Plants: Lecture 6 Flashcards
Xylem Review?
- Occurs because of water potential differences
- A passive process
- Moves water and minerals up the plant
- Moves from higher to lower potential
- Each step is lower than the one before it
- Pressure potential tends to have more effect, as the atmospheric pressure is much much much more negative than the plant pressure at any point.
What do phloem transport?
They transport sugar in solution, or sugar water.
- Sugar is sucrose (2 glucose)
Direction of phloem transport?
Phloem move things in any direction
Where does phloem transport occur?
It occurs in the sieve-tube elements
How does sugar water move through the sieve-tube elements?
It moves by the pressure-flow hypothesis. This process takes energy and this is explained by the pressure-flow hypothesis.
How does phloem transport occur?
- A companion parenchyma cell is connected to the sieve tube element (source cell) and actively pumps sugar water into the phloem. This addition of solutes decreases the water potential, pulling in water from an additional cell (xylem).
- Then, it will move to the sink cell through bulk flow by positive pressure.
- A sink parenchyma cell actively removes the sugar molecules from the sieve tube
- Water is then recycled by it being moved out of the sieve-tube and into the xylem where there is lower pressure
How does phloem transport work?
- Sugar water
- Pressure-flow hypothesis
- Moves from source to sink (receiving)
- Takes energy
Sources and sink?
The direction that phloem transport goes depends open what the plant wants at any particular time.
General Direction of phloem transport?
- Down in the summer and fall: glucose(leaves) - sucrose(stem) - starch(roots). For winter storage.
- Up in the Spring to make new leaves: starch (roots) - sucrose (stem) - glucose (leaves)
Water pressure?
- Water spontaneously moves from regions of higher to regions of lower water potential energy
- Water potential energy is the sum of solute (osmotic) potential energy and pressure potential energy.
- 2 main transport tissues: xylem (sap through tracheids & vessel elements) and phloem (sugar water through sieve-tube elements).
Aphid?
Aphids tap phloem
- They find a phloem and tap into it by pumping sugar water into their bodies from the sieve tube elements. Water would suck their insides out because of the pull.
Transport cell types in xylem vs phloem?
Xylem have tracheids and vessel elements.
Phloem have sieve-tube elements
What is transported in xylem and phloem?
Xylem transport water and minerals (sap)
Phloem transport sugar water and other elements
Direction of flow in xylem and phloem?
Xylem moves upward
Phloem move any direction
Mechanism in xylem and phloem?
Xylem use the transpiration - cohesion - tension mechanism
Phloem use a pressure flow mechanism
Is energy required in xylem or phloem?
Tracheids and vessel elements do not require energy for transport (passive)
Sieve-tube elements do require energy for transport (active)
Importance od photosynthesis?
- The source of all oxygen in the atmosphere. 50% from terrestrial plants and 50% from marine phytoplankton, macro algae, and protists.
- It is the first step in moving energy into the living world, the source of energy in our ecosystems
What does photosynthesis do?
- Fundamentally important to all life on earth
- Converts light energy into sugar
- Converts inorganic things like CO2 into organic things like sugar
Types of photosynthetic organisms?
- Land plants
- Multicellular alga
- Unicellular protists (marine)
- Cyanobacteria (single-celled prokaryotes)
- Purple sulphur bacteria
How do chloroplasts look?
- 2 membranes
- organelle
- contains chlorophyll pigment in thylakoids (small parts) which are part of granums
What is photosynthesis?
The production of glucose from sugar and water.
- Light energy uses CO2 and H2O to create carbohydrates (glucose)
Reactants and products in photosynthesis?
Reactants: 6CO2 and 12H2O
Products: C6H12O6 and 6H2O and 6O2
- Note that the 6O2 molecules come purely from water not from CO2
Electron transfer redox?
- CO2 is an electron acceptor and gets reduced in the reaction
- H2O is an electron donor and gets oxidized in the reaction
Electron transfer summary?
Water is split, loses electrons or gets oxidized, and electrons are transferred along with hydrogen ions from water to carbon dioxide, reducing it to sugar (glucose)