PLANT PHYSIOLOGY – QUESTION AND ANSWER COMPENDIUM
Introduction to plant physiology Foundations of plant
physiology.
1. What is plant physiology?
Plant physiology is the science of the study of the functioning of plants on
the cellular, tissue, organ, and whole plant levels. It investigates metabolic
pathways, growth, structural adaptations, reaction to environmental stimuli
and biochemical-biophysical interactions that help to maintain life.
2. What is the significance of plant physiology in the biology sciences?
Plant physiology is vital since it describes how plants can use sunlight to
process chemical energy, control water and nutrient uptake, produce organic
compounds, and react to stress. The processes are the basis of food
production worldwide, ecosystem operation, climate control, and
biotechnological innovation.
3. How can plant physiology be related to agriculture??
The study of plant physiology provides valuable information to agricultural
practices, which clarifies the effects of nutrient availability, water availability,
temperature, and light on crop performance. It influences the fertilizer
formulation, irrigation practices, growth regulators, control of pests as well
as genetic enhancement of yield, stress, and quality.
4. What are the most important disciplines of plant physiology?
Some of the key areas are photosynthesis, respiration, water relations,
mineral nutrition, development regulation, hormone biology, stress
physiology, transport mechanisms and development of plants.
5. What is the distinction between the study of Physiology of plants and that
of anatomy?
The science of plant physiology concerns the functions and the science of
plant anatomy concerns the structure. Physiology is the study of metabolic
processes whereas anatomy is the study of tissues, cells, and the structure
of organs.
6. What are the key organs of plants, which are involved in the physiological
activity?
The absorption, conduction, photosynthesis, reproduction, storage and
protection are some of the specialized functions that roots, stems, leaves,
flowers, fruits and seeds all play.
7. What are the roles of cells in physiological functioning of plants?
The organelles are present in the cell and they include chloroplasts,
mitochondria, vacuoles and ribosomes which play functions of synthesis,
generation of energy, storage and regulation. Their actions all determine
growth and adaptation of plant life.
8. What is the purpose of the chloroplasts to the plant?
Chloroplasts do photosynthesis, produce ATP, synthesize sugars, and control
the important metabolic routes. They are also involved in the synthesis of
lipids, nitrogen uptake and responses to stress.
9. In plants, what are the functions of mitochondria?
The mitochondria produce ATP by respiration, promote photorespiration and
regulate the redox potential in the cell. They are energy centers that are
vital in growth, development and tolerance to stress.
10. What physiological functions does the vacuole play?
The vacuole helps retain turgor pressure, store ions, metabolites, and
pigments, removes toxic substances and controls the pH. It is essential in the
expansion of cells.
Plant-water relations.
11. What is water potential?
Water potential is defined as the amount of potential energy of water within
a system which can be utilized to decide the direction in which water flows.
The water moves out of high potential to low potential.
12. What are the factors affecting water potential?
There are major components, which are solute potential, pressure potential,
gravitational potential, and matric potential. The solutes reduce the water
potential, and its increase can be achieved by pressure.
13. In plants, what benefit do osmosis provide?
Osmosis promotes the uptake of water by the cells, turgor, nutrient
transport, and mechanical stability.
14. What is transpiration?
Transpiration is the process in which water is lost on plant surfaces by
evaporation. It affects water movement, nutrient movement and the
temperature of leaves.
15. What is the way stomata control the gaseous exchange and water loss?
Guard cells are used in the regulation of opening of stomata through
alteration of turgor. They are sensitive to light, CO 2 concentration, humidity,
internal hormones as well as environmental signals.
16. What is the significance of the cohesion-tension theory?
The theory of cohesion tension provides the mechanism of movement of
water through xylem. The tension formed by transpiration and cohesion of
water molecules enables the continuous water columns to ascend between
leaves and roots.
17. What are the ways through which plants take in water in the soil?
Water is absorbed in the roots by root hairs through osmosis. Water travels
via apoplastic, symplastic or transmembrane routes till it gets to xylem.
18. What is root pressure?
Root pressure represents a positive pressure due to the accumulation of
active ions in the xylem. It can sometimes play a role in the movement of
water particularly during the nights or in small plants.
19. What are the environmental effects on transpiration?
The rate of transpiration is greatly affected by temperature, relative
humidity, wind speed, light intensity and soil moisture.
20. In What are the ways do plants reduce water ?
Plants reduce water loss via stomata control, waxy cuticles, leaf hair, leaf
folding, and decreased areas of the leaf, and specialized tissue, e.g.,
thickened epidermis.
The mineral nutrition and transport.
21. What nutrients are good in plants?
Essential nutrients are components that are needed to promote normal
growth and reproduction in plants. These are macronutrients (N, P, K, Ca,
Mg, S) and micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl, Ni).
22. Why is nitrogen essential?
Proteins, nucleic acids, enzymes, chlorophyll, and amino acids need nitrogen.
The deficiency leads to chlorosis and retarded growth.
23. The process of plant uptake of nitrogen How do plants take in nitrogen?
Nitrogen is absorbed into the plants in the form of nitrate and ammonium. It
is also possible that the atmospheric nitrogen is used by legumes by
symbiotic fixation by rhizobia.
24. What is the role of phosphorus?
Phosphorus plays an important role in ATP, nucleic acids and structure of
membranes. It facilitates the transfer of energy, cell division and root
development.
25. What is the importance of potassium in plant physiology?
Potassium controls the osmotic pressure, activation of enzymes, stomatal
activities and photosynthesis rates. It improves the tolerance to stress.
26. What are the mechanisms of nutrient transport in plants?
Nutrients move using the xylem or phloem using pressure-flow processes
transporting sugars and solutes along source-to-sink tissue distances.
27. What is the distinction between the xylem and phloem transport?
Water and minerals move in the same direction down to the shoots and up to
the roots, and sugars move in either direction between the source organs
and the sink organs, respectively.
28. What are the chief manifestations of nutrient deficiency?
The usual symptoms are chlorosis, necrosis, retarded growth, low fruiting,
thin stems, and deformity of leaves. All the elements generate characteristic
signs.
29. What are the benefits of the mycorrhizal fungi to nutrient uptake?
Mycorrhizae increase water uptake, micronutrient and phosphorus. They
enhance soil structure and make plants to be resistant to abiotic and biotic
stresses.
30. What are the differences in nutrient mobility of plants?
N, P, K, Mg are also transported between older and younger tissues with the
initial deficiency observed in old leaves.
Young tissues are the first to be affected by immobilized nutrients (Ca, Fe,
B).
Photosynthesis
31. What is photosynthesis?
Photosynthesis refers to the biochemical pathway by which the green plants,
algae and some bacteria use light energy to produce chemical energy. It
entails producing carbohydrates by the use of carbon dioxide and water and
it gives out oxygen as a by-product.
32. In plants, which ways do photosynthesis take place?
Photosynthesis takes place in the chloroplasts in both the stroma and the
thylakoid membranes of the chloroplasts which contains the Calvin cycle and
the light-dependent reactions respectively.
33. What are these two steps in the process of photosynthesis?
Photosynthesis consists of two processes:
The light-dependent reactions which are able to capture the light energy to
form ATP and NADPH.
The light-independent reactions (Calvin cycle), involving the fixation of
carbon dioxide into the carbohydrates with the help of ATP and NADPH.
34. What is the purpose of chlorophyll in plants?
The light is absorbed by chlorophyll particularly in the blue and red
spectrum. It is the main pigment which initiates photochemical reactions,
excite electrons.
35. What are the uses of light-harvesting complexes?
Photons are collected and energy channeled to the reaction centers by light-
harvesting complexes. They enhance the capacity of capturing light and
shielding chlorophyll against photodamage.
36. Explain what is meant by the Z-scheme of photosynthesis?
The Z-scheme is an account of the energy pathway of the electrons in the
electron transport chain of Photosystem II and Photosystem I. It generates
NADPH and creates a proton gradient to be used in the production of ATP.
37. What happens to the process of ATP synthesis during photosynthesis?
The photophosphorylation of ATP occurs. Electron transport can cause the
formation of proton gradients which drive ATP synthase to transform ADP
and inorganic phosphate to ATP.
38. What is photolysis of water?
Photolysis can be defined as the process of dividing water into oxygen,
protons and electrons. This happens in Photosystem II and supplies electrons
to substitute the electrons lost by excited chlorophyll.
39. What is the Calvin cycle?
The Calvin cycle refers to the chain of reactions involved in the fixation of CO
2 in organic compounds. It is composed of carbon fixation, reduction and
regeneration of the CO 2-acceptor molecule, ribulose-1, 5, bisphosphate
(RuBP).
40. Which enzyme is used in the carbon fixation?
RuBisCO (ribulose-1-bisphosphate carboxylase/oxygenase) is used in the
fixation of carbon dioxide. It is the richest enzyme on the Earth.
41. What is the difference between the photorespiration and photosynthesis?
When Oxygen instead of carbon dioxide is fixed by RuBisCO, then it is
referred to as photorespiration. It uses ATP and produces CO 2 that impairs
photosynthesis.
42. Why are C 4 plants more effective in photosynthesis?
C 4 plants reduce the process of photorespiration by the concentration of CO
2 around RuBisCO. Such spatial isolation enhances the process of carbon
fixation at high temperatures, high light, and low CO 2.
43. How does PEP carboxylase play its role in C 4 plants?
PEP carboxylase oxygenates the CO 2 to four-carbon compounds of high
affinity and does not react with oxygen. It is able to provide an effective
carbon capture even as stomata partially close.
44. Conservation of water by CAM plants How do CAM plants conserve
water?
As a response to CO 2 in the atmosphere, CAM plants open their stomata at
night and accumulate the CO 2 as malate. Stomata close and malate
releases CO 2 internally in the day and photosynthesis takes place. This is a
plan to minimize water wastage.
45. Among others, what is the influence of light intensity on photosynthesis?
There are two stages of photosynthesis, where the photosynthesis increases
with light intensity to a saturation point. Onward, the rate is constrained by
other factors like CO 2 concentration or enzyme activity.
46. What is the effect of temperature on photosynthesis?
The enzyme activity is influenced by temperature. Low temperatures retard
reactions, whereas high temperatures enhance photorespiration and
decimate the efficiency of carbon fixation.
47. What is the impact of CO 2 concentration on photosynthesis?
An increase in CO 2 concentration tends to accelerate the rate of
photosynthesis until the stage of RuBisCO saturation. C 4 plants do not
respond intensely to enrichment of CO 2 in as much as C 3 plants.
48. What is the need of the accessory pigments in plants?
Accessory pigments, which include carotenoids and xanthophylls, expand the
range of light acquired, prevent the effects of photooxidative stress, and
enhance the rate of photosynthesis.
49. What are the factors that result in photoinhibition?
Photoinhibition may occur because of excessive light, high temperatures,
drought and nutrient deficiencies that can destroy photosynthetic apparatus,
particularly Photosystem II.
50. What happens to plants who are overprotected against excessive light?
The mechanisms used by plants to avoid photodamage are heat dissipation,
activation of the xanthophyll cycle, syntheses of antioxidants, and structural
leaf changes.
RespIration and Energy Metabolism.
51. What is plant respiration?
Respiration: this is a metabolic process by which plants oxidize organic
compounds to form ATP, CO 2 and water. It gives the energy that is
necessary in growth, maintenance and biosynthesis.
52. How are the various major steps of respiration?
The respiration includes glycolysis, citric acid cycle and oxidative
phosphorylation using the electron transport chain.
53. Where does glycolysis occur?
The glycolysis takes place in cytosol. It hydrolyzes glucose to produce
pyruvate with the production of ATP and NADH.
54. What happens to pyruvate after the glycolysis process?
Pyruvate is delivered to mitochondria and changed into acetyl-CoA which is
returned to the citric acid cycle.
55. What is the citric acid cycle?
A group of enzymatic reactions are known as the citric acid cycle and oxidize
acetyl-CoA into CO 2. It produces NADH, FADH₂, and ATP.
56. What is the mechanism of the ATP production in mitochondria?
Mitochondria produce ATP by way of oxidative phosphorylation. The protons
are transported across the inner membrane by electron transport pumps and
this forms a gradient which drives ATP synthase.
57. What is the second pathway of oxidase that exists in plants?
The alternative oxidase (AOX) form of transporting electrons to oxygen is
independent of the pumping of protons. It is less protective of cells against
excessive reactive oxygen species but produces less ATP.
58. Why is the respiration necessary to the growth of plants?
Biochemical energy that is needed by the body to divide the cell, take in
nutrients, biosynthesize and maintain the structure is provided by
respiration.
59. What is the impact of the temperature on respiration?
As temperature rises, respiration rises up to the point that enzymes are
denatured. Too much heat will cause too much depletion of carbohydrates
and slow down the productivity of the plant.
60. The effects of low oxygen conditions on plants?
Fermentation is one of the anaerobic mechanisms that plants can use to
produce ethanol or lactate. They also alter the root architecture and increase
the aerenchyma formation.
Growth and development of plants.
61. What is plant growth?
Plant growth can be defined as irreversible and cell division, as well as cell
elongation, which increase the size, mass, and volume of a plant.
62. So what is the development in plants?
The development involves differentiation, morphogenesis and maturation
processes which give rise to the specialized tissues and organs.
63. What are meristems?
Regions of proliferating cells are known as Meristems.
Primary growth is propelled by apical meristems whereas the secondary
growth is facilitated by lateral meristems.
64. What is the mechanism of cell elongation?
The loosening of the walls, the uptake of water and the turgor pressure are
all needed in cell elongation. Auxin triggers the proton pumps rendering the
cell walls more pliable.
65. What is the role played by the cell cycle in the growth of the plant?
The DNA replication, mitosis and cytokinesis are controlled by the plant cell
cycle. Its control makes it grow and form tissues in an orderly manner.
66. What is the role of the environmental signals in controlling growth?
Light, temperature, availability of water, nutrients, and mechanical stimuli
affect the growth rates by regulating hormonal and gene expression.
67. What is tropism?
Tropism is directional development due to stimuli.
Plants are directed to the favorable conditions by phototropism,
gravitropism, hydrotropism, and thigmotropism.
68. What is the perception of plants to gravity?
Root cells with statoliths decrease in height through gravity stimulating
signaling pathways, which regulate directional growth.
69. What is photomorphogenesis?
Photomorphogenesis is light regulated development in plants. It involves
such processes as seedling de-etiolation and flowering induction.
70. What is the contribution of phytochromes in the development?
Phytochromes are light sensitive proteins which sense red and far-red light.
They control germination, shade avoidance, circadian rhythms and flowering.
Plant Hormones (PHYtohormones).
71. What are plant hormones?
Plant hormones are organic compounds which regulate growth, development
and physiological functions of plants in very low concentrations and are
endogenous.
72. What are the significant categories of plant hormones?
The key hormones are auxins, cytokinins, gibberellins, abscisic acid,
ethylene, brassinosteroids, jasmonates and salicylic acid.
73. What is the major role of auxins?
Auxins facilitated cell growth, apical dominance, root formation, vascular
development and tropic responses.
74. What is the location of auxins production?
Auxins are produced primarily in apices of the shoot, young leaves and
young seeds.
75. What is the effect of the auxins on phototropism?
Auxins are concentrated on the dark side of a stem, resulting in an increase
of cell elongation and bending towards the source of light.
76. What are the roles of the auxins in the development of roots?
Auxins induce side and additional root development. They control root
structure and improvement of nutrient foraging.
77. What are cytokinins?
Cytokinins are hormones which encourage the cell division, postpone the leaf
senescence, stimulate the growth of chloroplast and trigger the growth of
shoot.
78. In what location are the cytokinins produced?
The cytokinins are mainly produced in the root apical meristems and are
moved upwards through the xylem.
79. What is the interaction between the auxins and cytokinins?
The ratio guides the organ formation.
A high ratio (auxin to cytokinin) facilitates the growth of roots, whereas high
cytokinin to auxin ratio encourages growth of the shoot.
80. What are gibberellins (GAs)?
Gibberellins are hormones that stimulate the growth of stems, germination,
flowering and fruit development.
81. What is the mechanism by which the gibberellins stimulate seed
germination?
Gibberellins promote the production of hydrolytic enzymes mobilizing stored
nutrients which allows growth of embryos.
82. What is abscisic acid (ABA)?
ABA controls the stress reactions, seed dormancy, stomatal closure, and
drought, salinity, and cold tolerance.
83. Mention the importance of ABA under drought stress.
ABA causes a quick stomata closing which decreases transpiration and loss
of water and triggers stress-responding genes.
84. What is the role of ethylene in the physiology of plants?
Ethylene regulates the ripening of fruits, leaf falls, senescence and
mechanical stress.
85. commercially how is ethylene used?
It is used to coordinate the aspect of ripening, improve flowering and control
the maturation to market readiness.
86. What are brassinosteroids?
The brassinosteroid is a steroidal hormone that facilitates cell growth,
differentiation of vascularization and ability to withstand stress.
87. What are jasmonates?
Jasmonates control herbivore defense, enhance reproductive growth, and
alter herbivore defense.
88. What is the main role of salicylic acid?
Activation of systemic acquired resistance, defense against pathogens, and
involvement in thermotolerance are the functions of salicylic acid.
89. What is the means through which hormones incorporate the signals of
the environment?
Hormones are the internal messengers between the environmental stimuli
and gene expression, growth regulation and survival strategies.
90. What is the interaction between hormones during stress reactions?
Adaptive responses to hormones are coordinated by hormone crosstalk (in
particular, between ABA and ethylene, and between jasmonates and salicylic
acid).
In this section, a physiological explanation of the process of plant stress is
provided.
91. What is the physiology of plant stress?
Plant stress physiology studies the way plants sense, respond, and adapt to
unfavorable situations like drought, salinity, extreme temperatures and biotic
invasions.
92. What is abiotic stress?
Abiotic stress is the negative environmental conditions such as drought,
heat, cold, salinity, nutrient deficiency and UV radiation.
93. What is biotic stress?
Biotic stress is caused by living organisms that include pathogens, insects,
nematodes, and parasitic plants.
94. How do plants detect stress?
Plants apply the receptor proteins, membrane sensors and biochemical
signals as the means to sense the existence of stress and to activate the
stress-responsive pathways.
95. What is oxidative stress?
Oxidative stress arises when the reactive ovular species surpass the
detoxification ability causing damage to membranes, DNA and proteins.
96. PlantResponse Oxidative stress is regulated by plants in response to
stimuli.
Enzymatic (SOD, catalase, peroxidases) and non-enzymatic (vitamin C,
glutathione, flavonoids) antioxidants are used by the plants to counteract the
damage caused by oxidants.
97. What are the impacts of drought to plant physiology?
Drought causes water potential to be low, turgor to be low, photosynthesis to
be limited, nutrient uptake to be disrupted, and stomata to be closed.
98. What are the mechanisms of plant survival during the drought?
Plants boost root development, osmolyte build-up, stomatal control, ABA
signal transduction and strengthen cell walls.
99. What are the effects of salinity on plants?
Salinity produces ionic toxicity, osmotic stress, nutrient imbalance, and
metabolic disturbance.
100. Plant adaptation to salinity?
Plants do not include sodium in the roots, they compartmentalize the ions in
vacuoles, synthesize osmoprotectants, and increase antioxidant systems.
101. What are the effects of heat stress to plants?
Protein denaturation, membrane disruption, enzymes inhibition, and
membrane disruption all increase transpiration rate.
102. What are heat-shock proteins?
The heat-shock proteins are the molecular chaperones that stabilize the
proteins and help to repair the damage caused by heat.
103. What are the effects of cold stress on physiology?
Cold reduces the fluidity of the membrane, decreases reactions of
metabolism, raises ROS, and prevents photosynthesis.
104. How do plants adapt to cold?
Plants accumulate solutes, synthesize antifreeze proteins and change lipid
composition as well as cold-responsive genes.
105. What is the plant immune system?
Plant immune system is a system that is composed of localized and systemic
responses (SAR).
106. What is PTI?
Pattern-triggered immunity is the type of immunity in plants when the plants
recognize conserved pathogen molecules (PAMPs) and generate an immune
signal.
107. What is ETI?
A more specific and stronger defense is called effector-triggered immunity
and is initiated by intracellular receptors that have detected pathogen
effectors.
108. What are the ways in which the plants protect themselves against the
herbivores?
Toxins, thorns, trichomes, volatile compounds, and signaling molecules that
are used to repel herbivores are produced by plants.
109. What is systemic acquired resistance (SAR)?.
SAR offers prolonged and systemic immunity against infection in the whole
plant following a local infection. Salicylic acid and expression of defense
genes regulate it.
110. What is the significance of physiology of stress to agriculture?
Knowledge of plant stress responses can be used to develop climate
resistant crops, enhanced yields as well as sustainable production strategies.
Section 9: Mineral Nutrition and Soil Interactions.
111. What is the mineral nutrition in plants?
Mineral nutrition entails the intake, absorption and use of vital inorganic
compounds needed to develop and carry out plant growth and plant
physiological activities.
112. What are nutrients that are vital?
Essential nutrients are factors which a plant should acquire in the
environment to fulfill its life cycle. These are macronutrients and
micronutrients.
113. What are macronutrients?
Macronutrients are needed in great amounts. They are nitrogen, phosphorus,
potassium, calcium, magnesium and sulfur.
114. What are micronutrients?
The micronutrients are in trace form. These consist of iron and manganese,
zinc, copper, boron, molybdenum, chlorine, and nickel.
115. What is the reason why nitrogen is of importance to plants?
Nitrogen is a requirement of amino acids, nucleic acids, chlorophyll, and
most enzymes. It stimulates the growth of vegetation and protein
production.
116. What is nitrogen fixation?
Nitrogen fixation refers to the process of converting nitrogen in the
atmosphere into forms useful biologically by symbiotic bacteria, free-living
microorganisms or through industrial processes.
117. what role does phosphorus play in the physiology of plants?
Phosphorus plays an important role in ATP, nucleic acids, membrane
phospholipids and energy transport.
118. Why is potassium essential?
Potassium controls the movements of stomata, activation of enzymes,
osmotic pressure, and resistance to stress.
119. Which are the signs of deficiency which show shortage of nitrogen?
Deficiency of nitrogen leads to chlorosis of the old leaves, poor growth,
maturity retardation, and biomass reduction.
120. How does potassium deficiency affects the plant?
Deficiency of potassium causes marginal scorching of leaves, chlorosis, weak
stems and low quality of fruits.
121. What is the impact of soil pH on the nutrient availability?
The fertility of soils depends on the pH. The phosphorus and molybdenum
found in the acidic soils, and the iron, manganese and zinc found in the
alkaline soil are inhibited.
122. What is the way in which plants absorb minerals?
Membrane enclosed carriers and proton pumps help plants to take in
minerals passively, through transport, and actively by hydrolysis.
123. What is the rhizosphere?
Rhizosphere is the soil zone around the roots of plants where the activities of
the microorganisms, availability of nutrients and chemical interactions are
enhanced.
124. What are the functions of mycorrhizae in the nutrition of the mineral?
Mycorrhizal fungi are able to increase the nutrient uptake, especially
phosphorus, by extending the hypha net into the soil.
125. What is the effect of the root exudates on the soil interactions?
Root exudates adjust the microbial communities, funnel nutrients and govern
the soil structure using organic acids, sugars and secondary metabolites.
126. What is nutrient remobilization?
Nutrient remobilization entails redistribution of elements in the older tissues
to the younger developing organs during senescence or stress.
127. What is the relationship between the nutrient uptake and water
availability?
Minerals are transported by water to the roots. Drought causes a decrease in
uptake by decreasing mass flow and root hydraulic conductivity.
128. What is hydroponics?
Hydroponics is a no soil cultivation method in which crops are cultivated
using nutrient solutions. It makes it possible to maintain mineral nutrition
and productivity.
129. What is uptake efficiency of nutrients?
Nutrient uptake efficiency is the level of efficiency with which a plant absorbs
and utilizes mineral resources in comparison to its availability.
130. Why is mineral nutrition the key to food security?
Knowledge of mineral nutrition promotes sustainable fertilization, minimizes
the losses, boosts the quality of crops and increases agricultural output.
The relation of water to plants.
131. Explain the relationship between water and plant.
Plant water relations explain how plants can take in, carry and use water to
provide physiological functions like growth, cooling and movement of
nutrients.
132. What is water potential?
The free water energy is measured as water potential. It gives the water
direction of movement, always on the higher to lower potential.
133. What are the water potential constituents?
Water potential comprises of solute potential, pressure potential,
gravitational potential, and matric potential.
134. What is osmosis?
Osmosis is an act of movement of water through a semi permeable barrier
between a high water potential area and a low water potential area in a
passive manner.
135. What is transpiration?
Transpiration refers to the evaporation of water vapor by part of plants in the
air especially through stomata. It causes the movement of water and cools
leaves.
136. Cohesion tension theory What is cohesion tension theory?
The cohesion tension theory describes the movement of water in xylem.
Water is pulled up by cohesion between the molecules of water, and tension
created by transpiration.
137. What is the significance of turgor pressure?
Turgor pressure ensures that cells are held together, stimulates cells to
grow, aids in opening of stomata, and stabilization of tissues.
138. What is the mechanism of the stomata to control the water loss?
Guard cells open and close stomata in response to osmotic changes that are
caused by light, CO 2 concentration, humidity, and ABA.
139. What influences the transpiration rate?
Transpiration is affected by the light, temperature, humidity, wind, leaf
structure, and the soil moisture condition.
140. What is guttation?
Guttation is the leeching out of liquid water of the hydathodes of the end of
the leaves and is primarily seen during nighttime when the soil is wet.
141. What is root pressure?
Root pressure is defined as the positive pressure in the roots which is caused
by active ion buildup inside the xylem. It also helps in water flow particularly
when the level of transpiration is low.
142. What are aquaporins?
Aquaporins are proteins on the membrane which mediate the fast movement
of water through cell membranes.
143. What is wilting?
Wilting means a decrease in turgor pressure which leads leaves and stems to
be collapsed. It is an outcome of extreme water shortage.
144. What are the ways of adapting the plants to the conditions of water
scarcity?
In order to save water, plants grow deep roots, thick cuticles, small leaf area,
osmolytes, and stomatal regulation.
145. What is the impact of excess water to plants?
Flooding leads to hypoxia, root decay, nutrient imbalance, and low
photosynthesis level caused by low gaseous exchange.
146. What is hydraulic redistribution?
The movement of water within root systems through drier layers to wetter
layers of the soil is the passive movement of water within root systems,
which promotes drought tolerance, and is known as hydraulic redistribution.
147. What is the way the plants of the desert conserve water?
The desert plants have thick cuticles, sunken stomata, CAM metabolism,
succulent tissues and reflective surfaces.
148. What is the effect of the temperature on plant water relations?
The increase of the temperature enhances evaporation and transpiration,
which change the water balance and stomata behavior.
149. What is soil -plant-atmosphere continuum (SPAC)?
SPAC represents the network of water flows on the soil, plants and
atmosphere. It is run under water potential gradients.
150. So what is the importance of water relations to agriculture?
Climate variability relies on water relations to dictate crop productivity,
stress tolerance, irrigation efficiency and the overall health of the plant in
question.
Regulation of plant growth
151. What is plant growth?
Plant growth is the irreversible increase in size, mass and volume, which
occurs due to cell division, cell enlargement and even differentiation.
152. What are the key development stages of plants?
These stages are lag phase, log (exponential) stage and stationary stage
which are slow, rapid, and plateau growth respectively.
153. What is a sigmoid growth curve?
It is a S-shaped curve which displays the cumulative trend of plant growth
after its initiation to maturity.
154. Which are the primary and secondary growth?
Primary growth adds length with the assistance of apical meristems and
secondary growth adds thickness with the aid of lateral meristems.
155. What are growth regulators?
Growth regulators are organic compounds that are produced in very small
amounts and they affect the physiological functions such as growth,
development and reproduction.
Plant Hormones
166. What are auxins?
The growth promoting hormones are known as auxins and they promote cell
elongation, apical dominance, root initiation, and phototropism.
167. What is the most prevalent natural auxin?
The main endogenous auxin is the indole-3-acetic acid (IAA).
168. What are the key roles played by the auxins?
Auxins control stem growth, inhibit abscission of the leaves, promote root
growth and aid in the development of fruits.
169. What are gibberellins?
Gibberellins are hormones that trigger the growth of stems, germination of
seeds, flowering and enzyme production.
170. So what happens to gibberellins in germination?
They activate the production of hydrolytic enzymes such as -amylase that is
used to loosen locked away food in seeds.
The cytokinins, ethylene, and ABA.
171. What are cytokinins?
Cytokinins are hormones which stimulate the division of cells and slow aging
as well as improving nutrient mobilization.
172. What is the role of cytokinins in the tissue cultures?
High ratios of cytokinin to auxin cause them to stimulate shoot formation.
173. What is ethylene?
Ethylene is a gas hormone that is used in the process of the ripening of
fruits, senescence and in stress response.
174. What are some of the key impact of ethylene on plants?
Ethylene facilitates softening of fruits, abscission of leaves, flowering of some
species and reaction to mechanical stress.
Photomorpophoebic and phytochromic Systems
175. What is photomorphogenesis?
It is the light signal development of plants and it influences developmental
activities such as seedling formation, flowering.
176. What is phytochrome?
Phytochrome is a light receptor that is able to absorb red and far-red light to
control germination, shade avoidance and circadian rhythm.
177. How do we have the two types of phytochrome?
The former absorbs the far-red light and the latter absorbs the red light, Pfr
and Pr, respectively.
178. What is the mechanism of flowering regulated by phytochrome?
Measurement of the length of night and the conversion of Pr and Pf is used to
tell phytochrome whether to initiate flowering or not in the plant.
179. What is photoperiodism?
Potoperiodism refers to the biological behavior of plants in reaction to the
relativity of the day and night.
Day and short day plants (SDP) are defined as those day neutral plants that
are capable of flowering in response to photons of critical photophase length
(photophase) and the diurnal photon flux (G/m2/s). Long day (LDP) plants are
defined as those that do not flower in response to photons of the critical
photophase length (photophase) and the diurnal photon flux (G/m2/s).
180. What are short-day plants?
Flowering plants which require nights longer than a critical period (e.g.,
chrysanthemum).
181. What are long-day plants?
Flowering plants have a shorter night period than a predetermined period
(e.g., spinach).
182. What are day-neutral plants?
Photoperiod not involved in controlling the flowering of plants (e.g., tomato).
183. What is the part played by the critical night length?
It is the regulator of flowering reactions instead of day length.
184. What is the perception of plants towards photoperiod?
By means of phytochrome in leaves which transmits chemical signals to the
apex of the shoot so as to trigger flowering.
Plant Movements
185. What are tropisms?
Directional responses to stimuli include the growth towards or away of light,
gravity, and touch, which are called tropisms.
186. What is phototropism?
It is the development of a plant towards a light source because of the
asymmetry of the distribution of auxin.
187. What is geotropism?
The growth response to gravity is the one which makes roots positively
geotropic with the shoots negatively geotropic.
188. What is thigmotropism?
One of the responses to mechanical stimulation that is usually observed in
climbing plants and tendrils involves growth.
189. What are nastic movements?
Nastic movements are non-directional reactions to stimulus like in Mimosa
pudica leaf folding.
Plant Reproduction
190. What is sexual reproduction in plants?
It entails the formation of gametes, fertilization and development of seeds
that lead to genetic variation.
191. What is a flower?
The reproductive organ of the angiosperms is a flower that is aimed at
pollination and fertilization.
192. What is pollination?
Transfer of pollen grains between the anther and the stigma is known as
pollination.
193. What are there in the kind of pollination?
self pollination and cross pollination.
194. What benefits is there of cross-pollination?
It increases genetic diversity and improves the adaptability.
Fertilization and Seed Development.
195. What is the concept of the whole process of double fertilization?
It is a special process in angiosperms whereby a pollen grain fuses to an egg
resulting in the formation of a zygote, and another one develops endosperm.
196. What is endosperm?
Endosperm is a nutritive tissue which aids in developing the seedlings.
197. What is a seed?
A seed is a developed ovule which has an embryo, endosperm, and coat.
198. How does the germination of seeds take place?
Imbibition, enzyme activation and radicle emergence.
199. What is dormancy?
Dormancy is a survival mode whereby, the seeds are dormant until the
environment is favorable.
Mineral Nutrition
200. What is the mineral nutrition on plants?
Mineral nutrition is the process of obtaining, absorbing, moving, and using
inorganic nutrients which are needed in the growth and metabolism of
plants.
201. What are essential elements?
Minerals are the required components that a plant needs to grow normally,
procreate as well as to accomplish its life cycle.
202. What are the number of essential elements needed by the plants?
There are 17 essential elements that are needed by plants such as
macronutrients and micronutrients.
203.. What are macronutrients?
Macronutrients are the minerals that have to be taken in substantial
amounts, as they are nitrogen, phosphorus, potassium, calcium, magnesium,
and sulfur.
204. What are micronutrients?
Micronutrients are needed in low amounts and they are iron, zinc,
manganese, copper, boron, molybdenum, chlorine, nickel.
205. In plants what is the role played by nitrogen?
Nitrogen is needed in synthesis of amino acids, protein, nucleic acids and
chlorophyll.
206. What are the symptoms of the deficiency of nitrogen?
Deficiency in nitrogen leads to chlorosis, poor growth and decrease in the
size of the leaves.
207. What is the role of phosphorus?
Phosphorus plays an essential role in the formation of ATP, nucleic acids, as
well as in the energy transfer reactions.
208. What is the effect of potassium on the plant physiology?
Potassium controls stomata opening, activation of enzymes, osmotic and
stress tolerance.
209. What are the deficiencies of potassium symptoms?
The symptoms are scorching of leaves, marginal chlorosis and weak stems.
Mechanism of the Transport of Nutrients
210. How minerals are absorbed in the soil by plants?
Minerals are absorbed by plants through roots by passive diffusion,
facilitated diffusion, and active transport.
201. What is the active transportation in the uptake of minerals?
Active transport entails the movement of ions based on the concentration
gradient via ATP energy expenditure.
202. What are ion channels?
Membrane proteins that enable the passive movement of a particular ion
across membranes are known as ion channels.
203. What is the purpose of proton pumps?
Proton pumps generate electrochemical gradient which drives secondary
active movement of nutrients.
204. What is the apoplastic route?
It is transportation of water and minerals across the cell walls and
intercellular spaces.
205. What is the symplastic route?
It is translocation of materials within the cytoplasm linked by
plasmodesmata.
206. What is the casparian strip?
This is an endoderm band of suberin which blocks the apoplastic flow into
the stele, controlling ion entry.
207. What is so significant about the casparian strip?
It guarantees selective absorption of the minerals and prevents toxic ions.
208. What is xylem loading?
It involves the movement of ions in the root cells to the xylem to be
transported upwards.
209. What is the mode of transportation of the minerals by plants to the
shoots?
Minerals are moved through the xylem by means of transpiration push and
root pressure.
NITrogen metabolism in vivo at different gait speeds was studied in animals
with high functioning capacity of the sympathetic nervous system.
Nitrogen Metabolism
210. What is nitrogen metabolism?
The metabolism of nitrogen comprises absorption, assimilation, fixation,
reduction and integration of nitrogen in the biomolecules.
211. How do plants absorb nitrogen?
The plants take nitrogen in the form of nitrate (NO 3 - ) and ammonium (NH
4 + ).
212. What is nitrate reduction?
Nitrate reduction refers to conversion of nitrate to nitrite and this to
ammonium, done by such an enzyme.
213. In plants, what enzyme reduces nitrate to nitrite?
Nitrate reductase.
214.The name of the enzyme that transforms nitrite to ammonium is?
Nitrite reductase.
215. Ammonium assimilation, what is that?
It is the addition of ammonium into amino acids through GS-GOGAT pathway.
216. What is the biological nitrogen fixation?
The mechanism through which the ammonia is produced as the nitrogen-
fixing bacteria change atmospheric nitrogen (N 2 ) into ammonia.
217. What enzyme does the fixation of nitrogen take place?
Nitrogenase.
218. What are root nodules?
Root nodules are plant structures which contain symbiotic nitrogen fixing
bacteria like Rhizobium.
219. What is the reason why nitrogen fixation is a costly process?
Nitrogenase reaction involves huge quantities of ATP to break the triple bond
of N 2.
STress physiology: ABIotic stress.
220. What is abiotic stress?
Abiotic stress is damage due to non-living factors like drought, salinity,
temperature and radiation.
221. What is drought stress?
Drought stress refers to the situation when the amount of water available is
unable to cover plant physiological needs.
222. What happens to the plants when there is drought?
Plants close stomata, minimise leaf area, synthesize osmoprotectants and
increase root growth.
223. What are osmoprotectants?
Small molecules such as proline which stabilize proteins and membranes
upon dehydration.
224. What is salinity stress?
Salinity stress is caused by the excessive concentration of salt in soil which
impacts on ionic equilibrium and the absorption of water.
225. What is the impact of salinity on plant cells?
It leads to ionic toxicity, osmotic stress and disruption of membranes.
226. Which processes are useful in the survival of plants in salty
environments?
Ion compartmentalization, ion selective transport, osmotic adjustment and
antioxidant generation.
227. What is heat stress?
Heat stress Heat stress is an increased temperature which causes proteins to
be denatured, and it interferes with metabolism.
228. What are heat-shock proteins?
Heat-shock proteins (HSPs) are protective proteins, which refold protein
damage in the case of thermal stress.
229. What happens to plants when they are exposed to cold?
Through the deposition of antifreeze proteins, the logarithmic rise in
membrane unsaturation and the production of cryoprotectants.
Biotic stress: the effects of a given stress on physiological
processes.
230. What is biotic stress?
Living organisms like pathogens, herbivores and parasitic plants cause biotic
stress.
231. What are plant pathogens?
The disease causative agents are bacteria, fungi, viruses, nematodes, and
parasitic plants.
232Hypersensitive response (HR) What is the HS?
HR is a localised cell death response and limits the spread of pathogens.
233. What are phytoalexins?
Plants produce antimicrobial compounds when they are attacked by
pathogens.
234. What is the systemic acquired resistance (SAR)?
The expansion of a long-term and extensive-spectrum immune reaction,
which follows exposure to the pathogen.
235. What is the signaling, which mediates SAR?
Salicylic acid.
236. And what is induced systemic resistance (ISR)?
Defense reaction triggered by the useful microbes like rhizobacteria.
237. What role does jasmonic acid in when it comes to defense of plants?
The herbivory and wounding response is mediated by jasmonic acid.
238. Defense Ethylene is a defense hormone.
Ethylene gets into contact with other hormones to control disease resistance.
239. What are the mechanisms by which plants protect their food against
herbivores?
By mechanical devices (thorns), by poisonous metabolic products and by
defense proteins that are inducible.
The enzyme phytoplankton in plants.
240. What are plant enzymes?
Plant enzymes are the biological catalysts which increase metabolic
reactions that are necessary to aid growth and survival.
241. Which factors influence the enzyme activities?
Substrate concentration, inhibitors, temperature, and pH.
242. What are cofactors?
Cofactors are inorganic or organic molecules that are needed in enzyme
activity.
243. What is an enzyme inhibitor?
A material that weakens the action of enzymes by either stopping it or
changing its active site.
244. What does competitiveness inhibit start with?
An inhibitor competes against the substrate on the same active site.
245. What is non competitive inhibition?
An inhibitor attaches to a different part of the enzyme changing its shape
and decreasing its activity.
246. What is enzyme specificity?
This property is characteristic of an enzyme to catalyze a single reaction or
affinity to one type of substrate.
247. What is activation energy?
The lowest level of energy needed by a chemical reaction to take place.
248. What is allosteric regulation?
Inhibition of enzyme activity by binding to other sites other than the active
site.
249. What is the importance of enzymes in the plant physiology?
They control all of the key processes including respiration, photosynthesis
and nutrient assimilation.
XYLEM Organization and action.
250. What are tracheids?
The tracheids are long tapered ended xylem cells that are used to transport
water and support structure.
251. What are vessel elements?
Vessel elements are tube-shaped xylem cells and they are arranged in order
to create a vessel that is effective in transporting water.
252. Why are vessels more efficient than the tracheids?
They are less resistance to water flow and have higher diameters.
253. What is cavitation?
Cavitation is the development of air bubbles in the xylem vessels which
inhibit the flow of water.
254. What causes cavitation?
Drought, freezing, mechanical stress or pathogens invasion.
255. What is the mechanism of repair of plant cavitations?
With the help of root pressure, xylem refilling processes, and formation of
new xylem.
256. What is embolism?
An air bubble left in the xylem continually, breaking the water flow.
257. What are adaptation strategies to minimize the risk of cavitations?
Tubes that are narrow, lignified walls, and membranes in a pit that restrict
the movement of air.
258. What are pit membranes?
Permeable walls between xylem cells that control the movement of water
and avoid the spread of embolism.
259. What is the significance of lignification of xylem?
It reinforces the walls, helps to avoid the collapse under tension, and works
more effectively in terms of water transportation.
PHLOEM Structure and Functions.
260. What is the phloem?
The tissue that transports the sources of sugars, hormones and nutrients to
the sinks is called phloem.
261. What are sieve tube elements?
Nucleophiless specialized phloem cells which carry sugars using sieve plates.
262. What are companion cells?
Cells that are parenchyma in nature, and which facilitate the metabolism and
transport processes of sieve tube elements.
263. What is phloem loading?
Sugars can be transported into the phloem by the process termed moving
sugars into the phloem.
264. What are the phloem loading two types?
Apoptotic loading and symplastic loading.
265. What is apoplastic phloem loading?
Cell walls and membrane transporters help in the transport of sugars into the
phloem.
266. What is the phloem loading that is symplastic?
The plasmodesma transport sugars, one cell to another.
267. What is phloem unloading?
Movement of sugars in the phloem to sink tissues e.g. roots or fruits.
268. What is the hypothesis of pressureflow?
One of the theories describing sugar movement in the phloem on the basis of
the differences in osmotically generated pressure.
269. What is the reason phloem transport is a two way street?
Due to the variation in sugar requirements of various organs, when loading
and unloading takes place at the same time.
CARBON METABOLISM and PLANT ENERGY
270. What is carbon metabolism?
Carbon metabolism can be described as the process of fixation, storage, and
consumption of carbon molecules by plants.
271. What is carbon assimilation?
The addition of CO 2 to organic substances in the course of photosynthesis.
272. What is the photoassimilate partitioning?
Photosynthetic derived carbohydrates distribution to various plant organs.
273. Which are the determinants of carbon allocation?
The intensity of light, developmental phase, hormonal cues and nutritional
condition.
274. What are sink tissues?
Consuming or storing assimilates are stored in organs like roots, fruits, seeds
and young leaves.
275. What are source tissues?
Leaves that are mature and generate more sugars than use them up.
276. How does respiration play out in carbon metabolism?
Metabolic processes need ATP and reducing power which is obtained through
respiration.
277. This is what makes an organ a sink or a source.
Stage of development, energy requirements and photosynthetic abilities.
278. What is the significance of storage of carbohydrates in plants?
It provides survival in moments of stress, aids reproduction and resources
regeneration.
279. What is the impact of energy balance on the productivity of plants?
The energy balance would maintain maximum growth, effective use of
nutrients, and yield.
SEED PHYSIOLOGY
280. What defines the viability of the seeds?
Water content, genetic soundness, cell structure, and metabolic balance.
281. What is the significance of desiccation tolerance?
It enables the seeds to resist the high level of dehydration and make them
stay alive.
282. What are orthodox seeds?
Desiccation tolerant and dry cold storing seeds.
283. What are recalcitrant seeds?
Seeds which are unable to resist drying or freezing and have to be
germinated quickly.
284. What are the factors of dormancy-breaking?
Fluctuating temperatures, light, scarification and hormonal.
285. What is scarification?
One way of sacramentalizing the seed coat to facilitate water absorption and
germination.
286. What are the inner causes of dormancy?
High ABA, undeveloped embryos and physical hindrances caused by seed
coat.
287. How does GA break dormancy?
Gibberellins trigger the enzyme secretion which mobilizes stored food
reserves.
289. What is seed priming?
Guided hydration therapy which stimulates the rate and evenness of
germination.
290. That is, what are the environmental conditions that would increase
germination?
Proper heating, water, light and temperature.
