1. What are the major factors affecting photosynthesis?
Light intensity, CO2 concentration, temperature, water availability, chlorophyll concentration, mineral nutrients, and pH levels.
2. How does light intensity influence photosynthesis?
With increasing light intensity, the rate of photosynthesis will get higher to a certain point, and then it stabilises.
3. Why is CO2 necessary for photosynthesis?
Since CO2 is one of the raw materials needed for the Calvin cycle, then its concentration will directly affect the rate of photosynthesis.
4. What is the temperature range for optimum photosynthesis?
The optimum temperature varies amongst plants and it falls between 20°C – 30°C.
5. How do farmers ensure optimal photosynthesis of crops?
By manipulating light, CO2, water, nutrients and protection from extreme temperatures and pollution.
6. What is the compensation point in photosynthesis?
The compensation point is the light intensity at which the rate of photosynthesis exactly matches the rate of respiration. At this point, there is no net production or consumption of oxygen or carbon dioxide.
7. How does the availability of minerals affect photosynthesis?
Minerals like magnesium (part of chlorophyll), iron (involved in chlorophyll synthesis), and potassium (regulates stomatal opening) are crucial for photosynthesis. Their deficiency can significantly reduce photosynthetic efficiency.
8. How do plants adapt to low light conditions?
Plants adapt to low light by increasing chlorophyll content, enlarging leaf surface area, and optimizing leaf orientation. Some plants also have accessory pigments to capture a broader spectrum of light.
9. What is the light compensation point?
The light compensation point is the light intensity at which the rate of photosynthesis exactly balances the rate of respiration. Below this point, the plant consumes more glucose than it produces.
10. How do environmental pollutants affect photosynthesis?
Pollutants like sulfur dioxide and ozone can damage chlorophyll, reduce stomatal opening, and interfere with enzyme function. This can significantly decrease photosynthetic efficiency and overall plant health.
11. How does carbon dioxide concentration affect photosynthesis?
Increasing carbon dioxide concentration generally increases the rate of photosynthesis, as CO2 is a reactant in the process. However, like light intensity, there's a saturation point beyond which additional CO2 doesn't increase the rate further.
12. What is the role of water in photosynthesis?
Water is a reactant in photosynthesis. It's split during the light-dependent reactions to provide electrons and protons (hydrogen ions) for the production of NADPH and ATP. It also maintains the turgor pressure in plant cells, keeping leaves expanded to capture light.
13. How does light intensity affect the rate of photosynthesis?
As light intensity increases, the rate of photosynthesis also increases up to a certain point. After this point, other factors become limiting, and the rate plateaus. This relationship is known as light saturation.
14. How does temperature affect photosynthesis?
Temperature affects the rate of photosynthesis by influencing enzyme activity. As temperature increases, the rate of photosynthesis increases up to an optimal temperature. Beyond this point, enzyme denaturation occurs, and the rate decreases rapidly.
15. How do different wavelengths of light affect photosynthesis?
Different wavelengths of light affect photosynthesis to varying degrees. Blue and red light are most effective for photosynthesis as chlorophyll absorbs these wavelengths best. Green light is least effective as it's mostly reflected by chlorophyll, giving plants their green color.
16. How do stomata regulate photosynthesis?
Stomata are pores in leaves that control gas exchange. They open to allow CO2 in for photosynthesis and close to prevent water loss. Their regulation affects the availability of CO2 for photosynthesis and the plant's water status.
17. What is the importance of NADPH in photosynthesis?
NADPH (Nicotinamide Adenine Dinucleotide Phosphate) is a reducing agent produced in the light-dependent reactions. It provides the electrons needed to reduce carbon dioxide to glucose in the Calvin cycle.
18. What is the role of RuBisCO in photosynthesis?
RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the primary enzyme in carbon fixation. It catalyzes the first major step of carbon fixation in the Calvin cycle, adding CO2 to ribulose-1,5-bisphosphate.
19. What is photorespiration and how does it affect photosynthesis?
Photorespiration is a process where the enzyme RuBisCO fixes oxygen instead of carbon dioxide, producing no ATP and wasting energy. It reduces the efficiency of photosynthesis, especially in hot, dry conditions when stomata close and oxygen concentrations increase relative to CO2.
20. What is the role of ATP in photosynthesis?
ATP (Adenosine Triphosphate) provides the energy needed for various steps in photosynthesis, particularly in the Calvin cycle. It's produced during the light-dependent reactions and used in the light-independent reactions to power carbon fixation.
21. What is the role of accessory pigments in photosynthesis?
Accessory pigments like carotenoids and phycobilins absorb light at wavelengths not efficiently absorbed by chlorophyll. They transfer this energy to chlorophyll, expanding the range of light wavelengths useful for photosynthesis.
22. How does leaf anatomy contribute to efficient photosynthesis?
Leaf anatomy is optimized for photosynthesis with a thin, flat shape to maximize light absorption. The upper epidermis is often transparent, palisade mesophyll cells are tightly packed for efficient light capture, and spongy mesophyll allows gas diffusion.
23. What is the importance of the proton gradient in photosynthesis?
The proton gradient, established across the thylakoid membrane during the light-dependent reactions, drives ATP synthesis through chemiosmosis. This ATP is crucial for powering the Calvin cycle and other cellular processes.
24. How does atmospheric oxygen concentration affect photosynthesis?
High oxygen concentrations can inhibit photosynthesis by promoting photorespiration. Oxygen competes with CO2 for the active site of RuBisCO, leading to the wasteful fixation of O2 instead of CO2.
25. How do plants balance CO2 uptake and water loss through stomata?
Plants regulate stomatal opening to balance CO2 uptake for photosynthesis with water loss through transpiration. They typically open stomata when light is available for photosynthesis and close them under water stress conditions.
26. What is photosynthesis and why is it important?
Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy stored in glucose or other sugars. It's important because it provides the energy basis for nearly all life on Earth, produces oxygen as a byproduct, and helps regulate the Earth's carbon cycle.
27. What is the basic equation for photosynthesis?
The basic equation for photosynthesis is:
28. What role does chlorophyll play in photosynthesis?
Chlorophyll is the primary pigment in photosynthesis. It absorbs light energy, primarily in the blue and red parts of the spectrum, and converts it into chemical energy to drive the photosynthetic process.
29. What is the difference between light-dependent and light-independent reactions in photosynthesis?
Light-dependent reactions occur in the thylakoid membranes and require direct light energy to produce ATP and NADPH. Light-independent reactions (Calvin cycle) occur in the stroma and use the products of light-dependent reactions to fix carbon dioxide into glucose, not requiring direct light energy.
30. How do C3, C4, and CAM plants differ in their photosynthetic processes?
C3 plants use the standard Calvin cycle for carbon fixation. C4 plants have an additional step to concentrate CO2 before the Calvin cycle, making them more efficient in hot, dry climates. CAM plants temporally separate CO2 fixation and the Calvin cycle, opening their stomata at night to reduce water loss.
31. How does water stress affect photosynthesis?
Water stress reduces photosynthesis by causing stomata to close, limiting CO2 intake. It also reduces the efficiency of light-dependent reactions and can lead to wilting, which reduces the leaf area available for light capture.
32. What is the relationship between photosynthesis and cellular respiration?
Photosynthesis and cellular respiration are complementary processes. Photosynthesis produces glucose and oxygen, which are then used in cellular respiration to produce ATP. Respiration, in turn, produces CO2, which is used in photosynthesis.
33. How does leaf orientation affect photosynthetic efficiency?
Leaf orientation affects light interception. Many plants can adjust leaf angles throughout the day to optimize light capture. Some plants have vertically oriented leaves to avoid excessive light exposure and water loss in hot climates.
34. What is the role of the electron transport chain in photosynthesis?
The electron transport chain in photosynthesis transfers electrons from water to NADP+, creating NADPH. This process also pumps protons into the thylakoid space, creating a proton gradient that drives ATP synthesis.
35. What is the importance of the light-harvesting complex in photosynthesis?
The light-harvesting complex consists of proteins and pigments that capture light energy and funnel it to the reaction center chlorophylls. This increases the efficiency of light capture and allows photosynthesis to occur in lower light conditions.
36. How does the C4 pathway enhance photosynthetic efficiency in certain conditions?
The C4 pathway enhances efficiency by concentrating CO2 around RuBisCO, reducing photorespiration. This is particularly beneficial in hot, dry environments where stomata may be closed for long periods, limiting CO2 availability.
37. What is the role of phosphorylation in photosynthesis?
Phosphorylation is crucial in photosynthesis for producing ATP during the light-dependent reactions. This ATP provides the energy needed for carbon fixation and other cellular processes.
38. How do different types of stress affect photosynthetic rate?
Various stresses like drought, heat, cold, and salinity can reduce photosynthetic rate by affecting stomatal opening, enzyme activity, membrane integrity, and pigment content. Plants have evolved various mechanisms to cope with these stresses.
39. What is the quantum yield of photosynthesis?
The quantum yield of photosynthesis is the amount of carbon fixed or oxygen evolved per photon of light absorbed. It's a measure of the efficiency of light utilization in photosynthesis.
40. How does leaf senescence affect photosynthesis?
Leaf senescence, the process of leaf aging and death, gradually reduces photosynthetic capacity. It involves the breakdown of chlorophyll and other cellular components, redirecting nutrients to other parts of the plant.
41. What is the role of cytochromes in photosynthesis?
Cytochromes are electron carriers in the photosynthetic electron transport chain. They help transfer electrons from photosystem II to photosystem I, contributing to the generation of the proton gradient used for ATP synthesis.
42. How do plants adjust their photosynthetic machinery to changing light conditions?
Plants can adjust to changing light conditions through processes like state transitions (redistributing light-harvesting complexes between photosystems) and long-term acclimation (changing the ratio of photosystems or overall pigment content).
43. What is the importance of the Z-scheme in photosynthesis?
The Z-scheme describes the flow of electrons from water to NADP+ through photosystems II and I. It's crucial for understanding how light energy is converted into chemical energy (ATP and NADPH) during the light-dependent reactions.
44. How does elevated CO2 affect plant growth and photosynthesis in the long term?
Elevated CO2 initially increases photosynthetic rate and plant growth. However, long-term exposure can lead to acclimation, where plants may reduce their photosynthetic capacity or nitrogen content, potentially affecting plant nutrition.
45. What is the role of ferredoxin in photosynthesis?
Ferredoxin is an iron-sulfur protein that accepts electrons from photosystem I and transfers them to NADP+ reductase, which then reduces NADP+ to NADPH. This is a crucial step in producing the reducing power needed for carbon fixation.
46. How do aquatic plants adapt their photosynthetic processes to underwater environments?
Aquatic plants adapt to underwater environments by having thin leaves for better gas exchange, using bicarbonate ions as a carbon source, and having specialized chloroplasts and pigments to capture the available light spectrum underwater.
47. What is the role of the xanthophyll cycle in protecting plants from excess light?
The xanthophyll cycle helps protect plants from excess light energy by converting violaxanthin to zeaxanthin, which can dissipate excess energy as heat. This prevents damage to the photosynthetic apparatus under high light conditions.
48. How does the arrangement of chloroplasts within a cell affect photosynthetic efficiency?
Chloroplasts can move within cells to optimize light capture. Under low light, they spread out to maximize absorption. Under intense light, they cluster to shade each other, protecting against photodamage.
49. What is the relationship between photosynthesis and nitrogen fixation in legumes?
In legumes, photosynthesis provides the energy and carbon skeletons needed for nitrogen fixation by symbiotic bacteria. In return, fixed nitrogen enhances photosynthetic capacity by increasing the production of chlorophyll and other proteins.
50. How do C4 plants minimize photorespiration?
C4 plants minimize photorespiration by spatially separating initial CO2 fixation and the Calvin cycle. They concentrate CO2 around RuBisCO, reducing its oxygenase activity and thus photorespiration.
51. What is the role of plastoquinone in photosynthesis?
Plastoquinone is an electron carrier in the photosynthetic electron transport chain. It accepts electrons from photosystem II and transfers them to the cytochrome b6f complex, playing a crucial role in generating the proton gradient.
52. How does the source-sink relationship affect photosynthetic rate?
The source-sink relationship affects photosynthetic rate through feedback inhibition. When sinks (like growing fruits) are removed or full, excess photosynthetic products can accumulate in leaves, potentially downregulating photosynthesis.
53. What is the role of state transitions in optimizing photosynthesis?
State transitions involve the movement of light-harvesting complexes between photosystems I and II to balance the excitation of both photosystems. This helps optimize the efficiency of light utilization under changing light conditions.
54. How do plants protect their photosynthetic apparatus from photodamage?
Plants protect against photodamage through mechanisms like non-photochemical quenching (dissipating excess energy as heat), antioxidant systems, repair mechanisms for damaged proteins, and physical adaptations like leaf movements or wax layers.
55. What is the importance of cyclic electron flow in photosynthesis?
Cyclic electron flow around photosystem I generates ATP without producing NADPH. This helps balance the ATP:NADPH ratio required for carbon fixation and provides extra ATP for other cellular processes, especially under stress conditions.
