IB Bio: disease, diagrams, practicals

Gorter and Grendel

Investigated the surface area (SA) of membranes Notice that SA of an intact rbc was half of SA of the lipids when spread on a water surface Concluded that the cell membranes made of a bilayer of lipids with head groups facing the inside and outside of the cell and the tails of each layer facing inward toward each other

Diagrams

https://www.slideshare.net/PakLiam/ib-biology-draw-assessment-statements https://www.youtube.com/watch?v=Npb42kiqj8A

limiting factors of photosynthesis

limiting factor The law of limiting factors states that when a chemical process depends on more than one essential condition being favourable, the rate of reaction will be limited by the factor that is nearest its minimum value Photosynthesis is dependent on a number of favourable conditions, including: Temperature Light intensity Carbon dioxide concentration Temperature Photosynthesis is controlled by enzymes, which are sensitive to temperature fluctuations As temperature increases reaction rate will increase, as reactants have greater kinetic energy and more collisions result Above a certain temperature the rate of photosynthesis will decrease as essential enzymes begin to denature The Effect of Temperature on Photosynthetic Rate temperature photosynthesis Light Intensity Light is absorbed by chlorophyll, which convert the radiant energy into chemical energy (ATP) As light intensity increases reaction rate will increase, as more chlorophyll are being photo-activated At a certain light intensity photosynthetic rate will plateau, as all available chlorophyll are saturated with light Different wavelengths of light will have different effects on the rate of photosynthesis (e.g. green light is reflected) The Effect of Light Intensity on Photosynthetic Rate light intensity photosynthesis Carbon Dioxide Concentration Carbon dioxide is involved in the fixation of carbon atoms to form organic molecules As carbon dioxide concentration increases reaction rate will increase, as more organic molecules are being produced At a certain concentration of CO2 photosynthetic rate will plateau, as the enzymes responsible for carbon fixation are saturated Effect of Carbon Dioxide Concentration on Photosynthetic Rate CO2 concentration photosynthesis ninja icon Skill: • Design of experiments to investigate the eff

Hans and Eduard Buchner proved Pasteur wrong by

using an extract of yeast containing no yeast cells to convert sucrose into alcohol, disproving a part of the Vitalism Theory

Vitamin D Deficiency

usually restricted to individuals with highly limited sun exposure (e.g. elderly, certain ethnicities) While excess sun exposure is beneficial for vitamin D production, it also increases the risks of developing skin cancers

Stargardt's disease

•Affects around one in 10,000 children•Recessive genetic (inherited) condition•The mutation causes an active transport protein on photoreceptor cells to malfunction•The photoreceptor cells degenerate•the production of a dysfunctional protein that cannot perform energy transport•that causes progressive, and eventually total, loss of central visionThe treatment•Embryonic stem cells are treated to divide and differntiate to become retinal cells•The retinal cells are injected into the retina•The retinal cells attach to the retina and become functional•Central vision improves as a result of more functional retinal cellsThe future•This treatment is still in at the stage of limited clinical trials, but will likely be in usage in the future

Emphysema

a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae) Causes The major cause of emphysema is smoking, as the chemical irritants in cigarette smoke damage the alveolar walls The damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase This elastase, released as part of an inflammatory response, breaks down the elastic fibres in the alveolar wall A small proportion of emphysema cases are due to a hereditary deficiency in this enzyme inhibitor due to a gene mutation Treatments There is no current cure for emphysema, but treaments are available to relieve symptoms and delay disease progression Bronchodilators are commonly used to relax the bronchiolar muscles and improve airflow Corticosteroids can reduce the inflammatory response that breaks down the elastic fibres in the alveolar wall Elastase activity can be blocked by an enzyme inhibitor (α-1-antitrypsin), provided elastase concentrations are not too high Oxygen supplementation will be required in the later stages of the disease to ensure adequate oxygen intake In certain cases, surgery and alternative medicines have helped to decrease the severity of symptoms

• Use of defibrillation to treat life threatening cardiac conditions

Fibrillation is the rapid, irregular and unsynchronised contraction of the heart muscle fibres This causes heart muscle to convulse spasmodically rather than beat in concert, preventing the optimal flow of blood Fibrillation is treated by applying a controlled electrical current to the heart via a device called a defibrillator This functions to depolarise the heart tissue in an effort to terminate unsynchronised contractions Once heart tissue is depolarised, normal sinus rhythm should hopefully be re-established by the sinoatrial node

Gel electrophoresis

Gel electrophoresis is a laboratory technique used to separate and isolate proteins or DNA fragments based on mass / size Samples are placed in a block of gel and an electric current is applied which causes the samples to move through the gel Smaller samples are less impeded by the gel matrix and hence will move faster through the gel This causes samples of different sizes to separate as they travel at different speeds Overview of Gel Electrophoresis While both DNA and proteins are separated according to the same basic process, differences exist between the two protocols DNA Separation DNA may be cut into fragments using restriction endonuclease - different DNA samples will generate different fragment lengths Fragments separate because DNA is negatively charged due to the presence of a phosphate group (PO43-) on each nucleotide DNA samples are placed into an agarose gel and fragment size calculated by comparing against known industry standards Specific sequences can be identified by incorporating a complementary radiolabelled hybridisation probe, transferring the separated sequences to a membrane and then visualising via autoradiography (Southern blotting) Agarose Gel Electrophoresis (DNA) Electrophoresis (DNA) Protein Separation Proteins may be folded into a variety of shapes (affecting size) and have positive and negative regions (no clear charge) Proteins must first be treated with an anionic detergent (SDS) in order to linearise and impart a uniform negative charge Protein samples are placed into a polyacrylamide gel and sizes compared against known industry standards Separated proteins are transferred to a membrane and then target proteins are identified by staining with specific monoclonal antibodies (Western blotting)

Huntington disease

Huntington's disease is an autosomal dominant disorder caused by a mutation to the Huntingtin (HTT) gene on chromosome 4 The HTT gene possesses a repeating trinucleotide sequence (CAG) that is usually present in low amounts (10 - 25 repeats) More than 28 CAG repeats is unstable and causes the sequence to amplify (produce even more repeats) When the number of repeats exceeds ~40, the huntingtin protein will misfold and cause neurodegeneration This usually occurs in late adulthood and so symptoms usually develop noticeably in a person's middle age (~40 years) Symptoms of Huntington's disease include uncontrollable, spasmodic movements (chorea) and dementia

Hypertension

Hypertension is defined as an abnormally high blood pressure - either systolic, diastolic or both (e.g. > 140/90 mmHg) Common causes of hypertension include a sedentary lifestyle, salt or fat-rich diets and excessive alcohol or tobacco use High blood pressure can also be secondary to other conditions (e.g. kidney disease) or caused by some medications Hypertension itself does not cause symptoms but in the long-term leads to consequences caused by narrowing blood vessels

Bulimia

A serious eating disorder marked by binging, followed by methods to avoid weight gain.

John Gurdon

In the 1950's John Gurdon removed the nucleus from the body cell of a tadpole and transplants the nucleus into a tadpole egg cell . The egg cell with the transplanted nucleus developed as a normal zygote and created a tadpole with the same genome as the body cell nucleus . cloning

Wöhler

-Synthesized Urea using silver isocyanate and NH4Cl -This was the first time an organic compound was synthesized artificially -Helped to falsify theory of "vitalism" -Almost disproved idea that living organisms were composed of organic chemicals that could only be produced by living organisms =========================== Vitalism was a doctrine that dictated that organic molecules could only be synthesised by living systems It was believed that living things possessed a certain "vital force" needed to make organic molecules Hence organic compounds were thought to possess a non-physical element lacking from inorganic molecules Vitalism as a theory has since been disproven with the discovery that organic molecules can be artificially synthesised In 1828, Frederick Woehler heated an inorganic salt (ammonium cyanate) and produced urea Urea is a waste product of nitrogen metabolism and is eliminated by the kidneys in mammals The artificial synthesis of urea demonstrates that organic molecules are not fundamentally different to inorganic molecules

Factors affecting rooting of stem cutting

A stem cutting is a separated portion of plant stem that can regrow into a new independent clone via vegetative propagation All stems possess nodes, from which a leaf, branch or aerial root may grow - the region between nodes are called internodes Stem cuttings are typically placed in soil with the lower nodes covered and the upper nodes exposed Stem cutting is a common method employed to rapidly propagate plant species (including sugar cane, grapes and roses) There are a variety of factors that will influence successful rooting of a stem cutting, including: Cutting position (whether cutting occurs above or below a node, as well as the relative proximity of the cut to the node) Length of cutting (including how many nodes remain on the cutting) Growth medium (whether left in soil, water, potting mix, compost or open air) The use and concentration of growth hormones (e.g. IAA, IBA and NAA promote the formation of adventitious roots) Temperature conditions (most cuttings grow optimally at temperatures common to spring and summer) Availability of water (either in the form of ground water or humidity) Other environmental conditions (including pH of the soil and light exposure)

Modeling the small intestine

A core function of the digestive system is to break down large molecules into smaller subunits that can be absorbed by cells Cell membranes are impermeable to large molecules (polypeptides, polysaccharides) unless transport is facilitated by proteins The size-specific permeability of cell membranes can be modelled using dialysis tubing (Visking tubing) Dialysis tubing contains pores typically ranging from 1 - 10 nm in diameter and is semi-permeable according to molecular size Large molecules such as starch cannot pass through the tubing, however smaller molecules (such as maltose) can cross Unlike the membranes of living cells, dialysis tubing is not selectively permeable based on charge (ions can freely cross) Dialysis Tubing dialysis tubing Digestion Experiments Digestive enzymes like amylase can break down inpermeable polymers (starch) into permeable subunits (maltose) Dialysis tubing is impermeable to amylase and starch, but permeable to maltose (and water) Experiment 1: Measuring Meniscus Levels A length of dialysis tubing is attached to a thistle funnel and filled with starch solution (control condition) A second length of tubing is attached to a thistle funnel and filled with starch and amylase solution (experimental condition) Both apparatuses are placed in a beaker filled with water Over time, water will move into the tubing via osmosis (towards the solute) causing the meniscus level to rise The tube with amylase will have less solute (as starch is digested) and hence the meniscus level should not rise as much Experiment 2: Measuring Maltose Diffusion A length of dialysis tubing is filled with starch solution and suspended in a beaker of water (control condition) A second length of tubing is filled with starch and amylase solution and suspended in a beaker of water (experimental condition) The am

Scurvy

A deficiency in vitamin C levels will lead to the development of scurvy and a general weakening of normal immune function Common food sources of vitamin C include citrus fruits and orange juice

Kidney stones (renal calculus)

A kidney stone (renal calculus) is a solid piece of material formed in the kidneys from the minerals in urine If a kidney stone grows to sufficient size it may block the ureter, decreasing kidney function and causing painful urination In most cases, there is no known reason why a kidney stone forms, however dehydration is a common contributing factor Kidney stones may be prevented by limiting the dietary intake of minerals which form the stones (e.g. calcium) One current treatment for kidney stones involves the use of ultrasounds (shock wave lithotripsy) Sound waves from outside the body are used to shatter the kidney stones into smaller fragments Once disintegrated, the fragments of the kidney stone can be passed normally in the urine

Pneumothorax

A pneumothorax is an abnormal collection of gas in the pleural space that causes an uncoupling of the lung from the chest wall The pleural cavity is a thin, fluid-filled space between the lung and chest wall Surface tension of the pleural fluid causes the lung to adhere closely to the chest wall and thus inflate upon chest expansion If this cavity becomes filled with air (pneumothorax) or blood (haemothorax), the lung will collapse until the pressure is relieved The build up of fluid or gas will also compress other local organs (including the heart), resulting in life threatening complications A pneumothorax is typically treated by inserting a syringe into the pleural cavity and draining the excess liquid or gas

Measurement of transpiration rates using potometers

A potometer is a device that is used to estimate transpiration rates by measuring the rate of water loss / uptake When a plant is affixed to the potometer, transpiration can be indirectly identified by the movement of water towards the plant This water movement can be assessed as a change in meniscus level or by the movement of an air bubble towards the plant The initial starting position of the meniscus or air bubble can be adjusted by introducing additional water from a reservoir When measuring transpiration rates with a potometer, it is important to remember that not all water is lost to transpiration A small amount of water (~2%) is used in photosynthesis and to maintain the viable turgidity of plant cells

Respirometers

A respirometer is a device that determines an organism's respiration rate by measuring the rate of exchange of O2 and CO2 The living specimen (e.g. germinating seeds or invertebrate organism) is enclosed in a sealed container Carbon dioxide production can be measured with a data logger or by pH changes if the specimen is immersed in water When an alkali is included to absorb CO2, oxygen consumption can be measured as a change in pressure within the system The pressure change can be detected with a data logger or via use of a U-tube manometer Factors which may affect respiration rates include temperature, hydration, light (plants), age and activity levels An increase in carbon dioxide levels will indicate an increase in respiration (CO2 is a product of aerobic respiration) A decrease in oxygen levels will indicate an increase in respiration (O2 is a requirement for aerobic respiration)

Anorexia

Anorexia nervosa is an eating disorder in which individuals severely limit the amount of food they intake It is most common in young females with body image anxiety and can potentially be fatal if left untreated In severe anorexia, the body begins to break down heart muscle, making heart disease the most common cause of death Blood flow is reduced and blood pressure may drop as heart tissue begins to starve The heart may also develop dangerous arrhythmias and become physically diminished in size

Application: • Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-

Application: • Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively- labelled carbon dioxide Aphids are a group of insects, belonging to the order Hemiptera, which feed primarily on sap extracted from phloem Aphids possess a protruding mouthpiece (called a stylet), which pierces the plant's sieve tube to allow sap to be extracted The penetration of the stylet into the sieve tube is aided by digestive enzymes that soften the intervening tissue layers If the stylet is severed, sap will continue to flow from the plant due to the hydrostatic pressure within the sieve tube Extraction of Phloem Sap via an Aphid Stylet aphid stylet Measuring Phloem Transport Aphids can be used to collect sap at various sites along a plant's length and thus provide a measure of phloem transport rates A plant is grown within a lab with the leaves sealed within a glass chamber containing radioactively-labelled carbon dioxide The leaves will convert the CO2 into radioactively-labelled sugars (via photosynthesis), which are transported by the phloem Aphids are positioned along the plant's length and encouraged to feed on the phloem sap Once feeding has commenced, the aphid stylet is severed and sap continues to flow from the plant at the selected positions The sap is then analysed for the presence of radioactively-labelled sugars The rate of phloem transport (translocation rate) can be calculated based on the time taken for the radioisotope to be detected at different positions along the plant's length Example of Phloem Transport Rate Data aphid experiment Factors Affecting Translocation Rate The rate of phloem transport will principally be determined by the concentration of dissolved sugars in the phloem The concentration of dissolved sugars in the phloem sap will be affe

Application: • Models of water transport in xylem using apparatus including filter paper, porous pots or capillary tubing

Application: • Models of water transport in xylem using apparatus including filter paper, porous pots or capillary tubing The movement of water up the length of the xylem can be modelled using a number of simple apparatus These include capillary tubing, filter or blotting paper and porous pots Capillary Tubing: Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action) This is due to a combination of surface tension (cohesive forces) and adhesion with the walls of the tube surface The thinner the tube or the less dense the fluid, the higher the liquid will rise (xylem vessels are thin: 20 - 200 µm) Filter Paper: Filter paper (or blotting paper) will absorb water due to both adhesive and cohesive properties When placed perpendicular to a water source, the water will hence rise up along the length of the paper This is comparable to the movement of water up a xylem (the paper and the xylem wall are both composed of cellulose) Porous Pots: Porous pots are semi-permeable containers that allow for the free passage of certain small materials through pores The loss of water from the pot is similar to the evaporative water loss that occurs in the leaves of plants If the porous pot is attached by an airtight seal to a tube, the water loss creates a negative pressure that draws more liquid Models of Water Transport ninja icon Skill: • Measurement of transpiration rates using potometers A potometer is a device that is used to estimate transpiration rates by measuring the rate of water loss / uptake When a plant is affixed to the potometer, transpiration can be indirectly identified by the movement of water towards the plant This water movement can be assessed as a change in meniscus level or by the movement of an air bubble towards the plant The

Application: • Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples

Application: • Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing DNA sequencing refers to the process by which the base order of a nucleotide sequence is elucidated The most widely used method for DNA sequencing involves the use of chain-terminating dideoxynucleotides Dideoxynucleotides Dideoxynucleotides (ddNTPs) lack the 3'-hydroxyl group necessary for forming a phosphodiester bond Consequently, ddNTPs prevent further elongation of a nucleotide chain and effectively terminate replication The resulting length of a DNA sequence will reflect the specific nucleotide position at which the ddNTP was incorporated For example, if a ddGTP terminates a sequence after 8 nucleotides, then the 8th nucleotide in the sequence is a cytosine Determining Nucleotide Positions Using Dideoxynucleotides dideoxynucleotides Sequencing Dideoxynucleotides can be used to determine DNA sequence using the Sanger method Four PCR mixes are set up, each containing stocks of normal nucleotides plus one dideoxynucleotide (ddA, ddT, ddC or ddG) As a typical PCR will generate over 1 billion DNA molecules, each PCR mix should generate all the possible terminating fragments for that particular base When the fragments are separated using gel electrophoresis, the base sequence can be determined by ordering fragments according to length If a distinct radioactive or fluorescently labelled primer is included in each mix, the fragments can be detected by automated sequencing machines If the Sanger method is conducted on the coding strand (non-template strand), the resulting sequence elucidated will be identical to the template strand

Asthma

Asthma is a common, chronic inflammation of the airways to the lungs (i.e. bronchi and bronchioles) Inflammation leads to swelling and mucus production, resulting in reduced airflow and bronchospasm During an acute asthma attack, constriction of the bronchi smooth muscle may cause significant airflow obstruction Common symptoms of an asthma attack include shortness of breath, chest tightness, wheezing and coughing Severe cases of asthma may be life threatening if left untreated Asthma may be caused by a number of variable and recurring environmental triggers, including allergens, smoke, cold air, certain medications and arthropods (e.g. dust mites)

Atherosclerosis

Atherosclerosis is the hardening and narrowing of the arteries due to the deposition of cholesterol Atheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen (stenosis) The restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress) The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

John Cairns

Autoradiography Cells are grown in a solution containing radioactive thymidine (tritiated thymidine - 3H-T) The tritiated thymidine is incorporated into the chromosomal DNA of the cell (3H-T is used as thymidine is not present in RNA) The chromosomes are isolated by gently lysing the cells and fixing the chromosomes to a photographic surface The surface is then immersed in a radioactively-sensitive emulsion containing silver bromide (AgBr) The radiation released from the tritiated thymidine converts the Ag+ ions in silver bromide into insoluble metal grains Following a period of exposure, excess silver bromide is washed away, leaving the silver grains to appear as small black dots When the photographic film is developed, the chromosomal DNA can be visualised with an electron microscope Summary of the Process of Autoradiography autoradiography Chromosome Length John Cairns pioneered a technique for measuring the length of DNA molecules by autoradiography Previously, chromosome length could only be measured while condensed during mitosis (very inaccurate due to supercoiling) Cairns used autoradiography to visualise the chromosomes whilst uncoiled, allowing for more accurate indications of length By using tritiated uracil (3H-U), regions of active transcription can be identified within the uncoiled chromosome Uncoiled Chromosomes Identified with Autoradiography chromosome length Other Discoveries John Cairns was further able to use autoradiography to demonstrate key events which occur during chromosomal replication DNA replication involves formation of a replication bubble (and prokaryotic replication involves a single origin of replication) DNA replication is bi-directional (it occurs independently at both ends of the replication bubble) 1. Evidence for the Formation of Replication Bubbles (Prokaryotes)

Coronary Heart Disease

Blood pumped through the heart is at high pressure and cannot be used to supply the heart muscle with oxygen and nutrients Coronary arteries are the blood vessels that surround the heart and nourish the cardiac tissue to keep the heart working If coronary arteries become occluded, the region of heart tissue nourished by the blocked artery will die and cease to function There are several risk factors for coronary heart disease (CHD), including: Age - Blood vessels become less flexible with advancing age Genetics - Having hypertension predispose individuals to developing CHD Obesity - Being overweight places an additional strain on the heart Diseases - Certain diseases increase the risk of CHD (e.g. diabetes) Diet - Diets rich in saturated fats, salts and alcohol increases the risk Exercise - Sedentary lifestyles increase the risk of developing CHD Sex - Males are at a greater risk due to lower oestrogen levels Smoking - Nicotine causes vasoconstriction, raising blood pressure Mnemonic: A Goddess

ct corn

Bt corn is a genetically modified maize that incorporates an insecticide producing gene from the bacterium Bacillus thuringiensis This insecticide is lethal to certain types of larvae, particularly the European corn borer which would otherwise eat the crop Concerns have been raised that the spread of Bt corn may also be impacting the survival rates of monarch butterflies While monarch butterfly larva feed exclusively on milkweed, wind-borne pollen from Bt corn may dust nearby milkweeds Relationship between Bt Corn and the Monarch Butterfly Bt corn In 1999, a preliminary study was conducted investigating the association between exposure to Bt corn pollen and survivor rates among monarch caterpillars: Monarch caterpillars were fed milkweed leaves that had been dusted with pollen from Bt corn (to simulate spread via wind) Growth and mortality rates were compared against caterpillars fed on non-dusted leaves or leaves dusted with non-GM pollen Caterpillars exposed to Bt pollen were found to have eaten less, grew more slowly and exhibited higher mortality rates Effect of Bt Pollen on Survival Rates of Monarch Butterflies (Laboratory Conditions) Bt graph 1 Some scientists suggested that these results may lack validity as they do not accurately reflect natural conditions: There were higher amounts of Bt pollen on the leaves than would be found naturally (e.g. rain would diminish build up) Larva were restricted in their diet (in the field, larva could feasibly avoid eating pollen dusted leaves) A second study was conducted comparing the survivor rates of monarch butterflies based on proximity to Bt corn fields: There was no significant increase in mortality when monarch larva were placed in or near an actual Bt corn field From this it was concluded that exposure to Bt pollen poses no significant risk to monarc

Darwin

Charles Darwin's theory of evolution was based on a combination of Lamarckian ideas and recent fossil discoveries He theorised that species living today had been changed over time and stemmed from a single (or few) ancestral organisms He noted that although populations have the capacity to grow uncontrollably, limiting natural factors will restrict this growth Organisms which possess traits better suited to conditions would have an adaptive advantage and be more likely to reproduce These traits would hence become more common within the population and the species would gradually change over time Similar ideas were proposed at the same time by Alfred Wallace (he corresponded with Darwin but published separately)

Obesity

Clinical obesity (BMI > 30) describes a significant excess in body fat and is caused by a combination of two factors: Increased energy intake (i.e. overeating or an increased reliance on diets rich in fats and sugars) Decreased energy expenditure (i.e. less exercise resulting from an increasingly sedentary lifestyle) Individuals who are overweight or obese are more likely to suffer from hypertension (abnormally high blood pressure) Excess weight places more strain on the heart to pump blood, leading to a faster heart rate and higher blood pressure High cholesterol diets will lead to atherosclerosis, narrowing the blood vessels which contributes to raised blood pressure Hypertension is a common precursor to the development of coronary heart disease (CHD) Individuals who are overweight or obese are also more likely to suffer from type II diabetes (non-insulin dependent) Type II diabetes occurs when fat, liver and muscle cells become unresponsive to insulin (insulin insensitivity) This typically results from a diet rich in sugars causing the progressive overstimulation of these cells by insulin Hence overweight individuals who have a high sugar intake are more likely to develop type II diabetes

Gregor Mendel

Conducted monohybrid crosses using pea plants Showed that two alleles of a gene separate into different haploid gametes during mitosis Discovered the law of independent assortment for monohybrid crosses Crossed 2 pea plants of 2 different characteristics, controlled by 2 different genes: dihybrid crosses Developed ratio of 9:3:3:1 in dihybrid crosses ============================== First, he crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics Next, he crossed the offspring with each other (self-fertilization) and grew their seeds to similarly determine their characteristics These crosses were performed many times to establish reliable data trends (over 5,000 crosses were performed) As a result of these experiments, Mendel discovered the following things: When he crossed two different purebred varieties together the results were not a blend - only one feature would be expressed E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants When Mendel self-fertilised the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1 E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1 From these findings, Mendel drew the following conclusions: Organisms have discrete factors that determine its features (these 'factors' are now recognised as genes) Furthermore, organisms possess two versions of each factor (these 'versions' are now recognised as alleles) Each gamete contains only one version of each factor (sex cells are now recognised to be haploid) Parents contribute equally to the inheritance of offspring as a result of the fusion between randomly selected egg and sperm For each factor, one version is dominant over anoth

Calvin

Conducted the "lollipop experiment" Suspended Chlorella in a "lollipop" vessel; brightly illuminated the vessel Chlorella supplied with CO2 and HCO3- Initially placed carbon-12 before the experiment, but then replaced it with carbon-14 Killed samples of Chlorella with methanol Determined using an autoradiogram indicated that Glycerate-3-phosphate was the first product of carbon fixation ================================ The light independent reactions are also collectively known as the Calvin cycle - named after American chemist Melvin Calvin Calvin mapped the complete conversion of carbon within a plant during the process of photosynthesis Calvin's elucidation of photosynthetic carbon compounds is commonly classed the 'lollipop experiment' This is due to the fact that the apparatus he utilised was thought to resemble an upside-down lollipop Lollipop Experiment Radioactive carbon-14 is added to a 'lollipop' apparatus containing green algae (Chlorella) Light is shone on the apparatus to induce photosynthesis (which will incorporate the carbon-14 into organic compounds) After different periods of time, the algae is killed by running it into a solution of heated alcohol (stops cell metabolism) Dead algal samples are analysed using 2D chromatography, which separates out the different carbon compounds Any radioactive carbon compounds on the chromatogram were then identified using autoradiography (X-ray film exposure) By comparing different periods of light exposure, the order by which carbon compounds are generated was determined Calvin used this information to propose a sequence of events known as the Calvin cycle (light independent reactions)

Coronary Thrombosis

Coronary thrombosis is the formation of a clot within the blood vessels that supply and sustain the heart tissue (coronary arteries) Occlusion of a coronary artery by a blood clot may lead to an acute myocardial infarction (heart attack) Blood clots form in coronary arteries when the vessels are damaged as a result of the deposition of cholesterol (atherosclerosis) Atheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen (stenosis) The restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress) The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

Dehydration

Dehydration is a loss of water from the body such that body fluids become hypertonic Individuals will experience thirst and excrete small quantities of heavily concentrated urine (to minimise water loss) Blood pressure will drop (less water in plasma) and the heart rate will increase to compensate for this The individual will become lethargic and experience an inability to lower body temperature (due to lack of sweat) Severe cases of dehydration may cause seizures, brain damage and eventual death

Watson and Crick

Created models in discovering the structure of DNA Took several attempts before they were successful Used cardboard shapes to represent A-T and G-C Base pairs were equal in length From discoveries of Franklin and Wilkins, DNA was helical Used metal rods and sheeting to show the helical shape of DNA ============================= The structural organisation of the DNA molecule was correctly proposed in 1953 by James Watson and Francis Crick These British scientists constructed models to quickly visualise and assess the viability of potential structures Their efforts were guided by an understanding of molecular distances and bond angles developed by Linus Pauling, and were based upon some key experimental discoveries: DNA is composed of nucleotides made up of a sugar, phosphate and base - Phoebus Levene, 1919 DNA is composed of an equal number of purines (A + G) and pyrimidines (C + T) - Erwin Chargaff, 1950 DNA is organised into a helical structure - Rosalind Franklin, 1953 (data shared without permission) Making DNA Models Using trial and error, Watson and Crick were able to assemble a DNA model that demonstrated the following: DNA strands are antiparallel and form a double helix DNA strands pair via complementary base pairing (A = T ; C Ξ G) Outer edges of bases remain exposed (allows access to replicative and transcriptional proteins) As Watson and Crick's model building was based on trial and error, a number of early models possessed faults: The first model generated was a triple helix Early models had bases on the outside and sugar-phosphate residues in the centre Nitrogenous bases were not initially configured correctly and hence did not demonstrate complementarity

Meselson and Stahl

Cultured E. Coli for many generations in a growth medium, where the only source of nitrogen-15 Nitrogen in the bases of DNA was N-15 Transferred DNA sample to a medium with N-14 Spun the samples together in a centrifuge Found that after each generation of replicated DNA, there were an increasing number of DNA with N-14 strands Indicated that DNA replication is a semi-conservative process ================================ Meselson and Stahl were able to experimentally test the validity of these three models using radioactive isotopes of nitrogen Nitrogen is a key component of DNA and can exist as a heavier 15N or a lighter 14N DNA molecules were prepared using the heavier 15N and then induced to replicate in the presence of the lighter 14N DNA samples were then separated via centrifugation to determine the composition of DNA in the replicated molecules The results after two divisions supported the semi-conservative model of DNA replication After one division, DNA molecules were found to contain a mix of 15N and 14N, disproving the conservative model After two divisions, some molecules of DNA were found to consist solely of 14N, disproving the dispersive model

Cystic fibrosis

Cystic fibrosis is an autosomal recessive disorder caused by a mutation to the CFTR gene on chromosome 7 Individuals with cystic fibrosis produce mucus which is unusually thick and sticky This mucus clogs the airways and secretory ducts of the digestive system, leading to respiratory failure and pancreatic cysts Heterozygous carriers who possess one normal allele will not develop disease symptoms

Peter and Rosemary Grant

Daphne Major is an Island of the Galapagos archipelago. Darwin visited in 1835 and observed that the sizes and shapes of the finches varied according to their diet. Darwin hypothesized that an original finch species had diversified into the multiple species now found on different islands. Since early 1970s, the biologists Peter and Rosemary Grant have observed and tagged and measured the finches and their environmental changes and how these changes favored individuals in the population. Those individuals survived and passed on their characteristics to the next generation, illustrating natural selection in action.

Morgan

Developed the idea that linked genes account for anomalies found in dihybrid crosses Discovered sex-linkage whilst studying inheritance patterns in Drosophila "Some genes are located on the sex chromosomes" Found that ratios were non-Mendelian in some dihybrid crosses, due to sex linkage Provided an essential refinement to the theory that groups of genes that occur on the same chromosome ============================ Thomas Hunt Morgan provided a key contribution to our current understanding of gene linkage by discovering non-Mendelian ratios in Drosophila melanogaster (fruit flies) His breeding experiments involving fruit flies clearly demonstrated that linked genes were not independently assorted Sex Linkage When cross-breeding red-eyed wild types with white-eyed mutants, he discovered a clear sex bias in phenotypic distribution All female offspring of a red-eyed male were red-eyed, whereas all male offspring of a white-eyed female were also white-eyed Morgan described this distribution as 'sex-limited' inheritance and inferred it was caused by the gene for eye colour being located on a sex chromosome (i.e. X-linked) Gene Linkage Morgan went on to identify a number of different traits in fruit flies that did not conform to Mendelian ratios Certain phenotypic combinations occurred in much lower frequencies than was to be expected Based on this data, Morgan made two key proposals: The alleles for these traits were located on a shared chromosome (gene linkage) and hence did not independently assort Linked alleles could be uncoupled via recombination (crossing over) to create alternative phenotypic combinations, but these new phenotypes would occur at a much lower frequency Morgan also observed that the amount of crossing over between linked genes differed depending on the combination of traits This led to th

Diabetes

Diabetes mellitus is a metabolic disorder that results from a high blood glucose concentration over a prolonged period It is caused by the body either not producing insulin (Type I) or failing to respond to insulin production (Type II) It is treated with either insulin injections (Type I only) or by carefully monitoring and controlling dietary intake (Type II) Type I: usually occurs during childhood (early onset), body does not produce sufficient insulin, caused by the destruction of B-cells (autoimmune), requires insulin injections to regulate blood glucose Type II: usually occurs during adulthood (late onset), body does not respond to insulin production, caused by the down-regulation of insulin receptors, controlled by managing diet and lifestyle

Harvey (Blood)

Doctrines of Galen, a Greek philosopher, claimed that blood was made in the liver, pumped out by the heart, ad consumed by organs in the body Harvey found that blood flows through unidirectional vessels with valves Showed that heart pumps blood out the arteries and returns to the heart through the veins Showed that organs could not consume blood due to high pressure of blood traveling through vessels Predicted the presence of smaller vessels (capillaries) to link arteries to veins in tissues Microscopes had not been invented ================================ Our modern understanding of circulatory system is based upon the discoveries of 17th century English physician, William Harvey Harvey's findings were published in a book commonly called De Motu Cordis - On the Motion of the Heart and Blood Prior to Harvey's findings, scientists held to the antiquated views of the Greek philosopher Galen, who believed that: Arteries and veins were separate blood networks (except where they connected via invisible pores) Veins were thought to pump natural blood (which was believed to be produced by the liver) Arteries were thought to pump heat (produced by the heart) via the lungs (for cooling - like bellows) Based on some simple experiments and observations, Harvey instead proposed that: Arteries and veins were part of a single connected blood network (he did not predict the existence of capillaries however) Arteries pumped blood from the heart (to the lungs and body tissues) Veins returned blood to the heart (from the lungs and body tissues)

• Design of experiments to test hypotheses about factors affecting germination

Germination is the process by which a seed emerges from a period of dormancy and begins to sprout For germination to occur, a seed requires a combination of: Oxygen - for aerobic respiration (the seed requires large amounts of ATP in order to develop) Water - to metabolically activate the seed (triggers the synthesis of gibberellin) Temperature - seeds require certain temperature conditions in order to sprout (for optimal function of enzymes) pH - seeds require a suitable soil pH in order to sprout (for optimal function of enzymes) Additionally, certain plant species may require additional conditions for germination: Fire - some seeds will only sprout after exposure to intense heat (e.g. after bushfires remove established flora) Freezing - some seeds will only sprout after periods of intense cold (e.g. in spring, following the winter snows) Digestion - some seeds require prior animal digestion to erode the seed coat before the seed will sprout Washing - some seeds may be covered with inhibitors and will only sprout after being washed to remove the inhibitors Scarification - seeds are more likely to germinate if the seed coat is weakened from physical damage Experiments can be developed using any of these factors as an independent variable Germination can be measured by the rate of seed growth over a set period of time

Hemophilia

Haemophilia is an X-linked recessive condition that impairs the body's ability to control blood clotting It is more common in males than females (as males are hemizygous and have only one X chromosome) People with haemophilia (haemophiliacs) have lower levels of functional clotting factors in their blood plasma This means the normal coagulation cascade is impaired and fibrin formation does not occur Thus while a temporary scab may form (due to the formation of a platelet plug), a lasting blood clot cannot form Haemophiliacs can die from minor injuries, as the continued loss of blood flow cannot be prevented via clot formation There are different types of haemophilia with varying severities, depending on which specific clotting factor is defective Haemophilia A (clotting factor XIII deficiency) is more common than haemophilia B (clotting factor IX deficiency)

In vitro fertilisation

In vitro fertilisation (IVF) refers to fertilisation that occurs outside of the body (in vitro = 'in glass') It involves using drugs to suspend normal ovulation (down regulation), before using hormone treatments to collect multiple eggs (superovulation) Down regulation Drugs are used to halt the regular secretion of FSH and LH - this in turn stops the secretion of estrogen and progesterone By arresting the hormonal cycle, doctors can take control of the timing and quantity of egg production by the ovaries The drug treatment usually takes about two weeks and is typically delivered in the form of a nasal spray Superovulation Superovulation involves using artificial doses of hormones to develop and collect multiple eggs from the woman The patient is firstly injected with large amounts of FSH to stimulate the development of many follicles The follicles are then treated with human chorionic gonadotrophin (hCG) - a hormone usually produced by a developing embryo hCG stimulates the follicles to mature and the egg is then collected (via aspiration with a needle) prior to the follicles rupturing Fertilisation The extracted eggs are then incubated in the presence of a sperm sample from the male donor The eggs are then analysed under a microscope for successful fertilisation Implantation Approximately two weeks prior to implantation, the woman begins to take progesterone treatments to develop the endometrium Healthy embryos are selected and transferred into the female uterus (or the uterus of a surrogate) Multiple embryos are transferred to improve chances of successful implantation (hence multiple births are a possible outcome) Roughly two weeks after the procedure, a pregnancy test is taken to determine if the process has been successful In Vitro Fertilisation Procedure IVF shes fit Summary of the Key Stages of I

Trisomy 21 (Down Syndrome)

Individuals with Down syndrome have three copies of chromosome 21 (trisomy 21) One of the parental gametes had two copies of chromosome 21 as a result of non-disjunction The other parental gamete was normal and had a single copy of chromosome 21 When the two gametes fused during fertilisation, the resulting zygote had three copies of chromosome 21

Jaundice

Jaundice is a condition caused by an excess of bile pigment - bilirubin - within the body Bilirubin is produced as part of the natural breakdown of haemoglobin by the liver Normally, the liver conjugates this bilirubin to other chemicals and then secretes it in bile When there is an excess of bilirubin, it may leak out into surrounding tissue fluids Jaundice may be caused by any condition which impairs the natural breakdown of red blood cells, including: Liver disease - impaired removal of bilirubin by the liver may cause levels to build within the body Obstruction of the gall bladder - preventing the secretion of bile will cause bilirubin levels to accumulate Damage to red blood cells - increased destruction of erythrocytes (e.g. anemia) will cause bilirubin levels to rise The main consequence of jaundice is a yellowish discoloration of the skin and whites of the eyes (sclera) Other common symptoms include itchiness, paler than usual stools and darkened urine Jaundice may be resolved by treating the underlying cause for the build up of bilirubin within the body

Lamarck

Jean-Baptiste Lamarck, a French scientist, proposed that species changed as a result of the habitual use or disuse of a feature Excessive use would cause a feature to develop, while continued disuse would cause it to atrophy (similar to muscle growth) Lamarck proposed that these modified features could be passed on to successive generations, changing the species over time Lamarck's theory however was essentially flawed - cutting the tail off a rat does not produce tail-less offspring

John Cairns

John Cairns pioneered a technique for measuring the length of DNA molecules by autoradiography Previously, chromosome length could only be measured while condensed during mitosis (very inaccurate due to supercoiling) Cairns used autoradiography to visualise the chromosomes whilst uncoiled, allowing for more accurate indications of length By using tritiated uracil (3H-U), regions of active transcription can be identified within the uncoiled chromosome John Cairns was further able to use autoradiography to demonstrate key events which occur during chromosomal replication DNA replication involves formation of a replication bubble (and prokaryotic replication involves a single origin of replication) DNA replication is bi-directional (it occurs independently at both ends of the replication bubble)

Kidney Failure

Kidney diseases are conditions which incapacitate the kidney's ability to filter waste products from the blood Individuals with kidney diseases will demonstrate a reduced glomerular filtration rate (GFR) If untreated, kidney diseases can lead to kidney failure - which is life threatening Kidney diseases are conditions which incapacitate the kidney's ability to filter waste products from the blood Individuals with kidney diseases will demonstrate a reduced glomerular filtration rate (GFR) If untreated, kidney diseases can lead to kidney failure - which is life threatening Urinary Analysis Kidneys prevent the excretion of blood cells and proteins (during ultrafiltration), as well as glucose (selective reabsorption) Hence the presence of these materials in urine can be used as an indicator of disease Glucose: The presence of glucose in urine is a common indicator of diabetes (high blood glucose = incomplete reabsorption) Proteins: High quantities of protein in urine may indicate disease (e.g. PKU) or hormonal conditions (e.g. hCG = pregnancy) Blood cells: The presence of blood in urine can indicate a variety of diseases, including certain infections and cancer Drugs / toxins: Many drugs pass through the body into urine and can be detected (e.g. performance enhancing drugs) Using Urinary Analysis to Detect Disease urinary analysis Application: • Treatment of kidney failure by hemodialysis or kidney transplant Hemodialysis Kidney dialysis involves the external filtering of blood in order to remove metabolic wastes in patients with kidney failure Blood is removed and pumped through a dialyzer, which has two key functions that are common to biological membranes: It contains a porous membrane that is semi-permeable (restricts passage of certain materials) It introduces fresh dialysis fluid and removes

Klinefelter's Disease

Klinefelter syndrome (KS) is a condition that occurs in males when they have an extra X chromosome. Some males with KS have no obvious signs or symptoms while others may have varying degrees of cognitive, social, behavioral, and learning difficulties. Adults with Klinefelter syndrome may also have primary hypogonadism (decreased testosterone production), small and/or undescendent testes (cryptorchidism), enlarged breast tissue (gynecomastia), tall stature, and/or inability to have biological children (infertility), as well as an abnormal opening of the penis (hypospadias), and an small penis (micropenis). KS is not inherited, but usually occurs as a random event during the formation of reproductive cells (eggs and sperm) that results in the presence of one extra copy of the X chromosome in each cell (47,XXY). KS treatment is based on the signs and symptoms present in each person.[1][2][3] Life expectancy is usually normal and many people with KS have normal life. There is a very small risk of developing breast cancer and other conditions such as a chronic inflammatory disease called systemic lupus erythematosus

Lung Cancer

Lung cancer describes the uncontrolled proliferation of lung cells, leading to the abnormal growth of lung tissue (tumour) The abnormal growth can impact on normal tissue function, leading to a variety of symptoms according to size and location The tumours can remain in place (benign) or spread to other regions of the body (malignant) Lung cancers are the most common cause of cancer-related death worldwide for two main reasons: The lungs are vital to normal body function and thus the abrogation of their normal function is particularly detrimental to health The lungs possess a very rich blood supply, increasing the likelihood of the cancer spreading (metastasis) to other body regions The common symptoms of lung cancers include coughing up blood, wheezing, respiratory distress and weight loss If the cancer mass compresses adjacent organs it can cause chest pain, difficulty swallowing and heart complications There are many causes for lung cancer, including smoking, asbestos, air pollution, certain infections and genetic predispositions

Malaria

Malaria is caused by an endoparasite (Plasmodium falciparum) which reproduces inside red blood cells (but not sickle cells This protozoan uses mosquitoes as a host as well as humans In areas where malaria is common, there is a higher incidence of people who carry both alleles (i.e. are heterozygous) These individuals produce enough normal blood cells to avoid the more severe effects associated with sickle cell anaemia, but also produce enough sickle cells to confer an increased resistance to the malarial parasite This condition whereby the presence of both alleles is beneficial is known as heterozygous advantage

• Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively- labelled carbon dioxide

Measuring Phloem Transport Aphids can be used to collect sap at various sites along a plant's length and thus provide a measure of phloem transport rates A plant is grown within a lab with the leaves sealed within a glass chamber containing radioactively-labelled carbon dioxide The leaves will convert the CO2 into radioactively-labelled sugars (via photosynthesis), which are transported by the phloem Aphids are positioned along the plant's length and encouraged to feed on the phloem sap Once feeding has commenced, the aphid stylet is severed and sap continues to flow from the plant at the selected positions The sap is then analysed for the presence of radioactively-labelled sugars The rate of phloem transport (translocation rate) can be calculated based on the time taken for the radioisotope to be detected at different positions along the plant's length Factors Affecting Translocation Rate The rate of phloem transport will principally be determined by the concentration of dissolved sugars in the phloem The concentration of dissolved sugars in the phloem sap will be affected by: The rate of photosynthesis (which is affected by light intensity, CO2 concentration, temperature, etc.) The rate of cellular respiration (this may be affected by any factor which physically stresses the plant) The rate of transpiration (this will potentially determine how much water enters the phloem) The diameter of the sieve tubes (will affect the hydrostatic pressure and may differ between plant species)

A spirometer

Measuring Ventilation Ventilation in humans can be monitored in a number of ways: Via simple observation (counting number of breaths per minute) Chest belt and pressure meter (recording the rise and fall of the chest) Spirometer (recording the volume of gas expelled per breath) Spirometry involves measuring the amount (volume) and / or speed (flow) at which air can be inhaled or exhaled A spirometer is a device that detects the changes in ventilation and presents the data on a digital display A more simplistic method involves breathing into a balloon and measuring the volume of air in a single breath The volume of air can be determined by submerging the balloon in water and measuring the volume displaced (1ml = 1cm3)

• Setting up sealed mesocosms to try to establish sustainability

Mesocosms are enclosed environments that allow a small part of a natural environment to be observed under controlled conditions A terrarium is a small transparent container (e.g. glass or plastic) in which selected plants (or animals) are kept and observed Making a Self-Sustaining Terrarium A terrarium can be created using a glass or plastic bottle with a lid, according to the following steps: Building a verdant foundation Add a bottom layer of pebbles, gravel or sand - this layer exists for drainage (smaller vessels require thinner rock layers) Add a second thin layer of activated charcoal - this will prevent mold and help to aerate the soil Spread a thin cover of sphagnum moss (or use an organic coffee filter) to create a barrier between the lower layers and soil The final layer is the pre-moistened growing medium (i.e. potting mix) Selecting the right plants Ideally, choose plants that are both slow growing and thrive in a bit of humidity (e.g. most ferns, club moss, etc.) Inspect the plant thoroughly for any signs of disease or insects before introducing to the terrarium Maintaining appropriate conditions Ensure the terrarium is placed in a location that provides a continuous source of light Locate the terrarium in a place that does not experience fluctuating temperature conditions (i.e. avoid direct sunlight) Do not initially over-water the plants - once the right humidity is established, a terrarium can go months without watering Occasional pruning may be required - however, as level of soil nutrients decrease, plant growth should slow down

Pasteur

Method: Two experiments were setup In both, Pasteur added nutrient broth to flasks and bent the necks of the flasks into S Shapes Each flask was then heated to boil the broth in order than all existing microbes were Killed. After the broth had been sterilized, Pasteur broke off the swan necks from the flasks in Experiment 1, exposing the nutrient broth within them to air from above. The flasks in Experiment 2 were left alone. Results: The broth in experiment 1 turned cloudy whilst the broth in experiment 2 remained clear. This indicates that microbe growth only occurred in experiment 1. Supports cell theory: cells can only arise from pre-existing cells

Micropropagation

Micropropagation is a technique used to produce large numbers of identical plants (clones) from a selected stock plant Plants can reproduce asexually from meristems because they are undifferentiated cells capable of indeterminate growth When a plant cutting is used to reproduce asexually in the native environment it is called vegetative propagation When plant tissues are cultured in the laboratory (in vitro) in order to reproduce asexually it is called micropropagation The process of micropropagation involves a number of key steps: Specific plant tissue (typically the undifferentiated shoot apex) is selected from a stock plant and sterilised The tissue sample (called the explant) is grown on a sterile nutrient agar gel The explant is treated with growth hormones (e.g. auxins) to stimulate shoot and root development The growing shoots can be continuously divided and separated to form new samples (multiplication phase) Once the root and shoot are developed, the cloned plant can be transferred to soil Micropropagation micropropagation ninja icon Application: • Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species Micropropagation is used to rapidly produce large numbers of cloned plants under controlled conditions: Rapid Bulking Desirable stock plants can be cloned via micropropagation to conserve the fidelity of the selected characteristic This process is more reliable that selective breeding because new plants are genetically identical to the stock plant This technique is also used to rapidly produce large quantities of plants created via genetic modification Virus-Free Strains Plant viruses have the potential to decimate crops, crippling economies and leading to famine Viruses typically

Fusion of a tumor cell with an antibody-producing cell creates a hybridoma cell • Monoclonal antibodies are produced by hybridoma cells

Monoclonal antibodies are antibodies artificially derived from a single B cell clone (i.e. identical specific antibodies) An animal (typically a mouse) is injected with an antigen and produces antigen-specific plasma cells The plasma cells are removed and fused (hybridised) with tumor cells capable of endless divisions (immortal cell line) The resulting hybridoma cell is capable of synthesising large quantities of monoclonal antibody Production of Monoclonal Antibodies monoclonal antibodies ninja icon Application: • Monoclonal antibodies to hCG are used in pregnancy test kits Monoclonal antibodies can be used for both the therapeutic treatment and clinical detection of disease An example of therapeutic use involves the use of antibodies in the treatment of rabies An example of diagnostic use involves the use of antibodies in the detection of pregnancy Treatment Use Monoclonal antibodies are commonly used to provide immune protection for individuals who contract harmful diseases Because the rabies virus can potentially be fatal, injecting purified antibodies functions as an effective emergency treatment Monoclonal antibodies can be used to target cancer cells that the body's own immune cells fail to recognise as harmful Therapeutic monoclonal antibodies are named according to the source organism from which the antibodies were derived Mice antibodies ('-omab') are easier to synthesise than human antibodies but are less likely to be tolerated by the patient Examples of Therapeutic Monoclonal Antibodies monoclonal therapy Diagnostic Use Monoclonal antibodies can be used to test for pregnancy via the presence of human chorionic gonadotrophin (hCG) in urine hCG is a hormone produced by women during foetal development and thus its presence in urine is indicative of pregnancy Pregnancy tests use a pr

Modelling Digestion

Most food is solid and in the form of large complex molecules which are insolube and chemically inert (not readily usable) The process of digestion therefore performs two key functions: It breaks down insoluble molecules into smaller subunits which can be readily absorbed into body tissues It breaks down inert molecules into usable subunits which can be assimilated by cells and reassembled into new products Modelling Digestion A core function of the digestive system is to break down large molecules into smaller subunits that can be absorbed by cells Cell membranes are impermeable to large molecules (polypeptides, polysaccharides) unless transport is facilitated by proteins The size-specific permeability of cell membranes can be modelled using dialysis tubing (Visking tubing) Dialysis tubing contains pores typically ranging from 1 - 10 nm in diameter and is semi-permeable according to molecular size Large molecules such as starch cannot pass through the tubing, however smaller molecules (such as maltose) can cross Unlike the membranes of living cells, dialysis tubing is not selectively permeable based on charge (ions can freely cross) Dialysis Tubing dialysis tubing Digestion Experiments Digestive enzymes like amylase can break down inpermeable polymers (starch) into permeable subunits (maltose) Dialysis tubing is impermeable to amylase and starch, but permeable to maltose (and water) Experiment 1: Measuring Meniscus Levels A length of dialysis tubing is attached to a thistle funnel and filled with starch solution (control condition) A second length of tubing is attached to a thistle funnel and filled with starch and amylase solution (experimental condition) Both apparatuses are placed in a beaker filled with water Over time, water will move into the tubing via osmosis (towards the solute) causing the m

Albinism

Oculocutaneous albinism (OCA) is a group of rare inherited disorders characterized by a reduction or complete lack of melanin pigment in the skin, hair and eyes. These conditions are caused by mutations in specific genes that are necessary for the production of melanin pigment in specialized cells called melanocytes. Absent or insufficient melanin pigment results in abnormal development of the eyes, resulting in vision abnormalities, and light skin that is very susceptible to damage from the sun including skin cancer. Visual changes include nystagmus (involuntary side to side eye movement), strabismus and photophobia (sensitivity to light). Other changes include foveal hypoplasia (which affects visual acuity) and mis-routing of the optic nerves. All individuals with OCA have the above visual changes but the amount of skin, hair and iris pigment can vary depending on the gene (or type of OCA) and mutation involved. There are seven types of OCA (OCA1-7) caused by mutations in seven different genes. Oculocutaneous albinism is inherited as an autosomal recessive genetic condition.

William Bateson, Edith Saunders, and Reginald Punnett

One of the first cases of finding genetic characteristics that did not assort independently was reported in sweet peas by William Bateson, Edith Rebecca Saunders, and Reginald C. Punnett. They crossed a homozygous strain of peas having purple flowers and long pollen grains with a homozygous strain having red flowers and round pollen grains. All of the F1 had purple flowers and long pollen grains, indicating that purple was dominant over red and long was dominant over round. When they intercrossed the F1, the resulting F2 progeny did not appear in the 9:3:3:1 ratio expected with independent assortment. An excess of F2 plants had purple flowers and round pollen (the parental phenotypes). Now know that the 2 loci they examined lie close together on the same chromosome and therefore do not assort independently.

Analyzing oscilloscope traces

Oscilloscopes are scientific instruments that are used to measure the membrane potential across a neuronal membrane Data is displayed as a graph, with time (in milliseconds) on the X axis and membrane potential (in millivolts) on the Y axis A typical action potential will last for roughly 3 - 5 milliseconds and contain 4 key stages: Resting potential: Before the action potential occurs, the neuron should be in a state of rest (approx. -70 mV) Depolarisation: A rising spike corresponds to the depolarisation of the membrane via sodium influx (up to roughly +30 mV) Repolarisation: A falling spike corresponds to repolarisation via potassium efflux (undershoots to approx. -80 mV) Refractory period: The oscilloscope trace returns to the level of the resting potential (due to the action of the Na+/K+ pump) An action potential will only occur if the initial depolarisation exceeds a threshold potential of approximately -55 mV

Overhydration

Overhydration is a less common occurrence that results when an over-consumption of water makes body fluids hypotonic Individuals will produce excessive quantities of clear urine in an effort to remove water from the body The hypotonic body fluids will cause cells to swell (due to osmotic movement), which can lead to cell lysis and tissue damage Overhydration can lead to headaches and disrupted nerve functions in mild cases (due to swelling of cells) In severe cases, overhydration may lead to blurred vision, delirium, seizures, coma and eventual death

Phenylketonuria

Phenylketonuria (PKU) is a genetic condition that results in the impaired metabolism of the amino acid phenylalanine It is an autosomal recessive disease caused by a mutation to the gene encoding the enzyme phenylalanine hydroxylase Phenylalanine hydroxylase (PAH) normally converts excess phenylalanine within the body into tyrosine In people with PKU, the excess phenylalanine is instead converted into phenylpyruvate (also known as phenylketone) This results in a toxic build up of phenylketone in the blood and urine (hence phenylketonuria) Untreated PKU can lead to brain damage and mental retardation, as well as other serious medical problems Infants with PKU are normal at birth because the mother is able to break down phenylalanine during pregnancy Diagnosis of PKU is made by a simple blood test for elevated phenylalanine levels shortly after birth PKU is treated by enforcing a strict diet that restricts the intake of phenylalanine to prevent its build up within the body This low-protein diet should include certain types of fruits, grains, vegetables and special formula milk This diet should be supplemented with a medical formula that contains precise quantities of essential amino acids Patients who are diagnosed early and maintain this strict diet can have a normal life span without damaging symptoms

Design of an experiment to test hypotheses about the effect of temperature or humidity on transpiration rates

Potometers can be used to test a number of variables that may affect the rate of transpiration in plants These variables include temperature, humidity, light intensity and wind exposure Temperature: Increasing the ambient temperature is predicted to cause an increase in the rate of transpiration Higher temperatures lead to an increase in the rate of water vaporisation within the mesophyll, leading to more evaporation The effect of temperature variation can be tested experimentally by using heaters or submerging in heated water baths Humidity: Increasing the humidity is predicted to cause a decrease in the rate of transpiration Humidity is the amount of water vapour in the air - less vapour will diffuse from the leaf if there is more vapour in the air The effect of humidity can be tested experimentally by encasing the plant in a plastic bag with variable levels of vapour Light Intensity: Increasing the light intensity to which a plant is exposed is predicted to cause an increase in the rate of transpiration Increasing light exposure will cause more stomata to open in order to facilitate photosynthetic gas exchange The effect of light intensity can be tested experimentally by placing the plant at variable distances from a lamp Wind Exposure: Increasing the level of wind exposure is predicted to cause an increase in the rate of transpiration Wind / air circulation will function to remove water vapour from near the leaf, effectively reducing proximal humidity The effect of wind can be tested experimentally by using fans to circulate the air around a plant

Color Blindness

Red-green colour blindness is a genetic disorder whereby an individual fails to discriminate between red and green hues This condition is caused by a mutation to the red or green retinal photoreceptors, which are located on the X chromosome Red-green colour blindness can be diagnosed using the Ishihara colour test There are three different types of cone cells, each of which absorbs different wavelengths (trichromatic: red, green, blue) The genes responsible for producing red or green photoreceptors are located on the X chromosome (sex-linked) If either of these genes are mutated, red and green wavelengths cannot be distinguished As these genes are recessive and located on the X chromosome, red-green colour-blindness is more common in males Red-green colour-blindness can be diagnosed using the Ishihara colour test

Rosalind Franklin's and Maurice Wilkins' investigation of DNA structure by X-ray diffraction

Rosalind Franklin and Maurice Wilkins used a method of X-ray diffraction to investigate the structure of DNA DNA was purified and then fibres were stretched in a thin glass tube (to make most of the strands parallel) The DNA was targeted by a X-ray beam, which was diffracted when it contacted an atom The scattering pattern of the X-ray was recorded on a film and used to elucidate details of molecular structure Summary of the Process of X-Ray Crystallography x-ray crystallography From the scattering pattern produced by a DNA molecule, certain inferences could be made about its structure Composition: DNA is a double stranded molecule Orientation: Nitrogenous bases are closely packed together on the inside and phosphates form an outer backbone Shape: The DNA molecule twists at regular intervals (every 34 Angstrom) to form a helix (two strands = double helix) Photo 51 - Evidence for the Structure of DNA via X-Ray Diffraction Evidence: Overview Helix Twists Bases Strands Orientation Franklin's data was shared by Wilkins with James Watson (without Franklin's permission) who, with the help of Francis Crick, used the information to create a molecular model of the basic structure of DNA In 1962, Watson, Crick and Wilkins (but not Franklin) were awarded the Nobel prize for their contributions to DNA structure identification Link: The Structure of DNA - Cooperation and Competition ninja icon Understanding: • DNA structure suggested a mechanism for DNA replication Franklin's x-ray diffraction experiments demonstrated that the DNA helix is both tightly packed and regular in structure Phosphates (and sugars) form an outer backbone and nitrogenous bases are packaged within the interior Chargaff had also demonstrated that DNA is composed of an equal number of purines (A + G) and pyrimidines

Sickle Cell Anemia

Sickle cell anaemia is controlled by a single gene mutation (via a base substitution to the haemoglobin beta chain gene) The sixth codon is mutated (GAG → GUG) which changes the amino acid sequence (Glu → Val) Individuals who only possess the sickle cell allele will have abnormally shaped red blood cells that are destroyed by the spleen This leads to a reduction in red blood cells and a variety of health complications associated with reduced blood cell circulation These sickle-shaped cells are able to transport less oxygen from the lungs to respiring tissues, and they can get stuck in narrow blood vessels, resulting in a sickle cell crisis. This mutation also confers resistance to malaria.

Smallpox

Smallpox was the first infectious disease of humans to have been eradicated via vaccination When a disease stops circulating in a region it is considered eliminated - if it is eliminated worldwide, it is considered eradicated Smallpox was targeted for eradication in 1967 by the World Health Organisation (WHO), via a global vaccination programme The last known case of smallpox in a civilian was registered in 1977 and it was officially declared eradicated by WHO in 1980 The eradication of smallpox by vaccination was successful for a number of reasons: Smallpox was easily identifiable due to overt clinical symptoms, which helped to limit potential transmission Transmission only occurred via direct contact and there were no animal vectors or reservoirs to sustain the infectious agent The infection period was short lived (3 - 4 weeks) and the virus was stable and didn't mutate into alternate strains There was global cooperation and immunity was long-term so repeated booster shots were unnecessary

Starvation

Starvation describes the severe restriction of daily energy intake, leading to a significant loss of weight As the body is not receiving a sufficient energy supply from the diet, body tissue is broken down as an energy source This leads to muscle loss (as muscle proteins are metabolised for food) and eventually organ damage (and death)

Leukemia

The problem•Cancer of the blood or bone marrow, resulting in abnormally high levels of poorly-functioning white blood cells.The treatment•Hematopoetic Stem Cells (HSCs) are harvested from bone marrow, peripheral blood or umbilical cord blood•Chemotherapy and radiotherapy used to destroy the diseased white blood cells•New white blood cells need to be replaced with healthy cells.•HSCs are transplanted back into the bone marrow•HSCs differentiate to form new healthy white blood cellsThe benefit•The use of a patient's own HSCs means there is far less risk of immune rejection than with a traditional bone marrow transplant.

Harvey (Sexual Reproduction)

Tested Aristotle's theory of "males producing a seed forming an egg with a female's menstrual blood" Examined the uterus of a deer during mating season Expected to find deer eggs developing in the uterus Could not see that eggs were developing, as microscopes were not invented, and gametes were too small Concluded that Aristotle was wrong, but claimed that offspring was not a result of mating, which was also wrong Shows how research is hampered by deficiencies in the apparatus ============================= Debunking the 'Soil and Seed' Theory The 'soil and seed' theory was a popular doctrine for hundreds of years before it was eventually debunked by William Harvey William Harvey studied the sexual organs of female deer after mating in an effort to identify the developing embryo He was unable to detect a growing embryo until approximately 6 - 7 weeks after mating had occurred He concluded that Aristotle's theory was incorrect and that menstrual blood did not contribute to the development of a fetus Harvey was unable to identify the correct mechanism of sexual reproduction and incorrectly asserted that the fetus did not develop from a mixture of male and female 'seeds

HIV

The Human Immunodeficiency Virus (HIV) is a retrovirus that infects helper T cells, disabling the body's adaptive immune system It causes a variety of symptoms and infections collectively classed as Acquired Immuno-Deficiency Syndrome (AIDS) Effects of HIV HIV specifically targets the helper T lymphocytes which regulate the adaptive immune system Following infection, the virus undergoes a period of inactivity (clinical latency) during which infected helper T cells reproduce Eventually, the virus becomes active again and begins to spread, destroying the T lymphocytes in the process (lysogenic cycle) With a reduction in the number of helper T cells, antibodies are unable to be produced, resulting in a lowered immunity The body becomes susceptible to opportunistic infections, eventually resulting in death if the condition is not managed Transmission of HIV HIV is transmitted through the exchange of body fluids (including unprotected sex, blood transfusions, breastfeeding, etc.) The risk of exposure to HIV through sexual contact can be minimised by using latex protection (i.e. condoms) A small minority of people are immune to HIV infection (they lack the CD4+ receptor on TH cells that HIV requires for docking) HIV is a global issue, but is particularly prevalent in poorer nations with poor education and health systems

Carl Linnaeus

The binomial system of nomenclature is the formal system by which all living species are classified (taxonomy) It was initially developed by a Swedish botanist named Carolus Linnaeus in 1735 It is periodically assessed and updated at a series of international congresses which occur every 4 years The binomial system of nomenclature provides value because: It allows for the identification and comparison of organisms based on recognised characteristics It allows all organisms to be named according to a globally recognised scheme It can show how closely related organisms are, allowing for the prediction of evolutionary links It makes it easier to collect, sort and group information about organisms

Davson-Danielli model: fluorescent anti-body tagging

The evidence: In high magnification electron micrographs membranes appeared as two dark parallel lines with a lighter coloured region in between.Proteins appear dark in electron micrographs and phospholipids appear light - possibly indicating proteins layers either side of a phospholipid core. The model:•A protein-lipid sandwich•Lipid bilayer composed of phospholipids (hydrophobic tails inside, hydrophilic heads outside)•Proteins coat outer surface•Proteins do not permeate the lipid bilayer Interpreting the image:•The fracture occurs along lines of weakness, including the centre of membranes.•The fracture reveals an irregular rough surface inside the phospholipid bilayer•The globular structures were interpreted as trans-membrane proteins. Conclusion:This is contrary to the Davson-Danielli model which only involves proteins coating the surface of the membrane. A new model is needed to explain the presence of as trans-membrane proteins. Fluorescent antibody tagging •Within 40 minutes the red and green markers were mixed throughout the membrane of the fused cell.•This showed that membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer.•red or green fluorescent markers attached to antibodies which would bind to membrane proteins•The membrane proteins of some cells were tagged with red markers and other cells with green markers.•The cells were fused together.

Florey and Chain: Testing penicillin

The first chemical compound found to have antibiotic properties was penicillin, which was identified by Alexander Fleming in 1928 The discovery of penicillin was a fortuitous accident, resulting from the unintended contamination of a dish containing S. aureus A Penicillium mould began to grow on the plate and a halo of inhibited bacterial growth was observed around the mould Fleming concluded that the mould was releasing a substance (penicillin) that was killing the nearby bacteria Medical Applications The medical applications of penicillin as an antibiotic were demonstrated by an Australian scientist, Sir Howard Florey, in 1940 Working with another scientist (Ernst Chain) and a team of researchers, Florey tested penicillin on infected mice Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin The untreated mice died of bacterial infection while those treated with penicillin all survived - demonstrating its antibiotic potential Historical Significance In 1945, Howard Florey, Ernst Chain and Alexander Fleming were collectively awarded the Nobel Prize for Medicine Following the chemical determination of penicillin structure in 1945, several synthetic derivatives have since been created These derivatives (including methicillin) offer many benefits including a broader spectrum, more stability and greater tolerance

Models of water transport in xylem using apparatus including filter paper, porous pots or capillary tubing

The movement of water up the length of the xylem can be modelled using a number of simple apparatus These include capillary tubing, filter or blotting paper and porous pots Capillary Tubing: Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action) This is due to a combination of surface tension (cohesive forces) and adhesion with the walls of the tube surface The thinner the tube or the less dense the fluid, the higher the liquid will rise (xylem vessels are thin: 20 - 200 µm) Filter Paper: Filter paper (or blotting paper) will absorb water due to both adhesive and cohesive properties When placed perpendicular to a water source, the water will hence rise up along the length of the paper This is comparable to the movement of water up a xylem (the paper and the xylem wall are both composed of cellulose) Porous Pots: Porous pots are semi-permeable containers that allow for the free passage of certain small materials through pores The loss of water from the pot is similar to the evaporative water loss that occurs in the leaves of plants If the porous pot is attached by an airtight seal to a tube, the water loss creates a negative pressure that draws more liquid

Miller and Urey

The theory that living cells arose from non-living matter is known as abiogenesis This process is theorised to have occurred over four key stages: There was non-living synthesis of simple organic molecules (from primordial inorganic molecules) These simple organic molecules became assembled into more complex polymers Certain polymers formed the capacity to self-replicate (enabling inheritance) These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts) Miller-Urey Experiment The non-living synthesis of simple organic molecules has been demonstrated by the Miller-Urey experiment Stanley Miller and Harold Urey recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes Water was boiled to vapour to reflect the high temperatures common to Earth's original conditions The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen) This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions) The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules

Thrombosis

Thrombosis is the formation of a clot within a blood vessel that forms part of the circulatory system Thrombosis occurs in arteries when the vessels are damaged as a result of the deposition of cholesterol (atherosclerosis) Atheromas (fat deposits) develop in the arteries and significantly reduce the diameter of the vessel (leading to hypertension) The high blood pressure damages the arterial wall, forming lesions known as atherosclerotic plaques If a plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow If the thrombus becomes dislodged it becomes an embolus and can cause blockage at another site Thrombosis in the coronary arteries leads to heart attacks, while thrombosis in the brain causes strokes

Turner Syndrome

Turner syndrome is a chromosomal condition that affects development in females. The most common feature of Turner syndrome is short stature, which becomes evident by about age 5. An early loss of ovarian function (ovarian hypofunction or premature ovarian failure) is also very common. A chromosomal disorder in which a female is born with only one X chromosome

Wilkins and Franklin

Used X-ray diffraction, by scattering particles using beams of X-ray Wilkins developed a method that allowed for DNA molecules to be ordered enough for a diffraction pattern Franklin developed a method that allowed for a high-res detector to pick up sharp images of diffraction From experiments, it was determined that DNA was a helical molecule, and that the turns of the helix were 3.4 nm apart =========================== The Rosalind Franklin Controversy With Watson and Crick The final construction of a correct DNA molecule owed heavily to the X-ray crystallography data generated by Franklin This data confirmed the arrangement of the DNA strands into a helical structure The data was shared without Franklin's knowledge or permission and contributed profoundly to the final design Hence, Franklin is now recognised as a key contributor to the elucidation of DNA structure

Hershey-Chase Experiment

Used a virus that infected cells of E.Coli Wanted to determine if genes were made of protein or DNA DNA contains Phosphorus, Proteins contain Sulfur Therefore prepared a strain of P-32 with DNA and S-35 with proteins Found that the virus bound to the surface of E. Coli, and injected its DNA into the bacterium This was seen in the high radioactivity from P-32 levels rising in bacteria Gave strong evidence that genes were composed of DNA rather than protein ================================ In the mid-twentieth century, scientists were still unsure as to whether DNA or protein was the genetic material of the cell It was known that some viruses consisted solely of DNA and a protein coat and could transfer their genetic material into hosts In 1952, Alfred Hershey and Martha Chase conducted a series of experiments to prove that DNA was the genetic material Viruses (T2 bacteriophage) were grown in one of two isotopic mediums in order to radioactively label a specific viral component Viruses grown in radioactive sulfur (35S) had radiolabelled proteins (sulfur is present in proteins but not DNA) Viruses grown in radioactive phosphorus (32P) had radiolabeled DNA (phosphorus is present in DNA but not proteins) The viruses were then allowed to infect a bacterium (E. coli) and then the virus and bacteria were separated via centrifugation The larger bacteria formed a solid pellet while the smaller viruses remained in the supernatant The bacterial pellet was found to be radioactive when infected by the 32P-viruses (DNA) but not the 35S-viruses (protein) This demonstrated that DNA, not protein, was the genetic material because DNA was transferred to the bacteria

A spirometer

Ventilation in humans changes in response to levels of physical activity, as the body's energy demands are increased ATP production (via cellular respiration) produces carbon dioxide as a waste product (and may consume oxygen aerobically) Changes in blood CO2 levels are detected by chemosensors in the walls of the arteries which send signals to the brainstem As exercise intensity increases, so does the demand for gas exchange, leading to an increase in levels of ventilation Exercise will influence ventilation in two main ways: Increase ventilation rate (a greater frequency of breaths allows for a more continuous exchange of gases) Increase tidal volume (increasing the volume of air taken in and out per breath allows for more air in the lungs to be exchanged) Trends in Tidal Volume and Breathing Frequency ventilation trends Measuring Ventilation Ventilation in humans can be monitored in a number of ways: Via simple observation (counting number of breaths per minute) Chest belt and pressure meter (recording the rise and fall of the chest) Spirometer (recording the volume of gas expelled per breath) Spirometry involves measuring the amount (volume) and / or speed (flow) at which air can be inhaled or exhaled A spirometer is a device that detects the changes in ventilation and presents the data on a digital display A more simplistic method involves breathing into a balloon and measuring the volume of air in a single breath The volume of air can be determined by submerging the balloon in water and measuring the volume displaced (1ml = 1cm3)