64 Questions
What is the water potential of pure water in an open beaker at room temperature?
Zero
What happens to water potential when solutes are added to a solution?
It decreases
What supports plant cells and tissues and can be lowered by water limitations causing tissues to wilt?
Turgor pressure
What drives the transport of water and minerals from roots to shoots via the xylem?
Transpiration
What is the function of the Casparian strip in the endodermis of plant roots?
Blocks apoplastic transfer of minerals from cortex to the vascular cylinder
What allows water to withstand transpiration and is important for the transport of xylem sap?
Hydrogen bonding of water molecules
What is responsible for the diffusion of water vapor from moist air spaces on the leaf to the drier air outside via stomata?
Transpiration
What causes the air-water interface to retreat farther into the cell wall and become more curved during transpiration?
Evaporation of the water film
What type of work does ATP perform?
Chemical Work
Why are plants green?
Chlorophyll reflects green wavelength of light
What is the primary function of cellular respiration?
Extracting energy stored in sugars
What happens with free energy in a closed system?
Matter can’t flow in or out, but energy can
What is the role of Redox Reactions in respiration and photosynthesis?
Critical for transferring electrons
Why doesn’t equilibrium happen in living systems?
Energy still comes in, matter can’t enter or exit
What is the primary function of photosynthesis?
Harvesting solar energy
What is the reason for plants appearing to restore something to the air that is needed by animals?
Plants release oxygen during photosynthesis
What is the process by which sugars are moved throughout the plant?
Translocation
What is the major pathway for water loss in a plant?
Stomata
What causes positive pressure to drive phloem sap from source to sink?
Pressure flow
What mechanism opens and closes stomata?
Changes in turgor pressure
What is the process by which water is moved quickly through the xylem?
Bulk flow
What is the ratio, in percent, of the amount of moisture in a volume of air to the total amount which that volume can hold at the given temperature and atmospheric pressure?
Relative humidity
What is the process by which sugars are loaded into sieve-tube elements before being exported to sinks?
Sugar loading
What is the main reason for the movement of water into roots?
Water moves from areas where solute is lower to areas where solute concentration is higher (osmosis) exerting positive pressure
What is the process by which sugars are unloaded at the sink?
Sugar unloading
What is the process by which a gas bubble is introduced to the water column in xylem?
Cavitation
What is the mechanism that explains the movement of water through xylem?
Cohesion-tension mechanism
What is the process by which water is pulled into the surrounding cells and air spaces to replace the lost water?
Cohesion and adhesion in the ascent of xylem sap
What did C.B. van Neil discover about purple sulfur bacteria?
They use H2S instead of H2O for photosynthesis
Why does chlorophyll appear green?
It mainly absorbs red and blue light
What is the function of carotenoids in photosynthesis?
Protect chlorophyll from damage by excess light
What is the primary role of photosystems I and II?
Convert light energy to chemical energy
What is the main purpose of blocking photosynthetic reactions?
Prevent weed growth
What did Melvin Calvin identify in the Calvin cycle?
The carbon pathways
How many stages does the Calvin cycle have?
Three: fixation/carboxylation, reduction, and regeneration
What did W. Engelmann do in 1883 related to photosynthesis?
Exposed filamentous algae to different light wavelengths
What is the nature of sunlight crucial for photosynthesis?
Electromagnetic energy with visible light wavelengths
Where does the synthesis through the Calvin cycle occur?
In the stroma
What is the main product of the Calvin cycle?
Sugars for energy storage
What is the key process in which plants gain electrons from hydrogen atoms?
Splitting water
What is the enzyme responsible for catalyzing the reaction between RUBP and CO2?
Rubisco
In which type of photosynthesis do mesophyll cells pump CO2 into bundle-sheath cells, avoiding the use of RUBISCO?
C4 Photosynthesis
What is the main benefit of CAM photosynthesis in arid environments?
High water use efficiency rates
What is the major factor in plant distribution and why is it important on a smaller scale?
Water; it helps support the plant and regulate temperature
What is the route through which water and solutes cross cell walls and extracellular spaces?
Apoplastic Route
What is the force exerted by water molecules at the air-water interface called?
Surface Tension
What establishes the voltage across a membrane and is used to move solutes in plants?
Proton pump
What is the role of ion channels in plants?
Open and close in response to voltage across a membrane and other factors
What is the main function of rhizobia in association with legumes?
Help plants get nutrients from soil
What is the chemical potential of water or its capacity to do work called?
Water Potential
What is the main benefit of chloroplast avoidance movements in plants under high light conditions?
Reduce photodamage to plants
What is the main function of chloroplasts in plants?
Facilitate photosynthesis
Which enzyme catalyzes the reaction between RUBP and CO2, fixing CO2 80x faster than O2?
Rubisco
What occurs when rubisco adds O to RuBP instead of C, consuming O2 and producing CO2?
Photorespiration
What leads to O2 buildup and CO2 depletion, favoring photorespiration?
Stomata closing due to water stress
Which plants can only survive under high CO2 levels due to a lack of photorespiration?
Mutant Arabidopsis plants
What reduces losses to photorespiration in plants?
C4 and CAM mechanisms
Which plants involve spatial segregation of CO2 capture and concentration in mesophyll and bundle sheath cells?
C4 plants
Which plants fix CO2 at night and conserve water by closing stomata during the day?
CAM plants
Which plants exhibit CAM idling under severe water stress?
Incomplete/Facultative CAM plants
Which plants have high water use efficiency rates, 5 to 10 times more than C3 or C4 plants?
CAM plants
What movements reduce photodamage to plants under high light conditions?
Chloroplast avoidance movements
What does plant resource acquisition include?
Shoot and root adaptations
What is responsible for the spatial segregation of CO2 capture and concentration in C4 plants?
PEP carboxylase and Rubisco
Study Notes
Photosynthesis: Key Concepts and Processes
- W. Engelmann (1883) exposed filamentous algae to different light wavelengths
- C.B. van Neil (1930) discovered purple sulfur bacteria using H2S instead of H2O
- Plants split water to gain electrons from hydrogen atoms
- Photosynthesis occurs in two stages: light reactions in thylakoids and synthesis through the Calvin cycle in stroma
- Nature of sunlight: electromagnetic energy with visible light wavelengths crucial for photosynthesis
- Chlorophyll appears green because it mainly absorbs red and blue light
- Photosynthetic pigments include reaction center chlorophyll a, chlorophyll b, and carotenoids
- Light energy is converted to chemical energy through photosystems I and II
- Practical applications include blocking photosynthetic reactions to prevent weed growth
- The Calvin cycle fixes carbon from CO2 and produces sugars for energy storage
- Melvin Calvin identified the carbon pathways in the Calvin cycle
- The Calvin cycle has three stages: fixation/carboxylation, reduction, and regeneration
Photosynthesis and Resource Acquisition in Plants
- Rubisco enzyme catalyzes the reaction between RUBP and CO2, fixing CO2 80x faster than O2.
- Photorespiration occurs when rubisco adds O to RuBP instead of C, consuming O2 and producing CO2.
- Stomata closing due to water stress leads to O2 buildup and CO2 depletion, favoring photorespiration.
- Mutant Arabidopsis plants without photorespiration can only survive under high CO2 levels.
- Carbon dioxide concentrating mechanisms like C4 and CAM reduce losses to photorespiration.
- C4 photosynthesis involves spatial segregation of CO2 capture and concentration in mesophyll and bundle sheath cells.
- CAM plants fix CO2 at night and conserve water by closing stomata during the day.
- CAM plants have morphological features that minimize water loss and thick cuticles.
- Incomplete/Facultative CAM plants exhibit CAM idling under severe water stress.
- CAM plants have high water use efficiency rates, 5 to 10 times more than C3 or C4 plants.
- Chloroplast avoidance movements reduce photodamage to plants under high light conditions.
- Plant resource acquisition includes shoot and root adaptations, microbial mutualists, and water and mineral acquisition.
Test your knowledge of photosynthesis with this quiz on key concepts and processes. From the discovery of photosynthetic pigments to the stages of the Calvin cycle, this quiz covers the fundamental aspects of photosynthesis, including key experiments and practical applications.
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