CIE IGCSE Biology Reproduction PDF

Head to www.savemyexams.com for more awesome resources CIE IGCSE Biology Your notes 16.1 Reproduction in Plants & Humans Contents 16.1.1 Asexual Reproduction 16.1.2 Sexual Rep...

Head to www.savemyexams.com for more awesome resources CIE IGCSE Biology Your notes 16.1 Reproduction in Plants & Humans Contents 16.1.1 Asexual Reproduction 16.1.2 Sexual Reproduction 16.1.3 Sexual Reproduction in Plants 16.1.4 Sexual Reproduction in Humans 16.1.5 Sexual Hormones in Humans 16.1.6 Sexually Transmitted Infections Page 1 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 16.1.1 Asexual Reproduction Your notes Asexual Reproduction Asexual reproduction does not involve sex cells or fertilisation Only one parent is required so there is no fusion of gametes and no mixing of genetic information As a result, the offspring are genetically identical to the parent and to each other (clones) Asexual reproduction is defined as a process resulting in genetically identical offspring from one parent Page 2 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examples of Asexual Reproduction Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary Your notes fission: Page 3 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 4 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission Plants can reproduce asexually using bulbs and tubers; these are food storage organs from which budding can occur, producing new plants which are genetically identical to the parent plant: Page 5 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 6 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Some plants develop underground food storage organs that will develop into next years plants - they can take different forms, such as bulbs or tubers Some plants grow side shoots called runners that contain tiny plantlets on them (a good example of this are strawberry plants. These will grow roots and develop into separate plants, again being genetically identical to the parent plant: Some plants grow side shoots called runners that contain tiny plantlets on them. These will grow roots and develop into separate plants. Page 7 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Advantages & Disadvantages of Asexual Reproduction: Extended Your notes Specifically in crop plants, asexual reproduction can be advantageous as it means that a plant that has good characteristics (high yield, disease-resistant, hardy) can be made to reproduce asexually and the entire crop will show the same characteristics Page 8 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 16.1.2 Sexual Reproduction Your notes Gametes & Zygotes Sexual Reproduction Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other Fertilisation is defined as the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring Gametes A gamete is a sex cell (in animals: sperm and ovum; in plants pollen nucleus and ovum) Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells - we say they have a haploid nucleus This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes When the male and female gametes fuse, they become a zygote (fertilised egg cell) This contains the full 46 chromosomes, half of which came from the father and half from the mother - we say the zygote has a diploid nucleus Page 9 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Haploid & Diploid Cells: Extended The nuclei of gametes are haploid Your notes They contain half the number of chromosomes of a normal body cell In humans, this is 23 chromosomes The nucleus of a zygote is diploid It contains the same number of chromosomes as a normal body cell In humans, this is 23 pairs of chromosomes The zygote continues to stay diploid as it grows into a fetus and embryo during pregnancy Page 10 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Advantages & Disadvantages of Sexual Reproduction: Extended Your notes Most crop plants reproduce sexually and this is an advantage as it means variation is increased and a genetic variant may be produced which is better able to cope with weather changes, or produces significantly higher yield The disadvantage is that the variation may lead to offspring that are less successful than the parent plant at growing well or producing a good harvest Page 11 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 16.1.3 Sexual Reproduction in Plants Your notes Insect pollinated flowers Flowers are the reproductive organs of plants The role of flowers is to enable plant sex cells, or gametes to come together in fertilisation The male gametes of plants are found in pollen grains The female gametes of plants are in ovules The process by which pollen is transferred from the male part of a flower to the female part of a flower is known as pollination; this can be carried out in various ways, e.g. by insects or by wind Insect pollinated flower structure The most well known flower structure is that of the insect pollinated flower The parts of an insect pollinated flower include: sepals petals stamens filaments anthers carpel style stigma ovary ovules Insect pollinated flowers are adapted to allow insects to collect pollen from the male parts of the flower and easily transfer it to the female parts of another flower Insect pollinated flower diagram Page 12 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Insect pollinated flowers are adapted to attract insects and aid insect pollination Flower structure and function table Structure Description Sepal Protects unopened flower Petals Brightly coloured in insect-pollinated flowers to attract insects Anther Produces and releases pollen Filaments Provides support to the anther Page 13 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Sticky top of the female part of the flower which collects pollen Stigma grains Your notes Style A tube that connects the stigma and ovary Ovary Contains the ovules Ovule Structures inside the ovary that contain the female gametes Page 14 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Wind pollinated flowers Wind pollinated flowers are adapted so that wind can easily catch pollen grains and carry them to the Your notes stigmas of other flowers The anthers and stigmas of wind pollinated flowers hang outside the flower so that: pollen can easily be blown away by the wind pollen can easily be caught by the stigmas of other flowers Wind pollinated flower diagram Wind pollinated flowers have anthers that hang outside the flower on long filaments, and feathery stigmas that can catch pollen easily Page 15 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Pollination & fertilisation Pollen and pollination Your notes The pollen of different types of flower is adapted to aid pollination: Insect-pollinated flowers produce larger, heavier pollen grains that often contain spikes or hooks on the outside so they are better able to stick to insects Wind-pollinated flowers produce small, lightweight pollen grains that can be caught and carried easily by the wind Page 16 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes Observe the features of the different pollen grains 1. The pollen grains are large and have spikes around the outside 2. The pollen grains are small and smooth 3. The pollen grains are medium-sized and have wing-like structures on each side Consider how each feature may relate to the pollination method 1. Large pollen grains are likely to be too heavy to be picked up by the wind, and spikes will mean that they can catch onto the bodies of insects 2. Small pollen grains will be light enough to be carried by the wind 3. Wing-like structures will catch the wind easily Answer: B 1 only Pollination in insect and wind pollinated flowers Insect and wind pollinated flowers have structural adaptations which aid pollination: Page 17 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Structural adaptations of an insect pollinated flower table Your notes Feature Insect pollinated flower Petals Large and brightly coloured to attract insects Scent and Scent and nectar are produced to encourage insects to visit the flower nectar and push past stamen to get to nectar Anthers Held on stiff filaments within the flower so that they brush against insects Sticky stigmas within the flowers catch pollen grains when insects brush Stigma past Structural adaptations of a wind pollinated flower table Feature Wind pollinated flower Petals Small and dull, often green or brown in colour Scent and Scent and nectar are not produced; this would be a waste of energy nectar Held on long filaments outside the flower to release pollen grains easily Anthers into the wind Stigma Feathery stigmas outside the flower catch airborne pollen grains Pollination and fertilisation Pollination can be defined as: The transfer of pollen grains from an anther to a stigma This is distinct from fertilisation, which is: Page 18 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The fusion of a pollen nucleus with an ovum nucleus After pollination, the pollen nuclei travel to the ovule and fuse with female gametes in a process called Your notes fertilisation Plant fertilisation diagram Pollen nuclei travel down a pollen tube in order to fuse with the female gametes inside the ovule; this is fertilisation Exam Tip Students often get confused between pollination and fertilisation in plants; remember that they are not the same thing! Pollination is the transfer of pollen Fertilisation is the fusion of gametes Page 19 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Factors Affecting Germination of Seeds Germination is the start of growth in the seed Your notes Three factors are required for successful germination: Water - allows the seed to swell up and the enzymes in the embryo to start working so that growth can occur Oxygen - so that energy can be released for germination Warmth - germination improves as temperature rises (up to a maximum) as the reactions which take place are controlled by enzymes As carbon dioxide is not necessary for germination but also does not inhibit it, it makes no difference whether it is present or not Investigating Germination Set up 4 boiling tubes each containing 10 cress seeds on cotton wool Set each test tube as shown in diagram below Leave tubes in set environment for a period of time: A, B and C incubated at 20°C; D placed in a fridge at 4°C Compare results and see which tube has the greatest number of germinated seeds An investigation into the conditions required for germination of seedlings Conditions required for germination results table Test tube Factor being tested Seeds germinated A Water / moisture No Page 20 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources B Control (all factors present) Yes Your notes C Oxygen No D Warm temperature No The results of this experiment prove that all three factors are required for the successful germination of the seeds and if any one factor is missing the seeds cannot germinate Page 21 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Self- & Cross-Pollination: Extended Cross-pollination occurs when the pollen from one plant is transferred to the stigma of another plant Your notes of the same species This is the way most plants carry out pollination as it improves genetic variation Occasionally, the pollen from a flower can land on its own stigma or on the stigma of another flower on the same plant - this is known as self-pollination Self-pollination reduces genetic variety of the offspring as all the gametes come from the same parent (and are therefore genetically identical) Lack of variation in the offspring is a disadvantage if environmental conditions change, as it is less likely that any offspring will have adaptations that suit the new conditions well On the other hand, cross-pollination relies completely on the presence of pollinators and this can be a problem if those pollinators are missing (e.g. the reduction in bee numbers is of great importance to humans as bees pollinate a large number of food crops) - this doesn’t apply to wind-pollinated plants Pollen tube formation After pollination, the following sequence of events take place: A pollen tube grows from the pollen grain down the style until it reaches the ovary Nuclei from pollen travel down the tube The nuclei enter the ovule and fuse with the nucleus of the female gamete (fertilisation) After fertilisation the ovules develop into seeds and the ovary develops into a fruit Page 22 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 23 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Growth of the pollen tube and its entry into the ovule followed by fertilisation Exam Tip Remember that it is the nucleus of the pollen grain that travels down the pollen tube in the style for fertilisation and not the pollen grain itself. Make sure to be specific with your use of key words! Page 24 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 16.1.4 Sexual Reproduction in Humans Your notes The male reproductive system Structures of the male reproductive system The male reproductive system has several key components The structure and function of these components can be seen in the table below Structure Function Produces fluid called semen that provide Prostate gland sperm cells with nutrients Sperm passes through the sperm duct to be mixed with fluids produced by the glands Sperm duct before being passed into the urethra for ejaculation Tube running down the centre of the penis that can carry out urine or semen, a ring of Urethra muscle in the urethra prevents the urine and semen from mixing Contained within a bag of skin (scrotum) and Testis produces sperm (male gamete) and testosterone hormone Sac supporting the testes outside the body to Scrotum ensure that sperm are kept at a temperature slightly lower than body temperature Passes urine out of the body from the bladder Penis and allows semen to pass into the vagina of a woman during sexual intercourse The male reproductive system diagram Page 25 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The male reproductive system Page 26 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The female reproductive system Structures of the female reproductive system Your notes The female reproductive system has several key components The structure and function of these components can be seen in the table below Structure Function Connects the ovary to the uterus and is lined Oviduct with ciliated cells to push the released ovum down it. Fertilisation occurs here Contains ova (female gametes) which will Ovary mature and develop when hormones are released Muscular bag with a soft lining where the Uterus fertilised egg (zygote) will be implanted to develop into a foetus Ring of muscle at the lower end of the uterus Cervix to keep the developing foetus in place during pregnancy The muscular tube that leads to the inside of the woman's body where the males penis will Vagina enter during sexual intercourse and sperm are deposited The female reproductive system diagram Page 27 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The female reproductive system Page 28 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Gametes & Fertilisation What is fertilisation? Your notes Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell) It occurs in the oviducts Gametes have adaptations to increase the chances of fertilisation and successful development of an embryo Fertilisation diagram The sperm enters the egg cell during fertilisation which usually occurs in the oviduct Page 29 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Adaptations of Gametes Human gametes Your notes The human gametes are the egg and the sperm cells Egg and sperm cell diagram Comparing sperm and egg cells Adaptive features of the gametes The gametes are highly specialised cells with adaptive features designed to maximise the chances of successful reproduction These adaptive features are compared in the table below Gamete Adaptive feature Function Sperm allows the sperm to swim towards the has a flagellum (tail) egg contains enzymes in the head region to digest a route into the egg for (acrosome) fertilisation Page 30 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources to provide energy for movement of the contains many mitochondria flagellum Your notes to provide energy for cell division in the cytoplasm contains a store of energy developing zygote after fertilisation Egg to make an impenetrable barrier after jelly-like coating that changes after fertilisation to prevent more sperm fertilisation entering the egg Comparison of Male & Female Gametes Comparative Feature Sperm Egg Size Very small (45 µm) Large (0.15 mm) Round cell with few structure Head region, flagellum, Structure adaptations, covered in a jelly many structural adaptations coating Motility Capable of locomotion Not capable of locomotion Produced every day in huge Thousands of immature eggs in Numbers numbers (around 100 million each ovary, but only one is per day) released each month Page 31 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Pregnancy: growth & development of the fetus After fertilisation in the oviduct, the zygote travels towards the uterus Your notes This takes about 3 days, during which time the zygote will divide several times to form a ball of cells known as an embryo In the uterus, the embryo embeds itself in the thick lining (implantation) and continues to grow and develop The gestation period for humans is 9 months Major development of organs takes place within the first 12 weeks, during which time the embryo gets nutrients from the mother by diffusion through the uterus lining After this point the organs are all in place, the placenta has formed and the embryo is now called a fetus The remaining gestation time is used by the fetus to grow bigger in size The fetus is surrounded by an amniotic sac which contains amniotic fluid (made from the mother’s blood plasma) This protects the fetus during development by cushioning it from bumps to the mother’s abdomen The umbilical cord joins the fetus’s blood supply to the placenta for exchange of nutrients and removal of waste products Page 32 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The fetus in the uterus Page 33 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The placenta & umbilical cord: extended What is the the placenta and the umbilical cord? Your notes During the gestation period the fetus develops and grows by gaining the glucose, amino acids, fats, water and oxygen it needs from the mother’s blood The bloods run opposite each other, never mixing, in the placenta The fetus’s blood connects to and from the placenta by the umbilical cord The mother’s blood also absorbs the waste from the fetus’s blood in the placenta; substances like carbon dioxide and urea are removed from the fetus’s blood so that they do not build up to dangerous levels Movement of all molecules across the placenta occurs by diffusion due to difference in concentration gradients The placenta is adapted for this diffusion by having a large surface area and a thin wall for efficient diffusion Toxins and pathogens The placenta acts as a barrier to prevent toxins and pathogens getting into the fetus’s blood Not all toxin molecules or pathogenic organisms (such as viruses, eg rubella) are stopped from passing through the placenta (this usually depends on the size of the molecule) This is why pregnant women are advised not to smoke during pregnancy as molecules like nicotine can pass across the placenta Placenta and umbilical cord diagram Page 34 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The placenta Exam Tip It is worth learning at least two specific substances that move in either direction across the placenta – this is a common exam question and non-specific answers such as ‘waste products’ and ‘nutrients’ will not get any marks! Page 35 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 16.1.5 Sexual Hormones in Humans Your notes Secondary Sexual Characteristics Primary sexual characteristics are present during development in the uterus and are the differences in reproductive organs etc between males and females Secondary sexual characteristics are the changes that occur during puberty as children become adolescents They are controlled by the release of hormones - oestrogen in girls and testosterone in boys Human secondary sexual characteristics Female secondary sexual characteristics: Male secondary sexual characteristics: Page 36 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Some changes occur to both boys and girls, including growth of sexual organs and growth of body hair Emotional changes also occur due to the increased levels of hormones in the body These include more interest in sex and increased mood swings Page 37 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Menstrual Cycle Starts in early adolescence in girls (around age 12) and is controlled by hormones Your notes The average menstrual cycle is 28 days long Ovulation (the release of an egg) occurs about halfway through the cycle (day 14) and the egg then travels down the oviduct to the uterus Failure to fertilise the egg causes menstruation (commonly called a period) to occur - this is caused by the breakdown of the thickened lining of the uterus Menstruation lasts around 5 - 7 days and signals the beginning of the next cycle After menstruation finishes, the lining of the uterus starts to thicken again in preparation for possible implantation in the next cycle Changes in the lining of the uterus during the menstrual cycle Page 38 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Hormones of the Menstrual Cycle: Extended The menstrual cycle is controlled by hormones released from the ovary and the pituitary gland in the Your notes brain The roles of FSH and LH Page 39 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Changes in the levels of the pituitary hormones FSH and LH in the blood during the menstrual cycle FSH (follicle-stimulating hormone) is released by the pituitary gland and causes an egg to start maturing in the ovary Page 40 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources It also stimulates the ovaries to start releasing oestrogen The pituitary gland is stimulated to release luteinising hormone (LH) when oestrogen levels have reached their peak Your notes LH causes ovulation to occur and also stimulates the ovary to produce progesterone Page 41 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The roles of oestrogen and progesterone Your notes Changes in the levels of oestrogen and progesterone in the blood during the menstrual cycle Oestrogen levels rise from day 1 to peak just before day 14 Page 42 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources This causes the uterine wall to start thickening and the egg to mature The peak in oestrogen occurs just before the egg is released Progesterone stays low from day 1 – 14 and starts to rise once ovulation has occurred Your notes The increasing levels cause the uterine lining to thicken further; a fall in progesterone levels causes the uterine lining to break down (menstruation / ‘period’) Interaction between all four of the menstrual cycle hormones The pituitary gland produces FSH which stimulates the development of a follicle in the ovary An egg develops inside the follicle and the follicle produces the hormone oestrogen Oestrogen causes growth and repair of the lining of the uterus wall and inhibits production of FSH When oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (usually around day 14 of the cycle) The follicle becomes the corpus luteum and starts producing progesterone Progesterone maintains the uterus lining (the thickness of the uterus wall) If the ovum is not fertilised, the corpus luteum breaks down and progesterone levels drop This causes menstruation, where the uterus lining breaks down and is removed through the vagina - commonly known as having a period If pregnancy does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down and aborting the pregnancy It does this until the placenta has developed, at which point it starts secreting progesterone and continues to do so throughout the pregnancy Page 43 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Where hormones involved in the menstrual cycle are made and act Page 44 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 16.1.6 Sexually Transmitted Infections Your notes STIs & HIV/AIDS Unprotected sexual intercourse can lead to the transfer of pathogens via exchange of body fluids Infections passed on in this way are known as sexually transmitted infections (STIs) An example of an STI is HIV (Human Immunodeficiency Virus), the virus that usually leads to the development of acquired immunodeficiency disease (AIDS) HIV can also be spread via sharing needles with an infected person, blood transfusions with infected blood and from mother to fetus through the placenta and mother to baby via breastfeeding Page 45 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources How HIV Affects the Immune System Immediately after infection, people often suffer mild flu-like symptoms Your notes These symptoms pass and for a period of time infected people might not know they are infected The virus infects a certain type of lymphocyte of the body's immune system Normally lymphocytes seek out and destroy pathogens that enter the body, producing antibodies that attach to pathogens, enhancing phagocytic activity However HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat It then infects a certain type of lymphocyte and uses the cells’ machinery to multiply This reduces the number of lymphocytes of the immune system, and also the number of antibodies that can be made This decreases the body’s ability to fight off infections, eventually leading to AIDS (Acquired immunodeficiency) Page 46 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 47 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources How HIV affects lymphocytes Your notes Controlling the Spread of STIs The spread of STIs such as HIV are best controlled by: Limiting the number of sexual partners an individual has Not having unprotected sex, but making sure to always use a condom Getting tested if unprotected sex or sex with multiple partners has occurred Raising awareness by education programmes Page 48 of 48 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers