Endogenous Rhythms in Plants

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Questions and Answers

What is a characteristic of rhythms driven by an endogenous biological clock?

They only occur in the presence of light.

They can be reset by external factors. (correct)

They are only present in response to external signals.

They are influenced by temperature changes.

Which of the following is NOT a classification of biological rhythms?

Harmonic Rhythm (correct)

Lunar Rhythm

Circadian Rhythm

Annual Rhythm

What distinguishes the circadian rhythm from other types of biological rhythms?

It lasts for 28 days.

It is dependent on lunar phases.

It spans approximately 24 hours. (correct)

It follows an annual schedule.

What phenomenon is associated with diurnal plant movements?

Circadian rhythm patterns Signup and view all the answers

Which statement about synthetic auxins is true?

They act as effective weed killers when used correctly. Signup and view all the answers

What is the primary role of cytokinins in plant growth?

Promote overall cytokinesis and lateral bud growth Signup and view all the answers

How do gibberellins affect plant growth in relation to genetic dwarfism?

They reverse the effects of genetic dwarfism Signup and view all the answers

Which of the following is true regarding abscisic acid (ABA)?

ABA acts as an antagonist to growth-promoting hormones Signup and view all the answers

What environmental factor is NOT classified as abiotic?

Pests Signup and view all the answers

What is a major commercial benefit of gibberellins in agriculture?

Increasing the size of grapes Signup and view all the answers

Which statement best describes the synthesis of ethylene in plants?

It is derived from the amino acid methionine Signup and view all the answers

What is the relationship between genotype and environmental factors in determining yield?

The interaction between genotype and environmental stress influences yield Signup and view all the answers

Which of the following is an example of allelopathy?

Toxic substances released by plants to inhibit nearby growth Signup and view all the answers

What type of crop is specifically classified as a cool season crop?

Cole crops Signup and view all the answers

Which of the following is NOT an effect of high temperature on plants?

Increased fruit yield Signup and view all the answers

What is the primary effect of temperature on photosynthesis in most species?

Photosynthesis declines above 35 degrees Celsius Signup and view all the answers

Which type of plant is classified as a xerophyte?

Desert plants Signup and view all the answers

What is the importance of relative humidity in plant growth?

It influences wilt resistance and pest incidence Signup and view all the answers

Which environmental factor does NOT influence the amount and distribution of rainfall?

Soil type Signup and view all the answers

What is an undesirable effect of wind on plants?

Transpiration loss Signup and view all the answers

What are the necessary conditions for rain formation?

High RH and low temperature Signup and view all the answers

What is the definition of climate?

The average weather conditions over long periods of time. Signup and view all the answers

Which climatic factor is most important in agriculture?

Solar radiation Signup and view all the answers

Which type of plants are known as heliophytes?

Plants that prefer sunny environments. Signup and view all the answers

What does the solar constant measure?

The average amount of solar radiation received at the outer atmosphere. Signup and view all the answers

Which type of radiation is primarily used by plants during photosynthesis?

Photosynthetically active radiation (PAR) Signup and view all the answers

What is 'albedo' in relation to radiation?

The ratio of reflected radiation to the total incident light. Signup and view all the answers

How does daylength vary with latitude?

It increases as latitude from the equator increases. Signup and view all the answers

Which statement about winds is NOT a climatic factor?

Winds have no effect on local climate. Signup and view all the answers

What is infrared radiation primarily characterized by?

Wavelengths longer than visible light and shorter than microwaves Signup and view all the answers

Which of the following is NOT considered a greenhouse gas?

Oxygen (O2) Signup and view all the answers

Which factor does NOT influence the infiltration rate of water into soil?

Temperature of the surrounding air Signup and view all the answers

How have levels of greenhouse gases changed since industrialization?

Increased by about 25% Signup and view all the answers

What is a primary consequence of rising concentrations of greenhouse gases?

Increase in average surface temperature Signup and view all the answers

Which of the following describes soil structure?

The arrangement of soil particles into aggregates Signup and view all the answers

What is meant by soil permeability?

The ability of air and water to move through the soil Signup and view all the answers

Which of these properties does NOT describe physical soil properties?

Soil pH Signup and view all the answers

Study Notes

Endogenous Rhythms/Plant Movements

Many plant behaviors exhibit periodic oscillations, controlled by an internal time-measuring system (endogenous biological clock).
Manifestations: Diurnal rise and fall of leaves (sleep movements), diurnal photosynthesis.
Criteria to distinguish simple periodic phenomena and rhythm driven by an endogenous clock: Persistence in the absence of external cues, resourcing by external signals (light/temperature), no lasting effect of temperature on the timing.
Classification of Biological Rhythms: Circadian rhythm (24 hours), e.g., bean movement(hyponasty, epinasty), Fertility Tree of UPLB; Lunar rhythm (28 days), e.g., flowering of fire trees, cherry blossoms, Kapok; Ultradian rhythm (<24 hours).
Plant Movements: Growth movements (irreversible, due to differential growth), turgor movements (reversible, but not all the time, due to changes in cell volume).
Plant Responses to Stimuli: Tropisms (growth towards or away from a stimulus), positive tropisms (growth toward), negative tropisms (movement away), phototropism (towards light). Nastic movements (movement not oriented towards stimulus), photoasty, thigmotropism, thigmonasty, gravitropism, chemotropism, chemonasty, hydrotropism, hydronasty, thermonasty, photonasty.

The Biological Clock

Many aspects of plant behavior exhibit periodic oscillations controlled by an internal time-measuring system (endogenous biological clock).
Plant behaviors are controlled by an internal time measuring system.

Plant Movements - Categories

Growth Movements: Result of differential growth within an organ or between two different organs. Irreversible.
Turgor Movements: Result from volume changes in cells due to changes in osmotic pressure. Reversible (but not all the time).

Plant Responses to Stimuli

Tropisms: Result from differential growth of specific plant organs in response to a stimulus.
- Positive tropisms- Growth toward the stimulus (e.g., bending toward light).
- Negative tropisms- Growth away from the stimulus.
Phototropism: Movement in response to light.
Nastic Movements: Movement not oriented toward or away from an environmental stimulus.

Gravitropism

Shoots are negatively gravitropic (grow against gravity).
Roots are positively gravitropic (grow towards earth's center).

Thigmotropism

Directional response of plant organs to touch or physical contact with a solid object. (e.g., curling of vines)

Heliotropism

Solar tracking (e.g., sunflowers).

Photoperiodism

The response of an organism to seasonal changes in day length.
- Long-day plants: Flower when day length is longer than a critical value.
- Short-day plants: Flower when day length is shorter than a critical value.
- Day-neutral plants: Flower when they become mature, regardless of day length.

Dormancy

A slowdown in an organism's metabolic rate.
Seed dormancy: Inability of a viable seed to germinate.
Parthenocarpy: Fruit development without fertilization.

Senescence

The collective term for aging processes that lead to the death of a plant or plant part.
Leaf colors are an example, and a result of changes in light quality and photoperiod.

Hormones and Growth Regulation

Phytohormones: Organic substances, other than nutrients, that modify plant growth and development. Effective at low concentrations.
Auxins: Synthesized in shoot apical meristems, young leaves, seeds, and fruits.
- Promote growth.
- Toxic in large concentrations.
- Apical dominance (inhibiting activation of lower buds)
- Promote lateral and adventitious root development.
Indoleacetic Acid (IAA): A key auxin, chemically produced or synthesized from indole or tryptophan.

Cytokinins

Phenyl urea derivatives of adenine (a molecule in DNA)..
Found in actively dividing tissues (seeds, fruits, leaves, root tips, wound tissue).
Transported through xylem.
Promote cytokinesis, cell expansion, and axillary bud growth.

Gibberellins

Reversal of genetic dwarfism in plants.
Bolting of biennials (production of flowers during the first growing season)
Promote parthenocarpy (fruit development without fertilization).

Abscisic Acid (ABA)

Inhibits growth activities during environmental stress (e.g., drought).
An antagonist to other growth-promoting hormones.
Promotes seed dormancy.
Promotes stomata closure during water deficit.

Ethylene

Synthesized from the amino acid methionine.
Promotes flowering and leaf senescence.

Environmental Factors

Abiotic Factors: Climate (weather), edaphic (soil) factors (e.g., drought, salinity, acidity, lahar, La Niña, El Niño), greenhouse effect, global warming.
Biotic Factors: Beneficial organisms (pollinators, decomposers, natural enemies), pests (arthropods, pathogens, weeds, vertebrate pests), allelopathy.

Weather versus Climate

Weather: Atmospheric conditions in a specific area at a given time (hours or days).
Climate: Long-term weather pattern of an area (averaged over long periods). Seasonal patterns are part of climate.

Solar Radiation

Solar Constant: 2.0 cal/cm^2/min (with 15% fluctuation annually).
Amount of solar radiation that reaches the outer atmosphere.

PAR (Photosynthetically Active Radiation)

Used by plants for CO2 fixation during photosynthesis.
Classified based on light intensity requirements. (Heliophytes vs. sciophytes)

Albedo

Ratio of reflected radiation to total incident light.
Reflects how quickly and how much a surface is heated. (e.g., 50-60% in the polar regions).

Environmental Factors Affecting Crop Production

Phenotype: Genotype + Environment + (G*E).
G: Sets the limits for the phenotype, and E: Modifies the expression of the phenotype.
Weather (sun, cloud, temperature, wind, rain), variations from patterns, is part of weather (short term events), while climate is the long-term average weather pattern.

Photoenergetic effect:

Direct effect on photosynthesis.

Photocybernetic effect:

Effect on plant development.

Climate Factors

Solar Radiation: Most important in agriculture.
Temperature: Important in every chemical, physical, and biological process in plants. Minimum T below which rxn=0, optimum reaction at maximum T, Maximum T -above which reaction =0
Wind: Effects on lodging, grain shattering, transpiration, effects on plant form, sterility due to pollination loss, reduced CO2 levels and spread of diseases.
Precipitation (Rainfall): Water falling from the air.
Relative Humidity: Directly influences plant growth and disease or pest incidence.
Mist and Fog.

Roles of Water in Plant Growth:

Reactant in many biological processes.
Medium of transport for nutrients and other substances.
Temperature regulation.

Classification based on moisture need

Xerophytes: Desert plants
Hydrophytes: Aquatic plants
Mesophytes: Land plants

Soil structure

Grouping of soil particles (sand, silt, clay) into larger aggregates.
Arrangement of particles affects movement of air, water and roots.
Stable aggregates- allow rapid exchange of air and water, needed for plant growth.

Soil Texture & Structure

Texture= size and relative proportions of sand, silt and clay.
Structure: Arrangement of soil particles.

Soil Depth:

Thickness of soil materials (topsoil and subsoil).

Topography:

Physical configuration of the soil surface (drainage, erosion run-off etc...).

Infiltration Rate:

Velocity of water entering the soil. Affected by soil surface permeability, soil moisture content, soil surface conditions & plant cover, time and quantity of chemical use.

Chemical Properties

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Description

Explore the fascinating world of plant movements and their internal rhythms. This quiz covers the criteria to distinguish between simple periodic phenomena and rhythms driven by an endogenous clock, along with various classifications such as circadian and lunar rhythms. Test your knowledge on how plants respond to stimuli and exhibit growth movements.