Back to AI Flashcard MakerBiology /Biology IB HL - 9.1 Xylem Transport Part 3
What blocks the passage of water in the roots?
The stele is surrounded by an endodermis layer that is impermeable to the passive flow of water and ions (Casparian strip)
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Key Terms
Term
Definition
What blocks the passage of water in the roots?
The stele is surrounded by an endodermis layer that is impermeable to the passive flow of water and ions (Casparian strip)
How does water and minerals pass through the Casparian strip?
Water and minerals are pumped across this barrier by specialised cells, allowing the rate of uptake to be controlled
What does fertile soil type usually contain?
Fertile soil typically contains negatively charged clay particles to which positively charged mineral ions (cations) may attach
What 4 main minerals need to be absorbed by the plant?
Minerals that need to be taken up from the soil include Mg2+ (for chlorophyll), nitrates (for amino acids), Na+, K+ and PO43–
In what two ways may mineral ions be transported into the roots?
Mineral ions may passively diffuse into the roots, but will more commonly be actively uploaded by indirect active transport
What do root cells contain which is the main component of active transport? (indirect)
Root cells contain proton pumps that actively expel H+ ions (stored in the vacuole of root cells) into the surrounding soil
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| Term | Definition |
|---|---|
What blocks the passage of water in the roots? | The stele is surrounded by an endodermis layer that is impermeable to the passive flow of water and ions (Casparian strip) |
How does water and minerals pass through the Casparian strip? | Water and minerals are pumped across this barrier by specialised cells, allowing the rate of uptake to be controlled |
What does fertile soil type usually contain? | Fertile soil typically contains negatively charged clay particles to which positively charged mineral ions (cations) may attach |
What 4 main minerals need to be absorbed by the plant? | Minerals that need to be taken up from the soil include Mg2+ (for chlorophyll), nitrates (for amino acids), Na+, K+ and PO43– |
In what two ways may mineral ions be transported into the roots? | Mineral ions may passively diffuse into the roots, but will more commonly be actively uploaded by indirect active transport |
What do root cells contain which is the main component of active transport? (indirect) | Root cells contain proton pumps that actively expel H+ ions (stored in the vacuole of root cells) into the surrounding soil |
How do the H+ ions affect the positively charged mineral ions? | The H+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient |
How do the H+ ions affect the negatively charged mineral ions? | Negatively charged mineral ions (anions) may bind to the H+ ions and be reabsorbed along with the proton |
How is water taken into the root? What process? | Water will follow the mineral ions into the root via osmosis – moving towards the region with a higher solute concentration |
What will regulate the rate of water uptake? | The rate of water uptake will be regulated by specialised water channels (aquaporins) on the root cell membrane |
In what two ways can water move towards the xylem? | Once inside the root, water will move towards the xylem either via the cytoplasm (symplastic) or via the cell wall (apoplastic) |
How does water move in the symplastic pathway? | In the symplastic pathway, water moves continuously through the cytoplasm of cells (connected via plasmodesmata) |
How does water move in the apoplastic pathway? | In the apoplastic pathway, water cannot cross the Casparian strip and is transferred to the cytoplasm of the endodermis |
What are desert plants called? | xerophytes |
What are plants that grow in high salinity called? | halophytes |
Why must xerophytes have adaptations for water conservation? | Xerophytes will have high rates of transpiration due to the high temperatures and low humidity of desert environments |
Why must halophytes have adaptations for water conservation? | Halophytes will lose water as the high intake of salt from the surrounding soils will draw water from plant tissue via osmosis |
What are xerophytes? (definition) | Xerophytes are plants that can tolerate dry conditions (such as deserts) due to the presence of a number of adaptations |
What 6 (simple) adaptations can xerophytes have? | reduced leaves; rolled leaves; thick, waxy cuticle; stomata in pits; low growth; CAM Physiology |
How do reduced leaves help reduce water loss? | reducing the total number and size of leaves will reduce the surface area available for water loss |
How do rolled leaves help reduce water loss? | reducing the total number and size of leaves will reduce the surface area available for water loss |
How does a thick waxy cuticle help reduce water loss? | having leaves covered by a thickened cuticle prevents water loss from the leaf surface |
How do stomata in pits help reduce water loss? | having stomata in pits, surrounded by hairs, traps water vapour and hence reduces transpiration |
How does low growth help reduce water loss? | low growing plants are less exposed to wind and more likely to be shaded, reducing water loss |
How does CAM physiology help reduce water loss? | plants with CAM physiology open their stomata at night, reducing water loss via evaporation |