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Human Reproduction
Reproductive Biology
| Question | Answer |
|---|---|
| Define reproduction. | The ability to produce individuals (offspring) of the same species. |
| Name the male and female gametes. | Sperm and egg (ovum) respectively |
| State the three main regions of a sperm cell and their function. | 1) Head - contains haploid nucleus and enzyme-filled vesicles for dissolving its way into the egg cell 2) Middle piece - contains many mitochondria to release energy for swimming 3) Tail/flagellum - produces swimming movements |
| List 4 main structures found in an ovum. | 1) Cell surface membrane 2) Layer of jelly (zona pellucida) 3) Haploid nucleus 4) Cytoplasm containing yolk (food store) |
| What is the name of the process which occurs once a month in which an egg cell is released from the ovary? | Ovulation |
| What is conception(fertilization)? | The fusion of male and female gametes. |
| What is the gestation period in humans? | 9 months |
| What is parturition? | Birth |
| This structure carries urine from bladder to urethra | Ureter |
| This structure is the site of sperm storage and maturation | Epididymis |
| What is the function of the sperm duct (vas deferens) ? | Carries sperm from testes to penis by wave-like muscular contractions (peristalsis) |
| What is the function of the scrotum (sacs containing testes outside the body)? | They maintain optimum temperature for sperm below body temp since sperm cannot survive long at 37 degrees C. |
| This structure produces sperm and the hormone testosterone (sex hormone). | Testis |
| This structure carries urine from bladder during urination and sperm during ejaculation. | Urethra |
| What is the function of the prostate gland? | Adds alkaline fluid containing sugars to sperm. |
| What is the function of the seminal vesicle? | Adds fluid containing fructose fructose (for energy), enzymes and proteins to sperm. |
| What is the site of sperm production? | Seminiferous tubules |
| What changes in blood vessels occur which result in an erection? | Dilation of arteries supplying blood to the penis and constriction of veins removing blood from the penis. |
| Name the narrow tube which carries eggs from the ovaries to the uterus; has ciliated cells and is the site of fertilization. | Fallopian tube (oviduct) |
| What is the function of the ovary? | 1) Produce and release eggs 2) Produce hormones oestrogen and progesterone |
| What is the function of the cervix? | Produces mucous before and during ovulation; nourishes and protects sperm allowing them to live 3 to 5 days. Without this mucous, the sperm cannot survive nor be transported to fertilize the eggs. |
| This structure is a muscular sac wall; site of implantation of fertilized egg and embryo; site on which the placenta forms and cavity in which the foetus develops. | Uterus (womb) |
| What is spermatogenesis? | Sperm production |
| Where are the control centres which control spermatogenesis? | Pituitary gland and hypothalamus of the brain. |
| Name the hormone which is secreted by the hypothalamus, is released into the blood and stimulates the anterior lobe of the pituitary gland in spermatogenesis. | GnRH (gonadotrophin releasing hormone) |
| Name the hormone which is secreted by the anterior lobe of the pituitary gland. | ICSH (interstitial cell stimulating hormone) also known as luteinising hormone (LH) |
| What is the role of ICSH (interstitial cell stimulating hormone) in spermatogenesis? | Stimulates the leydig cells that produce testosterone. Testosterone acts on the seminiferous tubules and stimulates sperm production. |
| What is the role of FSH (follicle stimulating hormone) in spermatogenesis? | Stimulates the seminiferous tubules, including the Sertoli cells. They produce sperm in response. |
| What is the role of Sertoli cells? | To nourish sperm |
| What is oogenesis? | Production of ovum |
| What is the difference between the secondary oocyte and the ovum? | Secondary oocyte - the cell released from the ovary which has not yet completed meiosis. Ovum - the name given to the secondary oocyte after it has been fertilized and hence stimulated to complete meiosis II. |
| State 4 effects of oestrogen in the menstrual cycle. | 1) Repair of uterine lining after menstruation 2) Stimulate release of LH (luteinising hormone) 3) Inhibits production of FSH (follicle stimulating hormone) 4) Secondary sexual characteristics at puberty |
| Outline the main processes involving cellular division in oogenesis. | 1) Oogonium divides by mitosis 2) Cell grows into the primary oocyte 3) Primary oocyte undergoes meiosis I to form the first polar body and the secondary oocyte. NB. The cell remains at this stage until fertilization which triggers meiosis II |
| What happens to the secondary oocyte when it becomes fertilized? | Meiosis II occurs which forms the ovum and the second polar body. |
| What happens if the secondary oocyte is not fertilized? | Menstruation occurs and the unfertilized egg is shed along with the lining of the uterus. |
| Outline the main processed involving cellular division in spermatogenesis. | 1) Spermatogonium divide by mitosis to form primary spermatocytes. 2) These undergo meiosis I to form secondary spermatocytes. 3) These divide by meiosis II to form spermatids which develop into sperm cells. |
| What is one major difference between the cells produced at the end of oogenesis and spermatogenesis respectively? | The secondary oocyte does not complete meiosis II until it becomes fertilized. NB. It is still haploid though since the halving of chromosomes occurs in meiosis I. The sperm cell completes meiosis II before fertilization. |
| T or F. Oogenesis in females begins before birth but spermatogenesis in males begins at puberty. | T |
| State 4 functions of the sperm. | 1) Deliver a haploid nucleus with a set of paternal chromosomes to the female gamete and thus restore the diploid number 2) Stimulate meiosis II in the secondary oocyte 3) Increase genetic variation 4) Determine the gender/sex of the next generation |
| State 3 functions of the oocyte. | 1) Provide a haploid nucleus with a set of maternal chromosomes 2) Increase genetic variation 3) Provide energy supply for the developing embryo |
| What is the menstrual cycle? | The changes that occur within the ovary and uterus in human females. A repeat of events normally occurs every 28 days. |
| Step 1 in in the hormonal control of oogenesis and the menstrual cycle. | GnRH is secreted by the hypothalamus and stimulates the anterior pituitary gland to secrete FSH. FSH the travels in the blood to the ovaries. |
| Step 2 in the hormonal control of oogenesis and the menstrual cycle. | FSH molecules fit into receptor sites in the primordial follicles which stimulates the development of several follicles - only 1 will complete development. |
| Step 3 in the hormonal control of oogenesis and the menstrual cycle. | Granulosa cells of the developing follicle produce oestrogen which 1) stimulates the repair and development of the uterus lining and 2) inhibits the secretion of FSH by the anterior pituitary gland. |
| What is the purpose of oestrogen preventing the secretion of FSH. | It is a negative feedback mechanism which is important in preventing further follicles from being stimulated so that only one egg is produced at a time. |
| What happens when oestrogen levels build up to high levels mid-point in the cycle? | It triggers the secretion of LH |
| Step 4 in the hormonal control of oogenesis and the menstrual cycle. | After oestrogen levels have reached a maximum, LH and FSH are released in a surge . LH causes ovulation and stimulates the Graafian follicle to develop into the corpus luteum ('yellow body') |
| What is ovulation? | The release of the secondary oocyte from the Graafian follicle. |
| Describe the structure of an ovulated oocyte. | A cell whose nucleus is at metaphase I of meiosis surrounded by a cell layer known as the zona pellucida and a layer of granulosa cells known as the corona radiata which protects the oocyte up to fertilization. |
| Step 5 in the hormonal control of oogenesis and the menstrual cycle. | The corpus luteum secretes oestrogen and progesterone . Progesterone 1) causes the uterus to maintain its lining and 2) inhibits the release of LH by the anterior pituitary gland. |
| What is the purpose of progesterone preventing the secretion of LH ? | It is a negative feedback mechanism which works along with oestrogen. FSH is also inhibited. |
| Which hormone is responsible for the rise in body temperature of the female after ovulation? | Progesterone |
| Step 6 in the hormonal control of oogenesis and the menstrual cycle. | If fertilization does not occur, the corpus luteum degenerates , levels of oestrogen and progesterone decline, FSH is no longer inhibited and the endometrium breaks down causing menstruation. |
| What is a gonadotrophin? | A hormone which stimulates a gonad (testis or ovary). The two gonadotrophins are follicle stimulating hormone (FSH) and luteinising hormone (LH) |
| Step 1 in the hormonal control of spermatogenesis. | The hypothalamus secretes gonatrophin secreting hormone (GnRH) which stimulates the secretion of LH and FSH. |
| Step 2 in the hormonal control of oogenesis and the menstrual cycle. | FSH stimulates Sertoli cells to complete the development of spermatozoa from spermatids. |
| Step 3 in the hormonal control of oogenesis and the menstrual cycle. | LH stimulates the synthesis of the hormone testosterone by the Leydig cells (interstitial cells) of the testis. NB. LH is also known as interstitial cell stimulating hormone (ICSH). |
| Step 4 in the hormonal control of oogenesis and the menstrual cycle. | Testosterone 1) stimulates growth and development of the germinal epithelial cells (spermatogonia) to form sperm 2) works with FSH to stimulate Sertoli cells and 3) decrease levels of GnRH secretion from hypothalamus (negative feedback). |
| What is the result of testosterone's inhibition of the secretion of GnRH from the hypothalamus? | A decline in the levels of LH and FSH. |
| If sperm production happens too rapidly, the hormone inhibin is released. What is its role? | It reduces the secretion of FSH from the anterior pituitary gland. |
| Define copulation | Sexual intercourse. |
| Define capacitation. | The process of sperm activation while in the female genital tract. Changes occurring include: removal of layer glycoproteins and plasma proteins; loss of cholesterol from sperm head; increased permeability to calcium ions. |
| Give two effects of the increased permeability of the sperm to calcium ions during capacitation. | 1) Increases the beating activity of the sperm tail 2) Promotes of the acrosome reaction |
| Describe what happens in the acrosome reaction. | When sperm reaches secondary oocyte, the acrosome (in the sperm head) ruptures. Hydrolytic (digestive) enzymes such as hyaluronidase and proteases are released rapidly. |
| Define fertilization. | The fusion of the male and female gametes to form a diploid zygote. |
| State 3 differences between the sperm and the secondary oocyte in humans. | Sperm - 60 micrometers - acrosome present - centrioles present etc Secondary oocyte - 140 micrometers - no acrosome - no centrioles etc |
| Define polyspermy. | Fertilization of an ovum by more than one sperm. |
| What processes prevent polyspermy of the ovum ? | Fertilization triggers changes in the oocyte - the cortical reaction. Cortical vesicles are released by exocytosis through the cell surface membrane to lift the zona pellucida and make it impenetrable to other sperm. |
| What is referred to as the male pronucleus? | The nucleus of sperm inside an ovum at the beginning of fertilization (it is enlarged with less tightly coiled chromatin). This is just before it fuses with the female pronucleus to form the diploid zygote. |
| What is referred to as the female pronucleus? | The nucleus of an ovum after the sperm has entered to stimulate the completion of meiosis.This is just before it fuses with the male pronucleus to form the diploid zygote. |
| T or F. After the male and female pronuclei fuse, the zygote undergoes its first mitotic division. | T |
| This is the name for the hollow ball of cells which make up the embryo at the beginning stages of development. | Blastula |
| This is the name for the outer layer of cells of the blastula that later form the placenta. | Trophoblast |
| Describe the key events involved in implantation of the zygote. | 1) Blastocyst embeds into the lining of the endometrium 2) Trophoblast forms extensions (villi) into the endometrium to increase surface area for absorption of nutrients water and oxygen. |
| State the biological principle and method involved in a vasectomy. | Principle : No sperm in semen Method: Each vas deferens is cut and tied so sperm cannot pass from testis to urethra. |
| State the biological principle and method involved in tubal ligation. | Principle: No oocyte in oviduct Method: Oviducts are cut and tied so oocytes cannot pass along oviducts. |
| State the biological principle and method involved in the use of male and female condoms. | Principle: Sperm do not enter vagina during intercourse. Method: Condom is placed over penis or into vagina before intercourse. |
| State the biological principle and method involved in the use of diaphragm/cap. | Principle: Sperm do not enter cervix during intercourse. Method: Diaphragm is placed over the entry to cervix. |
| State the biological principle and method involved in the use of contraceptive pills. | Principle: No ovulation Method: Pills contain one or both ovarian hormones to prevent ovulation. |
| How do contraceptive pills generally work? | The contain synthetic oestrogens and progestins to prevent ovulation. They are taken for 20 days and then given a break for 5 days to allow menstruation to occur. |
| How does the combined pill work? | It contains oestrogen and progestins which act by negative feedback to inhibit secretion of GnRH, FSH and the mid cycle surge of LH. |
| How does the progestin-only ('mini pill') work? | It prevents ovulation similar to the combined pill but also causes thickening of cervical mucus to reduce changes of the sperm entering the uterus. |
| Name the hormone which is secreted as the first sign that fertilization has occurred. | human chorionic gonadotrophin (hCG) |
| What is the role of hCG? | It is similar to LH. It stimulates the corpus luteum to keep secreting oestrogen and progesterone which maintain the endometrium and prevent mentruation. |
| Define implantation. | The process whereby the blastocyst reaches and sinks into the endometrium 3-4 days after fertilization. |
| What is the placenta? | An organ made up of maternal and foetal tissues for the exchange of substances between foetal and maternal blood. It also functions as an endocrine gland. |
| Name the four extra-embryonic membranes which surround the developing foetus. | 1) yolk sac 2) allantois 3) chorion 4) amnion |
| Through which blood vessel does the foetus receive oxygenated blood? | Umbilical vein |
| Through which blood vessel is deoxygenated blood removed from the foetus? | Umbilical arteries (2 of them) |
| Which maternal blood vessel brings oxygenated blood to the placenta? | Uterine artery |
| Which maternal blood vessel brings deoxygenated blood away from the placenta? | Uterine vein |
| How are gases exchanged between maternal and foetal circulation? | O2 is released from the mother's haemoglobin , diffuses across thin barriers and combined with foetus' haemoglobin in its red blood cells. CO2 goes in the opposite direction |
| Why is important that maternal and foetal blood never come in direct contact? | The foetus has a different genotype from the mother. The barrier prevents the mother's immune system frm rejecting the foetus. It also prevents entry of pathogens, proteins etc. It also protects the foetus from the mother's high pressure of blood. |
| Name two methods by which nutrients can move across the placenta. | Facilitated diffusion (e.g. glucose) and active transport (e.g. amino acids) |
| List 5 functions of the placenta. | 1) Gas exchange 2)Provides nutrients 3) Provides antibodies 4) Removal of nitrogenous waste 5) Secretion of hormones (see hCG) etc etc etc |
| List 5 functions of the amnion. | 1) Secretes and contains amniotic fluid which protect the foetus from mechanical shock 2) Isolation from gravity 3) Maintains suitable temperature 4) Waste receptacle 5) Helps foetal muscle development |
| State two preconceptual care actions which can be taken by prospective mothers. | 1) Test for/ obtain immunity against rubella virus - which can have detrimental effects on a growing foetal 2) Take folic acid supplements - which aid in proper development of the foetus' neural tube and prevents spina bifida |
| Comment on the recommended energy intake (provided by carbohydrates, fats and proteins) for a pregnant woman. | Energy intake should not increase until the last three months of pregnancy and then by about 800 kJ a day. Proper, balanced nutrition is always recommended. |
| Comment on the recommened protein intake of a pregnant woman. | Additional 6g a day throughout pregnancy for the growth of tissues and muslce in uterus and foetus. |
| Comment on the recommended iron intake for pregnant women. | Women at risk of iron-deficiency anaemia should take a supplement of iron with vitamin C. |
| State two possible effects of alcohol intake during pregnancy. | Alcohol can cross the placenta and cause : 1) Premature delivery 2) Foetal alcohol syndrome (FAS) |
| List the effects of foetal alcohol syndrome. | 1) Stunted brain development 2) Abnormal limbs and heart defects 3) Increased risk of cleft palate 4) Possible learning diffulties throughout life |
| What is the effect of carbon monoxide from cigarette smoke on a developing foetus? | CO combines with haemoglobin in the foetus' red blood cells. This reduces the oxygen carrying capacity of both maternal and foetal blood. |
| What is the effect of nicotine from cigarette smoke on a developing foetus? | It reduces the diameter of the foetus' blood vessels thus reducing blood flow. It also affects the development of the nervous system and can reduced the size of a baby's lungs. |
| List the three phases of the ovarian cycle. | 1) Follicular phase 2) Ovulation phase 3) Luteal phase |
| List the three phases of the uterine cycle. | 1) Menstrual phase 2) Proliferative phase 3) Secretory phase |
| Describe what happens during the follicular phase of the ovarian cycle. | Development of primary follicle starts secretion of oestadiol; one dominant follicle develops into Graafian follicle |
| Describe what happens during the ovulation of the ovarian cycle. | Release of secondary oocyte |
| Describe what happens during the luteal phase of the ovarian cycle. | Corpus luteum secretes progesterone, reduction in oestrogen secretion, corpus luteum degenerates, less progesterone secreted. |
| What happens during the menstrual phase of the uterine cycle? | Menstruation (period) |
| What happens during the proliferative phase of the uterine cycle? | Repair and growth of the endometrium |
| What happens during the secretory phase of the uterine cycle? | Glandular activity in endometrium maintains its thickness; decrease in progesterone concentration leads to breakdown of endometrium |
| T or F. The changes which occur within the ovary and the uterus are collectively known as the menstrual cycle. | T |
| The changes that occur in the ovary are known as the | ovarian cycle |
| The changes that occur in the uterus are known as the | uterine cycle |
| Describe the events occurring in the hypothalamus and anterior pituitary gland during days 1-5 of the menstrual cycle. | Hypothalamus: secretion of GnRH starts Anterior pituitary gland: secretion of FSH and LH starts |
| Describe the events occurring in the hypothalamus and anterior pituitary gland during days 5-13 of the menstrual cycle. | Hypothalamus: oestradiol inhibits secretion of GnRH Anterior pituitary gland: FSH secreted, but gradually inhibited by low concentrations of oestradiol surge of LH secretion |
| Describe the events occurring in the hypothalamus and anterior pituitary gland during day 14 of the menstrual cycle. | Hypothalamus: secretion of GnRH Anterior pituitary gland: FSH and LH secreted |
| Describe the events occurring in the hypothalamus and anterior pituitary gland during days 15-18 of the menstrual cycle. | Hypothalamus: progesterone inhibits GnRH secretion; decrease in GnRH secretion Anterior pituitary gland: concentration of LH gradually decreases ; oestradiol decreases; progesterone inhibits FSH and LH secretion |
| Describe the events occurring in the hypothalamus and anterior pituitary gland during days 18-24 of the menstrual cycle. | Secretion of FSH and LH not inhibited |
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CAPE Biology Unit 1
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