Plants Lesson 6 Flashcards
Phloem Transport
It’s sugar in solution in sieve-tube elements by pressure-flow hypothesis. It requires energy unlike xylem.
How does phloem flow work?
Starts with the loading or pumping of sugar from the source cell (leaf) into the phloem. This causes the water potential to go down, then water comes in from the xylem, which creates pressure. The sugar water flows from higher pressure to lower pressure. When it reaches the sink cell in the storage root, it removes the sugar. However because the xylem pressure is lower than the sink cell, the water flows into the xylem.
What are source and sink cells?
Companion cells (parenchyma)
What direction can phloem flow?
It can go any direction (unlike the xylem), it just depends on what the plant wants to do.
The direction flow example?
In the summer/fall glucose is taking from the leafs then turned into sucrose in the stem. Then moved downwards to the roots where it’s turned into starch to be stored in the winter. Then in the spring, the plants want to use energy by turning the starch in the roots into sucrose in the stem, then upwards into the leaves to be turned into glucose.
Phloem and xylem pressure?
Phloem= positive pressure
Xylem= negative pressure
Aphid insect
Puts its mouth in the phloem and the sugar flows into the insects mouth.
Key points in transport in plants?
Water spontaneously moves from regions of higher to
regions of lower water potential energy.
In any region, water potential energy is the SUM of:
* solute (osmotic) potential energy (0 or negative)
* pressure potential energy (any value)
2 main tissues for transport
* Xylem: sap: tracheids and sometimes vessel elements
* Phloem: sugar water: sieve-tube elements
What are xylem and phloem are guided by what?
The second law of thermodynamics
Photosynthesis Importance
Source of oxygen in atmosphere: 50% terrestrial plants and 50% marine phytoplankton & macroalgae.
First step in moving energy into the living world; source of all energy in ecosystems. It converts inorganic stuff into organic stuff.
Photosynthetic organisms
Land plants, Cyanobacteria, multicelluar alga, unicellular protists, purple sulphur bacteria.
What’s on the leaf regarding photosynthesis?
Two membranes called the cubital layer (epidermis). On the inside is pigment (specifically in the thylakoids). The chloroplast is in the mesophyll cell. Stomata’s are almost always on the bottom of the leaves.
Where does the oxygen from photosynthesis come from?
The water and not the CO2.
What does the reaction in photosynthesis involve?
The transfer of electrons and breaking and forming of new bonds. 6CO2 is a electron acceptor and gets reduced (more negative) and the 12 H2O is an electron donor and gets oxidized.
Net Photosynthesis reaction
Energy (light) + 6CO2 +6H2O into C6H12O6 + 6O2
What is reduced and what’s oxidized?
CO2 reduced to C6H12O6
H2O oxidized to O2
What happens to water into photosynthesis?
Water is split, loses electrons (gets oxidized), and electrons are transferred along with hydrogen ions from water to carbon dioxide, reducing it to sugar.
The two stages of photosynthesis?
Light reactions and Calvin cycle (dark reactions)
Where is the light reaction?
In the thylakoid of the chloroplast.
Where is the Calvin cycle?
The stroma. This is also where the chloroplast DNA is in.
Steps of light reactions?
- Light hits chlorophyll (a pigment) molecule.
- e- ’s bounced to higher energy level & OFF chl molecule.
- Chl steals e- ’s from H2 O (oxidized). Because the chlorophyll wants the electrons back.
- Causes water molecule to fall apart: photolysis (breaking apart the water) to oxygen.
H 2O à 2H + + 2e - + O - e- ’s and H+ ’s from H2 O transferred to NADP+ (gets reduced): NADP+ + 2e- + H+ to NADPH (greater reducing power than H 2O)
- ADP + Pi yields ATP (chemical energy): Photophosphorylation (creating ATP from light).
Overview of light reactions
Light energy is converted first to chemical energy of NADPH and ATP. Oxygen gas O2 is released (comes from water).
Light reaction
H2O + light + NADP+ + ADP +Pi into O2 + NADPH (reducing power) + ATP (chemical energy)
It makes energy to be used by the Calvin cycle.
What are chemical bonds made from?
Electrons
NADP+ and NAD+
Oxidizing agents. Remove (accept) e- ’s from other molecules, including H2O (2 e- ’s & 1 proton [nucleus of H atom]). NADP+ in photosynthesis, NAD+ in respiration.
NADPH and NADH
Reducing agents. Place e- ’s on other molecules. NADPH in photosynthesis, NADH in respiration.
NADP+ and NADPH reaction
NADP+ + 2e- + H+ into NADPH. It’s reversible.
Chlorophyll absorption spectra
Accessory pigments broaden absorption.
Chlorophyll a (most common): Absorbs mostly violet-blue and red.
Chlorophyll b: Absorbs more blue and violet then a, and orange.
Carotenoids: Absorbs from purple to just before green. It’s what makes carrots orange/yellow in color.
Light absorbed causes photosynthesis. It’s driven by visible wavelengths.
Why are plants green?
Because chlorophyll a reflects green light and it’s not absorbed.
Photosynthesis action spectrum
The action spectrum (rate of photosynthesis) matches the combined absorption spectrum of chl a & accessory pigments including chl b, carotenoids.
Purple and red wavelengths
Purple: Shorter wavelength (380) and higher energy.
Red: Longer wavelength (750) and lower energy.
Dark reactions (Calvin cycle)
Make sugar (precursor). Occur in stroma of chloroplast. Use NADPH & ATP from light reactions. Supply light reactions with NADP+ & ADP. They don’t requite light. Founded by Melvin Calvin.
How does the Calvin cycle work?
Starts with 3 CO2 entering one at a time by rubisco.
Phase one (carbon fixation): Then it’s called 3-phosphoglycerate (c3) which is the first stable organic compound in photosynthesis (has 18 carbon). The 6ATP go in and 6ADP go out resulting in 1,3-Bisphosphoglycerate. Then 6 NADPH go in and 6 NADP+ and 6Pi go out.
Phase two (reduction): Then Glyceratdehyde-3-phospate, and one carbon chain leaves and turns into glucose. Resulting in G3P with 15 carbons.
Phase three (regeneration of the CO2 acceptor): The G3P has 3 ATP in, and 3 ADP goes out. Resulting in ribulose bisphospate (RuBP) which is the starting compound.
Then the cycle begins again.
What is at the start and end of the Calvin cycle?
RuBP
Calvin cycle reaction?
CO2 + NAPH + ATP into CH2O (sugar) + NADP+ + ADP + Pi
Rubisco
It’s a very special protein. Most abundant protein. Most important protein. Dual nature (grabs onto O2 and CO2). The stomate closes at night, and when it’s closed it results in lots of O2, not much CO2. Which causes Rubisco to grab onto O2, which does nothing for the plant, it takes up energy.
Photorespiration
Rubisco attaches O 2 to RuBP Metabolic pathway that
– consumes O2
– releases CO 2
– makes no ATP
– wastes energy
– decreases photosynthetic output
The solution to photorespiration?
A new enzyme: PEP carboxylase (PEPC). It grads onto CO2 and not O2.
C4 photosynthesis
Occurs in about 3% of species, like tropical grasses (corn and sugar cane). The light reaction occurs in the mesophyll cell which is where the PEPC is. Then the Calvin cycle occurs in the bundle-sheath cell, inside the mesophyll cells. It’s the spatial separation of steps.
C4 photosynthesis pathway?
In mesophyll cells, the enzyme PEPC adds CO2 to PEP. Then a four carbon compound conveys the atoms of the CO2 into a bundle-sheath cell via plasmodesmata. Then in the bundle-sheath cells, CO2 is released and enters the Calvin cycle via the action of rubisco.
Rubisco in C4 photosynthesis
Is only in bundle-sheath cells, thus kept away from
potentially low [CO2].
Mesophyll cells in C4 photosynthesis
O2 exits (light reactions), CO2 enters, and NO rubisco
CAM (Crassulacean acid metabolism) solution
10% flowering plants (like cacti, agave, and jade). The temporal separation of steps. At night the stomata are open and the organic acid cycle occurs. Then in the day the stomatas close and the Calvin cycle occurs. The plants becomes less acidic as the day goes on.
Plants respond to herbivores
Physical defenses:
– thorns
– trichomes
Chemical defenses:
– distasteful compounds
– toxic compounds (e.g., canavanine, unusual amino acid. Replaces arginine in insect proteins: death.
Some plants even “recruit” predatory animals
that help defend against specific herbivores
Example of plant response to herbivores?
A caterpillar eats a maize leaf. The wounding and chemical in saliva causes signal transduction pathway (this chemical reaction turns on gene). Then synthesis and release of volatile attractants makes it smell bad. Which recruites a parasitoid wasp that lays their eggs within caterpillars, then it eats it from the inside.
8 Hormones in plants
Abscisic acid, ethylene, auxins, cytokinins, gibberellins, brassinosteroids, jasmonates, and strigolactones.
Hormone
Organic substance produced by the organism, made in one place & transported to another place, where it affects growth and other
processes.
Hormone action
A hormone binds to a specific protein receptor, either
embedded in the plasma membrane or in the cytoplasm. Receptor protein’s conformation thus 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)
Regulates the stomate. In dry conditions it causes K+ to leave the guard cells, cause water to leave and the stomate to close.
Ethylene
A gas in most plant parts.
It promotes:
* Leaf abscission (shedding)
* Triple response in seedlings
* Fruit ripening
* Root hair production
It was discovered around 1901 by Neljubov in Russia. 1910: “emanations” from oranges caused premature ripening of bananas. Now the most commercially produced organic compound in the world—many uses.
Abscission & ethylene
Caused by a change (increase)in ratio of ethylene:auxin. In a healthy leaf auxin is present (leaf maintenance phase). Then in the shedding induction phase there is no auxin, ethylene produced, the ratio changes, and programmed cell death starts. Causes abscission layer to die and it causes the leaf to fall off.
What causes leafs to change color in the fall?
By the plant absorbing chlorophyll because they don’t want to waste it. The other pigments are left.
Ethylene & the triple response
If grouting then hits an object, the plant goes around it by making ethylene. Germinating pea seedlings grown in dark.
1. Slowing stem elongation
2. Stem thickening
3. Horizontal stem growth
The shorter and thicker the plant the more ethylene in it.
Effect of ethylene on fruit ripening
Promotes fruit ripening AND is produced during fruit ripening. Autocatalytic: promotes its own production.
Increases respiration. Tomatoes are picked green, and the human use ethylene to cause it to ripen. If picked super young they would never ripen without ethylene.
