Plant Water Regulation

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Questions and Answers

How does an increase in temperature affect the diffusion coefficient of water vapor?

It has no effect on the diffusion coefficient.

It causes the diffusion coefficient to fluctuate.

It decreases the diffusion coefficient.

It increases the diffusion coefficient. (correct)

What triggers the closing of stomata in plants during water stress?

Changes in water pressure of guard cells (correct)

Excessive light intensity

Increase in potassium ion concentration

Decrease in carbon dioxide concentration

What is a likely effect of temperatures exceeding 40 °C on plant physiology?

Enhanced nutrient absorption.

Increased transpiration rates.

Closure of the stomata. (correct)

Increased photosynthesis rates.

Which external factor greatly influences the velocity of transpiration in plants?

Relative humidity (A) Signup and view all the answers

What role does wind velocity play in transpiration?

It has an indirect effect by influencing humidity gradients. (C) Signup and view all the answers

What is one function of transpiration in plants?

Cooling the leaves and plant. (C) Signup and view all the answers

How do guard cells regulate the opening and closing of stomata?

By changes in their turgidity from potassium ion movement (A) Signup and view all the answers

What effect does high CO2 concentration have on stomata?

Completely closes them (A) Signup and view all the answers

In what form do plants typically absorb essential elements from the soil?

As individual ions in solution. (C) Signup and view all the answers

Why is cation exchange capacity (CEC) important in soil for plant nutrient availability?

It affects the solubility of nutrients for plants. (B) Signup and view all the answers

What role does abscisic acid play in the function of guard cells?

It induces the rapid exit of potassium ions from the cells (D) Signup and view all the answers

What characterizes passive transport of ions in plants?

It occurs without the need for external energy. (B) Signup and view all the answers

How does an increase in temperature affect transpiration?

Increases transpiration by lowering relative humidity (C) Signup and view all the answers

What is the primary ion responsible for controlling the turgidity of guard cells?

Potassium ion (C) Signup and view all the answers

What is diffusion in the context of plant physiology?

A spontaneous process favoring movement from high to low concentration. (A) Signup and view all the answers

During which condition do guard cells become turgid, causing stomata to open?

High potassium ion concentration (C) Signup and view all the answers

What type of cells are associated with sieve-tube elements in phloem?

Companion cells (D) Signup and view all the answers

Which substance constitutes the largest part of the substance transported by phloem?

Sugars (D) Signup and view all the answers

What is the most important nitrogen substance transported by the phloem?

Amino acids (B) Signup and view all the answers

Which of the following is NOT considered a substance transported by the phloem?

Pathogens (D) Signup and view all the answers

Which cation is most predominant in the phloem transport system?

Potassium (C) Signup and view all the answers

How do plant growth regulators influence phloem transport?

By regulating the equilibrium of promoters and inhibitors (A) Signup and view all the answers

What role does ATP play in phloem transport?

It provides energy for solute transport (C) Signup and view all the answers

Which of these substances is commonly detected in the phloem at low concentrations?

Organic acids (A) Signup and view all the answers

What are the zones of priority for solute transportation?

Rapid growth areas like buds and young leaves (D) Signup and view all the answers

How does a lack of water specifically affect sugar transport in sugarcane?

It decreases sugar transport by 90%. (A) Signup and view all the answers

Which temperature range is optimal for the transport of solutes?

20 - 30 °C (A) Signup and view all the answers

What is a significant limitation of diffusion as a mechanism for solute transport in phloem?

It is too slow to efficiently transport solutes. (C) Signup and view all the answers

Which of the following is required for the electro-osmosis mechanism to function?

Presence of a semi-permeable membrane with ionic permeability. (D) Signup and view all the answers

What is a primary objection to the pressure flow model of phloem transport?

It does not account for resistance in the sieve cells. (A) Signup and view all the answers

What effect does light have on solute transport?

It affects the source by influencing photosynthesis. (A) Signup and view all the answers

What is a limitation of the electro-osmosis model for phloem transport?

It cannot explain simultaneous flow of anions and cations. (A) Signup and view all the answers

What is the primary solute transported in the phloem?

Sucrose (D) Signup and view all the answers

Which direction do solutes move in the phloem?

From source to sink (B) Signup and view all the answers

What role do companion cells play in the transport of sucrose?

They actively accumulate sucrose against the concentration gradient. (D) Signup and view all the answers

At what velocity does solute transport occur in C4 plants?

More than 200 cm/h (A) Signup and view all the answers

Which type of tissue serves as a storage site for reserve substances in a plant?

Mature leaves (A) Signup and view all the answers

What characterizes the entrance of solutes into the phloem?

It requires selective and active transport mechanisms. (C) Signup and view all the answers

In general, where do lower leaves export solutes?

To the roots (B) Signup and view all the answers

What is the significance of the source and sink in phloem transport?

They determine the direction of transport. (D) Signup and view all the answers

Study Notes

Water Regulation in Plants

Plants maintain a continuous flow of water from roots to leaves, crucial for metabolic processes.
Water loss occurs through stomata; plants can short-term control this loss by closing stomata.
Stomata respond to water stress by opening or closing, allowing for CO2 uptake while conserving water.

Guard Cells Function

Guard cells, unique epidermal cells containing chloroplasts, control stomatal aperture through turgidity changes.
Potassium ions (K+) are the primary ions regulating guard cell turgidity, influencing water loss.
Abscisic acid facilitates the rapid exit of K+ from guard cells, causing stomata to close.

Factors Influencing Transpiration Rate

Relative humidity affects transpiration; lower humidity increases water loss.
Soil moisture levels correlate with root absorption capabilities, influencing overall plant water potential.
High atmospheric CO2 concentration can close stomata to balance transpiration and photosynthesis.
Increased light intensity opens stomata, promoting transpiration; absence of light leads to stomatal closure.
High temperatures enhance transpiration but can lead to stomatal closure if temperatures exceed 40°C.
Wind speed impacts transpiration indirectly by affecting humidity gradients.

Functions of Transpiration

Transpiration helps cool leaves and the entire plant.
It concentrates minerals absorbed from the soil, enhancing nutrient uptake.
It plays a vital role in water ascent through xylem, aiding nutrient distribution.

Nutrient Uptake by Roots

Plants absorb nutrients primarily in ionic form from the soil through root systems.
Cation exchange capacity (CEC) is essential for the availability of soluble nutrients in soils.

Ion Transport Mechanisms

Passive transport allows ions to move along chemical gradients without energy expenditure.
Diffusion signifies the movement of solutes from high to low concentration.

Phloem Transport Characteristics

Phloem primarily transports carbohydrates (mainly sucrose) and nitrogen compounds (e.g., amino acids).
Organic acids, inorganic ions, growth substances, and even viral particles can also be transported in phloem.
The transport rate is approximately 30-100 cm/h in C3 plants and over 200 cm/h in C4 species.

Source-Sink Dynamics

Source refers to sites of production or storage, while sink represents destinations for solute utilization.
Solutes typically move from sources like mature leaves to sinks in areas of growth or storage.

Environmental Influences on Transport

Light influences photosynthesis rates, consequently affecting the source's productivity.
Water potential impacts photosynthetic intensity and solute transport efficiency.
Temperature ranges of 20-30°C are optimal for solute transport; extremes hinder this process.

Theories of Phloem Transport Mechanisms

Pressure flow theory suggests solute movement driven by differences in pressure between sources and sinks.
Electro-osmosis describes ion movement through sieve plates, regulated by the charge of the membrane and ATP energy.

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Description

This quiz explores the importance of water in plant physiology, specifically focusing on how water is continuously cycled between the roots and leaves. It discusses the mechanisms plants use to manage water loss and the critical role of water in their metabolic activities. Understanding these concepts is key for studying plant biology.