Mark Schemes Flashcards
Differences between DNA and mRNA
IDENTIFY WHAT TOPIC THEY ARE TESTING YOUR KNOWLEDGE OF
RECORD RATES IN STANDARD FORM
1. DNA double stranded/double helix and mRNA single-stranded; 2. DNA (very) long and RNA short; 3. Thymine/T in DNA and uracil/U in RNA; 4. Deoxyribose in DNA and ribose in RNA; 5. DNA has base pairing and mRNA doesn’t/ DNA has hydrogen bonding and mRNA doesn’t; 6. DNA has introns/non-coding sequences and mRNA doesn’t;
Contrast requires both
parts of the statement
Induced fit model
1. (before reaction) active site not complementary to/does not fit substrate; 2. Shape of active site changes as substrate binds/as enzyme- substrate complex forms; 3. Stressing/distorting/bending bonds (in substrate leading to reaction);
Describing an enzyme controlled reaction graph
Why it levels off?
Always talk about substrate finishing, no more subtsrate, empty actice sites etc
1. (Rate of) increase in concentration of maltose slows as substrate/starch is used up OR High initial rate as plenty of starch/substrate/more E-S complexes; 2. No increase after 25 minutes/at end/levels off because no substrate/starch left;
Describe how the structure of starch and cellulose molecules are related to their function
Starch (max 3) 1. Helical/ spiral shape so compact; 2. Large (molecule)/insoluble so osmotically inactive; 3. Branched so glucose is (easily) released for respiration; 4. Large (molecule) so cannot leave cell/cross cell-surface membrane; Cellulose (max 3) 5. Long, straight/unbranched chains of β glucose; 6. Joined by hydrogen bonding; 7. To form (micro/macro)fibrils; 8. Provides rigidity/strength;
Function of
- DNA helicase
- DNA polymerase
- DNA helicase – (unwinding DNA and) breaking
hydrogen bonds / bonds between chains / bases /
strands; - DNA polymerase – joins (adjacent) nucleotides
OR forms phosphodiester bond / sugar-
phosphate backbone;
Differences between ATP and DNA nucleotide
1. ATP has ribose and DNA nucleotide has deoxyribose; 2. ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate (group); 3. ATP- base always adenine and in DNA nucleotide base can be different / varies;
Properties of water
Accept any three suitable properties e.g.: Is a metabolite Is a solvent Has a (relatively) high heat capacity Has a (relatively) large latent heat of vaporisation / evaporation Has cohesion / hydrogen bonds between molecules;;;
Properties of starch that make it good for storage
Any two from:
1. Insoluble (in water), so doesn’t affect water
potential;
2. Branched / coiled / (α-)helix, so makes
molecule compact;
OR
Branched / coiled / (α-)helix so can fit many
(molecules) in small area;
3. Polymer of (α-)glucose so provides glucose for
respiration;
4. Branched / more ends for fast breakdown /
enzyme action;
5. Large (molecule), so can’t cross the cell
membrane
Features of DNA and their importance in semi-conservative DNA replication
Weak / easily broken hydrogen bonds between
bases allow two strands to separate / unzip;
2. Two strands, so both can act as templates;
3. Complementary base pairing allows accurate
replication;
Emulsion Test
- (Mix / shake sample) with ethanol, then water;
2. White / milky (emulsion);
Combined action of endopeptidases and exopeptidases more efficient. Why?
Endopeptidases hydrolyse internal (peptide
bonds)
OR
Exopeptidases remove amino
acids/hydrolyse (bonds) at end(s);
2. More ends or increase in surface area (for
exopeptidases);
Respiratory Inhibitor
Something that inhibits respiration.
No respiration = no ATP produced
Thin pieces of leaf tissue examined using an optical microscope. Why is it important that leaves are thin.
- Single/few layer(s) of cells;
2. So light can pass through;
Why is it important that the student counted stomata in sevral parts of leaf tissue?
- Distribution may not be uniform
OR
So it is a representative sample; - To obtain a (reliable) mean;
Read questions carefully
SUGGEST AND EXPLAIN
Xerophytic Adaptations
1. Hairs so ‘trap’ water vapour and water potential gradient decreased; 2. Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased; 3. Thick (cuticle/waxy) layer so increases diffusion distance; 4. Waxy layer/cuticle so reduces evaporation/transpiration. 5. Rolled/folded/curled leaves so ‘trap’ water vapour and water potential gradient decreased; 6. Spines/needles so reduces surface area to volume ratio;
Rate of water uptake of plant not always same as transpiration rate
1. Water used for support/turgidity; 2. Water used in photosynthesis; 3. Water used in hydrolysis; 4. Water produced during respiration;
Organisms with no gas exhange system. How are they adapted?
1. Thin/small so short diffusion pathway; 2. Flat/long/small/thin so large surface area to volume ratio/surface area : volume;
Organism living in area with less oxygen. Look at the graph and explain how its haemoglobin allows it to survive in low pO2 conditions?
AS 2016 PAPER 2 3.3
- High/50% saturation (with oxygen)
below (pO2 of) 0.2 kPa; - (Oxygen) for respiration;
AS 2016 PAPER 2 3.4
1. Water potential higher in worm OR Lower water potential in seawater; 2. Water leaves by osmosis (and worm dies)
When investigating conditions in people
AS 2016 PAPER 2 6.1
- Large sample size;
- Individuals chosen at random;
- Are healthy;
- Equal number of males and
females; - Repeat readings;
Low FEV1
- Less carbon dioxide removed;
- Less oxygen (uptake/in blood);
- Less (aerobic) respiration/ATP
OR
(More) anaerobic respiration
Translocation
- (At source) sucrose is actively
(transported) into the phloem/sieve
element/tube; - By companion/transfer cells;
- Lowers water potential in
phloem/sieve element/tube and
water enters by osmosis; - (Produces) high (hydrostatic)
pressure; - Mass flow/transport towards
sink/roots/storage tissue; - At sink/roots sugars are
removed/unloaded;
