Reproduction and Growth.docx

**[Reproduction and Growth]** **[Plants]** Sexual reproduction is reproduction involving the fertilisation of gametes. Asexual reproduction is reproduction not involving gametes. Sexual reproduction in plants involves the production of flowers (1) [Functions of flower parts\ ]*Sepals\ *Enclose...

**[Reproduction and Growth]** **[Plants]** Sexual reproduction is reproduction involving the fertilisation of gametes. Asexual reproduction is reproduction not involving gametes. Sexual reproduction in plants involves the production of flowers (1) [Functions of flower parts\ ]*Sepals\ *Enclose and protect the flower before it opens and will sometimes close over the flower at night *Petals\ *- Most obvious part of the flower\ - Large, variously shaped and bright to attract pollinators\ - Produce scent to attract insects *Stamens\ *- Male part of the plant and consists of two parts\ - Anther: Produces pollen which forms male gametes\ - Filament: A long thin tube that holds the anther in place where it can most effectively carry out its job *Carpel\ *- Female part of the plant and consists of three parts\ - Stigma: Catches pollen\ - Style: Connects the stigma to the ovary and holds it in a suitable position to collect the pollen\ - Ovary: Has one or more ovules which contain the embryo sac. Egg sac contains the egg cell and two polar nuclei which will form the endosperm *Receptacle\ *- Thickened part of the pedicel from which the flower parts grow *Nectary\ *- Located at the base of the petals and produces nectar (a sweet sugary solution) [Development of gametes] [Female\ ]- Formed in the ovule contained in the ovary from a diploid megaspore mother cell when it divides by meiosis to form four haploid cells called megaspores\ - Called megaspores because they are much bigger than the pollen grain\ - Three of these haploid cells degenerate, leaving one\ - The surviving megaspore divides by mitosis three times, forming a total of 8 nuclei\ - Three of the surviving nuclei consist of two polar nuclei and an egg cell\ - This collection of nuclei is called the embryo sac [Male\ ]- Inside the anther are hollow tubes lined with diploid microspore mother cells\ - Each of these cells divide by meiosis, producing four haploid microspores. Each of these microspores then divide by mitosis to produce two nuclei\ - One of these is called the tube nucleus and its job is to control the growth of the pollen tube from the stigma, through the style to the ovary, and then to the micropyle of the ovule\ - The other nucleus is called the generative nucleus and it will divide by mitosis as it passes down the pollen tube to form male gametes\ - The pollen grain matures, forming a tough layer on the outside called the exine [Pollination\ ]Pollination is the transfer of pollen from an anther to a stigma. There are two types of pollination:\ - Self-pollination: Occurs when the anther and stigma are on the same plant. This leads to less variation and a greater chance of harmful variants occurring more often.\ - Cross-pollination: Occurs when the anthers and stigma are on different plants. [Methods of Cross-Pollination] *Insect Pollination\ *Bees visit the flower to collect nectar and pollen to feed their young, and as they do so, they become covered in pollen. As they fly from flower to flower, they carry pollen with them\ *Wind Pollination\ *Plants like wheat and barley produce copious amounts of very light pollen which drifts away on the slightest breeze [Fertilisation] \- This is the fusion of the male gamete with the female gamete to form a diploid zygote\ - Once the pollen grain lands on the stigma it produces a pollen tube, which grows down the style to the ovule\ - As the pollen tube grows down, the generative nucleus (n) divides by mitosis to form two sperm nuclei (male gametes) (n). The tube is guided by chemotropism and by the tube nucleus which dies when the tube enters the ovule by the micropyle\ - One male gamete fuses with the egg cell to form a diploid zygote, while the other male gamete fuses with the two polar nuclei to form a triploid endosperm nucleus. This is double fertilisation [Seed Formation\ ]- After fertilisation, the ovule starts to swell and the ovule wall begins to toughen up because it is going to form the seed coat(testa)\ - The zygote forms the seed embryo\ - The triploid endosperm nucleus divides rapidly to form a food storage tissue\ - The ovule develops into the seed\ - The integuments (outer wall of ovule) thicken and toughen to form the testa\ - When the seed is fully formed, it dries out and becomes dormant [Seed Structure and Formation\ ]- Embryo: Part of the seed that will develop into the new plant\ **- Testa: A tough and hard seed coat which protects the seed before germination.\ - Radicle: First part of the new plant to emerge from the seed, develops into the root\ - Plumule: Emerges soon after the radicle, develops into the shoot\ - Cotyledons: These are seed leaves which are formed by some of the embryo cells. These contain food reserves which are used in the early stage of germination. Plants can either have one cotyledon (monocot) or two cotyledons (dicot). They secrete enzymes which digest endosperm food, absorb it, and pass it on to the developing embryo** **In monocots, such as maize and wheat, food required by the developing embryo is stored in the endosperm. These are endospermic seeds.** **In dicots, such as the broad bean, the food is stored in seed leaves called the cotyledons. These are non-endospermic seeds.** **[Fruit Formation\ ]- The function of fruit is to protect the seed and allow for seed dispersal.\ - Varieties of seedless fruit have been developed for the consumer market e.g., watermelons. Seedless fruit is produced in one of two ways:\ a. By genetic selection of plants that produce very few seeds which are then propagated asexually\ b. Using plant hormones, to induce fruiting, without fertilisation e.g., Auxins** **[Seed Dispersal\ ]Dispersal is the carrying of fruit or seeds as far away as possible from the parent plant to ensure survival and minimise the chance of overcrowding and competition.** ***Animal Dispersal\ *- Fruit containing the seed is eaten by an animal and pass through its intestine. The seed will be attacked by the animal's digestive enzymes. Some plants need this to happen before they can germinate. For example. Tomato seeds and apple seeds** ***Wind Dispersal\ *- Seeds need to be light and have a large surface area to allow the wind to catch and carry them a long distance. For example, sycamore parachutes and dandelion parachutes** ***Self-dispersal\ *- When a pea pod dries in the sun, lines of weakness appear and the pod curls back and splits, causing the seeds to spring out. For example, Gorse** ***Water-dispersal\ *- Seeds contain pockets of air to keep them afloat to allow for dispersal over large distance. For example, yellow water lily** **[Dormancy]\ Dormancy is a period of greatly reduced growth or metabolism even conditions are suitable for germination.** ***Advantages of Dormancy\ *- Allows the plant to avoid adverse conditions which could damage or kill new growth\ - Gives the seeds more time to disperse and so reduces competition\ - Gives embryos time to mature before conditions improve** **[Dormancy in Agriculture and Horticulture\ ]*Breaking Dormancy\ *- Many plants maintain dormancy by having a waterproof Testa which prevents water entering the seed. Water can be added by soaking the Testa, breaking the seed coat by abrasion, or cracking the Testa\ -Soaking the seeds in chemicals to wash out inhibitors\ - Applying plant hormones such as gibberellins to the seeds** ***Using Dormancy\ *- Seeds can be kept at optimum storage conditions to allow a larger percentage of the seeds to survive and germinate\ - Maximising the growth season for the crop by using the optimum time of year to sow the seeds** **[Germination]** **Germination is when the embryo or seed begins to grow.** **[Requirements for germination\ ]- Water: Needed as a solvent to transport materials around the plant. Acts as a medium for plant hormones and enzymes to work\ - Oxygen: Used in aerobic respiration to provide the plant with energy to carry out its normal life functions\ - Suitable temperature: Needed for enzymes to work\ - Food: Food reserve in the seed must be digested and used to provide energy and the materials to make new plant tissues** **[Stages in Germination\ ]- The radicle emerges from the seeds and grows downwards forming the root\ - The plumule grows upwards forming the shoot. The plant continues to lose weight\ - The leaves break the surface, and the seedling begins to photosynthesise and produce glucose to feed itself and begin to form new tissue\ - The plant begins to gain weight\ - If the seed stays below the ground it is called hypogeal germination. If the seed is carried above the ground, it is called epigeal germination** **[Asexual Reproduction]** **Asexual reproduction does not involve gametes; therefore the offspring are genetically identical to the parents. Cloning plants is referred to as vegetative propagation.** **[Natural Propagation\ ]*Stem Tubers e.g., potatoes\ *- Tubers are swollen tips of underground stems\ - They have axillary buds that produce new shoots and roots using the stored food in the tuber\ - The parent tuber eventually dies away** ***Root Tubers e.g., sweet potatoes\ *- Swollen areas of lateral roots that store food and act as perennating organs, allowing the plant to survive from year to year\ - Perennating is the ability of a plant to survive from one germinating season to the next** ***Bulbs e.g., daffodils\ *- An underground swollen bud that can survive winter beneath soil until the following year\ - Have a small stem bearing a terminal bud and axillary buds enclosed in the bases of leaves swollen with food reserves\ - The axillary buds can grow, using some of the stored food and form foliage leaves and adventitious roots to form independent plants that become detached from the parent** ***Plantlets e.g., strawberry plants\ *- Miniature plants form along the edge of the leaf and fall off\ - Have miniature roots which grow into the ground and the new plant quickly becomes established\ - The strawberry plant produce modified stems called runners which grow over the surface of the ground. These runners have plantlets at the end, when these touch the ground, roots that are usually already present grow into the ground\ - When the plantlet is attached to the parent plant, it can receive nourishment which gives it a better chance of becoming established\ - When the plant is established, the runner withers and the new plant becomes independent** **[Artificial Propagation\ ]*Cuttings e.g., geranium\ *- Part of the shoot is removed and placed in soil or water to form roots\ - Rooting powder may be used to promote rapid root development** ***Layering e.g., blackberry\ *- A cut shoot is pegged into soil and develops into a new plant\ - After approximately one-year, adventitious roots grow and are cut off from parent plant** *Grafting e.g., apples\ ***- A shoot twig (scion) is removed and taped into the root stock\ - Both cambium layers unite to form one plant** ***Micropropagation e.g., bananas\ *- Individual cells i.e., stem, root, or leaf, can be removed from a plant and then grown in tissue culture\ - This is useful in the production of houseplants and commercial crops** **[Mandatory Practical -- Investigate the effect of water, oxygen and temperature on germination\ ]- Place cotton wool in each of four test tubes and label A, B, C and D\ - Place 10-12 seeds on top of the cotton wool in each of the test tubes\ - Set up each of the test tubes as follows:\ A: Leave the cotton wool dry (*without water*)\ B: Moisten the cotton wool and place the test tube in the refrigerator (*without the correct temperature*)\ C: Cover the seeds and cotton wool with a layer of cool boiled water. Pour a thin layer of oil over the water (*without oxygen*)\ D: Moisten the cotton wool (*water + oxygen + correct temperature*)\ - Place test tubes A, C and D in a warm room and leave for 3 -- 4 days.\ - Record which seeds germinated.** **Tube C (no oxygen), Tube A (no water) and Tube B (wrong temperature), will shoe no germination.\ Tube D (Water, oxygen, and correct temperature) will show germination as roots and shoots are visible** **[Mandatory Practical -- Use starch agar plates to show digestive activity during germination\ ]- Soak pea seeds overnight to soften the testa and initiate germination\ - Remove testa from all seeds and then boil half of these to kill the embryo and denature their enzymes\ - Split all the seeds in half and keep the half with the embryo attached\ - Wash with sterilising fluid to kill microorganisms on their surface\ - Place the dead seeds, inner surface down, on one starch agar plate\ - Place the living seeds, flat surface down, on one starch agar plate\ - Cover and leave the seeds to incubate at 20^o^C for two days\ - Remove the seeds and pour iodine solution over both plates** **- Under germinating (living) seeds, the agar stays brown. This shows the starch has been broken down, therefore enzyme action has taken place. The rest of the plate goes blue, showing that no digestion has taken place here\ - Under the dead seeds (control), the agar goes blue, showing that the starch has not been broken down and there has been no enzyme action** **\ ** **[Human Reproduction]** [Male Anatomy and Functions] (2) \- Sperm: The male gamete and can survive for up to five days\ - Epididymis: A tubular structure on the outside of each testis which stores immature sperm until ejaculation\ - Sperm duct (Vas deferens): Sperm that leave the epididymis during ejaculation is passed along the sperm duct by peristalsis to the urethra\ Seminal Vesicles: Add sugar solution to sperm in the sperm duct to feed them on their journey to the fallopian tube to fertilise the egg. Seminal fluid makes up 60% of sperm\ - Semen: A milky white sticky liquid of sperm and fluids from the seminal vesicles, the prostate gland, and the Cowper's gland\ - Cowper's Gland: Adds a thick and slippery fluid to the penis for lubrication during intercourse. Flushes the urethra before sperm arrives\ - Penis: Made of erectile tissue. When the male becomes sexually excited, blood vessels leaving the penis constrict, causing the penis to engorge with blood and become erect. After stimulation, ejaculation occurs and the penis deposits sperm around the opening of a female's cervix to allow it to enter the uterus as quickly as possible [Female Anatomy and Functions] (3) \- Ovaries: One ovary releases an egg every 28 days on average. The egg is the female gamete and survives for about two days\ - Oestrogen and progesterone: Hormones produced by the ovaries from puberty until menopause\ - Fallopian tubes: Lined with cilia with beat in unison to waft the egg towards the uterus. Fertilisation occurs in the top third of the fallopian tube\ - Uterus: A muscular sac which holds and nourishes the developing embryo\ - Endometrium: The innermost lining of the uterus and is the site of implantation and placenta formation. Thickens in preparation for the arrival of a fertilised egg. If a fertilised egg does not arrive, the lining is shed through the cervix and vagina in menstruation (a period)\ - Menstruation: A woman will lose approximately 30 to 90 ml of fluid over three to seven days\ - Cervix: Neck of the womb, blocked by a mucus plug for most of the month. Around the time of ovulation, the mucus thins out to allow sperm to swim through and enter the uterus\ - Vagina: During copulation, the vagina stimulates the penis to ejaculate and ensures sperm is deposited against the cervix. Lubricated with acidic mucus to prevent the growth of pathogenic microorganisms\ - Vulva: Outer lips of the vagina *\ *[Meiosis in the Production of sperm and eggs] *Sperm\ *The sperm-producing cells (diploid) in the tubules of the testes divide by **meiosis** and produce sperm(haploid). \- Head: Contains the haploid nucleus consisting of one set of chromosomes. The acrosome is a bag of digestive chemicals is to help penetrate the egg\ - Midpiece: Contains mitochondria which supply the energy necessary to complete the journey from the vagina to the top of the fallopian tube\ - Tail: Spins and produces the force necessary to propel the sperm and make them motile *Egg\ *After puberty, approximately 20 eggs are produced by meiosis each month. Usually only one continues to grow and the rest die off. After meiosis, a haploid egg is surrounded by a Graafian follicle. An egg can live for 24 - 48 hours (5) \- Haploid nucleus\ - Cytoplasm: Contains mitochondria and cell organelles\ - Non-cellular layer: The area where sperm burrows its way into the egg [Sexual Characteristics] \- Primary sexual characteristics: Any body structures directly involved with reproduction e.g., penis, vagina, uterus, testes\ - Secondary sexual characteristics: Features, both physical and behavioural, that develop at puberty under the influence of sex hormones and further distinguish males from females\ - Males: Main hormone involved is testosterone. Features that develop include a deepening of the voice, broadening of the shoulders, increased muscle mass, and the growth of facial, pubic, and underarm hair\ - Females: Main hormone involved is oestrogen. Features include enlargement of the breasts, widening of the hips, development of pubic and underarm hair and thickening of the layer of subcutaneous fat giving a more rounded figure. Progesterone keeps the endometrium built up and stops the uterus from contracting [The Menstrual Cycle] The menstrual cycle involves changes in the ovaries and uterus that makes pregnancy possible. The cycle starts between the ages of nine and fifteen at puberty. The first period, which marks the beginning of a woman's reproductive life, is called the menarche, and she will continue having periods until the menopause in her late forties or early fifties. [Process of Menstruation\ ]- Day one of the cycle is when menstruation occurs and lasts for four or five days\ - Day five marks the beginning of the build-up of the endometrium in preparation for the possible arrival of a fertilised egg during the fertile period. The Graafian follicle produces oestrogen which travels through the blood stream from the ovary to the uterus\ - The fertile period is when fertilisation is possible. Days 9 to 15 are the most fertile\ - Day 14 is when ovulation occurs. The egg is released when the Graafian follicle bursts. Follicle- stimulating hormone (FSH) and luteinising hormone (LH) concentrations peak just before ovulation due to a rapid rise in oestrogen levels, and cause the follicle to swell and burst\ - Days 15 to 21 is when the empty follicle transforms into a corpus luteum. This secretes the hormone progesterone, which maintains the endometrium, and makes it soft and spongy so that a developing embryo can easily embed in it\ - In days 21 to 28, if fertilisation has not occurred, the egg passes out of the uterus. The corpus luteum breaks down and progesterone production ceases. This causes the endometrium to begin to degenerate, and by day 28 is ready to break down and pass out through the cervix and vagina\ - If pregnancy occurs, the endometrium is maintained by a hormone called Human chorionic gonadotrophic hormone (hCG), produced by the placenta. It is the presence of hCG that is detected in pregnancy tests (6) [Hormones and the Menstrual Cycle] \- Follicle- stimulating hormone (FSH), produced by the anterior pituitary, starts the process by stimulating a primary oocyte to develop into an ovum inside the Graafian follicle\ - The developing Graafian follicle produces the hormone oestrogen, which travels around the body in the blood\ - Oestrogen does three things\ a. Repairs and thickens the endometrium\ b. Tells the anterior pituitary gland to stop producing FSH. This is called a feedback system because the production of one substance influences the production of another. This is negative feedback as it stops the other substance from being produced\ c. Tells the anterior pituitary to start producing luteinising hormone (LH). This is positive feedback since it causes an increase in production of the other substance\ - The day before ovulation, there is a marked increase in LH which causes the final maturation of the Graafian follicle and ovulation. This makes the female more receptive to the sexual advances of the male, but in humans it is not very marked since sexual activity is not tied to fertility\ - LH continues the inhibition of FSH, and a sudden surge in its production stimulates ovulation. It also stimulates the subsequent change of the remains of the Graafian follicle into the yellow-coloured corpus luteum\ - The corpus luteum produces progesterone. Progesterone inhibits both FSH and LH, and thickens the endometrium\ - If fertilisation does not occur, the lack of LH results in the corpus luteum degenerating and this stops the production of progesterone\ - If pregnancy occurs, hGC is produced by the placenta and maintains the corpus luteum and thus the production of progesterone, which keeps the endometrium built up [Menstrual Disorders] \- Benign growths in the wall of the uterus which can range in size\ - Symptoms include heavy bleeding, prolonged periods and abdominal pain\ - Caused because some cells have more oestrogen and progesterone receptors than others\ - Treatments can vary from painkillers in mild cases, to surgery in severe cases *\ *[Pregnancy] *Copulation\ *- The natural process of using the erect penis to deposit semen at the top of the vagina beside the cervix.\ - If sperm is collected from a donor and placed into the vagina or the uterus using a medical implement, this is called artificial insemination *Ovulation\ *- The release of an egg from an ovary on day 14 of the cycle. The egg can survive for two days\ - Sperm can survive in the fallopian tube for up to five days, if it meets an egg fertilisation can take place *Fertilisation\ *- The fusion of the haploid male and female gamete nuclei to form a diploid zygote\ - Takes place in the top third of the fallopian tube [Infertility] \- If a couple cannot conceive a child after a year of trying, they are infertile.\ - Doctors can provide assistance such as in vitro fertilisation [In vitro fertilisation] In vitro fertilisation is the fertilisation of eggs outside the womb, usually in a petri dish. \- Early in the menstrual cycle, the woman is given hormones to cause the production of several eggs\ - The developing follicles are monitored by ultrasound scanning\ - Immediately before ovulation, the eggs are removed through a narrow needle and transferred to a nutrient fluid in a petri-dish\ - The man's sperm is mixed with the eggs and incubated\ - After a few days, if fertilisation has taken place and the embryos have begun to grow, several embryos are placed in the uterus and hopefully one will implant and develop [Causes of Infertility ] *Males\ *- Low sperm count can be caused by smoking or excess consumption of alcohol\ - Low sperm mobility due to malformed sperm\ - Low testosterone levels due to endocrine gland failure can be overcome using hormone replacement therapy with testosterone\ - High temperature, from wearing tight underwear, can cause sperm to die *Females\ *- Fallopian tube blockage due to injury or infection caused by untreated subclinical infections such as chlamydia\ - Endocrine gland failure due to disease, injury or malformation can be treated by hormone replacement therapy (HRT) [Stages of Development] *Morula and blastocyst\ *- Immediately after fertilisation, the zygote begins to divide by mitosis, forming two, then four and then eight cells\ - By day three after fertilisation, it is a solid ball of 16 cells called a morula\ - As cell division continues, a cavity starts to form, which produces a hollow ball of cells called a blastocyst\ - Cells begin to change in structure and function, a process called differentiation\ - Around 7 days after fertilisation, the blastocyst has travelled as far as the uterus\ - It begins to make connections with the uterus that will eventually form the placenta. This is called implantation\ - A group of cells at one end of the blastocyst forms three distinct layers, each called a germ layer\ - Each germ layer develops into different tissues depending on its location. This is called a triploblastic arrangement The three layers that some of the tissues that develop from each are;\ - Endoderm: Innermost layer that forms the lining of the gut, the respiratory and the urinogenital system\ - Mesoderm: Middle layer that forms blood, bone and muscle\ - Ectoderm: Outermost layer that forms the skin, epidermis and the nervous system Up to 8 weeks old, the developing baby is called an embryo. From week 9 onwards it is called a foetus The amnion is a sac that forms around the embryo, and by the fourth week is filled with amniotic fluid. The amniotic fluid acts as a shock absorber and protects the baby. It allows the baby to move freely, especially in the later stages of pregnancy. (7) [Placenta] \- The placenta is a disc-shaped structure which is formed partly from the cells of the embryo, and partly from cells of the womb wall, and is connected to the foetus by the umbilical cord\ - It takes approximately 3 months to form\ - Foetal blood is carried to the placenta in two arteries in the umbilical cord and a vein carries the foetal blood back from the placenta to the foetus\ - The blood of the mother and foetus do not mix. *Functions of the placenta\ *- Gaseous exchange: Oxygen diffuses from the mother's blood into the baby's blood, while Carbon dioxide diffuse from the baby's blood to the mother's blood\ - Antibodies: Can be passed from the mother to the baby to give passive acquired immunity\ - Nutrition: Glucose, amino acids, fats, vitamins, and minerals pass from the other to the baby\ - Endocrine gland: Makes progesterone and hCG to maintain the pregnancy and diffuses into the bloodstream\ - Excretion: Metabolic waste such as carbon dioxide and urea pass into the mother's blood from the baby and are excreted by the mother\ - Protection: The placenta prevents the energy of many pathogens [Birth] The process of birth, called labour, occurs in three distinct stages *Cervical dilation\ *- Contractions of the uterus progress and strengthen for longer periods with a decreasing interval between them\ - The cervix dilates, and the mucus plug breaks free and passes out of the vagina as a sticky, jelly-like pink mucus\ - The amniotic sac bursts and passes out through the vagina\ - When the cervix has dilated to 10 cm wide, the second stage of birth begins *Delivery\ *- The contractions of the uterine muscle become stronger causing the baby to move slowly through the pelvis\ - The mother must push as the baby's head descends through the birth canal, then one shoulder followed by the other, then the rest of the baby slides out\ - Umbilical cord is clamped and cut\ - Baby breathes air. *Placental delivery\ *- The placenta and the rest of the umbilical cord (afterbirth) pass out of the body through the birth canal [Milk Production and Breastfeeding] \- Suckling the baby stimulates the anterior pituitary to produce two hormones, prolactin and oxytocin\ -Prolactin stimulates lactation while oxytocin stimulates the expression of milk from the breasts\ - Milk produced at the start of lactation is called colostrum, which is yellow in colour and rich in nutrients and antibodies\ - Milk produced later is white, thinner in consistency, and not as rich in antibodies (8) *Benefits of Breastfeeding\ *- Breast milk is the perfect food at correct temperature\ - It has a lot of advantages for the baby's growth and development\ - It has the correct level of sodium, phosphate, and essential amino acids in contrast to cow's milk\ - Sterile at room temperature.\ - Breast milk contains antibodies which protect against many diseases and allergies\ - Allows bonding of mother and baby\ - Can delay the return of the menstrual cycle if prolactin level is maintained high\ - Reduced risk of breast cancer [Birth Control Methods] The availability of contraception results in a decrease in population and some contraceptives can decrease sexually transmitted infections (STI). *Natural Methods\ *- Abstinence: Avoiding sexual intercourse prevents pregnancy and STI's\ - Withdrawal: Removing the penis from the vagina before ejaculation, only 75% effective at best *Artificial Methods -- Mechanical\ *- Condoms: Form a latex barrier between the sperm and the egg. They give protection against STI's once they are put on before any sexual contact. 99% reliable is used properly\ - Diaphragm: A rubber cap that fits over the cervix and blocks sperm from entering. No protection against STI's. Only 80 -- 95% effective as it can dislodge *Artificial Methods -- Chemical\ *- Contraceptive pill: Contains progesterone and oestrogen which prevent ovulation. 99% effective if correctly taken every day\ - Implants: Rods that are implanted under the skin which release chemicals thar prevent ovulation and make cervical mucus thicker. 99% effective *Surgical Methods\ *- Vasectomy: Involves cutting a man's sperm ducts and tying off the cut ends. 100% effective but difficult to reverse\ - Sterilisation: Involves cutting a woman's Fallopian tubes and tying off the cut ends\ - Intrauterine device (IUD): A copper t-shaped device is inserted into the uterus and prevents fertilization and implantation*\ *A diagram of a uterus Description automatically generated(9) **[Exam Questions]** [2014 -- HL -- Section B -- Question 7] 7\. (a) (i) Name a part of a seed in which food for germination is stored. Endosperm\ (ii) Name the three factors necessary for seeds to germinate.\ 1. Water\ 2. Oxygen\ 3. Suitable temperature\ (b) Answer the following questions on seed germination.\ (i) At the start of the investigation to show digestive activity during germination the seeds were sterilised.\ 1. Why is this necessary? To prevent the growth of microorganisms\ 2. How did you sterilise the seeds? By sipping in ethanol\ (ii) Name the substance that is used as a medium on which to germinate the seeds. Agar\ (iii) What substance, to be digested by the seeds, was added to the above medium? Starch\ (iv) What control did you use in this demonstration? Boiled seeds\ (v) How did you demonstrate that digestive activity had taken place?\ - Added iodine to the dishes\ - Area underneath germinating seeds did not turn blue-black or stayed red-yellow\ - Demonstrating that the starch was digested by the germinating seeds. [2014 -- HL -- Section C -- Question 14] 14\. Answer any two of (a), (b), (c).\ (a) (i) Name: 1. the site of production of a pollen grain and Anther\ 2. the structure on which it must land to complete pollination. Stigma\ (ii) Name two methods of cross pollination.\ Animal- Pollination\ Wind - pollination\ (iii) Many species of plant have mechanisms that prevent self-pollination. Suggest how such plants could benefit from this. Prevents inbreeding and enables variation amongst offspring\ (iv) Describe in detail the events that follow the arrival of a pollen grain at the destination referred to in (i), up to and including fertilisation.\ - Pollen tube is formed\ - Pollen tube grows down through the style and enters the embryo sac\ - Generative nucleus divides by mitosis\ -Two male gametes (sperm nuclei) are formed\ - One male gamete fertilises the egg cell\ - Other male gamete fertilises the polar nuclei in the embryo sac\ (v) Which part of a flower usually develops into a fruit? Ovary [2013 -- HL -- Section A -- Question 4] The diagram shows a strawberry plant from which a runner has given rise to a daughter plant.  The runner is a modified stem. How could you tell this from\ 1. external observation? As the runner has a leaf\ 2. viewing a thin section of it under the microscope? Presence of many vascular bundled\ (b) What term is used for the type of asexual reproduction that produced the daughter plant? Vegetative propagation\ (c) Would you expect the daughter plant to be haploid or diploid? Diploid\ Explain your answer. As the new plant forms directly by mitosis from the parent plant.\ (d) What evidence is there in the diagram that sexual reproduction has also taken place? Presence of strawberry fruit\ (e) Give one method, other than runners, and not involving seeds, that is used by horticulturists to produce new plants. Grafting [2013 -- HL -- Section C -- Question 13] 13\. (a) (i) In humans, widening of the female hips is one example of physical changes that distinguish the sexes but are not essential for reproduction. To what term does the definition in italics refer? Secondary sexual characteristics\ (ii) What term is used for the time in a young person's life when such changes take place? Puberty\ (iii) Name the hormone that maintains such changes throughout the life of a male. Testosterone A diagram of the uterus Description automatically generated \(b) The diagram shows the reproductive system of the human female.\ (i) Name the parts labelled A Vagina\ B Uterus\ C Endometrium\ D Fallopian Tube\ E Ovary\ F Cervix\ (ii) Using the letters from part (i), identify the following locations:\ 1. Where meiosis occurs. E\ 2. Where zygote formation occurs. D\ 3. Where implantation occurs. C\ (iii) Describe the role of oestrogen and progesterone in the control of the events of the menstrual cycle.\ Oestrogen: Repairs the endometrium\ Inhibits FSH\ Stimulates LH\ Progesterone: Maintains the endometrium\ Inhibits FSH\ Inhibits LH\ (c) Answer the following questions in relation to the development of a human zygote.\ (i) By which type of cell division does the zygote divide? mitosis\ (ii) Further divisions result in the formation of a morula. What is the next developmental stage after the morula? blastocyst\ (iii) The placenta forms from tissues of the mother and the foetus. Give two roles of the placenta.\ Transfer nutrients and antibodies from mother to foetus.\ Secrete progesterone\ (iv) Give one change experienced by the mother that indicates to her that the birth process is starting. Uterine contractions\ (v) Give a short account of the birth process.\ 1. Labour: the uterus begins to contract (caused by the hormone oxytocin). Uterine contractions cause the amniotic sac to break releasing the amniotic fluid ('breaking of the waters'). The contractions also cause the cervix to widen to allow for the next stage.\ 2. Delivery: involves the baby being passed out of the birth canal head first. Once the baby has been born, the umbilical cord is clamped and cut.\ 3. Afterbirth: the final stage of labour involves further contractions of the uterus to expel the placenta. [2010 -- HL -- Section C- Question 15] 15\. Answer any two of (a), (b), (c).\ (a) (i) What is semen? Sperm and seminal fluid\ (ii) Draw a labelled diagram of the reproductive system of the human male. On your diagram, indicate clearly and name the part at which each of the following occurs: 1. Production of sperm cells. 2. Maturing of sperm cells. 3. Mixing of fluid with sperm cells. 4. Transport of semen.  \(iii) State two secondary sexual characteristics of the human male. Deepening voice and broadening of shoulders\ (iv) What maintains the secondary sexual characteristics in the adult human male? Testosterone **[References]** 1. Scienceonline.com 2. Nagwa.com 3. Istockphoto.com 4. Embibe.com 5. Vectorstock.com 6. Dreamtimes.com 7. Istockphoto.com 8. Karger.com 9. Clevelandclinic.com