Plant Growth and Development

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Questions and Answers

What characterizes the aerenchyma in aquatic plants?

  • It is formed exclusively in leaves.
  • It contains large air spaces created through programmed cell death. (correct)
  • It functions primarily in photosynthesis.
  • It is found only in mature flowers.

What is the role of the abscission layer in plants?

  • To promote photosynthesis in leaves.
  • To regulate water uptake through the roots.
  • To facilitate the shedding of organs such as leaves and flowers. (correct)
  • To store excess nutrients during stress periods.

Which enzymes are involved in the separation of the abscission layer cells?

  • Amylase and protease.
  • Cellulase and pectinase. (correct)
  • Lipase and sucrase.
  • Phosphatase and nitrifying enzymes.

What happens to chlorophyll during the abscission process?

<p>It degrades, causing a change in leaf color. (C)</p> Signup and view all the answers

What does programmed cell death (PCD) result in during the development of unisexual flowers?

<p>The abortion of one type of flower while the other develops. (B)</p> Signup and view all the answers

In the plant physiology context, what is defined as 'stress'?

<p>Any change in condition adversely affecting plant growth. (A)</p> Signup and view all the answers

What is the primary function of tyloses that form in plants?

<p>To block the conducting vessels. (B)</p> Signup and view all the answers

What process occurs in the outer layer of cells following abscission?

<p>Suberization and development of periderm. (C)</p> Signup and view all the answers

What process leads to the death of plant parts due to senescence?

<p>Programmed Cell Death (C)</p> Signup and view all the answers

Which type of senescence occurs gradually throughout the year in certain plants?

<p>Evergreen Senescence (C)</p> Signup and view all the answers

In what environmental condition is senescence observed to occur more quickly?

<p>In dark environments (B)</p> Signup and view all the answers

What is the main function of proteolytic enzymes during senescence?

<p>To facilitate nutrient transport (A)</p> Signup and view all the answers

What type of cells die and disappear to ensure efficient water transport in plants during maturity?

<p>Protoplasts of xylem vessels (B)</p> Signup and view all the answers

Where does leaf abscission primarily take place in plants?

<p>At the base of the petiole (B)</p> Signup and view all the answers

What common stress can trigger accumulation of ABA leading to senescence?

<p>Water stress (A)</p> Signup and view all the answers

What anatomical change marks the abscission zone in leaf abscission?

<p>Thin-walled cells arranged transversely (B)</p> Signup and view all the answers

What causes the folding of leaflets in plants such as Mimosa pudica in response to stimuli?

<p>Movement of water in and out of parenchymatous cells (B)</p> Signup and view all the answers

Which type of movement is observed in plants like Drosera and Dionaea in response to touch?

<p>Thigmonastic movement (D)</p> Signup and view all the answers

What is the role of Ca2+ ions in the mechanism of seismonastic movement?

<p>They facilitate the movement of K+ ions, affecting cell turgor (A)</p> Signup and view all the answers

Which part of the plant primarily exhibits movement in response to stimuli such as touch?

<p>Leaflets of pulvinus (A)</p> Signup and view all the answers

What condition causes flexor cells in the pulvinus to become turgid?

<p>Increase in potassium concentration (B)</p> Signup and view all the answers

What happens to extensor cells when they become flaccid in response to touch?

<p>They lose water leading to drooping (A)</p> Signup and view all the answers

Which cells are primarily responsible for sensing mechanical stimuli in thigmonastic movements?

<p>Pulvinus parenchymatous cells (B)</p> Signup and view all the answers

In the mechanism of seismonastic movement, what happens to the plant cells upon stimulation?

<p>They alter their osmotic pressure rapidly (B)</p> Signup and view all the answers

What characterizes the function of parenchymatous cells in the context of plant movements?

<p>They allow for rapid changes in turgor pressure (C)</p> Signup and view all the answers

What is the primary reason that mimosa plants fold their leaves upon touch?

<p>To deter herbivores (A)</p> Signup and view all the answers

Flashcards

Aerenchyma in Aquatic Plants

Air spaces formed in roots and stems of aquatic plants for buoyancy and gas exchange.

Abscission Layer

Layer of cells that separates plant parts (leaves, flowers, fruits) from the main plant body.

Abscission Process

Physiological process where plants shed parts like leaves, flowers, fruits, and seeds.

PCD (Programmed Cell Death)

Mechanism for controlled cell death in plants, useful for development and response to stress.

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Unisexuaal Flower Development

Flower development where either male or female flowers develop while the other aborts.

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Tyloses

Cellular growths that block the conducting vessels in plants.

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Stress Physiology

Study of how plants adapt to changing environmental factors.

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Plant Stress

Any change in environmental conditions that affect plant growth negatively.

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Seismonastic movement

A plant's response to touch or shock by folding leaves and leaflets

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Mimosa pudica

A plant species known for its rapid leaf-closing response to stimuli.

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Pulvinus

Special plant tissue at the base of leaves or leaflets that controls plant response to stimuli.

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Flexor cells

Cells in the pulvinus that contract, leading leaflets to fold inward when stimulated.

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Extensor cells

Cells in the pulvinus that relax when stimulated thus enabling leaflet opening.

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Turgor pressure

Water pressure inside the plant cells that leads to cell stiffness.

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Plant stimuli

External factors like touch, shock, and pressure plant respond to

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Parenchyma cells

General plant cells responsible for structure and function in many plants.

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Water movement

Water entering or leaving cells to change turgor pressure.

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Photropism

Plant growth in response to light

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Senescence in Plants

A natural process where plant cells, tissues, or organs age and die, often in response to external conditions like stress or light.

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Programmed Cell Death (PCD)

Plant cell death that is part of a plant's natural development cycle or in response to external stress.

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Deciduous Senescence

Senescence that results in the complete seasonal loss of leaves in temperate regions.

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Abscission Zone

A specialized region at the base of the petiole, where leaf separation occurs.

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Water Stress and Senescence

Water deficiency in plants can trigger senescence through the production of a plant hormone called ABA.

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Nutrient Remobilization

Senescing plant parts release nutrients for use in other growing parts.

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Xylem Vessel Death

Specialized plant cells (xylem vessels and tracheids) die to become efficient water conductors.

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Types of Senescence

Senescence can take different forms in plants such as Top senescence,Deciduous senescence,Progressive senescence.

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Study Notes

Plant Growth and Development

  • Plants mature from meristematic cells through differentiation.
  • Dedifferentiation is the regaining of the ability to divide in differentiated cells.
  • Redifferentiation is the maturation of cells after division to perform specific functions.
  • Plant plasticity is the ability of plants to adapt to various environments.

Plant Growth Regulators (PGRs)

  • Plant growth regulators are chemical messengers synthesized in minute quantities in one part of the plant and transported to another, influencing physiological processes.
  • Five major groups of plant hormones are: auxins, gibberellins, cytokinins, ethylene, and abscisic acid.
  • Recently, brassinosteroids and polyamines have also been classified as plant hormones.

Auxins

  • Auxins are plant hormones that promote cell elongation and growth in stems and coleoptiles.
  • They also influence root growth, differentiation, and the development of lateral roots.
  • Naturally occurring auxins include Indole Acetic Acid (IAA), Indole Propionic Acid (IPA), Indole Butyric Acid (IBA), and Phenyl Acetic Acid (PAA).
  • Synthetic auxins include 2,4-D, 2,4,5-T, and NAA.

Gibberellins

  • Gibberellins are plant hormones involved in stem elongation, seed germination, and flowering.
  • They stimulate cell division and elongation, promoting growth.

Cytokinins

  • Cytokinins are plant hormones that promote cell division and differentiation, along with delaying aging and senescence.
  • They affect the development and growth of lateral buds in presence of apical buds.

Ethylene

  • Ethylene is a gaseous plant hormone that regulates ripening of fruits and induces the abscission of leaves.
  • It also plays a role in flowering and promotes the development of fruits.

Abscisic Acid (ABA)

  • ABA is a plant hormone that inhibits growth and promotes seed dormancy.
  • It influences the closing of stomata and helps plants adapt to stress.

Plant Movements

  • Plant movements are a response to external or internal stimuli.
  • Autonomic movements are spontaneous.
  • Paratonic movements are induced by external factors.
  • Tropic movements are directional in response to a stimulus.
  • Nastic movements are non-directional (independently of the stimulus).

Photoperiodism

  • Photoperiodism is the response of a plant to the length of day and night, affecting flowering.
  • Long-day plants flower when days are long, while short-day plants flower when days are short.
  • Day-neutral plants are not affected by photoperiod for flowering.

Vernalization

  • Vernalization is the process by which plants require low temperatures to induce flowering.
  • It is essential for certain plants to complete their life cycle.

Seed Germination and Dormancy

  • Seed germination is the process where a seed develops into a seedling under suitable environmental conditions.
  • Seed dormancy is a delay in germination, which is influenced by various external and internal factors.

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