Tag: reproduction

Asexual Reproduction The process resulting in the production of genetically identical offspring from one parent. Bacteria: Reproduce by binary fission, each bacterium divides into two. The generation time is the time taken for a cell to divide into 2. Fungi: Single-celled yeast reproduces by binary fission. All other fungi produce via spores. When the sporangium bursts it spreads the spores. Spores land and grow mycelium (roots) for example mushrooms Potatoes: The shoot from a potato goes back underground and the stem swells to form a new genetically identical potato. The swollen stem acts as a storage organ. Advantages Disadvantages Fast: no need to find mate, fertilise etc. No variation Good characteristics are kept Harmful genes transferred Overcrowding- fighting for food Sexual Reproduction Sexual reproduction: process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production of offspring that are genetically different from each other Fertilization: the fusion of gamete nuclei Nuclei of gametes are haploid, and that the nucleus of a zygote is diploid Advantages Disadvantages Produces genetically different offspring Takes lots of time and energy don’t all die from change in the environment Good characteristics can be lost Energy on improving appearances or pollen volume for pollination (plants) Sexual Reproduction in Plants Insect pollinated flowering plant Wind pollinated flower structure Functions Sepal: protect the flower bud. Petal: brightly coloured and scented and may have nectarines which are all used to attract insects, petals in wind pollinated flowers are tiny, and used for pushing the bracts (leaf-like structures) apart to expose stamens and stigma Anther: has pollen sacs with pollen grains which contain the male nucleus (male gamete). Stigma: platform on which pollen grains land Ovary: hollow chamber, ovules grow from the walls. Pollination Pollination: transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma). Agents of pollination: insects, birds, mammals, water and wind Insect Pollinated Wind Pollinated Large colourful petals – attract Dull petals Sweetly scented No scent Nectaries No nectaries Moderate amount of pollen Huge amount of pollen Pollen is spiky/sticky Pollen round and smooth Anther & stigma inside flower Anther & stigma hangs out Stick stigma Stigma hairy Flowers have stripes which act as guide-lines for insects Pollen tube: pollen grain lands on stigma and creates a tunnel down the style, through the micropyle, to the ovules. Structure of non-endospermic seed: Formation of a seed: the zygote divides many times by mitosis to form and embryo. The cotyledon is the food store. The testa stops drying out of embryo. Wind and animal dispersal are used by plants to colonise new areas; done because new areas have less competition for light, space and nutrients, so seeds are more likely to develop. Wind Dispersed Seed Animal Dispersed Seed Dandelion Apple (internal) Sycamore Bur (external) Germination A process controlled by enzymes Water: activates enzymes to turn insoluble food stores into soluble substances, and makes tissues swell so that the testa splits Oxygen: enters through the gaps in the testa (along with water), and is used in aerobic respiration. Temperature: must be suitable for enzymes to work (at optimum temperature). Sexual Reproduction In Humans Male reproductive system Testes: have many coiled tubes which produce sperm, and the cells between tubes produce testosterone. Scrotum: holds testicles Sperm duct: carries sperm from testicles to urethra. Prostate gland: makes seminal fluid Urethra: carries semen from sperm duct to tip of penis Penis: male sex organ, used to transfer semen to the female. Female reproductive system Ovary: contains follicles which develop into the ova and produces progesterone and oestrogen Oviduct (fallopian tube): carries the ovum to uterus Uterus (womb): where the fetus develops. Cervix: neck of uterus: a strong rigid muscle, moist by mucus with a small opening Vagina: receives penis during intercourse, and way out for baby at birth. Moist tube of muscle, flexible and secretes mucus Menstrual Cycle Day 1 to 5: In the ovary, FSH secreted by the Pituitary Gland to stimulate the maturation of ONE follicle in the ovary. In the uterus: the endometrium breaks down; menstruation Day 5 to 12: In the ovary the follicle keeps maturing In the uterus, oestrogen is secreted by follicle and the ovarian tissues to prepare the endometrium Day 13/14/15: In the ovary, LH is also secreted by the Pituitary Gland to trigger the release of the egg from follicle into the fallopian tube Day 15 to 28: In the ovary, LH triggers formation of Corpus Luteum In the uterus: progesterone is secreted by Corpus Luteum to keep endometrium thick, waiting for possible embryo implant. Day 28 – Scenario 1: Egg not fertilized No implantation takes place, the Corpus Luteum degenerates, causing a lack of progesterone. This means that endometrium is no longer thick, back to Day 1 Day 28 – Scenario 2: Egg is fertilized Implantation occurs. This makes the hormones to keep the Corpus Luteum maintained which means that progesterone is high. This keeps the Endometrium thick for pregnancy Hormones in Menstrual Cycle Oestrogen is secreted by the ovaries. It stops FSH being produced - so that only one egg matures in a cycle and it stimulates the pituitary gland to release hormone LH. Progesterone is a hormone secreted by ovaries. It maintains the lining of the uterus during the middle part of the menstrual cycle and during pregnancy. Follicle stimulating hormone (FSH) is secreted by the pituitary gland. It causes an egg to mature in an ovary and it stimulates ovaries to release hormone oestrogen Luteinizing hormone (LH): is also secreted by pituitary gland and causes mature egg to be released from ovary. Sexual Intercourse Penis fills with blood and becomes erect Vagina walls secrete a lubricant. Rubbing of the glans (end of penis) against the vagina wall sets of a reflex action, causes sperm to be released from the testes, and is transported by peristalsis along sperm ducts and urethra, where seminal fluid is added to make semen. The exit of semen from the penis is called ejaculation. Sperm then swim through the cervix and oviducts to the first third of the oviduct (from the ovary) where one combines with the egg. Fertilization The fusion of an ovum and a sperm to form a zygote. Development of zygote: One sperm penetrates Ovum membrane alters to form barrier against sperm Head of sperm (male nucleus) approaches and then fuses with the nucleus of the ovum. Zygote divides over and over, to make a ball of cells called an embryo. It implants itself in the wall of the nucleus (implantation) which is followed by conception Development of foetus: zygote is changed through growth (mitosis) and development (organization of cells into tissues and organs) Umbilical cord: contains umbilical artery which carries deoxygenated blood and waste products from foetus to placenta and umbilical vein which carries oxygenated blood and soluble food from placenta to foetus. (Contains foetus’ blood) Placenta: organ for exchange of soluble materials such as foods, wastes and oxygen between mother and foetus; physical attachment between uterus and foetus. (Contains mother’s blood) Amniotic sac: membrane which encloses amniotic fluid, broken at birth. Amniotic fluid: protects foetus against mechanical shock, drying out and temperature fluctuations Antenatal Care: Change in diet: More proteins → growth of foetus Slightly more fat → the new cells’ cell membrane More vitamin C and D → blood vessel walls and bones Iron → haemoglobin Calcium → growth of bones and teeth Guidance on motherhood Checks on foetus and mother including: weight check, blood tests, urine tests, blood pressure checks, ultrasound scanning etc. Labour and Birth Labour: The uterine muscular wall contract and cervix tries to relax, then contractions get more frequent. Contractions cause amniotic membrane to break and release amniotic fluid. Expulsion: Powerful Contraction pushes baby out. Afterbirth: Placenta is expulsed out. All contraction & pain gone Gamete Size Mobility Number Sperm Smaller Very mobile – use its tail Many more (300,000,000) Egg Larger Immobile – moved by peristalsis Fewer and limited Bottle feeding: Advantages Disadvantages Less painful More likely to develop illness Other people can feed baby Risk of wrong mixture May contain supplement vitamins and minerals Expensive Sex Hormones At puberty, the pituitary gland starts to stimulate the primary sex organs; the testes in males and the ovaries in females. Sex hormones – testosterone in males and oestrogen in females are released into the bloodstream. They only affect the target organs which have receptors which can recognize them. Causes secondary sexual characteristics such as the growth of pubic hair and maturation of sexual organs. Methods of Birth Control Natural: Abstinence: don’t have sex Rhythm method: don’t have sex during the fertile period, only during the safe period Chemical: Progesterone-only pill: pill which affects the uterus and makes implantation difficult Spermicide: a chemical applied as a gel, cream or foam which kills sperm. It is very unreliable on its own but makes barrier methods of contraception more effective. Mechanical: Condom: thin rubber covering over penis, it protects from impregnation and STDs, used by man Diaphragm: used by woman, prevent sperm entering uterus, reliable, must stay in place 6 hours after sex, needs a correct size Femidom: closed end, has a ring which gets pushed through cervix and open end’s ring lies against the labia IUD: plastic-coated copper coil, can be left inside for months or even years, has a string which is used to remove it out of the vagina, reliable, it irritates uterus wall preventing implantation Surgical: Vasectomy: sperm ducts are cut and tied Female sterilization: oviducts are cut and tied Artificial Insemination By donor: man’s sperm has a problem, making impregnation impossible, so a donor gives his sperm. In vitro fertilization: an ovum is fertilized outside a woman’s body. The fertilized ovum is implanted into the uterus. Fertility drugs: drugs which enhance reproductive fertility. For women, fertility medication is used to stimulate follicle development of the ovary. The side effect is multiple pregnancies. They contain varying amount of FSH and LH. Human Immunodeficiency Virus (HIV) Transmission: Intercourse, blood transfusion, organ transplant or sharing needle with infected person Prevention: Avoid intercourse with many partners Use a condom Don’t come in contact with other people’s blood How it affects the immune system: Infects and destroys lymphocytes Decreases efficiency of immune system Body becomes liable to infection by other pathogens