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AS Biology Mr Schofield UNIT 1 Chapter 1 Causes of Disease Causes of Disease… 1-Pathogens • What are pathogens? • How do they enter the body • How do they cause disease? What is a PATHOGEN? • A pathogen is an entity that causes disease – Bacteria – Virus’ – Fungi • The ability of that particular pathogen to cause a disease is known as its pathogenicity • Factors that effect pathogenicity include… – – – – Methods of attachment Toxin release Infectivity Invasiveness How do pathogens enter the body? • Bacteria and other micro-organisms can be transmitted usually in one of three ways. – Air – Water – Food • The BORNE trilogy!! • However they also enter through body openings and skin abrasions Air Borne • When an infected person breathes, coughs, or evan talks, the bacteria are passed into the atmosphere inside tiny droplets of water or mucus. • The pathogens are carried by air currents. • Sick Building Syndrome Water Borne • Water Borne bacterial infection results in Diarrhoea. • Diarrhoea effects over 1billion people a year and kills nearly 5 million (in a good year, i.e. one without a war or famine etc) • Famous example is Cholera, but the most common bacterial cause is E. coli… Food Borne • Salmonella food poisoning is caused by a highly motile gram negative bacteria. • S.typhimurium infects humans, poltry, pigs, cows and horses. It can also effect fish, especially those living in polluted water. • Many healthy animals are carriers, and the bacteria is found naturally in their faeces How do Pathogens cause disease? • When they get into a body area that is usually sterile… • Disease can result because of tissue damage or through tissue poisoning – Most bacteria are often found in our own “body flora” – Bacteria often reach sterile internal areas through small wounds and skin abrasions – E.g. Clostridium Tetani Tissue Damage • Bacteria attach to and penetrate cells. They may also break into blood and lymph vessels. • Pili and Fimbriaie allow bacteria to attach to membrane receptors • E.g. Neisseria Gonorrhoea – Attaches to manose receptors – Causes painful blocking and swelling or urethra and prostate in males, attacks ovaries in females Production of Toxins • Bacteria release toxins to break down and disable cells • There are two types of toxin – Exotoxins – Endotoxins Causes of disease… 2- Risk Factors: Lifestyle and Health • What is a biological risk? • The factors affecting the risk of cancer • The factors affecting the risk of Coronary Heart Disease (CHD) Risk factors and disease Chapter 2 Enzymes and the digestive system Enzymes and the Digestive system… 1Brief Anatomy and Physiology of the digestive system • What is the structure and function of the major parts of the digestive system? • How does the digestive system break down food both physically and chemically? The Oesophagus • Swallowed food is taken to the stomach via the oesophagus. • It is especially adapted for its purpose by having very thick muscular walls. – The outer cells are continuously rubbed away by friction (with the swallowed food), so the mucosa is folded. This also allows elastic expansion* . The epithelial layer also contains mucus glands for lubrication. * The Stomach • The stomach is a muscular bag that can swell out when full of food • The major roles of the stomach are – Temporary food storage – Mixing the stomach contents with gastric juices – A little digestion • Gastric juices (a mixture of HCl and the enzyme pepsin) are secreted from glands in the mucosa. Mucus is also secreted to protect the muscle tissue from the strong acid. The Small Intestine • The small intestine actually consists of three parts – The duodenum – The jejunum – The ileum • The duodenum is the upper part of the SI, the pancreas and gall bladder empty secretions into it. • Both the ileum and the duodenum have a folded mucosa with millions of finger like projections called Villi. Each villus has a very rich blood supply. Breakdown and digestion: an important distinction. • Food is physically and chemically BROKEN DOWN within the digestive system. This ensures that food molecules are small enough to be absorbed (digested) by the small intestine. • The large intestine does not absorb food molecules. It reabsorbs much of the water released into the digestive system during breakdown. Enzymes and the digestive system… 2Carbohydrates: Monosaccharides • What is the structure of a monosaccharide? • How would you carry out the Benedict's test for reducing and non reducing sugars? α-glucose Reducing or non-reducing? • All monosaccharides are reducing sugars!! • Some disaccharides are also reducing sugars • A reducing sugar is one which has a “free ketone or aldehyde group”. It is able to reduce the Cu2+ ions in CuSO4 to Cu+ Disaccharides • Disaccharides are formed when two monosaccharide units are combined together in a condensation reaction • Condensation reactions produce water. The two original units are joined together by a glycosidic bond. Name Reducing / Monosaccharide Monosaccharide Non-reducing Maltose Glucose Glucose Reducing Lactose Glucose Galactose Reducing Sucrose Glucose Fructose Non-Reducing Enzymes and the digestive system… 3Carbohydrates: Polysaccharides and carbohydrate digestion • How do α-glucose molecules link together to form starch? • What is the test for starch? • How is starch broken down by the digestive system? • How are sugars digested? • Lactose intolerance… Formation • Polysaccharides are formed by condensation reactions. Water is given off. • The monomers in a polysaccharide are linked together by a GLYCOSIDIC bond. Make sure you can draw the structure of a disaccharide, clearly showing the glycosidic bond! Starch • Starch (amylose) is a polysaccharide found in plants. It is the most common carbohydrate in our diet… • The enzyme amylase catalyses the breakdown of starch in the mouth (salivary amylase) and the small intestine (pancreatic amylase). Make sure you remember the test for starch… “It turns iodine blue/black” Carbohydrate enzymes Enzyme Substrate Location Salivary amylase Starch Mouth Pancreatic amylase Starch Small intestine Sucrase Sucrose Small intestine Maltase maltose Small intestine Lactase Lactose Small intestine Fructase Fructose Small intestine Lactose intolerance The heart warming tale of the little boy who had 8 teeth out in one sitting because he didn’t have enough lactase in his small intestine… Enzymes and the digestive system… 4Amino Acids • The structure of an amino acid • How are amino acids linked to form polypeptides? H H N H C O C OH R Generic formula for any amino acid Amino Acids • The base unit of proteins. • 20 naturally occurring molecules all have the same basic structure but a different R group • Of these 20, 9 are considered to be essential. We cannot synthesise them in our diet. • Amino acids form polypeptides as a result of condensation reactions. Protein Structure • All proteins are made from the “pool” of 20 amino acids. • Different proteins have different shapes because they are made from different combinations of amino acid. • There are four “stages” of protein structure: Primary, Secondary, Tertiary and Quarternary. IMPORTANT! Each protein has a precise and unique structure that is determined by the amino acid sequence. All molecules of a particular protein, such as amylase, have the same amino acid sequence. So the amino acid chain will always fold in the same way. Therefore the protein molecule will always have the same three dimensional shape. Enzymes and the digestive system…5Secondary and tertiary Structure • How are polypeptides arranged to form the secondary structure and then the tertiary structure of proteins? A polypeptide chain… • Despite their individual chemical differences, amino acids can be put into four different "families" depending on whether their R-groups are: – – – – acidic basic polar - not charged nonpolar The alpha helix Hydrogen Bond Tertiary Structure • Similar to 20 structure occurs when neighbouring residues in the same chain form bonds with one another. • This time Disulphide bonds/bridges. • Disulphide bonds form between Cysteine residues. A little diagram… A D E F G A T H Y V Z C s s C B T P K A N M Denaturisation • Each Protein functions between a specific minimum and maximum temperature • If the temperature exceeds the maximum limit the intermolecular forces of attraction which hold the molecule together break down. • As a result the amino acid chain unwinds, the molecule looses shape and therefore cannot function Another little diagram… A protein A denatured protein Quaternary Structure • Occurs in proteins made up from more than one polypeptide chain. • Good examples include Insulin and Haemoglobin. • Bonding between the different chains is the same as in tertiary proteins i.e. disulphide bonds, H bonds and other intermolecular forces Further 40 structure adventures • Quaternary structures have two basic shapes: Fibrous or Globular. • Globular proteins such as haemoglobin curl up into ball like structures. They are very important in the physiology of an organism. • Fibrous proteins such a collagen form long strands/chains. They are insoluble and are important in structures such as joints, skin and blood vessels Enzymes and the digestive system… 6Enzymes • How do enzymes speed up a chemical reaction? • How does the structure of an enzyme relate to its function? • The lock and key mechanism • The induced fit model Enzymes • Enzymes are globular proteins. • Enzymes are biological catalysts, they alter the rate of a chemical reaction within an organism without undergoing a permanent change. IMPORTANT Enzymes do not make a reaction happen and they do not carry out a reaction. Rather, they provide a surface for the reaction to take place over, therefore increasing the rate. Enzyme structure • Enzymes have a very specific 3d shape. • Shaping of an enzyme is the direct consequence of a deliberately arranged amino acid sequence during primary structure. (fig 2, pg 31). • The functional area of an enzyme is called the active site. The lock and key mechanism • Learn the diagram, make sure you can label it and explain it! The induced fit model • A progression of the lock and key theory. • It currently provides a better explanation for enzyme activity, such as how competitive inhibition can occur Enzymes and the digestive system… 7Factors effecting enzyme action • • • • • Measuring an enzymatic reaction Temperature pH Substrate concentration Inhibition. Chapter 3 Cells and the movement in and out of them Cells and the movement in and out of them… 1 – Investigating the structure of cells. • What is magnification and resolution? • What is cell fractionation? • How does ultracentrifugation work? Magnification • Cells are very small. Very small in fact. So so small they are probably many times smaller than the smallest thing you can imagine. • In order to see and study them we must use a microscope (obvious!), and YOU must understand the principles of magnification. Magnification again • Cell dimensions are expressed in micrometres (µm). Most cells range between 10-150µm. • Micrometres are part of the Système International (SI) derived units of measure. • The SI units of length are… Unit Symbol Relative size Equivalent in metres (using maths) Kilometre Km 1000 metres 103 Metre m 1000 millimetres 1 millimetre mm 1000 micrometres 10-3 micrometre µm 1000 nanometres 10-6 nanometres nm 1000 picometres (pm) 10-9 Resolution • The resolution or resolving power of a microscope is the minimum distance apart that two objects can be in order for them to appear as separate items. Cell Fractionation • Cell fractionation is the technique used to break up a cell so that a scientist may access the organelles inside it. • There are two stages to fractionation – Homogenation – Ultracentrifugation Cells and movement in and out of them… 2- Microscopy: Light v Electron • Microscopy • How do electron microscopes (EM) work? • What are the differences between a Transmission EM and a Scanning EM? • What are the limitations of electron microscopy? The Light Microscope • Light microscopes use convex lenses and a beam of light which can be natural or artificial. • However, because of the long wavelength of light, a light microscope will only distinguish between two object 0.2µm apart Why use electrons? • A “beam” of electrons has a much shorter wavelength. It is able to distinguish between objects only 0.1nm apart. • There are two types of EM; Transition or Scanning Cells and the movement in and out of them… 3 – The Eukaryotic Cell: Structure and function of the epithelial cell • Structure and function of the nucleus • Structure and function of the mitochondria • Structure and function of the rough endoplasmic reticulum • Structure and function of the Golgi • Structure and function of the microvilli • What does the ultrastructure of a cell tell us about its function? The Epithelial Cell • Like all animal (and plant) epithelial cells are eukaryotic cells. • A eukaryotic cell is defined as one which has a distinct membrane bound nucleus • Epithelial cells secrete and absorb material. They are found in the mouth, digestive system, reproductive system and the respiratory system. Organelles • Eukaryotic cells contain membrane bound structures (in the cytoplasm). These structures are called organelles • Organelles carry out different roles within the cell, e.g. protein synthesis • Most eukaryotic cells contain the same organelles yet some cells will contain more of certain organelles depending on their role Cells and movement in and out of them… 4- Lipids and the Fluid Mosaic Model • • • • What is a lipid? Fatty acids and Triglycerides… What is a phospholipid? What is the role of lipids in biology? What is the fluid mosaic model • How can we identify the presence of a lipid? Lipids • In the human body lipids take 3 different forms: fatty tissue, phospholipids (within the cell membrane) and as steriods… • Lipids have many roles within the human body, mainly within membranes but also… – An energy source – Waterproofing – Insulation – Protection Triglycerides • Triglycerides are formed by a condensation reaction between fatty acids and an alcohol molecule called glycerol. Three fatty acids bind to one molecule of glycerol. • Fatty acids are linked to glycerol by ester bonds Phospholipids • Phospholipids are very similar in structure to triglycerides except that one fatty acid has been replaced by a phosphate group. The Fluid Mosaic Model • First proposed in 1972… • “A dynamic structure in which much of the protein floats about, although some is anchored to organelles within the cell. Lipid also moves about”. • This model has been neither conclusively proven or disproven, but it is the best model yet to explain the known physical and chemical properties of the cell membrane. Cells and movement in and out of them… 5- Diffusion • What is diffusion and how does it occur? • What affects the rate of diffusion? • How does facillitated diffusion differ from diffusion What is diffusion • Diffusion is the net movement of molecules or ions from an area of high concentration to an area of low concentration. Make sure you understand this point!!... Diffusion is a passive process. It does not require ATP (energy) in order for it to occur. However, the particles need to have energy in-order for them to move about (their own Kinetic energy). The rate of diffusion • The factors that effect diffusion are… – Concentration gradient – The surface area – Thickness of the exchange surface • Diffusion can be described as Surface area x Concentration Gradient Length of diffusion pathway Diffusion and the epithelial cell • The properties of the epithelial cell and squemous epithelia make them ideal for the role at exchange surfaces… – Large SA – Short diffusion pathway – Rich blood supply – Moist environment Facilitated diffusion • Facilitated diffusion occurs through protein channels at specific points along the plasma membrane. • Facilitated diffusion is an entirely passive process. The vast majority of diffusion in human biology through the plasma membrane occurs this way… Cells and movement in and out of them… 6- Osmosis • What is osmosis? • What is water potential and how is it applied to pure water? • How does water potential affect osmosis? A definition… • Osmosis is… “The passage of water from a region of high water potential to a region of lower water potential through a semi (partially) permeable membrane” Another definition… • Water potential… “The ability of water molecules to move” Putting it into practise The water potential (ψ) of pure water at atmospheric pressure is zero. Water molecules in solution move around more slowly than those in pure water “(bonding folks!!)”. Since these molecules cannot move around as freely in solution the water potential is negative. Solutions always have a water potential that is less than zero; i.e. a negative water potential. • Which way will the water move? • Water molecules move to the region of lowest water potential Factors effecting water potential… Solute potential ψs • The concentration of solutes inside the cell is called the solute potential. It is always a negative value because solutes reduce the ability of water to move freely Pressure potential ψp • The cell membrane (or wall) exerts a force on the cell contents, in effect squeezing the contents of the cell and trying to force water out. It is usually a positive value Water potential of a cell (ψ) = Solute potential (ψs) + Pressure potential (ψp) Cells and movement in and out of them… 7- Active transport / cotransport • What is active transport? • What is co-transport? • How are the products of carbohydrate breakdown absorbed in the small intestine? Active Transport • “the movement of molecules or ions into or out of a cell from a region of LOWER concentration to a region of HIGHER concentration using energy and carrier molecules” Against the gradient • The cytoplasm of a cell usually holds reserves of molecules needed for metabolism. The reserves of useful molecules and ions do not escape through the plasma membrane. • However, when more of these useful substances are available for uptake into the cell, they will be readily absorbed by active transport. The role of ATP • ATP is energy! • Think of ATP as being like money. It is often referred to as the energy currency. • ATP binds to a receptor found inside the carrier protein on the cell membrane • ATP breaks down into ADP and an inorganic phosphate molecule. This breakdown “releases” energy and results in the channel protein opening… Co-transport • A combination of active transport and facilitated diffusion • TEXTBOOK. – Pg 64: Make sure you understand this diagram and the sequential explination. Symport Protein • Symport proteins are carrier proteins located intrinsically within plasma membranes… • Symport proteins often transport two different substances in opposite directions; in and out of the cell. They only work when both substances are present. Protein structure folks… The binding of a molecule to a protein will result in the protein changing its shape slightly, either hindering or helping another molecule to bind to it Cells and movement in and out of them… 8- Cholera • What causes cholera and what are the symptoms? Quick revision Prokaryotic cells. • Cholera is a bacterial disease, caused by the bacteria; Vibrio cholerae. • Bacteria are prokaryotic cells. How do they differ from eukaryotic cells? What is Cholera • Cholera is a water born bacterial disease which kills an estimated 120000 people each year. • The major symptom of cholera is extreme diarrhoea. • The majority of cholera cases occur on the African continent. • Why may 120000 be a very low estimate? How does cholera cause disease? • The flagellum is used in a corkscrew fashion to anchor the bacteria to the cell membrane of the epithelial intestinal wall • The toxin produced by the bacteria binds to receptors on the plasma membrane (blue bit) and causes ion channels within the membrane to open (red bit). • Chloride ions flood into the lumen of the small intestine, lowering its water potential The diarrhoea part • The increased Cl- concentration within the GI lumen reduces its water potential. It is HYPERTONIC to the inside of the cells. • Water moves from the cells into the lumen. • A concentration gradient is setup throughout the surrounding tissues. HIM John Snow Not him Cholera outbreak in London 1854 • John Snow investigated Cholera in Soho, London in 1854 • He collected evidence to show where cholera victims lived and where they got their water • 73 of 83 victims lived closer to Broad Street pump than any other pump • 8 of remaining 10 had drunk water from Broad Street pump • Snow removed handle of Broad Street pump (to disable it) • The epidemic then ended • John Snow collected data and presented his findings • His investigations confirmed his hypothesis that cholera was spread by contaminated water • He persuaded people to accept his findings in order to improve the health of many people • 30 years later Robert Koch finally isolated cholera bacteria Cells and movement in and out of them… 9- ORT/S • Oral Rehydration Therapy… • Oral Rehydration solutions… ORT • Oral Rehydration Therapy is needed to replace the fluids and solutes lost from the body during diarrhoea. • ORT using specialised solutions is a more effective method of rehydration than water alone. • ORT makes use of Symport proteins and active transport mechanisms within the SI ORS uses co-transport Oral rehydration solution (ORS) • ORS is simple and cheap • It is a solution of sugars and salts taken orally • It is used as a treatment for diarrhoeal diseases e.g. cholera • It’s saved 50 million lives in 25 years • Preferable to intravenous rehydration which is difficult to administer and could cause fluid overload and death • New ORS formulations are being trialled which are more effective • Added zinc reduces severity and duration of diarrhoea and has a protective function Making a better oral rehydration solution • A better ORS may provide nutrients that developing child needs • ORS based on rice-flour help children overcome malnutrition (high in starch) • At high concentrations rice-flour ORS too thick • Scientists can measure viscosity using a viscometer • Viscosity is measured in centipose (cp) • Below 1000 cp a solution flows like water • Between 10 000 and 30 000 cp soup-like flow • Above 35 000 cp will not flow out of a cup Viscosity • In everyday terms (and for fluids only), viscosity is "thickness." • Thus, water is "thin," having a lower viscosity, while honey is "thick" having a higher viscosity. • Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. An experiment to investigate the effect of different concentrations of amylase in reducing the viscosity of flour solutions • Make up amylase solutions – 0%. 20%. 40%. 50%. 60%. 70%. 80%. 100% • Place range of amylase solutions into water bath at 20oc • Add 5ml of amylase solution to 10ml flour solution: water bath 5 min • Add suitable amount of this solution into viscometer (2/3 ml) • Measure the viscosity of the rice-flour using viscometer • Calculate the mean viscosity for each amylase concentration • Repeat for each concentration of amylase. Questions on the experiment • What was the independent variable? • What was the dependent variable? • List the other variables that might influence the results. Describe how these confounding variables should be kept constant. • Suggest a suitable control • How can you make the results more reliable? • What affects the precision of the results? • What should be done with any anomalous results? Chapter 4 Lungs and Lung Disease Chapter 5 The heart and heart disease The Cardiac Cycle. Systole: • Systole is the term given to the contraction of cardiac muscle. • Atrial systole occurs when the atria contract and force blood into the ventricles. • Ventricular systole occurs when the ventricles contract and force blood out of the heart through the arteries Cardiac Cycle • Diastole • Diastole is the term given to cardiac muscle which is relaxed • During ventricular diastole the ventricles are in a relaxed state and fill with blood. Chapter 6 Immunity Immunity… 1- A Brief look at bacterial disease • The ability of a bacteria to cause disease is known as it’s pathogenicity • Factors that effect pathogenicity include… – Methods of attatchment – Toxin release – Infectivity – Invasiveness When does a colony of bacteria cause disease? • When bacteria get into a body area that is usually sterile • Most bacteria are often found in our own “body flora” • Bacteria often reach sterile internal areas through small wounds and skin abrasions – E.g. Clostridium Tetani Invasion and Colonisation • Bacteria attach to and penetrate cells. They may also break into blood and lymph vessils. • Pili and Fimbriaie allow bacteria to attatch to membrane receptors – E.g. Neisseria Gonorrhoea – Attaches to manose receptors – Causes painthful blocking and swelling or urethra and prostate in males, attacks overies in females Release of Toxins • Bacteria release toxins to break down and disable cells • There are two types of toxin – Exotoxins – Endotoxins Unit 2 The variety of Living Organisms Chapter 7 Variation Chapter 8 DNA and Meiosis DNA and Meiosis… 1- DNA • The structure of DNA… • The function of DNA and the triplet code… The Double Helix • DNA is a polynucleotide molecule comprised of repeating units of Phosphate, Deoxyribose sugar and an organic base. • The polynucleotide is arranged into a double helix structure… • The Double Helix was elucidated by James Watson and Francis Crick at Cambridge University in 1953. They based their hypothesis on x ray evidence produced by the pioneering female scientist Rosalind Franklin. Watson and Crick won Nobel prizes for their work. The Nucleotide… • The individual nucleotide is made up… Phosphate Base Sugar • A Phosphate group. • A pentose sugar: Deoxyribose. • An organic base (Adenine, Cytosine, Guanine and Thymine). Base Pairing • Textbook: Chapter 8, pg 131. The Triplet Code • DNA base sequences code for amino acids, which can be assembled to manufacture a protein. • A sequence of three bases codes for one specific amino acid. • Pg 136-137 DNA and Meiosis… 2- Genes • What is a gene? • How are genes arranged on DNA? • Alleles… A Gene • A sequence of DNA which codes (usually) for a specific protein or polypeptide. • An individual gene may have more than one form, these will differ very slightly from the others in their nucleotide sequence. • The different forms of a gene are called alleles. DNA and Meiosis… 3- Chromosomes • What is a chromosome? • Homologous chromosomes… Chapter 9 Genetic Diversity Genetic Diversity… 1- Diversity • Why are organisms different from one another? • What factors influence genetic diversity? • Selective breeding? Key principles… • The greater the number of different alleles of a gene within a species the greater the genetic diversity of the species… • The greater the diversity the wider the total range of characteristics across a species… • A species has a greater probability of adapting to a change in it’s environment if it has a wide spread of characteristics… Environmental Change • 5 events that may result in an environmental change… 1. 2. 3. 4. 5. Volcanic Eruption Flooding Drought Disease Hunting Genetic Bottlenecks • The Cheetah population shows very little genetic diversity. It is thought to have undergone several genetic bottlenecks. Describe a genetic bottleneck and explain how it may result in a population with very similar physical characteristics? • 6 Marks Answer… 1. 2. 3. 4. 5. 6. Chance event significantly reduces number within a population Surviving individuals have fewer alleles Less diversity Recovering population can only contain these alleles Less variety in genotypes of “new” population Less variety in phenotypes / physical characteristics A model answer… “A genetic bottleneck occurs when a chance event, such as major flooding, significantly reduces the number of organisms within the population of a particular species. Surviving members of the population have a reduced number of alleles amongst them and are therefore less genetically diverse than before. Subsequent generations of organisms from within this population can only contain the surviving alleles; consequently there will be less variety in the genotypes of these organisms and therefore less variety in the overall phenotype exhibited by members of this population” Artificial Selection: Cultivating Characteristics for our benefit… Wheat • • • Wheat grows in dry sunny conditions, producing grains on the end of a flowering stem called a rachis. Within each grain is an embryonic plant with a “food source”. Wheat grains are rich in carbohydrate and protein Modern wheat differs from ancestral wild wheat in three ways: 1. Strength of rachis 2. Size of grain 3. Chromosome number Selective Cultivation of wheat • Wheat growers use very intensive methods to produce high yields of wheat grain. They selectively cultivate wheat using four characteristics… 1. 2. 3. 4. Short stems Standing Power Resistance to shedding Resistance to fungi Suggest how each these four characteristics increase the yield of wheat… Why select for… Short stems… • • Less energy is used by the plant for stalk growth, making more available to the grain. A larger grain contains a greater amount of carbohydrate and protein Why select for… Standing Power… • Weak stalks are prone to collapse under the weight of the grain, especially during bad weather. • More grain will be collected from stalks that remain upright, allowing more to be sold and a greater profit to be made. Why select for… Resistance to shedding… • Grain is very lightweight and easily shed by strong winds and animal activity. • Less grain is lost before and during the harvest. Why select for… Resistance to fungi… • Wheat leaves are prone to fungal conditions such as mildew. • Maintaining healthy leaves promotes more efficient photosynthesis and healthy plant growth. Exam Questions… b) EXPLAIN why the DIVERSITY of animals is HIGHER natural woodland THAN in conifer plantations. • More light reaches the ground therefore more plants have the opportunity for photosynthesis. • There are a greater number of producers, increasing the size of the food web. • More plants provide more habitats, such as nesting sites for animals in c) …EXPLAIN how a programme of selection MIGHT affect the VARIETY OF ALLELES in a population. • Selection reduces the variety of alleles because only certain characteristics are allowed to continue. • Non selected alleles will reduce in frequency, selected alleles will increase. Think bottleneck ! Cattle • What products do we get from cattle? Chapter 10 The variety of life The Variety of Life… 1- Haemoglobin • Haemoglobin structure… • Loading and unloading oxygen… • Oxygen dissociation curves… Haemoglobin Human blood cell haemoglobin consists of: • 4 polypeptide chains or globins (2 alpha and 2 beta). • 4 iron-containing molecules (haem), one for each chain. • Each haem group contains one iron (Fe) atom in the middle of the molecule • Each iron atom is joined to 1 end of their respective globin – • Each iron atom bonds with one oxygen molecule • Hence, one haemoglobin is able to carry a maximum of 4 oxygen molecules Haemoglobin that combines with an oxygen molecule is called oxyhaemoglobin. Normal haemoglobin (with no oxygen molecule attached) is actually purplish red in colour. It only turns bright red (the colour that we see when we bleed) when it combines with an oxygen molecule. The variety of life… 2Oxyhaemoglobin Dissociation Curves • What are oxyhaemoglobin dissociation curves • What is the Bohr effect • Using an oxyhaemoglobin dissociation curve Approx concentration of O2 in alveoli Approx concentration of O2 in normally respiring tissue 1kNm-2 = 1kPa A Definition • A graph showing the amount of oxygen carried by haemoglobin in the blood plotted against the concentration of oxygen present. Important points to remember… • The partial pressure of oxygen in a healthy lung is approximately 13kPa. • At this concentration Hb is approximately 95% saturated. • The partial pressure of oxygen in a normally respiring tissue is approximately 5kPa The Bohr shift • The effect of increasing CO2 concentration on an Oxyhaemoglobin dissociation curve. • The greater the amount of CO2 the further the curve shifts to the right • In the presence of CO2, Hb gives up a greater amount of the oxygen it is carrying. Percentage saturation of Hb has decreased. It has given up more oxygen