B8 - REPRODUCTION 8.1 - Asexual and sexual reproduction 1. Define asexual reproduction. The process resulting in the production of genetically identical offspring from one parent. 2. Discuss the advantages and disadvantages to a species of asexual reproduction. Advantages The process is quick; Only one parent is needed; No gametes are needed; All the good characteristics of the parent are passed on to the offspring; They usually store large amounts of food that allow rapid growth when conditions are suitable Disadvantages There is little variation created, so adaptation to a changing environment (evolution) is unlikely; If the parent has no resistance to a particular disease, none of the offspring will have resistance; Lack of dispersal (e.g. potato tubers) can lead to competition for nutrients, water and light. 3. Define sexual reproduction. The process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically different offspring. 4. Discuss the advantages and disadvantages to a species of sexual reproduction. Advantages There is variation in the offspring so adaptation to a changing or new environment is likely, enabling survival of the species; New varieties may be created which may have resistance to disease; In plants, seeds are produced, which allow dispersal away from the parent plant, reducing competition; Disadvantages Two parents are usually needed (although not always- some plants can selfpollinate); Growth of a new plant to maturity from a seed is slow. B8 - REPRODUCTION 8.2 - Sexual reproduction in plants 1. Identify and draw, using a hand lens if necessary, the sepals, petals, stamens, anthers, carpels, ovaries and stigmas of one locally available, named insect-pollinated, dicotyledonous flower, and examine the pollen grains under a light microscope or photomicrographs. Insect pollinated, dicot. flower. And the pollen grains. 2. Use a hand lens to identify and describe the anthers and stigmas of one locally available, named, wind-pollinated flower. A-Bract, B-Feathery stigma, C-Anther loosely attached to the filament, D- Ovary Figure showing wind-pollinated flower 3. State the functions of the sepals, petals, anthers, stigmas and ovaries. Part Petal Sepal Petiole (stalk) Stamen Anther Filament Carpel Stigma Style Ovary Function Often large and coloured, to attract insects Protects the flower while in bud Supports the flower to make it easily seen by insects, and to be able to withstand wind The male reproductive part of the flower, made of anther and filament Contains pollen sacs, in which pollen grains are formed. Pollen contains male sex cells Supports the anther The female reproductive part of the flower, made of stigma, style and ovary A sticky surface that receives pollen during pollination Links the stigma to the ovary, through which pollen tubes grow Contains ovules, which develop into seeds when fertilised 4. Candidates should expect to apply their understanding of the flowers they have studied to unfamiliar flowers. 5. Define pollination. Transfer of pollen grains from the male part of the plant (anther) to the female part (stigma). 6. Name the agents of pollination. Wind; Animals including insects; Water 7. Compare the different structural adaptations of insect-pollinated and wind-pollinated flowers. Feature Petals Nectar Stamen Stigmas Pollen Bracts (modified leaves) Insect-pollinated Present- often large, coloured and scented Produced by nectaries to attract insects Present inside the flower Small surface area, inside the flower Smaller amounts- grains are often round and sticky, or covered in spikes to attach to the furry bodies of insects Absent Wind-pollinated Absent or small and inconspicuous Absent, or small and green Long filaments, allowing the anthers to hang freely outside the flower so the pollen is exposed to the wind Large and feathery, hanging outside the flower to catch pollen Larger amounts of smooth and light pollen grains, which are easily carried by the wind Sometimes present 8. Investigate and state the environmental conditions that affect germination of seeds: requirement for water and oxygen, suitable temperature. IGCSE Biology (Jones & Jones), p.190, activity 13.4 – ‘to find the conditions necessary for the germination of tomato seeds’. Environmental conditions affecting germination Environmental condition Water Oxygen Suitable temperature Light Explanation Absorbed through micropyle, needed to activate enzymes which convert insoluble food stores into soluble foods needed for growth and energy production. Needed for respiration, to release energy for growth and chemical changes for mobilization of food reserves For enzymes to work as enzymes work best at optimum temperature Not usually a requirement for germination but some seeds need a period of exposure to light before they germinate 9. Investigate and describe the structure of a non-endospermic seed in terms of the embryo (radicle, plumule & cotyledons) and testa, protected by the fruit. After fertilization, the ovule becomes a zygote; The zygote divides by mitosis to form an embryo plant; The ovule is now called a seed; The ovary becomes the fruit. Part of the seed Testa Structure Tough protective covering Cotyledons Radicle Plumule Micropyle Food store Part of embryo Part of embryo Tiny hole in testa Hilum A scar near the micropyle Function Stop embryo from being damaged, prevents bacteria and fungi from entering the seed Contains starch, protein and enzymes Grow into root Grow into shoot Water and oxygen enters the seed through this hole Where the seed was joined to the pod (ovary) 10. State that seed and fruit dispersed by wind and by animals provides a means of colonizing new areas. Dispersal of seeds is important, because it prevents too many plants growing close together; If this happens, they compete for light, water and nutrients, so that none can grow properly; Dispersal also allows the plant to colonise new areas. 11. Describe, using named examples, seed and fruit dispersed by wind and by animals. Wind dispersed fruit Dandelion Dandelion fruit has a group of fine hairs called a pappus; Pappus acts as a parachute and catches wind; The fruit counterbalances the pappus. Sycamore Sycamore has a wing with a large surface area; When fruit drops of the tree it spins, slowly down its descent; If caught by wind the seed will be carried away from the parent plant, reducing competition for nutrients, water and light. Animal dispersed fruit Succulent fruits e.g. blackberry They are coloured, juicy and nutritious and hence attracted by animals; When eaten seeds pass through the gut without getting digested and deposited with animal faeces far away from the parent plant. Hooked fruits e.g. bur Catch on to animal’s fur as it brushes past the parent plant; Eventually the seed drop off and gets dispersed far away from the parent plant. B8 - REPRODUCTION 8.3 - Sexual reproduction in humans 1. Identify on diagrams of the male reproductive system, the testes, scrotum, and sperm ducts, prostate gland, urethra and penis, and state the functions of these parts. Part Epididymis Penis Prostate gland Scrotum Seminal vesicle Sperm duct Testis (pl. testes) Urethra Function A mass of tubes in which sperm are stored Can become firm, to insert into the vagina of the female during sexual intercourse, to transfer sperm Adds fluid and nutrients to sperm, to form semen A sac that holds the testes outside the body, keeping them cooler than body temperature Adds fluid and nutrients to sperm, to form semen Muscular tube which links the testis to the urethra to allow the passage of semen containing sperm Male gonads that produce sperm To pass semen containing sperm through the penis, also carries urine from the bladder at different times 3. Identify on diagrams of the female reproductive system, the ovaries, oviducts, uterus, cervix and vagina, and state the functions of these parts. Part Cervix Funnel of oviduct Ovary Oviduct Function A ring of muscle that separates the vagina from the uterus Directs an ovum (egg) from the ovary into the oviduct Contains follicles in which ova (eggs) are produced Carries an ovum to the uterus, with propulsion provided by tiny cilia in the wall; also the site of fertilization Carries urine from the bladder Where the fetus develops Receives the male penis during sexual intercourse; sperm are deposited here Urethra Uterus Vagina 2. Compare male and female gametes in terms of size, numbers and mobility. Types of gamete Egg Sperm Structure 1. Is large in size 0.1mm because it has all cell components that is needed for the cell to grow and multiply; has yolk to nourish the embryo. 2. During ovulation, only one egg is released every month. 3. Ovum is immobile as the sperm moves towards it to fertilise it. 1. Size is very small 0.05mm. 2. During ejaculation millions of sperms are produced into the women’s vagina. 3. Sperms are highly mobile and can swim towards the oviduct with he help of its tail. 4. Describe the menstrual cycle in terms of changes in the uterus and ovaries. 5. Describe the fertilization in terms of the joining of the nuclei of male gamete (sperm) and the female gamete (egg). 1. During sexual intercourse, erect penis is inserted into vagina; 2. Semen is ejaculated into the neck of vagina; 3. Many sperms cluster around ovum but only one penetrates; 4. A fertilization membrane is secreted around the egg once one sperm enters; 5. The sperm nucleus fuses with egg nucleus to form zygote, this process is called fertilization. 6. Outline early development of the zygote simply in terms of the formation of a ball of cells that becomes implanted in the wall of the uterus. 7. Indicate the functions of the amniotic sac and amniotic fluid. Structure Amniotic sac Amniotic fluid Function A thin membrane, formed from cells of embryo, contains the amniotic fluid; It encloses the fetus and prevents entry of bacteria. Supports the fetus, protecting it from physical damage; It absorbs excretory materials (urine) released by the fetus. 8. Describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (no structural details are required). The placenta brings the blood supply of the fetus close to that of the mother, but prevents mixing; This is important because the fetus and mother may have different blood groups and any mixing can result in blood clotting; Also the mother’s blood pressure is higher compared to the fetus which might damage the fetal organs; Blood from fetus passes through the umbilical cord in the umbilical artery to the placenta. Substances that diffuse across the placenta are as follows: Type of substance Respiratory gases Soluble nutrients Disease-preventing substances Nitrogenous excretory substances Potentially harmful substances To fetus from mother Oxygen Amino acids, glucose, fatty acids, glycerol, vitamins, minerals, water Antibodies, antibiotics To mother from fetus Carbon dioxide Urea Alcohol, nicotine and other drugs, viruses, bacteria 9. Describe the advantages and disadvantages of breast-feeding compared with bottlefeeding using formula milk. Advantages of breast-feeding over bottle-feeding: There are antibodies present in the breast milk, giving the baby protection against infection; Foodstuffs are present in breast milk in the correct proportions; There are no additives and preservatives in breast milk; Breast feeding builds a bond between mother and baby; Breast milk does not require sterilization as there are no bacteria present that could cause intestinal disease; Breastfeeding triggers a reduction in the size of the mother’s uterus. Formula milk is much more expensive than breast milk, which is free. Advantages of bottle-feeding over breast-feeding: Someone else can feed the mother’s baby; This can also help the father to bond with the baby, if he is involved in feeding. 10. Describe the method of transmission of human immunodeficiency virus (HIV), and the ways in which HIV/AIDS can be prevented from spreading. HIV may result in AIDS Methods of transmission Unprotected sexual intercourse with an infected person Drug use involving sharing a needle used by an infected person Transfusions of unscreened blood Infected mother to fetus Feeding a baby with milk from an infected mother Use of unsterilized surgical instruments Ways of preventing its spread Use of condom for sexual intercourse Abstinence from sexual intercourse Screening of blood used for transfusions Use of sterilized needles for drug injections Feeding a baby with bottled milk when the mother has HIV Use of sterilized surgical instruments 11. Outline how HIV affects the immune system in a person with HIV/AIDS. HIV virus attacks some types of lymphocyte (white blood cells) in the bloodstream; Lymphocytes produce antibodies, which attack the antigens present on invading microbes; So HIV stops this happening - thus the person develops symptoms of AIDS; So they become vulnerable to infections (like pneumonia, tuberculosis and cancer); A person with AIDS usually dies of a collection of several illnesses.