Mix Examples-Plant Growth and Development Questions in English

(C) Phytoalexins are antimicrobial substances synthesized de novo by plants that accumulate rapidly at areas of pathogen infection.
They are generally phenolic compounds or terpenoids produced in the host cell for defense in response to fungal infection (Muller and Borger,$1940$).
These chemicals inhibit the growth of the parasite and help the plant in resisting the infection.

(A) $Cuscuta$ is a total stem parasite. These plants do not possess chlorophyll and therefore cannot perform photosynthesis. They derive their nutrition entirely from the host plant's stem by developing specialized structures called haustoria,which penetrate the host's tissues to absorb water and nutrients.

(D) The shedding of leaves in winter is a complex physiological process triggered by environmental factors.
$1$. The shortening of day length $(photoperiodism)$ and the fall in temperature act as external signals that initiate the process of leaf senescence.
$2$. In response to these signals,a specialized zone called the $abscission$ $layer$ forms at the base of the petiole.
$3$. This layer consists of thin-walled,cambium-like cells that are rich in protoplasm and starch.
$4$. Enzymes such as $cellulases$ and $pectinases$ are secreted,which degrade the middle lamella and cell walls,causing the leaf to detach from the branch.
Therefore,all the mentioned factors contribute to this process.

(B) After the leaf falls,the abscission zone is exposed to the air. To prevent water loss and pathogen entry,the cells of the leaf scar develop a protective layer. This layer is formed by the deposition of $suberin$ and $lignin$ on the cell walls,which makes the scar waterproof and protective. Therefore,the correct answer is $B$.

(A) Onion and garlic contain sulphur-containing compounds such as allicin and diallyl sulphide,which are responsible for their characteristic pungent flavour and antimicrobial properties.
Additionally,the tear-inducing substance in onions is a sulphur compound known as propanethial-$S$-oxide.

(D) Light plays a multifaceted role in plant life:
$1$. Photosynthesis: Light energy is essential for the synthesis of organic food from inorganic raw materials.
$2$. Growth and Movement: Light influences phototropism (movement towards light) and photomorphogenesis (light-mediated development).
$3$. Hormone Distribution: Light affects the synthesis and distribution of plant hormones like auxins,which regulate various physiological processes.
Therefore,all the given options are correct.

(D) Traumatin is a plant hormone, specifically a dicarboxylic acid, which is known as a 'wound hormone'.
It is produced by injured plant tissues and stimulates cell division in the surrounding cells to promote healing and repair of the damaged area.
Therefore, it is found in the injured portion of the plant.

(C) Tropical plants are adapted to warm temperatures. When they are moved to a temperate climate,the low temperatures (even if above freezing) cause physiological damage to their cellular membranes and metabolic processes,a phenomenon known as chilling injury. This prevents their growth and development.

(A) When the temperature drops below freezing,the water inside the plant cells freezes. This leads to the formation of ice crystals,which cause mechanical damage to the cell walls and membranes. Furthermore,the freezing of water outside the cells creates a water potential gradient that draws water out of the cells,leading to severe desiccation (dehydration) of the plant tissues. Both these factors combined result in the death of the plant.

(D) Plant hormones, also known as phytohormones, are chemical substances that regulate plant growth and development.
$Auxin$ is a well-known plant growth regulator involved in cell elongation and apical dominance.
$Gibberellin$ is another major class of plant hormones that promotes stem elongation, seed germination, and flowering.
$Morphactin$ is a synthetic plant growth regulator derived from fluorene$-9-$carboxylic acid, which acts as a growth inhibitor.
Since $Auxin$, $Morphactin$, and $Gibberellin$ are all classified as plant hormones, the correct answer is $All \text{ of the above}$.

(B) Plant hormones are chemical substances that regulate plant growth and development.
They are synthesized by the plant in very small quantities.
Unlike enzymes,which act as catalysts and are not consumed in the reaction,hormones are often expended or metabolized during the physiological processes they regulate.
However,in the context of typical biological comparisons,hormones are required in extremely low concentrations compared to many other regulatory molecules,though they differ fundamentally from enzymes because they are not catalytic proteins that remain unchanged after a reaction.

(D) Phytohormones (plant growth regulators) have various applications in agriculture and horticulture:
$1$. Parthenocarpy: Auxins and gibberellins are used to induce the development of seedless fruits without fertilization.
$2$. Grafting: Auxins are often applied to the cut surfaces of scions to promote root initiation and successful union.
$3$. Ripening of fruits: Ethylene is widely used to accelerate the ripening process in climacteric fruits like bananas and mangoes.
Therefore,all the mentioned processes utilize phytohormones.

(C) Rhizocaline is also known as the root-forming hormone.
It is synthesized in the leaves and then translocated in a polar manner down the stem to the site of root initiation.

(D) Plant hormones,also known as phytohormones,are chemical substances that regulate plant growth and development. They are diverse in their chemical structure. For example,$Auxins$ are indole compounds (aromatic),$Gibberellins$ are terpene derivatives,$Cytokinins$ are adenine derivatives (purines),$Abscisic$ $acid$ is a carotenoid derivative,and $Ethylene$ is a simple gaseous hydrocarbon. Among the given options,many plant hormones possess aromatic rings or are derived from aromatic precursors,making 'Aromatic compounds' the most chemically diverse and accurate classification for the majority of these regulators.

(D) Phytohormones (plant growth regulators) are chemical substances that regulate various aspects of plant life.
They control growth,development,physiological functions,rooting,flowering,and responses to environmental stimuli.
Therefore,they control all the listed processes.

(A) The correct answer is $A$.
$2, 4-D$ ($2$,$4$-dichlorophenoxyacetic acid) is a synthetic auxin,not a naturally occurring plant hormone.
$GA_2$ is a naturally occurring gibberellin found in plants.
Gibberellin is a class of natural plant growth regulators.
$IAA$ (Indole$-3-$acetic acid) is the most common naturally occurring auxin in plants.

(B) Auxin exhibits polar transport,meaning it moves in a specific direction (basipetal) through the plant tissues. In contrast,other plant hormones like Gibberellins,$ABA$ (Abscisic acid),and Cytokinins exhibit non-polar movement,as they are transported through the phloem and xylem in a non-directional manner throughout the plant body.

(A) Wound hormone is a chemical substance released by damaged plant cells to stimulate cell division in surrounding healthy cells to repair the wound.
It is chemically known as $traumatic \ acid$.
It is also commonly referred to as $necrohormone$ because it is produced in response to tissue necrosis or injury.

(A) The correct answer is $(A)$.
Morphactins are synthetic plant growth regulators that act as inhibitors of plant development.
They specifically inhibit the elongation of internodes,which leads to a reduction in stem length and often results in a dwarfed growth habit in plants.
In contrast,Gibberellins are known to promote internode elongation.

(A) The correct answer is $ (a) $.
Certain other natural growth hormones in plants are known as calines or formative hormones.
These substances are thought to be essential for the effect of auxin on root,stem,and leaf growth.

(C) Blue-violet light promotes internodal elongation and also increases the surface area of the leaf lamina. In contrast,green light is known to reduce the expansion of leaves compared to the full spectrum of visible light.

(A) When a green plant is kept in prolonged darkness,it cannot perform photosynthesis due to the absence of light.
As a result,the synthesis of chlorophyll is inhibited,and the plant develops long,weak stems with pale or yellow leaves.
This physiological phenomenon is known as $Etiolation$.

(B) Phytochrome exists in two interconvertible forms: $P_r$ (phytochrome red) and $P_{fr}$ (phytochrome far-red).
$P_r$ absorbs red light at $660 \ nm$ and is converted into $P_{fr}$.
$P_{fr}$ absorbs far-red light at $730 \ nm$ and is the physiologically active form that triggers various plant responses such as flowering,seed germination,and leaf expansion.
Therefore,the active form is $P_{730}$ (also known as $P_{fr}$).

(A) Photomorphogenesis is the light-mediated development of plants,where light acts as a signal rather than an energy source.
Phytochrome is a blue-green pigment protein that acts as a photoreceptor in plants.
It exists in two interconvertible forms: $Pr$ (which absorbs red light) and $Pfr$ (which absorbs far-red light).
These pigments regulate various developmental processes such as seed germination,stem elongation,and flowering in response to light signals.
Therefore,the correct answer is $A$.

(C) The directional growth movement of a plant organ in response to a light stimulus is known as phototropism.
$1$. Hydrotropism is the growth response to water.
$2$. Thigmotropism is the growth response to touch or physical contact.
$3$. Geotropism (or gravitropism) is the growth response to gravity.
Therefore,the correct answer is phototropism.

(A) Phototropism is the growth of an organism in response to a light stimulus.
$(a)$ $A$ $Heliotropic$ chamber is a specialized apparatus designed to demonstrate the phenomenon of phototropism in plants.
$(b)$ $A$ $Clinostat$ is used to demonstrate geotropism by eliminating the effect of gravity through slow rotation.
$(c)$ An $Arc$ $Auxanometer$ is used to measure the rate of growth in plants.
$(d)$ $A$ $Potometer$ is used to measure the rate of transpiration in a leafy shoot.
Therefore,the correct apparatus for demonstrating phototropism is the $Heliotropic$ chamber.

(A) Geotropism (or gravitropism) is the growth movement of plants in response to gravity.
While gravity is the primary stimulus,several internal and external factors can modify this response.
Internal factors include the physiological state of the root and shoot apices,which are the sites of perception and response.
External environmental factors such as temperature,light,and the concentration of atmospheric carbon dioxide $(CO_2)$ significantly influence the growth rate and the directionality of the geotropic response in plant organs.

(B) The bending of a plant stem towards a light source is a type of growth movement called phototropism.
Since the question specifically refers to the movement towards the sun or light,it is also commonly referred to as heliotropism.
Photoperiodism refers to the response of plants to the relative lengths of day and night.
Photonasty is a non-directional movement in response to light.
Hydrotropism is the growth movement of plant parts in response to water.

(D) $Thigmotropism$ is a directional growth movement of a plant in response to the stimulus of touch or physical contact.
Examples include the coiling of tendrils around a support and the growth of haustoria in $Cuscuta$ when they come into contact with a host plant.

(B) Nyctinasty is the circadian rhythmic movement of plants in response to the onset of darkness,often referred to as sleep movements.
Thigmonasty is a nastic movement in response to touch or mechanical stimulation.
In $Mimosa$ $pudica$ (touch-me-not plant),the leaves exhibit thigmonasty when touched and also show nyctinasty,where the leaflets fold up at night.

(A) The movement in the leaves of $Mimosa \text{ } pudica$ (touch-me-not plant) upon touching is known as seismonasty or thigmonasty.
This is a non-directional movement in response to a mechanical stimulus (touch).
It occurs due to the sudden loss of turgor pressure in the pulvinus cells at the base of the leaflets.
Therefore, the correct answer is $A$ (Seismonasty).

(D) clinostat is a device that rotates a plant slowly,typically at a constant speed,to eliminate the effect of gravity on plant growth. By continuously changing the orientation of the plant,the gravitational stimulus is nullified,allowing scientists to study the effects of geotropism (gravitropism). Therefore,it is primarily used to demonstrate or study geotropism.

(A) Tendrils are specialized structures in climbing plants that respond to touch or contact with a solid support.
When a tendril comes into contact with an object,the cells on the side touching the object grow more slowly than the cells on the opposite side.
This differential growth causes the tendril to coil or twine around the support.
This directional growth movement in response to touch or mechanical stimulus is known as $Thigmotropism$.

(B) The movement of a plant part in response to touch or mechanical stimulation is called $Thigmonasty$.
$Seismonasty$ is a specific type of $Thigmonasty$ where the movement occurs in response to shock or vibration (e.g.,the folding of leaves in $Mimosa$ $pudica$).
Since $Thigmonasty$ is the broader and more accurate term for touch-induced movement,it is the correct answer.

(A) The opening and closing of flowers in response to light intensity is known as photonasty.
In $Oxalis$, the flowers open in the morning due to the presence of light and close in the evening when the light intensity decreases.
This is a non-directional movement of plant parts in response to light, which is distinct from phototropism (growth movement towards light) or phototaxis (locomotory movement).

(D) Photonasty is the non-directional movement of plant parts in response to a diffuse stimulus of light. Unlike phototropism,which is a directional growth movement towards or away from a light source,photonasty is independent of the direction of the stimulus. Examples include the opening and closing of flowers in response to light intensity changes.

(D) The movement of leaves in $Mimosa$ $pudica$ (touch-me-not plant) upon stimulation is a type of thigmonasty (seismonasty).
This movement is caused by the loss of turgor pressure in the specialized cells located at the base of the leaflets and leaves,known as the pulvinus and pulvinules.
When touched,the cells in the pulvinus lose water to the intercellular spaces,leading to a decrease in turgor pressure,which causes the leaves to droop.
Therefore,all the mentioned factors contribute to this phenomenon.

(D) The opening of a flower and the drooping of a bud are primarily controlled by differential growth rates on the upper and lower surfaces of the floral organs.
When the growth is more rapid on the inner surface,it leads to the opening of the flower (Epinasty).
When the growth is more rapid on the outer surface,it leads to the closing of the flower or the drooping of a bud (Hyponasty).
Therefore,these movements are classified under nastic movements,specifically Epinasty and Hyponasty,which are growth-related movements.

(A) The movement in the "Touch-me-not" plant $(Mimosa pudica)$ in response to mechanical stimuli like touch or shock is called Seismonasty.
Seismonasty is a type of nastic movement where the plant organ responds to mechanical shock or vibration.
In $Mimosa pudica$, the leaves fold inward due to a sudden loss of turgor pressure in the pulvinus cells upon being touched.

(C) Thigmotropism is the directional growth movement of a plant in response to a touch stimulus.
It is most prominently observed in the tendrils of climbing plants.
When a tendril comes into contact with a solid object (support),the side in contact grows more slowly than the side away from the object,causing the tendril to coil around the support.
This adaptation helps the plant climb and gain access to sunlight.

(A) The correct matches are as follows:
$(a)$ Maheshwari: $(IV)$ Successful culture of an ovule of $Papaver$ using $IAA$ and kinetin.
$(b)$ Das: $(I)$ Pre-sowing treatment of seeds of $Phaseolus$ $aureus$ with $IAA$.
$(c)$ Went: $(II)$ $Avena$ curvature test,which is a bioassay for auxins.
$(d)$ Chakravarty: $(III)$ Work on seedless fruit in cucumber.
Therefore,the correct sequence is $a-IV, b-I, c-II, d-III$.

(C) The correct matches are as follows:
$(1)$ Auxin: $(II)$ Differentiation of xylem elements.
$(2)$ Gibberellin: $(III)$ Prevention of genetic and physiological dwarfism (it promotes stem elongation).
$(3)$ Cytokinin: $(IV)$ Found from tumour tissue of tobacco (specifically,kinetin was discovered from autoclaved herring sperm $DNA$ and later from tobacco pith).
$(4)$ Ethylene: $(I)$ Ripening and maturity of fruits.
Therefore,the sequence is $(1)-(II), (2)-(III), (3)-(IV), (4)-(I)$.

(D) $Clinostat$ is a scientific instrument that rotates a plant slowly at a constant speed. By rotating the plant,the gravitational force is applied equally to all sides of the plant stem or root over time. This effectively cancels out the directional influence of gravity,allowing researchers to study plant growth without the interference of $geotropism$ (gravitropism).

(B) The $Corpora \text{ } allata$ is an endocrine gland in insects that secretes Juvenile Hormone $(JH)$.
Juvenile Hormone is responsible for maintaining the larval or nymphal characteristics during molting.
When $Corpora \text{ } allata$ is removed, the level of Juvenile Hormone drops significantly.
In the absence of $JH$, the insect undergoes premature (precocious) metamorphosis and develops into an adult earlier than normal.

(A) Plants are killed in winter by frost primarily due to desiccation and mechanical damage to the tissues. When temperatures drop below freezing,ice crystals form within the intercellular spaces of the plant tissues. This process causes the withdrawal of water from the cells (desiccation) and the physical rupture of cell membranes and walls due to the expansion of ice,leading to tissue death.

(B) $Ephemerals$ complete their life cycle in a very short period,evading the dry season by disappearing and leaving their seeds behind. They are referred to as drought escapers or drought evaders.

(B) The correct answer is $B$.
Psammophytes are plants that are adapted to grow in sandy soils or shifting sand dunes.
Since deserts are primarily composed of sand,the introduction and cultivation of psammophytes can help stabilize the sand,improve soil structure,and initiate the process of ecological succession,eventually leading to the conversion of desert areas into greenlands.

(D) In xerophytes,adaptations are aimed at reducing water loss through transpiration.
These adaptations include the presence of sunken stomata,a thick waxy cuticle,and reduced leaf surface area (often modified into spines).
Therefore,having a larger number of stomata is incorrect,as xerophytes typically have fewer stomata to minimize water loss.

(A) physiological xerophyte is a plant that grows in a saline environment (halophyte) but exhibits the characteristics of a xerophyte because the high salt concentration in the soil makes it difficult for the plant to absorb water,creating a condition of physiological drought. $Salicornia$ is a classic example of a halophyte that behaves as a physiological xerophyte.