3.3 Organisms exchange substances with their environment - Mass Transport in Plants Flashcards
What is transpiration?
The loss of water vapour from the stomata by evaporation.
Transpiration plays a crucial role in water movement and temperature regulation in plants.
What are the four factors that affect the rate of transpiration?
- Light intensity
- Humidity
- Temperature
- Wind
These factors influence the evaporation of water from the plant’s surface.
What is the relationship between light intensity and transpiration?
There is a positive correlation.
Higher light intensity leads to more open stomata, increasing the surface area for evaporation.
How does humidity affect transpiration?
There is a negative correlation.
Increased humidity raises the water potential outside the leaf, reducing the water potential gradient and evaporation.
What is the effect of temperature on transpiration?
There is a positive correlation.
Higher temperatures increase kinetic energy, leading to faster-moving molecules and increased evaporation.
How does wind influence transpiration?
There is a positive correlation.
Wind removes humid air from around the leaf, maintaining the water potential gradient and promoting evaporation.
What is the cohesion-tension theory?
It explains how water moves up a plant against gravity through three principles: Cohesion, Capillarity (adhesion), and Root Pressure.
This theory is essential for understanding how plants transport water from roots to leaves.
Fill in the blank: The more _______ there is, the more kinetic energy, leading to faster-moving molecules in transpiration.
[temperature]
True or False: A higher water potential gradient increases evaporation.
True
A steeper water potential gradient facilitates the movement of water from areas of higher potential to lower potential.
What role do stomata play in transpiration?
They are the openings through which water vapour is lost from the plant.
Stomata can open and close to regulate water loss and gas exchange.
What is capillarity in the context of the cohesion-tension theory?
It refers to the adhesion of water molecules to the walls of xylem vessels, aiding in water transport.
Capillarity allows water to rise against gravity in narrow tubes.
What is root pressure?
It is the pressure within the roots that helps push water upwards through the plant.
Root pressure is generated by the active uptake of minerals and water from the soil.
What is a dipolar molecule?
A molecule with a slight negative charge on one end and a slight positive charge on the other end
Water is an example of a dipolar molecule.
What enables hydrogen bonds to form between water molecules?
The dipolar nature of water
The oxygen atom carries a slight negative charge while the hydrogen atoms carry a slight positive charge.
What is cohesion in the context of water molecules?
The sticking together of water molecules due to hydrogen bonds
Cohesion allows water to travel up the xylem as a continuous water column.
What role does adhesion play in the movement of water in plants?
Water sticks to other molecules, helping to hold the water column up against gravity
Adhesion occurs when water molecules form hydrogen bonds with the xylem walls.
How does capillarity affect the movement of water in narrow xylem?
The narrower the xylem, the greater the impact of capillarity
This is because more water molecules adhere to the walls, requiring less pull to draw up the liquid.
Fill in the blank: Water adheres to the xylem walls due to _______.
hydrogen bonds
This adhesion is crucial for water transport in plants.
True or False: Cohesion allows water to move upward through the xylem.
True
Cohesion creates a continuous water column that facilitates upward movement.
What is the effect of straw width on the required pull to draw up liquid?
The narrower the straw, the less pull is required
This demonstrates the principle of capillarity in water movement.
What is root pressure?
The pressure inside the root that increases as water moves in by osmosis, forcing water upwards.
What causes positive pressure in plants?
The increase in volume of liquid inside the root due to water entering by osmosis.
What is the effect of water vapor evaporating from stomata?
It creates a lower pressure inside the leaves, leading to more water being pulled up the xylem.
What is negative pressure in the context of plant water transport?
The pressure created when water is lost by transpiration, pulling more water up the xylem.
What role does cohesion play in water transport in plants?
Cohesion keeps water molecules stuck together, forming a continuous column in the xylem.
How does adhesion contribute to water movement in xylem?
Adhesion helps water molecules stick to the walls of the xylem, aiding in the upward movement.
What happens to the xylem as water is pulled up?
The xylem experiences tension and becomes narrower.
Fill in the blank: Water moves into the roots by _______.
osmosis
True or False: Cohesion and adhesion are both essential for the upward movement of water in plants.
True
List the key terms related to mass transport in plants.
- Root pressure
- Negative pressure
- Cohesion
- Positive pressure
- Continuous water column
- Adhesion
- Movement of water up the xylem
What is the tube responsible for the transport of organic substances in plants?
Phloem
Phloem transports substances such as sugars.
What is the process of transporting organic substances in plants called?
Translocation
Translocation is explained by the mass flow hypothesis.
What hypothesis explains the transport of organic substances in plants?
Mass flow hypothesis
This hypothesis describes how organic substances are moved through the phloem.
What are the long, thin cells in phloem that form a column called?
Sieve tube elements
These cells are named for their perforated end walls.
What is the function of companion cells in the phloem?
Provide ATP for active transport
Companion cells assist sieve tube elements by supplying them with energy.
What type of cells are sieve tube elements?
Living cells without a nucleus
They have very few organelles to facilitate sugar flow.
Fill in the blank: The end walls of sieve tube elements are perforated, like a _______.
sieve
What is the role of the lateral sieve area in sieve tube elements?
Facilitates transport of substances
This area allows for the movement of organic substances.
True or False: Sieve tube elements have a high number of organelles.
False
They contain very few organelles to reduce resistance to sugar flow.
What are the two main types of cells that make up phloem tissue?
Sieve tube elements and companion cells
These cells work together for effective transport of organic substances.
What is the mass flow hypothesis?
The mass flow hypothesis explains how organic substances, such as sucrose, move from the source (where they are produced) to the sink (where they are used).
What term describes the site of production in the mass flow hypothesis?
Source
What term describes the site of use in the mass flow hypothesis?
Sink
What substance moves in a solution from the leaves to respiring cells?
Sucrose
How does sucrose affect the water potential of the source cell?
Sucrose lowers the water potential of the source cell.
What process causes water to enter the source cell?
Osmosis
What happens to hydrostatic pressure in the source cell as water enters?
The hydrostatic pressure increases.
What is the water potential like in the respiring cell compared to the source cell?
The respiring cell has a more positive water potential.
What happens to water in the sink cell?
Water leaves the sink cell by osmosis.
What effect does water leaving the sink cell have on hydrostatic pressure?
It decreases the hydrostatic pressure in the sink cell.
What causes the solution to be forced towards the sink cell?
The higher hydrostatic pressure in the source cell compared to the sink cell.
What is the role of phloem in the mass flow hypothesis?
Phloem transports the solution from the source to the sink.
Fill in the blank: The site where photosynthesis occurs and produces sucrose is known as the _______.
Source
True or False: The sink cell has a lower water potential than the source cell.
False
What is the relationship between hydrostatic pressure and the flow of solution in plants?
Higher hydrostatic pressure in the source cell compared to the sink cell causes the flow of solution towards the sink.
Define osmosis.
The movement of water across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
What is the role of water potential in the mass flow hypothesis?
Water potential determines the movement of water into and out of cells, influencing hydrostatic pressure.
What is the process by which organic substances like sucrose are created in plants?
Photosynthesis
Occurs in the chloroplasts of leaves.
Which plant tissue is primarily responsible for the transport of water and nutrients?
Xylem
Transports water and dissolved minerals from roots to the rest of the plant.
What type of transport involves the movement of substances against their concentration gradient using energy?
Active transport
Uses ATP for energy.
What is the mechanism called that allows substances to move across a membrane with the help of a protein but without energy?
Facilitated diffusion
Involves carrier proteins.
What term describes the movement of two substances in different directions across a membrane?
Co-transport
Often involves the simultaneous transport of ions and other molecules.
What type of protein aids in the movement of substances across the cell membrane?
Carrier protein
Facilitates the transport of specific molecules.
What is the pressure exerted by the fluid within the xylem and phloem called?
Hydrostatic pressure
Influences the movement of liquids in plants.
What is the name of the tissue that transports sucrose from the leaves to other parts of the plant?
Phloem
Responsible for the transport of organic nutrients.
Fill in the blank: Sucrose diffuses down its concentration gradient into the _______ cell via facilitated diffusion.
companion
Companion cells assist in the transport of sucrose.
What is the effect of transpiration on the movement of water in plants?
Creates a gradient that pulls water upwards
Transpiration helps maintain the flow of water from roots to leaves.
What happens to the water potential in the sieve tube element when sucrose concentration increases?
Water potential decreases
Causes water to enter the sieve tube elements from xylem.
What process occurs when water moves from the surrounding xylem vessels into the sieve tube elements?
Osmosis
Water moves from areas of higher water potential to lower water potential.
True or False: The removal of water from the sieve tube element increases hydrostatic pressure.
False
The removal of water decreases the volume and hydrostatic pressure.
What happens to sucrose at the sink cell?
Used in respiration or stored as insoluble starch
Sucrose is actively transported into the sink cell.
How does the mass flow of sucrose occur within the sieve tube elements?
Down a hydrostatic pressure gradient
Driven by differences in pressure created by water movement.
What are the two methods used to investigate transport in plants?
Tracer experiments and ringing experiments
What does the tracer experiment prove about the transport of sugars?
It proves that it is the phloem that transports sugars and not the xylem
What is the process of tracing in plant transport studies?
Involves radioactively labelling carbon and observing its movement in the plant
How is radioactive carbon used in tracing?
Plants are provided with radioactively labelled carbon dioxide for photosynthesis
What happens to the thin slices of stems in the tracing experiment?
They are placed on x-ray film that turns black when exposed to radioactive material
What indicates the presence of phloem in the tracing experiment?
The section of the stem containing sugars turns black on the x-ray film
What is the purpose of the ringing experiment?
To demonstrate that phloem is responsible for sugar transport
What is done in a ringing experiment?
A ring of bark and phloem is peeled and removed from a tree trunk
What is observed after removing the phloem in the ringing experiment?
The trunk swells above the removed section
What does the analysis of the liquid in the swelling after a ringing experiment show?
It contains sugar, indicating that phloem is necessary for sugar transport
True or False: The xylem is responsible for transporting sugars in plants.
False
Fill in the blank: The process of _______ involves moving substances against a concentration gradient.
[Active transport]
What are the key terms associated with transport in plants? List at least three.
- Active transport
- Facilitated diffusion
- Co-transport
- Carrier protein
- Hydrostatic pressure
What is transpiration in plants?
Loss of water vapor through the stomata
Transpiration mainly occurs due to evaporation and is influenced by temperature, humidity, and light.
What is the relationship between transpiration and water potential?
Transpiration causes an upward pull of water due to tension created in the xylem
This tension results in narrower diameters of xylem vessels, increasing the efficiency of water transport.
What is translocation in plants?
Transport of organic substances, mainly sucrose, from sources to sinks
Translocation is essential for distributing nutrients throughout the plant.
How does mass transport of sucrose occur in plants?
Due to turgor pressure gradient in sieve tube elements
This gradient is created by the active transport of sucrose into the sieve tubes.
What role does turgor pressure play in plant transport?
It drives the flow of water and nutrients in the phloem
The turgor pressure is influenced by the osmotic movement of water.
What are tracers used for in plant biology?
To investigate the transport of organic substances in plants
Tracers can help visualize and track the movement of nutrients within plant systems.
Complete the sentence: Cohesion-tension theory links to the structure and function of water in _______.
biological molecules
How does the transport of sucrose relate to photosynthesis?
Sucrose is produced in photosynthesis and transported to various parts of the plant for energy and growth
This process links photosynthesis and respiration in plants.
What are the types of transport mechanisms involved in translocation?
Facilitated diffusion, active transport, and co-transport
Each mechanism plays a crucial role in moving substances across plant membranes.
