Chapter 7- Transport in plants Flashcards
What are the 2 transport systems in plants
Xylem
phloem
Give 4 reasons for the need of transport in plants
-move substances from where they are absorbed to where they are needed
-move substances from where they are made to places for metabolism
-move substances for storage
-diffusion in plants for both CO2 and oxygen are essential for photosynthesis and respiration
describe the arrangement of the vascular bundle in roots
the xylem are found at the centre and contains a series of arms between which the phloem is found
Describe the Epidermis
- a continuous layer on the outside of the plant and is one cell thick which provides protection. In leaves it contains pores called stomata
Describe the schlerenchyma fibres
They provide extra support for the stem
Describe the parenchyma
-Made up of thin cell walls which act as a storage unit for food
-they prevent wilting due to their turgidity
-the layer contains air spaces that allow gas exchange
-this layer forms the cortex in roots and in stems they create the pith
Describe collenchyma
These are cells that are a more modified version of parenchyma but contain more cellulose to provide extra strength
Describe the Endodermis
This surrounds the vascular tissue and is one cell thick in stems and in roots
Describe the mesophyll
-they are made up of specialised parenchyma cells
-they are found between the lower and upper epidermis
-they contain a lot of chloroplasts for photosynthesis
describe the pericycle in roots and stems
Roots- they are one cell thick and new roots can form from this layer
Stem- it is formed from a tissue called sclerenchyma This has dead, lignified cells for extra strength.
Describe the structure of xylem
- made up of dead cells called xylem vessels that have no end walls
- these cells form an end to end tube
- cells are reinforced with a waterproof material called lignin
- contain parenchyma cells and tracheid fibres
- these cells have non-lignigied pits for transporting water
- sclerenchyma cells provide extra support
what are the 2 function of the xylem
-provides mechanical support and strength
-allows long distance transport of water and mineral salts
what are the 5 steps taken for the transport of water to the leaves
1-this begins in the leaves
2-heat from the sun causes evaporation
3-resulting into a change of the water potential gradient in the leaf
4-therefore water moves from a higher potential to a lower potential down their gradient
5-this movement is passive as it is driven by evaporation
How is water replenished after transpiration
water leaves a xylem vessel through a non-lignified area (pit) by entering the cytoplasm or cell wall. this water replaces the water lost
which factors affect transpiration
-humidity
-wind
-temperature
-dry conditions
-light intensity (opening of stomata)
state 4 adaptations of xerophytes
1-thick cuticles preventing water loss
2-sunken stomata trap moist air to prevent a diffusion gradient
3- leaves have layers of hair to trap moist air
4-leaves are either spines or folded leaves to provide a small surface area and hide stomata
how does the hydrostatic pressure in the xylem differ
at the top of the xylem vessel the pressure becomes lower than at the bottom causing water to move in a continuous column
how is root pressure caused
-This is caused by the concentration of solutes in the xylem. When there’s the presence of solutes in the xylem, it causes a lower water potential and more water is needed to be drawn in
what are cohesion and adhesion forces
Cohesion- water molecules are attracted to each other through hydrogen bonding
Adhesion- water molecules are attracted to the cellulose and the lignin in the cell walls
Symplastic VS Apoplastic
symplastic- Water and solutes move through the cytoplasm, vacuole and plasmodesmata from cell to cell
Apoplastic- water and solutes move in between the cell wall through the intracellular spaces
what prevents the apoplastic pathway
The casparian strip present in the endodermis which is created by Suberin a waxy cuticle in the cell walls
mineral ions are absorbed by the process of
Active transport
how is hydrostatic pressure caused by translocation
High amounts of sucrose in a sieve element decreases the water potential, this causes water to move down its gradient. the water causes a mass flow of dissolves solutes and sucrose to the sink
outline how sucrose is loaded onto the phloem
1-this occurs by AT with a companion cell, the hydrogen ions are pumped into the companion cell
2-this creates high excess amount of hydrogen ions in the cell walls (apoplastic pathway)
3-the hydrogen ions can move back to the cell through a co-transporter, this has to include sucrose.
4-sucrose then moves from the cell walls to the cell and from there to the sieve tube, using the symplastic pathway.
What are the differences between the xylem vessels and sieve tube elements
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- xylem used dead cells while phloem uses living cells
- xylem vessels have lignified cell walls and phloem does not
- the xylem maintains a negative pressure in comparison to the phloem that has a positive pressure gradient
- sieve tubes have a thin layer of cytoplasm and no nuclei while the xylem is connected by end walls
