Edexcel AS Biology Unit 1 Exam Revision Notes
Explain the importance of water as a solvent in transport, including its dipole nature •
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!ess dense as a solid" Arctic solid" Arctic ecosystems float, ice insulates water beneath it etc.
#igh Specific #eat $apacity$apacity- Cells do not heat up or cool down easily, therefore can hold a fairly stable temp.
%resent naturally in all three states" Allows states" Allows the water cycle to function.
&ransparent - Allows photosynthesis underwater Cohesion - Generates surface tension, capillary uptake, transpiration etc.
'ood solvent" Essential solvent" Essential role in t ransport in biological systems.
(mmisci)le with hydropho)ic moleculesmolecules- Allows membranes to form and, therefore, control movement in / out of cells.
#igh latent heat of evaporation" Evaporation evaporation" Evaporation of water has a strong cooling effect and comparatively little water water is reuired to lose a lot of heat.
Buffer - !ater is capable of accepting and donating protons. "herefore acts as a buffer.
!ater !ater is a polar polar covale covalent nt compou compound. nd. #ue #ue to differenc difference e in electro-n electro-negat egativit ivities ies of of o$ygen and hydrogen, one end of the water molecule bears a slight negative charge, while the other end bears a slight positive charge. "his is called the dipolar nature of water. "he polar nature of water molecule makes it a good solvent.
*istinguish )etween monosaccharides, disaccharides and polysaccharides +glycogen and starch amylose and amylopectin- and relate their structures to their roles in providing and storing energy +."glucose and cellulose are not re/uired in this topic-
Glycogen structure and function Glycogen consists of a %&' glucose (oined by ), * and ), + glycosidic bonds. Glycogen has lots of branches which allows uick access to glucose. Also its a very compact molecule so its good for storage and is insoluble, so no osmotic effect and does not diffuse out of cells also can easily be hydrolysed by enymes into glucose and used for respiration. tarch structure and function tarch is a mi$ture of two polysaccharides of alpha- glucose- amylose and amylopectin. Amylose is straight chain of glucose (oined together with ),* glycosidic bonds. "he angles of the glycosidic bonds give it a coiled structure. "his makes it compact, so its really good for storage because you can fit more glucose into a small space in a cell. Amylopectin is a long branched chain of glucose (oined together by ),* and ),+ glycosidic bonds. ts side branches allow the enymes that break down the molecule to get at the glycosidic bonds easily. "his means that the glucose can be released uickly. tarch is insoluble, so no osmotic effect. *escri)e how monosaccharides 0oin to form disaccharides +sucrose, lactose and maltose- and polysaccharides +glycogen and amylose- through condensation reactions forming glycosidic )onds, and how these can )e split through hydrolysis reactions 'lucose 'alactose """""" !actose
'lucose 'lucose """"""" 2altose
'lucose
3ructose """"""" Sucrose
*escri)e the synthesis of a triglyceride )y the formation of ester )onds during condensation reactions )etween glycerol and three fatty acids and recognise differences )etween saturated and unsaturated lipids "riglycerides are the most common form of lipids. t consists of ) glycerol molecule and three fatty acid chains. "he 01 groups of glycerol and the -C001 group of each fatty acid are linked by an ester bond formed by condensation reactions.
aturated lipids dont have any double bonds between the carbon atoms in their hydrocarbon tail. 2nsaturated lipids do have double bonds between the carbon atoms in their hydrocarbon tails. "hese double bonds cause the chain to kink.
Explain why many animals have a heart and circulation +mass transport to overcome limitations of diffusion in meeting the re/uirements of organisms- -
"he heart is needed to pump blood around the body
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3any animals have a small surface area to volume ratio and many animals have a high metabolic rate.
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A circulatory system is needed to overcome limitations of diffusion.
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"he mass transport system in the circulatory stem carry raw materials from specialised e$change organs to the body cells, and to remove metabolic waste.
*escri)e the cardiac cycle +atrial systole, ventricular systole and di astole- and relate the structure and operation of the mammalian heart to its function, i ncluding the ma0or )lood vessels Atrial systole 4ressure in the atria increases as they fill with blood returning from the veins. ncreased pressure opens the atrioventricular valaves allowing blood to enter the ventricles. "he atria contract to force remaning blood into ventricles. 4entricular systole 5entricles contract from the base up, increasing the pressure and closing the atriventricular valaves. "he semilunar vales open and blood is forced into the ateries *iastole As the atria and ventricles rela$, pressure falls. n the ventricle, this causes closure of the semilunar valves. n the atria blood is drawn into the heart from the veins. &he structure and operation of the mammalian heart "he cavity of the heart is divided into four chambers. "he two upper chambers are thin walled atria. "here receive blood into the heart "he two lower chambers are thick walled ventricles. "he ventricles pump blood out of t he heart, with the muscular wall of the left ventricle much thicker than that of the right ventricle. Also the walls of the heart muscle are supplied with o$ygenated blood via coronary arteries.
"he atrio-ventricular valves are large valves, positioned to prevent backflow from the ventricles to atria. "he edges of these valves are supported by tendons anchored to the muscle walls of the ventricles below. "he valves on the right hand side are called the tricuspid valve and the valve on the left side is called the bicuspid valve or mitral valve. emilunar valves separate the ventricles from pulmonary artery and aorta.
Explain how the structures of )lood vessels +capillaries, arteries and veins- relate to their functions Artery
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Arteries carry blood from the heart to the rest of the body. "heyre thick-walled, muscular and have elastic tissue in the walls to cope with the high blood pressure caused by the heartbeat. "he inner lining %endothelium' is folded, allowing the artery to e$pand, this also helps it to cope with high blood pressure. 4eins
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5eins carry low-pressure blood towards the heart. 5eins contain valves to stop blood flowing backwards. 5eins have thinner muscles connective layer which carry blood with o$ygen to the lungs.
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!ide lumen offers less resistance to blood flow. $apillaries
Capillary walls are only one cell thick, which speeds up diffusion of substances e.g. glucose and o$ygen into and out of cells. "here are networks of capillaries in t issues called capillary beds, which increase the surface area for e$change. Blood $lotting 3ormation ). 4latelets are activated by substances released by the damaged artery wall. 6. 4latelets become sticky and form a platelet plug on the surface of the atheroma. 7. 4latelets release a clotting factor called thromboplastin. *. n the presence of calcium ions and vitamin 8, thromboplastin converts inactive prothrombin into active thrombin. 9. "his in turn converts the soluble fibrinogen into insoluble fibrin, which forms a network of fibres, trapping cells and debris to make a clot.
Atherosclerosis 3ormation ). Atherosclerosis is a disease in which the wall of arteries becomes furred up with fatty deposits called plaues or atheromas. 6. "here is damage to the endothelial lining of the artery. "his could be due to high blood pressure. "his is then an inflammatory response, and white blood cells move into the artery wall. 7. Cholesterol then builds up, and this leads to the formation of an atheroma. *. :e$t calcium salts and fibres also begin to build up, this results in a hard swelling called a plaue being formed. 9. "he artery then becomes narrower. "his then increases the blood pressure in the artery even more, making it more likely that the whole process will happen again.
3actors that increase the ris5 of $4* 'enetic6 ome alleles give you less protection from / greater risk of developing atherosclerosis. "o an e$tent, a higher chance of getting atherosclerosis does run in families. *iet; 1igh in saturated fats increases blood cholesterol level leads to atheroma formation, which leads to blood clots and therefore heart attacks or stroke.
Age6 Atherosclerosis occurs naturally as arteries become less elastic with age. Also more likely of getting C5# as you get older. 'ender ; ncidence is much higher for men than women. As women tend to have less stressful (obs and be at home more so less hypertension. #igh Blood %ressure6 increases risk of damage to the artery walls, which increases risk of atheroma formation leads to C5#. Smo5ing6 Chemicals damage endothelium triggering atherosclerosis. (nactivity6 E$ercise can reduce the risk of developing C1# and reduces blood pressure Benefits and Ris5s of treatment for $4* Antihypertensive6 -
*iuretics
Benefits; reduce blood pressure by decreasing blood volume. Ris5s6 diiness, nausea and muscle cramps. -
A$E inhi)itors
Benefits; reduce blood pressure by enhancing vasodilation. Ris5s6 diiness, impaired kidney function. -
Beta Bloc5ers
Benefits6
$alcium channel )loc5ers
=lock calcium channels in the muscles lining the arteries. "he blood pressure lowers because muscles cant contract. Ris5s6 constipation, headaches and diiness. -
Statins6 lower cholesterol level in the blood by blocking the liver enyme that makes cholesterol.
Ris5s6 nausea, constipation and diarrhoea. -
Anticoagulants e.g. warfarin; reduces risk of clot formation
Ris5s6 uncontrolled bleeding, dosage control is essential. -
%latelets inhi)itory drugs; e.g. aspirin, clopidofgrel; makes platelets less sticky
Ris5s; stomach bleeding.
#igh density lipoproteins are mainly protein. "hey transport cholesterol from body tissues to the liver where its recycled or e$creted. "heir function is to reduce total blood cholesterol when the level is too high. !ow density lipoproteins are mainly lipid. "hey transport cholesterol from the liver to the blood. "heir function is to increase total blood cholesterol when the level is too low.
!ifestyle advice to reduce the ris5 of $4* *iet cientific research has linked a diet high in saturated fat to an increased risk of C5#. "his information can be used to educate people about the risk of certain diets and to encourage them to reduce their saturated fat intake. cientific studies have also shown that obese people are more likely to develop C5#. 0besity indicators, like body mass inde$, can be used to assess if people are overweight or obese. 0besity indicators can be used to monitor the effects any changes in lifestyle have on the persons weight. Smo5ing cientific research has linked smoking to an increased risk of C5#. "his research had led to "5 adverts and warnings on cigarette packets about the risks of smoking. "he :1 encourages people to give up by giving free advice and prescribing nicotine patches. All of this encourages people to stop smoking and so reduce their risk of C5#. Exercise cientific research has linked inactivity to an increased risk of C5#. "his research has led to campaigns that encourage people to e$ercise more freuently to reduce their risk of C5#.
Evaluating design of studies to determine health ris5 factors &hings to loo5 out for6 Sample si7e" the greater the number of people used in a study, the more reliable the results. 4aria)le- the more variables that have been controlled in a study, the more reliable the results. *ata collection" think about all the problems with the method and see if bias has slipped in. the less bias involved in collecting the data, the more reliable the result. "alk about where the data was collected from.
$ontrols" the presence of controls increases the reliability of the results. Repetition )y other scientists" if other scientists produce the same results, then the results are more reliable.
%roperties of gas exchange surfaces in living organisms •
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>arge surface area to volume ratio %large surface area of alveoli'
"heyre thin- this provides a short diffusion pathway across the gas e$change surface. %"hin alveolus walls which also ensure rapid diffusion'.
"he organism also maintains a steep concentration gradient of gases across the e$change surface.
Explain how the structure of the mammalian lung is adapted for rapid gaseous exchange -
"he mammalian lung has small and millions of alveoli which increases the surface area in which diffusion takes place.
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"he alveoli is one cell thick, which reduces the diffusion distance and also makes the gases diffuse much more faster and efficient and the walls of the capillaries are also only cell thick . Alveoli are covered with capillaries.
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Concentration gradient is maintained by ventilation and by blood flow which increases the rate of diffusion. $ell mem)rane
8smosis is the net movement of water molecules from a region of high water concentration to a region of low water concentration, through a partially permeable membrane. *iffusion is the passive movement of molecules from a region of high concentration to a region of low concentration. 4articles diffuse down a concentration gradient. *iffusion, facilitated diffusion and osmosis are passive they do not re/uire energy
&he involvement of carrier and channel proteins in mem)rane transport •
$hannel proteins span the membrane and have a specific shape to transport specific particles. ome are gated ? they can be open or closed.
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$arrier proteins bind with the molecule or ion, change shape and transport the particle across the membrane. 3ovement can occur in either direction, depending on the concentration gradient.
3acilitated diffusion 3acilitated diffusion is the movement of molecules across cell membranes though protein channels and carrier proteins. >arge, polar molecules %e.g. sodium ions' or water-soluble molecule cannot pass through the hydrophobic central one of the phospholipids layer. "he process does not reuire the use of A"4 and therefore can only move substances down their concentration gradient. Active transport Active transport is an active method of movement through a membrane and therefore reuires the cell to e$pand energy in the form of A"4 in order to carry out the process. A&% supplies energy to change the shape of a carrier protein molecule when substances are moved against the concentration gradient ie from low to high concentration. &here are two types of $ytosis6 • •
Endocytosis, where substances are taken into the cell. Exocytosis, where substances are released from the cell.
Endocytosis involves the engulfing of solid particles e.g. bacteria by monocyte white blood cells. "his is called phagocytosis. Endocytosis could also involve taking in small volumes of liuid called pinocytosis e.g. by cells lining the small intestine. Exocytosis is involved in secretion, where a substance such as mucus or enyme is released from or secreted by the cell. Structure of the cell mem)rane
"he cell membrane is made up of a phospholipid )ilayer "he phosphate head of the phospholipid is polar and attracts water ? it is hydrophilic. "he fatty acid tails are hydropho)ic. n the cell membrane, the hydrophobic tails face inwards to avoid water, while the hydrophilic heads point outwards. Amino acids 9 proteins
An amino acid consists of a central carbon atom attached to an amino group, :16, a carbo$ylic group, C001, a hydrogen atom and a variable side group called the @< group. "he < group represents one of 6 different side chains.
Amino acids are linked together by peptide bonds to form dipeptides and polypeptides.
%roteins : structural levels
%rimary structure A linear seuence of amino acids (oined by peptide bonds Secondary structure Bolding and coiling of the primary structure. "here is a negative charge on the C0 of the carbo$ylic group and there is a positive charge on the :1 of the amino group. 1ydrogen bonding occurs between amino acids. 3any hydrogen bonds can hold together a heli$ structure and a beta pleated sheet made up of polypeptides laid parallel to each other. &ertiary structure Burther coiling and folding into a comple$ shape. " ertiary structure is held together by disulphide bridges, ionic bonds, hydrogen bonds and hydrophilic hydrophobic interactions. ;uaternary structure 3ore than ) polypeptide chain collided or twisted around each other. 3i)rous proteins -
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"hey are insolu)le and are important structural molecules eg keratin, collagen.
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Are folded into a compact spherical shape.
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"hey are solu)le and are important metabolic molecules eg enymes, antibodies and some hormones.
Explain the importance of the primary structure of an en7yme to its function 4rimary structure determines its three-dimensional folding. "he seuence of amino acids will determine which < groups appear in certain places this will cause the protein to coil and held up forming specific bonds
e.g. hydrogen or disulphide bridges in certain places due to the < groups this causes a specific shape which is important for enymes as their active site will only suit a specific molecule f it doesnt fit the enyme is useless so the primary structure %seuence of amino acid' is important in causing this correct shape for the enyme (ob.
*escri)e the three" dimensional +tertiary structure of an en7ymeEnymes are proteins. "he tertiary structure of an enyme is determined by the amino acid seuence in the polypeptide structure %the bonds that form between these when they start to find more in t he tertiary structure determine the 7# shape- these bonds include ionic, disulphides and hydrogen bonds, e.g. lots of cysteine amino acids will form disulphide bonds' enymes have an active site, which is what attaches to the substrate, and this active site is what gives enymes their high specificity. "he rest of the enyme is the supporting structure. Enymes are globular proteinsD they are soluble, roughly @round in shape.
Explain how the primary structure of an en7yme determines its three" dimensional +tertiary- structure and its properties "he primary structure is the basic seuence of amino acids in a poly peptide chain. "he structure of the <- group determines how the chain is folded. "he hydrophobic <- groups point inwards and are protected by the hydrophilic side chains. "his makes the enyme soluble which is useful as enymes speeds up metabolic reactions. "he chain of amino acids also decides the depression on the enyme called an active sight which is specific for a certain substrate. En7ymes are globular proteins which act as catalysts. "hey speed up chemical reactions by lowering the activation energy, and remain unchanged at the end of the reaction.
"he loc5 and 5ey hypothesis suggested an e$act match between the shapes of the substrate and active site.
"he induced fit hypothesis describes the active site moulding around the substrate once it is in place.
"he kinetic energy in the system is increasing. "herefore more molecules will have sufficient energy to meet the activation energy for the reaction. 0ptimum temperature for the enyme has been reached. At this point concentration of enyme/ substrate is the new limiting factor for the reaction. Enymes are starting to denature. "his causes in its tertiary structure, likely resulting substrate molecules will no longer being able to bind with the enymes active site, reducing the chance of a enyme- substrate comple$ forming therefore lowering the rate of reaction 2ononucleotides structure A mononucleotide consists of a deo$yribose or ribose linked to a phosphate and a base.
*NA contains * bases. "he purines are Adenine and Guanine. "he pyrimidines are Cytosine and "hymine. (n RNA the purines are Adenine and Guanine. "he pyrimidines are Cytosine and 2racil. #:A is made of two polynucleotide strands and <:A has one polynucleotide strand. <:A molecules are relatively short in length, compared with #:A. *NA *ou)le"#elix "wo complementary #:A strands (oin together by hydrogen bonding between the bases. Each base can only (oin with one particular partner, this is called complementary base pairing.
*NA Replication 1 "he #:A heli$ unips to form two single strands. Each original single strand acts as a template for a new strand.
< Bree- floating mononucleotides (oin to each original template strand by complementary base pairing- A with ", G with C.
= "he mononucleotides on the new strand are (oined together by the enyme #:A polymerase. 1ydrogen bonds form between the bases on the original and new strand.
: Each new #:A molecule contains one strand from the original #:A molecule and one new strand.
*escri)e how a molecule of mRNA is made during transcription #:A molecule unipsF as hydrogen bonds between strands break. Bree nucleotides line up along one strand of #:A- the antisense strand. "he nucleotides follow the complementary base pair pattern <:A polymerase, an enyme, bonds the nucleotides together, forming phosphodiester bonds in a condensation reaction forming the m<:A strand. Explain the nature of the genetic code "he genetic code is a triplet code. "he genetic code is linear and non-overlapping, and the genetic code can be degenerated, more than one codon can code for one amino acid.
%rotein synthesis &ranscription <:A copy of a gene is made in the nucleus. "he hydrogen bonds between the two #:A strands in a gene break, separating the strands and the #:A molecule uncoils at that point. 0ne of the strands is then used as a template to make an <:A copy, called messenger <:A. "he template strand is called the antisense strand. Bree <:A mononucleotides line up alongside the template strand. 0nce the <:A mononucleotides have paired up with their complementary bases on the #:A strand theyre (oined together, forming an m<:A molecule.
"he m<:A moves out of the nucleus through a nuclear pore, and attached to a ribosome in the cytoplasm.
&ranslation 3<:A leaves then nucleus, through the nuclear pores 3<:A travels to the ribosomes, where it is @read "<:A molecule will bind to a complementary reaction on the 3<:A chain. !hen two "<:A molecules are bound to the 3<:A their amino acids will react forming a peptide bond. "<:A molecule will break away from the amino acid and 3<:A chain and go into the cytoplasm to bond another specific amino acid for its triplet code. "hen eventually forming a polypeptide %primary structure' 'ene A seuence of bases on a #:A molecule coding for a seuence of amino acids in a polypeptide chain. Allele Alternative forms of a gene. *ominant An allele that is e$pressed when present in the genotype Recessive An allele that is only e$pressed in the absence of another dominant allele. #omo7ygous !here a diploid individual has 6 copies of the same allele present in the genotype. #etero7ygous !here a diploid individual has 6 different alleles present in the genotype. 'enotype "he alleles present in an organism for a particular characteristic. %henotype "he physical appearance of an organism with regard to a particular characteristic 3utations is a change in a base seuence on the #:A.
Effect of cystic fi)rosis6 the gas exchange 3ucus accumulates in the lungs, bacteria trapped in mucus increase the possibility of infections 3ucus can block bronchioles, which reduces the number of alveoli in contact with fresh air so reduces the surface area for gas e$change. Effect of cystic fi)rosis6 the digestive system 3ucus blocks the pancreatic duct, so digestive enymes cant reach the small intestine and food is not properly digested. "his leads to tiredness and difficulty in gaining weight.
Effect of cystic fi)rosis6 the reproductive system n women, mucus can block the cervi$ preventing entry of sperm. n men, the sperm duct is either missing or blocked with mucus, so sperm cannot leave the testes Summary6
the CB"< channel is non-functional, so chloride ions cannot pass out of the cell towards the lumen the sodium ion channels are open and sodium ions are continually absorbed from the mucus water is drawn out of the mucus by osmosis and it becomes much too viscous
"he cilia cannot move the viscous mucus ? it builds up in the airway and becomes infected. =ecause of low o$ygen levels in the mucus, anaerobic bacteria thrive. !hite blood cells invade the mucus, then die and release #:A making it even more viscous. 3ucus blocks the bronchioles, reducing the number of ventilated alveoli. "his reduces the efficiency of gas e$change.
'ene therapy Somatic therapy "his involves changing the alleles in body cells, particularly the cells that are most affected by the disorder. omatic therapy doesnt affect the individuals se$ cells though, so any offspring could still inherit the disease.
'ermline therapy "his involves changing the alleles in the se$ cells. "his means that every cell of any offspring produced from these cells will be affected by the gene therapy and they wont suffer from the disease. 'enetic screening (dentification of carriers Carrier testing shows whether people without a disorder carry an allele that can cause a disorder %e.g. CB' .Carrier testing allows people to make informed decisions about things like whether to have children and whether to carry out prenatal testing if the women is pregnant. $arrier testing social issues •
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Binding out the person is a carrier may cause emotional stress or affect the persons ability to find a partner.
0ther genetic abnormalities may be found, which could cause further stress.
$arrier testing ethical issues •
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"he tests arent always ) accurate- they could give a false result. "his means decisions could be based on incorrect information.
"here are concerns that the results of genetic tests could be used by employers or life insurance companies, resulting in genetic discrimination.
%reimplantation genetic diagnosis +%'*4G# is carried out on embryos produced by in vitro fertilisation %5B'. t involves screening embryos for genetic disorders before theyre implanted into the woman. "he advantages of 4G# are it reduces the chance of having a baby with a genetic disorder only embryos without the genetic disorders tested will be implanted. %'* Social issues t can be used to find out other characteristics %e.g. gender, eye colour' leading to concerns that in the future, embryos may be selected for other characteristics designer babies' %'* Ethical issues Balse results could provide incorrect information. %renatal testing 4renatal testing involves screening unborn babies %foetuses' for genetic disorders. "heyre offered to pregnant women with a family history of genetic disease. 4renatal testing allows
parents to make informed decisions. f the test is positive, the parent may decide to have the child or to have an abortion.
There are two types of test: ). Amniocentesis "his is carried out at )9-)+ weeks of pregnancy. A sample of amniotic fluid %the fluid that surrounds the fetus' is obtained using a very fine needle. "his fluid contains fetal cells. "he cell contains #:A, which can be analysed. 6. Chorionic villus sampling (CVS) "his is carried out at H-)6 weeks of pregnancy. A sample of cells is taken from the chorionic villi %part of the fetus that connects it to its mother' using a fine needle or a catheter %a t hin fle$ible tube'. "he cells contain fetal #:A, which can be analysed.
%renatal testing social issues 4renatal tests slightly increase the risk of miscarriage by around ).
%renatal testing ethical issues Balse results could provide incorrect information and some people consider it unethical to abort a fetus because it has a genetic disorder.