3.3 transport in plants Flashcards
Why do plants need a transport system
Large plants have a small SA:V - need specialised exchange surfaces/ transport system
What do plants need a regular supply of
Water
Nutrients
Minerals
Oxygen
Why can plants not use diffusion alone
High metabolic demand
Large size
Small SA:V
Diffusion is too slow
What is the vascular bundle made of
Xylem
Phloem
What does xylem transport
Water and mineral ions
What does phloem transport
Sucrose and amino acids
What does herbaceous dicotyledonous plants mean
Non woody stem , 2 seed leaves plant
How do you dissect a plant
Stain
Cut stem longitudinaly or transversely
Describe the structure of xylem tissue
Xylem vessels which carry water
Hollow tubes
Elongated
End region of cell lost
Non lignified pit
Thick, lignified wall
What is the purpose of pits in xylem
Lateral water movement
What is the purpose of lignin in xylem
Waterproof and lignin spirals reinforces vessels so it doesn’t collapse
How does a continuous column form in xylem
Dead cells aligned end to end , end regions have been lost
Why are narrow tubes in xylem beneficial
Prevents breaking easily, capillary action effective
What are assimilates
Sucrose and amino acids
What do phloem consists of
Sieve tube elements
Companion cells
What are sieve tube elements
Elongated tubes lined up end em to end with sieve plates at the end (of the sieve tube elements)
What do sieve tubes contain and why is it beneficial
No nucleus and very little cytoplasm - allows mass flow of sap
What do sieve plates allow
Movement of sap from elements
How are companion cells specialised
Large nucleus
Dense cytoplasm
Lots of mitochondria
How are companion cells and sieve tube elements joined
Plasmodesmata - gaps in cell wall that connects cell
What do companion cells do
carry out active processes to actively load assimilates into sieve tubes
How is the vascular bundle structured in the roots
Central core of xylem in X shape
Phloem in the arms of xylem
Endodermis around the vascular bundle
Layer of meristem in the epidermis
How is the vascular bundle arranged in the stem
Found on the outer edge - Phloem on the outside and xylem on the middle side
Cambium found in the middle
Cortex
How is the vascular bundle arranged in the leaf
Xylem ontop of the phloem in the veins of the leaf
Vascular bundle called a midrib
What is transpiration
Loss of water vapour from upper parts of the plant via evaporation and diffusion
What is the transpiration steam
Flow of water from the root to the leaves in plants where it’s lost by evaporation
What happens during transpiration
Water enters the leaf through xylem
Moves by osmosis into cells in spongy mesophyll
Water evaporates from cell walls of spongy mesophyll
Water vapour moves out of leaf through open stomata down the water potential gradient
How is water pulled up a stem
Transpiration pull/ stream (cohesion)
Root pressure (active process)
Capillary action (adhesion)
What is the importance of transpiration
Transports mineral ions up the plant
Maintains cell turgidity
Water for growth , cell elongation and photosynthesis
Keeps plant cool
How much water is lost by transpiration
95%
What environmental factors affect transpiration
Light intensity
Temperature
Humidity
Wind/ air movement
Water
How does light intensity impact transpiration
Bright LI = stomata open for photosynthesis = increases ROT
How does temperature impact respiration
Higher temp = more evaporation = more kinetic energy = water potential will increase so increased ROT
How does humidity impact respiration
Higher humidity = lowers rate of water loss - smaller water vapour potential gradient between air spaces in leaf and outside
How does wind/ air movement impact respiration
Moving air = water vapour carried away = maintains a water potential gradient
How does water impact transpiration
Little water in soil = plant cannot replace water lost = stomata close
How is water lost through leaves
lost as water vapour through open stomata
Which lowers water vapour pressure in gaps = more water moves down gradient
What is translocation
Movement of assimilates throughout the plant in the phloem
What are assimilates
Substances that have become apart if the plant (sucrose, amino acids)
What is the source
Part of the plant that loads assimilates into phloem sieve tubes
What is the sink
Part of the plant that removes assimilates from phloem sieve tubes
What are the order of processes in active loading
- Active transport
- facilitated diffusion
- Simple diffusion
- Osmosis
Explain how active loading works
Active transport of H+ ions out of the companion cells using ATP from mitochondria in companion cells - creates concentration gradient
H+ ions diffuse back into via facilitated diffusion through cotransport proteins and brings sucrose with it
Higher conc. of sucrose in companion cells then in the sieve tubes so sucrose moves by simple diffusion
Water potential in sieve tubes decrease so water moves in tubes by osmosis
What is plasmodesmata
Gaps in cell wall which connects two cells
What are the systems that water through plants
Apoplast
Symplast
Vacuolar
Explain the apoplast system
Water passes through spaces in the cell wall / between the cells
Doesn’t pass through plasma membranes into cells
Moves by mass flow
Explain the symplast system
Water enters cell through the plasma membrane and passes through the plasmodesmata from cells to the next
Explain the vacuolar pathway
Passes through vacuole as well as symplast
What is the casparian strip
Waxy, waterproof strip impervious to water and stops water entering by apoplast and forces it through the plasma membrane (symplast)
What is the casparian strip made of
Suberin
What is water potential
Measure of tendancy of water molecules to move from one place to another
How does water move in a concentration gradient
Down the concentration gradient
Moves from higher water potential to lower water potential
How does water move in cells in plants
Water leaves the cell down the water potential gradient
As higher conc of mineral ions and sugars outside the cell so there is a lower water potential (more negative)
Water moves from cell to more negative cell
How is water taken up by a plant
W.P is more negative in the cell so water moves in by osmosis
What does turgid meant
Cell full of water and exerts pressure on cell wall making it stiff
What is pressure potential
Water exerting pressure on walls
How is water lost from a plant
Transpiration (evaporation)
What happens when a plant is placed in salt solution
Has very negative water potential so water moves out
What happens if water loss continues in a plant
Cytoplasm and vacuole shrink
No longer turgid -> plasmolysis (plasma membrane shrinks) cell is now flaccid
What does plasmolysis mean
Plasma membrane shrinks
What are terrestrial plants
Plants living on land
How do terrestrial plants exchange gases
Through stomata
Why do stomata need to be open
Allow CO2 moves in
Water loss
Allow 02 to be removed as a product
explain adaptations of terrestrial plants
Waxy cuticle - reduce water loss by evaporation
Stomata on under surface of leaves - reduces evaporation from direct sun
Closed stomata at night - no light for photosynthesis
Deciduous plants lose leaves in the summer
What is a hydrophyte
Plant that’s adapted to living in water/ very wet ground
What is an example of a hydrophyte
Water lily
Adaptations of water lilies
Stomata on upper epidermis - exposed to gases
Large air spaces - buoyancy in stem, O2 diffuse quickly
Thin waxy cuticle - don’t need to conserve water
Wide, flat leaves - increases SA , lots of sunlight available
What is the difficulty with water lilies
Struggle with oxygen getting to submerged tissues
What is a xerophyte
Plant adapted to living in dry conditions/ arid conditions
What are examples of xerophytes
Cactus
Marram grass
Adaptions of cactus
Succulents - store water in stem, become fleshy and swollen
Stem is ribbed/ fluted - expand when water available
Spines - reduce SA and water loss
Widespread roots - water underground
Thick, waxy cuticle - reduce evaporation
Sunken stomata/ pits - create local humidity, reduces air exposure
Adaptations of marram grass
Thick, waxy cuticle - reduce evaporation
Stomata in pits, covered in hair reduce air movement, trap water
Dense spongy mesophyll - reduce water evaporation
Stomata on inner side of leaf - protected
Outer epidermis
