48 Questions
Which specific molecule in photosystem II primarily absorbs light during the light-dependent reactions?
Chlorophyll
What is the initial effect of light absorption in photosystem II?
Raising electrons in chlorophyll to a higher energy level
After electrons in photosystem II absorb light energy, to what component are they passed?
Electron transport chain
Why is the first discovered photosystem called photosystem II?
It was discovered after photosystem I
In what figure would you find the depiction of chlorophyll molecules absorbing light in photosystem II?
Figure 9.8
What molecules are produced during the light-dependent reactions?
ATP and NADPH
Where do the light-dependent reactions of photosynthesis occur?
In the thylakoids within chloroplasts
What is the primary role of chlorophyll in the light-dependent reactions?
To absorb light energy
What is one of the by-products of the light-dependent reactions?
Oxygen
What initiates the light-dependent reactions in photosynthesis?
Sunlight
In photosynthesis, what is the source of the high-energy electrons generated during the light-dependent reactions?
Water
What element is liberated as a by-product during the light-dependent reactions?
Oxygen
Which specific location within the chloroplast does the light-dependent reaction take place?
In the thylakoid membranes
What do the light-dependent reactions of photosynthesis convert ADP and NADP+ into?
ATP and NADPH
What type of energy is utilized in the light-dependent reactions of photosynthesis?
Light energy
Which of the following molecules are the primary energy carriers produced by the light-dependent reactions?
ATP and NADPH
Which molecules serve as the substrates in the conversion process during the light-dependent reactions?
ADP and NADP+
In light-dependent reactions, which components are correctly matched with their role?
Light energy: drives reactions, ADP and NADP+: converted substrates
What molecule is used in the Calvin cycle to produce a six-carbon sugar?
Carbon dioxide
Which process directly supplies the energy needed for the Calvin cycle?
Light-dependent reactions
What does the Calvin cycle use from the atmosphere to fuel the synthesis of sugars?
Carbon dioxide
In addition to sugars, which compounds are synthesized using the products of the Calvin cycle?
Proteins, fats, and nucleic acids
What is one of the end results of the Calvin cycle related to energy for organisms?
Synthesis of high-energy sugars
What creates the difference in H+ concentration across the thylakoid membrane?
The accumulation of H+ ions within the thylakoid space
What happens to the carbon dioxide used in the Calvin cycle?
It is converted into sugars and other compounds
In the process of ATP synthesis in chloroplasts, what role does ATP synthase play?
Allows H+ to pass through and harnesses the concentration difference to generate ATP
What happens immediately after electrons are released by photosystem II?
They flow down an electron transport chain
How is NADPH generated in the thylakoid membrane?
As electrons move from photosystem II to photosystem I
Which component is responsible for splitting water molecules to release electrons?
Photosystem II
Where does the energy to power ATP synthesis come from?
The kinetic energy of H+ ions moving through ATP synthase
What is the main purpose of the light-dependent reactions?
To generate ATP and NADPH
What is represented by the yellow line in the diagram?
The pathway of electron movement from photosystem II to photosystem I
What is a key difference between C4 and CAM plants in their photosynthetic adaptations?
C4 plants capture carbon dioxide during the day, while CAM plants capture it during the night.
Why do C4 plants require extra energy in the form of ATP?
To capture very low levels of carbon dioxide.
What is the primary purpose of the specialized chemical pathway in C4 plants?
To capture and utilize low levels of carbon dioxide.
Which of the following is not true about CAM plants?
They primarily use a four-carbon compound pathway.
What is the main advantage of the adaptations found in CAM plants?
Minimized water loss.
Why do most plants close their leaf openings in bright and hot conditions?
To conserve water.
What unique biochemical adaptation is found in all CAM plants?
Fixation of carbon dioxide into organic acids at night.
Which of the following plants is an example of a C4 plant?
Corn
Why does the rate of photosynthesis become high and similar in both plants at low light intensity?
As both plants adapt to low light intensity in the same way
What advantage does a higher rate of photosynthesis in strong light provide to the plant?
It enables faster growth and more energy storage
Which temperature range is optimal for enzyme function in photosynthesis?
0°C to 20°C
What primarily limits the rate of photosynthesis when light intensity reaches a certain level?
The saturation of chlorophyll molecules
Which adaptation helps plants survive in dry conditions?
Reducing leaf surface area
How does water scarcity affect photosynthesis?
Slows down and might stop photosynthesis
Why might photosynthesis rates slow down at temperatures below 0°C?
Enzyme activity decreases
What happens to the rate of photosynthesis as light intensity increases initially?
It increases proportionally
Study Notes
Photosynthesis
- Photosynthesis is the process by which plants take in carbon dioxide and water, and with the help of sunlight, produce sugars and oxygen.
Light-Dependent Reactions
- The light-dependent reactions occur in the thylakoids of chloroplasts and use energy from light to create ATP and NADPH.
- Oxygen (O2) is produced as a by-product of the light-dependent reactions.
- The light-dependent reactions include the steps of photosynthesis that directly involve sunlight.
Photosystem II
- The light-dependent reactions begin in photosystem II.
- Chlorophyll molecules in photosystem II absorb light, which raises electrons to a higher energy level.
- These high-energy electrons are passed from chlorophyll to the electron transport chain.
Hydrogen Ion Movement and ATP Formation
- Hydrogen ions (H+) accumulate within the thylakoid space.
- The buildup of hydrogen ions creates a difference in H+ concentration across the thylakoid membrane.
- ATP synthase harnesses the concentration difference of H+ to power ATP synthesis.
- The movement of electrons and H+ in the thylakoid membrane generates a proton gradient that drives ATP synthesis.
The Light-Independent Reactions (Calvin Cycle)
- The Calvin cycle uses six molecules of carbon dioxide to produce a single six-carbon sugar molecule.
- The energy for this reaction is supplied by molecules produced in the light-dependent reactions.
- The Calvin cycle uses carbon dioxide from the atmosphere and energy from light-dependent reactions to fuel the arrangement and assembly of sugars.
End Results of Photosynthesis
- Plants can grow and produce energy-rich sugars.
- Animals, including humans, can obtain energy from these sugars through cellular respiration.
- Photosynthesis produces the energy for nearly every organism on earth, including humans.
- The carbon dioxide used in the Calvin cycle is produced by cellular respiration in animals and the burning of fossil fuels, and from the decomposition of organisms.
Factors Affecting Photosynthesis
- Temperature, light, and water availability affect the rate of photosynthesis.
- Temperature: Most enzymes function best between 0°C and 20°C.
- Light: The intensity of light affects the rate of photosynthesis.
- Water: Water is a raw material of photosynthesis, and a shortage of water can slow down the rate of photosynthesis.
Photosynthesis Under Extreme Conditions
- C4 plants have a specialized chemical pathway that allows them to capture very low levels of carbon dioxide and pass it to the Calvin cycle.
- CAM plants use a different strategy in which carbon dioxide becomes incorporated into organic acids during photosynthesis.
- C4 plants include important crop plants like corn, sugar cane, and sorghum.
- CAM plants include pineapple, many desert cacti, and the fleshy "ice plant".
Explore the fascinating process of photosynthesis, from light-dependent and light-independent reactions to how plants store energy. Test your knowledge of this biochemical pathway!
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