bio questions Flashcards
Suggest and explain why the combined actions of endopeptidases and
exopeptidases are more efficient than exopeptidases on their own
Endopeptidases hydrolyse internal (peptide
bonds)
More ends or increase in surface area (for
exopeptidases);
The addition of a respiratory inhibitor stops the absorption of amino acids.
Use Figure 1 to explain why.
No/less ATP produced
Sodium (ions) not moved (into/out of cell);
No concentration gradient for sodium (to
move into cell with amino acid);
Give two reasons why it was important that the student counted the number of
stomata in several parts of each piece of leaf tissue.
So it is a representative sample
To obtain a (reliable) mean;
Other than the distribution of stomata, suggest and explain two xerophytic
features the leaves of this plant might have.
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;
Suggest two reasons why the rate of water uptake by a plant might not be the
same as the rate of transpiration.
- Water used for
support/turgidity; - Water used in photosynthesis;
- Water used in hydrolysis;
- Water produced during
respiration;
The species of tubifex worm in Figure 3 has 50% saturation of their
haemoglobin with oxygen at 0.08 kPa.
Explain how this enables this species to survive in water polluted with sewage.
High/50% saturation (with oxygen)
below (pO2 of) 0.2 kPa;
(Oxygen) for respiration;
Species of tubifex worm that live in ponds, lakes and rivers cannot survive in
seawater.
Use your knowledge of water potential to explain why they cannot survive in
seawater.
Water potential higher in worm
Water leaves by osmosis (and
worm dies);
Suggest two reasons why an increase in phosphate can be linked to growth of
the embryo.
(Phosphate required) to make RNA;
2. (Phosphate required) to make DNA;
3. (Phosphate required) to make
ATP/ADP;
4. (Phosphate required) to make
membranes;
5. (Phosphates required) for
phosphorylation;
The chilling requirement of seeds of certain plant species is considered to be an
adaptation for survival in countries with seasonal changes in environmental
conditions.
Suggest how this adaptation may enable these plant species to survive and
respond to seasonal changes.
Seeds/embryo remain
dormant/inactive in winter/cold
Seeds/plants develop in
spring/summer
HIV attaches to a specific protein receptor on helper T cells. A low percentage
of people have a mutation of the CCR5 gene which codes for this protein
receptor. This mutation results in a non-functional protein receptor.
Explain how this mutation can result in the production of a non-functional protein
receptor.
Change in DNA base/nucleotide
(sequence);
2. Change in amino acid
(sequence)/primary structure;
3. Alters (position of)
hydrogen/ionic/disulfide bonds;
4. Change in tertiary structure (of
receptor);
People with the CCR5 mutation show a greater resistance to developing AIDS.
Explain why.
Receptor) is not complementary
OR
(HIV) cannot bind/attach and
enter/infect (helper) T cell;
2. No replication (of virus)
OR
No destruction of (helper) T cell;
Some people produce a much higher ventricular blood pressure than normal.
This can cause tissue fluid to build up outside the blood capillaries of these
people.
Explain why.
More fluid forced/filtered out of
capillary/blood (due to high
pressure);
2. Less return of fluid (into
capillary/blood) due to pressure
Describe how the structures of starch and cellulose molecules are related to their
functions.
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;
Describe the processes involved in the transport of sugars in plant stems.
1)(At source) sucrose is actively
(transported) into the phloem/sieve
element/tube;
2. By companion/transfer cells;
3. Lowers water potential in
phloem/sieve element/tube and
water enters by osmosis;
4. (Produces) high (hydrostatic)
pressure;
5. Mass flow/transport towards
sink/roots/storage tissue;
6. At sink/roots sugars are
removed/unloaded;
The food eaten by a rabbit is digested mainly by microorganisms in its caecum.
The caecum is a section of intestine attached between the ileum and the large
intestine. The resulting semi-digested material leaves the anus of a rabbit as soft,
caecal droppings. The rabbit then eats these caecal droppings.
Use this information and Figure 2 to suggest how eating its own caecal droppings
helps a rabbit’s digestion and absorption of dietary protein.
- More/remaining/undigested (protein) broken
down; - (So more) amino acids absorbed;
- (Because) protein/food passes again through
stomach/ileum;
Role of single-stranded DNA fragments
- Template;
- Determines order of nucleotides/bases;
Role of DNA nucleotides
Forms complementary pairs / A – T, G - C
The scientists hypothesised that memory B cells had formed in the mice 180 days
after the 3rd injection.
Suggest and explain a practical method the scientists could use to test this
hypothesis.
- Inject vaccine (again)/meningitis antigen/
inactive antigen/dead/living bacteria/
pathogen/use a booster; - (Memory cells present if) faster/more
rapid production/higher concentration
antibody (than 1st injection) - Add enzyme attached to (second)
antibody against memory cell; - Colour change shows memory cell
present;
Explain why coloured water moved up the stalks.
- Water evaporates/is transpired (from leaves/
stalk/celery/plant); - Water potential gradient/lower water potential
creates tension/pulls up wate - Hydrogen bonds/cohesion/adhesion maintains
column;
Circle the most appropriate measure for this set of measurements.
Give a reason for your choice and find the value using the measurements from all
eight stalks.
why median
- (Presence of) outliers/80/70
OR
Small sample size/8 (measurements);
Describe the roles of iron ions, sodium ions, and phosphate ions in cells.
. -Haemoglobin binds/associates with
oxygen
- Co-transport of glucose/amino
acids (into cells);
3. (Because) sodium moved out by
active transport/Na – K pump;
4. Creates a sodium
concentration/diffusion gradient;
5. Affects osmosis/water potential;
-Affects osmosis/water potential;
7. Joins nucleotides/in
phosphodiester bond/in backbone
of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
9. Phosphorylates other compounds
(usually) making them more
reactive;
10. Hydrophilic/water soluble part of
phospholipid bilayer/membrane;
The movement of substances across cell membranes is affected by membrane
structure. Describe how.
-phospholipid bilayer allows diffusion of non polar/lipid soluble substances
- Phospholipid bilayer prevents diffusion of polar/charged/lipid soluble substances
- carrier proteins allow active transport
- channel/carrier proteins allow facilitated diffusion/co-transport
- shape/charge of carrier protein determines which substances are transported/moved
-number of channel/carrier proteins determine how much movement
- membrane surface area determines how much movement
- cholesterol affects fluidity/permeability
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule
- Condensation (reaction)/loss of water;
- (Between) phosphate and deoxyribose;
- (Catalysed by) DNA polymerase;
In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.
Describe how the separation of strands occurs.
- DNA helicase;
- Breaks hydrogen bonds between base pairs/ AT
and GC/complementary bases
OR
Breaks hydrogen bonds between polynucleotide
strands;
Explain how an arteriole can reduce the blood flow into capillaries
- Muscle contracts;
- Constricts/narrows arteriole/lumen;
What can you conclude from the appearance of valves in Figure 1 about heart muscle activity and blood movement between:
1. ventricles and arteries?
- Ventricle (muscles) relaxed
No (blood) backflow (into ventricles)
What can you conclude from the appearance of valves in Figure 1 about heart muscle activity and blood movement between:
. atria and ventricles?
. Atria (muscle) contracted;
4. Blood movement from atria (into ventricles);
When bread becomes stale, the structure of some of the starch is changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could help to
reduce weight gain.trrrrrr
- Less hydrolysis of starch;
- (To) maltose;
- (So) less absorption (of glucose)
Phloem pressure is reduced during the hottest part of the day. Use information in Figure 6 along with your understanding of transpiration and mass flow to explain why
. High (rate of) transpiration/evaporation;
2. Water lost through stomata
(Causes) less water movement from xylem to
phloem
Describe the processes involved in the absorption and transport of digested lipid
molecules from the ileum into lymph vessels.
Micelles contain bile salts and fatty
acids/monoglycerides;
2. Make fatty acids/monoglycerides (more) soluble
(in water)
Fatty acids/monoglycerides absorbed by
diffusion;
4. Triglycerides (re)formed (in cells);
5. Vesicles move to cell membrane;