Phases of Plant Growth and Plant Growth Regulators

Comprehensive question-and-answer study flashcards covering plant growth and development, meristem types, differentiation phases, mathematical growth models, auxin action, and plant movements.

How is plant growth defined?

An irreversible permanent increase in size of an organ or its parts, or even of an individual cell, accompanied by metabolic processes (both anabolic and catabolic) that occur at the expense of energy.

Why is the swelling of a piece of wood placed in water not considered growth?

It is a temporary increase in size due to imbibition that can be reversed, requiring no energy because materials are moved passively.

What is indeterminate growth in plants?

A pattern of growth where an organism continues to grow throughout its entire lifespan without a predetermined fixed size.

How do determinate and indeterminate tomatoes differ in height and growth behavior after flowering?

Determinate tomatoes are shorter (about $4\,\text{ft}$ tall) and stop growing after blooming, while indeterminate tomatoes are taller ($6\text{--}20\,\text{ft}$ tall) and keep growing even after flowering.

What occurs during the process of cellular differentiation in plants?

Cells stop dividing, start maturing, and take up specialized functions.

What is dedifferentiation in plants, and what are two examples of dedifferentiated cells?

Dedifferentiation occurs when differentiated cells that have lost the ability to divide regain that ability under certain conditions; examples include parenchyma cells dividing to form a callus under laboratory conditions and cells dividing uncontrollably to form a tumour.

What is redifferentiation?

The process where dedifferentiated cells divide and once again produce cells that can no longer divide but mature to perform specific functions.

What are the three phases of plant growth and their defining characteristics?

The meristematic phase involves constant division of cells in shoot and roots; the elongation phase involves cell enlargement, increased vacuole formation, and new cell wall deposition; and the maturation phase is when protoplasm and cell wall thickening attain maximum growth.

What is the mathematical equation for arithmetic growth, and what do its variables represent?

The equation is $L_t = L_0 + rt$, where $L_t$ is the length at time $t$, $L_0$ is the length at time zero, and $r$ is the growth rate.

What is the mathematical equation for geometric growth, and what curve does it produce?

The equation is $W_1 = W_0 e^{rt}$ (where $W_1$ is final size, $W_0$ is initial size, $e$ is the base of natural logarithm, $r$ is the growth rate, and $t$ is time of growth), which follows lag, log, and stationary phases to produce a sinusoidal curve.

What five environmental conditions are required for plant growth?

Water, oxygen, nutrients, light, and temperature.

From which embryonic plant structures do roots and stems develop?

Roots develop from the radicle, and stems develop from the plumule.

From which structures do leaves, flowers, fruits, and seeds arise?

Leaves, flowers, and fruits arise from axillary buds; seeds are inside fruits, so they are also derived from axillary buds.

What is the difference between a seedling and a plantlet?

A seedling is a young plant grown from seed, whereas a plantlet is a young or small plant produced through vegetative propagation/asexual reproduction and used as a propagule.

Why does the vegetative phase precede flowering in plants?

The vegetative phase must occur first so reproductive organs develop properly and because flowers require energy.

What is open growth in plants?

A form of growth in which meristem cells retain the capacity to divide and self-perpetuate, while their daughter cells lose the capacity to divide and form permanent tissues of the plant body.

What are the roles of primary and secondary growth in plants?

Primary growth is responsible for elongation of the plant along its axis via apical meristems, whereas secondary growth is caused by lateral meristems (vascular cambium and cork-cambium) that increase the girth of organs in dicotyledonous plants and gymnosperms.

What plant development phenomenon is demonstrated by the leaf differences shown in this diagram?

Plasticity (specifically heterophylly), showing distinct juvenile versus adult leaf forms in larkspur and terrestrial versus water habitat leaf forms in buttercup.

What is the developmental pathway of a plant cell from formation to death shown in this diagram?

A meristematic cell divides or undergoes plasmatic growth (protoplasm), expands via elongation and vacuole formation, undergoes maturation (differentiation) into a mature cell, enters senescence, and ends in death.

How does auxin influence vascular tissue differentiation in relation to sugar concentration?

Auxin combined with low sugar promotes xylem differentiation, whereas auxin combined with high sugar promotes phloem differentiation.

How does auxin trigger the plant movement shown in this phototropism diagram?

Greater light on the right side causes auxin quantity to become greater on the shaded left side, which triggers cell elongation on the left side and makes the plant bend toward the light.

How do roots and shoots differ in their response to gravity as illustrated in this diagram?

Roots are positively geotropic (growing downward toward gravity), while shoots are negatively geotropic (growing upward away from gravity).

How are parthenocarpy and rosette habit defined?

Parthenocarpy is the development of a fruit without fertilization, and rosette habit is the circular arrangement of leaves.

What are the definitions of abscission, senescence, and seed dormancy?

Abscission is the natural detachment of plant parts such as dead leaves and ripe fruit; senescence is the condition or process of aging; and seed dormancy is the state in which seeds are prevented from germinating.