Year 12 Biology Module 5 - Reproduction PDF
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This document discusses reproduction in biology, covering asexual and sexual reproduction. It touches on the concept of gametes, genetic variation and the role of reproduction in the survival of organisms in a given species. The summary covers both single-celled and complex organisms.
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Year 12 Biology Module 5 Reproduction R eproduction:a process where one or more parent organismsproduce of an offspring which is necessary for the continuation of life ○ Life spans carry between organisms. But all individual organisms will ultimately di...
Year 12 Biology Module 5 Reproduction R eproduction:a process where one or more parent organismsproduce of an offspring which is necessary for the continuation of life ○ Life spans carry between organisms. But all individual organisms will ultimately die ○ A species must successfully reproduce to pass on their favourable genes to their offspring and ensure the continuity of the species ○ In reproduction, the most critical characteristics of living organisms are are passed onto their offspring ○ There are many different methods or reproduction, which can occur as either sexual or asexual Asexual Reproduction: ○ Identical to parents (clones) ○ Does not involve gametes or fertilisation No production or fusion of gametes nd no mixing of genetic information to introduce variation ○ Only one parent cell is required and all the genetic material in the offspring is passed down from this single parent Involves one parent dividing to produce offspring so offspring are genetically identical to the parent and to each other ○ In unicellular organisms asexual reproduction is the main form or reproduction Eg. budding, binary fission ○ Disadvantages of asexual: With little or no variation in the population the whole group/species is vulnerable to sudden changes in the environment (selection pressures) such as drought, disease, or a new parasite or predator. Changes such as these may result in survival of few if any individuals ○ Many organisms (fungi and plants) alternate between the 2 as a normal part of their life cycle. This mechanism, known as thealternationof generationsinvolves a sexually reproducing, gamete bearing generation alternating with an asexually producing spore-bearing generation Sexual Reproduction:parent organisms - male and femaleof the same species ○ Gametes: Sperm male - Eggs female ○ In fertilisation the two cells fuse together ○ Produces offspring similar to parents but not identical ○ Fusion of two gametes (sex cells) which carry the genetic information from both parents and combine to produce genetically diverse offspring ○ Process of producing new organisms by the combination of genetic information from two individuals of different sexes ○ ffspring are genetically different from parents O ○ Introduces genetic variation ○ Sexual reproduction is a mechanism that has evolved to ensure continuity of species ○ During sexual reproduction a combination of genetic material from two parents is passed onto offspring ○ This genetic information from each parent is passed on in the form of chromosomes ○ Each species usually has two sets of chromosomes, arranged in homologous pairs ○ The homologous pairs are contained within somatic cells ○ {body (non reproductive) cells} ○ Every species has a characteristic number of chromosomes per cell (humans have 46 chromosomes camels have 70 tomatoes have 24) ○ The chromosome number is constant for each species and does not change from one generation to the next ○ The gamete contributed by each parent arehaploidscellsmeaning they contain only one copy of each chromosome which is half the regular number of chromosomes found in a typical body cells ○ Haploid cells are produced by a special type of cell division called osmosis ○ When a haploid sperm cell combines with a haploid egg, the egg is said to be fertilised and is no longer haploid but nowdiploid(cell with 2 copies of each chromosome) ○ Diploid cells contain the full set of chromosomes for the new organism ○ A fertilized egg egg is known as a zygote ○ The diploid zygote divides by mitosis to become an embryo with identical body cells that all have the diploid number of chromosomes Meiosis In sexual reproduction, ot prevent the chromosome number from doubling in each successive generation, a mechanism to ensure that each parent contributes only half of their chromosomes to the offspring is necessary M eiosis is a type of cell division that takes place in the reproductive organs of plant/animals, is important to maintain the characteristics of chromosome number during sexual reproduction When a cell involved in sexual reproduction divides by meiosis to produce gametes (sex cells) the chromosome number halves - that is, each resulting gamete contains only one set of chromosomes Sexual Reproduction If n=1 set of chromosomes then in humans, n=23 Human somatic cells are diploid (2n) and have 46 chromosomes, whereas humans gametes are haploid (n) and have 23 chromosomes (as a result of meiosis) Most animals are unisexual - there are separate male and female individuals. However a small range of animals are bisexual or hermaphrodites where each individual has both male and female reproductive organs Advantages of hermaphroditism ○ Advantageous to species with low population densities, or in animals that are non-motile where finding a mate is difficult (coral) Disadvantages of hermaphroditism: ○ Individuals must expend larger amounts of energy to grow and maintain two sets of organs ○ Is self-fertilisation occurs the gametes carry fewer possible combinations of genes therefore the offspring will have less variation Comparative table feature sexual asexual Parent number two one Genetics of offspring unique identical Type of cell division meiosis itosis, binary fission, M budding, vegetative propagation advantages igh genetic variation: H - High efficiency (time efficient population more likely to and low energy used) survive environmental change -Population size can increase rapidly -no need for mate -no need to care for offspring disadvantages - Low efficiency (costs time - Low genetic variation: Less and energy) likely to survive environmental -Slow reproduction rate change (selection pressures) -requires mate -can lead to large scale -fewer offspring produced extinction events organisms Animals plants fungi Plants fungi protists bacteria I nternal fertilisation Eggs are fertilised in the female body EXAMPLE: most mammals such as human beings, birds and some reptiles Internally fertilised egg may develop a shell and be laid in the external environment (oviparous) to complete its development (reptiles and birds) or it may continue Reptiles: most reptile eggs are fertilised internally then deposited outside for development Crocodiles: fertilisation occurs internally the female crocodile lays a small number of large yolky eggs in clutches along the sandbanks beside the sea or river. The eggs of most reptiles are considered in a soft but tough leathery shell ○ Exceptions are tortoises, geckos, crocodiles, which lay hard shelled eggs.the egg contains sufficient food reserves to last until the eggs hatch. ○ The offspring resemble miniature adults and aere able to crawl from the buried nest to surface and make their way into the water, a journey that makes them vulnerable to predation Advantages ○ Fewer gametes required;higher chance of fertilisation ○ Organisms not limited to aquatic/moist environmental requirements ○ Allows for more control of mate choice ○ Natural selection is quicker (improves health of population more quickly over time) Disadvantages ○ Requires more energy ○ Generally produces fewer offspring External fertilisation Both sperm and eggs are released into the environment and fertilised outside the body The chances of successful external fertilisation are increased by synchronisation of reproductive cycles, mating behaviours and release of gametes Advantages ○ Lower amount of energy and time ○ Often produces large number of offspring ○ Wide dispersal of young (reduced competition for resources) Disadvantages ○ Lower chance of fertilisation/gamete survival; ○ Organisms often limited to aquatic/moist environments to keep gametes alive EXAMPLE: fish, crustaceans, molluscs, some amphibians Staghorn coral is an example of a colony of invertebrates marine animals (polyps) that achieve fertilisation by shedding millions of gametes into the sea ○ Environmental cues, such as water temperature, tides and day length, help synchronise the reproductive cycle ○ When polyps in one colony start to spawn, pheromones released along with gametes stimulate nearby individuals to spawn, resulting in coordinated spawning over a wide area Compare and contrast internal and external fertilisation Aspect Internal Fertilisation External Fertilisation Definition ertilisation occurs inside the F ertilisation takes place outside F body of the female. the body, usually in water. Examples of Organisms ammals, reptiles, birds, and M ish, amphibians, and many F insects. aquatic invertebrates. Environment Required oes not rely on external D equires a water or moist R environmental conditions. environment to prevent gametes from drying out. Number of Gametes Released F ewer sperm and eggs, as arge numbers of sperm and L fertilisation is more controlled. eggs are released to increase chances of fertilisation. Chance of Fertilisation igher due to direct transfer of L H ower, as fertilisation depends sperm to egg. on random meeting of sperm and egg. Parental Investment sually higher, with more care U ypically lower, though some T for developing offspring (e.g., species guard eggs (e.g., frogs). pregnancy). Survival Rate of Offspring igher, as offspring are often H ower, as many eggs and L protected within the parent’s larvae are vulnerable to body or eggs. predators. Energy Cost to Parents igher due to pregnancy, H ower, but significant energy L mating rituals, or internal may still be used to produce development. many gametes. Adaptation to Environment ommon in terrestrial C ore common in aquatic M organisms and those with environments where external fewer offspring. fertilisation is feasible. SC Questions H Q1) Which of the following is an advantage for animalsusing internal fertilisation rather than external fertilisation? A) It prevents dehydration of gametes. B) It involves a large number of gametes. C)It relies on adaptations such as mating rituals. D) It allows gametes to combine to form unique offspring. 2) Justify why internal fertilisation can be more advantageous than external fertilisation in Q ensuring the continuity of species. (5 marks) Internal fertilisation has a higher chance of success as there is a smaller area in which the gametes are released increasing the chance of collision and fusion of gametes. Although there are less zygotes being produced, internal fertilisation is still more advantageous as the success rate of offspring survival is much higher. Zygotes have a higher chance of survival in internalised fertilisation too as the temperature in which the zygote grows is regulated, chance of predation is eliminated and all other external environmental factors have a lower effect on the zygote in an internal environment. Once the offspring is born its chance of survival is further enhanced by the care provided by the parents whereas in external fertilisation the parents are often absent to care for offspring forcing them to search for food and safety themselves. Overall these factors work together to increase the chance of survival of the species from fertilisation to a portion of time after the birth of the offspring leading to an increased chance of species continuity. 3)Students tested the hypothesis that the numberof eggs/young produced was greater in animals Q using external fertilisation than those using internal fertilisation. They obtained the following data from secondary sources. a) What conclusion can be drawn from the data? Justify your answer. 3 marks The hypothesis that a higher number of offspring are produced through external fertilisation is not supported by this set of data. The mean for internal fertilisation (43) is slightly higher than that of species using external fertilisation (40). However, the high standard deviation (55) in the internal group means that there is significant variability. Some species with internal fertilisation like the kangaroo produce very few offspring, while others like the loggerhead turtle produce many. This could skew the average. ) Justify an improvement to the students’ experimental design to test the hypothesis. (2 marks) b The data set is currently skewed due to some animalssuch as kangaroos and guppy fish having vastly different numbers of offspring by eliminating outliers the data set can be improved. c ) Explain one advantage of animals using external fertilisation. (2 marks) Animals using external fertilisation expend less energy and time in producing offspring. Worksheet a l Reproduction -one parent produces offspring withgenetic makeup that is identical to the parent’s. It occurs in most simple, single celled organisms such as bacteria and some multicellular organisms such as fungi, some plants, and even a few animals. Sexual Reproduction -two parents produce a new organismthat has a combination of genes from both parents, and it is not identical to either one. It occurs most often in complex organisms. 1) Complete the following table comparing asexual and sexual reproduction. ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Number of parents 1 2 Genetic info compared identical similar to the parents omplexity of organism C simple complex that usually uses this method xample of organisms E bacteria , protists, fungi Plants, animals that usually uses this method 2) Complete the following table: Process Description ype of T Example of organism reproductio n (sexual or asexual) Mitosis asexual bacteria itosis is the process by which a cell M replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division. Budding a type of asexual reproduction in which a A sexual Yeast, coral new organism develops from an outgrowth or bud due to cell division at one particular site Parthenogenesis r eproduction without fertilization, an ovum asexual ants, wasps, and bees developing into a new individual without fertilization by a sperm Fragmentation a piece of the body, or fragment, of the asexual ungi, lichens, molds, F parent breaks off and develops into an worms, independent offspring. Fertilisation he sperm from a male meets an ovum T sexual mammals from a female and fuses to form a zygote ) Classify the following as either Sexual or Asexual Reproduction. Give the specific type if 4 Asexual. (a) A small piece of a cactus breaks off the plant, falls to the ground, and begins to grow. fragmentation (b) Pollen from a male poplar tree fertilises sex cells on a female poplar tree. sexual (c) Two earthworms each produce sperm and eggs and fertilise each other. sexual (d) A flatworm is cut in half and grows into two flatworms. fragmentation Hormones H ormonesare chemical substances that act as messengersin the body, coordinating many aspects of functioning, including metabolism and reproduction, so that actions within the body are synchronised Thepituitary glandis an endocrine gland attachedto the base of the brain and just above the roof of the mouth referred to as the master gland. It secretes hormones that stimulate or inhibit other endocrine glands, regulating the release of their hormones for growth, metabolism and reproduction Hormones that specifically affect the growth or functioning of the reproductive organs or the development of secondary sex characteristics are called sex hormones, they are produced in special tissues in the ovaries or testes and in the pituitary gland and adrenal cortex The reproductive organs in mammals are present at birth, but only mature and begin their reproductive function when stimulated by hormones secreted during puberty. T he gonads (reproductive organs) become functional at puberty and the reproductive cycle commences Gametes are produced in the male and female gonads by a process known asgametogenesis Major hormone istestosterone- but oestrogen, LHand FSH are also present in lower amounts in females and help support healthy sperm Testosterone triggers the production of LH and FSH which trigger sperm production Continuous process- millions of sperm cells produced daily (but take 2.5 months to mature) The production of sperm is called spermatogenesis and is controlled by hormones in humans In humans spermatogenesis includes the interaction of three glands: hypothalamus in brian, pituitary gland, leydig cells in the testes In males LH stimulates the production of testosterone and FSH stimulates the production of a protein by sertoli cells in the testes, to maintain testosterone at a level high enough to promote spermatogenesis When the hormone inhibin is secreted it reduces the levels of FSH in the body Gonadotropin - maturing of sex organs during puberty T he sperm consists of the head, neck, middle piece and tail The entire body of the sperm is covered by a plasma membrane The head consists of a cap-like structure called the acrosome which contains digestive enzymes that help in fertilisation of the ovum. It also contains a haploid nucleus The middle piece consists of many mitochondria which provide energy to the sperm for locomotion, it also contains the centrioles The tail is for the motility of the sperm Key processes of female reproduction Ovulation Release of ovum (egg cell) from ovary Happens about 28 days All ova are produced before birth and stored in ovaries, but are not matured yet During each ovarian cycle, an ovum matures and is released If more than one ovum is released this can result in fraternal twins (non-identical) Ovarian cycle First 14 days is follicular phase FSH (follicle stimulating hormone) starts the maturation of the follicle The cells lining the follicle secrete oestradiol Oestradiol (a type of oestrogen, both are acceptable in hsc answers) promotes the production of LH (luteinising hormone). oestradiol peaks at day 12 causes a leak in LH which triggers ovulation (ovum released from follicle) M ature follicle is known asGraafian follicle(there's 10-14days from primary follicle to graafian follicle) Fallopian tube can be called an oviduct Luteal phase day 15-28 LH causes burst follicles to build up lutein (yellow protein). The follicle is now thecorpus luteum. It secretes progesterone (to develop endometriumand maintain pregnancy with oestradiol) ○ Endometrium is the layer of tissue lining the uterus. Corpus luteum breaks down once placenta produce progesterone or if pregnancy does not occur If pregnant: Hormonal triggers lets body know it is pregnant Corpus luteum stays in the ovary and continues to produce progesterone for 3 months and allows for the endometrium to stay healthy After those 3 months the placenta is fully formed and becomes the main source of nutrients If not pregnant:the corpus luteum gets expelled fromthe body alongside Menstrual cycle Menstrual cycle starts with the menstrual period (menses) which lasts about four days. During this time, the endometrium (lining of the uterus) breaks down and tears away. This is accompanied by bleeding which is known asmenstruation First day of menstrual period marks the beginning of the follicular phase which ends on the day of ovulation Following menstruation, a new endometrial lining forms in the uterus over about 5-12 days known as the pre-ovulation phase. Ovulation takes place in an ovary 13-15 days after the start of menstruation, but this timing varies person to person Fertilisation - The fusion of two haploid games (male and female) to form a diploid zygote - It takes place in the fallopian tube in humans - Presence of progesterone helps sperm mature so that they penetrate the ovum hen sperm reach the egg cell, they must cross three layers. W They physically push through the first membrane which still hsa follicle cells attached These protective cells release enzymes to assist penetration by the sperm. When the acrosome (protective cap) of a sperm comes into contact with the glycoproteins of the next barrier, the zona pellucida (2nd layer) The acrosome fuses with the cell membrane of the sperm hear, allowing the tip of the sperm to release enzymes that assist its penetration Egg can be called the oocyte Many sperm reach the cell membrane (plasma membrane) which is the last barrier. Surface proteins allow one sperm to penetrate this barrier, triggering the release of enzymes by the egg that destroy the glycoproteins in the zona pallucida and cause electrical changes, preventing other sperm from entering. The first sperm to penetrate the inner barrier causes the ovum to immediately go under cell division A single sperm penetrates each available ova (egg) resulting in one or more zygotes T he zygote begins mitosis and divides into two cells which then divide further into a blastocyst (ball of undifferentiated cells) I mplantation: key hormones during implantation Oestrogen promotes growth of the endometrium of the uterus Progesterone stimulates the secretion of mucus by the cells lining the endometrium and the growth of blood vessels Once implantation occurs, progesterone suppresses uterine activity, supporting foetal development and reducing the risk of the foetus being distrubed or expelled by uterine contractions Progesterone also reduces the mother’s immune response to foetal antigens Implantation Typically occurs 6-10 days after ovulation Blastocyst travels down fallopian tubes into uterus and implants in the endometrium (prepared by progesterone and oestrogen) Once implanted, the cells continue to divide and form an embryo (developing offspring) If the egg is not fertilised and implantation does not occur, the corpus luteum begins to degenerate about 8-10 days after ovulation, forming a mass of fibrous tissue known as the corpus albicans. The endometrium breaks down and passes out of the vagina Blastocyst contains the inner cell mass which go on to form the embryo The outer cells of the blastocyst are called trophoblast cells - initiate the formation of a placenta Implantation involves the trophoblast cells of the blastocyst secreting enzymes that break down some of the endometrial cells This allows the blastocyst to enter the lining and implant, where it continues to undergo further cell division (mitosis) Once the blastocyst has implanted into the uterine wall, the placenta begins to release hormones, such as human chorionic gonadotropin (HCG) Pregnancy and birth Following internal fertilisation the young completes embryonic development inside the body of the mother in an organ known as the uterus which nurtures and protects embryo Once one or more fertilised eggs implant into the uterine wall, a placenta develops, connecting the young to a supply of nutrients and oxygen that passes from the bloodstream of the mother to the developing young Excretory waste such as nitrogenous waste and co2 from the embryo diffuse across the placenta to the mother’s body, where they are excreted with the mother’s own waste As the placenta forms and grows, it develops the ability to produce hormones Week 6-9 of pregnancy- placenta takes over from the ovaries as the main producer Progesterone is important for: correct foetal development, stopping womb contractions until labour, preventing lactation, strengthening muscles of pelvic wall to prepare for labour Hormones and the Placenta: - estrogen levels increase steadily until birth and have a role in maintaining, controlling and O stimulating the production of other pregnancy hormones, development of many foetal organs, stimulating the growth and correct function of the placenta, promoting growth of maternal breast tissue and preparing mother for lactation - Relaxin helps prepare body for childbirth, increasing elasticity of ligaments and expansion of pelvis Pregnancy: - Previse levels of these hormones are needed for foetal development - Embryo itself also plays a role in producing hCG which maintains corpus luteum for the first trimester T he mother gives birth to live tongue that are mature and therefore have a greater chance of cervical This type of development, where live young are born, is described as viviparous Placental mammals produce one to few young at a given time and they invest a large amount of energy in parental care, increasing the chance of survival of the young When the foetus is fully developed (usually)prostadlandisare secreted by the uterus which make it sensitive tooxytocin Oxytocin causees the uterine muscles to contract and the cervix to relax The hormone relaxin is also produces and this further aids the softening of the cervix Contractions cause secretion of prostaglandin and oxytocin, which cause more contractions and so on Hormones in labour and birth Endorphins: reduce pain and suppress the immune system. Helps trigger release of prolactin to prepare breasts for lactation Adrenaline: stimulates contractions Progesterone: levels drop towards end of pregnancy, oestrogen levels keep rising Foetal cortisol: rises, which boosts oestrogen secretion by the placenta in month 8 As the contractions increase in intensity beta-endorphin hormones are release. These act as a natural form of pain relief and promote feelings of elation ○ Responsible for the development of the babies organs Lung development Maturing of liver at birth Very close to the birth, a surge of adrenaline is released by the mother’s body causing very strong contractions that lead to the birth A fter the birth oof the baby, oxytocin secretions continue causing the uterus to contract and expel the placenta Prolactine (a hormone produced in the pituitary gland) stimulates milk production inn the breasts As the contractions Positive and negative feedback loops W hen a stimulus causes a reaction which produces the same stimulus (i.e processes that causes itself to repeat), this is apositive feedback loop Since prostaglandins and oxytocin and oxytocin cause contractions, they can be used in medical procedures such as induction (to start labour artificially) or abortion (to terminate a pregnancy) Oestrogen amd progesterone prevent contractions these drop during labour How is success maximised? Mammals have several reproductive mechanisms to maximise reproductive success ○ Internal fertilisation to increase the likelihood that gametes will meet (all 3 subclasses of mammals) ○ Implantation of the embryo into the uterine wall, with internal development the embryo (marsupials and eutherians) to increase the embryo’s chance of survival ○ Pregnancy to allow the developing young to be protected from the external environment, have a constant nutrient supply and complete gestation period (short in marsupials, prolonged eutherians, whose young are well developed when they are born) Key hormones summary Testosterone:sperm production Oestrogen:development of ova; supports sperm production Progesterone: prepares endometrium for implantation,helps mature sperm, maintains pregnancy FSH (follicle stimulating hormone):helps folliclesin ovary to mature (to release ova), supports sperm production LH (luteinizing hormone):promotes development andcorpus luteum hCG (human chorionic gonadotropin):maintains corpusluteum Oxytocin:triggers contractions for birth Sexual reproduction in plants T he plants on earth from less advanced plants such as mosses and ferns to cone-bearing plants (gymnosperms) and flowering plants (angiosperms) have developed a range of reproductive strategies strategies to ensure the continuity of species Ion angiosperms, flowers are the reproductive structure of a plant Some flowers contain both male and female reproductive parts, while other flowers only contain one or the other Different types of plants have different gametes - many use pollen and ova (angiosperms) while others use spores (conifers) Sexual reproduction increases the genetic variation but is risky for plants as they cannot move to find a mate - they rely on wind, water or animals for fertilisation Stamen- male reproductive organs carpel - female reproductive organs Pollination Transfer of pollen from the anthers to the stigma Pollinators eg. bees can easily get pollen on their bodies when they feed As pollinators move from flower to slower they help transfer pollen when eggs are fertilised by pollen, they becomes seeds and the ovary develops into the fruit of a plant Self pollinationoccurs when pollen fertilises theova of the same plant Self pollinationoccurs when pollen fertilises theova of a different plant ○ Both are sexual reproduction In plants self pollination requires less energy as there is no requirement for the plant to produce structures to attract pollinators (bright petals or nectar). These plants can grow in areas where insects or other animals that visit plants are either absent or scarce Even if both parts are present, many species of angiosperms do not self pollinate Instead they can only cross-pollinate and have mechanisms to help ensure cross pollination occurs Cross pollination ensures genetic variation in offspring In some angiosperm species the stamens and stigma ripen at diff times - this reduces the likelihood of self pollination occurring 1. For fertilisation to occur the male gametes inside pollen must be carried from the anthers to the female part of a flower, called the stigma. This process of the gamete transfer is called pollination. Pollen transfer to the stigma of flower is aided by pollinators (bees, wind/water dispersal) 2. Pollen is composed of a tube cell and a generative cell. Once pollen has been deposited on the stigma the pollen’s tube cell creates a pollen tube from the stigma down the style, towards the ovary 3. The two sperm cells enter one of the ovules within the plant’s ovary. The ovule contains 2 polar nuclei and an egg. Inside the ovule, one sperm cell fertilises the egg to form a zygote. The other sperm cell combines with two polar nuclei to form the endosperm which provide nourishment for the zygote 4. After fertilisation, an ovule matures into a seed. The seed contains the fertilised egg (zygote) amd the endosperm. The seed may then be dispersed to gametes 5. The zygote develops into an embryo which will grow into a new plant cell division (mitosis) after the seed germinates 6. After fertilisation,the petals of the flower die off and the ovary grows into a fruit to nourish and protect the seeds, and encourage dispersal when they are mature Seed dispersal The success of seed dispersal depends on the type of agent that the plant relies on Fruits may be dry (such as banksia pods, gum nuts) or fleshy (such as apples, dragon fruit) Dry fruits often have inbuilt ‘explosive’ mechanisms for dispersal by air, wind or water (abiotic agents). They are usually light so that they can float on air or water Fleshy fruits often rely on insects, birds or mammals for dispersal (biotic agents) - animals eat the fruit, move along and then egest the seeds, usually some distance away from the parent plant Advantages It is an advantage for seeds to be dispersed over a wide distance, as this helps prevent overcrowding and competition for light, water and soil nutrients Widespread distribution increases the chance of the continuity of the species in other locations in case rere is a sudden change in the local environment such as fire or disease Asexual reproduction in plants S ome adult plants produce vegetative organs, such as bulbs, tubers, rhizomes, and suckers from which new plants can arise. This is equivalent to cloning an adult plant as the offspring are genetically identical to the adult These methods of asexual reproduction include: ○ cuttingsc ○ runners ○ Rhizomes ○ suckers ○ Tubers ○ Bulbs ○ Plantlets on leaf margins RUNNERS Stems which grow horizontal form above the ground; have nodes where the buds are formed; buds grow into a new plant Example: strawberries, mint, spider plant In the cultivated strawberry for example, the leaves, flowers, and roots are produced at every alternate node on the stem runner. Just beyond each second node, the tip of the node turns up and thickens producing new roots and run a new shoot that continues the runner RHIZOMES Horizontal underground stems that produce shoots to become new plants They can give rise to a new shoot at each node Gardeners often propagate ferns by splitting the rhizomes ○ Examples: bamboo, ginger, many ferns (same as runners but underground) TUBERS Large underground food storage structures (part of the root system) that can bud and produce more plants ○ Examples include: potatoes, sweet potatoes, dahlia’s BULBS A short term underground stem that can produce a new plant (and multiply) Food storage organs with fleshy leaves that store food and can grow and develop into new plants Food storage units that can grow from a stem Example: onions, garlic, lilies, tulip SUCKERS The roots of some plants produce modified roots called suckers or sprouts Trees and shrubs that sucker, such as reeds, wattles and blackberries, can spread quickly into a vacant habitat after disturbance The wattle sends up shoots from the outer roots and these grow into separate plants if the pae=rent shrub dies ○ This allows for rapid regrowth after a decline in numbers (after bushfire or drought for example) Advantages of asexual reproduction E nables organisms to reproduce quickly without having to find a mating partner For plants, which are immobile, finding a mate is complicated. Being genetically identical may give organisms a comparative advantage if they live in an enviromnmetn to which theu are well adapted More common in harsh environments where organisms are so specific that there is little benefit in genetic variation within the population ○ In these habitats when favourable conditions arise suddenly, organisms can reproduce quickly and effectively Asexual reproduction in animals I t is not only members of the plant kingdom that undergo asexual reproduction it is common in other organisms where it may be advantageous for the parent and young to be genetically identical Mechanisms of asexual reproduction in animals include budding, binary fission, sporogenesis, fragmentation and parthenogenesis Fungi Eukaryotic, heterotrophic organisms, can be single celled or multicellular, eg yeasts, moulds, mushrooms Reproduce by fragmentation, budding or spores Multicellular fungi usually grow as tiny branching filaments called hyphae that spread through the material on which the fungus feeds forming the main body of the fungus called mycelium A single hypha consists of one or more microscopic cells surrounded by a cell wall. A spores are tiny, unicellular reproductive cells thatare produced in great numbers by organisms such as fungi (e.g moulds and mushrooms and some plants (mosses and ferns) Most multicellular fungi reproduce by producing a huge number of spores. Spores are tuny cells that form on special structures Structures called sporangia can produce very large numbers of of spores, which are light and easily dispersed travelling long distances by wind. Spores are very light therefore very easily dispersed If a spore lands where there is moisture and food, it many germinate and produce hyhae As the hyphae branch and grow out in all directions, they develop into mycelium Spores are usually single cells produced by fragmentation of the mycelium or within specialised structures (sprangia, gametangia, sporophores, etc) Fungi produce spores asexually and/or sexually Asexual reproduction using spores in fungi T he special hyphae the produce spores aee aploiud for most of their cycle When a fungus reprroduces asexually, the spores released from these hypae are produced by mitosis These spores are haploid and identical to the parent fungus Example: penicillin species sexual reproduction using spores in fungi V ery complex When fungi reproduce sexually, two hyphae from 2 different mycelia fuse to create a diploid zygote The zygote undergoes meiosis to produce haploid spores that contain genetic material from both parent cells - this leads to variation in a fungal species These spores end up on the fruiting body of the fungus, the mushroom. Whis releases the spores into the environment fragmentation A multicellular fungus can divide into fragments Each fragment becomes a separate organism, all with identical genetic material Can also happened in other species such as starfish Budding ost species of fungi are multicellular. Unicellular species of fungi aee referred to are yeasts M Yeasts reproduce asexually-with most yeasts reproducing by the process of budding. During budding a bulge wdforms on the side of the cell The cell creates an exact copy of its nucleus for the new organism The bud then detaches from the parent cell as a separate (but genetically identical) organism Budding occurs in 2 stages: ○ Formation of a bug on the side of the cell followed by nuclear division to provide each cell with a genetically identical nucleus. Note: the bud is initially smaller than the parent cell but grows in size as it matures ○ After the bud is nearly as large as the parent, cytokinesis occurs (the separation of the cytoplasm to form two separate cells) Bacteria B acteria are prokaryotic These unicellular organisms have cells without nuclei or membrane bound organell;es, bacteria typically have their dna as a single circular chromosome While they are single celled they often live in colonies. ○ Example: disease-causing bacteria such as E.coli or beneficial gut bacteria such as lactobacillus species Bacterial Reproduction by binary fission Binary fission is the main method of asexual reproduction in unicellular organisms such as bacteria (prokaryotes) and protists (unicellular eukaryotes) Most bacteria have one chromosome, which consists of a circular dna molecule Within this chromosome is a region called the origin of replication This is the starting point from which the chromosome begins to replicate After the origin is duplication, one copy of the origin moves to the opposite end of the cell Once the entire chromosome has been duplicated, the cell begins to elongate, as it gets ready to divide into two The division of the cytoplasm is call cytokinesis It involves the plasma membrane growing inwards at the centre of the cell and a new cell wall being formed for each of the daughter cells Since the two copies of the origin have moved to opposite ends of the cell, one copy of the chromosome will end up in each of the daughter cells Binary fission typically results in the formation of two daughter cells that are genetically identical to the parent organism Occasionally mutations occur during the process of dna replication This can cause slight variations in the daughter cells protists Example of a protist: amoeba Eukaryotic, mostly unicellular organisms Can reproduce both sexually and asexually Asexual - binary fission or budding Sexual- meiosis and fertilisation Asexual reproduction in protists Binary fission in protists is like bacterial fission but the entire nucleus and all other necessary structures are replicated not just dna Multiple fission also occurs among some protists herr the nucleus divides repeatedly to produce a number of daughter nuclei, which eventually become daughter cells This involved mitosis and the formation of a spindle within the cytoplasm of the cell to distribute chromosomes equally ○ EXAMPLE: AMOEBA Budding occurs when a daughter cell/s gradually grows from the body of the parent cell, eventually detaching when they mature Daughter cells contain an exact copy of parents dna U nlike fission where the parent cell becomes 2 daughter cells, budding results in the parent cell remaining the same after the daughter cell/s detach Sexual reproduction in protists Sexual reproduction involves two fundamental processes meiosis and fertilisation Haploid protists ○ Two haploid cells fuse to form a zygote ○ Zygote undergoes meiosis to form new haploid cells ○ Example: plasmodium ○ Diploi Diploid protists ○ Adult diploid cell undergoes meiosis to produce haploid cell (gametes) ○ Fertilisation of different haploid cells form a diploid zygote which develops into an adult diploid Reproductive technologies Agriculture is the cultivation and breeding of animals Get rest from divya The products of these industries meet a wide range of human needs such as clothing, medicines, tools, furniture, artistic display and economic gain/profit Agriculture must be sustainable for long-term cervical of humans and environment Increased population→ increased demand The increase in scientific knowledge on plant and animal reproduction had led to huge advancements in agriculture Biotechnology - use of living organisms or processes for human benefit in industrial and other uses Includes: ○ Reproductive technology - used to assist to manipulate reproduction ○ Genetic technology - used to manipulate or utilise genetic material selective breeding Two parents with desirable traits are selected and read together producing offspring with these traits Likely the earliest form of biotech used to domesticate dogs for up to 14000 years Used widely in agriculture to produce ideal strains of crops or livestock What is it? Farmers selectively mate plants and animals with desirable traits Steps: Determine the desired characteristics Interbreed parent who show the desired characteristics Select the offspring with the best form of hr trait and breed these offspring Continue until the population reliably reproduces desirable characteristics Benefits: Encourages plant and animal characteristics that are more beneficial to farmers (high milk production, quality meat, greater crop yield)
