Transport in plants Flashcards
(49 cards)
1
Q
What are dicotyledonous plants?
A
- Plants that have two seed leaves
- Also have vascular tissue distributed throughout the whole plant
2
Q
What other tissue do vascular bundles contain and what do they do?
A
- Collenchyma and schelerenchyma for strength and support to help the plant
3
Q
Why do plants need a transport system?
A
- Every cell of a multicellular plant needs a regular supply of oxygen, water, nutrients and minerals
- plants are not very active and their respiration rate is low, the demand for oxygen is low
- this demand can be met by diffusion
- demand for sugar and water is still high
- plants need a transport system to move water and minerals from the roots to the leaves, sugars from the leaves to the rest of the plant
- Especially important as a plant must be able to transport substances up the stem against gravity
4
Q
Describe the structure of the xylem and phloem in the young root?
A
- Found at the centre of a young root
- arrangement (X) provides strength to withstand the pulling forces which roots are exposed to
- around the vascular bundle there is endodermis which acts as a water supply for the xylem vessels
- in the endodermis there is a layer of meristem cells called the pericycle
5
Q
Describe the xylem and phloem in the stem
A
- Xylem is on the inside to provide support and flexibility, phloem on outside
- inbetween xylem and phloem there is cambium which is a layer of meristem cells that divide to form new xylem and phloem cells
6
Q
Describe the arrangement of xylem and phloem in a leaf
A
- vascular bundles form the midrib and veins of a leaf
- a dicotylendonous leaf has a branching network of veins that get smaller as they spread from the midrib
- xylem is loacted ontop of phloem
7
Q
What does the xylem tissue consist of?
A
- Vessels to carry the water and dissolved mineral ions
- fibres to help support the plant
- living parenchyma cells which act as packing tissue to separate and support vessels
8
Q
What does lignin do?
A
- impregnates the walls of the cells, making them waterproof and in turn killing them
- strengthens vessel walls and prevents vessels from collapsing
- keeps vessels open even at times when water may be short in supply
9
Q
What happens to the end walls and contents of the xylem?
A
- the end walls and contents decay, leaving a long column of dead cells with no contents (a tube)
10
Q
What are the patterns formed by lignin and what do they do?
A
- spiral
- annular
- reticulate
- prevents the vessel from being too rigid and allows flexibility of the stem or branch
11
Q
What happens when lignification is not complete?
A
- It leaves gaps in the cell wall that forms bordered pits
- bordered pits in two adjacent vessels are aligned to allow water to leave one vessel and enter the next
12
Q
What are adaptations of xylem to their function?
A
- xylem vessels are made from dead cells aligned from end to end to form a continuous column (flow of water is not impeded, no cell contents)
- The tubes are narrow so that the water column does not break easily and capillary action can be effective
- bordered pits allows water to move sideways (no cross walls)
- Lignin allows xylem to stretch as the plant grows, allows flexibility
- Lignin thickening prevents the walls from collapsing
13
Q
Describe the structure and function of phloem
A
- used to transport assimilates around the plant
- sucrose is dissolved in water to form sap
- sieve tube elements are lined up end to end to form tubes, no nucleus or cytoplasm leaving space for mass flow of sap
- at the ends of sieve tubes there are perforated cross walls called sieve plates which allow movement of sap
- companion cells have mitochondria to produce the ATP needed for active processes, carry out metabolic processes needed to load assimilates into sieve tubes
14
Q
What does assimilates consist of?
A
- sucrose and amino acids
15
Q
What is the plasmodesmata?
A
- cytoplasmic connections betweeen adjacent plant cells, passing through pits in cell walls
- The plasmodesmata is a channel through the plant cell wall that allows molecules and substances to move in and out of the cell.
16
Q
Why is water important for the plant?
A
- Turgor pressure= supports the plant, helps drive roots through soil
- Loss of water through leaves cools the plant
- Transports mineral ions and assimilates
- needed for photosynthesis
17
Q
How does water move into the root from the soil?
A
- Mineral ions are absorbed from the soil which lowers the water potential of the cytoplasm
- Water moves across the root cortex by osmosis via the apoplast pathway
- Mineral ions are actively transported into the medulla which lowers the water potential
- This causes water to follow by osmosis
18
Q
How are root hair cells adapted as exchange surfaces?
A
- their microscopic size meas they can penetrate between soil particles
- each microscopic hair has a large SA:V ratio and there are thousands on each root tip
- each hair has a thin surface layer through which diffusion and osmosis takes place quickly
- concentration of solutes in cytoplasm of root hair cells maintains a WP gradient between soil water and cell
19
Q
What is the symplast pathway?
A
- Water moves through the symplast (the continuous cytoplasm of the living plant cells connected by the plasmodesmata)
20
Q
What is the apoplast pathway?
A
- movement of water through the apoplast (the cell walls and the intracellular spaces)
21
Q
What is the role of the casparian strip?
A
- It is made of waterproof subarin which stops water in the apoplast pathway
- water is forced into the cells to create a WP gradient
- the casparian strip is a band of waxy material
- prevents toxins reaching the rest of the plant as there are no transport proteins in the plasma membrane)
22
Q
How does water enter the xylem?
A
- endodermal cells actively transport mineral ions into xylem
- WP of xylem is lower than the endodermal cells
- water moves by osmosis into xylem cells
- results in root pressure and gives water a small push up the xylem
23
Q
Describe the process of transpiration
A
- water diffuses out of stomata through the substomatal air space
- water vapour evaporates from the cell walls of the spongy mesophyll cells into substomatal air
- this reduces the water potential of those cells compared to the ones adjacent
- water moves by osmosis from adjacent cell
- water moves from xylem to cells next to xylem
- water is drawn up xylem in a continuous stream to replace the water lost
24
Q
Describe the movement of water through the plant
A
- (water uptake and movement across root)
- Cohesion of water enables water to move by mass flow and is pulled by tension from above
- Movement of water out of the xylem creates low HS pressure and tension
- Osmosis moves water across leaf which then evaporates from the cell surface
- Diffusion of water vapour out of leaf
25
What is the transpiration stream?
- movement of water up xylem from roots to replace that lost by transpiration
26
What is cohesion tension?
- the pull of water and the attraction between water molecules causing tension in the xylem vessels which brings about movement
27
What is evidence for the cohesion tension theory?
- Tree trunks changing size, increases at night and redues when transpiration is greatest due to pressure
- plant will wilt as water can longer be drawn up, the column has been broken
28
What are 5 factors affecting the rate of transpiration?
1. Temperature (high temp, more evap, more diffusion due to more Ek, decrease humidity, diffuse out of leaf)
2. more gas exchange as stomata are open
3. high humidity
4. wind
5. water availability
29
Define transpiration
- the evaporation of water from the leaves of a plant
- occurs when the plant opens stomata to exchange oxygen and CO2
30
What is meant by source?
Any part of the plant that loads sucrose into the sieve tube
31
Give examples of sources
- green leaves
- storage organs like tubules
- food stores in seeds when GERMINATING
32
What is meant by sink?
- Anywhere that removes sucrose from the phloem sieve tubes
- Sucrose can be used for respiration and growth in a meristem or converted to starch for storage in roots
33
Give examples of sinks
- growing roots
- roots actively transporting mineral ions
- meristems actively dividing
34
Describe the active loading of the phloem
1. H+ ions actively pumped out of companion cell using energy from the hydrolysis of ATP
2. High conc of H+ ions cause facilitated diffusion back into companion cell.
3. Sucrose is carried with H+ ions through cotransport proteins
4. Increasing conc of sucrose in companion cell causes it to diffsue through plasmodesmata into sieve tube
35
What is the significance of the endodermis?
1. Helps regulate the movement of water, ions and hormones into and out of the vascular system
2. May store starch or protect the plant against toxins moving into the vascular system
3. once water has entered the medulla it cannot pass back due to the casparian strip blocking the apoplast pathway of endodermal cells.
4. Acts as a final filtration device before the water and dissolved mineral ions reach the stele
36
How can a sieve tube transport sucrose during different times of the year?
1. Early spring, roots, starch converted to sucrose, enables growth in spring
2. Sugars made in photosynthesis converted to sucrose, loaded into sieve tubes, happens during late spring, summer and early autumn which makes leaves green
37
Describe the process of the cohesion tension theory
1. Minerals are actively transported into the xylem which lowers WP and causes water to follow by osmosis
2. Cohesion of water enables water to move by mass flow
3. Water is pulled up by tension from above
4. Tension is caused by the movement of water out of the xylem, this also causes low HS pressure
38
How does root pressure cause water to be pushed up?
- Action of endodermis moving minerals into medulla and xylem by active transport draws water into medulla by osmosis
- Pressure in the root medulla builds up and forces water into xylem
- This pushes water up the xylem
39
What does capillary action do?
-Plants use capillary action to bring water up the roots and stems to the rest of the plant
- The water molecules are attracted to the stem (adhesion)
- Adhesion is used to help force the water up from the ground and disperse it through the plant
40
What must plants living on land be adapted to?
- Reduce the loss of water
- replace the water that is lost
41
Name examples of how terrestrial plants can reduce water loss by adaptations
- Waxy cuticle on the leaf
- Stomata under side of leaf, reduces evaporation due to direct heating from the sun
- Stomata close at night
- Deciduous plants lose leaves in winter when ground is frozen and when temps are too low for photosynthesis
42
What are xerophytes?
A plant that is adapted to living in arid conditions
42
What are adaptations of marram grass?
1. Leaf is rolled longitudinally, humid air inside, reduce water lost by evap
2. Thick waxy cuticle on outer side of rolled leaf
3. Stomata on inner side, protected by enclosed air space
4. Stomata in pits and hairs, reduces air movement
5. Spongy mesophyll is dense, less air space, less SA for evap
43
How do Cacti overcome arid conditions?
- They are succulents, they sotre water in their stems, stem is ribbed to expand when water is available
- Leaves are reduced to spines to reduce SA
- Stem is green for photosynthesis
- Roots are widespread to take advantage of any rainfall
44
What are hydrophytes?
- Plants that live in water
45
How are water lillies adapted?
- Large air spaces in leaf, keeps leaves afloat so that they are in air and can absorb sunlight
- Stomata on upper epidermis so that they are exposed to the air to allow gaseous exchange
- leaf stem has many large air spaces, helps with buoyancy and allows oxygen to diffused quickly to roots for aerobic respiration
46
How do hydrophytes transpire?
- Hydathodes that can release water droplets which then evaporate from leaf surface
47
Describe the arrangement of vascular tissue in woody and non woody stems
- in non-woody plants the bundles are separate and discreet
- in woody plants the bundles are separate in young, in older they form continuous rings
- this arrangement provides strength and flexibility to withstand the bending forces
48
How can we measure transpiration rate?
- Potometer
- Plant cutting placed in water filled tube that contains an air bubble
- Rate of transpiration is calculated by measuring the movement of the air bubble over time
