Transport in Plants

State 3 ways most plants conserve water or gain better access to water

Cuticles Roots Not too many stomata, can close if necessary

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)

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

Describe the structure of xylem and explain how it is adapted for its function

Dead cells - empty, hollow tubes - no resistance to water No end walls between cells - no resistance for water Cell walls strengthened with lignin - provide support for the plant

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

Name the 2 pathways by which water travels across the root to the xylem

Apoplast and symplast pathways

Describe how the water and assimilates in phloem move from source to sink

As sucrose enters the sieve elements it reduces the water potential causing water to enter by osmosis. This increases the hydrostatic pressure at the source causing mass flow towards the sink where there is lower hydrostatic pressure due to sucrose being used by cells, water potential in sieve rising and water moving out into surrounding tissues by osmosis down a gradient.

State 3 examples of xerophytic plants and 3 hydrophytic plants

Cacti, conifers, marram grass Water lilies, water cress, bullrushes, duckweed

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.

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 increases When stem is cut, in most cases, air drawn in rather than water leaking out If air bubble is created, water cannot move up stem as transpiration stream broken - no longer continuous cohesion between molecules

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 transpiration Temperature - more transpiration Wind - moves saturated air away from leaves so dry air replaces it, more transpiration Humidity - air can hold less water, transpiration decreases Soil water availability - less water available, less transpiration

Describe the environmental conditions where water loss, or water access, may become a real problem for plant species

Deserts, sand dunes, dry and salty, cold and icy

Describe the symplast route for phloem loading and explain how it occurs

Diffusion through cytoplasm and plasmodesmata of successive cells down concentration gradients.

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 "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 bundle Casparian 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 lignin Root 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.

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

Give examples of what sucrose can be converted into, and what purpose each serves

Glucose for respiration, starch for storage

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.

Define the terms "herbaceous" and "dicotyledonous

Herbaceous - plant with no woody tissue Dicotyledonous - plants with two cotyledons in the seed

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.

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), dark Humidity - put plant in bag Temp. - heater Wind - fan

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 transported Perforated ends - let water, sucrose through easily Companion cells have many mitochondria to produce ATP for active transport

Describe the ways that the root hairs of root hair cells are adapted as exchange surfaces

Long projection increasing surface area Microscopic size so can penetrate between soil particles reducing distance for diffusion Thin surface layer through which diffusion and osmosis can take place quickly Concentration of solutes in cytoplasm maintains water potential gradient into cells

Describe how companion cells are adapted for their function

Many mitochondria to produce ATP for active transport Infoldings in cell membranes to increase surface area for transport

Describe and explain sources of evidence for the processes involved in translocation

Radioactive CO2 is incorporated into sugars during photosynthesis and the radioactivity in the phloem Removing a ring around the tree trunk removes phloem not xylem. Swelling occurs above cut in summer, below in spring Aphids pierce phloem - feed on plant sugars Poisoning mitochondria stops translocation Movement in phloem is far to fast to be explained by diffusion pH of companion cells is higher than surrounding tissue cells Concentration of sucrose is higher at source than sink Hydrostatic pressure is higher at source than sink

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

Define the terms "source", "sink", and "assimilates" in relation to translocation

Source - Region of a plant that produces assimilates by photosynthesis or from storage materials Sink - Region of a plant that requires assimilates for its metabolic needs Assimilates - The products of photosynthesis that are transported around a plant

State 3 examples of sources and 3 examples of sinks

Sources - green leaves, storage organs e.g. tubers, seeds when germinating Sinks - growing shoots, growing roots, fruits

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 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 - waterproof Rate of air bubble moving along capillary is rate of water uptake which is assumed to equal rate of transpiration.

State the form in which carbohydrates are transported in plants

Sucrose

Describe the process of phloem unloading and explain how a concentration gradient is maintained from the phloem into cells requiring the sucrose

Sucrose leaves sieve tubes by active transport or diffusion to surrounding cells where it is used, maintaining concentration gradient. As sucrose leaves, water potential of tubes increases so water follows by osmosis.

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

Define the term "translocation"

The movement of organic solutes around a plant in the phloem

Define the term "phloem loading" and state the two main ways this occurs

The transport of sucrose into the phloem to be transported. Actively and passively

Describe adaptations xerophytes have for conserving, storing or accessing water and for each adaptation explain how it benefits the plant

Thick waxy cuticle - reduced transpiration Sunken stomata - creates humid environment around stomata Reduced numbers of stomata - reduced transpiration Reduces leaves (reduce SA:V ratio) Hairy leaves - traps humid air Curled leaves - traps humid air Succulents (store water in specialised parenchyma) Leaf loss (when water not available) Root adaptations (Long and deep/wide area near surface) "Avoiding problems" - Dying an dleaving seed for when water returns, bulbs or tubers, dormant, surviving complete dehydration

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 functions of the transport systems in plants

Transport water, minerals, sucrose etc. from where it is made/collected to where it is needed/excreted

Describe the apoplast route for phloem loading and explain how it occurs

Using ATP, hydrogen ions are actively transported out of companion cells into the surrounding tissue Hydrogen ions diffuse back into companion cells down the diffusion gradient. They pass through cotransporter proteins in the membrane bringing sucrose with them into the companion cell which then diffuses through the plasmodesmata into seive cells.

Describe adaptations of hydrophytes and for each adaptation explain how it benefits the plant

Very thin/no waxy cuticle Many stomata on upper surfaces, always open Reduced structure - water supports them Wide flat leaves - spread across surface to collect light Small roots Large surface area of stems and roots under water Air sacs - enable floating Aerenchyma - specialised parenchyma with lots of air spaces - buoyancy - few barriers to oxygen transport Aerial roots for intake of oxygen

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 stomata This causes water to leave the xylem in the leaves, reducing the pressure (creating a tension) in the xylem A column of water is drawn up the stem, the transpiration stream This column stays intact due to the hydrogen bonds between the molecules, cohesion The pull creates a negative pressure in the xylem vessels which explains why they're lignified and rigid - they won't collapse This is a passive process.

Describe two problems faced by hydrophytes

Water logging - air spaces must be filled with air not water for plant to survive Obtaining oxygen Leaves needing to float to reach the light for photosynthesis

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)

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.

Define the terms "xerophyte" and "hydrophyte"

Xerophytes - plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment Hydrophytes - plants with adaptations that enable them to survive in very wet habitats or submerged in/at the surface of water.

State the function of xylem and phloem

Xylem - transports water and minerals and structure Phloem - transports sucrose (and amino acids etc.)

Name the two types of transport vessels in vascular bundles

Xylem and phloem

Compare the structure and function of xylem and phloem

Xylem dead, phloem alive Xylem contain lignin Xylem transport water, phloem sucrose Phloem have companion cells

Define the terms "adhesion" and "cohesion"

adhesion - sticking together of particles of different substances cohesion - sticking together of particles of the same substance

Describe 5 functions of water in plants

maintaining cell turgidity for structure and growth transporting nutrients and organic compounds throughout the plant comprising much of the living protoplasm in the cells serving as a raw material for various chemical processes, including photosynthesis through transpiration, buffering the plant against wide temperature fluctuations

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 pass sieve plate - an area of relatively large pores present in the common end walls of sieve tube elements companion 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.

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 cells guard cell - cells that can open and close the stomatal pores controlling gaseous exchange and water loss in plants

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 stomata transpiration stream - the movement of water through a plant from the roots until it is lost by evaporation from the leaves transpiration pull - the force which aids in drawing the water upward from roots to leaves

Define the terms "vascular system" and "vascular bundles"

vascular system - a system of transport vessels in animals or plants vascular bundles - the vascular system of herbaceous dicots. composed of xylem and phloem tissue