Chapter 9 - Transport in Plants Flashcards
What are the functions of the xylem? [3]
Conduct water and dissolved minerals from roots to other parts of the plant [1]
Acts as a channel for water to pass through [1]
Provides mechanical support for the plant [1]
What are the adaptations of the xylem? [2]
Long hollow tubes with no cross walls / protoplasm to provide a continuous lumen which reduces resistance to water flow to increase rate of water flow [1]
Inner walls of xylems strengthened by lignin to provide support and prevent collapse of vessels [1]
What are the functions of the phloem? [1]
Translocate manufactured food through sieve tubes from leaves to other parts of the plant [1]
What are the adaptations of the phloem? [3]
Thin layer of cytoplasm with little protoplasm to reduce resistance to flow of substances which increases rate of flow of substances [1]
Have sieve tube elements with degenerate protoplasm, arranged end to end with porous sieve tubes between them to allow rapid flow of manufactured food. [1]
One companion cell is associated with each sieve tube element, and has numerous mitochondria to release energy for active loading of sugars into sieve tubes via active transport [1]
How are vascular bundles arranged in a stem? [5]
Xylem and phloem are grouped together [1]
Vascular bundles arranged in a ring around a central pith, which is a storage tissue [1]
Phloem lies outside xylem with a cambium tissue between them which divide and differentiate to form new vascular tissues and thicken the stem [1]
Cortex between vascular bundles and epidermis, which is a storage tissue for starch [1]
Stem covered by epidermis, protected by a waxy, waterproof cuticle that reduces evaporation of water from stem [1]
How are vascular bundles arranged in the root? [4]
Xylem and phloem alternate with each other at the center of root [1]
Cortex of the root is a storage tissue, innermost layer called the endodermis [1]
Piliferous layer is outermost layer and bears root hairs [1]
Each root hair is a tubular outgrowth of an epidermal cell to increase S.A to vol. ratio for faster absorption [1]
Define translocation. [1]
The transport of manufactured food substances in the phloem of plants [1]
What are the three translocation studies? Explain. [6]
Using aphids [1] - removing an aphid from its proboscis after being anaesthetised with CO2 and it inserts its proboscis into the stem to feed. Phloem sap containing sucrose and amino acids will continue to exude, showing there is pressure in phloem sap (formed due to active loading of sugar causing water enters phloem for increased pressure - active unloading of sugar causes water to exit phloem for decreased pressure) [1]
Using ringing experiment [1] - removing outer ring of bark (phloem tissue) - bulge seen above cut region due to accumulation of phloem sap + lower w.p causes water to enter cell and contribute to swelling [1]
Using radioactive carbon isotopes [1] - Supplying radioactive carbon isotope to leaf and allow photosynthesis to occur, then expose cross section of leaf to XRAY film and test for presence of radioactivity [1]
How is water absorbed by the roots of a plant? [6]
Each soil particle has a thin film of liquid surrounding it, as soil solution is a dilute solution of mineral salts. [1]
Root hairs on the roots are one-cell thick and long and narrow for increased S.A to vol ratio for faster absorption of water + dissolved minerals. [1]
Soil is more concentrated due to presence of sugars and minerals, hence they diffuse into root hair cells down concentration gradient (or by active transport - ions are moved against conc. gradient by energy released from mitochondria in root hair cells) [1]
Sap in root hair cell now has lower w.p, so water enters root hair by osmosis. [1]
Root hair cell now has higher w.p than the next cell, so water moves to the next cell, and onto the next cell by osmosis - continues till water enters xylem vessels and moves up the plant [1]
Dissolved minerals diffuse from cell to cell till it reaches the xylem vessels and moves up the plant. [1]
What are the adaptations of root hair cells? [3]
Long narrow protrusion for increased S.A to vol. ratio for faster rate of absorption [1]
Presence of cell membrane to prevent cell sap from leaking out, so root hair cells will have lower w.p than soil solution and allow water to enter by osmosis [1]
Many mitochondria - release energy for aerobic respiration for active transport of ions into cells [1]
Define the three ways of moving water against gravity. [6]
Root pressure [1] - pressure to force water upwards (a short distance) resulting from constant entry of water from soil to roots by osmosis [1]
Capillary action [1] - movement of water up very narrow tubes (eg xylems) due to forces of attraction b/w water molecules (cohesion) and forces of attraction b/w water and xylem walls (adhesion). [1]
Transpiration [1] - Loss of water vapour from aerial parts of the plant through diffusion. [1]
Define transpiration. [1]
The loss of water vapour from aerial parts of the plant through diffusion. [1]
Define transpirational pull. [1]
A suction pulling force caused by transpiration that results in water to move up the xylem. [1]
How is transpirational pull produced? [4]
Water moving out of mesophyll cells form a thin film of moisture around cells [1]
Water from this film of moisture evaporates to form w.v in the intercellular air spaces –> saturated with w.v [1]
Stomata opens to receive CO2 for photosynthesis, hence allowing loss of w.v from intercellular air spaces in leaf to surr. by diffusion (transpiration) - consequence of gaseous exchange [1]
Movement of water out of mesophyll cells to replace evaporated film of moisture decreases cell sap w.p, so mesophyll cells absorb water via osmosis from cells deeper in the leaf and these cells absorb water from xylem vessels –> transpirational pull [1]
What affects rate of transpiration? Explain. [8]
Humidity [1] - more humidity, increased conc. of w.v in surr, decreased w.v conc. gradient, decreased rate of transpiration [1]
Wind / Air Movement [1] - more wind, more w.v that accumulates outside stomata due to transpiration is removed by the wind, increased diffusion gradient, increased rate of transpiration [1]
Temperature [1] - increased temp, increased rate of evaporation and movement of water molecules, increased rate of transpiration [1]
Light Intensity [1] - increased light intensity, increased stomatal opening, increased rate of transpiration [1]
