Biology AS Level model answers revision

1. Alveoli are one cell thick; capillary walls one cell thick
2. walls are made of flattened epithelial cells; short diff. dis.
2. alveoli are covered in capillaries [network - increase SA]
3. reduces diffusion distance (short diffusion distance)
4. large SA provided by alveoli (air sacs)
5. concentration gradient is maintained by breathing
6. also maintained by blood flow
7. large numbers of red blood cells; O2 combines w haemoglobin
8. Fick’s law - diffusion rate proportional to surface area

1. Mass flow generated by heart;blood flow maintains conc. grad.
2. Network of capillaries means all cells are close to blood
3. Double circulatory system leads to efficient gas exchange
4. Network of capillaries; large SA - fast diffusion (Fick’s law)
5. Capillaries have thin cell walls; small diffusion distance

1. Gas exchange occurs via diffusion through cell membrane
2. O2 enters cell, CO2 leaves cells } both are small/non-polar
3. Move down the concentration gradient
4. Large SA to V ratio

1. Blood flows at a higher pressure
2. Blood can flow at a lower pressure/slower into the lungs
3. Less damage to the lungs
4. Ref. to more efficient gas exchange/transport of gases

1. one side of heart transports blood; other to lungs
2. separation of oxygenated/deoxygenated blood
3. good for maintaining concentration gradient
4. b.p lower to lungs, higher to body
5. need for good supply of O2; v. high metabolism, v active

Large surface area to volume ratio
2. Low metabolic rate/low metabolism
3. Diffusion is fast enough for exchange of gases/waste
4. Movement of blood back into heart is fast enough
5. All cells are very close to heart

1.idea that there are four chambers
2. correct ref to relative position of atria and ventricles
3. idea of left and right sides separate/septum
4. ref to the muscular nature of the walls
5. ref to the cardiac muscle
6. idea of relative thickness of ventricle walls
7. correct ref to position of semilunar valves
8. correct ref to semilunar valves
9. ref to position of tendons/cords/papillary muscles
10. correct ref to position of aorta/pulmonary artery
11. correct ref to position of vena cava/pulmonary vein
12. correct ref. to coronary arteries; ref to SAN

1. Arteries have thick walls; capillary walls one cell thick
2. Arteries - lots of collagen; capillaries - no collagen
3. Arteries - muscle cells; capillaries - no muscle cells
4. Arteries - elastic tissue (allows for recoil); collagen - none
5. Arteries - narrow lumen; capillaries - even narrower

1. Elastic tissue - recoil/stretch; maintain press. w/ no damage
2. Smooth muscle - can exert pressure/contract
3. Smooth lining - reduces friction/smooth blood flow
4. Collagen - helps avoid damage or rupture
5. Narrow lumen - helps maintain high blood pressure

1. Capillary has thin wall (one cell thick, no collagen)
2. So, has a short diffusion distance, ensuring fast diffusion rate

1. Smoking; platelets sticky & reduces O2 cap. of haemoglobin
2. Inactivity; leads to energy imbalance, weight gain, obesity, b.p.
3. Diet high in salt - high b.p. (or diet high sat. fats. - LDL:HDL)
4. ! important to maintain LDL;HDL ratio as it controls chol.

1. leads to energy imbalance; can cause weight gain/obesity
2. leads to diabetes; risk factor for CVD
3. increase of blood pressure; increases risk of damageupture
4. higher chance of atherosclerosis; narrowing of lumen
4. higher LDL;HDL level; linked with CVD

1. carbohydrates a source of a high amount of energy
2. if the energy input (carbohydrates) is greater than the output
3. weight is gained/energy imbalance
4. excess carbohydrates are converted into fat

1. blood clot leads to reduced blood flow
2. less/no oxygen reaches heartrain
3. less aerobic respiration; no ATP produced
4. brain/heart needs a lot of ATP to function
5. lactic acid produced from anaerobic
6. lactic acid inhibits enzymes/is toxic

1. Events lead up to clot; e.g. damage to endothelial cells/lining
2. Release of thromboplastin; converts prothrombin to thrombin
3. Thrombin is an enzyme (globular protein)
4. Thrombin converts fibrinogen to fibrin
5. Fibrin (fibrous protein) forms a mesh of fibres
6. Platelets & red blood cells get trapped; form blood clot
7. Stickier platelets form blood clots faster
8. Blood clot restricts blood flow; lack of O2; heart attack/stroke

1. Damage to endothelial cellsupture
2. Triggers an inflammatory response
3. WBC accumulate in the area; build up of choles./platelets
5. Harden to form plaque (atheroma) (build up of fibres/Ca2+)
6. Narrowing of lumen/ less elasticity/high b.p less blood flow
7. Process is self perpetuating (high bp leads to more damage)

1. ref to phospholipid bilayer; and phospholipids in bilayer
3. hydrophilic head and hydrophobic tail
4. hydrophilic attracted to H2O, hydrophobic moves away
5. proteins (channel protein and carrier protein)
6. different locations of proteins (extrinsic, intrinsic..)
7. glycoproteins - for cell recognition; cholesterol within memb.

1. Ethanol causes the membrane to be disrupted
2. Lipids dissolve in ethanol; proteins denatured by ethanol
3. This disrupts the vacuole membrane; escape of pigment

1. Increase in temperature increases the Ek; disrupts membrane
2. Phospholipids move more; cell membrane more permeable
3. Proteins denature above certain temp. ; increase permeability
4. Pigment escapes when disrupted; disruption of vac. membrane

1. Active transport uses ATP (requires energy)
2. Uses only carrier proteins; bind to molecule & change shape
3. Transports molecules against the conc. gradient

1. Uses protein channels (open/close) and carriers (change shape)
2. Can carry large/polar molecules down concentration gradient

1. DNA Helicase [named enzyme] unravels the DNA strand
2. Replication is semiconservative; one new strand made
3. Mononucleotides line up along the strand
4. Via complementary base pairing; form H bonds between them
5. Phosphodiester bonds form between mononucleotides
6. Via condensation reaction
DNA Polymerase attaches nucleotides; DNA Ligase connects fragments

mRNA 1. mRNA transcribe DNA template; is copy of genetic code
2. mRNA is made up of codons that code for specific amino acids
3. the mRNA contains the code for the new protein/polypeptide
3. the mRNA moves out of the nucleus, & binds to the ribosomes
5. and is used in translation [acts as template for translation]
tRNA 1. tRNA attaches to one specific amino acid (one)
2. amino acids line up on mRNA via complementary base pairing
3. peptide bonds form via condensation); released by tRNA
2. tRNA then binds to mRNA
3. amino acids join via peptide bonds

1. mRNA binds to ribosome
2. tRNA attaches to one specific amino acid each
3. codon/anticodon interaction/complementary base pairing
4. formation of hydrogen bonds between the bases
5. peptide bonds form between the amino acids; released tRNA
6. peptide bonds formed via condensation reactions

1. gene is seq. of bases
2. that code for seq. of amino acids in protein
3. gene mutation alters the DNA triplet codon
4. therefore can change amino acid sequence
5. STOP codon can be coded for
6. this may change the shape of the protein/enzymes
7. therefore causing change of the active site; a.s is specific

1. Change in base sequence changes the amino acid structure
2. Changes the shape of the protein; alters its function
3. CFTR protein (channel) cannot transport Cl-
ions into cells
4. The protein channel is open for Na+; absorbed by mucus
4. Water doesn’t move out of cells/ doesn't dilute; via osmosis
5. Sticky mucus which cannot be removed by cilia in lung

1. Gene mutation changes the DNA base sequence
2. Alters the primary structure; sequence of amino acids
3. Changes the position of R groups on amino acid
4. Affects how it is folded, what tertiary bonds form (name one)
5. This changes final 3D shape of the protein; changes active site
6. Active site is specific; binds to substrate to form complex

1. somatic involves body cells; germ line involves gametes
2. somatic can’t be inheritederm line can be inherited
3. somatic legal; germ line is illegal
4. somatic is temp. treatmenterm line could be cure

1. ref. to virus; e.g. liposome, virus and plasmid
2. idea of inserting functional gene that codes for CFTR protein
3. method of getting into longs; e.g. nebuliser
4. CFTR protein made via transcription/translation
5. allows chloride ions to leave cells
6. water moves out of cells via osmosis
7. mucus becomes less sticky

1. Use named vector (e.g. liposome or altered virus or plasmid)
2. Introduce healthy gene into body cells (name,e.g. cells in lung)
3. Normal gene is transcribed & translated; healthy protein made
4. Instead of faulty protein
3. Suitable delivery method (e.g. injection or nebuliser)
4. Treatment needs to be repeated (due to cell replacement)

1. Thick mucus builds in reproductive system; blocks cervix
2. Prevents sperm from reaching egg, fertilization impaired

1. Right of life; abortion is murder
2. False +ve/-ve; abortion of healthy fetusirth of disorder
3. Stress to parents - increased change of miscarriage

needs to be homozygous to be expressed in phenotype

will be expressed in phenotype independent of pair

1. Enzyme is a globular protein
2. It has an active site which is specific to its substrate
3. It forms an enzyme-substrate complex by binding to substrate
4. Form bonds between R groups; such as disulphide bridges

1. Insoluble - no osmotic effect, will not dissolve
2. Large molecule - will not move out of cell
3. Large molecule - it can store large amounts of energy
4. Compact - can store large amounts of energy in small space
5. Very branched - easily hydrolysed (to release glucose)
- made of alpha glucose and held by 1,4 and 1,6 glycosidic bonds

1. Water is a solvent and can dissolve non-polar/ions
2. Water has a dipole nature; can form weak H bonds
3. This makes it adhesive and cohesive
3. Water is fluid and can assist mass flow