3.1.3 Transport In Plants Flashcards
Structure and function of root hair cell?
Collect water and mineral nutrients that are present in the soil and take up these in solution up through the roots to the rest of the plant.
Structure and function of epidermis?
Protects against water loss, regulates gas exchange, secretes metabolic compounds, and absorbs water and mineral nutrients
Structure and Function of Piliferous layer?
Region of the epidermis of the root; produces abundant root hairs and is involved in the uptake of water and nutrients
Structure and function of endodermis?
A single layer of cells that borders the cortex of a root. The endodermis functions allows the root to select what gets into the vascular core.
Structure and function of the cortex?
The outermost layer of the stem or root of a plant. It transports materials into the central cylinder of the root through diffusion and stores food in the form of starch
Structure and Function of the casparian strip?
A band of waterproof tissue that is found on the side and walls of the endodermis of roots. The strip prevents the water from entering the pericycle except through the cytoplasm of endodermal cells. This may be important in producing root pressure
Structure and Function of pericycle?
Provide support,structure + protection cells surround the xylem and phloem in the stem
What is the symplast pathway?
The symplast pathway is where water moves between cytoplasm/vacuoles of adjacent cells across the cortex of the root.
What is the apoplast pathway?
the apoplast pathway can only take water a certain way; near the xylem, the Casparian strip forms an impenetrable barrier to water in the cell walls, and water must move into the cytoplasm to continue. Through the cell walls of the cells.
What are the connecting passages called?
Plasmodesmata
What is a monocotyledonous plant?
1 seed leaf
What is a dicotyledonous plant?
2 seed leaves
What are parenchyma?
Packing cells of the plant?
What does the position of the vascular bundle determine?
In the stem, the position of the vascular bundle (in a ring) helps to support the stem against sideways forces
Why is water important?
It is a substrate for photosynthesis
It is a pathway for transport of mineral ions through the plant
It provides support through turgidity
Evaporation may help to cool leaf surfaces
Describe the process of water transport through the plant?
Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Water is drawn from the cells in the xylem to replace that which has been lost from the leaves.
Water molecules inside the xylem cells are strongly attracted to each other. There is strong cohesion between the molecules because of hydrogen bonding. A continuous column of water is therefore pulled up the stem in the transpiration stream by evaporation from the leaves.
As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots.
Atmospheric conditions affecting transpiration?
Wind
High Temperatures
Low Humidity
High Light Intensity
What are the 2 functions of the xylem?
Support and transport of water and mineral ions
Structure and function of Xylem?
Dead cells when functioning in the xylem.
Long and hollow; several columns of cells fusing together end to end
No end cell walls = hollow tube
Tannin deposits
Lignificad secondary walls = provide extra mechanical strength. Lignin found in rings, spirals or tubes.
Bordered pits without lignin where water leaves the xylem and moves into other cells of the plant.
No nucleus, no cytoplasm, no vacuoles one lignified cells.
Waterproof due to lignin
What tissue is the phloem made out of?
Living tissue
What is the function of the phloem?
Transporte food in organic solutes from the leaves.
Supplies cells with sugars and amino acids needed for cellular respiration and the synthesis of other molecules.
How many ways can transport travel in the phloem?
2 ways
What is the structure of sieve tube elements in the phloem?
Cells joined end to end to form long hollow structure.
Not lignified.
Walls perforate today form sieve plates which are porous.
Filled with phloem sap.
Mature cells have no nucleus.
What structures do companion cells form in phloem?
Form with sieve cells.
Liked to elements by plasmodesmata.
Maintained nucleus and organelles because companion cells are metabolically active.
Function like a life support system for plants.
What are the 3 mechanisms of water transport?
Capillarity
Root pressure
Cohesion tension theory
Explain capillarity
Against the force of gravity., narrow diameter.
Strong intermolecular forces of attraction between water molecules- cohesion.
Attraction between water and sides of vessel - adhesion
Capillarity cannot act alone due to the maximum height capacity travelled by capillarity.
Explain root pressure theory?
Result of active secretion of ions across endodermal cells of the root and subsequence osmotic flow.
Again root pressure is too small to act alone but does play a contributory role.
Explain the cohesion tension theory?
When a water molecule is lost via transpiration another one is pulled along by the processes of cohesion and tension. Water is polar which means that molecules are attracted to one another which creates surface tension.
Transpiration pull which utilises capillary action and the inherent surface tension is the primary mechanism of water movement in plants.
How does the gradient of water potential change as you’ve towards the stomata?
The gradient of water potential decreases as you move towards the stomata as water leaves the stomata in the form of water vapour
What is transpiration?
Transpiration: is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by the diffusion of water vapour through the stomata
What is translocation?
Translocation is the movement of organic compounds from where they are made at their source, to where they are required at their sink. It is an active process which can be used to transport phloem up or down the plant.
Examples of sources?
Green leaves
Stems
Storage organs
Food stored in seeds
Examples of sinks?
Growing roots
Active processes
Meristem cell activity
Developing stores eg fruits
What graph proves the cohesion tension theory?
Dendograph
What kind of process is translocation?
An active process
Explain the process of translocation in plants?
Aerobic respiration in the mitochondria produces ATP
H+ ions are pumped out
Cotransporter protein or proton pump
H+ ions then return to companion cells with a sucrose molecule
This sucrose then diffuses into sieve tube elements
What is the mass flow hypothesis?
The mass flow Hypothesis suggests that there is a passive movement of sucrose from the phloem where it is most concentrated to other areas like growing tissues were sucrose is less concentrated i.e. the sink
Explain the mass flow hypothesis?
Source cells (mesophyll cells) produce sucrose during photosynthesis which decreases the water potential of the cell. Water diffuses vía osmosis from the xylem down a w.p gradient.
Causes hydrostatic pressure to build up and sucrose molecules to be forced out of the cell into the phloem.
Pressure pushes sucrose down towards the sink cells = mass flow hypothesis
At the sink cell, the sucrose is either used for respiration or converted into insoluble starch for storage.
Evidence that the phloem is the tissue for translocation?
Ringing / girdling
Carbon-14 labelled sucrose (radioactive tracers)
Experiments using aphids
At what point are stomata closed?
When water leaves the guard cells and therefore the guard cells are flaccid
At what point are stomata open?
Stomata are open when the guard cells are turgid, filled with water.
Mechanism for the opening of the stomata?
Blue light
ATP —> ADP + Pi
This reaction produces energy to pump H+ ions out = active transport
PROTON PUMP
H+ ions renter taking Cl- ions through passive transport > co transport
Potassium back in to balance charges
Decrease w.p
Water enters vía osmosis down a w.p gradient
Explain the adaptation of sunken stomata?
Creates a chamber of humidity which Traps water vapour and keeps humidity high. This reduces the W.p gradient which reduces evaporation. As a result transpiration is reduced.
Explain how a covering of leaf epidermal hairs helps xerophytes survive in their habitat?
The presence of hers creates a chamber of high humidity to trap water vapour.This reduces a w.p gradient which reduces evaporation. As a result of reduced evaporation the transpiration rate is also reduced.
Explain why water loss from a plant is unavoidable?
Transpiration, and resulting water loss, is unavoidable as the leaves’ stomata need to be open to let in carbon dioxide for photosynthesis.
Adaptations of hydrophytes?
Thin / no waxy cuticle - transpiration is not an issue
Presence of aerenchyma
Stem hypertrophy
Submerged dissected leaves
Location of stomata
What are aerenchyma and what do they do?
Aerenchyma is a modified parenchyma, where the cells are arranged with regular air spaces or air chambers to facilitate diffusion of gases to provide buoyancy to aquatic plants such as lotus and water hyacinth.
How does the location of stomata on hydrophytes and xerophytes differ?
Xerophytes - lower surface to reduce transpiration rate
Hydrophytes-
