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)
Chloroplast function?
- Light reactions occur in the thylakoid membrane
- Calvin cycle (dark reactions” occur in the stroma (where DNA is)
Steps of the light reactions?
- Light hits chlorophyll molecule
- electrons are bounced to a higher energy level or off the chlorophyll molecules
- Chlorophyll steals electrons from water
- Causes water molecule to fall apart through photolysis (creates oxygen)
- Electrons and hydrogens from water are transferred to NADP+ and gets reduced.
- ADP and P yields ATP though photophosphorylation (production of ATP in the presence of light)
Overview of light reactions?
- Light energy is converted first to chemical energy of NADPH and ATP.
- Oxygen gas is released (comes from water)
Light reactions summary?
H2O + light + NADP + ADP + P –> O2 + NADPH + ATP
- The products are used to make sugar in dark reactions
What is NADP?
- Oxidizing agents
- Remove (accept) electrons from other molecules, including H2O
- NADP is in photosynthesis and NAD is in respiration
NADPH?
- Reducing agents
- Place electrons on other molecules
- NADPH is in photosynthesis and NADH in respiration
NADP + 2e + H –> NADPH?
Goes in one direction for light reactions and the other direction for dark reactions
Chlorophyll absorption spectra?
- Light reactions occur due to the pigments and determine leaf colour
Chlorophyll a?
- Absorbs mostly violet-blue and red-orange
- Reflects or transmits green light (which is why plants are green)
Accessory pigments broaden absorption.
Chlorophyll b and Carotenoids?
- Chlorophyll b extends the wavelengths used in photosynthesis by making them available. All plants have this pigment but not all photosynthesizers
- Carotenoids are what make carrots orange and green
Photosynthesis action spectrum?
- shows how much oxygen is released from light at different wavelengths.
- It matches the absorption spectrum and is where light is absorbed by pigments, the wavelengths are most effective at photosynthesis. It matches the COMBINED absorption spectrum of chl an and accessory pigments.
Visible light wavelengths?
Photosynthesis is driven by visible wavelengths which is overall a small part pf the spectrum.
Dark Reaction introduction?
- Don’t require light
- Make sugar
- Use NADPH and ATP from light reaction
- Supply light reaction with NADP and ADP
- Uses products of the light reactions
Steps of Calvin Cycle?
- CO2 comes in (inorganic)
- Enzyme attaches RuBP to CO2
- Creates a 6-carbon
- “C3” is created - first stable carbon compound produced in photosynthesis and contributes to C3 photosynthesis.
- Becomes G3P which will turn into glucose
- 1 G3P becomes glucose and then the other 5 continue to move through the cycle and repeat.
- 5 other molecules get converted back into RuBP (Ribulose Biphosphate)
Important part of Calvin cycle?1
CO2 attaches to RuBP with Rubisco (enzyme)
Forms 3-Phosphoglycerate
Then forms G3P
Calvin Cycle Reaction?
CO2 + NADPH + ATP –> CH2O + NADP + ADP + P
Rubisco?
Very important protein (enzyme)
- Most abundant protein
- Most important protein
- Dual nature which presents a problem with the plants.
Ribulose-1, 5-biphosphate carboxylase oxygenate?
Carboxylase adds CO2 o something
Oxygenase adds O2 to something
What is photorespiration?
Metabolic pathway it undergoes if attached to O2
- Consumes O2
- Releases CO2
- Makes no ATP
- Wastes energy
- Decreases photosynthetic output
Issue with photorespiration?
Uses a lot of energy of the cell all to do nothing.
C4 Photosynthesis?
- Calvin cycle is kept away from the atmosphere, not having problems of Rubisco and O2 interactions
- Set of cells around vascular tissue (bundle sheath cells) that is surrounded by mesophyll cells, where PEP carboxylase resides
- Cells exposed to the atmosphere (near stomates) are mesophyll cells. CO2 then enters the cell and is grabbed onto by PEPC, which forms oxaloacetic acid (4 carbons)
- Oxaloacetic acid is turned into maltase, which h is shunted down into a bundle sheath cell that takes the malate and reconstitutes CO2 which enters the Calvin cycle.
- Separated from the Calvin cycle and rubisco at first to prevent O2 attachment
Solution to photorespiration?
A new enzyme: PEP Carboxylase
C4 summary?
Mesophyll cells
- O2 exits (light reactions)
- CO2 enters
- No rubisco
Rubisco
- is only in bundle-sheath cells
- thus kept away from potentially low CO2 concentration
What is CAM?
Crassulacean acid metabolism
- 10% of flowering plant species
- most succulents
- temporal separation of steps
What is C4?
- 3% of flowering plant species
- 50% of grasses, maize, sugarcane
- Spatial separation of steps
CAM?
Plants open stomates at night, taken in CO2 and uses PEPC to turn the CO2 into acids (malic acid maltate) and at dawn it closes its stomates and turns the malic acid into CO2, which enters the Calvin cycle.
Examples of CAM Plants?
- Cacti
- Blue agave
- Pineapple
Light reaction overview?
- carried out by molecules in the thylakoid membranes
- convert light energy to the chemical energy of ATP and NADPH
- split water and release oxygen gas to the atmosphere
Dark reaction overview?
- take place in stroma
- use ATP and NADPH to convert CO2 to the sugar G3P
- Return ADP, inorganic phosphate, and NADP to the light reactions
Plant reactions are mediated by?
Plant reactions are mediated by hormones
Plants respond to herbivores how?
- Physical defences (thorns and trichomes)
- Chemical defences (distasteful or toxic compounds) which can be used as medicines.
- Some even recruit predators animals that help defend against specific herbivores.
Example of predator recruit>
Maize leaf gets bitten into by caterpillar and sends a signal (volatile attractants) to recruit a parasitoid wasp that lays eggs in the caterpillars.
How many hormones are there?
- Abscisic acid
- Ethylene
- 6 others that don’t matter.
What is a hormone?
An organic substance made in one place and transported to another place where it affects growth and other processes.
- Chemical produced in one area and transported to another where it can have an effect.
Hormone action?
- A hormone binds to a specific protein receptor, either embedded in the plasma membrane or in the cytoplasm
- Receptor protein’s conformation then changes
- Stimulates the production of relay molecules in the cytoplasm
- Relay molecules trigger various responses to the original signal
- Plants have a wide variety of signal transduction pathways, each triggered in response to specific environmental stimuli
Abscisic acid “ABA”
In charge of stomate regulation
- In dry conditions ABA stimulates stomate closure and causes K+ to leave the guard cells.
Control of transpiration by stomates?
Cues to open at dawn:
- Light
- CO2 depletion
- Circadian rhythm
Dry conditions:
- Abscisic acid: hormone
- Causes K+ to leave guard cells
- Stimulates stomate closure
Ethylene?
Where
- Most plant parts
Major functions
- Leaf abscission (shedding)
- Triple response in seedlings
- Fruit ripening
- Root hair production
History of ethylene?
- Discovered around 1901 in Russia
- 1910 we knew that emanations from oranges caused premature ripening of bananas
- Now the most commercially produced organic compound in the world (has many uses)
Abscission?
Caused by an increase in the ratio of ethylene:auxin
The triple response?
- slowing stem elongation
- stem thickening
- horizontal stem growth
Effect of ethylene on fruit ripening?
- Promotes fruit ripening and is produced during fruit ripening
- Autocatalytic: promotes its own production
- Increases respiration
Example of ripening?
All tomatoes are picked completely unripe and factories use ethylene to ripen the plants when ready to sell.
