Antimicrobial Properties The term antimicrobial properties regards the
Antimicrobial Properties The term antimicrobial properties regards the ability to kill and/or slow down growth of bacteria / fungi and other micro-organisms. Antimicrobial properties practical Extract the filter paper that’s' soaked in extract place it on an agar plate (growth medium) with (bacterial lawn Micrococcus luteus) using the aseptic technique. Seal the plate/petri dish taping it on opposite ends but not completely cutting of the supply of oxygen as aerobic processes would not be possible. Incubate for 24 hours at the temperature 25 o. C and ensure that the temperature does not get to 37 o. C as this is human body temperature and allows and encourages growth of pathogenic bacteria. You have to find and measure the clear area (inhibition zone) which shows the area of no bacterial growth. The inhibition zone should be present around the filter paper soaked in extract, if the extract inhibits bacterial growth and has diffused out of the disc and killed the bacteria. Use a filter paper disc soaked in distilled water as a control for comparison and to show that any difference between discs is to the extract. Repeat practical x 3 The lid was secured in this way as it reduces contamination of culture and allows aerobic conditions / entry of oxygen and prevents anaerobic conditions reducing growth of harmful anaerobic bacteria being cultured. The discs should be sterilised before being soaked in the extract so no bacteria/ microbes are alive on them this prevents contamination by microbes that could be harmful/pathogenic and could compete with Micrococcus luteus on the plate and affect the growth of Micrococcus luteus. The petri dish must be sterile to prevent contamination by other bacteria and prevent competition between bacteria. It also stops pathogenic bacteria being cultured and makes the investigation valid. A suitably prepared petri dish has to have agar and bacteria need to be distributed evenly (bacterial lawn) with a single bacterial strain. Should be prepared using aseptic technique with sterile plates.
Tensile Strength The tensile strength of a fibre is it’s ability to resist stretching / being broken when pulled the tensile strength is a measurements of the maximum load / force which can be applied before breaking point Core practical Tensile strength Place stems in buckets and cover with water. Leave for ten days (RETTING) to remove/separate the soft tissues from the fibres by microbial / bacterial decomposition. Suspend fibres with weights on. Use fibres of the same diameter and same initial length add weights with increment’s of 25 g until the measurable breaking point is reached. Ensure that repeated readings x 3 are taken at each weight increment using different fibres. Wear goggles for safety in case fibre snaps and wear steel toe shoes to protect against falling weights. Keep these variables the following variables constantly the same: temperature and humidity. Factors to be kept constant in this investigation -Length (of fibre) -Diameter (of fibre) -Temperature -Stored for the same length of time -Same way of applying the masses -Same humidity -Water content of fibre / level of drying Fibres were collected from only one plant in stage 1 to remove genetic variation as same genotype is needed. Fibres need to be grown in same conditions / same composition/same age. This allows the practical to give comparative results that are valid. Mineral Deficiencies Plants require water for: photosynthesis, structural rigidity, transportation of minerals and temperature regulation. Plants require mineral ions: They require magnesium ions to create chlorophyll. They require nitrate ions for making DNA and protein as well as chlorophyll production. Nitrate ions are also required for plant growth / fruit production and seed production. Calcium ions are required to make calcium pectate (pectin) which acts as intercellular cement that help hold cells together. Mineral deficiency practical Using 6 nitrate ion concentrations from 0 -25% grow seedlings for 2 weeks measuring root lengths to make judgements on the optimum nitrate concentration. Repeats at each concentration x 3 and keep the temperature constant as well as light intensity and volume of the mineral solution. The control is the soil with a 0% nitrate ion concentration. There has to be uniformity of seedlings, they have to be genetically similar so are all selected from the same parent plant and have the same age and same original root length. The solutions contain magnesium and calcium ions at a constant concentration in all the soils. Factors that were controlled in this investigation: -Water / humidity -Light -Minerals / soil type / p. H -CO 2 -Temperature -Altitude
Observing Mitosis How you would prepare a root tip squash to observe the stages of mitosis. -Use a short length of root tip (roughly 5 mm). -Acidification. -Add stain acetic orcein. -Warm using bunsen burner -Break open tip with mounted needle. -Mount in stain. -(Gently) squash under coverslip o slide. -Warm microscope slide (to intensify staining) Use the tip of an onion root as it is the site of cell division (mitosis) and has actively dividing cells. The cells are warmed in acid during the preparation of the slide to soften the material/macerate separate the cells. Squash during preparation to get a single layer of cells that are spread out. Stain with acetic orcein to make the chromosomes /chromatids visible. Warm slide to intensify staining Totipotency Asexual reproduction results in low genetic diversity as population of a species has a small gene pool. -Asexual reproduction leads to all offspring being genetically identical as they have the same alleles. The is no meiosis/ no recombination of genetic material variation is only possible as a result of mutation You must cover the beaker with clear plastic film for safety. -To allow light in for photosynthesis. For reducing water loss and preventing the entry of organisms that would affect plant growth. To prevent microbes/bacteria from contaminating and creating harmful pathogenic microorganisms Factors to keep constant in this investigation -Volume of solution -Light -Temperature -Concentration of mineral ions -p. H Totipotency and plant tissue culture Use a sample of safely cut explants from both tissues. -Use aseptic conditions by lighting a Bunsen burner to form convection currents which help prevent contamination. -Place explants into nutrient agar (growth medium) and incubate the two samples for 24 hours in the same conditions. Same level of light, same temperature, p. H and allow cells to grow into a callus. Use growth regulators. Cells / tissue can differentiate cells can become whole plants.
Cell Cycle & Mitosis The role of the cell cycle. Responsible for growth of organisms from an increase in cell numbers. –Allows asexual reproduction / production of clones. Repairs tissues by replacing cells. -Controls cell growth and division by mitosis Interphase Mitosis Cytokinesis In S phase cells prepare to divide by semiconservative replication so that new cells will have same quantity of DNA as parent. DNA replication (S 1) must occur in the genetic material before the chromosomes become visible. How the cell cycle will be affected in cells that have become cancerous. There would be a shorter growth or G phase -Shorter interphase. -Shorter / faster cycle. -Usual controls/ ‘stops’ effective so cell divides uncontrollably and cells do not become specialised The significance of anaphase Means that daughter cells will be genetically identical to parent cell and maintains chromosome number Why the DNA content of the cell doubles. To prepare for DNA replication so that DNA content can halve so that new cells will have the same amount as original DNA content as it will have been restored during cytokinesis Function/importance of spindle Attachment of centromeres. -Separation of (daughter) chromatids
Cell Cycle & Mitosis phases: INTERPHASE Prophase: During prophase chromosomes / chromatids condense and become visible. Centrioles move to opposite poles -There is a formation of spindle-fibres. -The nucleolus disappears -There is the breaking down of nuclear envelope in prophase Metaphase: The nuclear envelope has been broken down before metaphase -At metaphase chromosomes / centromeres attach to spindle fibres -Chromosomes / chromatids are lined up at equator Anaphase: Centromeres divide -spindle fibres contract. -Chromatids separate -Chromosomes / chromatids move towards (opposite) poles. Telophase: Spindle fibres have now vanished -Chromosomes uncoil and become invisible. –There’s the reformation of the nuclear envelope so there are two nucleoli CYTOKINESIS The cytoplasmic division of a cell at the end of mitosis, bringing about the separation into two daughter cells. (sometimes counted as part of Telophase) Difference between mitosis and meiosis
Cell Organization organ (organ) system Tissues - Tissues are groups of (similar) cells often from the same point of origin working together to performing a function. Organs - Organs are a number of tissues that work to together to perform a particular function
Protein Transport -protein produced by ribosome - ribosomes held on attached to r. ER -proteins stored and transported within r. ER - proteins folded assume 3 -D shape tertiary structure within (lumen of) r. ER produce vesicles and so packages proteins -vesicles fuse with Golgi apparatus. -Golgi modifies and processes protein into a glycoprotein by adding and trimming carbohydrates. –Water is removed to concentrate. -Golgi produces lysosomes / secretory vesicles. Gametes & Meiosis
Gametes & Meiosis Sperm produced by mitosis and meiosis Cell division in males occurs in the Seminiferous tubule Egg The Human sperm cell is adapted for it’s function Flagellum to propel it to the egg -Smaller size to aid mobility and make it possible to produce sperm in large numbers. -Haploid number of chromosomes / only one of each chromosome 23 chromosomes rather than 46 so normal diploid number restored at fertilisation. -Acrosome to digest way (in)to egg. -Mitochondria provide energy for swimming The human egg cell is adapted for its function. haploid nucleus with 23 chromosomes so that diploid number of chromosomes is restored at fertilisation. -Lipid droplet food store supplies energy and nutrients for division. -Large (cell) size / surface area increases the chance of fertilisation. -Cortical granules / lysosomes (in cytoplasm) and zona pellucida to prevent more sperm entering (polyspermy). -Release of a chemical to attract sperm (chemotaxis). -Membrane with ‘(sperm) receptors’ on surface to allow sperm to bind. -m. RNA present to allow early translation of transcription factors. Haploid nucleus. Half the number of chromosomes found in a normal somatic cell , containing one chromosome from each homologous pair. The type of nucleus found in gametes a nucleus is an organelle with a double-membrane bound structure Meiosis DNA replicated to two identical chromosomes (chromatids). -DNA condenses to form (doublearmed) chromosomes (from two sister chromatids) there is homologous pairing of chromosomes. First division occurs homologous pairs separated. -Chromosome number halves. -Second division occurs pairs of sister chromatids separated four new cells (gametes) which are genetically different produced. Crossing over (before 1 st meiotic division) homologous pairs of chromosomes pair up the chromatids twist around each other parts of the chromatid break off and join the other chromatid creating a different combination of alleles in all 4 daughter cells Independent assortment Copy of each chromosome randomly assigned to each cell leads to large number of different combinations. Importance of the Haploid nucleus Has 23 half the required chromosome number, at fertilisation the full diploid number 46 is restored 23 complementary pairs of chromosomes allowing mixing of alleles through independent assortment and crossing over allowing for genetic variation.
Fertilisation in humans Fertilisation Mitochondria is in sperm cells as they carry out aerobic respiration and provide ATP energy to move the flagellum which allows sperm to propel towards the egg towards the oviduct. When a sperm cell reaches an egg cell it makes contact with the receptor on the zona pellucida (glycoprotein jelly coat surface of ovum) this causes the acrosome to swell and fuse with the sperm cell surface membrane. The acrosome reaction occurs, digestive enzymes are released via exocytosis from the acrosome which means the sperm are able to move through the zona pellucida to the cell membrane. Meiosis (II) completes. The cell membrane fuses with sperm head. The egg cell releases cortical granules into the space between the zona pellucida and cell membrane. The zona pellucida thickens so only one sperm fertilises the egg cell. (prevents polyspermy) the tail is discarded only the nucleus enters the egg cell membrane. The nuclei of both gametes fuse and a zygote forms with full 46 diploid number of chromosomes. Pollen tube nucleus The advantages to flowering plants of increased pollen tube growth are that it is more likely to reach the ovule and fertilisation more likely to occur within a shorter time period The function of the pollen tube in fertilisation in flowering plants. -Forms a pathway and grows down through the style. -Grows towards egg cell. Digestive enzymes aid the growth of the pollen tube. They breakdown the style through digestion and break down proteins / pectin / middle lamella. Hydrolysis occurs. The digestive enzymes make it easier for pollen tube to grow as there is reduced resistance and supply nutrients and energy for pollen tube growth. The pollen tube then transports the generative nucleus / haploid nuclei / male gametes and fuses with embryo sac membrane and allows male nuclei to enter embryo sac Double Fertilisation In plants, a double fertilisation occurs the first fertilisation involves a male gamete nucleus fusing with the egg cell nucleus the function of this fertilisation is -To produce a zygote. -To produce full 46 diploid number of chromosomes. -To allow mixing of genes to create genetic variation. In the second fertilisation, the other male gamete nucleus fuses with two polar nuclei forming a (triploid) endosperm nucleus that has the function of a food store/source. Fertilisation in flowering plants A grain of pollen lands on the stigma. -Grain absorbs water and splits open. -Pollen tube grows out of the pollen grain down the style 3 male nuclei present. -One tube nucleus on tube’s tip and two male gamete nuclei behind it. -Enzymes from tube digest surrounding cells to make a way through for the pollen tube. Tube grows through micropyle once it reaches the ovary and into embryo sac within the ovule. -Tube nucleus disintegrates and tip of pollen tube bursts to release 2 male nuclei one nucleus fuses with egg nucleus to form a zygote. There is division by mitosis to form embryo the other male nucleus fuses with two other polar nuclei at the centre of the embryonic sac to form triploid endosperm nucleus food store double fertilisation
Cell Differentiation is the process by which a cell becomes specialised. Stem cells are undifferentiated cells that can give rise to other types of cell with no limit to division there are two types of stem cell PLURIPOTENT- undifferentiated cells with some genes that are deactivated/switched off. They can give rise to most specialised cell types but not totipotent stem cells/extra embryonic cells TOTIPOTENT- undifferentiated cells with all genes activated/switched on can give rise to all 216 cell types. They have no limit to division. They’re only present in the early life of an embryo Sources of human stem cells. Extra embryonic cells: -Cord blood. -Umbilical cord. -Placenta. -Fertilised egg. -Zygote. -Blastocyst. -(early) embryo. -Bone marrow. -Brain. -Connective. -Skin. -Liver cells. -Addition of adult nucleus to enucleated egg cell Differential gene expression results in cell specialisation chemical stimulus causes some genes to be switched off or switched on. Only switched on genes produce m. RNA is translated and protein synthesis occurs leading to different proteins being produced which (permanently) modify cell (to become specialised) e. g. red blood cells have no nucleus (this is a permanent modification) The gene locus is the position of a gene on a chromosome
Stem Cells in Medicine Embryonic stem cell research is more advanced than adult stem cell as embryonic cells are easier to work with than adult stem cells. -Embryonic cells are (relatively) undifferentiated whereas adult stem cells are less so. -Embryonic stem cells are totipotent / pluripotent able to become any kind of cell in the body but adult stem cells are multipotent able to become only a limited number of cell types. Embryonic stem cells have a wider range of clinical applications then adult stem cells. Regulatory authorities -Examine proposals of research to see if they’re carried out for good reason licensing and monitoring centres ensure that fully-trained staff carry research out. Guidelines and codes of practice are set out to ensure scientists are working in a similar manner. They monitor developments in research to ensure any changes are regulated and guidelines are up-to-date providing advice and information to the government and professionals to promote the science involved in the research, and aid society in understanding the benefits. Regulating authorities should include people involved in human embryo research and people not involved in embryo research as people involved in embryo research are able to (fully) understand the science and recognise what is possible benefits / risks while judging in an informed manner. On the other hand people not involved in embryo research can give a balanced /alternative / wider view. Less objection to use of stem cells from unfertilised egg cells. Embryos that have been produced from human egg cells which have not been fertilised by sperm. These embryos never survive past a few days. This is because some of the genes needed for development are only active in chromosomes from the sperm. There's less opposition to the medical use of stem cells from these embryos than from normal embryos as these / unfertilised embryos are not viable and the main problem is usually related to objections with discarding viable embryos. There is no objection to discarding non-viable embryos as rights from moment of fertilization are not in play. Arguments for and against embryonic stem cell research: FOR: • Potential for alleviating human suffering • Culturing patient’s own cells to provide replacement tissues/organs (in brain damage) • Stem cells from IVF would otherwise be discarded • Embryos should not be considered as human at an early stage - (awareness that only cells at a very early stage are used) • Use of non-embryonic cells will need a development phase using embryonic cells -(more can be done with embryonic stem cells) • Ethically questionable to use embryonic stem cells but these objections are outweighed by the greater evil of not using embryonic stein cells to alleviate human suffering • Could be excesses but these can be regulated AGAINST: • Embryonic stem cells are (potential) people from the moment of conception • Objectionable on religious/ethical grounds • Pressure on women to produce surplus embryos • Cloning/stem cell techniques may get into the wrong hands/regulation might be difficult to police / might be thin edge of a wedge like designer babies • It will soon be possible to use non-embryonic stem cells so research into the use of embryonic stem cells is unnecessary • Although there are some advantages there could be unexpected dangerous consequences therefore not worth the risk
Stem Cells in Medicine Source of PLURIPOTENT stem cells. A fertilised egg can be used as a source of human pluripotent stem cells. The fertilised egg is allowed to grow for a few days and divide several times a blastocyst is formed which is a hollow ball of cells. Cells in inner cell mass are pluripotent and so are harvested for the procedure of extraction of cells. The source of fertilised egg cells is spare embryos from after IVF (superovulation) Source of MULTIPOTENT stem cells (multipotent) are obtained from body tissues of an adult e. g. bone marrow can be extracted through a simple operation but there is discomfort to the patient. The needle is injected into the centre of a bone and a small quantity of bone marrow removed. Adult stem cells are not flexible and are limited in use so can only specialise to become a few cell types Source of TOTIPOTENT stem cells. Embryonic stem cells are obtained from early embryos that are created in an IVF lab. Stem cells are removed after 4 -5 days and the embryos are destroyed. Embryonic stem cells can develop into all 216 cell types. Embryonic stem cells are more likely to cause immune system rejection than adult somatic stem cells. They are totipotent until the blastocyst phase where the cells become pluripotent. New treatments using stem cells have potential risks to the health as there is a risk of infection and disease through pathogens from the donor. There is also a risk of infection from contaminated equipment during the procedure. There is the risk of the development of cancer as well as immune system rejection. There is also an increased susceptibility to infections due to the use of immunosuppressant drugs Stem cells culturing allows cells to multiply in a petri dish with a nutrient agar growth medium. They are placed in an incubator using sterile conditions and aseptic technique to produce more (identical) cells The cell differentiation stage allows a cell to become specialised (in function) The cell then stops dividing and one type of cell can be used to produce a specific type of tissue e. g. connective tissue
Variation & Inheritance Genetic diversity within a species depends on the number of different alleles in a population the (gene pool) and the frequency of the alleles VARIATION (In Meiosis)- Independent assortment leads to genetic variation as there is the random aligning of chromosomes creating new combinations of alleles. Crossing over further increases genetic variation as there is the breaking and re-joining of chromatids on the same chromosome pair. Crossing over recombines genes and alleles producing recombinants. -Random fertilisation also leads to a variation in the genetic combinations within the offspring. Mutations also leads to genetic variation Variation of genotype leads to a variation of phenotype some characteristics are monogenic (controlled by one gene) they allow for discontinuous variation. Most characteristics are polygenic at different loci (controlled by many genes) and are responsible for to continuous variation such as height. The environment influences phenotypes Height – polygenic you can influence height through nutrition. Malnutrition limits a child’s maximum height. Monoamine Oxidase A (MAOA) – monogenic is an enzyme that breaks down monoamines. Low levels of MAOA cause mental health problems. Antidepressants and tobacco reduce MAOA levels. Cancer risk is also influenced by diet. Animal hair colour can depend on seasonal and temperature influences e. g. dark hair in summer but white hair in winter. Certain genes are required to trigger the change. Continuous variation individuals in a population vary within a range no distinct categories can be given. Continuous variation includes skin colour / mass / height and more. These are polygenic characteristics. In polygenic inheritance, the phenotypes are affected by forms of genes called alleles found at many loci on chromosomes. Discontinuous variation is when there are two or more distinct categories and an individual only falls into one of these categories e. g. gender / blood group. These are monogenic characteristics. In monogenic inheritance, the phenotypes are affected by one form of gene called an allele found at one locus on a chromosome The term genotype regards the genetic make-up of a cell or organism. The term phenotype regards the appearance of a cell or organism it is dependent on the genotype and environmental factors. Inheritance from both parents is co-dominance of alleles
Adaptation & Evolution Bacteria often adapt to changing conditions quickly as they have faster life cycle and have greater selection pressures e. g. antibiotic use. There is plasmid transfer in bacteria. There's a larger number of bacteria hence a larger gene pool and increased likeliness of a mutation. Adaptations occur due to a selection pressure (change in environment) such as competition / predation. A random mutation occurs within the population of the species. Individuals with this (advantageous allele) are more likely to survive and breed then other members of the species. The advantageous allele (mutation) is passed on to future generations increasing the number of individuals with this adaptation in the population meaning there is an increased frequency of the advantageous allele in the population. The less well adapted are unlikely to survive and compete and may face extinction in the environment.
Classification Taxonomy is the science of classification - naming & organising organisms into groups based on similarities and differences Use of binomial name is unique and more precise it means that there is less confusion since species have different non-scientific names in countries. The systems avoid this problem by using two names first = genus name second = species name Molecular phylogeny is the study of evolutionary history of organism groups it measures the relation between species. The DNA and proteins are examined and the more closely related the more similar the molecules Kingdom Woese Classification 3 Domain system: Comparison sources Phylum • Fossil records • Homologous features • Evolutionary history • DNA Base sequence • Ecological Niches Class -The domains include Bacteria, Achaea and Eukarya -Prokaryotae are in Archaea and Bacteria -Other kingdoms (organisms with a nucleus) in Eukarya -Archaea and bacteria distantly related, so classified into two domains Order Family Genus Species are reproductively isolated and produce offspring that are sexually viable /fertile they have many features in common (homologous) Linnaeus Classification system
Transpiration & Plant Stems Xylem vessels/Sclerenchyma fibres Similarity -Both support. –Both contain lignin. -Both associated with vascular bundles. -Both dead Differences -Only xylem vessels transport water / minerals such as nitrates. They have different positions within the vascular bundle. -Only Xylem vessels have open ends. –They have different types of lignin deposition. Cohesion is the attraction between like molecules such as water molecules they have the (tendency) to stick together by hydrogen bonding which is possible due to the polarity of water molecules A Xylem vessel is a tube that forms when a long row of cells dies and the end walls of the cells break down it is adapted for the transport of water/mineral ions and support in a plant. It is adapted for water transport as it’s a structure of hollow tubes with no living contents/ organelles to obstruct water flow and no end walls this allows vertical movement of water in columns. The xylem tissue is waterproof as it is lignified and so keeps water in the vessel so less water is lost. There are pores to allow sideways movement of water. It is adapted for support as it has lignified walls and Sclerenchyma fibres are bundles of dead cells running vertically with hollow lumens and no end walls they contain thickening lignin and extra cellulose to aid support and help to withstand tension. Plant cell walls are largely made up of cellulose. Cellulose molecules consist of b glucose molecules joined together in very long chains. These cellulose molecules lie parallel, bound together by hydrogen bonds making up microfibrils. Water moves through xylem vessels in the transpiration stream due to forces of adhesion there’s a intermolecular force between water and cellulose / lignin as well as forces of cohesion intermolecular forces between water molecules due to hydrogen bonding and the polarity of water molecules. This means water can be pulled up xylem by transpiration with evaporation as the driving force. A difference in water potential is created increasing the level of hydrostatic pressure/root pressure increasing the level of osmosis in roots. Roles of water in a plant -pollen tube growth -photosynthesis -component of cytoplasm and sap -water as a solvent -water as a transport medium -involved in thermoregulation -role in structural support -involvement in hydrolysis -turgor changes Stem cross-section Sclerenchyma fibres Phloem Cambium Xylem Cortex Epidermis
Cohesion-tension theory: Evaporation from the leaves (transpiration) puts water in the xylem under tension as water potential is reduces and there is negative pressure so water is pulled up via the apoplast pathway. Water molecules cohere as they form hydrogen bonds so water a single column. Transpiration is the loss of water vapour from the surface of the plant, mainly from the leaves. Water moves along the water potential gradient. Less water is lost at upper surface of leaves as there are more stomata on the lower surface and there is a thicker waxy cuticle on the upper surface. Environmental factors that influence water loss in a leaf -Temperature increase gives more (kinetic) to water molecules on surface of spongy mesophyll cells. -Humidity increase means more water vapour around leaf stomata reduces diffusion gradient (of water vapour through stomata). -Light intensity increase causes stomata to open/widen so more diffusion of water vapour from air spaces (in spongy mesophyll). –Water stress extremely high temperature and high winds cause the stomata to close leading to less diffusion. Starch/Cellulose fibres Structure and function of starch: -Contains amylose and amylopectin. Amylose : -Long unbranched chains with 1 -4 glycosidic bonds in a coiled structure so it’s compact so can fit more into a small space. Amylopectin: -Long branched chains with 1 -4 and 1 -6 glycosidic bonds that side branches which can be broken down quickly. It is insoluble so water doesn’t cause it to swell via osmosis Structure of a plant cell wall: -Cellulose as microfibrils. -Cellulose molecules held together by hydrogen bonds. A cellulose microfibril is a bundle of over 36 cellulose molecules in a net like arrangement in the primary cell wall. Matrix / hemicelluloses and pectins are also besides the cellulose. There are primary and secondary cell walls. The secondary cell wall has a different arrangement and contains lignin to increase its strength and support. Structure of cellulose contains beta glucose the glucose molecules are joined by condensation reactions to form 1 - 4 glycosidic bonds there are inversions of alternate glucose molecules in the unbranched straight chain. A microfibril is composed of 50 -80 cellulose molecules/chains. Cellulose chains are held together by hydrogen bonds. Plant fibre Strength is due to cellulose microfibrils in the cell wall in a net-like arrangement of microfibrils. The secondary cell wall is thicker and increases the strength of plant fibres.
Sustainability Fossil fuels release carbon dioxide and increase the rate of global warming as green house gas pollution increases. Plastic is from oil and oil is a non-renewable resource (fossil fuel) the use of these resources has lead to a generation of non-biodegradable waste however plants / starch are renewable as plants can be re-grown and their fibres are often biodegradable so do not accumulate and take up landfill space. The advantages of using plant fibres are that they are biodegradable and use renewable material they are obtainable as they can be grown easily and locally. Fibre extraction is more suited to developing countries as it is cheaper. Use of plant fibres also reduces the use of fossil fuels. The disadvantages of using plant fibres are that ropes made from plant fibres aren’t as strong and bags made out of paper are less strong than plastic bags and disintegrate when wet. Degradation of waste requires aerobic organisms, so little happens in deep landfill sites and closer to the surface, methane (a greenhouse gas) is often produced
Drug Testing & Drugs from Plants Drugs can be tested on rats before testing on humans as laboratory rats have reduced genetic variability and have a similar / well known metabolism. This process means that there is no physical harm to a human. The process also allows us to look for potential toxicity and possible adverse effects. The main problem is ethical issues with the harm subjected on lab rats. Method used to trial a new drug: Animal cell culture tested for humans PI- Preliminary small scale tests on (healthy) volunteers. Independent / official body of scientists and medics UK Medicines Control Agency decides whether work can progress to next phase PII- Drug tested on small groups of volunteer patients / people who already have the disease PIII- Larger 1000 to 3000 group of patients people who already have the disease are placed randomly in two groups one group given medical product the other a placebo (dummy/sugar pill with no active ingredient) as a control. This is a double blind test/trial as neither patients nor doctors know who has the active compound. Statistics are used to analyse the results and test for any significance of the drug being tested A Placebo is a dummy/sugar pill with no active ingredient used as a control and is given to 1 of 2 groups, the drug being tested is given to the other of the 2 groups. The placebo effect shows a recorded improvement because of the emotional state of the patient. They believe that it will work and they have belief that they are receiving the drug. The placebo process is used to test the effectiveness of a drug. A Double-blind trial is were neither doctors nor patients know the group with the placebo or the group with the drug being tested group. This P 3 process reduces bias allowing scientists to attain valid results. William Withering’s Digitalis Soup used foxglove extracts to treat dropsy. The active drug was digitalis. He extracted the drug from the plant soup and tested it on patients to find a suitable dosage using the trial and error method. His methods could not be used as part of a modern clinical trial as only sick patients were treated and there were high risk doses which meant some patients nearly died. He had no placebo / control and did not use a double blind test/trial. His trials had no control from a regulatory body and he had a small sample size.
Biodiversity & Endemism The niche of a species is the role of the species within its habitat and its interactions with other living organisms e. g. prey and predators as well as its interactions with the non-living environment e. g. gas exchange. A niche is unique to species there is competition if two species occupy the same niche. The species richness is the number of different species in a habitat at any one time. Species diversity is the number and abundance of each of the different species in an area. Genetic diversity is the variation of alleles within a gene pool of a species. The term endemic refers a species that is restricted in its distribution and only found in one specific location. A habitat is the area in which an organism lives Biodiversity is the number, range of taxa and variety of species. Variety / diversity within species and Variety / diversity of ecosystems. The gene pool is the complete set of alleles in a species Measurement of species diversity: count the number of different species the higher the number of species, the greater the species richness. A limitation is that there is no indication of the abundance of each species so count the number of different species and number of individuals using a biodiversity index. Measurement of species diversity: choose an area at random within the habitat to sample in order to reduce bias (technique should be the same every time). Count the number of individual species using: a quadrat for plants, a sweepnet for airborne insects, pitfall trap for ground insects and a net for aquatic animals. Repeat x 3 and estimate the total number of different species. Measurement of genetic diversity: genetic diversity is the variety of alleles in the gene pool of a species the greater the variety of alleles, the greater the genetic diversity. It is Measured by phenotype as different alleles code for different versions of the same characteristics. The larger the number of phenotypes, the greater the diversity. It is also measured by genotype a sequence of base pairs in the DNA is analysed the order of bases in alleles is different. By sequencing DNA, similarities and differences are observed the larger the number of alleles, the greater the genetic diversity. A reduction in genetic diversity is when there is a reduced variety and number of different alleles in a species gene pool
Conservation & Biodiversity - Zoos maintain genetic diversity in endangered species using captive breeding programmes this includes the careful selection of mates and allowing only to mate with a different individual to previous mating. They only allow those with different genes to mate, they ensure they are creating genetic variation using (DNA profiling/genetic testing). They record details on individuals keeping (studbooks), using this information they outbreed individuals using inter-zoo animal movement to maintain genetic diversity. When a species has successfully increased in number zoos attempt to reintroduce the species into the wild. Factors which might lead to the extinction are conflict with farmers / agriculture and destruction of an animals natural habitat. Isolation (Isolated populations breed less successfully). Climate change in the species habitat. Removal of prey species this has an influence on the food chain. Poaching also reduces population numbers. Transferring individuals from one zoo to another increases genetic diversity in the species because it allows outbreeding / mating with genetically different individuals and reduces inbreeding / mating with parents / siblings which reduces genetic diversity. Zoos keep animals in captivity to: prevent extinction by protecting animals from poachers/predation and keeping and breeding populations when their natural habitat lost. They use captive breeding programmes to increase the numbers of a species and prepare species for reintroduction into the wild. They maintain genetic diversity by collecting data using studbooks, carefully selecting mates and outbreeding individuals. Zoos study and research animals to better understand means of conservation so that they can educate people and raise awareness to support conservation programs. Zoos prepare species for reintroduction by reinforcing wild behaviour e. g. reducing food intake to encourage hunting. They carefully select a habitat and raise awareness of local population to ensure that the animals and people are safe. Problems with re-introduction and captive breeding are that conditions are difficult to re-create in captivity and some species do not breed e. g. some lizards. There are ethical issues , it is agued that it is cruel and immoral to keep animals captive. Reintroduced species could bring disease or may not retain their natural behaviours in the wild
Conservation & Biodiversity - Seedbanks Seed banks work by storing seeds in cool, dry conditions. Seeds can be stored for a long time. Viability tests are carried out at regular intervals. It involves less maintenance/labour and is less costly than conserving living plants. Less space needed so large numbers of plants can be stored meaning greater genetic variety. Seeds do not need to be stored in their original habitat and are likely to survive for longer as they can be frozen. Seeds are less likely to be damaged by vandalism or a natural disaster and are less likely to be affected by disease or eaten by herbivores. Seed germination is tested at regular intervals to checking seed viability / germination success. It allows new seeds to be produced as stored seeds may need replacing due to decay and death. It is better to store seeds from several individual plants of one species rather than seeds from one individual plant as there is greater genetic variety/ a wider gene pool with many different alleles. This reduces the chances of inbreeding and reduces the chance of storing seeds with low viability or disease. Seeds need to be dried and then stored in cold conditions as this inhibits germination by slowing down enzymes / biochemical reactions and slows down the rate of decay / microbial activity therefore prolongs seed survival. Drying reduces freezing effect
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