Transpiration in Plants
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Questions and Answers

How does high relative humidity affect transpiration rates?

  • It increases transpiration rates by providing more water vapor for the plant to absorb.
  • It increases transpiration rates by creating a more humid environment around the leaves, making it easier for water to evaporate.
  • It decreases transpiration rates by reducing the difference in water vapor concentration between the leaf and the atmosphere. (correct)
  • It has no effect on transpiration rates.

    • Which of the following is NOT a factor influencing transpiration?

  • Wind and Air Movement
  • Plant Type
  • Relative Humidity
  • Soil Salinity (correct)

    • What is the main pathway for water loss in transpiration?

  • Lenticular Transpiration
  • Cuticular Transpiration
  • All pathways contribute equally to water loss.
  • Stomatal Transpiration (correct)

    • How do guard cells regulate stomatal opening and closing?

    <p>Guard cells have specialized pumps that actively transport water into or out of the cells, causing them to swell and open or shrink and close the stomata. (C)</p> Signup and view all the answers

    What is the primary role of transpiration in plants?

    <p>To regulate the plant's internal temperature. (A)</p> Signup and view all the answers

    What is the relationship between root absorption and transpiration?

    <p>Transpiration drives root absorption by creating a negative pressure that pulls water up from the roots. (A)</p> Signup and view all the answers

    Which of the following would likely decrease transpiration rates?

    <p>Increased soil moisture (D)</p> Signup and view all the answers

    How does leaf area size influence crop yield?

    <p>Larger leaf area increases the amount of PAR captured, enhancing photosynthesis and improving yield. (D)</p> Signup and view all the answers

    Which factor directly determines the distribution of light among leaves at different canopy heights?

    <p>Extinction coefficient (K) (B)</p> Signup and view all the answers

    What is the influence of photoperiod on long-day plants in decreasing photoperiod?

    <p>Extended vegetative growth and a delayed transition to flowering. (A)</p> Signup and view all the answers

    What is the relationship between light interception and crop dry matter production?

    <p>There is a linear relationship between light interception and dry matter production. (A)</p> Signup and view all the answers

    What is the rate of leaf appearance called, and to which plants does it apply?

    <p>Phyllochron, applicable only to plants in the grass family. (C)</p> Signup and view all the answers

    How does canopy architecture affect light penetration and interception?

    <p>Canopy architecture enhances light penetration and interception at deeper canopy levels. (A)</p> Signup and view all the answers

    What are the factors influencing leaf expansion rate?

    <p>Water stress, nitrogen nutrition, and canopy architecture. (A)</p> Signup and view all the answers

    How does photoperiod affect day-neutral crops?

    <p>Day-neutral crops are unaffected by photoperiod. (A)</p> Signup and view all the answers

    Which factor is directly influenced by the length of day?

    <p>Time of crop emergence (A)</p> Signup and view all the answers

    What is the primary role of source organs in plants?

    <p>To produce carbohydrates (B)</p> Signup and view all the answers

    How does nitrogen nutrition affect grain yield in crops?

    <p>It enhances chlorophyll formation (C)</p> Signup and view all the answers

    What is the impact of water supply on leaf characteristics?

    <p>It influences leaf size and longevity (A)</p> Signup and view all the answers

    What is a characteristic feature of C4 plants related to translocation?

    <p>They exhibit faster translocation rates (D)</p> Signup and view all the answers

    During which growth stage are leafy vegetables most sensitive to water supply?

    <p>During active vegetative growth (A)</p> Signup and view all the answers

    What effect does higher nitrogen status have on plant leaves?

    <p>It enhances leaf expansion and increases LAI. (D)</p> Signup and view all the answers

    What is LAIcrit?

    <p>The threshold where 95% of incoming PAR is intercepted. (A)</p> Signup and view all the answers

    What happens when LAI exceeds LAIcrit?

    <p>Additional leaf growth has diminishing returns. (D)</p> Signup and view all the answers

    How does water availability affect LAI?

    <p>Adequate water supports sustained growth, maximizing PAR interception. (B)</p> Signup and view all the answers

    What is a consequence of having too low of an LAI?

    <p>Insufficient light interception due to large gaps. (C)</p> Signup and view all the answers

    What can agricultural practices optimize for maximum crop yield?

    <p>LAI through nitrogen fertilization and irrigation. (B)</p> Signup and view all the answers

    How does high plant population density affect light interception?

    <p>It enhances light interception by reducing gaps. (C)</p> Signup and view all the answers

    What can lead to reduced leaf expansion and longevity?

    <p>Drought stress. (B)</p> Signup and view all the answers

    What is a potential consequence of too high LAI?

    <p>Increased self-shading and senescence. (A)</p> Signup and view all the answers

    What role does light interception efficiency play in crop yield?

    <p>More effective light interception promotes better crop yield. (B)</p> Signup and view all the answers

    What effect do horizontal leaves have on light penetration to lower layers of a canopy?

    <p>They result in reduced light penetration. (B)</p> Signup and view all the answers

    Which statement accurately describes axillary leaf production in annual species?

    <p>They increase leaf area exponentially. (A)</p> Signup and view all the answers

    What happens to nutrients during leaf senescence?

    <p>Nutrients are mobilized to younger leaves. (B)</p> Signup and view all the answers

    What does a high Leaf Area Index (LAI) potentially indicate?

    <p>Higher energy costs from excess biomass. (D)</p> Signup and view all the answers

    What is defined as the total green leaf area per unit ground area?

    <p>Leaf area index (LAI). (B)</p> Signup and view all the answers

    What is one limitation of achieving 100% light interception in a crop canopy?

    <p>Inherent reflection and canopy gaps. (B)</p> Signup and view all the answers

    Which of the following factors influences crop productivity through its effect on optimal LAI?

    <p>Temperature. (B)</p> Signup and view all the answers

    If a ground area has 2 m² of green leaf area, what is the Leaf Area Index?

    <p>2.0 (C)</p> Signup and view all the answers

    Which of the following is NOT a consequence of leaf senescence?

    <p>Increase in leaf area. (D)</p> Signup and view all the answers

    How does early axillary leaf production benefit a plant?

    <p>Enhances leaf area and light capture. (C)</p> Signup and view all the answers

    Flashcards

    Transpiration

    Loss of water from plants in the form of vapor.

    Factors Influencing Transpiration

    Includes temperature, humidity, wind, soil moisture, and plant type.

    Evaporation Phase

    Water evaporates from mesophyll cells to intercellular spaces.

    Stomatal Transpiration

    Major pathway for water loss (80-90%).

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    Effects of Temperature

    Higher temperatures increase transpiration, but can close stomata in extreme heat.

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    Plant Adaptation

    Arid-adapted plants like cacti transpire less.

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    Soil Moisture

    Limited water decreases transpiration by inducing stomatal closure.

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    Source Organs

    Organs like mature leaves that produce carbohydrates for plants.

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    Sink Organs

    Organs like fruits and seeds that store carbohydrates produced by source organs.

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    C4 Plant Advantage

    C4 plants have a faster translocation rate due to specialized anatomy and increased phloem.

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    Role of Nitrogen in Plants

    Nitrogen affects grain yield by influencing leaf size, longevity, and canopy expansion.

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    Impact of Water on Growth

    Water influences leaf size and grain filling, and can shorten critical growth periods if reduced.

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    Leaf Area Index (LAI)

    A measure of leaf area per ground area, affecting PAR capture.

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    Photosynthetically Active Radiation (PAR)

    The light spectrum used by plants for photosynthesis.

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    Light Interception

    The ability of a canopy to capture light for photosynthesis.

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    Crop Dry Matter Production

    The amount of biomass produced by crops, linked to light interception.

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    Extinction Coefficient (K)

    Measures light distribution within a canopy based on leaf area.

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    Phyllochron

    The rate of leaf appearance in grass family crops.

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    Canopy Architecture

    The arrangement and orientation of leaves in a canopy.

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    Leaf Expansion Rate

    The speed at which leaves increase in size.

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    Photoperiod

    The length of day, influencing plant growth stages.

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    Horizontal Leaves

    Leaves that lie flat, capturing more light at the canopy but less light below.

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    Axillary Leaf Production

    The rapid growth of side leaves that increases overall leaf area significantly.

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    Annual vs. Perennial Leaf Growth

    Annual plants produce axillary leaves faster than perennial plants do.

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    Leaf Senescence

    The aging process of leaves where nutrients are redirected to younger leaves or storage.

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    100% Light Interception

    The theoretical maximum percentage of light that can be captured by a canopy, which is unattainable due to gaps.

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    Canopy Gaps

    Spaces in a plant canopy that allow light to penetrate less efficiently.

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    High LAI Consequences

    Very high leaf area index can increase energy costs without significant yield benefits.

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    Temperature's Effect on LAI

    Temperature influences growth and productivity by affecting leaf production and senescence.

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    Optimal LAI for Productivity

    The ideal Leaf Area Index that maximizes crop yields without excess biomass costs.

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    Light Interception Efficiency

    The effectiveness of a plant canopy in capturing light for photosynthesis.

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    Too Low LAI

    Insufficient leaf area resulting in less than 50% light interception.

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    Too High LAI

    Excessive leaf area leading to self-shading and inefficient resource use.

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    Critical Leaf Area Index (LAICRIT)

    The LAI threshold at which 95% of incoming light is intercepted.

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    Nitrogen Status

    The level of nitrogen in soil, crucial for plant growth and chlorophyll production.

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    Plant Population Density

    The number of plants in a given area, influencing competition and light interception.

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    Water Availability

    The amount of water accessible to plants, vital for growth and leaf longevity.

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    Drought Stress

    A condition caused by insufficient water, limiting leaf growth and health.

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    Monitoring LAI

    The practice of measuring LAI to manage crops and optimize growth.

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    Study Notes

    Transpiration in Plants

    • Transpiration is the loss of water from plants in the form of water vapor.
    • Phases include evaporation from mesophyll cells and diffusion into the atmosphere.
    • Temperature and relative humidity influence transpiration rates.
    • Wind increases transpiration by replacing humid air around leaves with drier air.
    • Soil moisture availability impacts transpiration rates.
    • Plant type (e.g., arid-adapted plants) affects transpiration rate.

    Stomatal Functions

    • Stomata, controlled by guard cells, regulate water loss and gas exchange.
    • Guard cells swell open when turgid; they close when flaccid.
    • 80-90% of water loss in plants occurs via stomata.
    • Additional water loss occurs via the cuticle, and 1-5% via lenticels.

    Importance of Transpiration

    • Regulates water movement in plants.
    • Provides water for photosynthesis.
    • Transports minerals from roots to leaves.
    • Cools the plant through evaporation.
    • 3,000-4,000 gallons of water can be transpired by an acre of corn daily.
    • A large oak tree can transpire 40,000 gallons annually.

    Photosynthesis

    • Photosynthesis is the process of converting light energy into chemical energy to produce carbohydrates.
    • It takes place in cells, primarily in the leaves.
    • Photosynthesis has light-dependent and light-independent (Calvin Cycle) reactions.
    • Light reactions occur in thylakoids, splitting water into O2 and H+ producing ATP and NADPH.
    • Light-independent in the stroma, fixing CO2 into carbohydrates.

    Radiation Use Efficiency (RUE)

    • RUE is the efficiency of converting PAR into biomass.
    • PAR (Photosynthetically Active Radiation) is the wavelength of radiation that plants use.
    • 400-700nm wavelength.
    • Under agricultural conditions, 0.1-3% of radiant energy is converted into organic matter.

    C3 and C4 Photosynthesis

    • C3 plants fix CO2 via Rubisco, and are susceptible to photorespiration (inefficient process).
    • C4 plants fix CO2 via PEP carboxylase, which minimizes photorespiration, resulting in higher water-efficient performance.
    • Plants like wheat, rice, and soybean are C3, while maize, sugarcane are C4.

    Leaf Area Index (LAI)

    • LAI is a measure of total green leaf area per unit ground area.
    • LAI is important to capture light because a leaf canopy affects the amount of light that reaches the soil
    • Higher LAI values result in increased light interception leading to increased photosynthetic rates and crop yield.
    • LAI is controlled by phyllochron, timing of crop emergence, and leaf expansion rate.

    Photosynthesis and Translocation

    • Photosynthesis and product movement are simultaneous processes.
    • Excess photosynthates are stored for later use, transported by phloem and plasmodesmata.
    • Plants use 70-80% of photosynthates within 6 hours of photosynthesis
    • C4 plants generally have faster rates of translocation due to specialized structures.

    Factors Influencing Plant Yield

    • Temperature, nitrogen availability, solar radiation, water supply, plant density, pests and diseases are key factors.
    • Optimal temperature ranges exist for different crops and varieties.
    • Nitrogen is critical for chlorophyll formation and leaf expansion.
    • Water stress can reduce leaf size, and longevity affecting LAI.

    Strategies for Maximizing Yield

    • Strategies to maximize yield include improving light interception, adapting to water stress, using optimal population densities, and minimizing the effects of disease, pests, and weeds.

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    Description

    Explore the fascinating process of transpiration in plants, including the roles of stomata and guard cells in regulating water loss. Understand how environmental factors like temperature and humidity influence transpiration rates. This quiz also covers the crucial importance of transpiration for plant health and function.

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