of blood in the menstrual cycle. Female sex hormones promote the development of female secondary sexual characteristics including breasts and body hair.
In sperm production, the hormones from the pituitary are also controlled by the hypothalamus. The pituitary gland releases both the L.H and F.S.H hormones into the bloodstream. The levels of both L.H and F.S.H rise during the early stages of puberty which makes it possible for the testes to grow and mature. The LH helps the Leydig cells in the testis make the male sex hormone testosterone. Testosterone is responsible for the development of male secondary sex characteristics and functioning of the male reproductive organs. The hormone FSH from the pituitary gland with the testosterone acts on the seminiferous tubules in the testes to stimulate the production of sperm.
Cell division is the process by which a cell, called the parent cell, divides into two cells, called daughter cells. It also enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by cell division from gametes. And after growth, cell division allows for continual renewal and repair of the organism.
Mitosis is a process of cell division which produces new cells for replacement and growth of damaged or worn-out body cells. There is a production of two daughter cells from a single parent cell which make daughter cells identical to the parent cells. Before a cell divides, its chromosomes are copied exactly. This process is called replication. There are the same number (46) of chromosomes as the parent cell.
Looking at the diagram below, you can see that there is a series of division stages – prophase, metaphase, anaphase and telophase. When the cells grow and prepare to divide by replicating their DNA, this is known as interphase. Interphase comes before the division stages. The prophase phase is where the chromosomes are getting shorter and fatter due to them condensing. Centrioles (protein) begin to move to opposite ends of the cell. A network of protein fibres are formed across it – this is called the spindle. The chromosomes lie free in the cytoplasm when the nuclear membrane breaks down – the nuclear envelope disappears. The metaphase is where in the middle of the cell, the chromosomes which contain two chromatids line up and become attached to the spindle by the centromere. The anaphase occurs when the spindles divide as the centromeres are attached to the chromatids. Chromatids are pulled to opposite poles, centromere first as the spindles contract. The telophase is where the chromatids arrive at the opposite poles on the spindle. They are then called chromosomes again as they uncoil and become long and thin. Around each group of the chromosomes, a nuclear membrane forms so there are now two nuclei. Two daughter cells which are identical to the original cells occur after the cytoplasm divides. The daughter cell will then begin mitosis again by starting at the interphase part of the cycle.
Mieosis produces half the number of chromosomes (23) that are in the parent cells. This type of cell division is essential for sexual reproduction as it only takes place in the ovaries or testes for it to produce gametes. Gametes have the haploid number of chromosomes (23) as there’s only one copy of each chromosome. In the females, the gametes are care ova (egg cells) and in the males they are the sperm cells. A zygote is formed when both egg and sperm cells join at fertilisation. This then divides and develops into a new organism. As the haploid egg and haploid sperm joins fuses together, it produces a cell with the normal diploid number of chromosomes. This is because half the chromosomes come from the father (the sperm) and half are from the mother (the egg).
In mitosis there are two divisions which are known as meiosis 1 and 2. Both divisions have four stages which are shown in the following diagram. Just like mitosis, these stages are called the prophase, metaphase, anaphase and telophase. The homologous pairs of chromosomes are separated in meiosis 1. This means that in the daughter cells there are only half the number of chromosomes. Meiosis 2 works like mitosis as it splits the pairs of chromatids that make up each chromosome. Meiosis ends up in four haploid cells (gametes) that are genetically different from each other.
When comparing both mitosis and meiosis, you can see that the purpose of mitosis is to make daughter cells identical to the parent cells - eg during growth and repair. Meiosis on the other hand is to produce sex cells (gametes). Mitosis takes place in all the cells apart from gametes whereas in meiosis, this cell division takes place in the reproductive organs (ovaries and testes). In mitosis, two daughter cells are produced however in meiosis, four gametes are produced. The number of chromosomes are different too as in mitosis there is the same number as in the parent cells but there are only half as many as in the parent cells in meiosis. The original number of chromosomes is restored when two gametes fuse together to form a zygote. The parent and daughter cells in mitosis do not differ genetically as all the genetic material is copied exactly. In meiosis, they contain a mixture of chromosomes from two parent gametes. This means that they cannot be identical. Lastly there is a variation between daughter cells between mitosis and meiosis. There are no variations between daughter cells for mitosis as they are clones of each other however in meiosis they are genetically different from each other because during the division, the chromosomes get shuffled up.
I have nearly finished my essay - done 1,850 words - How can I analyse the 1st bit about hormones. I am rubbish at analysing things. Do you think that the essay is ok?
Your essay is great, yes the question is asking for the comparison of meiosis and mitosis so you've got it right!
I'm a biochemist so I should really be able to remember all this stuff (remember doing it at A level) but alas my memory is bad now! So I quite enjoyed the revision down to reading your essay ;D
I dont think you have anything to worry about
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
- somebody PLEASE help me! LOL
