chapter 4 plant physiology Flashcards
(76 cards)
1
Q
Transport of CO2 and O2 in the leaves
A
- CO2 enters through the leaves for photosynthesis
- O2 leaves through the leaves as a product of photosynthesis
2
Q
Transport of CO2 and O2 in the roots
A
- CO2 leaves the roots as a product of metabolism/ cellular respiration
- O2 enter the roots to be used in cellular respiration
3
Q
Transpiration
A
- the movement of water and mineral nutrients from soil to the atmosphere via plants
- water will evaporate from leaf cells at <100% RH
4
Q
How much water is moved through transpiration per day?
A
- 0.5 gallons/day in one corn plant
- 52 gallons/day in one large maple
- transpiration is not seen
5
Q
Evapotranspiration
A
- landscape level movement of water from soil to atmosphere
6
Q
Where does water enter the plant?
A
- water enters through the fine roots
- these are found in the first couple inches in the soil
- the soil surface is significant
- deeper roots are for support
- water travels from the fine roots to the xylem
7
Q
What controls transpiration?
A
- controlled by guard cells of the stomata
- turgid guard cells open the stoma
8
Q
Why are stoma generally open in the day and closed at night?
A
- photosynthesis occurs with sunlight
- being open allows CO2 to get in but also allows loss of water
- closed at night to prevent excess water loss through stoma and transpiration
9
Q
What are xerophytes?
A
- dry plants that often have CAM photosynthesis
- close stomates during the day
10
Q
How does water move in and out of guard cells?
A
- overall controlled by K+
- more K+ in a cell = water will move into cell because of gradient
- when guard cells are turgid they open the stoma
11
Q
Why does increase in turgor pressure open the stomate?
A
- cellulose microfibrils of guard cells expand in length when hydrated
- because they are surrounded by other cells they elongate as much as they can and create the stromal opening
12
Q
What are leaf adaptations to growing in arid environments?
A
- epicuticle and several layers of epidermis
- sunken stomates with hair coverings
- sunken stomates and hairs help keep dry wind from causing excess water loss while still allowing CO2 in
13
Q
Types of water movement in plants
A
- apoplastic: water enters through cellulose that surrounds cortical cells, allows water to move more readily
- symplastic: water enters through cortical cells and moves from cell to cell, water is moved less readily
14
Q
Transpiration-cohesion theory
A
- water has cohesive and adhesive properties
- cohesive: water can stick to other water molecules via H bonding
- adhesive: water can stick to the cell wall in dead xylem cells. water interacts with polar substances. cellulose also has partial charges that can interact with water.
15
Q
How does water have cohesive and adhesive properties?
A
- the H2O molecule has both a partially positive and partially negative charge
- this allows H bonding between water molecules
- cellulose also has partial charges so it can form H bonds with water
16
Q
What is water potential
A
- water’s free energy or its ability to do work
- composed of solute potential and pressure potential
- solute potential + pressure potential = water potential
17
Q
Solute potential
A
- the effect of dissolved solutes on water potential
- always less than or equal to zero
- water moves toward more solute
- increase in solute [ ] decreases the solute potential (makes it more negative)
- add more solute = solute potential is more negative
- if no solute present, solute potential is 0
- cannot be positive
18
Q
Pressure potential
A
- effect of hydrostatic pressure of water potential
- most cells have a + pressure potential also called turgor pressure
- functional xylem cells have - pressure potential also called tension
19
Q
What is significant about the pressure potential of functioning xylem cells?
A
- they have a negative pressure potential or tension
- water is under tension and because of H bonding properties water can be pulled up the xylem
20
Q
Which way does water move?
A
- water always moves to the more negative water potential
- or toward the lower free energy
21
Q
Movement of water in a plant
A
- soil, root epidermal cell, parenchyma cell, functional xylem cell, leaf mesophyll (parenchyma) cell, atmosphere
22
Q
How does water move up the plant?
A
- the total water potential is more negative as you move up the plant
- water flows to the more negative water potential
- ex. root epidermal cells have a -0.1 MPa water potential and the soil has a 0 MPA water potential, so water moves from the soil to root epidermal cells
23
Q
What energy is used to transport this water?
A
- the flow of water to a lower free energy
- no ATP used
24
Q
What are the effects of soil salinity on soil and plant water potential?
A
- solute potential of soil becomes more negative and so its water potential becomes more negative
- if it gets too negative, the water won’t be able to get into the plant
25
Why do parenchymal cells have a more negative solute potential?
- leaf parenchyma produces sugars from photosynthesis and store them, so they have more solute
- stem parenchyma also stores carbs which makes the solute potential more negative
- leaf parenchyma has more sugars, so it is more negative
26
What are the major essential nutrients for plants?
- nitrogen
- phosphorous
- potassium
- magnesium
- sulfur
- calcium
27
Importance of nitrogen for plants
- needed to make proteins, aa, and chlorophyll
- 4 N molecules needed per chlorophyll molecule to chelate the magnesium
28
Importance of phosphorous for plants
- needed to make ATP, nucleic acids, and phospholipids
- phospholipids are important for membranes
29
Importance of potassium for plants
- needed for guard cell regulation
- more in guard cell = stomates open
30
Importance of magnesium for plants
- component of chlorophyll
- used by various enzymes
31
Importance of sulfur in plants
- needed to make proteins and aa
32
Importance of calcium in plants
- component of the cell wall
33
Other minerals used by plants
- boron, chlorine, manganese, iron, nickel, copper, zinc, Mo: absorbed from soil and can act as cofactors for some enzymes
- hydrogen, carbon, and oxygen
34
How do plants get H, C, and O?
- carbon is from CO2 and photosynthesis in leaves
- oxygen and hydrogen from water through the roots
35
What are benefits of hydroponic production?
- less weight
- higher value of crop over winter
- better pest control
- better cost efficiency in the long run
36
How were essential plant nutrients discovered?
- plants were grown in lab
- some lacked certain nutrients in water
- if a nutrient was missing and caused abnormal growth it was considered an essential mineral
37
What is phytoremediation?
- the use of plants to clean up contamination from soils, sediments, and water
- works because plants absorb nutrients from the soil even if they are not necessary for them
- takes advantage of the unique and selective uptake capabilities of plant root systems
- environmentally friendly and potentially cost effective
38
Translocation of sugars
- occurs in LIVING phloem sieve tube members
- requires ATP (chemical energy)
- moves sucrose form source to sink
- described by the pressure flow hypothesis
39
What are the source and sink in the translocation of sugars?
- source: any part of the plant that is photosynthetic and produces sugars like the leaves or some stems
- sink: non-photosynthetic areas like the roots, storage areas, and some stems
40
Explain the pressure flow hypothesis
- in the source: sucrose is actively transported (uses ATP) into cells to increase the [] inside the cell, because of this water also moves into the cell
- movement of water into the source cells increases and creates pressure to move the sucrose and water
- water moves through sieve tube members until it reaches the sink cell
- depending on the [ ] of sucrose in the area of the sink cell, sucrose moves out of the cell via active transport or down its gradient - both require and transport protein
- even though water is moved in this process this is NOT the main transport of water in plants
41
How does water and mineral nutrient transport differ from sugar transport in vascular plants?
- water and minerals are transported via xylem
- xylem cells are dead at function
- sugars are transported via phloem
- phloem is alive at function
- movement of water does NOT require an energy source
- movement of sugars does require and energy source (ATP)
42
Sugar and Slavery
What two plants provide virtually all the commercial sucrose worldwide?
- sugar cane and sugar beet
- led to the triangular trade from the 1500s-1800s
- britain, west africa, and the west indies
43
What was traded in the triangular trade?
- britain received rum and sugar from the west indies & shipped firearms, cloth and salt to west africa
- west africa recieved from britain & sent salves to the west indies
- the west indies received from west africa & shipped rum and sugar to britain
44
Metabolism
- cellular respiration processes
- glucose broken down to create energy
- oxygen is the final electron acceptor and becomes water
45
Photosynthesis
- plants use light energy from the visible spectrum for photosynthesis
46
What is the visible spectrum
- wavelengths from 400-700
- 40% of the radiant energy from the sun
47
Photosynthetic pigments and green plants
- primary pigments: donate electrons in photosynthesis
- accessory pigments: part of light harvesting system
48
What are the primary pigments in photosynthesis?
- chlorophyll 680 (PS2)
- chlorophyll 700 (PS1)
49
What are the accessory pigments in photosynthesis?
- the rest of the chlorophyll a's
- chl b
- carotenoids: carotenes (orange) and xanthophylls (yellow)
- form pigment/protein complexes in the thylakoid membrane
- transfer light to primary chl a so it can donate the electrons
50
Chlorophyll structure
- amphipathic
- hydrophilic ring with Mg2+ and 4 N molecules that chelate the Mg2+
- hydrophobic hydrocarbon tail that allows chl to imbed into the membrane
- chl a: R group is CH3
- chl b: R group is a CHO
51
Carotenoid structure
- mainly hydrophobic hydrocarbons that imbed into the membrane
52
Are carotenoids or chlorophylls broken down in the fall?
- chlorophylls are broken down in the fall
- longer nights during the fall trigger chl breakdown
53
Why is chl broken down rather than carotenoids?
- chl is made of Mg2+ and 4 N molecules
- N is the most limited essential nutrient for plants
- so chl is broken down so the plant can keep and store the Mg2+ and N until spring
- carotenoids made mostly of carbons and lost with leaves falling but C is easier for plants to get and make more when needed
54
How is N the most limited mineral for plants to get if it is prominent in the atm?
- the N in the atm cannot be absorbed and fixed by plants
- it is absorbed by bacteria and fixed and released into the soil
- BUT when N is fixed it is mainly made into nitrate and nitrite
- nitrate and nitrite are negatively charged so they do no bind well to soil elements and leak OUT of the soil
- continual leaking from the soil prevents or makes it harder for plants to absorb N
55
Absorption spectrum details
- chls absorb blues, purples, and reds but reflect greens
- carotenoids absorb green and reds but reflect yellows
- blues and reds spectrum primarily drive photosynthesis
56
Photosynthesis phases
1. light reactions: photochemical phase
- occur on the thylakoid membrane
- convert light to ATP and NADPH
2. Calvin cycle: biochemical phase
- occurs in the stroma
- converts CO2 into sugars and eventually sucrose with the use of ATP and NADPH
57
Order of electron movement in photosynthesis light dependent reactions
- PSII (photosystem 2) w chl a 680
- plastoquinone
- cyt b6f complex
- plastocyanin
- PSI w chl a 700
- ferredoxin
- ferredoxin-NADPH reductase
58
Significance of light reactions?
- occur in the thylakoid membrane
- movement of electrons creates a H gradient in the lumen of chloroplasts
- ferredoxin-NADPH reductase reduces an NADP molecule to NADPH
- ATP synthase uses the H gradient made to synthesize ATP
- ATP and NADPH are made into the stroma and needed for the Calvin cycle that also occurs in the stroma
59
Why is NADPH significant?
- it is made from the light reactions
- it is the electron source that is needed in the calvin cycle
60
Ph difference of the lumen and stroma
- lumen: 5
- stroma: 8
- lumen has 1000x more H+ making it much more acidic
61
Calvins Experiment
- experiment was used to determine the intermediates and processes of the calvin cycle
62
Rubisco enzyme
- Ribulose bisphosphate carboxylase/oxygenase
- enzyme responsible for the carbon fixation in the C3 cycle
- can aid in photorespiration or carboxylation
63
Photorespiration
- rubsico catalyzes the combining of O2 to RuBP
- oxygenase activity
- this is not a benefit b/c no C is being brought into the plant
- O2 %: 20-21% (used to be 0-1%)
- percentage was brought up by plants photosynthesizing
64
CO2 fixation (carboxylation)
- Rubisco combines RuBP and CO2 to ultimately form sugars
65
Photorespiration and CO2 fixation
- competing reactions at the same active site of Rubisco
- because both CO2 and O2 can bind
66
Rubisco concentration
- 4mM in the stroma (500x the [CO2])
- this is unique because normally there is a higher [ ] of substrate rather than enzyme
- makes rubisco the most abundant protein on earth (25% of total leaf protein)
- because plants make up most of the biomass
67
Rubisco affinity
- fixed CO2 80x faster than O2
- higher affinity for CO2
- good for plants so they can make sugars
- at 25 degrees CO2 fixation outruns oxygenation only by 3:1
- at higher temps, photorespiration increases
68
O2 and CO2 concentrations
- O2: ~20% in atm
- CO2: ~0.04% in atm
- bad news for plants because more oxygen is available rather than CO2
69
C4 cycle properties
- found in tropical grasses (maize, sugar), warm-season prairie grasses (big and little bluestem). crabgrass, pigweed, etc.
- seen mainly in monocots but some dicots
- leaves have thick-walled bundle-sheath cells
- has more energy requirements
- works well at high temps but not in lower temps
70
C4 cycle purpose and costs
- increases CO2 concentration in bundle sheath cells
- plants can reduce photorespiration and water loss in hot, dry environments
- increases CO2 concentration allows stomates to be closed more to prevent water loss
- it costs ATP (less efficient if env is not hot and dry)
71
C4 mechanisms process:
- PEP is carboxylate into OAA via PEP carboxylase in the chloroplasts of leaf mesophyll cells (fixes CO2 more readily via PEPC)
- OAA is transferred to bundle sheath cell chloroplast in the form of malate
- malate is decarboxylated into pyruvate (CO2 that comes off is taken into the Calvin cycle)
- pyruvate is converted to PEP in the leaf mesophyll in a series of steps (requires ATP)
- enhances CO2 [ ] to limit photorespiration
72
CAM cycle properties
- aka crassulacean acid metabolism
- an adaptation to arid environments
- CAM plants open stomates at night and keep them closed during the day
- also uses PEPC as initial carboxylation enzyme
- same intermediates as C4 but used in different ways
73
CAM plant examples
- cacti
- pineapple
- agave
- some orchids
74
CAM at night
- stomates are open at night to allows CO2 in
- CO2 is used to convert PEP to OAA via PEPC in the chloroplast of leaf mesophyll cell
- OAA is transferred as malate to the vacuole of leaf mesophyll cell
- malate remains in vacuole until day time
75
CAM in the day
- malate is transferred to the chloroplast
- malate is decarboxylated into CO2 and pyruvate
- CO2 is used in Calvin cycle
- pyruvate can be converted to PEP via ATP to be used again at night
76
Cellular respiration
- break down glucose to create energy
- glycolysis, pyruvate DH, CAC, ETC
- O2 is the terminal electron acceptor
