Transpiration (General) and Stomata Questions in English

(D) During the daytime,light triggers the process of photosynthesis in guard cells,which leads to the production of organic acids (like malate) and the accumulation of potassium ions $(K^+)$.
This accumulation of solutes lowers the water potential inside the guard cells.
As a result,water enters the guard cells from the surrounding subsidiary cells via osmosis.
The increase in turgor pressure causes the guard cells to swell and the stomatal pore to open.

(C) Guttation is the exudation of water droplets from the margins or tips of leaves through specialized structures called hydathodes.
It occurs when the rate of water absorption by roots is high and the rate of transpiration is very low, typically during the night or early morning.
This high water content in the plant creates a $Positive root pressure$, which forces the water out through the hydathodes.
Therefore, $Positive root pressure$ is the primary cause of guttation.

(B) Transpiration is a controlled process because the plant regulates it through the opening and closing of stomata in response to environmental conditions.
In contrast,Guttation is an uncontrolled process. It occurs through hydathodes (specialized pores) when root pressure is high and transpiration is low,typically at night or early morning. The plant cannot regulate the loss of water through guttation as it does with transpiration.

(B) The correct answer is $(b)$.
Guttation is the process of exudation of liquid droplets from the margins or tips of leaves through specialized structures called hydathodes.
The liquid released during guttation is not pure water; it contains $0.6-2.5 \text{ g/L}$ of various solutes.
These solutes include organic compounds such as carbohydrates,organic acids,amino acids,and enzymes,as well as inorganic ions like $Ca^{2+}, Mg^{2+}, K^+, Na^+, CO_3^{2-}, SO_4^{2-},$ and $Cl^-$.
Transpiration,on the other hand,involves the loss of water in the form of vapor,which is generally pure water.

(C) Guttation is the process of exudation of water droplets from the margins or tips of leaves through specialized structures called hydathodes.
It typically occurs under conditions of high soil moisture and low transpiration,such as at night or early morning.
Unlike transpiration,where water is lost as vapor,in guttation,water is lost in liquid form along with some dissolved solutes.

(C) Guttation is the process of exudation of water droplets from the margins or tips of leaves of uninjured plants.
This occurs through specialized pores called hydathodes.
It usually happens during the night or early morning when the rate of transpiration is low and root pressure is high.

(B) Guttation is the process of loss of water in the form of liquid droplets from the margins and tips of leaves.
This process occurs through specialized pores called $Hydathodes$.
$Hydathodes$ are typically found at the tips or margins of leaves.
Each $Hydathode$ consists of a group of loosely arranged,colourless parenchymatous cells known as $Epithem$,which are associated with the vein endings.

(B) Guttation is the process of exudation of liquid droplets from the margins of leaves through specialized structures called hydathodes.
Unlike transpiration,which involves the loss of pure water vapor,the liquid lost during guttation is not pure water.
It contains various dissolved organic and inorganic substances,including mineral salts like $Ca^{2+}$,$Mg^{2+}$,$K^+$,$Na^+$,$CO_{3}^{2-}$,$SO_4^{2-}$,and $Cl^-$.
Therefore,the correct answer is $B$.

(A) Guttation is the process of exudation of water droplets from the margins of leaves through specialized structures called hydathodes.
This phenomenon typically occurs during the night or early morning hours when root pressure is high and transpiration is low.
Therefore,the most appropriate time among the given options is the morning.

(D) Transpiration is the evaporative loss of water by plants,which occurs mainly through the stomata in the leaves.
$(a)$ It helps in the regulation of plant body temperature through cooling.
$(b)$ It creates a transpiration pull that aids in the absorption and distribution of mineral salts from the soil to various parts of the plant.
$(c)$ It facilitates the circulation of water throughout the plant body.
$(d)$ Bleeding (or exudation) is the loss of sap from injured or cut parts of a plant,which is a process distinct from transpiration.
Therefore,$D$ is the correct answer.

(A) Guttation is the process of exudation of liquid droplets from the margins or tips of leaves.
This phenomenon occurs through specialized pores called $Hydathodes$.
$Hydathodes$ are permanently open pores usually found at the vein endings of leaves.
Unlike transpiration,which involves the loss of water in the form of vapor through $Stomata$,guttation involves the loss of water in liquid form.

(B) Hydathodes are specialized pores found on the margins or tips of leaves in many herbaceous plants.
They are involved in the process of guttation,which is the exudation of water droplets from the uninjured margins of leaves.
This process typically occurs when root pressure is high and transpiration is low,such as during the night or early morning.
Therefore,the correct function performed by hydathodes is guttation.

(A) The starch-glucose interconversion theory,also known as the starch-sugar hypothesis,was originally proposed by Lloyd $(1908)$ and later modified by Sayre $(1926)$. However,the specific mechanism involving the role of $pH$ and the enzyme phosphorylase in the interconversion of starch and glucose was extensively studied and supported by $Yin$ and $Tung$ $(1948)$. Therefore,they are credited with the development of this theory.

(A) The proton transport concept,also known as the active $K^+$ transport theory,was proposed by $Levitt$ in $1974$. This theory explains that the opening of stomata is driven by the active transport of $H^+$ ions out of the guard cells and the simultaneous uptake of $K^+$ ions into them. It successfully integrates the classical $pH$ theory proposed by $Scarth$ with the modern active $K^+$ transport mechanism.

(A) The starch-sugar interconversion theory was proposed by $J.D. Sayre$ in $1926$.
He observed that the $pH$ of guard cells increases during the day (due to photosynthesis consuming $CO_2$),which activates the enzyme phosphorylase to convert starch into sugar.
This increase in sugar concentration lowers the water potential of the guard cells,causing water to enter via osmosis,leading to stomatal opening.
Conversely,at night,the $pH$ decreases,causing the conversion of sugar back into starch,leading to stomatal closure.

(B) potometer is an apparatus used to measure the rate of water uptake by a leafy shoot.
Since the vast majority of water absorbed by the roots is lost through transpiration from the leaves,the rate of water uptake is approximately equal to the rate of transpiration.
Therefore,potometers are primarily used to measure the rate of transpiration.

(D) beech tree loses water through transpiration every day in an amount equal to $5$ times the fresh weight of its leaves.
For an acre of beech trees,the total water lost via transpiration per day is approximately $3000$ gallons.
Therefore,the correct option is $D$.

(A) In a dorsi-ventral leaf,the distribution of stomata is unequal.
Most dicot leaves are dorsi-ventral,meaning they have a distinct upper (adaxial) and lower (abaxial) surface.
The lower surface (abaxial) typically contains a significantly higher density of stomata compared to the upper surface (adaxial).
Since transpiration primarily occurs through stomata,more water is lost from the lower surface of the leaf.

(B) The concentration of $CO_2$ in the atmosphere is typically around $0.03\%$.
An increase in the concentration of $CO_2$ from the normal level of $0.03\%$ to $0.05\%$ triggers the closure of stomata.
$CO_2$ acts as an antitranspirant because it reduces the rate of transpiration by inducing stomatal closure.

(C) Sayre proposed the $pH$ theory of stomatal movement.
He observed that stomata open when the $pH$ of guard cells is high (alkaline or neutral,around $7.0$) and close when the $pH$ is low (acidic,around $5.0$).
In an atmosphere of ammonia vapours,the $pH$ inside the guard cells increases,which leads to the opening of stomata even at night.
Therefore,the correct answer is $C$.

(A) When a plant in a potometer is placed under a fan or in bright light,the rate of transpiration increases significantly.
Transpiration is the process of water loss from the aerial parts of the plant,primarily through the stomata.
$A$ fan increases wind speed,which removes the water vapor layer around the leaf,while bright light increases the temperature and promotes stomatal opening.
Since the rate of water absorption is directly proportional to the rate of transpiration,the water column in the potometer moves faster to compensate for the lost water.
Therefore,the air bubble in the capillary tube will move faster.

(D) Root pressure is a positive pressure that develops in the roots due to the active absorption of mineral ions and subsequent water uptake.
Transpiration pull is the negative pressure generated by the evaporation of water from the leaves.
During the day,especially under sunny conditions or fast winds,the rate of transpiration is very high,creating a strong transpiration pull that dominates root pressure.
However,during the late night or early morning,the stomata are closed and transpiration is minimal or absent.
Consequently,the root pressure becomes the dominant force,which can lead to the phenomenon of guttation.

(A) The opening and closing of stomata are regulated by the turgidity of guard cells. The accumulation of $K^+$ ions in guard cells decreases the water potential,leading to the influx of water via osmosis. This increases the osmotic pressure and turgor pressure,causing the guard cells to swell and the stomatal pore to open. Thus,potassium is essential for maintaining osmotic pressure.

(B) According to the active potassium transport theory,the opening and closing of stomata are regulated by the movement of $K^+$ ions in and out of the guard cells.
During the day (in light),$K^+$ ions accumulate in the guard cells,which lowers the water potential,causing water to enter the cells via osmosis. This increases turgor pressure,leading to the opening of stomata.
In darkness,the process reverses: $K^+$ ions move out of the guard cells into the surrounding subsidiary cells. This causes water to follow the ions out of the guard cells,leading to a decrease in turgor pressure and the subsequent closing of the stomata.

(B) The unidirectional movement of water from roots to the leaves against gravity in plants is primarily explained by the $Transpiration$ $Pull$ theory.
Transpiration is the process of loss of water in the form of water vapor from the aerial parts of the plant.
This loss of water creates a negative pressure (tension) in the xylem vessels, which pulls the water column upwards from the roots to the top of the plant.
Therefore, transpiration is the driving force for the ascent of sap.

(D) Transpiration is a vital physiological process in plants. Its significance includes:
$1$. Cooling effect: It maintains the plant at a lower temperature through evaporative cooling.
$2$. Transpiration pull: It creates a negative pressure (suction force) that pulls water and dissolved minerals upwards from the roots to the leaves.
$3$. Ascent of sap: It is the primary driving force for the upward movement of water and minerals (ascent of sap) against gravity.
Therefore,all the given options are correct.

(B) The opening and closing of the stomatal pore are regulated by the turgor pressure of the guard cells.
When the concentration of solutes in the guard cells decreases,the water potential of the guard cells increases.
As a result,water moves out of the guard cells via osmosis.
This loss of water leads to a decrease in turgor pressure,causing the guard cells to become flaccid.
Consequently,the stomatal pore closes.

(A) The opening and closing of the stomatal aperture are regulated by the turgor pressure of the guard cells.
When the guard cells become turgid due to water influx,their thin outer walls bulge outwards and force the thick inner walls into a crescent shape.
This movement pulls the inner walls away from each other,thereby opening the stomatal pore.
Therefore,the correct condition for the opening of the stomatal aperture is when the thin outer walls of the guard cells bulge outwards.

(A) When the rate of transpiration exceeds the rate of water absorption,the water content in the plant cells decreases. This leads to a loss of turgor pressure in the cells,causing the leaves to lose their rigidity and droop,a condition known as wilting. If this state persists for a long time,it can lead to permanent damage,but the immediate physiological response is wilting.

(C) Transpiration is the evaporative loss of water from the aerial parts of the plant.
$1$. It facilitates the absorption and transport of minerals from the soil to the leaves.
$2$. It maintains the shape and structure of plants by keeping cells turgid.
$3$. It provides a cooling effect on the plant surface through evaporation.
$4$. Excessive transpiration leads to water stress,which can cause wilting.
$5$. Stomatal opening is regulated by the turgor pressure of guard cells,which is influenced by light,$CO_2$ concentration,and water status,but transpiration itself is the result of stomatal opening,not the cause of it.
Therefore,the statement that transpiration causes the stomatal pore to open is false.

(A) Wilting occurs when the turgor pressure in plant cells decreases. This happens when the rate of water loss through transpiration exceeds the rate of water absorption by the roots. As a result,the cells lose their turgidity,leading to the drooping or curling of leaves. Therefore,the correct condition is when the rate of transpiration is higher than the rate of absorption.

(A) Transpiration is the evaporative loss of water from the aerial parts of plants.
Its primary functions include:
$1$. Creating a transpiration pull for the absorption and transport of water and minerals from roots to leaves (Ascent of sap).
$2$. Maintaining the shape and structure of plants by keeping cells turgid.
$3$. Cooling the leaf surfaces,sometimes by $10-15^{\circ}C$,through evaporative cooling.
$4$. Supplying water for photosynthesis.
Excretion of minerals is $NOT$ a function of transpiration; minerals are typically absorbed along with water and utilized by the plant,not excreted through this process.

(D) The opening and closing of stomata depend on the turgidity of the guard cells.
When guard cells lose water,they lose their turgidity and become flaccid.
During this process,the thick and elastic inner wall of the guard cells regains its original shape,which causes the stomatal pore to close.
Therefore,all the given options are correct.

(B) $1$. Evaporation is a purely physical process where water molecules escape from a surface into the atmosphere due to thermal energy.
$2$. Transpiration is a physiological process occurring in living plants,where water vapor is lost from the aerial parts (mainly stomata) of the plant.
$3$. Because transpiration involves living tissues and is regulated by the plant (e.g.,opening and closing of stomata),it is classified as a physiological process,whereas evaporation is not.

(D) The pressure generated by the osmotic movement of water into a cell is called turgor pressure. It is the force responsible for pushing the plasma membrane against the cell wall.
Stomata open due to an increase in the turgor pressure of the guard cells,and they close due to a decrease in turgor pressure.
When guard cells become turgid,they swell and bulge outwards,which causes the stomatal pore to open.
Conversely,when they become flaccid,the pressure on the cell wall decreases,causing the stomata to close.

(A) Stomata are specialized pores found in the epidermis of leaves and other green parts of plants.
They play a crucial role in gaseous exchange ($CO_2$ and $O_2$) and transpiration.
In most plants,stomata open during the daytime to facilitate the uptake of $CO_2$ required for photosynthesis and to release $O_2$ produced as a byproduct.
This opening is regulated by the turgor pressure of guard cells.

(A) Guard cells regulate the opening and closing of stomata,which directly controls the rate of transpiration. Transpiration is the evaporative loss of water by plants,occurring mainly through the stomata in the leaves. During photosynthesis,the opening of stomata also facilitates the exchange of gases like $CO_2$ and $O_2$.

(B) Transpiration pull is the suction force generated in the xylem vessels due to the loss of water vapor from the leaves through stomata.
For this process to be effective, the following conditions are required:
$1$. $Open \text{ stomata}$: This allows the escape of water vapor into the atmosphere.
$2$. $Warm \text{ air}$: This increases the rate of evaporation, thereby increasing the pull.
$3$. $Wet \text{ soil}$: This ensures that there is sufficient water available for the roots to absorb, maintaining the water column continuity.
Therefore, the correct combination is $Open \text{ stomata}$, $warm \text{ air}$, and $wet \text{ soil}$.

(D) Transpiration is affected by both external and internal factors.
Internal factors include the number and distribution of stomata,percent of open stomata,water status of the plant,and canopy structure.
Sunken stomata are a structural adaptation in plants (especially xerophytes) that reduce the rate of transpiration by creating a humid microclimate around the stomatal pore.
$O_2$,$CO_2$,and $N$ are gases or nutrients,not structural internal factors regulating transpiration rate.

(B) Transpiration pull is the force generated by the evaporation of water from the leaves,which pulls the water column upwards through the xylem.
For this pull to be maximum,the rate of transpiration must be high.
$1$. Open stomata are necessary for water vapor to escape from the leaf.
$2$. $A$ dry atmosphere (low humidity) increases the water potential gradient between the leaf interior and the outside air,promoting rapid evaporation.
$3$. Moist soil ensures that the plant has an adequate supply of water to maintain the transpiration stream without causing water stress.
Therefore,the combination of open stomata,dry atmosphere,and moist soil creates the ideal conditions for maximum transpiration pull.

(B) During the day,photosynthesis leads to the production of malic acid,which dissociates into $H^+$ and malate ions.
$H^+$ ions are pumped out of the guard cells,and $K^+$ ions enter the guard cells to form potassium malate.
This accumulation of potassium malate increases the osmotic pressure inside the guard cells,causing water to enter by osmosis.
As a result,the guard cells become turgid,leading to the opening of the stomata.

(A) In a dorsiventral (dicot) leaf,the distribution of stomata is unequal. The abaxial (lower) surface typically contains a much higher number of stomata compared to the adaxial (upper) surface. Since transpiration occurs primarily through stomata,the rate of transpiration is significantly higher towards the abaxial surface.

(D) The water potential of pure water is defined as zero,which is the maximum value. In certain conditions,such as high soil moisture and low transpiration,the water potential within the leaf tissues can become positive due to the development of root pressure. When the rate of transpiration is very low and water absorption is high,water is forced out of the leaf through specialized pores called hydathodes in the form of liquid droplets. This process is known as $Guttation$.

(B) Transpiration is the process of water loss from the aerial parts of plants,primarily through stomata.
Factors affecting transpiration include light,temperature,humidity,wind speed,and soil water availability.
$A$. Companion cells are involved in phloem loading and unloading,not directly in the transpiration process.
$B$. Constant temperature implies no change in temperature,meaning it does not act as a variable factor influencing the rate of transpiration.
$C$. Xylem elements are the conduits for water transport,but the rate of transpiration is determined by external environmental factors and stomatal regulation,not by the xylem elements themselves.
$D$. Soil moisture directly affects the water potential of the plant and the availability of water for transpiration.
Among the given options,'Constant temperature' represents a state of no change,making it ineffective as a variable factor influencing the rate of transpiration.

(C) The opening and closing of stomata are primarily regulated by the turgor pressure of the guard cells.
When the guard cells take up water,they become turgid,causing the stomatal pore to open.
Conversely,when water leaves the guard cells,they become flaccid,leading to the closure of the stomatal pore.
This process is influenced by various factors like light,$CO_2$ concentration,and potassium ion $(K^+)$ flux.

(D) Transpiration is the process of loss of water in the form of water vapor from the aerial parts of the plant.
Transpiration is inversely proportional to the relative humidity of the atmosphere.
When the atmospheric humidity is high,the water potential gradient between the leaf interior and the atmosphere decreases,which reduces the rate of transpiration.
Therefore,transpiration is lowest in high atmospheric humidity.

(C) Cobalt chloride $(COCl_2)$ paper is a chemical indicator used to detect the presence of moisture.
When dry,$COCl_2$ paper is blue in color.
As water vapor is released from the leaf through the process of transpiration,the paper absorbs this moisture.
The reaction between the anhydrous $COCl_2$ and water results in the formation of hydrated cobalt chloride,which is pink in color.
Since the lower epidermis of a leaf contains a higher number of stomata,the rate of transpiration is higher there,causing the color change to occur more rapidly.

(B) When a leafy twig is immersed in water, the process of $Transpiration$ can be demonstrated. Even when the twig is cut and placed in water, the stomata remain open for some time, allowing water vapor to escape from the leaf surface into the surrounding air or water medium. This experiment is often used to show that water loss occurs through the leaves due to the pull generated by the evaporation of water, which is the fundamental principle of $Transpiration$.

(D) Transpiration is the process of water loss from the aerial parts of plants,primarily through stomata. The rate of transpiration is influenced by several factors related to stomata:
$1$. Number of stomata: $A$ higher density of stomata generally increases the potential for water loss.
$2$. Distribution of stomata: The arrangement and location of stomata on the leaf surface affect the rate of diffusion.
$3$. Percentage of open stomata: The degree of stomatal opening (aperture) is the most critical factor in regulating the rate of transpiration.
Therefore,all these factors collectively determine the rate of transpiration.

(B) Transpiration is the process of water loss in the form of water vapor from the aerial parts of the plant,primarily through the stomata.
For transpiration to occur,a water potential gradient must exist between the substomatal cavity (inside the leaf) and the external atmosphere.
Water moves from a region of higher water potential to a region of lower water potential.
Since the substomatal cavity is usually saturated with water vapor (high humidity),transpiration occurs only when the external atmosphere is drier (lower humidity) than the substomatal cavity.
Therefore,the correct condition is that the humidity in the atmosphere must be lower than that in the substomatal cavity.