Factors affecting photosynthesis Questions in English

(D) Carbon dioxide $(CO_2)$ is a major limiting factor for photosynthesis.
Under normal atmospheric conditions,the concentration of $CO_2$ is approximately $360-400 \ ppm$.
Most $C_3$ plants show increased rates of photosynthesis and biomass production at higher $CO_2$ concentrations (up to $500-600 \ ppm$),a phenomenon known as $CO_2$ fertilization effect.
Therefore,a concentration of $400 \ ppm$ is well within the range that promotes healthy growth and photosynthesis in plants.

(B) The accumulation of end products of photosynthesis,such as sugars and starch,in the assimilatory cells (mesophyll cells) leads to a feedback inhibition of the process. This is known as product inhibition. As the concentration of these products increases,the rate of photosynthesis decreases because the plant cannot utilize or transport the synthesized food fast enough to maintain the initial rate of metabolic activity.

(D) The sun is the ultimate source of energy for all ecosystems on Earth.
However,only a small fraction of the incident solar radiation is photosynthetically active radiation $(PAR)$.
Plants capture only about $2-10\%$ of the $PAR$.
When considering the total incident solar radiation reaching the Earth's surface,higher plants utilize only about $1-2\%$ of it for the process of photosynthesis to produce organic matter.

(C) Solarization is a phenomenon where excessive light intensity leads to the photo-oxidation and destruction of chlorophyll pigments. This process inhibits photosynthesis and can eventually lead to the death of cellular components or the plant tissue itself due to the accumulation of reactive oxygen species.

(D) Photosynthesis is a complex physiological process that requires several key factors to occur efficiently.
$1$. $Light$: It provides the energy required for the excitation of electrons in chlorophyll.
$2$. $Chlorophyll$: This pigment is essential for capturing light energy.
$3$. $Water$ $(H_2O)$: It acts as a source of electrons and protons through photolysis.
$4$. $Carbon dioxide$ $(CO_2)$: It is the raw material for the synthesis of carbohydrates.
$5$. $Optimum temperature$: Enzymes involved in the Calvin cycle and light reactions function optimally within a specific temperature range.
Since all these factors are necessary for the process, the correct answer is $D$.

(A) The rate of photosynthesis is influenced by several external factors such as light intensity,light quality (wavelength),carbon dioxide concentration,and temperature.
Duration of light (photoperiod) primarily affects flowering and other developmental processes in plants rather than the immediate rate of photosynthesis.
Therefore,the rate of photosynthesis does not directly depend on the duration of light.

(C) Photosynthesis is a light-dependent process. As light intensity increases,the rate of photosynthesis increases up to a certain point. However,at very high light intensities,the rate of photosynthesis does not increase further because other factors (like $CO_2$ concentration or temperature) become limiting. Furthermore,extremely intense light can cause photo-oxidation of chlorophyll,leading to a decrease in the rate of photosynthesis. Therefore,photosynthesis is maximum at moderate light intensities,not continuous intense light.

(C) According to Blackman's Law of Limiting Factors,the rate of a physiological process is limited by the factor that is present in the least amount relative to its optimum requirement.
In the atmosphere,the concentration of $CO_2$ is very low $(0.03-0.04\%)$,which is far below the saturation point for photosynthesis in most $C_3$ and $C_4$ plants.
Therefore,$CO_2$ concentration is the major limiting factor for photosynthesis under normal field conditions during the day.

(B) Hydrophytes (aquatic plants) live submerged in water. While atmospheric $CO_2$ diffusion into water is slow,these plants have adapted to utilize the bicarbonate ions $(HCO_3^-)$ dissolved in the water as a source of carbon for photosynthesis. Therefore,they are not strictly limited by the low concentration of dissolved $CO_2$ in the water,as they can efficiently convert $HCO_3^-$ into $CO_2$ within their tissues.

(D) The Law of Limiting Factors was proposed by $F.F. Blackman$ in $1905$.
According to this law,if a chemical process is affected by more than one factor,then its rate will be determined by the factor which is nearest to its minimal value,as it is the factor which directly affects the process if its quantity is changed.

(B) The Law of Limiting Factors was proposed by $F. F. Blackman$ in $1905$.
According to this law,if a chemical process is affected by more than one factor,then its rate will be determined by the factor which is nearest to its minimal value.
This factor is directly responsible for limiting the rate of the process and is known as the limiting factor.

(C) Photosynthesis is an enzymatic process,and the activity of enzymes is highly dependent on temperature.
For most $C_3$ plants,the optimum temperature for photosynthesis ranges between $20 ^\circ C$ and $25 ^\circ C$.
For $C_4$ plants,the optimum temperature is generally higher,often ranging between $30 ^\circ C$ and $45 ^\circ C$.
Considering the general range provided in standard textbooks for photosynthesis,the most appropriate range is $20 - 35 ^\circ C$ as it encompasses the optimal activity levels for various plant types.

(B) The compensation point is the light intensity at which the rate of photosynthesis exactly equals the rate of respiration in a plant.
At this specific point,the amount of $CO_2$ produced during respiration is exactly consumed by photosynthesis,and the amount of $O_2$ produced during photosynthesis is exactly consumed by respiration.
Therefore,there is no net gaseous exchange between the plant and the surrounding environment.

(C) The Law of Limiting Factors was proposed by $F.F. Blackman$ in $1905$. According to this law,if a chemical process is affected by more than one factor,then its rate will be determined by the factor which is nearest to its minimal value. This factor is known as the limiting factor because it directly affects the rate of the process.

(B) Photosynthesis is an enzymatic process that is highly sensitive to temperature. Most enzymes involved in the Calvin cycle and light reactions have an optimal temperature range. When the temperature exceeds $35^{\circ}C$,the enzymes involved in photosynthesis (such as RuBisCO) begin to denature or lose their efficiency rapidly. Respiration,while also enzymatic,is generally more heat-stable than photosynthesis. Therefore,as temperatures rise significantly above the optimum,the rate of photosynthesis declines much more sharply and rapidly than the rate of respiration.

(D) The formation of chlorophyll in young plant seedlings is a light-dependent process.
In the absence of light,seedlings become etiolated (pale and elongated).
When exposed to light,the synthesis of chlorophyll is triggered,allowing the plant to begin photosynthesis.
Therefore,light is the essential factor that induces chlorophyll formation.

(B) The synthesis of chlorophyll in angiosperms is a light-dependent process.
Light acts as a signal for the activation of enzymes required for chlorophyll biosynthesis.
In the absence of light,plants become etiolated and fail to produce chlorophyll,leading to a pale yellow appearance.
Therefore,light is essential for the synthesis of chlorophyll in angiosperms.

(D) Herbicides are chemicals used to control or kill unwanted plants (weeds).
Many herbicides,such as those belonging to the urea or triazine groups,act by interfering with the photosynthetic process.
$1$. They inhibit the photolysis of water,which is the splitting of water molecules into $H^+$,electrons,and $O_2$ during the light-dependent reactions.
$2$. Consequently,this leads to the inhibition of $O_2$ evolution.
$3$. Some herbicides also interfere with the transport or translocation of organic solutes (assimilates) from source to sink,thereby starving the plant.
Since all these effects are associated with the action of various herbicides,the correct answer is $D$.

(D) Herbicides are chemical substances used to control or kill unwanted plants (weeds).
Many herbicides,such as $DCMU$ ($3$-($3$,$4$-dichlorophenyl)$-1,1-$dimethylurea),act by blocking the electron transport chain in photosynthesis.
Specifically,they inhibit the photolysis of water,which is the light-dependent splitting of water molecules.
Since the photolysis of water is responsible for the release of $O_2$ during photosynthesis,its inhibition directly leads to the inhibition of $O_2$ evolution.
Furthermore,some herbicides interfere with the metabolic processes required for the translocation of organic solutes (sugars) through the phloem.
Therefore,all the listed options are recognized effects of various types of herbicides.

(A) External factors are environmental conditions that influence the growth and development of plants.
Light,water,and pollutants are all environmental (external) factors.
Enzymes are biological catalysts that are synthesized within the plant cells to regulate metabolic processes; therefore,they are considered internal factors.

(B) The correct answer is $B$.
Statement $B$ is incorrect because $C_4$ plants show higher rates of photosynthesis at higher temperatures,whereas $C_3$ plants have a lower temperature optimum.
$C_4$ plants are adapted to warmer environments and possess a mechanism to minimize photorespiration,allowing them to perform efficiently at higher temperatures.
Conversely,$C_3$ plants perform better at cooler temperatures.
Other statements are correct:
$1$. Increasing $CO_2$ concentration up to $0.05\%$ acts as a fertilizer for $C_3$ plants.
$2$. Tomato and bell pepper are greenhouse crops grown in $CO_2$-enriched environments.
$3$. Light saturation for $CO_2$ fixation occurs at $10\%$ of full sunlight,except for plants in shade or dense forests.

(C) Light is a limiting factor for plants that grow in shade or in dense forests where light intensity is low.
However,for plants growing in deserts,light is abundant and rarely a limiting factor because they are exposed to direct sunlight for most of the day.
In such environments,other factors like water availability or temperature are more likely to be limiting factors for photosynthesis.

(C) The Law of Limiting Factors was proposed by $F.F. Blackman$ in $1905$.
According to this law,if a physiological process is controlled by a number of separate factors,the rate of the process is limited by the factor which is present in the least amount relative to its optimum requirement.
This factor is known as the limiting factor.

(D) Statement $(I)$ is correct: In dense forests or shaded areas where light is a limiting factor,humidity is generally higher due to reduced evaporation and transpiration.
Statement $(II)$ is correct: High light intensity leads to photo-oxidation of chlorophyll,which damages the pigment and reduces the rate of photosynthesis.
Statement $(III)$ is correct: $C_4$ plants are adapted to high temperatures and exhibit higher photosynthetic efficiency at higher temperatures compared to $C_3$ plants,which have a lower temperature optimum.
Since all statements $(I)$,$(II)$,and $(III)$ are factually correct,there are no incorrect sentences.
Therefore,the correct option is $D$.

(A) Photosynthesis is driven by the absorption of light energy by photosynthetic pigments,primarily chlorophyll $a$ and $b$.
According to the action spectrum of photosynthesis,the rate of photosynthesis is highest in the red and blue regions of the visible light spectrum.
Among the given options,red light is the most effective for photosynthesis,while green light is the least effective because it is mostly reflected by leaves.

(D) The correct answer is $D$ (Bell pepper).
$C_3$ plants are those that perform the Calvin cycle as the primary pathway for carbon fixation.
Bell pepper $(Capsicum \text{ } annuum)$ is a $C_3$ plant commonly grown in greenhouses to optimize yield and quality.
Sugarcane is a $C_4$ plant.
Pinus is a gymnosperm and not typically classified as a greenhouse crop in this context.
Carrot is a root vegetable, but bell pepper is the classic example of a $C_3$ greenhouse crop mentioned in the context of $CO_2$ fertilization experiments.

(A) is correct: $C_3$ plants show increased photosynthesis with higher $CO_2$ levels,whereas $C_4$ plants show saturation at much lower levels of $CO_2$.
$R$ is correct: The current atmospheric concentration of $CO_2$ is $0.03-0.04$ percent. An increase in concentration up to $0.05$ percent (or $500 \ ppm$) leads to an increase in $CO_2$ fixation rates in many plants,particularly $C_3$ plants.

(D) The correct answer is $D$.
$A$: High light intensity causes photo-oxidation of chlorophyll,which leads to a decrease in the rate of photosynthesis. This is a correct statement.
$B$: $C_3$ plants show a response to increased $CO_2$ levels,and saturation occurs at levels beyond $450 \ \mu L L^{-1}$. This is a correct statement.
$C$: $C_3$ plants show increased rates of photosynthesis with higher $CO_2$ concentrations,as they are limited by current $CO_2$ levels. This is a correct statement.
$D$: $C_4$ plants show saturation at about $360 \ \mu L L^{-1}$,not $260 \ \mu L L^{-1}$. Therefore,this statement is incorrect.

(C) The Law of Limiting Factors was proposed by $F. F. Blackman$ in $1905$.
It states that if a chemical process is affected by more than one factor,then its rate will be determined by the factor which is nearest to its minimal value.
This factor is directly responsible for limiting the rate of the process,hence it is called the limiting factor.

(A) Blackman's law of limiting factors states that when a process is conditioned as to its rapidity by a number of separate factors,the rate of the process is limited by the pace of the slowest factor.
This law was proposed by $F.F. \text{Blackman}$ in $1905$ specifically in the context of the rate of photosynthesis.
According to this law,if a plant is photosynthesizing,its rate will be determined by the factor that is present in the least amount relative to its requirement,such as light intensity,$CO_2$ concentration,or temperature.

(D) Plants are living organisms that interact with their environment to survive and grow.
External factors, also known as abiotic factors, play a crucial role in plant physiology and development.
$1$. $Light$: Essential for photosynthesis, phototropism, and flowering.
$2$. $Water$: Necessary for metabolic processes, nutrient transport, and maintaining turgidity.
$3$. $Temperature$: Influences the rate of enzymatic reactions, respiration, and transpiration.
Since all these factors significantly influence plant life, the correct answer is $\text{All of the above}$.

(B) In terrestrial habitats,plants play a significant role in influencing the local climate,specifically temperature and rainfall patterns.
Transpiration is the process by which water evaporates from the aerial parts of plants,such as leaves.
This process releases water vapor into the atmosphere,which contributes to local humidity and can influence cloud formation and rainfall.
Additionally,the cooling effect of transpiration helps regulate the temperature of the surrounding environment.
Therefore,transpiration is a key biological process that affects the microclimate of terrestrial ecosystems.

(D) In most dicotyledonous plants,the lower surface of the leaf is better adapted for gas exchange because it contains a higher density of stomata. Placing stomata on the lower surface helps in reducing the rate of transpiration by keeping them away from direct sunlight,while still allowing efficient $CO_2$ uptake and $O_2$ release for photosynthesis.

(B) In the eastern states of India,the monsoon season is characterized by heavy cloud cover.
Photosynthesis is a light-dependent process.
During the monsoon,the intensity and duration of sunlight reaching the plants are significantly reduced due to persistent cloud cover.
Since light is a limiting factor for photosynthesis,the reduced availability of light leads to a decrease in the rate of photosynthesis,which ultimately results in lower rice production.

(A) The Law of Limiting Factors was proposed by $F.F. Blackman$ in $1905$.
According to this law,if a chemical process is affected by more than one factor,then its rate will be determined by the factor which is nearest to its minimal value,and this factor is known as the limiting factor.

(A) When plants grow in low-intensity light (shade conditions),they often undergo morphological and physiological adaptations to maximize light capture. One such adaptation is the development of broader leaves or an increase in the size of photosynthetic units to increase the surface area for light absorption. This allows the plant to maintain an efficient rate of photosynthesis despite the limited light availability.

(C) The correct answer is $C$.
$C_3$ plants have a lower optimum temperature for photosynthesis,whereas $C_4$ plants have a higher optimum temperature and show response to higher temperatures.
Option $A$ is correct as light saturation for $CO_2$ fixation occurs at $10\%$ of full sunlight.
Option $B$ is correct because current atmospheric $CO_2$ concentration is limiting for $C_3$ plants,and an increase up to $0.05\%$ enhances the rate of photosynthesis.
Option $D$ is correct as tomato and bell pepper are greenhouse crops grown in $CO_2$-enriched environments to increase yield.

(A) Photosynthesis is an enzymatic process,and enzymes are sensitive to temperature. As the temperature rises above $35^{\circ}C$,the enzymes involved in photosynthesis (such as RuBisCO) begin to denature,leading to a sharp decline in the rate of photosynthesis. Conversely,respiration is less sensitive to high temperatures compared to photosynthesis. Therefore,at temperatures above $35^{\circ}C$,the rate of photosynthesis decreases significantly faster than the rate of respiration.

(D) Stomata are small pores present on the epidermis of leaves and other aerial parts of plants,which facilitate gas exchange and transpiration.
In submerged hydrophytes (plants that grow completely underwater),stomata are absent because gas exchange occurs directly through the general body surface via diffusion in the water.
Therefore,the correct option is $D$.

(C) The $CO_2$ compensation point is defined as the specific atmospheric concentration of $CO_2$ at which the rate of photosynthesis exactly equals the rate of respiration in a plant.
At this point,the net exchange of $CO_2$ between the plant and the atmosphere is zero,meaning the $CO_2$ produced by respiration is entirely consumed by photosynthesis.
The Assertion is correct.
The Reason states that the compensation point is reached when $CO_2$ uptake is less than that generated through respiration,which is incorrect.
At the compensation point,the rate of $CO_2$ uptake is exactly equal to the rate of $CO_2$ release (respiration).
Therefore,the Assertion is correct,but the Reason is incorrect.

(A) $D.C.M.U.$ (Dichlorophenyl dimethyl urea) is a potent herbicide that acts as a photosynthetic inhibitor.
It specifically blocks the electron flow from Photosystem $II$ $(PSII)$ to plastoquinone by binding to the $Q_B$ binding site.
Because the electron transport chain is blocked,the photolysis of water (which requires a continuous supply of electrons to the oxidized $P_{680}$ reaction center) is also inhibited.
Therefore,both the Assertion and the Reason are correct,and the Reason provides a correct explanation for the Assertion.

(N/A) Light is a limiting factor for photosynthesis. Leaves receive less light for photosynthesis when they are in the shade.
Therefore,the leaves or plants in the shade perform less photosynthesis compared to those kept in direct sunlight.
To compensate and increase the efficiency of light absorption,the leaves in the shade develop a higher concentration of chlorophyll pigments.
This increased chlorophyll content makes the leaves appear darker green to capture as much available light as possible.
Thus,the leaves or plants in the shade are darker green than those kept in the sun.

(N/A) Light is a limiting factor in the region where the rate of photosynthesis increases linearly with an increase in light intensity. In the given graph,this corresponds to the initial rising region indicated by the first arrow.
$(b)$ In the region where the rate of photosynthesis becomes constant (plateau region),light is no longer a limiting factor. Other factors such as temperature,carbon dioxide concentration,or water availability become the limiting factors.
$(c)$ The point where the curve flattens represents the light saturation point. At this intensity,the rate of photosynthesis reaches its maximum,and further increases in light intensity do not increase the rate of photosynthesis.

(N/A) Photosynthesis is influenced by both internal and external factors.
Internal factors: These include the number,size,age,and orientation of leaves,mesophyll cells,chloroplasts,internal $CO_2$ concentration,and the amount of chlorophyll.
Blackman's Law of Limiting Factors: If a chemical process is affected by more than one factor,its rate is determined by the factor nearest to its minimal value. This factor directly limits the process if its quantity is changed.
External Factors:
$1$. Light: There is a linear relationship between incident light and $CO_2$ fixation at low light intensities. At higher intensities,the rate plateaus as other factors become limiting. Light saturation occurs at $10\%$ of full sunlight. Excessive light can cause chlorophyll breakdown.
$2$. Carbon dioxide concentration: $CO_2$ is a major limiting factor. Atmospheric concentration is low $(0.03-0.04\%)$. $C_3$ and $C_4$ plants respond differently; $C_4$ plants saturate at $360 \mu l L^{-1}$,while $C_3$ plants saturate beyond $450 \mu l L^{-1}$.
$3$. Temperature: Dark reactions are enzymatic and temperature-sensitive. $C_4$ plants have a higher temperature optimum compared to $C_3$ plants. Tropical plants generally have higher temperature optima than temperate plants.
$4$. Water: Water stress causes stomata to close,reducing $CO_2$ availability. It also causes leaf wilting,reducing surface area and metabolic activity.

(D) Light affects the process of photosynthesis in three main ways:
$1$. Light Intensity: The rate of photosynthesis increases with an increase in light intensity,although very high intensity can lead to the photo-oxidation of chlorophyll.
$2$. Light Quality: The visible spectrum $(400-700 \ nm)$ is most effective for photosynthesis,with red and blue light being absorbed most efficiently by chlorophyll.
$3$. Light Duration: The duration of exposure to light influences the total photosynthetic yield over time.
Therefore,the correct answer is $D$.

(N/A) The concentration of $CO_2$ is a major limiting factor for photosynthesis.
$1$. $C_3$ plants: These plants show an increase in the rate of photosynthesis with an increase in $CO_2$ concentration up to $450 \ \mu L/L$. Since $RuBisCO$ has a lower affinity for $CO_2$ and also acts as an oxygenase,higher $CO_2$ levels suppress photorespiration,thereby increasing productivity.
$2$. $C_4$ plants: These plants show saturation at much lower levels of $CO_2$ (around $360 \ \mu L/L$). Because $C_4$ plants have a $CO_2$ concentrating mechanism (the $C_4$ cycle) that ensures $RuBisCO$ operates in a high $CO_2$ environment,they do not show significant increases in photosynthesis at higher $CO_2$ concentrations compared to $C_3$ plants.

(A) The concentration of $CO_2$ is a major limiting factor for photosynthesis.
$C_3$ plants show saturation at about $450 \mu L L^{-1}$ of $CO_2$ concentration.
$C_4$ plants show saturation at about $360 \mu L L^{-1}$ of $CO_2$ concentration.
Therefore,$C_3$ plants respond to higher $CO_2$ concentrations and show increased rates of photosynthesis at higher levels compared to $C_4$ plants,which saturate at lower levels.

(B) The effect of temperature on photosynthesis varies between $C_3$ and $C_4$ plants due to their different photosynthetic pathways.
$C_4$ plants respond to higher temperatures and show higher rates of photosynthesis at higher temperatures compared to $C_3$ plants.
$C_3$ plants have a lower temperature optimum,typically ranging from $20^{\circ}C$ to $25^{\circ}C$.
$C_4$ plants have a higher temperature optimum,typically ranging from $30^{\circ}C$ to $45^{\circ}C$.
Therefore,$C_4$ plants are better adapted to warmer climates.

(N/A) No,photosynthetic organisms at different depths in the ocean do not receive the same quality and quantity of light. As depth increases,light intensity decreases (quantitative change) and the spectral quality changes because water absorbs different wavelengths of light at different rates (qualitative change).
To adapt to these conditions,organisms possess diverse photosynthetic pigments that can absorb specific wavelengths of light available at their respective depths:
$1$. Green Algae (Chlorophyceae): Contain Chlorophyll-$a$ and Chlorophyll-$b$,which are efficient at absorbing red and violet-blue light,typically found in shallower waters.
$2$. Brown Algae (Phaeophyceae): Contain Chlorophyll-$a$,$c$,and the accessory pigment Fucoxanthin,which helps in absorbing green and yellow light.
$3$. Red Algae (Rhodophyceae): Contain Chlorophyll-$a$,$d$,and the accessory pigment Phycoerythrin,which is highly effective at absorbing blue-green light that penetrates deeper into the ocean.

(B) The rate of photosynthesis is influenced by the intensity and quality of light.
Plants growing in the understory of tropical rain forests have adapted to low light conditions.
These plants possess specialized pigments and leaf structures that allow them to efficiently capture and utilize the filtered light that reaches the forest floor.
Therefore,they can perform photosynthesis even at lower light intensities,although the rate of photosynthesis may be lower compared to plants in direct sunlight.