Photoperiodism and Vernalization Questions in English

(A) Vernalisation is the process where the flowering of plants is promoted by exposure to low temperatures.
It prevents precocious reproductive development late in the growing season and enables the plant to have sufficient time to reach maturity.
Parthenocarpy refers to the development of fruit without fertilization.
Bolting is the internode elongation just prior to flowering in rosette plants.
Plasticity refers to the ability of plants to follow different pathways in response to the environment or phases of life.

(A) The experimental results show that the plant flowers when exposed to a $12 \ hr$ continuous dark period.
Short Day Plants $(SDP)$ require a dark period longer than a critical duration to flower.
Since the plant flowers under a $12 \ hr$ dark period,it indicates that this duration is sufficient to meet its critical dark period requirement.
Therefore,this plant is categorized as a Short Day Plant.

(A) The phenomenon where flowering is promoted by a period of low temperature is known as Vernalization.
This process is particularly significant in many biennial and some monocarpic plants.
Biennial plants are monocarpic plants that normally flower and die in the second season.
By subjecting these plants to cold treatment,the transition from the vegetative phase to the flowering phase is accelerated.
Therefore,monocarpic plants (including biennials) show a stimulated flowering response after cold treatment.

(C) Phytochrome is a pigment found in plants that acts as a photoreceptor. It is primarily involved in sensing light quality and duration,which regulates various developmental processes such as flowering,seed germination,and stem elongation. Specifically,phytochrome plays a crucial role in $Photoperiodism$,which is the physiological reaction of organisms to the length of day or night. Therefore,the correct answer is $Photoperiodism$.

(C) Florigen is a hypothetical hormone or signaling molecule that is believed to be responsible for inducing flowering in plants. It is synthesized in the leaves in response to photoperiodic stimuli and then transported to the shoot apical meristem to initiate the transition from vegetative growth to reproductive growth (flowering).

(D) Vernalization is the process by which flowering is induced or promoted by exposure to low temperatures for a specific period. This ensures that plants flower only during the favorable season. It is a physiological response to cold treatment,commonly observed in winter varieties of wheat,barley,and rye.

(B) Short-day plants $(SDP)$ require a photoperiod shorter than a critical duration to flower.
Additionally,they require a long,continuous,and uninterrupted dark period (night) to trigger the flowering response.
If the dark period is interrupted by even a brief flash of light,the flowering process is inhibited.
Therefore,the correct condition is a photoperiod shorter than the critical length and a long uninterrupted night.

(D) Plants that flower multiple times a year regardless of the specific photoperiod (day length) are known as day-neutral plants. Since the tree flowers in October,January,and July in North India,it experiences vastly different day lengths and temperatures during these months. Because it flowers consistently despite these environmental variations,it is considered to be both photo-insensitive and temperature-insensitive. Therefore,it is a day-neutral plant that does not rely on specific environmental triggers like photoperiod or vernalization to initiate flowering.

(D) Phytochrome exists in two interconvertible forms: $Pr$ (inactive form,absorbs red light) and $Pfr$ (active form,absorbs far-red light).
When a plant is exposed to continuous red light,the $Pr$ form is converted into the $Pfr$ form.
However,the $Pfr$ form is unstable and undergoes degradation or reversion back to $Pr$.
In a state of continuous red light,the plant maintains a dynamic equilibrium where the rate of synthesis of $Pr$ and the rate of degradation/conversion of $Pfr$ reach a steady state,ensuring the plant can continue to respond to light stimuli.

(B) Phytochrome is a proteinaceous pigment found in plants that acts as a photoreceptor. It exists in two interconvertible forms: $P_r$ (which absorbs red light at $660 \ nm$) and $P_{fr}$ (which absorbs far-red light at $730 \ nm$). This pigment plays a crucial role in photomorphogenesis,including seed germination,stem elongation,and flowering.

(B) The physiological response of plants to the relative lengths of light and dark periods is called $Photoperiodism$.
$Phototropism$ refers to the growth of a plant in response to a light direction.
$Phototaxis$ is the movement of an organism in response to light.
$Vernalization$ is the induction of a plant's flowering process by exposure to the prolonged cold of winter.
Therefore,the correct answer is $Photoperiodism$.

(A) Phytochrome is a proteinaceous pigment that acts as a photoreceptor in plants.
It exists in two interconvertible forms: $P_r$ (which absorbs red light) and $P_{fr}$ (which absorbs far-red light).
It plays a crucial role in light-dependent developmental processes such as photoperiodism,seed germination,and flowering.

(D) Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. Plants are classified based on their response to photoperiods into three categories: Long-day plants,Short-day plants,and Day-neutral plants.
$1$. Long-day plants $(LDP)$ flower when the day length exceeds a critical duration. Examples include Spinach ($Spinacia$ $oleracea$),Wheat,and Radish.
$2$. Short-day plants $(SDP)$ flower when the day length is shorter than a critical duration. Examples include Tobacco and Glycine max (Soybean).
$3$. Day-neutral plants flower regardless of the day length. An example is Mirabilis jalapa.
Therefore,Spinach is a long-day plant.

(B) The plants described are $Short-day$ $plants$ $(SDP)$.
$SDP$ require a continuous dark period longer than a critical duration to flower.
When the dark period is interrupted by a brief flash of light, the physiological process required for flowering is inhibited.
Since the interruption of the night phase prevents flowering, these plants are classified as $Short-day$ $plants$.

(A) Phytochrome exists in two interconvertible forms: $P_r$ and $P_{fr}$.
$P_r$ is the inactive form of phytochrome that absorbs red light.
The absorption peak for the $P_r$ form is approximately $660 \, nm$.
Upon absorbing red light,$P_r$ is converted into the active $P_{fr}$ form.
Conversely,the $P_{fr}$ form absorbs far-red light at approximately $730 \, nm$ to convert back into the $P_r$ form.
Therefore,the correct wavelength for the $P_r$ form is $660 \, nm$.

(B) Phytochrome is a light-sensitive pigment found in plants that acts as a photoreceptor.
Chemically,it is a chromoprotein,which consists of a protein part and a light-absorbing pigment molecule called a chromophore.
It plays a crucial role in various plant developmental processes such as flowering,seed germination,and stem elongation by sensing red and far-red light.

(D) The response of plants to periods of day and night (light and dark) is known as $Photoperiodism$.
$Phototropism$ is the growth of an organism in response to a light stimulus.
$Phototaxis$ is the movement of an organism in response to light.
$Vernalization$ is the induction of a plant's flowering process by exposure to the prolonged cold of winter.

(D) The site of perception of light or dark duration (photoperiod) is the leaves.
Although the flowering occurs at the shoot apex,the hormonal signal (florigen) is synthesized in the leaves upon exposure to the appropriate photoperiod and then translocated to the shoot apex to induce flowering.
Therefore,the leaves are considered the primary site of perception for photoperiodic stimuli.

(C) It has been demonstrated that flowering in plants is more of a response to the dark period than to the light period.
In short-day plants $(SDP)$,the plants can flower in complete darkness if supplied with exogenous nutrients.
Flowering is inhibited in $SDP$ if the dark period,which is essential for flowering,is interrupted by a flash of light.
Therefore,the Reason is incorrect because a light break during the dark period prevents flowering in short-day plants,rather than inducing it.

(A) The Assertion is correct because phytochrome is a photoreceptor pigment that regulates various developmental processes,including flowering,in response to light.
The Reason is also correct. Phytochrome exists in two interconvertible forms: $P_R$ (inactive) and $P_{FR}$ (active). When exposed to red light,$P_R$ is converted to $P_{FR}$. The $P_{FR}$ form is the physiologically active form that migrates to the nucleus or interacts with signaling pathways to induce floral development in shoot buds.
Since the active form $P_{FR}$ is the specific component of the phytochrome system that triggers the flowering response,the Reason correctly explains the Assertion.

(A) Vernalization is the process of inducing or accelerating flowering in plants by exposing them to low temperatures. This phenomenon was first described by $T.D.$ Lysenko in $1928$.
The Assertion is correct because vernalization specifically refers to the promotion of flowering through cold treatment.
The Reason is also correct because the perception of the cold stimulus occurs primarily in the apical meristem (shoot apex) of the plant,where it triggers the production of a hypothetical flowering hormone called vernalin.
Since the Reason correctly identifies the site where the process described in the Assertion occurs,it serves as a valid explanation.

(B) Vernalization is a process where the flowering of plants is promoted or accelerated by exposing them to a period of low temperature.
This process ensures that plants flower during a favorable season.
The term 'vernalization' was coined by $T.D.$ Lysenko in $1928$.
It is believed that a hypothetical hormone called 'vernalin' is produced in the plant as a result of this cold treatment,which triggers flowering.
The perception of the cold stimulus occurs primarily in the actively dividing cells,specifically the apical meristem of the shoot or the embryo.
Since both the Assertion and the Reason are scientifically accurate,but the Reason explains the location of the process rather than the mechanism of acceleration,the correct choice is $B$.

(N/A) Photoperiodism refers to the response of plants with respect to the duration of light (i.e.,period of day and night). On the basis of its response to the duration of light,a plant is classified as a short-day plant,a long-day plant,or a day-neutral plant.
Short-day plants flower when they are exposed to light for a period less than the critical day-length (e.g.,Chrysanthemum).
Long-day plants flower when they are exposed to light for a period more than the critical day-length (e.g.,radish).
When no marked correlation is observed between the duration of exposure to light and the flowering response,plants are termed as day-neutral plants (e.g.,tomato).
It is hypothesised that the hormonal substance responsible for flowering is formed in the leaves,subsequently migrating to the shoot apices and modifying them into flowering apices. Photoperiodism helps in studying the response of flowering in various crop plants with respect to the duration of exposure to light.
Vernalisation is the cold-induced flowering in plants. In some plants (such as the winter varieties of wheat and rye and biennials such as carrot and cabbage),exposure to low temperature is necessary for flowering to be induced. The winter varieties of rye and wheat are planted in autumn. They remain in the seedling stage during winters and flower during summers. However,when these varieties are sown in spring,they fail to flower. Similar response is seen in cabbage and radish. Vernalisation helps in shortening the period of growth and enables the plant to flower at the appropriate time.

(C) The flowering response in plants is regulated by the duration of light exposure,a phenomenon known as photoperiodism.
Short-day plants $(SDP)$ require a light period shorter than a critical duration to flower.
Long-day plants $(LDP)$ require a light period longer than a critical duration to flower.
If a given location provides the specific critical photoperiod required by both types of plants,they can flower simultaneously.
Therefore,the simultaneous flowering is possible if both plants receive their respective required photoperiods.

(NO) defoliated plant will not respond to the photoperiodic cycle.
It is hypothesized that the hormonal substance responsible for flowering is synthesized in the leaves. This substance subsequently migrates to the shoot apices and modifies them into flowering apices.
Therefore,in the absence of leaves,the perception of light does not occur,and the plant fails to respond to the photoperiodic stimulus.

(N/A) Photoperiodism is the physiological response of plants to the relative lengths of light and dark periods.
It is a developmental response to the duration of light exposure,which is crucial for the transition from vegetative growth to flowering.
Based on their photoperiodic requirements,plants are classified into three categories:
$1$. Long-day plants: These require a longer duration of light than a critical period to flower.
$2$. Short-day plants: These require a shorter duration of light than a critical period to flower.
$3$. Day-neutral plants: These do not show any correlation between exposure to light duration and the induction of flowering.
The site of perception of light/dark duration is the leaves,which synthesize a hormonal substance that migrates to the shoot apices to induce flowering.

(N/A) Vernalisation is the process by which the flowering of a plant is promoted by exposure to a period of low temperature.
It prevents precocious reproductive development late in the growing season and enables the plant to have sufficient time to reach maturity.
Many food plants,such as wheat,barley,and rye,have two kinds of varieties: winter and spring varieties.
The 'spring' variety is normally planted in the spring and comes to flower and produces grain before the end of the growing season.
'Winter' varieties,if planted in spring,would normally fail to flower or produce mature grain within a span of a flowering season.
Hence,they are planted in autumn,germinate,and come out as small seedlings during winter.
They resume growth in the spring and are harvested around mid-summer.
Vernalisation thus refers to the specifically promoted flowering by a period of low temperature.

(N/A) In many plants,a specific duration of light is required to induce or promote flowering. This phenomenon is known as photoperiodism.
Plants have the ability to measure the duration of light exposure.
For example,some plants,known as long-day plants,require exposure to light for a duration exceeding a critical period to flower.
Conversely,other plants,known as short-day plants,require exposure to light for a duration less than a critical period to flower.
Some plants,called day-neutral plants,are not affected by the duration of light exposure for flowering.

(N/A) $(1)$ Photoperiodism and flowering are closely linked. For example,in long-day plants,if the dark period is interrupted,or in short-day plants,if the light period is interrupted,the flowering response is inhibited. Furthermore,the pigment phytochrome is responsible for sensing these light periods to trigger flowering.
$(2)$ Plants possess specific abscission layers. The process of shedding leaves,flowers,and fruits is known as abscission. This process helps in maintaining hormonal balance within the plant. After the shedding of old or damaged parts,the plant initiates the growth of new structures. This renewal process increases the overall vitality of the plant. During this phase,hormones like auxins,gibberellins,and cytokinins are involved,where the regulation of auxin levels promotes new growth and enhances plant longevity.

(N/A) $(1)$ Development is a term that includes all changes that an organism goes through during its life cycle from germination of the seed to senescence.
$(2)$ Light period (Photoperiod) refers to the duration of light exposure that an organism,particularly a plant,receives,which influences various physiological processes such as flowering.

(N/A) Photoperiodism is the physiological response of plants to the relative lengths of light and dark periods.
$Nicotiana$ $tabacum$ is classified as a short-day plant $(SDP)$.
Short-day plants require a light period shorter than a certain critical duration to induce flowering.
If these plants are exposed to a light period longer than their critical day length,the flowering process is inhibited.
This occurs because the plant requires a specific duration of uninterrupted darkness to synthesize the flowering hormone,often referred to as florigen.
Exposure to light beyond the critical limit disrupts this dark-period requirement,thereby preventing the transition from vegetative growth to reproductive flowering.

(N/A) As soon as a seed germinates,the plant enters a vegetative growth phase. During this phase,the plant perceives light stimuli (photoperiodism) and synthesizes florigen,a hypothetical flowering hormone,which eventually induces the transition to the reproductive phase.
$(B)$ This vegetative growth period is advantageous because it allows the plant to accumulate sufficient biomass,develop a robust root and shoot system,and reach physiological maturity. This ensures the plant has enough energy and structural integrity to support the development of reproductive structures like flowers,fruits,and seeds,thereby increasing the chances of successful reproduction.

(A) $(1)$ Auxins are the plant hormones that initiate rooting in stem cuttings.
$(2)$ Phytochrome is the pigment involved in photo-perception (photoperiodism) in flowering plants.

(D) Some annual food plants,such as wheat,do not flower unless they experience a low temperature. They remain vegetative during spring (a warm period) but grow further to bear flowers and fruits only after receiving low temperatures (in winter).
The low temperature in winter prevents precocious reproductive development in autumn,thus enabling the plant to reach vegetative maturity before the reproductive phase.
Thus,when spring varieties are planted in spring,they flower and bear fruits prior to the end of the growing season. However,if winter varieties are planted in spring,they fail to flower and produce mature grains before the end of the growing season,as they could not perceive the low temperature of winter. This phenomenon is known as $Vernalization$.

(B) Annual winter wheat plants require a full growing season to complete their vegetative growth before initiating flowers and fruits. By sowing in autumn,they are exposed to low temperatures throughout the winter,which is essential for them to reach vegetative maturity. They resume growth in spring and produce flowers and grains by mid-summer.
$(B)$ The process of using chilling or cold treatment to promote or accelerate flowering is called vernalisation. It shortens the juvenile or vegetative phase,thereby hastening the transition to the reproductive phase. This stimulus is perceived specifically by meristematic cells,such as the shoot tip,embryo tip,root apex,and developing leaves.
$(C)$ Gibberellic acid $(GA)$ treatment can replace the cold treatment and induce early flowering by reducing the vegetative growth period in many long-day plants.

(A) $(1)$ Stress. $ABA$ (Abscisic acid) is known as a stress hormone because it increases the tolerance of plants to various kinds of stresses.
$(2)$ Vernalization. Cold treatment is a method used to induce flowering in plants,a process known as vernalization.

(C) Photoperiodism is the physiological reaction of organisms to the length of day or night.
It occurs in both plants and animals.
It is defined as the developmental responses of organisms to the relative lengths of light and dark periods.
Photoperiod exclusively affects the reproduction in seasonal breeders,as these organisms rely on specific day lengths to trigger their reproductive cycles.

(B) Short day plants $(SDP)$ are also known as long night plants because they require a continuous or critical dark period for flowering to occur.

(A) Photoperiodism is the physiological response of plants to the relative lengths of light and dark periods. It was first studied and described by $W.W.$ Garner and $H.A.$ Allard in $1920$ while working on tobacco plants $(Nicotiana \, tabacum)$.

(A) Long-day plants $(LDP)$ flower only when they are exposed to a light period longer than a certain critical duration.
Based on the provided graph,the critical photoperiod for the long-day plant is approximately $12$ hours.
Therefore,for flowering to occur in a long-day plant,the duration of the light period $(A)$ must be greater than the critical value (i.e.,$A > 12$ hours).
Among the given options,$A=13$ hours and $B=11$ hours satisfies the condition where the light period is longer than the critical photoperiod.

(A) The term vernalization was introduced by $Lysenko$.
$Chouard$ defined it as the acquisition of the ability to produce flowers by low temperature treatment.
Vernalization is affected by two factors: water and oxygen.
In the absence of proper water and $O_2$ content,the chilling treatment becomes ineffective.

(A) Florigen is a hypothetical hormone that has not yet been chemically isolated. It is synthesized in the leaves in response to specific photoperiodic conditions. Once produced,it is transported to the shoot apical meristems (growing points) to induce flowering. It specifically triggers the transition from vegetative growth to reproductive growth (flowering) without directly inhibiting or stimulating overall plant growth.

(B) The effect of photoperiod on the growth and development of plants,particularly on the induction of flowering,is known as photoperiodism.
This phenomenon was first studied by Garner and Allard in $1920$.

(C) Photoperiodic stimulus is perceived by the fully developed leaves of the plant.
Research by Knott $(1934)$ demonstrated that even a single leaf or a small portion of a leaf (as little as $1/8$ of the total leaf area) is sufficient to perceive the photoperiodic stimulus and initiate the flowering response.

(D) The plant described is a Short Day Plant $(SDP)$ because it requires a minimum of $10$ hours of darkness to flower.
This $10$ hours is known as the critical dark period.
For flowering to occur,the plant must be exposed to a dark period equal to or greater than the critical dark period.
Condition $II$ provides exactly $10$ hours of darkness,which meets the requirement.
Conditions $III$ and $IV$ provide less than $10$ hours of darkness,so the plant will not flower under these conditions.
Therefore,the plant will flower under condition $II$.

(C) Short-day plants are those that flower when the day length is shorter than a critical period. Among the given options,$Glycine \ max$ (soybean) is a classic example of a short-day plant. $Brassica \ campestris$,$Raphanus \ sativus$,and $Papaver \ somniferum$ are generally considered long-day plants.

(B) Garner and Allard $(1920)$ first observed photoperiodism in 'Maryland Mammoth',a variety of tobacco ($Nicotiana$ $tabacum$).
They discovered that this plant could be induced to flower in summer by reducing the duration of light exposure through artificial darkening.
Conversely,it could be kept in a vegetative state during winter by providing supplemental light.
This discovery established the concept of photoperiodism,which is the response of plants to the relative lengths of light and dark periods.

(C) $LDP$ (Long Day Plant): These plants flower when they receive a photoperiod longer than the critical photoperiod. Examples include henbane,wheat,oat,beet,spinach,radish,and lettuce.
$SDP$ (Short Day Plant): These plants flower when the photoperiod is shorter than the critical period. Most winter plants are $SDP$,e.g.,potato,bean,tobacco,rice,and sugarcane.
$DNP$ (Day Neutral Plant): These plants can blossom throughout the year regardless of the photoperiod. Examples include tomato,maize,cotton,and pepper.
Among the given options,only $IV$ (Radish) is a long day plant. Therefore,the correct option is $C$.