9.1-9.5 Transport in plants Flashcards
(54 cards)
1
Q
Why do plants require a transport system?
A
- to ensure that all the cells of a plant receive a sufficient amount of nutrients
2
Q
How do plants receive sufficient amounts of nutrients?
A
- xylem tissue
- phloem tissue
3
Q
What is the role of xylem tissue?
A
- enables water as well as dissolved minerals to travel up the plant in the passive process of transpiration
4
Q
What is the role of phloem tissue?
A
- enables sugars to reach all parts of the plant in the active process of translocation
5
Q
Description of the vascular bundle in the roots.
A
- xylem and phloem are components of the vascular bundle which serves to enable
transport of substances as well as for structural support
he xylem vessels are arranged in an X shape in the center of the vascular bundle. - this enables the plant to withstand various mechanical forces such as pulling
- the X shape arrangement of xylem vessels is surrounded by endodermis, which is an
outer layer of cells which supply xylem vessels with water. - an inner layer of meristem cells known as the pericycle
6
Q
Description of the vascular bundle in the stem.
A
- xylem is located on the inside in non-wooded plants to provide support and
flexibility to the stem - phloem is found on the outside of the vascular bundle
- there is a layer of cambium in between xylem and phloem, that is meristem cells
which are involved in production of new xylem and phloem tissue
7
Q
Description of the vascular bundle in the source/ leaf.
A
- the vascular bundles form the midrib and veins of a leaf
- dicotyledonous leaves have a network of veins, starting at the midrib and spreading
outwards which are involved in transport and support
8
Q
Features of the xylem tissue are …
A
- transport water and minerals
- serve to provide structural support
- long cylinders made out of dead tissue with open ends = can form continuous column
-vessels contain pits which enable water to move sideways into other vessels - thickened with a tough substance (lignin) which is deposited in spiral patterns to allow the plant to remain flexible
- water can only flow upwards
9
Q
Features of phloem tissue are …
A
- tubes made of living cells
- involved in translocation which is the movement of nutrients to storage organs and growing parts of the plant
- consist of sieve tube elements and companion cells
- sieve tube elements form a tube to transport sugars such as sucrose, in the dissolved
form of sap and can be transported upwards or downwards - companion cells are involved in ATP production for active processes such as loading
sucrose into sieve tubes - cytoplasm of sieve tube elements and companion cells is linked through structures
known as plasmodesmata
10
Q
Plasmodesmata is …
A
are gaps between cell walls which allow
communication and flow of substances such as minerals between the cells
11
Q
Transpiration is …
A
- the process where plants absorb water through the roots, which then moves up through the plant and is released into the atmosphere as water vapour through pores in the leaves
- carbon dioxide enters, while water and oxygen exit through a leaf’s stomata.
12
Q
Transpiration stream is …
A
- the movement of water up the stem, enables processes such as photosynthesis, growth and elongation as it supplies the plant with water which
is necessary for all these processes
13
Q
What does the transpiration stream provide the plant with?
A
- required minerals
14
Q
How does the plant control it’s temperature?
A
- via evaporation of water
15
Q
When does transpiration involved osmosis?
A
- water moves from the xylem to the mesophyll cells
16
Q
When does transpiration involve evaporation?
A
- from the surface of mesophyll cells into intercellular spaces and diffusion of water vapour down a water vapour potential gradient out of the stomata
17
Q
How can the rate of transpiration be measured?
A
- by using a potometer
- where water vapour lost by the leaf is replaced by water in the capillary tube
18
Q
What is physically measured on the potometer?
A
- measuring the movement of the meniscus can be used to determine the rate of transpiration
19
Q
Factors affecting the rate of transpiration include …
A
- number of leaves
- number/size or position of
stomata - presence of waxy cuticle, the amount of light present
- the temperature
- humidity
- air movement
- water availability.
20
Q
Xerophytes are …
A
- plants adapted to living in dry conditions
21
Q
What are the adaptations of xerophytes benefiting?
A
- minimises water loss
22
Q
What are the adaptations of xerophytes?
A
- smaller leaves to reduce the surface area for water loss
23
Q
What do xerophytes respond to?
A
- low water availability by closing the stomata to prevent
water loss
24
Q
How does xerophytes prevent water loss via evaporation?
A
- densely packed mesophyll
- thick waxy cuticle
25
What xerophytes contain to trap moist air and what does this do?
- hairs
- pits
- reduces water vapour potential
26
What do the leaves of xerophytes do and why?
- roll up leaves
- to reduce the exposure of lower epidermis to the atmosphere
- by trapping air
27
Hydrophytes are ...
- plants that actually live in water such as water lilies
28
What adaptations do hydrophytes have for their environment?
- very thin or absent waxy cuticle as they don’t need to conserve water
- many constantly open stomata are found on the upper surfaces of leaves to maximise gas exchange
- wide, flat leaves give a large surface area for light absorption
- air sacs are found in some hydrophytes to enable leaves to stay afloat
- many large air spaces to make leaves and stems more buoyant
29
How does water enter the roots?
- root hair cells
- moves into the xylem tissue located in the center of the root
30
What does the water uptake through the root hair cells cause and why?
- water potential gradient
- the water potential is higher inside the soil than inside the root hair cells due to the dissolved substances in the cell sap
31
What is the purpose of root hair cells in movement of water in the roots?
- to provide a large surface area for the movement of water to occur
32
How are minerals absorbed through the root hair cells and why?
- active transport
- as they need to be pumped against the concentration gradient
33
What are the two ways that water can be taken up by the root hair cells can move across the cortex of the root into the xylem?
- symplast pathway
- apoplast pathway
34
How does water transport through the symplast pathway?
- enters the cytoplasm through the plasma membrane
- passes from one cell to the next through plasmodesmata
35
Plasmodesmata is ...
- the channels which connect the cytoplasm of one cell to the next
36
How does water transport through the apoplast pathway?
- water moves through water filled spaces between cellulose molecules in the cell walls
37
What is the benefit of water not passing through the plasma membrane?
- it can carry dissolved mineral ions and salts
38
What happens when the water reaches the endodermis?
- it encounters a layer of
suberin which is known as the Casparian strip which cannot be penetrated by water
39
What has to occur for the water to cross the epidermis?
- the water that has been moving through the cell walls must now enter the symplast pathway
40
What happens once the water has moved across the epidermis?
- the water continues down the water potential gradient from cell to cell until it reaches a pit in the xylem vessel which is the entry point of water
41
How is water removed from the top of the xylem vessels into the mesophyll cells?
- down the water potential gradient
42
What is the push of water upwards aided by?
- root pressure
43
What is root pressure causing?
- where the action of the endodermis moving minerals into the xylem by active
transport drives water into the xylem by osmosis, thus pushing it upwards
44
How is the flow of the water maintained and what do these two forces in combination support?
- with the help of surface tension of water
- the attractive forces between water molecules known as cohesion
- tension-cohesion theory and capillary action
45
What is tension-cohesion theory and capillary action?
- the forces involved in cohesion cause the water molecule to adhere to the walls of xylem, thus pulling water up
46
Translocation is ...
- an energy requiring process which serves as a means of transporting assimilates such as sucrose in the phloem between sources which release sucrose - - such as leaves and sinks e.g. roots and meristem which remove sucrose from the phloem
47
How does sucrose enter the phloem?
- active loading
- where companion cells use
ATP to transport hydrogen ions into the surrounding tissue, thus creating a diffusion
gradient, which causes the H+ ions to diffuse back into the companion cells
48
Where does the sucrose diffuse into after facilitated diffusion in the companion cells?
- sucrose diffuses out of the
companion cells down the concentration gradient into the sieve tube elements through
links known as plasmodesmata
48
Active loading is a form of what?
- facilitated diffusion
- involving cotransporter proteins which allows the returning H+ ions to
bring sucrose molecules into the companion cells, causing the concentration of sucrose in the companion cells to increase
49
What happens in the sieve tube elements once sucrose has entered?
- water potential inside the tube is reduced
- causing water to enter via osmosis
- increasing the hydrostatic pressure of the sieve tube
50
How does water move around the sieve tube?
- from an area of higher
pressure to an area of lower pressure
51
How is sucrose eventually removed from the sieve tube?
- active transport or diffusion
- into the surrounding cells
- increasing the water potential of the sieve tube
52
How does water leave the sieve tube?
- osmosis
- reducing the pressure in the phloem at the sink
53
Summarise translocation.
- the mass flow of water from the source to the sink down the
hydrostatic pressure gradient is a means of supplying assimilates such as sucrose to where they are needed
