Syllabus Edition
First teaching 2014
Last exams 2024
1 markThe movement of phloem sap is an active process.
Which of the following is the most suitable explanation for this?
Phloem sap flows from the source to the sink.
ATP is required to load organic compounds into the phloem at the source.
Water leaves the phloem sieve tube at the sink.
Water moves into the phloem at the source by osmosis.
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1 markWhich of the following is not a structural feature of phloem tissue?
Lignified cell walls to withstand the hydrostatic pressure.
Columns of sieve tube cells.
Companion cells containing cell components that facilitate the loading and unloading of organic compounds.
Sieve plates with pores allows for the continuous movement of organic compounds.
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1 markWhich of the following aphid characteristics makes them suitable to use when investigating phloem transport rates?
I and IV only.
I, III, and IV only.
II, III, and IV only.
I, II, III, and IV.
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1 markThe micrograph below shows part of a cross section of a plant stem.
Which of the structures A-D represents the xylem tissue?
Image courtesy of Doc. RNDr. Josef Reischig, CSc. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported license. Reused and distributed under conditions found at: https://creativecommons.org/licenses/by-sa/3.0/
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1 markWhich row correctly identifies a structure and its related function in a companion cell?
| Structure | Function | |
| A. | Many mitochondria present | Translation of polypeptides that will form cell surface membrane proteins |
| B. | Nucleus and cell organelles | Carrying out the cell processes of the sieve tube cells |
| C. | Plasmodesmata | Linking adjacent companion cells with each other |
| D. | Small amount of cytoplasm present | Facilitating the movement of assimilates |
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Which of the following correctly identifies a source and a sink in a plant?
|
Source |
Sink |
|
| A |
Sprouting potato tubers |
Growing apples |
| B |
Growing apples |
Sprouting potato tubers |
| C |
Young, growing potato tubers |
Mature leaves |
| D |
Growing apples |
Young, growing potato tubers |
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The following steps describe the process of translocation.
What is the correct order of the steps?
III → II → IV → I
III → I → IV → II
I → III → IV → II
I → IV → III → II
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Which of the following statements apply to phloem sieve tubes?
I only
II and III only
I, II and IV
III and IV only
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Why can the symplastic pathway for loading sucrose be considered a passive process?
Sucrose moves from the companion cell into the sieve tube through plasmodesmata
Sucrose is carried against its concentration gradient into the companion cell through a co-transporter protein
H+ ions are pumped out of companion cells by proton pumps
Transfer cells contain many mitochondria to provide energy for the proton pumps to work
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Which of the following describes the apoplast route along which sucrose is loaded into phloem sieve tubes?
I only
I and II only
I, II and IV
I, III and IV
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Which of the following does not contribute to generating a high hydrostatic pressure at the source?
A high solute concentration in phloem sieve tubes due to the loading of sucrose
The incompressibility of water molecules
The rate at which sucrose is converted to starch in storage tissue
Rigid plant cell walls made of cellulose
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Girdling, or ring-barking, involves the removal of a strip of bark around the entire circumference of a tree trunk. This removes the outer part of the vascular bundles which results in the death of the entire tree over time.
What could be a possible explanation for this?
Xylem is removed from the vascular bundles, so water and mineral salts cannot be transported to the leaves
Phloem is removed from the vascular bundles, so sugars cannot be transported to the roots
Xylem is removed from the vascular bundles, so sugars cannot be transported to the roots
Phloem is removed from the vascular bundles, so water and mineral salts cannot be transported to the leaves
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The following photomicrograph shows the vascular bundle in a root.
Which letter identifies the phloem?
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Aphid stylets can be used to measure phloem transport rates in plants. It was found that the transport rate in stylets located close to a source was much higher compared to those located close to a sink.
What could be a possible explanation for this?
The hydrostatic pressure at a sink is low due to the buildup of sucrose in the phloem sieve elements
The hydrostatic pressure at a sink is high due to water moving into phloem sieve elements by osmosis
There is a high hydrostatic pressure at the source due to the incompressibility of water
There is a low hydrostatic pressure at the source due to a low solute concentration in the sieve tube elements
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Why are radioisotopes considered to be such important tools in studying translocation?
It provides a way to track the distribution of molecules between sources and sinks in a plant
To determine the order in which carbon compounds are generated
It provides a way to determine the rate of carbon fixation in a plant
Radioactive molecules contribute to the hydrostatic pressure in xylem vessels
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1 markThe following statements describe steps in the movement of sucrose along the apoplast pathway.
Which of the following represents the correct order of the steps?
IV → I → V → II → III
I → IV → V → III → II
IV → I → V → III → II
I → V → IV → III → II
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1 markWhich of the following best describes the factor that determines the direction of mass flow of phloem sap between leaves and fruit?
The active loading of sucrose into phloem sieve tubes near the fruit will create a hydrostatic pressure gradient that will facilitate mass flow between the leaves and fruit.
The movement of water molecules in the phloem sieve tubes from the leaves to the fruit will contribute to the hydrostatic pressure gradient between them.
The movement of organic compounds into the phloem sieve tubes near leaves will increase the hydrostatic pressure in the sieve tubes and create a pressure gradient between leaves and fruit.
The unloading of organic compounds from the phloem sieve tubes at the fruit will increase the osmolarity of the sieve tubes and create a hydrostatic pressure gradient between the leaves and fruit.
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1 markAn aphid is located 6 cm from a source of 14C on a plant. It takes 15 minutes for the 14C to reach the aphid.
Which of the following gives the correct phloem flow rate in cm hr-1?
0.4
1.5
24
90
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1 markAphids secrete a sugary liquid called honeydew when they feed on phloem sap. Honeydew is produced in the guts of aphids and contains molecules known as oligosaccharides. Oligosaccharides consist of a small number of monosaccharides linked together and those produced by aphids are less soluble than sucrose.
Scientists investigated the effect of phloem sap sucrose concentration on the production of oligosaccharides in the guts of aphids.
Which of the following is the most likely explanation for the data?
Aphids produce more oligosaccharides when consuming high sucrose phloem sap in order to increase honeydew production in their guts.
Aphids produce more oligosaccharides when consuming high sucrose phloem sap in order to decrease the osmolarity of the gut contents.
Aphids produce more oligosaccharides when consuming high sucrose phloem sap in order to increase the osmolarity of the gut contents.
Aphids produce more oligosaccharides when consuming high sucrose phloem sap in order to prevent an excess of water from moving into the cells.
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1 markCertain heavy metals, e.g. zinc and chromium, are considered toxic to plants. Research suggests that some of these metals can alter the outcome of the events that occur within the electron transport chain inside plant cells.
Fruit trees grown in soils containing high levels of heavy metals have been found to produce fruits that are much smaller than those produced by trees grown in soil with low concentrations of the metal.
Which of the following statements provides the most important and reasonable explanation for this observation?
Loading of organic compounds in the apoplast pathway cannot occur due to a lack of proton pump activity.
Loading of organic compounds in the apoplast pathway cannot occur due to non-functional membrane transport proteins.
Loading of organic compounds through the symplast pathway cannot occur due to a lack of proton pump activity.
Unloading of organic compounds cannot occur at the source due to a lack of membrane transport proteins.
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