Transport in plants Flashcards
Why do plants need transport systems?
Plants need water for photosynthesis, chemical reactions and to keep cells turgid
Plants need sugars for respiration and building organic molecules
Plants need to remove waste products
Structure and function of Xlylem
Xylem transports water and dissolved mineral ions from roots to leaves
Structural support
Dead hollow cells with no end cell walls
no organelles or cytoplasm
Cell wall contains lignin - strengthens vessels
Cell wall contains pits to allow movement of water into and out of vessel
Describe the cross section of a stem
Xylem vessels found on the right of the inside
Phloem tissues located in the middle of vascular bundle
Surrounded by sclerenchyma
Cambium in between xylem and phloem
Describe the cross section of a root
Xylem forms cross structure in center which is surrounded by phloem
Describe the cross section of a leaf
Xylem found on top of vascular bundle and phloem found underneath
Structure and function of phloem
Phloem transports sucrose and amino acids from source to sink
Made of sieve tube elements and companion cells - connected by plasmodesmata
Sieve tube elements are living and joined end to end to form sieve tubes.
End of cell consists of sieve plate with pores
Sieve cells have no organelles and very little cytoplasm
Companion cell contains nucleus and lots of mitochondria to provide energy for active loading
Describe how water enters the xylem
High concentration of water in soil and low concentration in root
Water diffuses by osmosis through root cortex and endodermis to the xylem
Symplast pathway - water travels from celle to cell through the cytoplasm
Cells connected by plasmodesmata
Apoplast pathway - Water passes from cell to cell through cell walls
- this is the main way
Vacuolar pathway - water passes from cell to cell through the vacuoles
What is the function of the casparian strip
In the apoplast pathway, water avoids the cell memebrane so cell cant monitor what goes into cell
Casparian strip is impermeable to water which forces water to take symplast pathway before it reaches the xylem
How does water move through the xylem?
Water moves against gravity due to tension and cohesion
Cohesion - water molecules form hydrogen bonds with each other which causes them to stick and create a column of water
Transpiration pull - water evaporates from the leaves and pulls water towards the leaves due to the cohesion of the water molecules
Adhesion - water is attrcated walls of xylem so it can rise up xylem
What factors affect rate of transpiration?
Light intensity - increasing light intensity increases rate because plants photosynthesize more so stomata open for longer so more water leaves the leaf
Temperature - increasing temperature increases rate because water molecules have more kinetic energy so water diffuses out faster
Wind - windier conditions increase rate because water molecules out side leaf are blown away so there is steeper concentration gradient
Humidity - more humid decreases rate because more water molecules outside leaf so less steep concentration gradient
What are the adaptations of xerophytes?
Waxy layer on epidermis - reduces evaporation of water because water cant pass through
Sunken stomata - shelter stomata from wind so less water lost
Hairs on epidermis - trap water to reduce concentration gradient
Spines - reduces surface area for water loss
Rolled leaves - traps water to reduce water concentration gradient
Closed stomata - reduces transpiration during the day
What are the adaptations of hydrophytes?
Stomata on upper surface - stomata aren’t submerged under water
Air spaces - to float and store oxygen for respiration
Flexible leaves and stems - prevent damage from water currents
Explain the process of mass flow
Sucrose moves from companion cell into sieve tube element by active transport
This reduces water potential of sieve tube element
Water moves into phloem by osmosis, which increases hydrostatic pressure
High hydrostatic pressure by source and low hydrostatic pressure by sink
Solute moves down pressure gradient to sink
Solute moves into sink cell and is converted to other molecules
when solute is removed, water potential increases and water moves out of phloem by osmosis
Explain active loading
Companion cell actively transports H+ ions into surrounding cells
Hydrogen ion gradient created between surrounding cells and companion cell
H+ ions move back into companion cell down concentration gradient through co-transporter protein
sucrose molecule is also transported into companion cell with H+ ion against concentration gradient
