Test: Plant Growth & Development - 4 - ACT MCQ

Auxins are the phytohormones present in plants which has several important roles to play in plant life. It is usually seen at the tip of  shoots, at the meristematic region.

Water provides the medium for enzymatic activities needed for growth in the plants as water is a common medium which is easily available to the plants and most of the enzymes known for the plants can get easily dissolved in the water.

Every plant organism has an optimum temperature range best suited for its growth. Any deviation from this range could be detrimental to the survival of the plant.

Auxin is a group of several natural (and artificial) plant hormones; the most common and physiologically important auxin is indoleacetic acid (IAA). Some manufactured, or synthetic, auxins have structures similar to that of IAA. The synthetic auxin naphthalene acetic acid stimulates root development on stem cuttings and is used for asexual propagation, particularly of woody plants with horticultural importance.
Thus, the correct answer is option A.

Auxin is a plant hormone that plays important role in phototropism, growth movement in response to light. It promotes cell elongation. It is unequally distributed in the plant cells. It is transported towards the shady side and thus present in higher concentration. However, less auxin is transported towards the illuminated side. Due to this, the plant to grow more on the shaded side and bend in the direction of the light source. It shows phototropic response where faster cell elongation is seen on the shaded side than on the illuminated side. 

• Development includes all the changes undergone by a living plant from seed emergence to death.
• Dedifferentiation is regaining the lost capacity of cells or tissues of plants to divide under special conditions.
• Redifferentiation is the further maturation of dedifferentiated cells thereby specializing for a particular function.
• Differentiation is the division and growth of cells in order to mature.

• Differentiation leads to elongation and thickening of sclerenchyma cells. 
• Development includes all the changes undergone by a living plant from seed emergence to death.
• Dedifferentiation is regaining the lost capacity of cells or tissues of plants to divide under special conditions.
• Redifferentiation is the further maturation of dedifferentiated cells thereby specializing for a particular function.

Ethylene is a fruit ripening hormone. It also induces femaleness in plants. Auxins are the hormones responsible for cell elongation in plants. High auxin concentration increases the synthesis of ethylene and hence help to promote femaleness in dioecious plants. Thus the correct answer is option A.

• Redifferentiation leads to the formation of secondary xylem and phloem.
• Redifferentiation is the maturation of dedifferentiated cells thereby specializing for a particular function.
• Development includes all the changes undergone by a living plant from seed emergence to death.
• Dedifferentiation is regaining the lost capacity of cells or tissues of plants to divide under special conditions.
• Differentiation is the division and growth of cells in order to mature.

• Indeterminate growth means growth of plant is unspecified and is carried out till the plant survives.
• Plants are capable of indeterminate growth as they possess perpetually embryonic tissues called meristems.
• Plant parts such as leaves, thorns and flowers have determinate growth.
• Indeterminate growth is not synonymous to immortality, the plant continues to thrive, divide and mature.

• Ethylene is a volatile gaseous hormone. GA, ABA and Auxin are acidic in nature.
• GA and Auxin are growth promoters while ABA is a growth inhibitor.

The answer is Option A - Phototropism.

The phenomenon of phototropism is the growth of organisms in response to light. Charles Darwin and his son Francis Darwin were among the early scientists to study phototropism. They found that light is perceived by the tip of the plant shoot, and this perception leads to growth further down the shoot.

Later, it was discovered that a hormone, named auxin, is responsible for this effect. Auxin accumulates on the side of the plant facing away from the light source, and causes cells on that side to elongate, thus bending the plant towards the light. This played a major role in the discovery of auxin, which is one of the main plant hormones.

While auxins do also influence other processes like root initiation, gravitropism, and apical dominance, their role in phototropism was significant to their discovery.

So, based on your question, phototropism (Option A) is the correct answer.

Plant growth is generally indeterminate, not determinate. This means that plants typically continue to grow as long as they live, unlike animals which have a determinate growth and stop growing after reaching a certain age or size. The meristematic tissues in plants (such as the apical meristem, lateral meristem etc.) allow for continuous growth and production of new cells. This is a key characteristic of plants. So, the statement that plant growth is generally determinate is incorrect.

GA acts antagonistically to ABA. IAA is synthetic auxin. Kinetin delays senescence. Ethylene promotes abscission of older parts.

(A) Auxin - (IV) Promotes flowering in pineapple: Auxins are a class of plant hormones that influence cell growth by altering cell elongation. However, the role of promoting flowering in pineapple is actually played by Ethylene. Therefore, there's an error in this match.

(B) Gibberellin - (III) Increase in the length of grape stalks: Gibberellins are plant hormones that stimulate stem elongation, seed germination, and flowering. They are known to increase the length of grape stalks.

(C) Cytokinin - (II) Overcoming apical dominance: Cytokinins are plant hormones that promote cell division and delay leaf senescence. They also play a role in overcoming apical dominance, encouraging the growth of lateral buds.

(D) Ethylene - (I) Promotes female flower formation in cucumber: Ethylene is a gaseous plant hormone which regulates a wide range of biological processes. It is known to influence sex determination in certain plants, promoting female flower formation in cucumber.

Ethylene is the hormone responsible for enhancement of the respiration rate of fruits thereby leading to its early ripening. Auxin and GA₃ induces parthenocarpy of fruits. ABA acts as a stress hormone.

Gibberellic acid (GA) is a plant hormone that stimulates cell elongation, germination, and influences a variety of developmental processes, including maturation and seed production. In the forestry industry, it is often used to hasten the maturity period and stimulate early seed production in juvenile conifers.

To explain the correct answer in detail:

- Growth curve typically follows an S-shaped or sigmoid pattern.
- Initially slow growth accelerates, then steadies.
- This curve signifies growth in phases.
- "Both 1 & 2" (S-shaped and sigmoid) are correct.
- S-shaped growth reflects steady acceleration.
- Sigmoid denotes a "S"-like curve with acceleration, then deceleration.
- These curves are common in various fields like biology, economics, and technology.

The hormone that promotes internode/petiole elongation in deep water rice is Ethylene.

Ethylene is a plant hormone that plays a critical role in growth and development, including responses to environmental stimuli. In the case of deep water rice, when the plants are submerged, the ethylene concentration increases and promotes rapid internodal elongation, which allows the plant to keep its leaves above the water surface.

So, the correct answer is Option B - Ethylene.

To control weeds, the widely used herbicides are 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). Here's why:

- 2,4-D (2,4-dichlorophenoxyacetic acid): It mimics natural auxin hormones in plants, causing uncontrolled growth and eventually killing weeds.
- 2,4,5-T (2,4,5-trichlorophenoxyacetic acid): Also an auxin-like herbicide used for weed control.

These herbicides are effective due to their hormonal effects on plant growth, disrupting normal development in weeds.

• Cytokinins are derived from adenine.
• Auxins are derivatives of indole compounds.
• Abscisic acid is derived from carotenoids.
• Ethylene is derived from methionine.

Ethylene increases the number of female flowers and fruits in certain plants such as cucumber. Gibberellins are used to increase the size of fruits in some plants.

The correct answer is A: Antiauxins.

- Antiauxins are compounds that inhibit the action of auxin.
- They work by blocking or reducing the effects of auxin in plant cells.
- By interfering with auxin activity, antiauxins can regulate various plant growth processes.
- Examples of antiauxins include compounds like PCIB and TIBA.
- Understanding antiauxins is crucial in manipulating plant growth and development effectively.

The ability of plant to follow different pathways and produce different structures in response to environment is called plasticity.

During differentiation, cells lose their ability to divide and form permanent cell.

The process where the differentiated cells again lose the ability to divide and form permanent cells is called redifferentiation.

• The site of perception of light in plants during photoperiodism is leaf.
•  The site of perception of low temperature stimulus during vernalisation is shoot apex and embryo.
•  Axillary bud are not sites of perception of photoperiod.

Auxin is a growth promoter, generally produced by the growing apex of stem and root of the plants.

Auxins, help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering, e.g., in pineapples. Auxins also help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits.

Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity e.g. heterophylly in cotton, coriander and larkspur. In such plants, leaves of juvenile plant are different in a shape from those in mature plants.

Maize does not show plasticity.

Some synthetic auxins are used as weedicides. 2, 4-D is widely used to remove broad leaved weeds or dicotyledonous weeds in cereal crops or monocotyledonous plants.

Auxins like IAA and IBA are used to induce parthenocarpy. IAA also stimulate nodule formation.

Auxin like NAA is used to increase dwarf shoots.