Chapter 7: Transport in Plants Flashcards
Why do plants not need a high surface area to volume ratio?
Thay has very extensive root networks that only need simple diffusion. It is not as compact as animal cells are.
What are the main reasons for why transport is important in plants?
- To move absorbed substances to where they are needed.
- To move produced substances like glucose from e where they are produced to where they are needed.
- To move substances to their respective storage organs.
How are plants adapted for maximum oxygen absorption?
they are flat and have large surface areas.
Why do plants not need any complex transport mechanisms for oxygen transport?
The branching nature of the plant provides sufficient surface area. The oxygen is a waste product of photosynthesis.
What is the xylem?
It is the plant tissue that carries water and mineral ions from the roots to the cells. It works in 2 directions.
What is the phloem?
It is the plant tissue that carried the products of photosynthesis to the other parts of the plant.
What is the parenchyma?
It is the cellular tissue, typically soft and succulent found chiefly in the softer parts of the leaves, pulp of fruits, bark and pith of stems.
What is the function of of the parenchyma cells.
They function in storage and photosynthesis and as the bulk of ground and vascular tissues.
Describe the activity of parenchyma cells.
They are very metabolically active
What are the collenchyma cells?
They are cells that are similar to parenchyma, but have cellulose deposits which makes them stronger
Where do we find the collenchyma cells?
In the midrib
What is the endodermis?
It is the inner layer of cells in the cortex of a root and some stems surrounding a vascular bundle.
How does the endodermis prevents water from seeping through?
It has an impermeable ring of Suberin around it to form the Casparian strip that prevents water from seeping through.
What is Suberin?
It is an impermeable and inner waxy substance in the cell wall of corky tissue.
What is the nature of the casparian strip?
it is hydrophobic
What are mesophyll cells?
They are a type of specialised parenchyma cells that are able to photosynthesise.
What are the two types of mesophyll cells?
Palisade and Spongy
What is the pericycle?
It is a thin layer of plant tissue between the endodermis and phloem that encircles the vascular tissue.
What is a feature of the pericycle and its respective function due to that feature?
It is meristematic
It allows lateral root initiation and allows for secondary root growth
What is the pericycle cells made of?
Parenchyma and Sclerenchyma
Describe the xylem vessel
The xylem is made of cells called xylem vessel elements, which are reinforced by lignin.
What are the functions of xylem vessels?
They transport water through long distances and give the plant mechanical strength
What is a vascular bundle?
It is a bundle like structure formed by the xylem and phloem.
What is the function of sclerenchyma fibres?
They provide support to the xylem vessels due to their lignified nature.
Why do both the stems and the roots require xylem?
Because they have to withstand strains caused by each other.
What is the function of the sieve tube elements in the phloem?
The long transport of of organic compounds in the phloem is carried out by the living cell known as a the sieve tube elements.
What is the pith?
Is a tissue in the stems made from soft, spongy parenchyma.
What is the function of the pith?
It stores transport nutrients and provide support from the centre
What is the difference in the structure of xylem and phloem in roots and stems?
In the xylem it is alternating and in the phloem it is radial/angular/on the same axis.
What are meristems?
Is the region of a tissue in plants that is actively dividing found mainly in root tips and the vascular cambium.
What is vascular cambium?
It is a single layer of meristematic that undergo expansion during the transition from primary growth to secondary growth.
Why does the vascular cambium have to divide and replicate?
In order to replace phloem and xylem.
What happens in case the vascular cambium is absent?
The parenchyma cells, which have meristematic activity will divide.
Describe the nature of water transport.
It is a passive process that is driven by evaporation from leaves.
What is transpiration?
The loss of water vapor from a plant to its environment, by diffusion down a water potential gradient ; most transpiration takes place through the stomata in leaves.
What is the function of guard cells?
They regulate the influx of CO2 and water.
Why are stomata on the underside of the leaf?
They are under leaf in order to reduce the exposure to sunlight and to prevent damage to osmotic balance when it rains.
How does water enter a plant cell?
Through a non-lignified region called the pit.
What are the factors that affect transpiration?
Humidity
Wind speed and temperature
Light intensity
Very dry conditions
What is the main function of transpiration?
To act as a cooling mechanism.
What is the difference between the epidermis of monocots and of dicots?
Monocots have longer epidermis and dicots have a more rounded epidermis.
What can we investigate using an epidermal peel?
We can investigate whether or not stomata close under certain conditions.
What is the instrument that can be used to compare rates of transpiration?
A Potometer
How can we use a Potometer to know the rate of transpiration?
Water is drawn by the capillary tubing as it transpires, so the air-water meniscus will move.
A graph can be plotted for the movement of the meniscus to understand the rate of transpiration.
What are Xerophytes?
They are plants that have adapted to survive in conditions where water is in short supply and where water loss has to be kept to a minimum.
Why might the leaves of a Xerophyte roll up?
So that they will expose their thick cuticle outside.
Why do Xerophytes have hairs
Hairs trap water vapour and will therefore reduce the the water potential gradient, which reduces the loss of water.
What are the ways that water might move from the xylem across to the phloem?
It may take the symplastic or apoplastic pathways.
What are the characteristics of xylem tissue?
- The Cells are joined end to end to form tubes
- The Cells are dead
- The Cell walls are thickened with lignin.
What are vessel elements?
It is a dead, lignified cell found in xylem specialised for the transporting of water and support; the ends of the cell break down and join to form a xylem vessel.
Describe the structure of Xylem tissue.
They are composed of xylem vessel elements joined end to end and supported by lignified sclerenchyma fibres.
What are the two types of lignification in the xylem?
Annular thickening composed of lignin rings and spiral thickening composed of lignin spirals.
What are trachieds?
They are interlinked tapered cells, that serves in the transport of water and mineral ions.
How does water move up the xylem?
Down a hydrostatic water potential gradient.
Why do plants have lignified cell walls?
Lignification is there to prevent the collapse of the xylem due th high water potential gradient
What does cohesion and adhesion mean?
Cohesion means that the water molecules form hydrogen bonds between each other allowing the the water to move in an unbroken column during transpiration.
Adhesion means that the water molecules attach to the walls of the xylem to ensure that the column of water does not separate away from it.
Why might the vascular bundles be made of xylem with very small diameters?
This is to prevent air lock.
What does air lock mean?
Air lock happens when the water column breaks due to an air bubble and there is no longer a hydrostatic water potential gradient.
What part of the xylem allows to bypass an air lock?
The pit.
What does root pressure mean?
It is when the plant raises the water potential by secreting solutes to lower the water potential and cause an influx of water.
What happens at the casparian strip when water moves from the root hair to the xylem?
Once water enters the endodermis, the casparian strip uses its suberin to block the apoplastic pathway. The only way will be through the endodermal cytoplasm.
What is the role of passage cells?
They allow the control of movement of mineral ions.
What is the role of root hair?
They increase the surface area to absorb mineral ions like nitrate and magnesium.
What are mycorrhinzas?
It is when the root hair like fungi absorb water for the plant in exchange for some of the organic molecules.
What are the different mechanisms used by the plant in order to transport mineral ions?
Active transport, Facilitated diffusion and diffusion.
What does translocation mean?
Is the movement of assimilates (substances made by the plant) either through the phloem or the xylem to move organic substances within the plant.
What are the structures present in the phloem that aid translocation?
Sieve elements, companion cells, parenchyma and fibres.
What is a sieve tube
They are living structures structures present in the pholem that. Are attached to the phloem that are absent of nucleus or ribosome and have very little cytoplasm.
What are sieve plates?
they are pored structures that are formed when sieve elements are met end to end. They all the free flow of liquids.
Why is it very difficult to extract phloem sap?
Cutting the phloem causes a reduction in pressure and the sieve tubes block phloem flow so the sap does not escape.
What is callose?
It is a carbohydrate that repairs damages caused to the phloem to prevent any excess loss of phloem sap.
How the mass flow of sucrose into the phloem work?
Sucrose is loaded causing an decrease in the water potential, which causes an inward flow of water which increases the pressure potential.
describe the loading of sucrose into the phloem.
H+ ions are pumped in by a companion cell to fluctuate the the water potential gradients and to convert ATP to ADP to provide energy for the active transport of, both which aid the mass flow into the phloem. The sucrose is carried by a co transporter protein.
How does the unloading of sucrose from the phloem occur?
It is a similar process to that of loading of sucrose. However during unloading, the sucrose is broken down by enzymes and so, the concentration gradients and therefore the water potential gradients fluctuate.
Differentiate between the xylem cells and the phloem cells.
Xylem is dead, phloem is living
Xylem cells are lignified and thus, they are able to die and still continue mass flow. Phloem cells encourage mass flow my not having a nucleus.
Xylem cells do not form any end walls while phloem forms sieve plates
Xylem doe snot have any self repairing mechanism, but phloem has callose
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