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BIO 431 Plant Physiology Exam 2 Review Questions with Correct Answers
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BIO 431 Plant Physiology Exam 2 Review Questions with Correct Answers
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BIO 431 Plant Physiology Exam 2Review Questions with Correct Answers
What is phloem translocation? - Answer-The process of moving sugars through the
plant
How does sucrose move between the source and sink cells? - Answer-There is a higher
turgor pressure at the source end due to phloem loading and a lower turgor pressure at
the sink end due to phloem unloading
How does water move in the phloem STE? - Answer-Water moves by bulk flow due to a
pressure gradient. There is a water potential gradient
How does Phloem loading occur? - Answer-From the site of photosynthesis to ste-cc By
a short pathway (3-4 cells) and by symplast or apoplast pathways
Primary active transport - Answer-1st step. Creates energy potential that can be used
by the secondary active transport to transport sugar across the cell membrane.
Symport - Answer-Movement of protons and substrate in the same direction (inport)
Antiport - Answer-Proton and substrate move in different direction (export)
Symplastic pathway - Answer-Sugar moves through plasmodesmata all the way to
companion cell ST complex.
Apoplastic Pathway - Answer-Through plasmodesmata until it is loaded across
membrane from parenchyma cell into companion cell/sieve element
What usually surrounds the phloem and xylem, and is used for structure and support? -
Answer-Fibers
What are the bundle sheath cells? - Answer-sclerenchyma fibers protects the vascular
tissue
What allows the tree to create new cells year after year? (rings) - Answer-The vascular
cambium
Sieve tube elements are - Answer-Living highly modified cells containing cell
membranes, ER, plastids, and membranes. They have thickened primary cell walls
without lignin due to high pressure. They are connected to eachother with a continuous
cell membrane between cells. They contain sieve plate pores.
,Sieve plate pores are - Answer-modified plasmodesmata connecting one cell to
another.
2 Different types of Sieve cells - Answer-Sieve tube elements (angiosperms) and sieve
cells (gymnosperms)
What are companion cells? - Answer-Parenchyma cells associated with sieve tube
elements, having a cytoplasmic connection and provide metabolic support with the STE
How does water move through xylem and phloem? - Answer-Xylem movement of water
is completely passive, but phloem translocation requires energy to move sugar
(loading/unloading)
How are companion cell organelles distributed - Answer-Along the cell wall nearest to
the STE
STE characteristics of angiosperms - Answer-Sieve plates that are completely open,
with STE joined together. P-protein is present in all eudicots and many monocots, and
companion cells act as sources of ATP and other compounds
What is p- protein? - Answer-Unique mechanism for plants to deal with damage to
phloem and to leaves. Only exists in angiosperms. Composition varies in different
species. Phloem has positive pressure. Sugar solution in phloem flows out. P-Protein
forms plugs in sieve plate pores to maintain hydro static pressure. Short term solution
What is callose - Answer-Most plants have it. Glucose polymer :like starch and
cellulose. Rapidly synthesized. Once damaged, neighboring cells begins sealing within
20 minutes. Sieve plate pores are sealed and it is a long term solution.
How do scientists determine phloem sap composition? - Answer-Aphids mouth part gets
stuck right into phloem. it gets chopped off and positive pressure is maintained. (or
honeydew from the aphids exudate). Now we also have really small needles.
What is a source cell - Answer-An actively photosynthesizing region that is a net
exporter or a producer (leaves specifically mature ones)
What is a sink cell - Answer-A cell that does not produce enough energy to support its
own growth. (roots stem developing organs.) Function in respiring, building cells and
tissues, and storage
What examples of sink cells becoming sources - Answer-seeds germinating, potatos
sprouting new plants
What affects the mechanism of moving sugars from source to sink - Answer-We must
consider the structure of the phloem STE, the translocation flow rate, different directions
of translocation, transfer of PS from cells to STE and from STE to target cells.
, What is the most widely accepted model of phloem translocation? - Answer-The
pressure-flow model (Munch)
Describe the pressure flow model - Answer-(Bulk flow) hydro static pressure gradient.
From source to sink. Translocation in the phloem is linked to flow of water in the xylem.
(1.) sugar is moved against concentration gradient from source to phloem STE.
(2.) Lower water potential in the phloem causes water to flow from the xylem leading to
an increased pressure potential in the phloem near the source.
(3.) Simultaneously, sugars at the sink are being unloaded against the concentration
gradient, causing water to flow back into the xylem.
2 Types of Sugars - Answer-Reducing and Non reducing
What are reducing sugars? - Answer-Sugars that are more likely to react in phloem. Not
usually found in phloem. Exposed aldehydes or ketone groups. Likely to produce
reactive oxygen species. Reacts with membrane components, causing damage to the
cell. D-glucose, D-Mannose, D-Fructose
What are non reducing sugars - Answer-Sugars that are made from several sugar
molecules usually moved inside phloem. Sucrose, raffinose, stachyose, verbascose, or
sugar alcohols (Reduced aldehyde group.)
Most Common amino acids in the phloem - Answer-Glutamate and Asparatate.
(Important cellular components and signalling molecules)
Ureides - Answer-Is only found in plants with nitrogen fixing bacteria. Formed in nodules
in the root by the bacteria.
Phloem is involved in moving substances _______________________, while xylem is
involved in _____________________ from _________________ to
________________. - Answer-Phloem is involved in moving substances long distance,
(Ex: from leaf to leaf),
while xylem is involved in water and mineral movement from bottom to top.
Why do plants transport sucrose in the phloem? - Answer-It is a small, mobile non
reducing sugar which has greater stability and is less likely to react. It is a glucose and
fructose disaccharide, which has high free energy of hydrolysis.
Pathway of translocation of photosynthates from source to sink depends on - Answer-
Proximity of source to sink.
Developement stage (Young leaves, and seeds start as sinks and later become
source).
Direct vascular connections (on the same vascular bundle).
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