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Flashcards in mistakes on recent papers Deck (20)
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1
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.

A

substrate binds to the active site forming an esc, active site changeds shape to be complementary to the substrate.
m3- this reduces activation energy.

2
Q

how to stop reactions involving enzymes

A

use inhbitors so that escs do not form
boil or add strong acid to denature enzyme
freeze so this lowers Ek so less escs can form

3
Q

what to say when questions like why did they repeat

A

allows anomalies to be identified, makes the averages more reliable, allows concordant results, allows a mean to be calculated, more representative

4
Q

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation

A

amino acid brought by trna to ribosome, anticodon binds on trna binds to the codon on the mrna, amino acids join by condensation reaction using atp

5
Q

to suggest why iron-deficient plants have a reduced growth rate.

A

less thyalkoid membrane, smaller sa, less light absorption, less psynth

6
Q

compare 2 cells with 1st mag less thann 2nd one

A

second one smaller still then compare every single feature

7
Q

Explain how water enters a plant root from the soil and travels through to the endodermis. (5)

A
  1. Water enters root hair cells;
  2. By osmosis;
  3. Because active uptake of mineral ions has created a water potential gradient;
  4. Water moves through cortex;
  5. Down water potential gradient;
  6. Through cell vacuoles and cytoplasms (symplastic pathway);
  7. And through apoplastic pathway (cell walls);
8
Q

Root pressure is a force that is partly responsible for the movement of water through xylem in stems. Explain how the active transport of mineral ions into the xylem vessels in the roots results in water entering these vessels and then being moved up the xylem tissue. (5)

A
  1. Entry of ions leads to a reduced water potential;
  2. Water potential established between xylem and surrounding cells;
  3. Plasma membranes of surrounding cells are partially permeable;
  4. Water enters xylem by osmosis;
  5. Volume of water in xylem increases;
  6. Cannot move back due to gradient;
  7. Pressure in xylem increases and forces water upwards.
9
Q

In daylight, most of the water evaporates from the leaves but some is used by the plant. Describe the ways in which this water could be used by the plant. (6)

A
  1. (water is used in) the light-dependent reactions of photosynthesis;
  2. electrons from water enable ATP production / H+ are used to reduce NADP / produces O2;
  3. (water can be used in) hydrolysis reactions within the plant;
  4. to create turgor;
  5. as a solvent for transport;
  6. as a medium for chemical reactions;
  7. component of cells / cytoplasm;
10
Q

Describe two features you would expect in the leaves of a tree adapted to a dry environment. Explain how each feature helps the tree’s survival. (6)

A

Sunken stomata;
water evaporation into pit creates local humidity;
increased humidity reduces gradient for water evaporation;
close arrangement of stomata;
diffusion shells of individual stomata overlap;
interferes with water diffusion and slows evaporation;
restriction of stomata to lower side of leaf;
rate of air movement below leaf less/ heating effect of sun less;
gradient for water evaporation reduced/ water molecules have less
kinetic energy;

thick cuticle/wax/suberin (on upper surface);
(wax/suberin )waterproof;
water unable to diffuse onto surface to evaporate,
presence of trichomes/ hairs;
surface traps water close to leaf surface;
increased humidity reduces gradient for water evaporation;
reduced leaves/spines/small surface area to volume;
less surface area for evaporation;
more distance across leaf for water to diffuse;
rolled leaves;
stomata enclosed in localised humidity;
increased humidity reduces gradient for water evaporation;

11
Q

Xylem transports water through a plant. Describe and explain how the cells of xylem are adapted for this function. (5)

A

Thick cell walls;
Withstand tension / negative pressure;
Lignin in cell walls strengthens it
Walls waterproof / withstand tension / negative pressure;
Xylem cells have no end walls / tubular (not hollow);
So a continuous column of water;
Xylem vessels are stacked on top of each other;
So a continuous column of water;
Have no cytoplasm / hollow;
Reduces resistance to flow of water / so a continuous column of water;
Xylem cells have pores / pits (in side walls);
Enable sideways flow / by-pass blockages / allows entry or exit of water;
Narrow tubes;
Allows capillarity / increased surface area for adhesion;
(Molecules in) cell walls;
Allows adhesion

12
Q

describe binary fission in bacteria

A

replication of dna, replication of plasmids, division of the cytoplasm

13
Q

The people in group B were recovering from an asthma attack.
Explain how an asthma attack caused the drop in the mean FEV shown in the figure
below.

A

Muscle walls of bronchi / bronchioles contract;

  1. Walls of bronchi / bronchioles secrete more mucus;
  2. Diameter of airways reduced;
  3. (Therefore) flow of air reduced
14
Q

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.
Details of breathing are not required.

A

Trachea and bronchi and bronchioles;

  1. Down pressure gradient;
  2. Down diffusion gradient;
  3. Across alveolar epithelium.
15
Q

A laboratory has oat plants containing the resistance gene and a supply of plasmids. Describe how bacteria may be produced which have the resistance gene in their plasmids. (6)

A
  1. Cut desired gene (from DNA) of oat plant;
  2. Using restriction endonuclease (restriction enzyme);
  3. Cut plasmid open;
  4. With (same) restriction endonuclease;
  5. Sticky ends/unpaired bases attached;
  6. Use (DNA) ligase to join;
  7. Return plasmid to (bacterial) cells;
  8. Use of Ca2+/calcium salts/electric shock
16
Q

The polymerase chain reaction (PCR) can be used to produce large quantities of DNA. Describe how the PCR is carried out. (6)

A
  1. DNA heated to 90-95°C;
  2. Strands separate;
  3. Cooled to temperature below 70°C;
  4. Primers bind;
  5. Nucleotides attach;
  6. By complementary base pairing;
  7. Temperature 70-75°C;
  8. DNA Polymerase joins nucleotides together;
  9. Cycle repeated;
17
Q

founder effect

A

A founder effect occurs when a small group splits off from the main population to found a colony

18
Q

bottleneck effect

A

when a populations numbers are reduced

19
Q

genetic drift

A

mechanism of evolution in which allele frequencies in a population change over generations due to chance

20
Q

Explain how amino acid molecules may be linked to form a polypeptide chain which is folded into a specific tertiary shape. (6)

A
  1. Condensation;
  2. removal of water molecule;
  3. from amino and carboxyl groups;
  4. forming peptide bonds;
  5. same amino acids in same sequence;
  6. bonds form between R-groups/side chains;
  7. e.g. sulphur-containing amino acids / ionic bonds / hydrogen bonds;
  8. bonds form in same place;