AS Biology: Edexcel - Unit 1: lifestyle, Transport, Genes and Health

In multicellular organisms, diffusion across the outer membrane would be too slow because of the large distance the substances would have to travel to reach all the cells. They need glucose and oxygen for aerobic respiration for energy.

• A lot of important substances in biological reactions are ionic. (one +ion and one -ion)

• Because water is dipolar, the positive end of a water molecule will be attracted to the negative ion, and the negative end of a water molecule will be attracted to the positive ion.

• Ths means the ions will get totally surrounded by water molecules - they'll disolve.

• So water's dipole nature makes it useful as a solvent for other polar molecules.

Ateries

Thick-walled, muscular and have elastic tissue in the walls to cope with the high pressure caused by the heart beat. The inner lining (endothelium) is folded, allowing the artery to expand - high pressure.

Vein

Wider than equivalent arteries, very little elastic or muscle tissue. Contain valves to stop the blood flowing backwards- low pressure. Blood flow through veins is helped by contraction of the body muscles surrounding them.

Capillaries

Only one cell thick- speeds up diffusion. Networks of capillaries in tissue - increase surface area.

Ventricular diastole, atrial systole:

Ventricles - relaxed. Atria - Contract. SL valves - closed. AV valves - open.

Ventricular systole, atrial diastole:

Atria - Relaxed. Ventricles - Contract. SL valves - open.. AV valves - closed. Blood leaves via pulmonary artery and aorta.

Ventricular diastole, atrial diastole:

Ventricles - relaxed. Atria - relaxed. SL valves - closed. AV valves - open. Blood re-enters via vena cava and pulmonary vein.

• The left ventricles of the heart has thicker, more muscular walls than the right ventricle, because it needs to contract powerfully to pump blood all the way round the body. Th right side only needs to get blood to the lngs which are nearby.

• The ventricles have thicker walls than the atria, because they have to push blood out of the heart whereas the atria just need to push blood a short disrance into the ventricles.

• The atrioventricular (AV) valves link the atria to the ventricles and stop blood flowing back into the atria when the ventricles contract.

• The semi-lunar (SL) valves link the ventricles to the pulmonary artery and aorta, and stop blood flowing back into the heart after the ventricles contract.

Lifestyle factors

• Diet - high in saturated fat. High in salt.

• High blood pressure

• Smoking

• Inactivity

Factors beyond your control

• Genetics

• Age

• Gender

Describe the data -

Increases as increases Increases as decreases Decreases as increases Decreases as decreases

Draw conclusions -

Positive correlation / negative correlation

Check any conclusions are valid -

Be careful that any conclusions match the data

• Sample size : Greater sample size - more reliable the results.

• Variables : more variables controlled - more reliable the results.

• Data collection : the less bias - the more reliable the results.

• Controls : presence of controls increases the reliability of the result.

• Repitition by other scientists : more repititions - more reliable result.

• Risk can be defined as the chance of somthing unfavourable happening.

• People's perception of risk may be very different from the actual risk: People may overestimate the risk - media can make this worse. Some people may underestimate the risk - due to lack of information.

Weight Gain :- If energy in take is higher than energy output, the excess energy will be truned into fat reserves by the body, so the person will gain weight.

Weight loss:- If energy in take is lower than energy output, the body will have to get more energy from somewhere. It'll turn some of its fat reserves into energy.

Monosaccharides:

• Carbohydrates are made from monosaccharides.
• Glucose is a monosaccharides with six carbon atoms in each molecule.
• Structure makes it solube - easily transportable. chemical bonds - lots of energy.

Diaccharides: Two monosaccharides joined together.

• Glycosidic bond - condensation reaction to join - hydrolysis reaction to break.
• Maltose - Glucose + Glucose - 1-4 glycosidic bond.
• Lactose - Glucose + Galactose - 1-4 glycosidic bond.
• Sucrose - Glucose + fructose - 1-2 glycosidic bond.

Polysaccharides: More than two monosaccharides

• Amylose - lots of Glucose - 1-4 glycosidic bonds
• Amylopectin - lots of Glucose - 1-4 and 1-6 glycosidic bonds - side branches.
• Glycogen - Glucose - 1-4 and 1-6 glycosidic bonds - more side branches

• Triglycerides are formed by condensation reactions and broken up by hydrolysis reactions.

• Three fatty acids and a single glycerol molecule are joined together by ester bonds.

• Monosaccharides are joined together by glycosidic bonds in condensation reactions to form diasaccharides and polysaccharides.

• Disaccharides and Polysaccharides are broken apart by a hydrolysis reaction back into monosaccharides.

HDLs (high densitiy lipoproteins)

• They are mainly protein.
• They transport cholesterol from body tissues to the liver where it's recycled or excreted.
• Their function is to reduce total blood cholesterol when the level is too high.

LDLs (low densitiy lipoproteins)

• They are mainly lipid.
• Tehy transport cholesterol from the liver to the blood where it circulates untill needed by cells.
• Their function is to increase total blood cholesterol when the level is too low.

High total blood cholesterol level and high LDL level have both been linked to an increased risk of CVD.

1) Make up range of different concentrations of caffeine solutions and a control solution with no caffeine at all. 2) Transfer one Daphnia into the dimple on a cavity slide. 3) Place the slide onto the stage of a light mcroscope and focus it on the beating heart of the Daphnia. 4) Place a small drop of caffeine solution onto the Daphnia. 5) Count the number of heartbeats in 10 sec and multiply this by six for beats per min. 6) Repeat this 10 times using the same concentration but different Daphnia. 7) Don't forget to keep all other factors constant. 8) Repeat the experiment using the other concentrations. 9) Compare the results to see how caffeine concentration affects heart rate

Heart Rate increases as caffeine concentration increases.

• They can't give consent.

• Some people think its more acceptable on invertebrates as thay are simpler organisms - less sophisticated nervous system.

• Some people believe it's unethical to cause distrass or suffering to any living organism.

First you need to make a calibration curve:

1) Make up several vitamin C solutions of different known concentratons. 2) Measure out a set volume of DCPIP (blue dye - colourless in vitamin C) into a test tube. 3) Add one of the vitamin C solutions to the DCPIP, drop by drop, using a pipette. 4) Gently shake the test tube for a set length of time after each drop of vitamin C solution is added. 5) When the solution turns colourless, record the volume of vitamin C solution that has been added. 6) Repeat the experiment twice more, with the same solution and take and average of the three readings. 7) Make sure you keep all the other variables constant during the experiment. 8) Repeat the above procedure with each solution. 9) Use the results to make a line graphn, showing volume of vitamin C solution against its concentration - this is the calibration curve. Then you can test the unknown solution in the same way as the known concentrations and use the graph to finds its concentration.

Antihypertensives - Reduce High Blood Pressure

Benefits

• They reduce blood pressure, so there's less chance of damage occurring to the walls of the arteries. This reduces the risk of atheromas forming and blood clots developing.
• Different types work indifferent ways, so they can be given in cobination.
• Blood pressure can be monitored at home, so they can be given in combination.

Risks

• Palapitations (rapid beating of the heart)
• Abnormal heart rhyms
• Fainting, headaches and drowsiness
• Allergic reactions
• Depression

Plant Satins - reduce cholesterol in the blood.

Benifits

Statins reduce the risk of developing CVD.

Risks

They can reduce the absorbtion of some vitamins from the gut.

Anticoagutants - Reduces the formation of blood clots.

Benifits

• Prevent any existing blood clots from growing any larger.
• Prevent any new blood clots from forming.

Risks

• If the patient is badly injured the reduction in blood clotting can cause excessive bleeding, which can lead to fainting or death.
• Allergic reactions.
• Osteoporsis (weakened bones)
• Swelling of the tissues
• Can damage the fetus if taken during pregnacy.

Platelet inhibitory Drugs - Reduce formation of Blood clots.

Benefits

• Can be used to treat people who already have blood clots or CVD.

Risks

• Rashes
• Diarrhoea
• Nausea
• Liver function problems
• Excessive bleeding after injury.

Gases diffuse across a surface called the gas exchage surface.

Features that insrease the rate of diffusion:

• Large surface area
• Thin - short diffusion pathway
• Steep concentration gradient

The mammalian lungs have the following features which all help to increase the rate of gas exchange:

• Many alveoli provide a large surface area for diffusion to occur across.

• The alveolar epitheluim and capillaret endothelium are each only one cell thick, giving a short diffusion pathway.

• All the alveoli have good blood supply from capillaries - they constantly take away oxygen and bring more carbon dioxide, maintaining the concnetration gradient.

• Breathng in and ot refreshes the air in the alveoli, keeping the concnetration gradients high.

Cell Membranes - Fluid mosaic structure.

They contain:

• Phospholipid bilayer - fluid (constantly moving)
• Protein molecules are scattered through the bilayer, like a mosaic.
• Some proteins have a polysaccharide (carbohydrate) chain attached - these are called glycoprotein.
• Some lipids also have a polysaccharide chain attached - glycolipids.
• Cholesterol - between phospholipids - makes membrane rigid.

How to investigate how temperature affects beetroot membrane permeability:

• Cut five equal sized pieces of beetroot and finse them to remove any pigment released during cutting.
• Place the five pieces in five different test tubes, each with 5cm3 of water.
• Place each test tube in a water bath at a different temperature, for the same length of time.
• Remove the pieces of beetroot from the tubes, leaving just the coloured liquid.
• Now you need to use a colourimeter - a machine that passes light through the liquid and measures how much of that light is absorbed. The higher the absorbance, the more pigment released, so the higher the permeability of the membrane.

Increasing the temperature increases membrane permeability.

Increasing the Alcohol concentration Increases membrane permeabitity.

Osmosis is the diffusion of water molecules across a partally permeable membrane, from an area of higher concentration to an area of lower concentration.

Water molecules will diffuse bothe ways through the membrane, but the net movement of water molecules.

Passive Transport

Diffusion - the net movement of particles from an area of higher concentration to an area lower concentration. Passive process - no energy is needed.

Facilitated Diffusion - Larger molecules and charged atoms diffus throgh carrier proteins or channel proteins in the cell membrane. Passive process - no energy is needed.

Active transport - uses energy to move molecules and ions across the cell membranes, against a concentration gradient. Attaches to carrier protein. Energy from ATP.

Endocytosis - If too large to be taken into a cell by carrier proteins. Instead surround by a section of cell membrane.Membrane then pinches off to form a vesicle inside the cell.

Exocytosis - substances produced by the cell can be released by this method.The vesicle containing the substance fuse with the cell membrane and release their contents outside the cell.

Mononucleotides

Phosphate - sugar - Base.

RNA and DNA

• DNA and RNA are polynucletides - lots of mononlucleotides joined together.
• The sugar in DNA is deoxyribose and in RNA its ribose sugar.
• In DNA there are four bases - adenine (A), thymine (T), cytosine (S) and guanine (G). In RNA, uracil (U) replaces thymine (T).
• The mononucleotides are joined through condensation reactions between the phosphate of one mononucleotides and the sugar group of another.
• Two complementary DNA strands join together by hydrogen bonding between the bases.
• Adenine always pairs with thymine (A-T) and guanine aways pairs with cytosine (G-C).
• The two DNA strands wind up to form the DNA double-helix.

• Hydrogen bonds between the two DNA strans in a gene break, separating the strands, and the DNA molecule uncoils at that point.

• One of the strands is then sed as a template to make and RNA copy (mRNA).

• Free RNA mononucleotides line up alongside the template strand. Once the RNA mononucleotides have paired up with their complementary bases on the DNA strand they're joined together, forming an mRNA molecule.

• The mRNA moves out of the nucleus through a nuclear pore, and attaches to a ribosome in the cytoplasm. DNA re-forms.

• The mRNA attches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome.

• tRNA molecules attach themselves to the mRNA by complementary base pairing.

• The two amino acids attached to the tRNA molecules are joined together by a peptidebond.

• The tRNA molecules move away.

• The chain is ended when there's a stop signal on the mRNA molecules.

• The polypeptide chain moves away form the ribosome and translation is complete.

A gene is a sequence of bases that codes for the sequence of amino acids in a protein.

• Polypeptide chains (proteins) are made from amino acids.

• Different proteins have a different number and order of amino acids.

• It is the order of monomucleotide bases in a gene that determines the order of amino acids in a particular protein.

• Each amino acids coded for by a sequence of three bases in a gene.

• Different seqences of bases cade for different amino acids.

• Some amino acids are coded for by more than one triplet.

• Other triplets are used to tell the cell when to start and stop production of the polypeptide chain - these are called start and stop signals.

Induced Fit

The subsrate 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 as well.

Specificity

• Enzymes are very specific - they usually only catalyse one reaction.
• This is because only one substrate will fit into the active site.
• The active site's shape is determined by the enzyme's 3D struture.
• Each different enzyme has a different 3D struture and so a different shaped active site.
• If the substrate doesn't match the active site, the reaction won't be catalysed.
• If the 3D struture of a protein is altered in any way, the shape of the active site will change. This means the substrate won't fit into the active site and the enzyme will no longer be able to carry out its function.

• The DNA helix unzips to form two single strands. Each single strand acts as a template for a new strand.
• Free-floating monomucleotides join to each original template strand by complementary base pairing - A with T, G with C.
• The mononucleotides on the new strand are joined together by enzyme DNA polymerase. Hydrogen bonds form between the bases on the original and new strand.
• Each new DNA molecule contains one strand from the original DNA molecule and one new strand.

Mutations are changes to the base sequence of DNA.

Types of Errors

• Substitution - one base is substitued with another.
• Deletion - one base is deleted.
• Insertion - an extra base is added.
• Duplication - one or more bases are repeated.
• Inversion - a sequence of bases is reversed.

Cystic fibrosis is a genetic disorder caused by a mutation in a gene. The protein the gene codes for is important for mucus production.

Gene - A sequence of bases on a DNA molecule that codes for a protein, which results in a characteristic.

Allele - A different version of a gene.

Genotype - The alleles a person has.

Phenotype - The characteristics the alleles produce.

Dominant - An allele whose characteristic appears in the phenotype even when there's only one copy.

Recessive - An allele whose charateristics only appears in the phenotype if two copies are present.

Homozygote - An organism that carries two copies of the same allele.

Heterozygote - An organism that carriers two different alleles.

• The cilia are unable to move the mucus towards the troat because it is so thick and sticky.

• This means the mucus builds up in the airways.

• Some airways can become completely blocked by mucus - gas exchange can't take place in area below the blockage.

• This means that the surface area available for gas exchange is reduced, causing breathing difficulties.

• Sufferers are also more prone to lung in fections as mucus containing microorganisms can't be removed.

• The tube that connects the pancreas to the small intestine can become blocked with mucus - preventing digestive enzymes produced by the pancreas form reaching the small in testine. this reduces the sufferers ability to digest food and so fewer nutrients can be absorbed.

• The mucus can cause cysts to form in the pancreas. These inhibit the production of enzymes, which also reduces the ability to digest food and absorb nutrients.

• The mucus lining the small intestine is abnormally thick - this inhibit the absorption of nutrients.

In men, the tubes connecting the testicles to the penis are absent in some sufferes and can become blocked by thinck mucus in others. This means that any sperm produced can't reach the penis.

In women, thickened cervical mucus can prevent the sperm from reaching the egg. The sperm has to travel through this mucus to reach the egg - thick mucus reduces the motility of the sperm, reducing it's chances of making it to the egg.

Gene therapy involves altering the alleles inside cells to cure genetic disorders.

Somatic theraphy - this involves changing the alleles in body cells.

Germ line therapy - this involves changing the allels in the sex cells.

• Carrier testing is offered to individuals with a family history of genetic disorders.
• It shows whether people without a disorder carry an allele that can cause a disorder.
• Couples can be tested before having children to determine the chances of any future children having the disorder.
• Carrier testing allows people to make informed decisions about things like whether to have children and whether to carry out prenatal testing if the woman is pregnant.

Social and Ethical issues:

• Finding out you're a carrier may cause emotional stress.
• The tests aren't always 100% accurate.
• There are concerns thath the results of genetic tests could be used by emplors or life insurance companies.

PGD is carried out on embroyos produced by IVF. It involves screening embryos for genetic disorders before they're implanted into the woman. This aviods the issue of abortion.

Social and Ethical issues:

• It can be used to find out other characteristics - leading to concerns of designer babies.
• False results could provide incorrect information.

Prenatal tests involve screening unborn babies for genetic disorders.

Amniocentesis

Carried out at 15 - 16 weeks. Sample of amniotic fluid is obtained using a very fine needle. This fluid contains fetal cells. The cells contain DNA, which can be analysed.

Chorionic villus sampling (CVS)

This is carried out at 8 - 12 weeks. A sample of cells is taken from the chorionic villi (cord) using a fine needle or a catheter. The cells contain fetal DNA, which can be analysed.

Social and Ethical issues:

• Prenatal tests slightly increase the risk of miscarriage (by 1%)
• Fasle results could provide incorrect information.
• Some people consider it unethical to abort a fetus because it has a genetic disorder.