Biology Multiple Choice Questions on “Phloem Transport”.
1. The phloem sap consists of _________
a) amino acids
b) sucrose
c) hormones
d) stachyose
Answer: b
Clarification: Phloem sap consists of water and sucrose. Other than those, other sugars such as stachyose along with hormones and amino acids are also transported by phloem tissue.
2. Sucrose is translocated through phloem can be demonstrated by ________
a) ringing the stem
b) defoliation
c) grafting
d) root pressure
Answer: a
Clarification: Defoliation is the detachment of leaves from the branch. Grafting is a method of vegetative propagation. Root pressure is responsible for upward movement of water and minerals in xylem. Ringing of stem in girdling experiment is the method of explain the translocation of sucrose is carried out through phloem.
3. The source and sink relationship is variable.
a) True
b) False
Answer: a
Clarification: The function of the source and sink is interchangeable. During the favorable season, leaves acts as a major source transferring food to sugar storage organs which act as a sink. During dry season, these storage organs act as a source and the sink leaves as well as other organs become the sink.
4. Define exudation.
a) Coming out of xylem sap from tips of leaves
b) Loss of water from living aerial tissue in form of vapors
c) Oozing out of liquid from pores and wounds
d) Movement of substances through vascular bundles
Answer: c
Clarification: Exudation is the coming out of liquid substances from pores and wounds. Guttation is the coming out of xylem sap from tips of leaves. Transpiration is the loss of water from living aerial tissue in form of vapors. Movement of substances through vascular bundles is known as translocation.
5. Statement A: The process of phloem loading is an active process.
Statement B: The process of phloem unloading is a passive process.
a) Both the statements are true
b) Both the statements are false
c) Statement A is true but Statement B is false
d) Statement B is true but Statement A is false
Answer: c
Clarification: Both the process of sucrose loading and unloading in the phloem tissue is an active process. It is facilitated by the process of osmosis taking place in the adjacent xylem tissue. It develops the water potential gradient which aids the mass movement of sucrose.
6. Who gave the mechanism of pressure flow hypothesis?
a) Ernst Munch
b) Henry Dixon
c) Steward
d) Adolph Fick
Answer: a
Clarification: Ernst Munch gave the Mass flow hypothesis. Transpiration stream theory was given by Henry Dixon. Starch Sugar Inter-conversion Theory was given by Steward. Adolph Fick gave the diffusion rate theory.
7. Sugar solution flows from region of low turgor pressure to region of high turgor pressure.
a) True
b) False
Answer: b
Clarification: Sugar solution flows from region of high turgor pressure to region of low turgor pressure. It is based on the water potential gradient developed by adjacent xylem carrying out osmosis. It is an active process.
8. Which condition develops during the process of loading at the phloem tissue?
a) No change
b) Isotonic
c) Hypotonic
d) Hypertonic
Answer: d
Clarification: Hypertonic condition is developed during the process of loading at the phloem tissue. Isotonic condition develops in equilibrium condition. Hypotonic condition occurs in turgid cells which then swell as the water concentration in cell increases many times.
9. Which is the most accepted mechanism for the translocation of sugars from source to sink?
a) Pressure flow hypothesis
b) Cohesion-tension theory
c) Root pressure theory
d) Imbibition
Answer: a
Clarification: Pressure flow hypothesis is the most accepted mechanism for the translocation of sugars from source to sink. Cohesion-tension theory explains the process of transpiration. Root pressure theory demonstrates the movement of xylem sap. Imbibition is the reason behind emergence of seedlings out of the soil.
10. Statement A: Xylem is multi-directional in nature.
Statement B: Phloem is unidirectional in nature.
a) Both the statements are true
b) Both the statements are false
c) Statement A is true but Statement B is false
d) Statement B is true but Statement A is false
Answer: b
Clarification: Xylem is unidirectional in nature. It can be best explained by root pressure theory. Phloem is bidirectional, and sometimes multi-directional in nature. It can be best explained by pressure flow hypothesis.