OCR AS Biology F212

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  • Created by: J.H
  • Created on: 25-05-13 11:09

Biological Molecules- Water 1

  • Thermal Stability -The hydrogen bonds in liquid water restrict the movement of water molecules, so a relatively large amount of energy is needed to increase the temperature of water. This keeps the temperature of large bodies of water, such as lakes and oceans, stable even when the temperature changes dramatically. The evaporation of water requires a relatively large amount of energy. Which means evaporation removes the heat from the surface. So heat energy is used in evaporation. Importance- Land based organisms use evaporation as a cooling mechanisms e.g panting and sweating.                                                                              
  • Hydrogen Bonds – Cohesion  - Water molecules stick to each other creating surface tension creates surface tension; some small organisms can move across the surface of the water.

  • Solvent – Because water is polar, the positive end of a water molecule will be attracted to the negative ion, and the negative end of the water molecule will be attracted to the positive ion.This means that ions will get totally surounded by water molecules - in other words, they will dissolve. So waters polarity makes it useful as a solvent for other polar molecules. Importance- Metabolic processes in all organisms rely on chemicals being able to react together in solution.  

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Biological Molecules- Water 2

Transport Medium – Water remains liquid over a large temperature range and can act as a solvent for many chemicals.This makes it an ideal transport medium

Involved in Metabolic Reactions – Water  takes part as a reactant in some chemical processes.

Water Freezing- Water freezes, forming ice on the surface. Water beneath the surface becomes insulated and less likely to freeze.

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Proteins

Primary Structure – The sequence of amino acids in the polypeptide chain.

Secondary Structure – Hydrogen bonds form between the amino acids in the chain.Causing it to coil to form a alpha helix or fold into a beta pleated sheet.

Tertiary Structure – Hydrogen Bonds, Ionic Bonds, Disulfide Bridges, Hydrophobic Interactions, (see book).

Quaternary Structure – The way these polypeptide chains are assembled together. E.g. haemoglobin is made up of four polypeptide chains, bonded together.

 

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Proteins 2

Haemoglobin

  • Globular Protein
  • Chain of amino acids
  • Alpha helical secondary structure
  • Hydrogen, ionic, disulfide, hydrophobic bonds in tertiary structure
  • 4 polypeptide chains (2 alpha, 2 beta)
  • 1 haem group per polypeptide
  • Fe2+ ion in haem

Collagen

  • Fibrous Protein
  • High proportion of glycine
  • 3 polypeptide chains
  • Chains form a tight coil held by hydrogen bonds
  • Ends of parallel molecules are staggered
  • Covalent bonds form between adjacent molecules
  • Prevents lines of weakness
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Carbohydrates

Carbohydrates

Alpha Glucose – OH is below carbon 1

Beta Glucose – OH is above carbon 1

Amylose

  • Energy Store (Plants)
  • Polysaccharide                 oAlpha Glucose
  • 1,4 glycosidic links
  • Non-branched                   o Compact

Amylopectin

  • Energy Store (Plants)
  • Polysaccharide
  • Alpha Glucose
  • 1,6 glycosidic links      o Branched
  • Insoluble to not affect water potential   o Easily hydrolysed
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Carbohydrates part 2

Cellulose

  • Plant Cell Walls
  • Beta Glucose
  • 1,4 glycosidic links
  • Each glucose molecule is rotated 180 to its neighbour
  • Straight chains
  • Adjacent chains held by hydrogen bonds

Glycogen

  • Energy Store (Animals)
  • Polysaccharide
  • Alpha Glucose
  • 1,4 glycosidic links and 1,6 glycosidic links
  • Branched and Compact
  • Insoluble to not affect water potential
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Lipids

Lipids

Triglyceride

  • 1 Glycerol Molecule                                                    o 3 Fatty Acids

  • Ester Bonds

Phospholipid

  • 1 Glycerol Molecule                                                     o 2 Fatty Acids

  • 1 Phosphate

Cholesterol

  • 4 carbon rings

  • Hydrophobic

  • Hormones & Vitamin D                                                   o Cause gallstones and atherosclerosis

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Experiments

Protein

  • Biuret A and Biuret B
  • Blue to Lilac

Reducing Sugar

  • Benedicts
  • Warm
  • Blue to Brick Red

Non-Reducing Sugar

  • Hcl
  • NaOH
  • Benedicts
  • Warm
  • Blue to Brick Red
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Experiments 2

Starch

  • Iodine
  • Brown to Black

Lipids

  • Alcohol
  • Water
  • White Emulsion

Colourmeter see notes.  

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Enzymes

Enzymes

  • Globular proteins.
  • Soluble in water.
  • Specific 3D shape.
  • Catalyse chemical reactions inside and outside cells.

Enzymes are Specific to the Substrate they act on

  • Tertiary structure form the active site.

Lock and Key Theory

  • Active site has a specific shape that is complementary to the substrate.

Induced Fit Theory

  • Enzyme changes shape slightly as the substrate binds with the active site.
  • Makes active site fit more closely around the substrate.

Change in shape put stress on bonds in substrate so reaction occurs more easily

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Factors Affecting Enzyme Controlled Reactions

Enzymes Concentration – Increases rate of reaction.

  • More active sites available.
  • More chance of substrate colliding with active site.
  • More product produced.

Temperature – Molecules move about more at high temperatures.

  • More frequent collisions
  • More enzyme substrate complexes formed
  • High temperature denature enzymes
  • Molecules vibrate more breaking the tertiary bonds of the enzyme.

pH – Change from the optimum reduces rate of reaction.

  • H+ ions interact with R groups of amino acids.
  • Affects bonding of active site.
  • Eventually denatures the enzyme.

 

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Factors Affecting Enzyme Controlled Reactions part

Substrate Concentration – Increases rate of reaction.

  • Greater chance of substrate binding with the active site.
  • More product formed as more substrate is converted.

 Inhibitors

 Competitive

  • Competes with the substrate for the active site.
  • Similar shape to the substrate so it can fit in the active site.
  • Blocks the active site.
  • Prevents substrate binding.

Non-Competitive

  • Binds to site other than the active site.
  • Distorts the shape of the enzyme and active site.
  • Increasing substrate concentration has no effect.

Both types of inhibition are reversible.

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Prosthetic Groups and Co-enzymes

Co-enzymes – Small organic non-protein molecules. The role of co-enzymes is often to carry chemical groups between enzymes so they link together enzyme-controlled reactions that need to take place in sequence.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

  • Bind for a short time to the active site.

A co-enzyme that is a permanent part of an enzyme is a prosthetic group. It is vital to its function and contributes to its final 3D shape.

Ion Cofactors – ions bind to the enzyme or substrate.

  • makes the enzyme substrate complex form more easily because it affects the charge distribution and, sometimes changes the shape of the enzyme substrate complex.
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Poisons and Drugs

Poisons

  • either inhibit or over-activate enzymes

Potassium Cyanide – Inhibits cell respiration.

  • Non-competitive inhibitor for cytochrome oxidase found in mitochondria.
  • Inhibition decreases the use of oxygen so ATP cannot be made.

Drugs

Antibiotics - Interfere with a number of enzyme controlled reactions in bacterial cells.

Penicillin – Inhibits a bacterial enzyme that forms cross links when making bacterial cell walls.

  • Prevents new cells being made.
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DNA and RNA

DNA

  • Phosphate Group.
  • Deoxyribose Sugar.
  • Nitrogenous Bases – Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
  • Polynucleotide.
  • Polynucleotide Double Strand

RNA

  • Phosphate Group.
  • Ribose Sugar.
  • Nitrogenous Bases – Adenine (A), Uracil (U), Cytosine (C), Guanine (G).
  • Polynucleotide.
  • Polynucleotide Single Strand.
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DNA Replication

  • Hydrogen bonds break between the two polynucleotide DNA strands.
  • Double helix unwinds.
  • Free nucleotides bind to complementary bases.
  • A to T, C to G.
  • The nucleotides on the new strand are joined together by the enzyme DNA polymerase.
  • Hydrogen bonds reform.
  • Semi conservative – 1 new strand, 1 original strand.

Gene – a sequence of DNA nucleotides that code for a protein.

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Protein Synthesis (see notes for more info)

  • Transcription.
  • DNA unwinds.
  • Hydrogen bonds break.
  • Reveals a particular sequence of bases.
  • RNA nucleotides align with bases.
  • mRNA is formed.
  • mRNA leaves nucleus through nuclear pore.
  • Translation.
  • mRNA attaches to ribosome.
  • tRNA brings amino acid to ribosome.
  • each tRNA is attached to a specific amino acid.
  • Anti-codons attach to codons.
  • Peptide bonds form between adjacent amino acids.
  • Forming a polypeptide.
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Diet

Balanced Diet – consists of all nutrients required for health in appropriate proportions.

 

Obesity – A form of malnutrition.

  • Caused by consuming too much energy.
  • Excess energy is deposited as fat in the adipose tissue.
  • Excess body fat impairs health.
  • BMI> 30

Diet and CHD – Deposition of fatty substances in the walls of the coronary arteries (Atherosclerosis). This increases the pressure and the heart becomes deficient in oxygen.

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Diet part 2

Salt – Affect water potential of blood (more water is held in blood increasing pressure).

  • Hypertension damages inner lining of artery.

Cholesterol – Found in food and produced by the liver.

  • Needs to be transported in the blood as its insoluble.
  • Combines with proteins to make lipoproteins.

High Density Lipoproteins

  • Good
  • Combination of unsaturated fat, cholesterol and proteins
  • Carry cholesterol from tissues back to liver
  • Liver converts it to bile or breaks it down
  • Lower fatty deposition

Low Density Lipoproteins

  • Bad
  • Combination of saturated fats, cholesterol and proteins
  • Carries cholesterol from liver to tissue
  • High concentration causes fat deposition on artery walls.
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Food Production

Food Production

  • Plants use photosynthesis.
  • Plants convert light energy into glucose then starch.
  • They absorb minerals from the soil and make other biological molecules.
  • Herbivores make use of these molecules.
  • Humans are omnivores – gain nutrition directly from eating plants and indirectly by eating animals.

Fertilisers & Pesticides

Fertilisers - Replace minerals in soil – minerals have been used by previous crops.

  • Increase growth rate and size of crops. Increase yield.

Pesticides – Treat animals and plants to kill pests.

  • Increase crop yield.
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Food Spoilage

  • Caused by microbes.
  • Microbes use external digestion – secrete enzymes onto food and absorb the brokendown products.
  • Some bacteria cause poisoning.

Preventing Food Spoilage

  • Cooking – heat denatures enzymes and other proteins and kills the micro-organisms.
  • Pasteurising – heating (72 degrees centigrade for 15 seconds) and rapidly cooling( to 4 degrees centigrade) kills harmful micro-organisms.
  • Drying, salting and coating in sugar – dehydrates and kill micro-organisms as water leaves by osmosis.
  • Smoking – forms a hardened, dry outer surface and smoke contain antibacterial chemicals.
  • Pickling – acid pH kills micro-organisms by denaturing enzymes and other proteins.
  • Irradiation – ionising radiation kills micro-organisms by disrupting their DNA structure.
  • Cooling and Freezing – ****** enzyme activity so their metabolism, growth and reproduction is very slow.
  • Canning – food is heated and sealed in air tight containers
  • Vacuum Wrapping – microbes cannot respire aerobically.
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Using Micro-organisms

Advantages

  • Production of protein can be many times faster than animal or plant protein.
  • Production can be increased or decreased according to demand.
  • There are no animal welfare issues
  • A good source of protein for vegetarians
  • The protein contains no animal fat or cholesterol.

Disadvantages

  • Many people do not want to eat fungal protein or food that has been grown on waste.
  • The microbes are grown in a huge fermenter and need to be isolated from the material that they grow on.
  • The protein needs to be purified to ensure it is uncontaminated.
  • The conditions needed for the useful micro-organisms to grow are also ideal for pathogenic organisms.
  • The proteins do not have the taste or texture of traditional protein sources.
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Health and Disease

 

Health – a state of physical, mental and social well-being not just the absence of disease.

 

Disease – a departure from good health caused by a malfunction of the mind or body.

 

Parasite – an organism that lives in or on another living thing, causing harm to its host.

 

Pathogen – an organism that causes disease.

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Infectious Disease

Malaria- Plasmodium          o Female Anopheles Mosquito feeds on blood.

  • Plasmodium infects the liver and red blood cells, and disrupts the blood supply to vital organs.
  • Infection limited to where anopheles mosquito can live.       o Global warming may affect spread.

Tuberculosis (TB) -Mycobacterium tuberculosis.                                                  o Found in the lungs.

  • Transmitted by droplet infection.   o Increased risk due to overcrowding, poor ventilation, poor health and diet, homelessness.
  • Some strain are resistant to antibiotics.

AIDS- Human Immunodeficiency Virus.

  • Contracted by sharing needles, blood transfusions, unprotected sex.
  • Attacks T helper cells in the immune system.
  • Develops into AIDS and the body can no longer resist disease.
  • The person will die of something other than AIDS, e.g. common cold.
  • Worldwide pandemic.
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Primary Defences

Skin – Outer epidermis is made of keratinocytes.

  • As they mature the cytoplasm is replaced by the protein, keratin.

 

Mucus Membranes – epithelial layer contains goblet cells that work with ciliated cells.

  • Found in genital areas, a.nus, ears, and nose.

Eyes are protected by antibodies in the clear fluid.

Ear canal is lined with wax.

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Secondary Defences

Macrophages

  • Made in bone marrow.                                                 oTravel as monocytes in the blood.
  • Settle in body organs especially in lymph nodes.        o Change from monocytes to macrophages here.

Neutrophils

  • Made in bone marrow.                                                 o Have multi-lobed nucleus.
  • Travel in blood.
  • Squeezed into tissue fluid and released in large numbers if infected.

How Phagocytes Work

  • Phagocyte attaches to the pathogen.
  • Receptor on the phagocyte recognises the antigen on the pathogen.
  • The pathogen is engulfed as the phagocytes membrane folds inwards.
  • The pathogen is trapped inside a vacuole called a phagosome.
  • Lysosomes fuse with the phagosome and release enzymes into the phagosome.
  • The pathogen is broken down into harmless nutrients.
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Antibodies

  • Antibody (a protein molecule that can identify and nuetralise antigens.)
  • Y shaped – Four polypeptide chains held together by disulfide bridges.
  • Constant region – enables the antibody to attach to phagocytic cells and helps in the process of phagocytosis.
  • Variable region – has a specific shape and differs from one type of antibody to another. This is the result of its amino acid sequence. It ensures that the antibody can attach only to the correct antigen. The shape of the variable region is complementary to that shape of the antigen, and can bind to that antigen.
  • More than 1 variable region – allows attachment of more than one pathogen.
  • Hinge region – allows flexibility, this allows the branches of the Y-shaped molecule to move further apart in order to allow attachment to more than one antigen. 

  Action of Antibodies

  • Antibodies attach to antigens on the cell surface of the pathogen – pathogen cannot bind to host cell – Neutralisation.
  • Some larger antibodies have several binding sites/regions and can attach several pathogens at once – Agglutination.
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Cell Signalling

Cell signaling - The immune response is a specific response to the detection of pathogens in the body. It involves a coordinated response between a wide range of cells. In order to work together effectively, these cells need to communicate.

Identification – The first signaling is done by the pathogen.

·         The pathogen carries antigens on its cell surface.

·         These act as flags to say I am foreign. These are detected by our body cells.

Sending Distress signals – The internal cell organelles such as lysosomes will attempt to fight the invader. This damages the path. cells causing parts of the pathogen to be attached to the host plasma membrane. This has two effects:

·         They act as distress signals and can be detected by cells from the immune system.

·         They can act as markers to indicate that the host cell is infected – T killer cells can recognise that the cell is infected and must be destroyed.

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Immunity

Natural Passive - Antibodies provided via the placenta or breast milk. This makes the body immune to diseases that the mother is immune to. Useful in first year of life when immune system is developing.

Artificial Passive - Immunity provided by injection of antibodies made by another individual.

Natural Active - Immunity provided by antibodies made in the immune system as a result of infection. A person suffers from the disease once and then is immune.

Artificial Active - Immunity provided by antibodies made in the immune system as a result of vaccination. A person is injected with a weakened, dead or similar antigens and this activates the immune system.

Vaccination

  • To stimulate protection of B&T memory cells without causing illness.
  • Herd Vaccination - >80% of the population vaccinated.
  • Ring Vaccination – immediate vaccination of the local area when a new case is reported.
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New Drugs

  • Discovered by accident.(Discovery of penicillin by Alexander Fleming.
  • Traditional medicine.
  • Anaesthetics (opium from poppies).
  • Observing wildlife (monkeys rub citrus oils on their coats to act as insecticides).
  • Modern Research, scientists have used traditional plant medicines and animal behavior as a starting point in thier search for new drugs. Research into the plants used allows them to isolate the active ingredient.  
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Effects of smoking

Chronic Bronchitis

  • Inflammation of the lining of the airways. Along with damage to cilia and the overproduction of mucus. This causes mucus to collect in the lungs. Increases your chance of a lung infection. 

Emphysema

  • Loss of elasticity in the alveoli, which causes it to burst. The lungs have a reduced surface area as larger air spaces are formed. Means less surface area for gaseous exchange.
  • Loss of elasticity makes it harder to exhale. In severe cases, breathing will become more shallow and rapid and the blood will be less oxygenated causing fatigue.

Lung Cancer

  • Carcinogens in tar enter the cells in lung tissue.
  • Affects genetic material and causes a mutation – if the genes affected are involved in cell division then cancer will result.
  • May take 20-30 years to develop.
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Effects of Nicotine and Carbon Monoxide part 1

Nicotine

·         Stimulant, increases adrenaline production, increases heart rate, breathing rate and causing the constriction of the arteries.

·         Causes the platelets to become sticky, increasing the risk of a blood clot – risk of a stroke.

Carbon Dioxide

·         Binds preferentially to haemoglobin creates carboxyhaemoglobin. This reduces the oxygen carrying capacity of the blood.

·         Carbon monoxide can also damage the lining of the arteries.

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Problems caused by Nicotine and Carbon Monoxide

Atherosclerosis

  • Carbon Monoxide damages the lining of arteries, the damage is repaired by the action of white blood cells. This encourages deposition of fatty substances, the deposits include LDLs  
  • Deposits are called atheroma’s (includes fibres, dead erythrocytes and platelets).
  • Deposits build up under the endothelium in artery wall reducing the size of the lumen.
  • The process is known as atherosclerosis.

Coronary Heart Disease (CHD)

  • Atheroma’s (Atherosclerosis) in the coronary arteries cause CHD.
  • CHD can take three forms: o Angina, which is a severe pain in the chest, which may extend down the left arm or up into the neck.
  • Heart attack- death of part of a part of the heart muscle, usually caused by a clot in the coronary artery blocking the flow of blood to the heart muscle.
  • Heart failure- when the heart cannot sustain its pumping action; this can be due to the blockage of a major coronary artery.
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Problems caused by Nicotine and carbon monoxide

Stroke

  • Death of part of the brain tissue.
  • Caused by the loss of blood flow to that part of the brain.
  • A blood clot floating around in the blood blocks a small artery leading to part of the brain.
  • OR an artery leading to the brain bursts (haemorrhage).   
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Cardiovascular Diseases

  • Arteriosclerosis is the hardening of the hardening of the artery walls, which makes them even less flexible. This is caused by deposition of minerals, such as calcium, in the walls and particularly in the atheromas.
  • Factors which increase the risk of CHD?
  • Age
  • Sex- men are more likely to die of CHD under 50 than women.
  • Cigarette smoke
  • Obesity
  • High blood pressure ( hypertension)
  • High blood chlosterol concentration
  • Physical inactivity
  • Diet (high levels of saturated fats)
  • High salt intake
  • Absence of of healthy fats (called polyunsaturated fats) such as omega-3
  • Absence of antioxidants such as vitamens A,C and E.
  • Genetic factors
  • Diabetes
  • Stress
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Evidence linking smoking to disease

Evidence

Epidemiological Evidence - (the study of the distribution of a disease in populations and the factors that influence its spread)

  • Regular smokers are 3X more likely to die prematurely.
  • 50% likely to die from smoking related diseases.
  • 25% of smoker die from lung cancer.
  • 98% of people with emphysema are smokers.

 Experimental Evidence

  • Experiments on dogs
  • Cigarettes contain carcinogens.
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Biodiversity

Species – a group of organisms with similar morphology (shape) and physiology. They are able to breed with each other to form fertile offspring. 

Habitat – a place where an organism lives, suitable for the survival and reproduction of a particular species. 

Biodiversity – the variation of life within an ecosystem, habitat or the world.

Biodiversity includes:

  • All the deferent plant, animal, fungus and microorganisms species worldwide.
  • The genes they contain, and the ecosystems of which they form a part.
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Sampling

Sampling is important in measuring the biodiversity of a habitat. A habitat may be too large and the numbers of organisms too great to make an accurate count. A sample is much quicker and gives a representation of the whole habitat.

Random Quadrats

  • Frame quadrats are used
  • Thrown randomly – even if the area looks reasonably uniform.

Transect

  • Used to observe how vegetation changes.
  • A transect is a line taken across the area and samples are taken at regular intervals.

Species Richness – the number of species present in a habitat, expressed as a number.

Species Evenness – The relative number of individuals in a species.

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Simpson's Index

D= 1 – (Σ(n/N)2)

  • D = the value of the diversity in the area.
  • N = the total number of organisms for all species.
  • n = the total number of organisms for a particular species.
  • A high value indicates a diverse habitat. The habitat tends to be stable and able to withstand change.
  • A low value suggests habitat dominated by a few species. A small change to the environment could damage or destroy the whole habitat.
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Variation (Types)

Variation – the presence of variety of differences between individuals. Variation can occur within a species and between species,

Continuous Variation

Where there are two extremes and a full range of intermediate values between those extremes. Most individuals are closer to the mean value. The number of individuals at the extremes is low.

  • Height
  • Length of Leaves
  • Thickness of trunk/stem

Discontinuous Variation

Where there are two or more distinct categories with no intermediate values.

  • Sex
  • Blood Groups
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Causes of Variation

Genetic Causes of Variation

The genes we inherit from our parents provide information that is used to define our characteristics. The combination of alleles that we inherit is not the same as that in any other living thing (unless identical twins).

 

Environmental Causes of Variation

  • An overfed pet can become obese
  • Human skin will tan and become darker with exposure to sunlight.
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Adaptation

  • A feature that enhances survival and long term reproductive success.
  • Behavioral adapt. - is an aspect of the behavior of an organism that helps it to survive the conditions it lives in.
  • Physiological/ biochemical adapt.- A physiological or biochemical adaptation is one that ensures the correct functioning of cell processing.
  • Anatomical (Structural) adapt.- Any structure that enhances the survival of the organism is an adapt.  

Example: Xerophytes

  • Behavioural – close stomata when little water is available, open stomata at night to conserve water.
  • Physiological – the mechanism by which a plant can open and close its stomata, folds its leaves to store water.
  • Anatomical – shallow widespread roots increases exposure to water, fleshy stem or leaves store water, small leaves reduces surface area.
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Cell Signalling part 2

Antigen presentation – Macrophages in the lymph nodes take this a step further. They act like phagocytes to engulf and digest the pathogen, but not full digesting it.

·   They separate out the antigens and incorporate them into the cell surface membrane.

·    This is exposed by the surface of the macrophage, which becomes known as antigen presenting cell.

·     Its function is to the lymphocytes that can neutralise that particular antigen.     

Instructions - A range of cytokines are released by cells. These chemical signals act as instructions to their target cells. Communication using cytokines includes the following:

· Macrophages release monokines: that attract neutrophils, stimulate B cells to differentiate and release antibodies.

·  T cells, B cells and macrophages release interleukins, which can stimulate proliferation and differentiation of B and T cells.

 o Many cells can release interferon, which can inhibit virus replication and stimulate the activity of T killer cells. 

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The specific immune response

Memory cells- are cells that circulate in the blood after an immune response. They speed up the response to a subsequent attack by the same pathogen.

 

Lymphocytes- are white blood cells that circulate around the body in the blood and lymph. B cells mature in the bone marrow, while T cells originate in the bone marrow but mature in the thymus gland.   

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Starting the responce

Starting the response:- An invading pathogen has foreign antigens.

·         Detected by specific T and B lymphocytes which have the correct receptor molecule on their membranes.

·         Shape is complementary to the shape of the antigen.

·         Once the antigens are detected the immune response begins.

·         However may be only few or one correct T and B lymphocytes in the body. Takes them some time to find antigens.

·         The presentation of foreign antigens by a number of cells increases the chances that the correct B and T lymphocytes will locate the antigens.

·         Cells that are attacked by the pathogen will display antigens on their surface.

·         Macrophages in the lymph system can become antigen- presenting cells. Thus many copies of pathogens antigens are displayed.

·         Clonal Selection is the selection of the correct B and T lymphocytes.

· Clonal expansion is the increase in numbers of the of theses lymphocytes. The increase is needed before they can become effective in fighting the pathogen. They divide via mitosis a number of times.

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Differentiation

·         The B and T lymphocytes do not manufacture the antibodies directly. Once selected the T lymphocytes develop or differentiate into three types of cell:

·         T helper cells (Th ) – which release cytokines (chemical messengers) that stimulate the B cells to develop and stimulate phagocytosis by the phagocytes.

·         T killer cells (Tk )- which attack and KILL infected body cells.

·         T memory cells (Tm )

The B lymphocytes develop into two types of cell:

·         Effector or Plasma cells, which flow around in the blood, manufacturing and releasing the antibodies. 

·         B memory cells that remain in the body for a number of years and act as the immunological memory.

Time – All this means that it may be a few days before the number of antibodies in the blood starts to rise. The immune response leaves memory cells in the body. If there is a second invasion by the same pathogen, these can stimulate the production of plasma cells and antibodies much more quickly.

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Observations by Darwin

  • Offspring generally appear similar to their parents.
  • No two individuals are identical.
  • Organisms have the ability to produce large numbers of offspring.
  • Populations in nature tend to remain fairly stable in size.

Conclusions

  • There is a struggle to survive.
  • Better adapted individuals survive and pass on their characteristics.
  • Over time, a number of changes may give rise to a new species.
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Natural selection

Natural selection is the mechanism of evolution. It assumes there is variation in a population that gives some individuals a selective advantage. The best adapted organism will survive, reproduce and pass on their alleles for the favourable characteristic to the next generation.  

Selective forces include:

·         Availability of food.

·         Predators

·         Diseases

·         Physical and Chemical factors- e.g. growing in a very shading place.  

Speciation – the formation of a new species.

·         A reproductive barrier causes speciation.

·         Geographical separation – prevents effective interbreeding between the individuals of two populations. AKA Allopatric speciation.

·         Behavioral change- courtship isn’t recognised.

·         Physical change- sexual organs are no longer compatible and they cannot mate.    

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Evidence of Evolution

Fossils

·         Many fossil species were much larger than modern species, but otherwise appeared very similar.

·         Darwin saw the similarities of fossils with modern species.

Problems –

  • Some are damaged or destroyed by the movement of rocks.
  • Gaps in the records due to fossils only forming in certain conditions.

DNA

  • Genes can be compared by sequencing the bases in DNA
  • This shows that closely related species evolved.
  • The more similar the gene sequence the closer species are related.
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How Species Evolve

 

  1. Variation must occur before evolution can take place.
  2. Once variation exists, then the environment can 'select' the variations that give an advantage.
  3. Individuals with an advantage will survive and reproduce.
  4. Therefore they pass on their advantageous characteristics (inheritance).
  5. The next generation will be better adapted to their environment. Over time, the group becomes well adapted to the environment (adaptation).
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Implications of Evolution

Insects

  • Cause damage to crops and carry disease.
  • Pesticides are designed to kill pests.
  • Insecticides apply a very strong selection pressure.
  • If the insect is susceptible it will die. If it has some form of resistance, it will survive.
  • This allows it to reproduce and pass on the resistance characteristics.
  • The resistance quickly spreads through the whole population.

Micro-organisms

  • Use of antibiotics is a very powerful selection pressure on bacteria.
  • Antibiotic resistant bacterial survive and reproduce to create a resistant strain of bacteria.
  • Overuse and incorrect use of antibiotics has led to strains of bacteria resistant to virtually all the antibiotics in use.
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Implications of Evolution

Insects

  • Cause damage to crops and carry disease.
  • Pesticides are designed to kill pests.
  • Insecticides apply a very strong selection pressure.
  • If the insect is susceptible it will die. If it has some form of resistance, it will survive.
  • This allows it to reproduce and pass on the resistance characteristics.
  • The resistance quickly spreads through the whole population.

Micro-organisms

  • Use of antibiotics is a very powerful selection pressure on bacteria.
  • Antibiotic resistant bacterial survive and reproduce to create a resistant strain of bacteria.
  • Overuse and incorrect use of antibiotics has led to strains of bacteria resistant to virtually all the antibiotics in use.
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Classification

Classification – the process of sorting living things into groups. Natural classification does this by grouping things according to how closely related they are. Natural classification reflects evolutionary relationships.

 

Phylogeny – the study of the evolutionary relationships between organisms.

 

Taxonomy – the study of the principles of classification.

 

Hierarchy

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

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The five KINGDOMS ( 3 of 5)

Prokaryotae have …

  • No nucleus.                                                      o Smaller ribosomes.
  • Loop of naked DNA.                                       o No membrane-bound organelles.
  • Respiration not in mitochondria in mesosomes.  o Smaller cells than Eukaryotes.
  • May be free living or parasitic.

Protoctista

  • Eukaryotes.                                                       oMostly single celled.
  • Wide variety of forms.                        o Show various plant-like or animal-like features.
  • Autotrophic or heterotrophic nutrition – some photosynthesis, some ingest prey, some feed using extracellular enzymes and some are parasites.  

Fungi

  • Eukaryotes                                                           o Walls made of chitin
  • Have a mycelium, which consists of hyphae           o Cytoplasm is multi-nucleate
  • Mostly free-living, some saprophytic (cause decay)
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The Five Kingdoms (4 and 5)

Plantae

  • Eukaryotes                                                                   o Multicellular
  • Cellulose cell walls
  • Produce multicellular embryos from fertilised eggs
  • Autotrophic nutrition (photosynthesis)

Animalia

  • Eukaryotes                                                                   o Multicellular
  • Heterotrophic nutrition
  • Usually able to move around
  • Fertilised eggs develop into a ball of cells called a blastula.
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Maintaining Biodiversity

Reasons for Conservation

  • Ethical– All living organisms have a right to survive and to live in the way in which they have become adapted.
  • Aesthetic – We experience a feeling of joy and wellbeing when observing the infinite variations of nature. We experience a feeling of joy and wellbeing when observing the infinite variations of nature.
  • Sources of Food, Clothing, Drugs, Renewable fuels and other industrial materials e.g. wood.  
  • Value of natural ecosystem $33 x 1012
  • Maintaining biodiversity will maintain genetic diversity in species and allows us to integrate new alleles into intensively farmed species as the climate changes.
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Consequences of Global Warming

Agriculture

  • Higher CO2 levels for photosynthesis.
  • Higher temperature increases growth rate.
  • Longer growing seasons.
  • Greater evaporation of water and therefore greater precipitation.
  • A change in distribution of precipitation.
  • Loss of land due to rise in sea levels.

Diseases

  • Crops grown in new areas will encounter new diseases and pests.
  • Higher temperatures provide longer growing time for pests.
  • More pests may be able to cause greater infestations earlier in the year.
  • This will mean lower yields and less food for humans.
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Conservation

In Situ Conservation

Protecting the species in its natural habitat by minimising human impact on the natural environment and protecting the natural environment.

  • Legislation
  • Conservation parks – National parks, Nature reserves, Sites of Special Scientific Interest and local nature reserves.
  • Repopulation

Ex Situ Conservation- means conserving an endangered species by activities that take place outside its normal environment.

  • Expensive
  • Many animals fail to breed successfully outside their natural environment.
  • Space is limited, limits numbers of individuals, which restricts the genetic diversity.
  • Decrease in genetic diversity of a pop. Results in lack of variation.
  • Means species is less able to adapt to changing cond., less likely to be able to breed.
  • Have to be able to survive reintroduction.
  • Sometimes reintroduced members of species are not accepted by wild members of the species.
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Conservation part 2

Seed Banks

  • Collection of seed samples.
  • Grown for food, building materials for rural communities, to disease resistant crops for agriculture.
  • Can also be used for habitat reclamation and repopulation.

CITES (The Convention on International Trade in Endangered Species of wild Fauna and Flora.)

Aims to ensure that international trade in specimens of wildlife does not threaten their survival.

  • Transport of most endangered – illegal
  • Transport of risk of endangered – export permit needed
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Convention on Biological Diversity

  • Promotes sustainable development.                                   o Encourages cooperation between countries.

Environmental Impact Assessments                                           o Must be undertaken before any major development.

  • Avoid or minimise adverse effects on the biological diversity of the area.

Criteria

  • Size of the development.                                                             o Environmental sensitivity of the location.
  • Types of impact expected.

Stages

  • Developer complies an environmental statement.
  • Statement is publicised.                o Authority takes it into account when making planning decisions.

EIA is                                                   o A way of measuring the significant environmental impact of a development.

  • Improves planning and design of development.        o Useful to consider alternative approach to a development.
  • Results in final proposal being more environmentally acceptable.
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