B2 EXAM BRIEFING. Monday 11 th June, 9.00 AM

Transcription

1 B2 EXAM BRIEFING Monday 11 th June, 9.00 AM

2 HOMEOSTASIS & RESPONSE Topic 5

3 Homeostasis Blood glucose conc. Body T Water levels Negative feedback loops

4 Human Nervous System Reflexes; fast, automatic (non-conscious, brain not involved) responses to certain stimuli.

5 Required Practical GCSE Required Practical Biology 2 Investigating reaction time Reaction time the time it takes for you to react. You need to detect the stimulus (eyes) and send an impulse to the brain (sensory neurone) and down to the hand (motor neurone) What s the point of the practical? To find out how a certain variable affects reaction time. IV: volume of caffeinated drink consumed (ml) DV: distance ruler caught at (mm) (from this reaction time can be calculated) CV: person catching ruler, same hand, drop height, distance hand is spaced (mm), position arm is resting, other food & drink consumed What may they ask us about? - Control variables what had to be kept the same and how did you do it? - Why is it important to repeat? Calculate means etc - Range of results, resolution of measurements, uncertainty of results - Ethical considerations - Use of control groups to compare to Example Apparatus - Dropping a metre stick - Or using an online reaction test to measure reaction time (reaction distance with metre stick). - Many IV s could be tested e.g. the effect of listening to music, drinking alcohol, drinking caffeine, taking drugs or medicines, gender, age, amount of practice Results - People react quicker with practice and if they are concentrating. - They react slower if distracted in any way.

6 The Brain Area of the brain Cerebal cortex Medulla Cerebellum Function(s) Outer wrinkly layer consciousness, memory, intelligence, language. Controls unconscious activities (e.g. breathing, heartbeat) Muscle co-ordination Brain is complex, delicate. Difficult to investigate only 1 part. Difficult to identify effects of damage/ treatment. Treatment can potentially cause further damage. How to study; Damage in specific locations can cause symptoms which suggest which area involved. Electrically stimulating brain tricks neurone into firing. Observe effect. MRI- observe areas of brain active during activity.

7 The Eye Structure Cornea Pupil Iris Lens Retina Suspensory ligaments Ciliary muscle Sclera Optic nerve Function Transparent outer layer that refracts light into the eye. The hole through which light enters. Contains muscles that control the width of the pupil and therefore how much light enters the eye. Focuses light onto Retina Contains cells sensitive to light intensity and colour. Control the shape and thickness of the lens Controls the shape and thickness of the lens. Tough, supportive wall of the eye. Carries impulses from the receptors on the retina to the brain.

8 The Eye- different light conditions Conditions Bright Light Dim Light Circular muscles in Iris Radial muscles in iris Contract Relax Relax Contract Width of Iris Increases Decreases Results on pupil Width decreases Width increases Light entering eye Decreases Increases Consequence Less light enters eye prevents damage to retina or eye being unable to distinguish details. More light enters eye allows eye to distinguish more detail.

9 The Eye- Lenses Hyperopia Myopia Or: Contact lenses- popular, lightweight, sports, soft = more comfortable but infection risk Laser eye surgery- vaporise cornea tissue (thinner = refract less). Precise, risk complications. Replacement lens- higher risk of eyesight damage & vision loss.

10 Control Body T Core body temperature increase Core body temperature decrease Body hair Sweat glands Blood vessels near skin Lies flat -> does not trap air (insulator) around body -> increases heat loss to environment. Sweat produced ->sweat evaporating transfers energy to environment Vasodilation: blood vessels near skin dilate -> more blood flows near skin -> more heat lost to environment (and you go red!) Stand up -> traps layer of insulating air -> reduces heat lost to environment. Less sweat produced. Skeletal muscles contract to force additional respiration. Vasoconstruction: blood vessels near skin constrict -> more blood flows through core -> prevents heat loss (you go pale).

11 Human Endocrine System Pituitary gland Pancreas Thyroid Adrenal glands Ovaries Testes Master gland releases hormones that controls other endocrine glands. Insulin (blood glucose) Thyroxine (metabolism, heart rate, temperature) Adrenaline (fight / flight response) Oestrogen (menstrual cycle) Testosterone (puberty, sperm production)

12 Controlling Blood Glucose Conc. Glucose rises (eat food) Normal blood glucose level. Glucose falls (exercise) Insulin produced by the pancreas causes glucose to move into cells (respiration). Excess converted to glycogen for storage. Negative feedback loop Glucagon added by the pancreas is released and glycogen converted back to glucose. Normal blood glucose level. Cause Type 1 diabetes Pancreas fails to produce suff. Insulin Type 2 diabetes Body cells no longer respond to insulin Characteristics High blood glucose levels Obesity = risk factor Treatment Insulin injections Carb controlled diet & exercise

13 Maintaining Water & Nitrogen Balance Cells are affected by osmotic changes. Too much or too little = do not function efficiently. Lungs & skin: water loss by exhalation & sweat (no regulation). Kidneys: remove excess water, ions & all urea. Filtration: all substances absorbed Selective reabsorption in kidney tubules: useful substances (all glucose, some ions, right amount of water. Anti-diuretic hormone (ADH) (negative feedback) Waste products: Protein amino acids deaminated into ammonia (toxic) immediately converted into urea (safe excretion) Varying ions, varying water

14 Treatment How it works Advantages Disadvantages Dialysis Kidney Failure Transplant Person s blood flows past partially permeable membrane surrounded by dialysis fluid. Small molecules (ions, waste) through, not large molecules (e.g. protein). Dialysis fluid has same conc. Ions & glucose to prevent loss from body by diffusion. Healthy kidney donated from dead person/ live donor (only 1 kidney needed to survive). No rejection. Intrusive- 3 times per week, 3-4 hours, large machine. Infections, blood clots. Regulate diet to prevent ion build up. Limit fluid intake as kidneys can t remove excess water. Expensive. Only cure. Risk to donor. Rejection- antigens on donor kidney aren t recognised by WBC. Lymphocytes produce antibodies. Need to tissue type & take antirejection drugs- not fail-safe, immune system supressed. Long waiting lists. Risky major operation.

15 Hormones in Human Reproduction Hormone Made Where? When in Cycle? Body s Response FSH Pituitary 5-14 and 16+ Stimulate egg cell to become follicle Oestrogen Ovary 7-15 Stimulate uterus lining rebuild LH Pituitary 14 Stimulate egg release from follicle Progesterone Ovary Complete uterus lining development

16 Contraception & Infertility Treatment Contraception Hormonal Non-hormonal Infertility Oral contraceptives inhibit FSH (by high oestrogen levels)- no eggs mature Injection/ implant/ skin patch- slow release progesterone- inhibit maturation & release of eggs, thickens cervical mucus. +: 99+% effective. +: reduced risk some cancers -: not 100% effective -: side effects (headaches, nausea, irreg. bleeding, fluid retention. -: no STD protection. Barrier (condoms & diaphragms)- prevent sperm reaching egg Intrauterine devicesprevent implantation of embryo OR release hormone Spermicidal agents- kill sperm Abstaining when egg may be in fallopian tube (oviduct) Surgical sterilisation FSH & LH injections to stimulate egg maturation & release. IVF: 1. FSH & LH injection = multiple eggs 2. Eggs collected 3. Eggs fertilised in lab using sperm 4. Fertilised eggs grow into embryos in incubator embryos transferred to womb (increase chance of pregnancy) Micro-tools allow embryos to be genetically tested. Time-lapse imaging monitors growth in lab. Emotionally & physically stressful, low success rate, multiple births- risk to mother & babies

17 Negative Feedback Thyroxine Thyroid gland (neck) Regulate basal metabolic rate Stimulates protein synthesis Released in response to thyroid stimulating hormone (TSH), released by pituitary gland Adrenaline Adrenal glands (above kidneys) Response to stressful/ scary situation Brain detects sends nervous impulse to adrenal glands secret adrenaline Fight-or-flight response triggers mechanisms to increase supply of oxygen & glucose to brain & muscles e.g. inc. heart rate

18 Plant Hormones Tips of shoots & roots, moves backwards to stimulate cell elongation in cells behind tips. No tip = no auxin = no growth. Gibberellins: initiate seed germination Ethene: controls cell division Uses of plant hormones: Killing weeds Broad-leaved weeds absorb selective weedkiller. Disrupts normal growth. Cuttings with rooting powder Clones. Grow quickly. Growing cells in tissue culture Only a few cells needed to be added to growth medium

19 INHERITANCE, VARIATION & EVOLUTION Topic 6

20 Asexual & Sexual Reproduction Mitosis Only 1 parent, no gametes, no mixing of genetic info. Clones. Meiosis Gametes fuse. Variation 1. Duplicate, pair up. Genetic information swaps over. 2. Pairs line up in centre. 3. Pairs pulled apart. 4. Second division gametes produced. Each gamete genetically different. Malarial parasite- asexual in human host, sexual in mosquito. Fungi- sexually for variation, asexual by spores. Plants- seeds sexual, e.g. runners asexual Mitosis Meiosis + Only 1 parent needed, time effic., faster, many identical offspring Variation, survival advantage (nat. select.), selective breeding inc. food

21 DNA- Structure Genome: whole genetic material of organism. Human has been mapped- medical importance Identify gene = disease Understanding & treatment of genetic disorders Tracing human migration patterns Nucleus chromosomes DNA gene Polymer, 2 strands, double helix; 4 different nucleotidesalternating sugar & phosphate group & 1 of 4 bases (A with T, C with G) attached. Some parts of DNA don t code for proteins; switch genes on & offcontrol whether gene expressed.

22 Protein Synthesis & Mutations Gene = small section of DNA. Codes for specific protein. Change in DNA may = change in protein synthesised = mutation. Mutations occur continuously. Most do not alter protein, or only slightly but appearance/ function not changed. Few mutations = different shape protein. Enzyme active site no longer fits the substrate binding site Structural protein loses strength Proteins synthesised on ribosomes. Carrier molecules bring specific amino acids to add to growing protein chain according to template. Complete protein chain folds into specific shape- enzyme, hormone, collagen. Types of mutation: Substitutions Deletions Insertions

23 Genetic Inheritance Some characteristics controlled by single gene e.g. fur colour, colour blindness. Most characteristics result of multiple genes interacting. Allele = version of a gene. Two genes present = genotype. Operate to develop characteristics expressed (phenotype). Dominant allele always expressed Recessive allele expressed only if 2 copies present (homozygous) Sex determination: 23 rd chromosome Both diagrams show 1:1 ratio 1 in 2, 50%, 0.5 or ½ chance of offspring being female or offspring being male. Remember to identify which offspring are which. Probability of two separate outcomes can be multiplied together.

24 Inherited Disorders Polydactyly Extra fingers/ toes- not life-threatening. Dominant allele- no carriers Cystic fibrosis Disorder of cell membranes- thick, sticky mucus in air passages (difficulty breathing) & in pancreas. Recessive allele- carriers (~1 / 25 people) Pre-implantation genetic diagnosis (PGD): embryos screened before implantation during IVF by removing 1 cell. Chorionic villus sampling (CVS): weeks pregnancy. Cells taken from placenta (same genes as embryo), genes analysed. + _ Stop suffering from certain inherited disorders Treating disorders = During IVF most embryos destroyed Don t have to terminate, can be prepared Screening for desirable characteristics- implication = genetic conditions Rejected embryos from PGD destroyed- could by humans, unethical CVS can cause miscarriage Screening = expensive

25 Variation Genome & its interaction with environment determine development of phenotype. Variation within a population; Usually extensive Due to genes inherited, environmental causes & a combination of these. Variants arise from mutations (occur continuously) Most have no effect on phenotype Some influence phenotype Very few determine phenotype if new phenotype is suited to an environmental change, this can lead to relatively rapid change in species (evolution)

26 Evolution inc. Development of Theory Charles Darwin; 1. All individuals within species show range of variation for particular characteristic. 2. Some individuals will be more suited to their environment. 3. These well suited individuals more likely to survive, and breed. 4. Useful characteristic passed on to offspring. Not a perfect theory; Could not give explanation for why new characteristic appeared or how beneficial adaptation passed on (lack of scientific understanding) Current theory of evolution by natural selection: 1. All individuals within species show range of variation for particular characteristic. 2. Some genetic variants = characteristics more suited to their environment. Better chance of survival, more likely to breed. 3. Genetic variants responsible for useful characteristics more likely to be passed on to next generation. Over time, genetic variant for useful characteristic will accumulate in population. Changing of inherited characteristics of population = evolution. New species = speciation. Alfred Russel Wallace also worked on this idea- developed speciation theory independently of Darwin, then collaborated.

27 Selective Breeding Selective Breeding Animals- produce more meat / milk Crops resist disease Dogs with gentle temperament Decorative plants 1. Select organisms with desired characteristics. 2. Breed with each other. 3. Select best offspring & breed. 4. Continue over several generations. Inbreeding- all best organisms are related & are bred together Has been carried out for thousands of years.

28 Genetic Engineering (also in Ecology topic) Transfer gene responsible for a desirable characteristic from one organism into another s genome. Can be carried out in early stage of development- organism develops with characteristic (phenotype) coded for by gene. Uses: GM crops- improve size/ taste/ resistance to disease/ insects/ herbicides. +: inc. yield, developing nations diets often lack nutrients- fortified food e.g. golden rice. -: reduce biodiversity? Some people not sure GM is safe, superweeds if genes get into natural environment Sheep can produce e.g. drugs in milk. Gene therapy- research GM treatments for inherited disorders caused by faulty genes. Bacteria produce human insulin: 1. Insulin gene cut out of human DNA using enzymes. 2. Same enzymes used to cut bacterial DNA and different enzymes used to insert human insulin gene. 3. Bacteria multiply. Insulin produced while growing is purified.

29 Cloning Embryo transplants- +: quickly produce ideal offspring +: study of clones could lead to greater understanding development of embryos Preserve endangered species -: reduced gene pool -: cloned animal might not be as healthy as normal ones -: clone humans? Unsuccessful attempts = severely disabled? Human rights of clone? Tissue culture- preserve rare species, commercially suitable. Adult cell cloning- Cuttings- older, simpler.

30 Mendel & other Scientists discoveries Mid-19th Century; Gregor Mendel carried out breeding experiments on plants. 1 st cross & 2 nd cross. Observations: inheritance of each characteristic is determined by units that are passed on to descendants unchanged. Hereditary units are dominant or recessive.

31 Evidence for Evolution Discovery of genetics Fossil record Remains of organisms Formed by: Lack of decay due to lack of oxygen (no aerobic respiration) / lack of moisture, right temperature or ph (enzymes in decomposers cannot function) are absent. Replacement by minerals Preserved traces e.g. casts, footprints, burrows, root traces See changes in organisms developed slowly over time Early organisms soft bodied- very few traces remainpreservation rare & mostly destroyed by geological activity. Therefore scientists cannot be certain how life began on Earth Bacteria evolve to become resistant to antibiotics MRSA. Doctors should only prescribe antibiotics correctly, patients should finish course, agricultural antibiotics should be restricted

32 Classification Linnaeus: Binomial: genus & species Developments in microscopes & understanding of biochemical processes led to new models of classification: Woese: three-domain system Archaea (primitive bacteria usually in extreme environments Bacteria Eukaryota (includes protists, fungi, animals, plants Evolutionary Tree:

33 ECOLOGY Topic 7

34 Communities Plants compete for; Light, space, water, mineral ions (soil) Animals compete for; Food, mates, territory Interdependence: species within a community depend on other species for; Food, shelter, pollination, seed dispersal etc. Stable community = all species and environmental factors are in balance, population sizes remain fairly constant.

35 Abiotic & Biotic Factors Abiotic (non-living) Biotic (living) light intensity temperature moisture levels soil ph and mineral content wind intensity and direction carbon dioxide levels for plants oxygen levels for aquatic animals. availability of food new predators arriving new pathogens one species outcompeting another so the numbers are no longer sufficient to breed. Adaptations Features which help an organism survive. Structural, behavioural, functional. Extremophiles: live in high T (e.g. deep sea vents), p, salt conc. conditions. Microorganisms.

36 Levels of Organisation (food chains) inc. Trophic Levels & Pyramids of Biomass Quaternary consumer/ top carnivore Tertiary consumer Secondary consumer Primary consumer Producer (photosynthesis transfers ~1% incident energy) Pyramid of biomass- mass of dry organic matter on each trophic level. Largest at the bottom to support food chain. Only ~10% passed on. Lost due to: Not all ingested (some egested- faeces) Lost as waste e.g. CO2 + H2O in respiration, H2O + urea in urine

37 Required Practical What s the point of the practical? To find out how different factors affect how species are distributed Sampling GCSE Required Practical Biology 1 Measuring population size Population: all the individuals of a species in a particular area. Abiotic factors: non-living factors biotic factors: living factors Distribution: how the individuals are spread out across a certain area Results - Random sampling used when you want to know how the organisms are spread out across an area. Example Apparatus - Line transect used when you want to see how one particular feature (e.g. a river/road/building) affects an area. You take samples in a line (called a transect) and repeat to compare the difference near and far from the feature. - Quadrat frame of a certain size used to isolate a particular area so you can see what s in that certain space What may they ask us about? - Accuracy of measurements is it 100% accurate? - Reproducibility and validity of data is it completely fair? - Calculate means and work out the total number in a certain area. - How could you improve the sample to make it more representative?

38 How Materials Are Cycled

39 Decomposition Temperature: correct T for enzymes. Hot = denature, cold = slow Oxygen availability: aerobic respiration by microorganisms Water availability: decay faster in moist as decomposers need water Number decay organisms: more microorganisms & detritus feeders = faster

40 Required Practical Decay 1. 5cm 3 lipase in test tube, 5cm 3 milk, 5 drops Cresol red (or phenolphthalein), 7 cm 3 of sodium carbonate solution into second test tube. Water bath to 0 C (ice). 2. Transfer 1 cm 3 of lipase into the milk test tube. Immediately start timing. 3. Stir the contents of the milk test tube until the solution turns yellow. 4. Record the time taken for the colour to change to yellow, in seconds. 5. Repeat for C with 10 C interval. 6. Calculate rate:

41 Biogas Mostly methane, burned as a fuel. Plant material & animal waste decayed through anaerobic respiration. Batch generator Small batches Manually load waste & clear by-products +: not filled as often -: no steady rate of biogas Continuous generator Large-scale +: steady rate of biogas, bigger quantity -: more difficult to install

42 Biodiversity & Maintaining Biodiversity Great biodiversity = stability of ecosystems. Reduces dependence on one species for food, shelter, maintenance of environment. Humans must maintain good level biodiversity to ensure survival Maintaining biodiversity: breeding programmes for endangered species protection and regeneration of rare habitats reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop reduction of deforestation and carbon dioxide emissions by some governments recycling resources rather than dumping waste in landfill. Waste Management Pollution can occur: in water, from sewage, fertiliser or toxic chemicals in air, from smoke and acidic gases (inc. CO2; global warming & climate change) on land, from landfill and from toxic chemicals. Pollution kills plants and animals which can reduce biodiversity.

43 Impact of Environmental Change Environmental changes affect the distribution of species in an ecosystem. temperature availability of water composition of atmospheric gases. The changes may be seasonal, geographic or caused by human interaction. Demands on the Environment Increasing human population (medicine & farming); actions have widespread effect. Demand for higher standard of living further increasing demands. Raw materials running out fast that can be replaced.

44 Land Use Land available for animals & plants is reduced by: Building Quarrying Farming Dumping waste Peat bogs = anoxic = lack of decay Peat used faster than forms Destruction of peat bogs for compost = less habitat & less biodiversity CO2 released as microorganism begin to decay (respiration) Deforestation Tropical areas have suffered to: Provide cattle land & rice fields Grow crops for biofuels -: less biodiversity -: more CO2 released into atmosphere during burning to clear land -: less photosynthesis

45 Global Warming Consequences: Rising sea level = habitat loss. Changes in distribution of organisms Some may become more widely distributed, others less widely. Changes to migration patterns Less biodiversity

46 Factors Affecting Food Security Food security: having enough food to feed a population. Biological factors threatening food security include: increasing birth rate changing diets in developed countries means scarce food resources are transported around the world new pests and pathogens that affect farming environmental changes that affect food production; widespread famine due to lack of rainfall Cost of agricultural inputs Conflicts affect availability of food & water Sustainable methods must be found to feed all people on Earth.

47 Sustainable Fisheries Overfishing Fishing quotas Net size Farming Techniques Efficiency of food production Factory farming (heated & restricted movement) Fish cages (restrict movement) High-protein animal feed +: higher efficiency = more food +: cheaper +: better standard of living for farmers -: ethical: unnatural, cruel. Growing demand for animal welfare focussed products. -: crowded conditions = diseases spread -: high energy requirement (T controlled) Role of Biotechnology Large quantities microorganisms cultured for food. Fusarium (fungus) produces mycoprotein (protein rich suitable food Grown on glucose syrup, aerobic respiration, biomass harvested & purified. See Genetic Engineering GM crops could provide more food or food with an improved nutritional value e.g. golden rice. Human insulin from GM bacterium.

48 Key Ideas Topic 8 Life processes depend on molecules; structure is related to function. Cells (fundamental unit) may be part of highly adapted structures inc. tissues, organs & organ systems, enable living processes to be performed effectively. Living organisms may form populations of single species, communities of many species & ecosystems, interacting with each other, with the environment and with humans in many different ways. Living organisms are interdependent & show adaptations to their environment. Life on Earth: dependent on photosynthesis (green plants & algae trap light from Sun, fix carbon dioxide & combine it with hydrogen from water produce organic compounds and oxygen. Organic compounds: fuel for respiration = allow other chemical reactions nec. for life Chemicals in ecosystems are continually cycling Characteristics of living organism influenced by genome & interaction with environment Evolution: process of natural selection. Accounts for biodiversity & how organisms are all related to varying degrees.