Plant transport

• Describe the functions of the transport systems in plants

  Transport water, minerals, sucrose etc. from where it is made/collected to where it is needed/excreted
• Explain 2 reasons why multicellular plants have to have transport systems

  Distances to large for diffusion to be effective and transport fast enough.Surface area to volume ratio too small
• Define the terms "herbaceous" and "dicotyledonous

  Herbaceous - plant with no woody tissueDicotyledonous - plants with two cotyledons in the seed
• Define the terms "vascular system" and "vascular bundles"

  vascular system - a system of transport vessels in animals or plantsvascular bundles - the vascular system of herbaceous dicots. composed of xylem and phloem tissue
• Name the two types of transport vessels in vascular bundles

  Xylem and phloem
• Draw, label and annotate diagrams of transverse sections (cross-sections) through a typical stem of an herbaceous dicotyledonous plant

  
• Draw, label and annotate diagrams of transverse sections (cross-sections) through a typical root of an herbaceous dicotyledonous plant

  Endodermis surrounds vascular tissue with casparian strip which blocks apoplast pathways so all water and solutes must go through living cell - controls what enters the plant

  
• Draw, label and annotate diagrams of transverse sections (cross-sections) through a typical leaf of an herbaceous dicotyledonous plant

  
• State the function of xylem and phloem

  Xylem - transports water and minerals and structurePhloem - transports sucrose (and amino acids etc.)
• Describe the structure of xylem and explain how it is adapted for its function

  Dead cells - empty, hollow tubes - no resistance to waterNo end walls between cells - no resistance for waterCell walls strengthened with lignin - provide support for the plant
• Describe the patterns of lignification in xylem and state its function

  Spirals round the xylem vessels. Strength and structure
• Draw, label, and annotate a diagram of a longitudinal section through a xylem vessel to show its structure and adaptations for its function

  
• Define the terms "sieve tube element", "sieve plate", and "companion cell"

  sieve tube element - an element of phloem tissue consisting of a longitudinal row of thin-walled elongated cells with perforations in their connecting walls through which food materials passsieve plate - an area of relatively large pores present in the common end walls of sieve tube elementscompanion cell - A specialised parenchyma cell, located in the phloem of flowering plants and closely associated with the development and function of a sieve-tube element.
• Describe the structure of phloem and explain how it is adapted for its function

  Little cytoplasm, no organelles - room for water, sucrose etc. to be transportedPerforated ends - let water, sucrose through easilyCompanion cells have many mitochondria to produce ATP for active transport
• Draw, label, and annotate a diagram of a longitudinal section through phloem tissue to show the two types of cell, their structure and adaptation for their function

  
• Compare the structure and function of xylem and phloem

  Xylem dead, phloem aliveXylem contain ligninXylem transport water, phloem sucrosePhloem have companion cells
• Define the terms "transpiration", "transpiration stream", and "transpiration pull


  transpiration - the loss of water vapour from the stems and leaves of a plant as a result of evaporation from the surfaces of cells inside the leaf and diffusion down a concentration gradient out of the stomatatranspiration stream - the movement of water through a plant from the roots until it is lost by evaporation from the leavestranspiration pull - the force which aids in drawing the water upward from roots to leaves
• Explain why water loss is inevitable for plants

  Have to open stomata to allow diffusion of CO2 into plant for photosynthesis to produce glucose for respiration.
• Outline the route water takes through a plant

  Water moves into roots by osmosis. Travels through roots to centre where enters xylem vessels. Drawn up xylem by transpiration pull to leaves where it is lost via evaporation (or used on the way)
• Define the terms "stomata" and "guard cell"

  stomata - pores in the surface of a leaf or stem that may be opened and closed by guard cellsguard cell - cells that can open and close the stomatal pores controlling gaseous exchange and water loss in plants
• Define the terms "adhesion" and "cohesion"

  adhesion - sticking together of particles of different substancescohesion - sticking together of particles of the same substance
• Explain how transpiration results in water moving through the plant (the cohesion-tension theory), and state whether it is an active or passive process

  Water evaporates through the stomata in the leaves (transpiration)This creates an osmotic gradient causing water to move across the cells in the leaf to the stomataThis causes water to leave the xylem in the leaves, reducing the pressure (creating a tension) in the xylemA column of water is drawn up the stem, the transpiration stream This column stays intact due to the hydrogen bonds between the molecules, cohesionThe pull creates a negative pressure in the xylem vessels which explains why they're lignified and rigid - they won't collapseThis is a passive process.
• Explain why the cohesion-tension theory is named the way it is

  Tension is created by the loss of water by transpiration as water is pulled up to replace it. Cohesion allows the water to be pulled as it holds itself in a constant stream
• Draw, label and annotate a diagram to show the transport of water through a plant

  
• Describe 3 sources of evidence for the cohesion-tension theory

  Changes in the diameter of trees - when hot, transpiration at highest, tension at highest, diameter shrinks - when cold, transpiration lower, tension lower, water collects in xylem, diameter increasesWhen stem is cut, in most cases, air drawn in rather than water leaking outIf air bubble is created, water cannot move up stem as transpiration stream broken - no longer continuous cohesion between molecules
• Explain how guard cells can open and close stomata

  When conditions are favourable, guard cells pump in solutes by active transport causing guard cells take up water by osmosis and become turgid. Because their inner walls are rigid they are pulled apart, opening the pore. In less favourable conditions, hormonal signals from the roots cause guard cells to lose turgor water is lost and the inner walls move together closing the pore.
• State 5 environmental factors that can affect the rate of transpiration and for each explain how they have their effect

  Light - more photosynthesis, needs CO2 to diffuse in, stomata open, more transpirationTemperature - more transpirationWind - moves saturated air away from leaves so dry air replaces it, more transpirationHumidity - air can hold less water, transpiration decreasesSoil water availability - less water available, less transpiration
• Draw, label and annotate a diagram of a potometer to show how it can measure transpiration rate

  Stem must go in water immediately after being cut to maintain the transpiration stream through the plant and avoid introducing air bubbles. Then cut stem again once under water to remove the part that could potentially have air bubbles.Seal all joins with vaseline - waterproofRate of air bubble moving along capillary is rate of water uptake which is assumed to equal rate of transpiration.

  
• Describe how to conduct an experiment using a potometer to investigate the effect of one, named, environmental factor (or experimental manipulation) on the rate of transpiration

  Light - lamp (with screen to prevent heat), darkHumidity - put plant in bagTemp. - heaterWind - fan
• Describe 5 functions of water in plants

  maintaining cell turgidity for structure and growthtransporting nutrients and organic compounds throughout the plantcomprising much of the living protoplasm in the cellsserving as a raw material for various chemical processes, including photosynthesisthrough transpiration, buffering the plant against wide temperature fluctuations
• Describe the ways that the root hairs of root hair cells are adapted as exchange surfaces


  Long projection increasing surface areaMicroscopic size so can penetrate between soil particles reducing distance for diffusionThin surface layer through which diffusion and osmosis can take place quicklyConcentration of solutes in cytoplasm maintains water potential gradient into cells
• Explain why water move from the soil into root hair cells

  Root hair cell has a lower water potential than the surrounding soil so water moves into the cell by osmosis
• Name the 2 pathways by which water travels across the root to the xylem

  Apoplast and symplast pathways
• Describe the symplast pathway of water movement

  (Living route) Water moves through the living part of the cell (the protoplast bounded by the cell surface membrane) It may move through the vacuole (sometimes called the vacuolar pathway)
• Explain the importance of water potential gradients for the movement of water through a plant.

  To get from the root hair cell to the centre of the root, the water passes through each successive cell by osmosis down a water potential gradient
• Describe the apoplast pathway of water movement

  (Non living route) Water moves between cells or through the cell wall, both of which are non-living
• Define the terms "endodermis", "Casparian strip", and "root pressure"


  Endodermis - an inner layer of cells in the cortex of a root and of some stems, surrounding a vascular bundleCasparian strip - a band of cell wall material deposited in the radial and transverse walls of the endodermis, and is chemically different from the rest of the cell wall - the cell wall being made of lignin and without suberin - whereas the Casparian strip is made of suberin and sometimes ligninRoot pressure - pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves. The active transport of ions into the xylem by the endodermis creates the water potential gradient which causes water to enter the xylem. This pushes the water up the xylem.
• Describe structure, function and location of the Casparian strip


  Casparian strip is sections of cell wall that contain suberin which is waterproof. This blocks the apoplast pathway ensuring that anything crossing the endodermis has to go through the living part of the cell/ This means that the endodermis controls movement into the xylem and therefore the rest of the plant, blocking potentially toxic substances as it has no membrane proteins to let them through.
• Explain the role of active transport by endodermal cells for the movement of water

  Actively transport ions such as nitrate ions into the xylem, decreasing the water potential in the xylem so that water enters by osmosis
• Describe the evidence for the role of active transport in moving water from root endodermis into the xylem

  If a stem is cut close to where it emerges from the soil, liquid oozes from the cut surface caused by pressure from below.