biology unit 1 questions

Describe how an unsaturated triglyceride is synthesised.

• (one) glycerol and three fatty acids (1) • joined by {condensation reaction / ester bond} (1) • by enzymes (1) AND • (at least) one fatty acid is {unsaturated / has a CC double bond} (1)

Explain why a stent is used in the treatment of atherosclerosis in a coronary artery

to widen (the lumen of) the (coronary) artery / (blood) vessel (1) • so that more blood can flow to the heart {cells / muscle} (1) • for respiration (in the heart muscle) / so that heart muscle can contract (1)

Explain why this gene is unlikely to be located on the X chromosome.

because individual 6 was a female non-taster (1) • and her father was a taster (1

Cystic fibrosis is caused by mutations in a gene coding for the CFTR protein. (a) Explain why a mutation in this gene results in the production of very thick, sticky mucus.

because the mutated gene results in a faulty (CFTR) protein (1) • so chloride ions do not move out of the cells (1) • decreasing the water potential inside the cell (1) • therefore water {leaves the mucus / enters the cells} by osmosis

State the meaning of the term mutation

change in the base {sequence / order} of DNA

State the meaning of the term correlation.

a change in one variable is reflected in a change in another variable

Explain the role of the primary structure in determining the properties of the protein labelled in the diagram

because the sequence of amino acids determine the {tertiary / quaternary} structure of the protein (1) • by determining the {position / type} of bonds that form between the R groups (1) • {hydrophobic / non-polar} {(R) groups / amino acids on (the outside of) the part of the protein that is embedded in the fatty acid tails (1) • {hydrophilic / polar} {(R) groups / amino acids} (on the outside of) the part of the protein that is {amongst the phosphate heads / facing the cytoplasm / facing the aqueous environment} (1

Compare and contrast the structure of the aorta with the structure of the pulmonary artery.

Similarities: • both have walls containing {muscle cells / elastic fibres / an endothelial cell lining / an (outer) collagen layer} (1) • both have a valve (at the point they leave the heart) (1)

Differences: • aorta has a {lumen with a wider diameter / thicker wall / more elastic tissue / more muscle tissue / more collagen} (1) • aorta has branches to more organs (1)

Explain how the structure of glycogen relates to its role as an energy storage molecule.

{polymer of glucose / polysaccharide} therefore has a high energy content (1) • {large molecule / polymer / polysaccharide} therefore {insoluble / has no osmotic effect} (1) • branched structure therefore {broken down / energy released / hydrolysis is} faster (1) • compact therefore has a high energy density (1)

Explain the properties of amino acids located on the outer surface of the haemoglobin, for example at position Q

must have R groups that are {polar / hydrophilic} (1) • so that the {haemoglobin / protein} {can dissolve in (red blood cell) cytoplasm / is soluble in water}

Explain why the oxygen dissociation curve of adult haemoglobin is different from that of fetal haemoglobin

oxygen dissociation curve for {maternal / adult} Hb is shifted to the right of curve for fetal Hb (1) • because oxygen needs to diffuse from {maternal / adult} blood into fetal blood (1) • therefore fetal haemoglobin needs to have a higher affinity for oxygen

Explain how dietary antioxidants reduce the risk of CVD

because antioxidants reduce free radicals (1) • free radicals cause {cell damage /tissue damage / oxidative stress / damage to endothelial lining} (1) • (antioxidants) reduce {plaque / atheroma} formation (1)

Devise a study to confirm that antioxidants reduce the risk of CVD.

use (a large number of) {healthy individuals / individuals with no known heart condition} (1) • who have similar (lifestyle and non-lifestyle) risk factors (1) • compare group given antioxidants to a group using other preventative treatments (1) • monitor the incidence of heart disease over a (long) period of time

Explain how the three-dimensional structure of lactase affects the mechanism of action of this enzyme.

lactase is soluble because of its {globular shape / external polar R groups} (1) • (and therefore) lactase collides with lactose (1) • active site of lactase is complementary to the lactose (1) • Formation of enzyme-substrate complex lowers the activation energy

Explain why the circulation of a butterfly is different from the circulation of a mammal.

(because the insect is small) the cells will not be far from the {sinuses / blood} (1)  (so) diffusion can supply the {oxygen / nutrients / named nutrient} (from the blood) (1)  because the insect is small it does not have {double circulation / blood vessels / closed circulatory system / complex circulatory system / high pressure}

OR  because the insect has a low {metabolic rate / oxygen demand} (1)  diffusion can supply the oxygen (from blood / tracheoles) / the oxygenated and deoxygenated blood does not need to be kept separate (1)  because the insect is small it does not have {double circulation / blood vessels / closed circulatory system / complex circulatory

Describe the structure of collagen.

fibrous protein (1)  {triple / three stranded} helix (held with hydrogen bonds) (1)  (short) repeating sequences of amino acids / high {hydroxyproline / proline / glycine} content / every third amino acid is glycine

Discuss the implications of screening embryos for aneuploidy before implantation. (

preimplantation) screened embryos still result in miscarriages so raising false hopes (1)  issues surrounding the embryos (that have aneuploidy) (1)  false (positive) results resulting in unnecessary {wastage / destruction} of embryos (1)  other (genetic) defects may be found (1)eth

Describe the bonding in this double-stranded RNA molecule.

phosphodiester bonds between (adjacent) {ribose and phosphate / (mono)nucleotides} (in each strand) (1)  covalent bonds attaching base to a {ribose (sugar) / sugar} (1)  {hydrogen / H} bonds between (complementary) bases (holding two strands together) (1)  {hydrogen / H} bonds holding double helix together

Describe how the structure of capillaries relates to their function

single layer of cells / pores / small diameter , thin cells / walls e.g. (single layer) gas exchange / diffusion of gases (in the lungs) (pores) plasma forced out / WBC leave / molecules can leave (small diameter) all cells close to capillaries

Explain why veins need valves along their length.

to prevent backflow (of blood) (1) • (as blood is usually returning) {under low pressure / (often) against gravity} (1)

State the meaning of the term biological catalyst

{protein / found in organisms} (1) • that {decreases activation energy / speeds up (the rate of) reaction} (without being used up) (1)

The properties of gas exchange surfaces include

: • a large surface area

• a short diffusion distance

• a high concentration gradient.

Describe how mammalian lungs are adapted to have each of these three properties.

lots of alveoli for large surface area (1)

• {single-celled / thin-walled} {alveoli / capillaries} for short diffusion distance (1)

• good blood supply for high concentration gradient (1

Compare and contrast the structure of glucose with the structure of glycogen.

Similarities :

• αlpha glucose (1)

• contain C, H and O (only) (1)

Differences

• glucose is a monosaccharide and glycogen is a polysaccharide (1)

• glycogen has (1-4 / 1-6) glycosidic bonds but glucose does not

explain the role of the bases adenine cytosine guanine theymine in the DNA structure

form base pairs to hold the two {polynucleotide / strands} together (1)

• because of the number of hydrogen bonds that each type of base can form (1)

• a {large base / purine} bonds with a {small base / pyrimidine} (1)

• so that the strands are paralle

Describe the structure of a nucleotide pair.

contain {deoxyribose / pentose / 5 carbon sugar}, phosphate and bases (1)

• (mononucleotides / bases) held together by hydrogen bonds (1)

• between {complementary bases / named example}

Explain the role of DNA polymerase in a replication bubble.

lines up nucleotides (along each strand) , forms phosphodiester bonds (between adjacent nucleotides) , repairs mistakes in replication

Describe the structure of collagen.

fibrous protein (1)

• (protein) composed of {three polypeptide chains / three-stranded / triple} helix (1)

• held by hydrogen bonds (between the chains) (1) • credit details of the chains (1)

Explain the role of collagen in the wall of the aorta

gives (the wall) (tensile) strength (1)

• so that the aorta {does not get damaged by / can withstand} pressure (of the blood leaving the heart)

Osmosis can be defined as the movement of free water molecules through a partially permeable membrane, down a water potential gradient. Explain this definition.

• (free water molecules) because some water molecules are {restricted / prevented} from movement (1)

• (partially permeable membrane} because membrane allows some (types of) molecules to pass through it (1)

• (down a water potential gradient) because water molecules move {from a dilute solution to a more concentrated one / from a high osmotic potential to a lower one / from a high solute potential to a lower one} (1)

Explain why a person might have to take several types of drugs to reduce the risk of CVD

because many factors cause CVD (1) • different drugs treat different conditions

The amino acid Glu is hydrophilic (polar) and the amino acid Val is hydrophobic (non‑polar). Suggest why this mutation causes haemoglobin molecules to stick together.

• the R groups (of these two amino acids) have different {properties / bonding} (1)

• glu may have repelled polar groups on other haemoglobin molecules (1)

• {val / hydrophobic R group / hydrophobic part} might form other (hydrophobic) interactions (with other haemoglobin molecules) (1) • (part of haemoglobin containing) val (R group) turns away from {water / cytoplasm} (1

Sickle cell disease can result in death. Explain why the changes in the structure of haemoglobin and the shape of the red blood cells could result in death in a person with sickle cell disease.

• (change in structure of haemoglobin) haemoglobin {binds / carries} less oxygen (1)

• (shape of red blood cell) smaller surface area so less oxygen diffuses in / red blood cells get lodged in blood vessels preventing flow of blood to cells

• therefore less oxygen to {cells / tissues} so {less available for (aerobic) respiration / switch to anaerobic respiration} (1)

• credit an example of why less oxygen to cells could be fatal (

Thromboplastin is stored inside platelets.

Explain the advantages of storing thromboplastin inside platelets.

• to keep thromboplastin separate from prothrombin (1)

• so that prothrombin will not be converted into thrombin (1)

• the blood clotting process will be prevented (1)

• to have thromboplastin {available / released quickly} (when needed) (1)

Explain why enzymes are described as biological catalysts.

because they are found in living organisms (1)

• because they speed up the rate of reaction (without being used up)

Explain why the velocity of blood flow in the large arteries is slower than the velocity of blood flow in the aorta.

• blood in aorta is under higher pressure as it has just been pumped out of the {heart / (left) ventricle} • aorta branches into many arteries /(blood flowing through) more vessels (1)

• the {friction / resistance} between blood and vessel (slows the velocity down) (1)

• blood cannot be pushed through because of {loss of elasticity in arteries / less elastic recoil} (1)

Explain why the total surface area of the capillaries needs to be so high.

• more plasma is able to leave (the capillaries) (1) • results in faster diffusion (1)

• more capillaries are in contact with the cells (in the tissue) (1)

Describe two structural features of insoluble fibrous proteins.

long (chains of amino acids / polypeptides / proteins) (1)

• repeating sequences of amino acids (1)

• high proportion of {small / non-polar / hydrophobic} {R groups / amino acids} (1) • (parallel) chains held with {cross links / hydrogen bonds}

Describe the secondary structure of a polypeptide.

• ß {pleated / sheet} / α helix (1)

• (held together by) hydrogen bonds (between amino acids) (1)

Explain why it is important that a person’s perception of a risk is close to the actual risk.

• lifestyle can be modified (to reduce the risk / slow down progression ) (1)

• they could have a {blood / health} test (to assess the risk / check on the progression) (1)

• medication can be {prescribed / taken} (to reduce the risk / slow down progression) (1) • if perception is greater than actual, an unnecessary change may be made (1)

Explain why an increase in temperature increases the fluidity of the membrane

• because {phospholipids / molecules} have more (heat / kinetic) energy (1)

• because {forces / interactions} between {fatty acid chains / phospholipids} break (1)

• therefore phospholipids can move around (within the membrane) / phospholipid bilayer} more (1)

Explain why a decrease in cholesterol increases the fluidity of the membrane.

• cholesterol interacts with {phospholipids / fatty acids} (1)

• (if less cholesterol) movement of phospholipids no longer restricted (by interaction with cholesterol) (1)

Explain how a protease breaks down elastin.

active site (of protease) {binds to / fits} the {elastin / substrate} (1)  activation energy lowered (by the protease) (1)  breaking the peptide bonds (1)  by hydrolysis (1

Give two reasons why some women may have given unrealistic estimates of their daily energy intake.

 they did not want to admit to how much energy they consumed (1)

 they had not kept a record of the food that they had eaten (1)

 they did not know the energy content of the different foods that they were eating OR they did not know {how to do it / that they could do it} (1)

Explain why a diet that is low in saturated fat is likely to reduce the risk of CVD.

because this results in less cholesterol (in diet / in blood) (1)

 therefore {no / less} {plaque / atheroma / blood clot} (1)

 to {block / narrow} the coronary artery (1)  therefore, blood will be able to continue flowing to the {heart / cardiac} {cells / tissue / muscle} (1)

Compare and contrast the structure of the model shown in the diagram with that of the fluid mosaic model of membrane structure.

Similarities:

 both have proteins (1)

 both have {phospholipid / phospholipid bilayer}

(1) Differences:

 FMM has proteins {embedded / intrinsic}, but DDM has proteins {outside / in a layer/ extrinsic} (  FMM has cholesterol but DDM does not (1)  FMM has {glycoproteins / glycolipids} but DDM does not (1)

Suggest how damage to the cell membrane could result in cell death.

because the phospholipids (and proteins) {can move / are fluid} (within the membrane) (1)  therefore {phospholipids / fatty acids} can interact (hydrophobically) (1)

Cells can repair damage to the cell membrane. This involves fusion of parts of the membrane around the edge of the damage.

Explain why parts of the membrane are able to fuse together to repair the damage

 more {membrane / phospholipid / protein / glycoprotein / glycolipid / cholesterol} needs to be made (1)

 membrane needs restructuring / proteins added to membrane (1)

 increase rate of {respiration / ATP synthesis / release of energy} (1)

Describe the structure of a triglyceride

one glycerol and three fatty acids (1)

 (joined together by) ester {bonds / links / groups} (1)

Explain why large lungs and a large heart would help a yak to survive at high altitude

 because large lungs would have a large volume of air {in the alveoli / taken in} (1)

 because there would be {more alveoli for gas exchange / large surface area for more gas exchange / larger surface area for gas exchange} (1)  because large heart could pump more blood (1)  therefore supplying cells with sufficient oxygen (1)

Compare and contrast the structure of an mRNA molecule with that of a tRNA molecul

Similarities:

• both consist of {(RNA mono) nucleotides / ribose sugar / U, A, C and G / phosphodiester bonds} (1) • both are single-stranded (1)

Differences:

• mRNA has codons and tRNA has anticodons

• mRNA does not have hydrogen bonds but tRNA does (1)

• mRNA does not have an amino acid binding site but tRNA does (1)

The volume of blood in the left ventricle changes during the cardiac cycle. Explain these changes

• increase in volume {when (left) atrium contracts (squeezing its blood into ventricle) / during atrial systole} (1)

• decrease in volume {during ventricular systole / when ventricles contract / when blood is pumped out (of aorta)} (1)

• (some) increase in volume {during (cardiac / ventricular) diastole / when ventricle starts to fill} (1)