Flashcards in Transport In Plants Deck (31):
What is the vascular system?
Xylem and phloem tissue in plants. Xylem is for carrying water and minerals and phloem is for carrying sugars
What is parenchyma?
Packing and supporting tissue
What are the functions of xylem?
Transport of water and mineral ions up a plant
Structural support for the plant
What is xylem?
Dead cells fused to form hollow vessels, strengthened by lignin
Why are there pits in the xylem wall?
To allow water to move out into adjacent xylem vessels or other cells
What is the purpose of xylem parenchyma cells?
To store food
What is the function of phloem vessels?
To transport solutes (e.g. sugars and amino acids) up and down a plant
What are phloem vessels?
Siege tube elements (living cells) joined end to end forming a tube with internal pores (sieve plates)
What are companion cells?
Cells that carry out all the metabolic functions of the phloem tissue (as tubes lack nuclei). Materials pass into sieve tubes via plasmodesmata
What are 3 roles played by water in plants?
Maintaining turgor, transport medium for mineral ions and sugars, raw material in photosynthesis
How are root hair cells adapted for water uptake?
Long and narrow so have large SA:V ratio, able to penetrate between soil particles to reach water, active transport of mineral ions into vacuole gives it a low water potential, creating a gradient and water diffuses in by osmosis
What is the symplast pathway?
Movement of water through the cytoplasm
What is the apoplast pathway
Movement of water through the cell walls
What does the casparian strip do and why?
Forces water in the apoplast pathway into the symplast pathway to prevent toxic solutes from continuing to move up the plant and stops water from returning to the root cortex from xylem vessels
What is root pressure?
Initial flow of water into vascular tissue helps to force water up stem (although transpiration pull is a more significant factor)
How does water first enter the xylem?
Endodermal cells pump mineral ions into the xylem by active transport, water diffuses into xylem by osmosis due to a lower water potential in the xylem
What is transpiration?
The evaporation of water from a plants leaves (from cells in the leaves, diffusing out through stomata)
What is the transpiration pull?
Water is pulled up xylem vessels to replace the water lost through transpiration
What is the transpiration stream?
An unbroken chain of water molecules hydrogen bonding together that is pulled up the xylem vessels (exhibiting cohesion)
How does capillary action aid transpiration?
Water molecules adhere to the sides of xylem vessels, aiding the movement of the transpiration stream up the narrow vessels
What evidence is there for the cohesion-tension theory?
Trees become narrower when they transpire (due to tension in xylem during transpiration)
Air sucked up (rather than water leaking out) when a stem is cut
Water no longer moves up a broken stem as the air breaks the transpiration stream
Which cells control the opening and closing of stomata?
What instrument is used to measure transpiration rates?
What is translocation?
Movement of organic solutes through phloem sieve tubes
Occurs from sources to sinks
What is glucose converted into to be transported around a plant and why?
Sucrose, because it is much less reactive than glucose, preventing unwanted and potentially dangerous reactions from occurring in a plant during translocation
What are some examples of sources in plants?
Green leaves and stems, storage sites (e.g. tubers)
What are some examples of sinks in plants?
Developing seeds and fruits (which are laying down food stores), growing roots
How is sucrose loaded into phloem cells?
H+ ions are pumped out of companion cells by active transport, creating a proton gradient. Protons and sucrose are co-transported into the companion cells by facilitated diffusion (H+ ions move down concentration gradient). The sucrose can then move into the phloem through plasmodesmata.
What are some adaptations of xerophytes?
Sunken stomata, fewer stomata, lower leaf SA, Thick waxy cuticle, curled leaves, increased water storage (e.g. cacti), Long roots
What are some adaptations of hydrophytes?
No waxy cuticle (or very thin), Open stomata on upper surface of floating leaves, less internal structural support, air sacs and floating leaves, small roots