Question
Fluids inside unicellular and multicellular organisms allow materials to be moved.
(a) Explain how vesicles are used by cells to move materials.
(b) Describe the transport of carbon compounds such as sucrose and amino acids in phloem.
(c) Outline how food is moved from the stomach to the large intestine.
Answer/Explanation
Answer:
(a)
a. fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;
b. materials taken into cells by endocytosis/vesicle formation;
c. Paramecium takes in food / phagocytes engulf pathogens / another example;
d. materials released from cells by exocytosis/by vesicle fusing with plasma membrane;
e. neurotransmitter released at synapses / protein secretion / secretion from gland cell / another example;
f. movement/transport of materials (inside vesicles) within cells/through the cytoplasm/between organelles/from an organelle to the (plasma) membrane/from the (plasma) membrane to an organelle;
g. movement of proteins from the rough ER to the Golgi / another example;
(b)
a. transport/translocation in (phloem) sieve tubes;
b. flow of sap through pores in end walls/sieve plates;
c. sugar/amino acids are transported dissolved in water/sap;
d. loaded into phloem (companion cells/sieve tubes) by active transport;
e. protons pumped out and sucrose then enters by cotransport;
f. high solute concentration created in phloem/sieve tube;
g. water enters (sieve tube) by osmosis;
h. hydrostatic pressure in sieve tube increases;
i. unloading from sieve tubes in sink/in roots;
j. water leaves by osmosis lowering the hydrostatic pressure;
k. sap movement (in phloem) from higher to lower pressure;
l. movement from source/leaves to sink/roots;
(c)
a. by muscles (contracting);
b. peristalsis/waves of muscle contraction followed by relaxation;
c. longitudinal muscle pushes food along the intestine when it contracts;
d. circular muscle constricts the intestine to ensure movement only onwards/not back to stomach;
e. movement (from stomach to large intestine) via the small intestine/duodenum/ileum;
Question
The diagram shows a nephron from a mammal.
(a) Identify:
(i) structure X [1]
(ii) structure Y. [1]
(b) State the region of the kidney in which the loop of Henle is situated. [1]
(c) Explain the role of the hormone ADH in osmoregulation. [2]
(d) Outline two adaptations for water conservation in leaves of desert plants. [2]
Answer/Explanation
a i proximal convoluted tubule/PCT;
a ii glomerulus/Bowman’s capsule;
b medulla;
c a. ADH secreted if blood is hypertonic/solute concentration too high/water content too low/dehydrated;
b. aquaporins open/more aquaporins in (plasma membranes of cells in DCT/collecting duct) with ADH;
c. DCT/collecting duct becomes more permeable to water/reabsorbs more water (from filtrate);
d Mark the first two answers only (thick) wax layer/cuticle; hairs on leaves/rolled leaves; sunken stomata/stomata in pits/stomata opening at night/CAM physiology; (leaves reduced to) spines/needles/no/few/small leaves/low surface area (to volume ratio) of leaves; thick stems/water storage tissue/vertical stems (to avoid most intense sunlight);
Question
Increases in the frequency and severity of drought are part of climate change in many areas
of the world. Drought represents one of the major threats to food security as it can drastically
decrease crop yield.
Water stress occurs when the demand for water exceeds its availability. A water stress index
of 0.0 indicates non-water-stressed plants with normal transpiration and 1.0 is maximum
water stress with much less transpiration.
(a) Define transpiration.
A study was carried out on sorghum (Sorghum bicolor), an important cereal crop. The
sorghum plants were grown for 15 weeks after the date of planting. Flowering occurred
in week 9. There were 3 treatment groups in the study:
y Control: plants were watered throughout the study
y Pre-flowering drought: no water until week 9, followed by normal watering
y Post-flowering drought: normal amounts of water until week 9, but none after.
(b) (i) Compare the changes in water stress of the pre- and post-flowering drought
plants over the period shown on the graph.
(ii) Using the data, evaluate the hypothesis that sorghum plants are more vulnerable
to drought after flowering.
It was known that plant growth under certain drought conditions is intimately linked to
microbial communities in the root and in the soil around the root. The scientists took samples
from both the root and soil, identified the bacterial phyla present and classified them into
two groups: Gram-positive and Gram-negative bacteria.
The graph shows the abundance in the root of the three most common Gram-positive phyla,
a, b and c, and the three most common Gram-negative phyla, d, e and f, found at week 8
(before flowering), under control conditions and pre-flowering drought conditions.
(c) Distinguish between pre-flowering drought plants and control plants in terms of
the effect of water availability on the relative abundance of Gram-positive and
Gram-negative bacteria in the root.
The relative abundance of Gram-positive and Gram-negative bacteria in pre-flowering
drought conditions was compared over time inside the root and in the soil around the root.
(d) (i) Compare and contrast the relative abundance of Gram-negative bacteria in the
soil and the roots of pre-flowering drought plants.
(ii) Suggest a reason for the changes in relative abundance of bacteria in the soil
around the root between week 8 and week 9.
Scientists inoculated the roots of the sorghum plants with one of two different species
of Gram-positive bacteria. One set of plants was grown under drought conditions and
the control with normal water. They compared the fresh mass of the roots of these
two groups of plants.
(e) (i) Deduce the effect of drought on the fresh mass of the roots that have not been
inoculated (X).
(ii) Compare and contrast the effect of the inoculations with Gram-positive I (Y) and
Gram-positive II (Z) on the fresh mass of control and drought roots.
(iii) Suggest a reason for the observed effects of the inoculations in sorghum plants
under drought conditions.
(iv) Suggest an advantage of using bacterial inoculation, as shown in this study, over
traditional selective breeding to obtain crops that are more resistant to drought.
Answer/Explanation
Ans:
a) loss of water/evaporation through the stomata/leaves;
b) i. a. in both groups drought/lack of water causes (significant) increase in water stress index;
b. in both groups, with water, water stress index close to values for the control/not significantly
different;
c. both groups have no changes between weeks 14 and 15 / values remain constant in weeks
14 and 15;
ii.
a. (the hypothesis is supported as) more immediate response to drought in post-flowering
plants than pre-flowering;
b. at week 5 of pre-flowering drought the stress index has only reached 0.15 whereas after
two weeks of post-flowering drought it is 0.5 and/or after five weeks it is nearly 0.8
OR
larger/higher/greater level response to drought in post-flowering plants than pre-flowering;
c. stress index reaches a maximum of 0.56 pre-flowering but 0.78 post-flowering / much higher
at week 15/end of study;
d. stress index remains high for post flowering;
c)
Gram-positive more common in pre-flowering drought while Gram-negative more common in
control;
Gram-negative e and f never present in (pre-flowering) drought;
d) i. a. both groups have an increase from week 1 to week 2;
b. there is an (overall) decrease (in the relative abundance of Gram-negative) in both after
week 2 / lower abundance from weeks 3 to 8;
c. both increase (greatly) after week 8/starting from week 9/flowering/end of drought
period/with water onwards;
d. both have similar abundance after week 8/from week 9/end of drought period onwards;
e. both plateau in the last weeks;
f. other correct similarity e.g., the overall pattern is similar for both roots and soil over the entire
study / overall similar trend;
Difference:
g. the soil has more Gram-negative than the root in the drought period/up to week 8/until
flowering / OWTTE;
ii.
a. Gram-positive are more resistant/better adapted to drought conditions
OR
Gram-negative are more resistant/better adapted to conditions with water;
b. Gram-positive outcompete the Gram-negative in drought conditions
OR
Gram-negative outcompete Gram-positive in conditions with water;
c. water allows for greater metabolism/reproduction of Gram-negative;
e) i.
drought causes a (very large) drop in the fresh mass (compared to controls) / decrease in
range of fresh mass;
ii.
a. in drought condition root, both inoculations have a higher mean of root fresh mass
compared to no inoculation;
b. in control conditions root, a (slightly) lower mean (of the root mass) in both inoculations
compared to no inoculation;
c. II/Z has a (slightly) higher mean than I/Y in the drought root;
d. Inoculation increases the range of fresh mass values (in both cases) / more in control
conditions;
iii. a. Gram-positive bacteria may have a symbiotic/positive relationship with the sorghum;
b. Gram-positive bacteria may provide plants with oxygen/more nutrients/change pH;
c. Gram-positive bacteria may help to retain/absorb more water;
iv. faster/cheaper to develop to resistance to drought / known way to increase yield during
drought;