9.2 - Water Transport in Multicellular Plants Flashcards
How do plants transport water without a heart?
Unlike animals, plants do not have a heart. Instead, water moves through the xylem due to transpiration pull, root pressure, and capillary action.
What are the main roles of water in plants? (5)
- Provides turgor pressure for support.
- Drives cell expansion (e.g., roots pushing through concrete).
- Cools the plant through evaporation.
- Transports minerals and sugars in solution.
- Acts as a reactant in photosynthesis.
What is turgor pressure, and why is it important?
Turgor pressure is the hydrostatic pressure exerted by water inside plant cells.
It supports stems and leaves, acting as a hydrostatic skeleton.
How does turgor pressure compare to human blood pressure? What does this show?
Leaf cell turgor pressure ≈ 1.5 MPa (11,251 mmHg).
Human systolic blood pressure ≈ 120 mmHg.
This shows that plant cells experience much higher pressure than human arteries!
How does water loss help plants?
Transpiration (water evaporation) helps to cool the plant.
Water carries mineral ions from roots to leaves.
Why is water essential for photosynthesis?
Water is a raw material for photosynthesis.
It provides hydrogen ions needed to produce glucose and oxygen.
How does water enter a plant from the soil?
Water moves into root hair cells by osmosis.
It then moves through the root cortex via the symplast and apoplast pathways.
What are the symplast and apoplast pathways?
Symplast pathway: Water moves through the cytoplasm via plasmodesmata.
Apoplast pathway: Water moves through cell walls and intercellular spaces.
What is the function of root hair cells?
Root hair cells are specialized epidermal cells that act as the exchange surface for water and mineral absorption from the soil.
How are root hair cells adapted for water absorption? (4)
- Microscopic size – allows them to fit between soil particles.
- Large SA:V ratio – maximizes water uptake.
- Thin cell wall and membrane – speeds up diffusion and osmosis.
- Maintains a water potential gradient – contains solutes that attract water by osmosis.
Why does a large surface area help in water absorption?
A larger surface area allows more water molecules to move into the root by osmosis, making absorption more efficient.
Why does water move into root hair cells by osmosis?
Soil water has a high water potential (very few dissolved minerals).
Root hair cell cytoplasm has a lower water potential due to dissolved solutes.
Water moves down the water potential gradient into the root hair cell by osmosis.
What substances lower the water potential in root hair cells?
Sugars, mineral ions, and amino acids dissolved in the cytoplasm and vacuole.
What are the two pathways water can take across the root to the xylem?
Symplast Pathway – through the cytoplasm of cells via plasmodesmata.
Apoplast Pathway – through the cell walls and intercellular spaces.
How does water move in the symplast pathway?
Water moves through the cytoplasm of living plant cells, connected by plasmodesmata, by osmosis.
What maintains the water potential gradient in the symplast pathway?
As water leaves a root hair cell by osmosis, its water potential falls, ensuring a continuous flow of water from the soil into the root hair cell.
How does water move in the apoplast pathway? By what forces?
Water moves through the cell walls and intercellular spaces, driven by cohesion and tension forces.
Why does water continue moving in the apoplast pathway?
As water enters the xylem, it pulls more water behind it due to cohesion (water molecules sticking together), creating a continuous flow.
Why do the cell walls allow easy water movement in the apoplast pathway?
The cellulose structure has a loose, open network that offers little resistance to water movement.
What is the difference between a symplast pathways and a vacuolar pathway?
A vacuolar pathway is the same as the symplast pathway when the water moves through the cells vacuoles in addition to the cytoplasm.
Rank the three water movement pathways, from slowest to quickest.
- Vacuolar pathway
- Symplast pathway
- Apoplast pathway
What is the endodermis, and why is it important? 🌱
The endodermis is a layer of cells surrounding the vascular tissue (xylem and phloem) in roots. It contains the Casparian strip, which controls water movement.
What is the Casparian strip, and what does it do?
The Casparian strip is a waxy band of suberin that runs around endodermal cells, creating a waterproof barrier that forces water from the apoplast pathway into the symplast pathway.
Why is the diversion of water into the symplast pathway important?
It ensures that toxic solutes in soil water cannot enter the xylem, as the selectively permeable membrane filters substances.
What role do mineral ions play in water movement into the xylem?
Endodermal cells actively transport mineral ions into the xylem, lowering its water potential, which causes water to move in by osmosis.
What is root pressure, and how does it help water movement?
Root pressure is the force created by active transport of minerals into the xylem, which moves water upward by osmosis.
Is root pressure the main force moving water up the xylem?
No, root pressure helps, but transpiration pull is the main driving force for water movement in the plant.
What is root pressure, and where does it occur?
Root pressure is the pressure exerted in the xylem of plants, driving the movement of water upwards through the plant. It occurs in the roots, particularly when active transport moves water from the root endodermis into the xylem.
How do poisons like cyanide affect root pressure?
Cyanide affects the mitochondria in root cells and prevents the production of ATP. Without ATP (the energy source), active transport is halted, causing root pressure to disappear.
What is the relationship between temperature and root pressure?
Root pressure increases with a rise in temperature and decreases when temperature falls. This suggests that chemical reactions, which are temperature-dependent, are involved in generating root pressure.
How do oxygen levels and respiratory substrates affect root pressure?
If levels of oxygen or respiratory substrates decrease, root pressure also decreases. This supports the idea that active transport requires cellular respiration to provide the necessary energy for the process.
What is guttation, and how is it related to root pressure?
Guttation is the process where xylem sap is forced out of special pores at the ends of leaves under specific conditions, such as when transpiration is low (e.g., overnight). This phenomenon is evidence of root pressure, as the sap is driven up from the roots into the leaves.
