Unit 2

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Structure of water molecules

Water is made up of two hydrogen atoms covalently bonded to one oxygen. The bonds are very strong, and very difficult to split.

A covalent bond is an electron-sharing bond, and the sharing is not equal.

The oxygen atom gets slightly more than it’s fair share, and this gives it a very small negative charge (δ-). The hydrogen atoms have a very small positive charge (δ+).

These charges mean that the water molecules are attracted to each other. The positively charged hydrogen atoms on one molecule are attracted to the negatively charged oxygen atoms. This attraction is a hydrogen bond.

In solid water-ice – the hydrogen bonds hold the water in a rigid lattice formation.

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Water, heat and temperature

As heat energy is added to the water, a lot of the energy is used to break the hydrogen bonds. Because so much heat is used for this, there is less heat energy available to raise the temperature.

Water requires lots of heating to increase its temperature by much - high specific heat capacity.

Being largely water, your body does not change its temperature quickly. Large changes in the temperature of your external environment have relatively small effects on the temperature of your body - useful property of water.

The energy needed to break the hydrogen bonds between water molecules also affects water’s boiling point. Because of the hydrogen bonds, water is liquid at room temperature. If water was not a liquid at the temperatures found on Earth, then life as we know it would not exist here.

When liquid sweat lies on the surface of the skin, the water in the sweat absorbs heat energy as it evaporates. The heat needed to do this is called latent heat of evaporation. 

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Solvent Properties

Water is an excellent solvent.

The tiny charges on its molecules attract other molecules or ions that have charges on them. The molecules and ions spread around and in between the water molecules. This is called dissolving.

When an ionic compound such as NaCl dissolves in water, the sodium ions and the chloride ions become separated from each other. This makes it easy for them to react with other ions or molecules.

Water can flow, therefore it can carry dissolved substances from one place to another.

This happens in the blood, xylem vessels and phloem sieve tubes of plants. 

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Density and viscosity

Water molecules are pulled closely together by the hydrogen bonds between them, and this makes water a relatively dense liquid.

Most living organisms, containing a lot of water, have a density which is quite close to that of water. This makes it easy for them to swim.

It takes quite a lot of effort to swim through water. You have to push aside the molecules, which are attracted to one another and therefore reluctant to move apart. We say that water is a fairly viscous fluid.

This is why aquatic organisms are often streamlined; their shape helps them to cut through water more easily.

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Cohesion and surface tension

Water molecules tend to stick together. This is called cohesion.

Within a body of water, each water molecule is attracted to others all around it. However, on the surface, the uppermost molecules only have other molecules below them, and not above.

So they are pulled downwards. These pulling forces draw them closer together than in other parts of the body of water. This is called surface tension.

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Protein structure

Proteins are made of many amino acids linked together in long chains.

All amino acids have a central carbon atom, which forms a bond with a carboxyl group, -COOH.

There is another bond with a hydrogen atom, and a third bond with an amine group, - NH2. 

The fourth bond, however, can be with any one of a whole range of different groups - called the R group.

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Polypeptide chains

The amino acids that make up a protein are linked during protein synthesis.

Here, separate amino acids are brought close together to react and form a linkage between them called a peptide bond.

Peptide bonds are very strong; they involve covalent bonds.

As the peptide bond is formed, two hydrogen atoms from one amino acid on one oxygen atom from another amino acid join together to form a water molecule - condensation reaction.

A long chain of amino acids is formed, all linked together by peptide bonds - polypeptide chain.

Proteins can be broken down by breaking their peptide bonds - hydrolysis reaction, as the combination with a water molecule breaks the peptide bond.

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Primary structure

The sequence in which the amino acids are arranged in a polypeptide chain is the primary structure.

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Secondary Structure

Polypeptide chains do not usually lie straight, so some parts of the chain may coil into an α–helix.

Other parts of the polypeptide chain may adopt a different regular structure, called a β–pleated sheet (also known as a β–fold.)

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Tertiary structure

The chain can now fold around itself even more

Overall shape formed is called the tertiary structure.

Held together by hydrogen bonds, and also by three other types of bonds - disulphide bonds, ionic bonds and hydrophobic interactions.

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Quaternary Structure

Quaternary structure:

The quaternary structure is made when several chains fit together to make a complete molecule. This shape is held by the same kinds of bonds as the tertiary structure.


β-Polypeptide chains in haemoglobin wind around themselves and around a haem group at the centre. Four of these join together to make a haemoglobin molecule. (Quaternary structure).

In haemoglobin, the chain is curled up into a ball, forming a globular protein(tertiary structure).

Enzymes are also globular proteins. In some other proteins, such as collagen, the shape is long and thin. Collagen is a fibrous protein

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Collagen - a fibrous protein

Collagen is an important structural protein.

It consists of three polypeptide chains,each in the shape of a helix. These three helical polypeptides wind around each other.

The small size of the amino acids in collagen allow the three strands to lie close together and form a tight coil. These strands are held together by hydrogen bonds.

Each complete, three-stranded molecule of collagen interacts with other collagen molecules running parallel to it. Bonds form between R groups in molecules lying next to each other. These cross-links hold many collagen molecules side by side, forming fibrils.

The ends of the parallel molecules are staggered - if they were not, there would be a weak spot running right across the collagen fibril.

Fibrils associate to form bundles called fibres.

Collagen has tremendous tensile strength - that is, it can resist strong pulling forces.

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Comparison of globular & fibrous proteins


Example - Haemoglobin, enzymes, antibodies

Primary structure - Very precise, usually made up of non-repeating sequences of amino acids formaing a chain that is always the same length

Solubility - Often soluble in water

Functions - Usually metabolically active, taking part n chemical reaction in/around cells


Examples - Collagen, Keratin, Elastin

Primary - Often made up of a repeating sequence of amino acids & chain can be varying length

Solubility - Insoluble in water

Functions - Usually metabolically unreactive, with a structural role

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Carbohydrate Structure

Carbohydrates are substances whose molecules are made of sugar units - saccharides. The general formula for this sugar unit is CnH2nOn.

A carbohydrate whose molecules contain just one sugar unit is called a monosaccharide. (e.g. Glucose, fructose and galactose).

Glucose can exist in two forms: α-glucose and β-glucose

Two monosaccharide molecules can link together to form a disaccharide. For example, two alpha glucose molecules can react to form maltose. This is a condensation reaction.

The linkage formed between two monosaccharides is called a glycosidic bond.

It involves a covalent bond and is very strong.

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Polysaccharides - Amylose

Linking together thousands of alpha glucose molecules with 1-4 glycosidic bonds produces the carbohydrate amylose - found in starch.

This is how plants store the carbohydrate that they make in photosynthesis.

Starch is insoluble and metabolically inactive, so does not interfere with chemical reactions inside the cell, nor does it affect water potential.

Amylose molecules coil around to form a long spiral. This makes them very compact, so a lot of starch can be stored in a small space.

The coil is held in shape with hydrogen bonds.

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Polysaccharides - Cellulose

Cellulose is also a polysaccharide made of thousands of glucose molecules. But instead of alpha glucose, it is made of beta glucose molecules, linked with beta 1-4 glycosidic bonds.

Cellulose molecules do not coil, but lie straight.

Rather than forming hydrogen bonds within themselves, each molecule hydrogen bonds with tis neighbour.

This produces bundles that lie side by side.

These bundles are called fibrils, and they form larger bundles called fibres.

They make up cellulose cell walls, which are structurally very strong. 

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Polysaacharides - Cellulose

Cellulose is also a polysaccharide made of thousands of glucose molecules. But instead of alpha glucose, it is made of beta glucose molecules, linked with beta 1-4 glycosidic bonds.

Cellulose molecules do not coil, but lie straight.

Rather than forming hydrogen bonds within themselves, each molecule hydrogen bonds with tis neighbour.

This produces bundles that lie side by side.

These bundles are called fibrils, and they form larger bundles called fibres.

They make up cellulose cell walls, which are structurally very strong. 

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Polysaccharides - Glycogen

Animals store carbohydrates as glycogen

This has a structure similar to amylose- it is made up of alpha glucose molecules linked by 1-4 glycosidic bonds.

However, unlike amylose, it also hasbranches where 1-6 glycosidic bonds are formed.

This makes it more difficult for glycogen molecules to form helices, so they are not as tightly coiled as starch molecules.

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Lipid Structure


Lipids are a group of substances that- like carbohydrates- are made up of carbon, hydrogen and oxygen.

They are insoluble in water.


Triglycerides get their name because their molecules are made of three fatty acids attached to a glycerol molecule.

Fatty acids are acids because they contain a carboxyl group-COOH.

Thecarboxyl group of fatty acids are able to react with the hydroxyl group of the glycerol, forming ester bonds. These involve covalent bonds, and so are very strong.

The breakage of an ester bond is a hydrolysis reaction.

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Triglycerides are insoluble in water as none of their atoms carry an electrical charge, so they are not attracted to water molecules - hydrophobic.

They are rich in energy, and are often used as energy stores in living organisms.

1g of triglyceride can release twice as much as 1g of carbohydrate when it is respired, so they make compact and efficient stores.

In humans, cells in adipose tissue are almost filled with globules of triglycerides, and they make very good thermal insulators.

Animals who live in cold environments often have thick layers of adipose tissue beneath the skin.

Stored triglycerides also provide a place in which fat-soluble vitamins can be stored.

A saturated fat is one in which the fatty acids all contain as much hydrogen as they can.

An unsaturated fat, however, has one or more fatty acids in which at least one carbon atom is linked to another by a double bond. 

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A phospholipid is like a triglyceride in which one of the fatty acids is replaced by a phosphate group.

Whereas the fatty acid tails of a phospholipid are hydrophobic, the phosphate heads are hydrophilic - they are attracted to the water molecules. This is because the phosphate group has a negative charge, so is drawn  to the positive hydrogen in the water molecules.

So, when in water, the two ends of the phospholipid do different things.

The phosphate head is drawn towards water molecules and dissolves in them.

The fatty acid tails are repelled by water molecules and avoid them.

In water, the phospholipid molecules arrange themselves in a sheet called a bilayer.

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Cholesterol and other substances with similar structures, which are formed from it, are called steroids.

There are a huge number of different kinds of steroids in the body.

Many of them are hormones - e.g. testosterone and oestrogen.

Cholesterol itself is a major constituent of plasma membranes, where it helps to regulate fluidity of the membrane

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The biuret test for proteins

The test solution needs to be alkaline:

1) Add a dew drops of sodium hydroxide solution

2) Add some copper(II) sulphate solution

If protein is present, the solution is turns purple

If there’s no protein present, the solution stays blue

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The iodine test for starch

Add iodine dissolved in potassium iodine solution to the test sample

If starch is present, the sample changes from browny-orange to a dark, blue-black colour

If there’s no starch present, the sample stays browny-orange

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The emulsion test for lipids

1) Shake the test substance with ethanol for a minute

2) Pour solution into water

If lipid is present, there is a milky emulsion above the solution

If there is no lipid present, the solution will stay clear

The more lipid there is, the more noticeable the milky colour will be 

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The Benedict's test for reducing sugars

Include monosaccharides and some disaccharides

1) Add Benedict’s reagent to a sample and heat it

2) Solution should not boil

If reducing sugar is present, colour precipitate will form - green/yellow/orange/red

If sample stays blue, no reducing sugar present

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The Benedict's test for non-reducing sugars

If the result of the reducing sugars test is negative, could still contain non-reducing sugars

1) Take a new sample and boil it with dilute hydrochloric acid

2) Neutralise it by adding sodium hydrogencarbonate

3) Heat sample with Benedict’s reagent

If  non-reducing sugar is present, colour precipitate will form – green/yelllow/orange/brick red 

If sample stays blue, no non-reducing sugars present

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Measures the strength of a coloured solution by seeing how much light passes through it

Measures absorbance – the amount of light absorbed by the solution

The more concentrated the colour of the solution, the higher the absorbance is

Its difficult to measure the colour precipitate from Benedict’s test

E.g. when estimating glucose concentration you measure the concentration of the blue Benedict’s solution that’s left after the test - paler the solution left, the more glucose there was

The higher the glucose concentration, the lower absorbance of the solution

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Making a calibration curve

Make up several glucose solutions of different concentrations – e.g. 10mM, 20mM and 30mM – but should be same volume

Do a Benedict’s test on each solution – use the same amount of reagent in each case – has to be large enough volume to react with all the sugar in the strongest solution and still have some reagent left over

Remove any precipitate from the solutions – either leave the test for 24 hours so the precipitate settles out or centrifuge them

Use a colorimeter with a red filter to measure the absorbance of the Benedict’s solution remaining in each tube

Use the results to make the calibration curve showing absorbance against glucose concentration

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A DNA molecule is made of two long chains of nucleotidemolecules, linked together to form a twisted ladder.

Each chain is called a polynucleotide.

Each nucleotide contains a phosphate group, a five carbon sugar and a nitrogenous base.

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DNA stands for deoxyribonucleic acid.

Each nucleotide in a DNA molecule contains a phosphate group, the five-carbon sugar, deoxyribose, and an organic base.

The base in DNA can be any one of four. These are adenine, guanine, thymine and cytosine. (A,G,T and C).

Adenine and Guanine each contain two rings in their structure. They are known as purine bases.

Thymine and cytosine have only one ring. They are known as pyrimidine bases.

In DNA, two chains of nucleotides lie side by side. They are said to be antiparallel.

The bases of one chain link up with the bases of the other by means of hydrogen bonds.

The whole molecules twists to produce the double helixshape.

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Complementary base pairing

The key to the ability of DNA to hold and pass on the code for making proteins in the cell is the way in which the bases link up.

One large base - a purine base - links with one smaller base - a pyrimidine base.

can only link with T, and C can only link with G. This is called complementary base pairing.

This ensures that the code carried on a molecule of DNA can be copied perfectly over and over again. 

It also allows the code on the DNA to be  used to instruct the protein-making machinery in a cell to construct exactly the right proteins.

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DNA replication

DNA replication takes place during interphaseof the cell cycle.

The method by which DNA is replicated is called semi-conservative replication.

This is because each of the new DNA molecules is made of one old strand and one new strand of DNA.

1) Hydrogen bonds between the bases are broken

2) Free nucleotides are present in the nuclues

3) Free nucleotides pair up with complementary exposed bases.

4) The new strand is linked together

There are now 2 DNA molecule - each contains one old strand and one new one.

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The role of DNA

DNA carries a code that is used by the cell when making proteins.

The sequence of bases in the DNA molecules determines the sequence of amino acids that are strung together when a protein molecule is made on the ribosomes.

A length of DNA that codes for making one polypeptide is called a gene.

The code is read in triplets of bases.

A sequence of three bases in a DNA molecule codes for one amino acid. It therefore determines the primary structure of the proteins that are made.

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Structure of RNA

There are also polynucleotides which contain the sugar ribose rather than deoxyribose.

They are therefore called ribonucleic acids, or RNA for short.

RNA is generally single stranded, while DNA is generally double stranded.

RNA always contains the base uracil instead of thymine.

While DNA stores the genetic information in the nucleus of the cell, RNA is involved with using that information to make proteins.

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A sequence of  DNA nucleotides that codes for a protein (polypeptide)

Proteins are made from amino acids

Different proteins have different number and order of amino acids

The order of nucleotide bases in a gene – determines the order of amino acids in a particular protein

Each amino acid is coded for by a sequence of three bases in a gene

Different sequences of bases code for different amino acids

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Gene mutations

Mutations are changes in the base sequence of an organism’s DNA

If sequence of bases in a gene changes, the sequence of amino acids in the protein it codes for may also change

May affect the way the protein folds up and so its overall 3D shape

As a result, a different or non-functioning protein could be produced

E.g. - All enzymes are proteins

If there’s a mutation in a gene that codes for an enzyme – then that enzyme may not fold up properly

May produce an active site that’s the wrong shape and so a non-functional enzyme

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DNA, RNA and protein synthesis

All the reactions and processes in living organisms need proteins

DNA carries the instructions to make proteins - vital for protein synthesis

DNA molecules are found in the nucleus of the cell

Ribosomes assemble proteins

DNA is too large to move out of the nucleus - so a section is copied into a molecule called mRNA

Leaves the nucleus and joins with a ribosome in the cytoplasm - where it can be used to synthesise a protein

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Biological catalysts

Catalyse metabolic

Can be intracellular - within cells

Can be extracellular - outside cells e.g. blood

Globular proteins

Active site is a specific shape - part of the enzyme where the substrate molecules                          jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj   determined by the enzyme’s tertiary structure

The substrate has to fit into the active site - must be complementary

It they do not fit - reaction won’t catalyse

Substrate binding to an enzyme’s active site - enzyme-substrate complex is formed

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How enzymes speed up a reaction

Activation energy - certain amount of energy needed to supply the chemicals to start the reaction.

Reduces the amount of activation energy needed in the chemical reaction - lowers temperature

Enzyme-substrate complex forms - lowers activation energy

If 2 substrate molecules need to be joined - attaching to enzyme hold them close together - reducing any repulsion between the molecules so they can bond more easily

If the enzyme is catalysing a breakdown reaction - fitting into the active site puts a strain on bonds in the substrate

This strain means the substrate molecule breaks up more easily

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Lock and Key model

Early theory

Substrate fits into the enzyme - like a lock fits a key

Active site + substrate = complementary shape

This is the order of the hypothesis:

1) Substrate fits into the enzyme’s active site

2) Forms enzyme-substrate complex

3) Forms enzyme-product complex

4) Substrate breaks down - enzymes remains unchanged after the reaction

Scientists realised this was not the case:-

New evidence showed that the enzyme-substrate complex changed shape slightly to complete the fit - Locks the substrate in more tightly to the enzyme

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The 'induced fit' model

Helps explain why enzymes are so specific - only bond to one particular substrate

Substrate doesn’t only have to be the right shape to fit the active site - it has to make the active site change shape in the right way

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Factors affecting enzyme activity - temperature

Rate of enzyme-controlled reaction increases when temp increases

More heat means more kinetic energy - so molecules move faster

Makes the substrate molecules more likely to collide with the enzyme’s active sites

Energy of these collisions also increases - means each collision is more likely to result in a reaction

Rate of reaction continues to increase until the enzyme reaches its optimum temperature

Rise in temperature makes the enzyme’s molecules vibrate more

If the temperature goes above a certain level - vibration breaks some of the bonds that hold the enzyme in shape

The active site changes shape and the enzyme and substrate no longer fit together

Enzymes is denatured - no longer functions as a catalyst

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Factors affecting enzyme activity - pH

All enzymes have an optimum pH value - pH at which the rate of an enzyme-controlled reaction is at its fastest

Most human enzymes work best at pH 7 (neutral) but there are exceptions

E.g. Pepsin - works best at acidic pH 2 – useful as it is found in the stomach

Above and below the optimum pH - H+ and OH- ions found in acids & alkalis can break the iconic bonds & hydrogen bonds

Hold the enzymes tertiary structure in place - makes the active site change shape so the enzyme is denatured

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Factors affecting enzyme activity - enzyme concent

More enzyme molecules there are in a solution - more likely substrate molecules is to collide with one to form an enzyme-substrate complex

Increasing the concentration of the enzyme - increases the rate of reaction

If the amount of substrate is limited - ultimately there’s more than enough enzyme molecules to deal with all the available substrate - so adding more enzyme has no further effect

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Factors affecting enzyme activity - substrate conc

Higher the substrate concentration, faster the reaction

More substrate molecules means a collision between substrate and enzyme is more likely, so more active sites will be used, more enzyme-substrate complexes will be formed - only up until a ‘saturation’ point though

After that there are still substrate molecules, but all the active sites are full

Adding more substrates makes no difference, enzyme concentration becomes a limiting factor

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Cofactors & coenzymes

Some enzymes will only work if there is another non-protein substance bound to them - cofactors

Some cofactors are inorganic, work by helping the enzyme and substrate to bind together, but don’t directly participate in the reaction

So aren’t used up or changed in any way

E.g. Manganese ions are cofactors found in hydrolase, enzymes that catalyse the hydrolysis of chemical bonds

Organic cofactors (coenzymes) participate in the reaction and are changed by it, almost like a second substrate

Often act as carriers, moving chemical groups between different enzymes continually recycled during this process

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Competitive & non-competitive inhibitors

Enzyme activity can be prevented by enzyme inhibitors - molecules that bind to the enzyme that they inhibit

Can be competitive or non-competitive

Competitive inhibitors - similar shape to that of the substrate molecules, competes with the substrate molecules to bind to the active site

But no reaction takes place, instead they block the active site so no substrate molecules can fit in it

How much the enzyme is inhibited depends on the relative concentrations of the inhibitor and substrate, e.g. high concentration of the inhibitor, it’ll take up nearly all the active sites so hardly any of the substrate will get to the enzyme

Non-competitive inhibitors - bind to enzyme away from its active site & causes active site to change shape so substrate molecules can no longer bind to the active site (different shape)

Increasing the concentration of the substrate won’t make any difference as enzyme activity will still be inhibited

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Reversible & non-reversible inhibitors

Inhibitions can be reversible – don’t bind permanently to an enzyme away from its active site, which causes the active site to change shape so the substrate molecules can no longer bind to it

What type they are depends on the strength of the bonds between the enzyme and the inhibitor

If they’re strong, covalent bonds, inhibitor can’t be removed easily so inhibition is irreversible

If they’re weaker hydrogen bonds or weak ionic bonds, inhibitor can be removed so inhibition is reversible

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Metabolic poisons

Interfere with metabolic reactions (reactions that occur in cells), which causes damage, illness or death - often enzyme inhibitors


Cyanide is a non-competitive inhibitor of cytochrome c oxidase, which is an enzyme that catalyses respiration reaction. Cells that can’t respire, die

Malonate is a competitive inhibitor of succinate dehydrogenase, which catalyses respiration reactions as well

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Medicinal drugs

Some medicinal drugs are enzyme inhibitors

E.g. some antiviral drugs are reverse transcriptase inhibitor. Reverse transcriptase is an enzyme which catalyses the replication of viral DNA, so inhibitor prevents virus from replicating

E.g. some antibiotics like penicillin inhibits the enzyme transpeptidase catalyses the formation of proteins in bacterial cell walls. It weakens the cell wall which prevents the bacterium from regulating its osmotic pressure and as a result the cell bursts. Bacterium is killed

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Balanced diet

Carbohydrates provides energy

Fats (lipids) acts as an energy source - provides insulation - makes up cell membranes - physically protects organs

Proteins needed for growth - repair of tissues - makes energy

Different vitamins have different functions - e.g. vitamin D is needed for calcium absorption - vitamin K is needed for blood clotting

Different mineral salts have different functions - e.g. iron is needed to make haemoglobin in the blood - calcium is needed for bone formation

Fibre aids the movement of food through the gut.

Water is used in chemical reactions as people need a constant supply of water to replace what is lost through sweating, urinating and breathing.

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Caused by having too little or too much of some nutrients in your diet

There are 3 causes:

Not having enough food so you get too little of every nutrient                                                      E.g. in many third world countries people have very little food, which makes them malnourished

Malabsorption - where your body isn’t able to absorb the nutrients from digestion into your bloodstream properly which causes deficiency illnesses.                                                 j        E.g. coeliac disease reduces absorption of nutrients from the small intestine, which can lead to deficiency illness

Having an unbalanced diet - may contain too little of a nutrient or too much, which can lead to deficiency illnesses. Diet can be unbalanced if it provides too much of a nutrient and can lead to health problems.                                                                                                          ffffff E.g. too little iron in your diet can lead to iron deficiency anaemia or too many carbohydrates or fats in your diet can lead to obesity                                           

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Over-nutrition can lead to obesity (a conditioned defined as being 20% over the recommended body weight

It can increase the risk of - developing Type 2 diabetes / Arthritis / high blood pressure / Coronary heart disease / some forms of cancer

Main cause of obesity - eating too much sugary or fatty food, which contain a lot of energy

Getting too little exercise, means that the body takes in more energy than it uses up, excess energy is stored as fat, which increases body weight

People can also be obese due to an underactive thyroid gland in your neck that releases certain hormones

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Body Mass Index (BMI)

Used as a guide to help decide whether someone is, underweight / normal / overweight / obese

Calculated from their height and weight

BMI = Body Mass (kg) / Height (m)2

Underweight = below 18.5

Normal = 18.5 -24.9

Overweight = 25 -29.9

Moderately obese = 30 – 40

Severely obese = above 40

Isn’t always reliable as it doesn’t take into account how much of the body mass is made up of fat, could result in a high BMI even though they’re not overweight

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Coronary Heart Disease (CHD)

CHD is a result of reduced blood flow to the heart and can lead to chest pain and heart attacks

Caused by atherosclerosis, the narrowing & hardening of coronary arteries (blood vessels that supply the heart)

Diets that are high in cholesterol and salt can increase the risk of atherosclerosis and CHD

Blood cholesterol level - some cholesterol is needed for the body to function normally. Cholesterol needs to be attached to a protein to be moved around do the body forms lipoproteins - substances composed of both protein and lipid

The body is able to regulate its total blood cholesterol level using lipoproteins -> 2 different types, one increases risk of CHD, and other decreases risk

Diet high in salt can cause high blood pressure & can increase the risk of damage to artery wall - Damaged walls have an increased risk of atheroma formation, which causes atherosclerosis and increases the risk of CHD

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Low density lipoproteins (LDLs) are mainly lipid

Transports cholesterol from the liver to the blood and it circulates until needed by cells.

Function is to increase blood cholesterol when the level is too low

Diet high in saturated fats raises the LDL level

More cholesterol is transported to the blood, increasing total blood cholesterol - increases the build-up fatty deposits in the artery walls -> called atheromas. At places in the wall where they’ve been damaged, causing atherosclerosis and can lead to CHD

High density lipoproteins (HDLs) are mainly protein

Transport cholesterol from body tissues to the liver where its recycled/excreted

Function is to reduce blood cholesterol and when the level is too high

Diet high in polyunsaturated fat raises HDL level - more cholesterol is transported from the blood to the liver, decreasing total blood cholesterol and decreasing the risk of CHD

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Human food supply

Humans rely on plants for food, as plants are at the start of all food chains

Plants use the energy from sunlight to convert carbon dioxide & water into complex organic compounds

Humans and other animals then eat, digest and absorb the compounds, which they use for energy and to grow

Plants are grown for both direct consumption and to feed animals which we then eat

Many modern farming methods aim to maximise productivity by increasing plant and animal growth

Farmers do this using fertilisers, pesticides, antibiotics and selective breeding

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Chemicals which increase crop yields by providing minerals that plants need to grow

Minerals in the soil are used up during cell growth

Fertilisers replace these minerals so that a lack of minerals doesn’t limit growth of the next crop

There are 2 different types of fertilisers:

Natural fertilisers – use organic matter and include manure and sewage sludge

Artificial fertilisers – use inorganic matter and contain pure chemicals as powders or pellets

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Chemicals that increase crop yields by killing pests that feed on the crops, means fewer plants are damaged or destroyed

Pests include – microorganisms, insects, mammals (e.g. rats)

May be specific and kill only one pest species or broad and kill a range of different species

Advantage of broad spectrum pesticides - can kill a wide range of pests in one go

Disadvantage - may harm some non-pest species

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Animals use energy fighting diseases, which reduces the amount of energy available for growth, giving them antibiotics means animals can use more energy to grow, increasing food productions

Antibiotics help promote growth of animal - may influence bacteria in animal’s gut, which allows animals to digest food more efficiently & can increase the growth rate of the animal & its size

Giving animals antibiotics makes it less likely bacterial diseases will pass from them to humans


Using antibiotics in farming can increase the chance of bacteria becoming resistant to them, making it more difficult to treat disease in the future

Animals naturally have some bacteria inside, which are useful & could be killed by the antibiotics

Chance that the antibiotic may be present in animal products which humans consume, meaning that the antibiotic could also have unwanted effects in our bodies.

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Selective Breeding

Involves selecting plants/animals with useful characteristics to reproduce together in order to increase productivity

General method is the same for both crops & plants:

1.  Select plants/animals with useful characteristics that will increase food productions

2.  Breed them together

3.  Select the offspring with the best characteristics and breed them together

4.  Continue this over a few generations until a high-yielding plant or animal is produced 

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Selective Breeding of crops

Often involves selecting plants with characteristics, such as high yield, disease resistance or pest resistance

E.g. corn

Farmer needs a long strain of corn plant that is tall and produces lots of ears

So he breeds a tall corn strain with one that produces multiple ears

He selects the offspring that are tallest and have the most ears & breeds them together

Farmer continues this until he produces multiple ears of corn

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Selective Breeding of animals

Involves selecting animals with useful characteristics, such as fast growth rate, and high meat, milk or eggs yield

E.g. meat

Farmer wants to produce cows with high meat yields

He breeds together his largest cows and largest bulls

Selects the offspring that are the largest & breeds them together

He continues this over several generations until cows with very high meat yields are produced

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Arguments for and against selective breeding

Arguments for selective breeding

Produces high-yielding animals and plants

Can be used to produce the animals and plants that have increased resistance to disease, which means farmers have to use fewer drugs and pesticides

Animals & plants could be bred to have increased tolerance bad conditions

Arguments against selective breeding

Can cause health problems - e.g.  some types of chicken have been bred to grow quickly but this has meant their hearts and lungs can’t support their increased body mass, causing them distress

Reduces genetic diversity, the plants/animals with the best characteristics are usually closely related so breeding them together can lead to inbreeding. This reduces the gene pool and can make the plant/animal population susceptible to disease

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Microorganisms in food production

Microorganisms such as bacteria, yeast and other fungi are used in the production of many foods and drinks

Some microorganisms can convert sugar into other substances that humans can then use for food production. E.g:-

Bread - made by mixing yeast, sugar, flour and water into a dough. Yeast turn the sugar into ethanol and carbon dioxide -> it’s the CO2 that makes the bread rise

Wine - made by adding yeast to grape juice. Yeast turn the sugar in the grape juice into ethanol and carbon dioxide

Cheese - made by adding bacteria to milk. Bacteria turn the sugar in milk into lactic acid, which causes the milk to curdle. An enzyme is then used to turn the curdled milk into curds and whey. Curds are separated off and left to ripen into cheese

Yoghurt - made by adding bacteria to milk. Bacteria turn the sugar in the milk into lactic acid, causing the milk to clot and thicken into yoghurt

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Microorganisms in food production - advantages and


Populations of microorganisms grow rapidly under right conditions so food is produced quickly

Microorganisms can grow on a range of inexpensive materials

Environment can be artificially controlled, so it can potentially grow food anywhere & any time

Optimum conditions for growth are easy to create -> e.g. right temp, supply of materials & pH


High risk of food contamination - conditions created to grow the desirable microorganisms are also favourable to harmful microorganisms, causes food to spoil or if eaten cause illnesses like food poisoning

Conditions required to grow microorganisms can be simple to create, but small changes in temp or pH can easily kill the microorganisms

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Food spoilage

Deterioration of food’s characteristics -> e.g. appearance, taste, texture, odour

Caused by the growth of unwanted microorganisms, such as bacteria and yeast

As microorganisms multiply, they secrete enzymes which break down molecules in the food

It’s the breakdown of molecules in food that causes the food to spoil

Some microorganisms may also produce water products, which contributes to food spoilage & could cause food poisoning, if the food is eaten

Food poisoning can affect anyone but some parts of the population are more susceptible to it

E.g. the very young, the elderly and people who are malnourished are more likely to be affected as they have a weaker immune system

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Preventing food spoilage

By either killing the microorganisms or depriving the microorganism of the conditions they need to grow - either slows down or stops their growth

Salting - adding salt to foods, inhibits the growth of the microorganisms & interferes with their ability to absorb water which they need to survive. Water usually moves into the cell of microorganisms by osmosis. Salting food lowers the water potential of the environment outside the microbial cells, causing the microorganisms to lose water.

Adding sugar - inhibits the growth of microorganisms which interferes with their ability by osmosis. E.g. high sugar content of fruit jams reduces the growth of microorganisms giving the jam a long shelf life

Freezing - freezers keep foods below -18°C - slows down enzyme controlled reactions taking place in microorganisms, which freezes water in the food, so microorganisms can’t use it. It can preserve foods for many months

Pickling in vinegar - has a low pH, which denatures enzymes in microorganisms & prevents the enzymes from properly functioning, inhibits the microorganisms’ growth

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Condition that impairs the normal functioning of an organism, can be infectious, non-infectious, acute or chronic

Infectious diseases - Can be passed between individuals, caused by infection with pathogens or parasites. Pathogen -> organism that cause disease e.g. HIV -Virus that causes AIDS Parasite -> Organism that lives on or in another organism and causes damage to that organism, some cause disease so they are also pathogens e.g. Tapeworms, parasitic worms that live in the digestive system of vertebrates

Non-infectious disease - Caused by, genetic defects / nutritional deficiencies / lifestyle & environmental factors, e.g. Coronary Heart Disease (CHD), non-infectious disease of heart

Acute diseases - Only cause a problem for a short period of time, symptoms usually appear rapidly. E.g. cold or acute bronchitis

Chronic diseases - More persistent (you can have them your whole life), symptoms often appear slowly, but progressively worse as time goes on e.g. diabetes / chronic bronchitis

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The immune system - Primary defences

Body has a number of primary defences to help prevent pathogens and parasites from entering it


Acts as a physical barrier, blocks pathogens from entering the body                                         Acts as a chemical barrier, produces antimicrobial chemicals to lower pH, inhibiting the growth of pathogens

Mucous membranes:-

Protect body openings that are exposed to environment, e.g. mouth / nostrils / ears / genitals  Some mucous membranes secrete mucus, sticky substance that traps pathogens and contains antimicrobial enzymes                                                                                                     

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The Immune Response

If a pathogen or a parasite gets past primary defences and enters the body, the immune system will respond

Immune response is the body’s reaction to a foreign antigen

Antigens are molecules found on the surface of cells, usually proteins or polysaccharides

When a pathogen invades the body, antigens on its cell surface are identified as foreign which activates cells in the immune system

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Main stages of the immune response - Phagocytosis

A phagocyte is a type of white blood cell which carries out phagocytosis - engulfment of pathogens

Found in the blood and tissues

The first cells to respond to a pathogen inside the body

1) Phagocyte recognises the antigens on a pathogen

2) Cytoplasm of the phagocyte moves around the pathogen - engulfing it

3) Pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte

4) A lysosome fuses with the phagocytic vacuole

5) Enzymes break down the pathogen and it is absorbed into the cytoplasm

Phagocyte then presents the pathogen’s antigens. It sticks the antigens on its surface to activate other immune system cells

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Main stages of the immune response - T lymphocyte

Another type of white blood cells, which surface's is covered with receptors which bind to antigens presented by the phagocytes

Each T lymphocyte has a different receptor on its surface -> when the receptor on the surface of a T lymphocyte meets a complementary antigen, it binds to it - each T lymphocyte will bind to a different antigen

This process activates T lymphocyte and is known as clonal selection

The activated T lymphocyte then undergoes clonal expansion - it divides to produce clones, which then differentiate into different types of T lymphocytes

Different functions:-

Some activated T lymphocytes called helper T cells, release substances activates B lymphocytes

Some attach to antigens on a pathogen and kill the cell

Some become memory cells

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Main stages of the immune response - B lymphocyte

Type of white blood cell

Covered in antibodies (proteins that bind with antigens) - forms an antigen-antibody complex

Each B lymphocyte has a different shaped antibody on its membrane so different ones bind to different shaped antigens

When the antibody on the surface of a B lymphocyte meets a complementary shape, it binds to it

Each B lymphocyte will bind to a different antigen

Together with the helper T cells, it activates the B lymphocyte - clonal selection

The activated B lymphocyte then divides into plasma and memory cells by mitosis - clonal expansion

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Main stages of the immune response - Antibody prod

Plasma cells are clones of the B lymphocyte

They secrete loads of the antibody, specific to the antigen

Antibodies will bind to the antigens on the surface of the pathogen to from lots of antigen-antibody complexes

This is the signal for the immune system to attack and destroy the pathogen

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Cell signalling and the immune response

How cells communicate

A cell may release a substance that binds to the receptors on another cell. This causes a response of some kind in the other cell

Important in the immune response, as it helps activate all the different types of white blood cells that are needed


Helper T cells release substances that bind to receptors on B lymphocytes

Activates the B lymphocytes

The helper T cells are signalling to the B lymphocytes that there’s a pathogen in the body

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Antibody structure

Proteins made up of chains of amino acids monomers linked by peptide bonds

Variable regions of the antibody form the antigen binding sites - the shape of the variable region is complementary to particular antigens - variable regions differ between antibodies

The hinge region allows flexibility when the antibody binds to the antigens

The constant region allows binding to receptors on immune system cells is the same in all antibodies

Disulfide bridges hold the polypeptide bonds

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The role of antibodies in clearing infections

1) Agglutinating pathogens

Each antibody has 2 binding sites, so an antibody can bind to 2 pathogens at the same time. Pathogens become clumped together - phagocytes then bind to the antibodies. So phagocytosis happens to a lot of pathogens all at once

2) Neutralising toxins

Antibodies can bind to the toxins produced by pathogens - prevents the toxins from affecting human cells, so toxins are neutralised/inactivated. The toxin-antibody complexes are also phagocytosed

3) Preventing the pathogen binding to human cells

Antibodies bind to the antigens on pathogens, blocking the cell-surface receptors, & they need this to bind to host cells, which means the pathogen can’t attach or infect the host cells

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The primary immune system response

When an antigen enters the body for the first time, it activates the immune system called the primary response

It’s slow as there aren’t many B lymphocytes that can make the antibody needed to bind to it. The body will produce enough of the right antibody to overcome the infection, while the person starts to shows symptoms of the disease

After being exposed to an antigen, both T and B lymphocytes produce memory cells. Memory cells remain in the body for a long time - memory T lymphocytes remember the specific antigen so will recognise it 2nd time around - records the specific antibodies needed to bind to the antigen

Person is now immune - their immune system has the ability to respond quickly to a second infection

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The secondary immune response

If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response - secondary response

Memory B lymphocytes divide plasma cells, that produce the right the antibody to the antigen

Memory T lymphocytes divide into the correct type of T lymphocytes to kill the cell carrying the antigen

The secondary response often gets rid of the pathogen before you start to show any symptoms

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Maintaining immunity

Memory B and T lymphocytes only have a limited lifespan, which means that someone who is immune to a particular pathogen won’t always stay immune forever. Once all of the memory B and T lymphocytes have died, the person may be susceptible to attack by the pathogen again

Immunity can be maintained by being continually exposed to the pathogens - you continue to make more and more memory B and T lymphocytes

E.g. – people who live in malarial areas are constantly exposed to the malarial pathogen will build up a limited immunity to malaria                                                                                               If they move away from the malarial area, they’ll have no further exposure to the pathogen & may eventually lose the immunity they have                                                                                      If they then returned to the area, they would undergo a primary immune response when they encountered the malaria pathogen again 

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Active and passive immunity

Active immunity - when your immune system makes its own antibodies, after being stimulated by an antigen

Natural active immunity - where you become immune after catching a disease

Artificial active immunity - where you become immune after you’ve been given a vaccination, contains a harmless dose of antigen

Passive immunity - given antibodies made by a different organism, so your immune system doesn’t produce any antibodies of its own

Natural active immunity - baby becomes immune due to the antibodies it receives from its mother through the placenta & in breast milk

Artificial active immunity - become immune after being injected with antibodies from someone else

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If B lymphocytes are too busy dividing to build up their numbers to deal with a pathogens, so you end up suffering from the disease.

Vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing the disease, so you become immune without getting any symptoms. Antigens may be free or attached to a dead or attenuated pathogen

May be injected or taken orally – Disadvantages: could be broken down by enzymes in the gut & molecules of the vaccine may be too large to be absorbed into the blood

Booster vaccines are given later on to make sure that more memory cells are produced

If most people in a community are vaccinated, disease becomes extremely rare - Means that even if people who haven’t been vaccinated are unlikely to get the disease as there is no one to catch it from -> herd immunity

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Problems with developing vaccinations

Vaccinating against a disease isn’t always straightforward

For example:-

Some pathogens can change their surface antigens

Means that when you’re infected, the memory cells produced from the vaccination won't recognise the different antigens

The immune system has to start from scratch and carry out a primary response against these new antigens

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Problems with developing vaccinations - Influenza

Causes influenza (flu)

Proteins on the surface of the influenza virus act as antigens, triggering the immune system

These antigens can change regularly - forming new strains of the virus

Every year there are different strains of the virus so a different vaccine has to be made

Laboratories collect samples of these different strains & organisations test the effectiveness of different influenza vaccines - e.g. World Health Organisation (WHO)

New vaccines are developed every year - only the most effective against the recently circulating influenza viruses is chosen

Governments and health authorities then implement a programme of vaccination using the most suitable vaccine

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Sources of medication

Changing antigens also mean that some pathogens can rapidly develop resistance to drugs that are used against them

So scientists need to be constantly developing new drugs, to target resistance strains of pathogens as well as developing drugs for diseases that are currently incurable

Many medicinal drugs are manufactured using natural compounds found in plants, animals or microorganisms.

E.g. penicillin is obtained from a fungus - some cancer drugs are made using soil bacteria - daffodils are grown to produce a drug used to treat Alzheimer’s disease

Only a small proportion of organisms have been investigated so far, so it’s possible that plants or microorganisms exist that contain compounds that could be used to treat currently incurable diseases

Possible sources of drugs need to be protected by maintaining the biodiversity on Earth

If we don’t protect it, some species could die out before we get a chance to study them

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Parasitic disease caused by Plasmodium - single-celled parasites


Plasmodium parasites are transmitted by mosquitoes, mainly female Anopheles mosquitoes that carry the parasites

Mosquitoes are vectors - they don’t cause the disease themselves but spread infection by transferring parasites from 1 host to another

Mosquitoes transfer the plasmodium parasites into an animal’s blood when they feed on them

Infection - infect the liver cells and red blood cells & disrupt the blood supply to vital organs

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Malaria lifecycle

1) A person with malaria has the Plasmodium in their blood

2) When the Anopheles female mosquito sucks the blood, the Plasmodium develops in the mosquito and migrates to its salivary gland, where it causes infection of an uninfected person when bitten.

3) The Plasmodium migrates to the liver when a person is bitten

4) So that the parasitic stages can multiply in the liver then migrate into the blood, ready to be transmitted to someone else. 

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Malaria vaccine

Less common causes include - careless and unhygienic medical practices & using blood transfusions with unscreened blood & unsterilised needles

Best solution would be a vaccine but - plasmodium spends most of its life cycle hidden inside human cells & only exposed in the bloodstream for a very short period of time so it doesn’t give immune system long to recognise & destroy it - 4 different species because of mutation and variation, so each species has different antigens, different species will require different vaccines

Malaria is limited only to the areas where the Anopheles mosquito can survive currently only tropical areas

But with the effects of global warming becoming more apparent possible that the disease could spread further north

Mosquito nets are good for prevention - stops the mosquitoes infecting people

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Tuberculosis (TB)

Caused either by the bacterium Mycobacterium tuberculosis

Whilst TB can infect many parts of the body - it is usually found in the lungs

TB infects as much as 30% of the world’s population, but it is being inactive (or controlled by the immune system) in most people

It is spread by droplet infection - i.e. by sneezing - which expels hundreds of droplets containing the bacteria.

They also release droplets containing the liquid with bacterium in

As different strains become more resistant to the treatments - they became less effective, which causes the number to rise even more.

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TB causes

Conditions which make the spread of tuberculosis more likely include: Overcrowding in a house / Poor ventilation / Poor diet / Homelessness / Living or working with people who have migrated from areas of high TB-concentration

The disease can also be contracted from cattle milk and meat & has been largely eradicated in the developed world but still remains a common problem in the underdeveloped world

The number of infected people from TB have been increasing each year now for decades - the WHO declared it a public health emergency in 1993.

The disease is most common in south-eastern Asia and sub-Saharan Africa.

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HIV & AIDS transmission

Acquired Immunodeficiency Syndrome (AIDS) is a disease caused by Human Immunodeficiency Virus (HIV)

Transmission - via unprotected sexual intercourse or from mother to fetus through the placenta, breast milk or in childbirth or infected bodily fluids e.g. sharing needles, transfusion

It’s made up of genetic material, RNA, and some proteins, e.g. the enzyme reverse transcriptase.

The outer coating is Capsid (protein) and it has a lipid bilayer.

Doesn’t have the equipment to replicate on its own e.g. enzymes and ribosomes so it uses the host cells ability to do it instead.

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HIV & AIDS infection

The virus attaches to receptor on the cell membrane of the host cell

The capsid ‘uncoats’ and releases the RNA into the cytoplasm.

Reverse transcriptase makes a complementary strand of DNA from viral RNA strand

So the now double-stranded DNA can be inserted into the human DNA.

The host cell enzymes are used to make viral proteins from the viral DNA

Viral proteins are assembled into new viruses which bud from the cell and go onto infect other cells.

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HIV & AIDS treatment

Anti-HIV drugs is sometimes called combination therapy as people usually take at least three different drugs together

HIV treatment doesn’t cure HIV but reduces the amount of HIV to undetectable levels. With an undetectable amount, HIV is not able to damage your immune system

HIV treatment does not cure HIV, but it stops the virus from reproducing in your body

The drugs themselves contain inhibitors that inhibit the enzyme reverse transcriptase, to stop the virus infiltrating into the DNA of the host cells

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HIV & AIDS prevention

Main cause is unprotected sex, prevention is to use barrier contraceptives e.g. condoms

Screening blood donor volunteers, ensures that those who do not know they are HV-positive do not donate any bodily fluids & guarantees that HIV isn’t affecting those already weakened by other infections.

Not sharing hypothermic needles

Taking antiviral drugs during pregnancy, confirms that the baby will not have HIV when it is born if the mother is HIV-positive.

Stopping the stigma that comes along with HIV, allows more people to be open about their disease & encourages more people to be tested

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Global impact HIV, TB and Malaria

Most common in sub-Saharan Africa and other developing countries because of limited access to good healthcare: Drugs are not always available but people are less likely to be diagnosed/treated. Blood donations aren’t always screened for infectious diseases so surgical equipment isn’t always sterile.

Limited health education to inform people how to avoid certain diseases so fewer people know about the transmission of HIV can be prevented by safe-sex practises.Limited equipment to reduce the spread of infection e.g. people need mosquitoes nets to reduce the chance of infection. Overcrowded conditions increases the risk of TB infections by droplet transmission

Prevalence of these diseases slows down social and economic development as increases death rates and reduces productivity. Fewer people are able to work and can’t afford high healthcare costs.

Important to study global distributions of diseases, info can be used to find out where people are most at risk, important for research, allows organisations to provide aid where it’s needed most, data collected can be used to predict where epidemics are most likely to occur

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The hardening of arteries due to the formation of fibrous plaques (atheromas) in the arterial walls

Atheromas contains low density lipoproteins (LDL)

LDL contains mixture of protein + cholesterol, & its how cholesterol is transported around the body

Formation of an atheromas begins when damage occurs to the lining of an artery, allows LDL to enter & collect in the arterial walls

Build-up of LDL triggers an immune response so white blood cells also move into the area

Over time more white blood cells, lipids and connective tissue build up and harden to form a fibrous plaque at the site of damage -> the atheroma

Atheroma partially blocks the lumen of the artery, restricting blood flow

Cigarette smoke contains nicotine and carbon dioxide causes an increase in blood pressure

Increased blood pressure causes damage to arteries leading to the formation of more atheromas

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Coronary Heart Disease (CHD)

CHD is when coronary arteries have lots of atheromas in them which restricts blood flow to heart

Reduction in blood flow reduces the amount of oxygen an area of the heart gets and forces the heart to respire anaerobically causes pain (angina) or a heart attack

Smoking increases risk for 2 reasons:

Carbon monoxide in cigarette smoke irreversibly combines with haemoglobin reducing the amount of oxygen transported in the blood & reduces the amount of oxygen available to tissues, including the heart.                                                                                                                              Nicotine in cigarette smoke makes platelets sticky increasing the chance of blood clots forming, if clotting happens in the coronary arteries it could cause a heart attack. Presence of atheromas increases the risk of blood clots forming

CHD can be treated using a stent - are tube-like structures can be placed in obstructed arteries to increase the diameter of the artery and increase blood flow means more oxygen can reach the heart so the heart muscle can respire aerobically

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Rapid loss of brain function due to disruption in the blood supply to the brain can be caused by a blood clot in an artery leading to the brain, reduces the amount of blood and therefore oxygen that can reach the brain

Nicotine increases the risk of stroke, it increases the risk of clots forming

Carbon monoxide increases the risk of stroke, & reduces the amount of oxygen available to the brain by combining with haemoglobin

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Lung cancer

Cigarette smoke contains many carcinogens - chemicals that can cause a cell to become cancerous

Carcinogens may cause mutations in the DNA of lung cells and could lead to uncontrolled cell growth & formation of a malignant (cancerous) tumour

Malignant tumours grow uncontrollably, blocking air flow to areas of the lung decreasing gas exchange and leads to a shortness of breath, as the body is struggling to take in enough oxygen as tumour uses lots of nutrients and energy to grow

Causes weight loss

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Chronic Bronchitis

Type of chronic obstructive pulmonary disease (COPD) - group of diseases that involve permanent airflow reduction

Long-term inflammation of the mucous membrane lining the bronchi

Bronchi are lined with goblet cells which produce mucus to trap microorganisms & lined with cilia that ‘beat’ to move the mucus towards the throat so it can be removed

Tar in cigarette smoke damages the cilia causes the goblet cells to produce more mucus. Mucus accumulates in the lungs & causes increases coughing to try and remove the mucus

Microorganisms multiply in the mucus & cause lung infections that lead to inflammation, which decreases gas exchange

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Chronic lung disease involving the breakdown of the alveoli. It can be caused by smoking or lung-term exposure to air pollution

Type of COPD

Tar in cigarettes smoke causes a build-up of mucus which leads to infection and inflammation of the lungs. Inflammation attracts phagocytes to the area which produce an enzyme that breaks down the protein elastin - an elastic protein found in the walls of alveoli

Loss of elastin means the alveoli can’t recoil to expel air, it remains trapped in the alveoli. Leads to destruction of the alveoli walls and reduces the surface area of the alveoli

Loss of elastin and reduction in the surface area of the alveoli, reduces the rate of gas exchange in the alveoli so less oxygen is absorbed into the bloodstream and transported around the body. Lack of oxygen reaching the cells leaves sufferers feeling tired & weak (fatigued)

Other symptoms of emphysema include shortness of breath & wheezing

People with emphysema have an increased breathing rate as they try to increase the amount of air reaching their lungs

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Refers to the variety of living organisms in an area

Habitat diversity - the number of different habitats in an area - e.g. coastal area could contain many different habitats, beaches, sand dunes, mudflats, salt marshes etc.

Species diversity - the number of different species and the abundance of each species in an area - e.g. woodland areas contain many species of plants, insects, birds and mammals

Genetic diversity - variation of alleles within a species or a population of a species - e.g. human blood type is determined by a gene with 3 different alleles

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Collecting data on biodiversity

Choose an area to sample, to avoid bias the sample should be chosen at random, makes it more likely that your sample is representative of the population you’re sampling i.e. the sample shares as many characteristics as possible with the population

Record the number of different species or count the number of individuals of each species

For plants, use a quadrat                                                                                                       For ground insects, use pitfall trap - small pit insects fall in & can’t get out as its filled with water     For flying insects, use a sweepnet                                                                                         For aquatic animals, use a net

Repeat process & calculate the mean of your repeat results -> makes your estimate more reliable

The number of individuals for the whole area can then be estimated by taking an average of the data collected in each sample, multiplying it by the size of the whole area

When sampling different habitats & comparing them, always use the same sampling techniques

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Species richness & species evenness

Species richness - number of different species an area.                                                       Higher number of species, greater the species richness.                                                       Hi. Measured by taking random samples of a habitat, counting the number of different species

Species evenness - measure of the relative abundance of each species in an area.                  More similar the population size of each species, greater the species evenness                         Measured by taking random samples of a habitat, counting the number of individuals of each different species

The greater the species richness and evenness in an area, higher the biodiversity

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Simpson's Index of Diversity

Useful way of measuring species diversity

Formula: D = (1 – Ʃ (n/N)2

n = total number of organisms in one species

N = total number of all organisms

Always a value between 0 and 1

Closer the index is to 1, more diverse the habitat, greater its ability to cope with change

Low index values suggest habitat is more easily damaged by change, less stable

The greater the species richness and evenness, higher the value of Simpson’s Index

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Estimating global biodiversity

The total number of species on Earth, which includes named species (scientists have named between 1.5 and 1.75 million species - is not exact & no central database of all named species) and unnamed species (scientists agree a large population of the species on Earth haven’t been named - many are known but not discovered)

Estimates for global diversity ranges from 5 million and 100 million - most recent estimates are around 14 million

Why they have different ideas:-

Different scientist have different techniques to make their estimates                                       Relatively little is known about some groups of organisms, there could be more than we think e.g. bacteria and insects                                                                                                        Biodiversity differs in different areas of the world - greatest diversity is near equator, decreases nearer the poles, & tropical forests are largely unexplored could mean current estimates are too low Estimates of global diversity change as scientists find out new things - example of the tentative nature of scientific knowledge

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Climate change and global diversity - Part 1

Changing environmental conditions

Climate change will affect the environmental conditions in different areas in different ways, some places will get warmer, and others will get colder. These changes are likely to affect global diversity as most species need a particular climate to survive & a change may mean that an area that was inhabitable becomes uninhabitable & vice versa -> may cause and increase or decrease in biodiversity.                                                                                                                         May force some species to migrate to a suitable are causing a change in species distribution. Migrations usually decrease biodiversity in the areas they migrate, if there isn’t a suitable habitat to migrate, if it’s a plant, or if the change is too fast the species may become extinct, decreasing biodiversity

Causing the spread

Changing climate may also contribute to the spread of disease. One reason is that the ranges of some insects that carry disease might increase, i.e insects that can no longer live in their original habitat, move somewhere else taking the disease with them.                                             Change in distribution could lead to an increase in biodiversity -> spread of diseases could reduce biodiversity, with some species suffering population decline or even extinction.

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Climate change and global diversity - Part 2

Changing agricultural patterns

Changes in temp, rainfall, timing of seasons and frequency of flood & draught will affect patterns of agriculture, may also affect biodiversity. E.g. areas that were previously too hot or dry to support much biodiversity can be farmed, increasing the biodiversity in an area.

Different crops need different conditions, as the climates in an area changes so will the type of crops grown - could disrupt food chains -> some existing species may be left without a source of food & new food sources will be provided for other species could increase/decrease biodiversity in an area

Possible that extreme weather events & unexpected conditions like a flood, drought or change in the timing of the seasons might result in crop failure - Could disrupt food chains and decrease biodiversity.

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Importance of biodiversity - economic reasons

Many species of animals and plants are important to the global economy - products derived from plant and animal species are traded on a local & global scale

Food and drink - plants & animals are the source of many food & some drinks

Clothing - many fibres and fabrics are made from plants & animals, e.g. cotton from plants and leather animals

Drugs - many are made of compounds from plants, e.g. painkiller morphine is made from poppies

Fuels - use a number of organisms to produce renewable fuels - fossil fuels are non-renewable so other sources are of major economic importance

Other industrial materials - huge variety of materials are produced from plant & animal species

Important to conserve all organisms we currently use to make products as well as those we don’t currently use - they may provide us with new products in the future e.g. new drugs for diseases we can’t yet cure

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Importance of biodiversity - ecological reasons

Maintaining biodiversity are all down to the complex relationships between organisms and their environments

Disruptions of food chains - some species of bear feed on salmon which feed on herring - if number of herring decline, it can affect both the salmon and bear populations

Disruption of nutrient cycles - decomposers like worms improve the quality of soil by recycling nutrients - if worm numbers decline, soil quality will be affected which will affect the growth of plants and the amount of food available to animals

Loss of habitats - hedgerows are wildlife corridors enable organisms to move between habitats safely - they’re removed species can become isolated & availability of food and nesting sites will be reduced

Climate change - C02 is stored in trees and bogs, so the destruction of forests and peat bogs contributes to climate change

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Importance of biodiversity - ethical & aesthetic r

Ethical reasons

Some believe that we should conserve species – as it’s the right thing to do

Many believe organisms have the right to exist – shouldn’t become extinct due to as a result of human activities

Some think we have a moral responsibility – to conserve biodiversity for future human relations

Spiritual and religious reasons for conservation - harmony with natural world is important to many beliefs

Aesthetic reasons

Others believe we should conserve biodiversity, brings joy to millions of people

Areas rich in biodiversity provide an attractive environment that people can enjoy, more biodiversity, more visitors the area is likely to attract 

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Importance of biodiversity - agricultural reasons

Pollinators – Many fruit & veg crops are pollinated by insects like bees & butterflies = higher the diversity of insects; more pollinators there are

Protection against disease – Majority of our food comes from only a few species of plants = if a disease/pest affects these few, the supply is at risk - the more crop varieties there are; the less chance there is that all the crops will be

Source of food – many species are used as food sources for humans and livestock = more different species there are; the more possible sources there are to choose from

New varieties – Plant varieties are needed for cross-breeding = wild plants can be bred with domesticated plants to produce new varieties with improved characteristics - new varieties of crops can be bred to cope with climate change -> more varieties of crop there are; the more characteristics there are to choose from

Pest control - Number of animals like frogs, birds and hedgehogs are natural predators of crop pests like slugs = more of these organisms there are; the less pests there will be

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Types of conservation - In situ

In situ conservation means conservation on site - protecting species in their natural habitat


Establishing protected areas like national parks & nature reserves = habitats and species are protected by restricting urban development, industrial development and farming

Controlling or preventing the introduction of species that threaten local diversity - control some species in certain areas away from predators or areas of high food competition

Protecting habitats - e.g. controlling water levels to conserve wetlands or coppicing (trimming trees) to conserve woodlands, allows organisms to continue living in their natural habitats

Restoring damaged areas - such as coastline polluted by an oil spill

Promoting particular species - could be by protecting food sources or nesting sites

Giving legal protection to endangered species - e.g. making it illegal to kill them

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In situ conservation advantages & disadvantages


Often both species and their habitat are conserved - means that larger populations can be protected

Less disruptive than removing organisms from their habitats

Chances of the population recovering are greater than ex situ methods


Can be difficult to control some factors that are threatening a species, such as – poaching / predators / climate changes

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Ex situ conservation

Ex situ conservation means off site - involves protecting a species by removing part of the population from a threatened habitat and placing it in a new location = often a last resort


Relocating an organisms to a safer place

Breeding organisms in captivity then reintroduced them to the wild when they are strong enough - breeding is carried out in animal sanctuaries and zoos

Botanic gardens are controlled environments used to grow a variety of rare plants

Seed banks - seeds can be frozen and stored in seed banks for over a century without losing their fertility, provides a useful source of seeds if natural reserves are destroyed

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Ex situ conservation advantages & disadvantages


Things like predation and hunting can be managed more easily

Competition for resources can be reduced

Possible to check the health & treat animals for diseases

Can be used to reintroduce species that have left an area


Difficult & expensive to create and sustain the right environment

Less successful than in situ

Many species can’t breed successfully in captivity

Don’t adapt to their new environment when moved to a new location

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Environmental Impact Assessment (EIAs)

An assessment of the impact a development might have on the environment such as building a new shopping centre or power station

Involves estimating biodiversity on the project site & evaluating how the development might affect biodiversity

Identifies ways that biodiversity could be conserved

Studies any threatened or endangered species on the project site and the laws relating to their conservation - is used to decide on planning stipulations

Measures that will have to be implemented if the project proceeds e.g. might involve relocating or protecting endangered species

Local authorities are often under pressure from conservationists who argue that developments damage the environment and disturb wildlife and feel that habitats should be left alone

EIA’s ensure that decision makers consider the environmental impact of development projects & are used by local authorities to decide if and how projects will proceed

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Conservation and international cooperation

Conservation is much more likely to be successful when countries work together, e.g. some endangered species are found in lots of countries, it would be pointless making hunting a species illegal in one country if poachers just go and hunt them in another country

Information about threats to biodiversity needs to be shared and countries need to decide on conservation methods and implement them together

Rio Convention on Biodiversity - an international agreement that aims to develop international strategies on the conservation of biodiversity & how to use animal and plant resources in a sustainable way -> convention made it part of international law that conserving biodiversity is everyone’s responsibility & it provides guidance to governments on how to conserve biodiversity

CITES Agreement - convention on International Trade in Endangered Species -> an agreement designed to increase international cooperation in regulating trade in wild animals & plant specimens – it helped conserve species by limiting trade through licensing & by making it illegal to trade in products made from endangered animals such as rhino ivory & leopard skins. Member countries all agreed to make it illegal to kill endangered species 

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Act of arranging organisms into groups based on their similarities and differences, which makes it easier for scientists to identify them and to study them

Taxonomy – the study of classification -> all involve placing organisms into groups

In a taxonomic hierarchy - 8 levels of groups (taxonomic groups) – Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Further down the hierarchy you go - more groups at each level, but fewer organisms in each group

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Naming systems

Nomenclature - naming system used for classification is called the binomial system

All organisms are given one internationally accepted scientific name in Latin that has 2 parts – 1st the name is the genus and has a capital letter & 2nd is the species and is all in lowercase

Binomial system helps to avoid the confusion of using common names, e.g. Americans called a type of bird a cockatoos but Australians call them flaming galahs

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The 5 kingdoms

Prokaryotae - Prokaryotic, unicellular (single-celled), no nucleus, less than 5 um, e.g. bacteria

Protoctista - Eukaryotic cells, usually live in water, single celled or simple multicellular organisms, e.g. algae

Fungi - Eukaryotic, chitin cell wall, saprotrophic (secrete extracellular enzymes to digest dead/decaying organisms), reproduce using spores, e.g. moulds & yeast

Plantae - Eukaryotic, multicellular, cell walls made of cellulose, photosynthesise, contains chlorophyll, autotrophic (produce their own food), e.g. mosses & ferns

Animalia - Eukaryotic, multicellular, no cell walls, heterotrophic & consume plants and animals, e.g. mammals & fish

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Study of evolutionary history of groups of organisms tells us who is related to who & how closely they are related

All organisms have evolved from shared common ancestors, closely related species separated away from each other most recently

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Evidence for classification

Molecular evidence - gathering molecular evidence involves analysing the similarities in proteins and DNA = more closely related organisms will have more similar molecules can compare things from different organisms like: How DNA is stored & sequence of DNA bases & sequence of amino acids

Embryological evidence - involves looking at the similarities in the early stages of an organism’s development, e.g. fish and salamander embryos are more similar than salamander & turtles, which suggests salamanders are more closely related to fish than to turtles

Fossil record - provides evidence of how organisms evolved from one another and how closely related they are, e.g. fossils of Archaeopteryx, a reptile with feathers that enabled it to fly provides evidence that birds evolved from dinosaurs

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5 kingdoms vs 3 domains

1990, 3 domains were proposed (large super kingdoms)

Organisms with cells that contains a nucleus -> Domain = Eukarya

Unicellular organelles without a nucleus were in the Prokaryotae kingdom – but this kingdom is split into 2 domains – Bacteria & Archaea

The Prokaryotae were reclassified due to new evidence that showed large difference between the Archaea and Bacteria

Molecular evidence: enzyme RNA polymerase (needed to make RNA) is different in Bacteria and Archaea, + Archaea have similar histones to Eukarya but not Bacteria

Cellular evidence: bonds of lipids in cell membrane of Bacteria/Archaea are different, + development & composition of flagellae in Bacteria & Archaea are different

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Dichotomous keys

Used to identify organisms and provides a way to identify organisms based on observable features, e.g. colour, types of leaves

Consists of a series of questions:

  • Each with only 2 possible answers
  • Each answer leads to the name of the organism or another question
  • Until the organism is identified
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The differences that exist between individuals

Every individual organism is unique - even clones show some variation

It can occur:

Within species - variation within species is called intraspecific variation = variation normally occurs in characteristics

Between species - variation between different species is called interspecific variation

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Continuous variation

When the individual in a population vary within a range - no distinct categories or gaps between them

For example:

Animals – height = humans can be any height within a range e.g. 139 cm not just tall or short                      – milk yields = cows can produce any volume of milk within a range

Plants – number of leaves = a tree can have any number of leaves within a range                                        mass = the mass of seeds from a flower head varies within a range

Microorganisms – width = the width of E. coli bacteria varies within a range                                                           – length = the length of the flagellum can vary within a range

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Discontinuous variation

When there are two or more distinct categories - each individual falls into only one of these categories = no intermediates

For example:-

Animals – sex = humans can be either male or female                                                                                blood group = humans can be group: A, B, AB & O

Plants – colour = courgettes are either yellow, dark green or light green                                                      seed shape = some pea plants have smooth seeds, others have winkled seeds

Microorganisms – antibiotic resistance = bacteria are either resistant or not                                                               pigment production = olny some types of bacteria can produce coloured pigment

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Causes of variation

Genetic variation - different species have different genes -> individuals of the same species have the same gene but have different versions of them called alleles. The alleles an organism has make up its genotype - differences in genotype result in variation in phenotype. Phenotype (characteristics) inherit genes from parents, which means that variation caused by genetic factors is inherited

Environmental factors- variation can be caused by differences in the environment, e.g. climate, food, lifestyle = characteristics controlled by environmental factors can change over an organisms life. Only affected by environmental factors, e.g. accents & pierced ears

Both genetic and environmental factors - genetic factors determine the characteristics an organism’s born with & environmental factors can influence how some characteristics develop                     E.g. height = genes determine how tall an organism can grow                                                 E.g. tall parents tend to have tall children but diet/nutrition affect how tall it actually grows

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