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Plant Physiological Ecology
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Plant Physiological Ecology
Plant Physiological Ecology
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1
Question
What is net photosynthesis and how is it calculated?
Answer
Net photosynthesis is the increase or decrease of gross (true) photosynthesis minus photorespiration and dark respiration. It is calculated as Net Photosynthesis = Gross Photosynthesis - Dark Respiration.
2
Question
What processes contribute to gross photosynthesis and dark respiration in plants?
Answer
Gross photosynthesis includes light and dark reactions, while dark respiration involves both aerobic and anaerobic respiration.
3
Question
Why must plants maintain a positive carbon balance, and what environmental factor influences this?
Answer
Plants must maintain a positive carbon balance to support survival, growth, and reproduction. The presence of other plants influences the amount of photosynthetically active radiation (PAR) each plant receives, affecting their carbon balance.
4
Question
How does carbon allocation within a plant affect its growth?
Answer
Carbon allocation influences how plants survive, grow, and reproduce. Under ideal conditions, allocating carbon to leaf tissue promotes the fastest growth, especially when exposed to less sunlight, by increasing the photosynthetic surface area.
5
Question
Explain the concept of 'carbon balance' in plants beyond just net photosynthesis.
Answer
Carbon balance involves the balance between CO₂ uptake through photosynthesis and loss through respiration. It accounts for the total carbon uptake over time, considering photosynthesis per leaf area multiplied by total leaf surface area, minus respiration per time multiplied by the mass of living tissue.
6
Question
How do plants exchange heat with their environment to maintain positive net photosynthesis?
Answer
Plants exchange heat with their environment through convection and evaporation (for terrestrial plants) or convection alone (for aquatic plants). Absorbed radiation powers metabolic processes, heats leaves, and surrounding air.
7
Question
Why is Rubisco considered a costly molecule for plants, and what role does it play?
Answer
Rubisco is costly because it accounts for about 40% of chloroplast protein and is likely the most abundant protein on Earth. It catalyzes the start of the Calvin Cycle, which is essential for carbon fixation during photosynthesis.
8
Question
What are the differences between sun-adapted (shade-intolerant) and shade-adapted (shade-tolerant) plants?
Answer
Sun-adapted plants (shade-intolerant) thrive in high-light environments and often allocate resources differently to maximize photosynthesis. Shade-adapted plants (shade-tolerant) are adapted to low-light environments and have morphological and physiological traits suited for limited light.
9
Question
What is phenotypic plasticity in the context of plant adaptation to light environments?
Answer
Phenotypic plasticity refers to the variation in photosynthetic and morphological responses among individuals of the same species grown in different light conditions, allowing adaptation to either high-light or low-light environments.
10
Question
What physiological changes occur in seedlings grown under low light conditions?
Answer
Seedlings grown under low light conditions experience a lower rate of respiration, a decrease in light compensation point, a decrease in maximum rate of net photosynthesis at light saturation, greater specific leaf area (larger and thinner leaves), and allocate more carbon to leaf production with less to roots.
11
Question
What key trade-offs did Stuart Davies study in his greenhouse experiments on Macaranga seedlings?
Answer
Stuart Davies studied the trade-offs among leaf respiration rate, light compensation point, and maximum rate of net photosynthesis in seedlings of nine Macaranga species.
12
Question
How do C₄ plants prevent the cost of photorespiration?
Answer
C₄ plants prevent photorespiration by incorporating CO₂ into four-carbon compounds in mesophyll cells and bundle sheath cells, effectively concentrating CO₂ and minimizing oxygen interference with photosynthesis.
13
Question
Describe the main steps of the C₄ carbon cycle as shown in the flow chart.
Answer
In the mesophyll cell, PEP carboxylase converts PEP into oxaloacetate (4C), which is then converted into malate (4C). Malate moves into the bundle sheath cell and is converted into pyruvate (3C). Pyruvate returns to the mesophyll cell to begin the cycle again. Inside the bundle sheath cell, malate releases CO₂, which enters the Calvin Cycle to produce sugars.
14
Question
Why have some plants evolved alternative photosynthetic pathways in warmer and drier environments?
Answer
Plants adapted to warmer and drier environments have evolved alternative photosynthetic pathways like C₄ and CAM to increase water-use efficiency and better manage water demand under heat and drought stress.
15
Question
What are some plant responses to moisture stress?
Answer
Plants respond to moisture stress through leaf curling and wilting, inhibition of chlorophyll production leading to leaf loss, becoming drought deciduous, and adopting modified photosynthetic pathways.
16
Question
What is the relationship between plant water demand and temperature, and how does it affect stomatal behavior?
Answer
Water demand increases with temperature. Plants must balance stomatal opening: closing stomata reduces water loss but also limits CO₂ intake and evaporative cooling, leading to lower photosynthesis rates and higher leaf temperatures.
17
Question
What is meant by phenotypic plasticity in the context of plants adapting to different light environments?
Answer
Phenotypic plasticity refers to the variation among individuals of the same species grown under different light conditions, such as shade-intolerant species adapting to high light and shade-tolerant species adapting to low light environments.
18
Question
How does the water-use efficiency of C₄ plants compare to other plants for a given degree of stomatal opening?
Answer
For the same stomatal opening and water loss, C₄ plants typically fix more carbon, resulting in greater water-use efficiency compared to other plant types.
19
Question
What difference exists between the C₄ and CAM photosynthetic pathways in terms of spatial and temporal separation?
Answer
C₄ photosynthesis separates carbon fixation and the Calvin cycle spatially between mesophyll and bundle sheath cells (spatial separation), while CAM photosynthesis separates these steps temporally by fixing CO₂ at night and performing the Calvin cycle during the day (temporal separation).
20
Question
How does water loss per gram of CO₂ gained compare among CAM, C₄, and C₃ plants?
Answer
CAM plants lose 50-100 grams of water per gram of CO₂ gained; C₄ plants lose 250-300 grams of water per gram of CO₂ gained; and C₃ plants lose 400-500 grams of water per gram of CO₂ gained.
21
Question
What is Crassulacean Acid Metabolism (CAM) and how does it help plants conserve water?
Answer
CAM is a carbon fixation pathway used by some plants, such as succulents, where stomata open at night to incorporate CO2 into organic acids. During the day, stomata close to reduce water loss, and CO2 is released from organic acids for use in the Calvin cycle. This process improves water efficiency in plants.
22
Question
How do C₄ plants differ in carbon fixation compared to other plants, and what advantage does this give them?
Answer
C₄ plants fix more carbon for a given amount of stomatal opening and water loss, which leads to greater water-use efficiency. They are commonly found in grasses native to tropical and subtropical regions.
23
Question
What role does nitrogen play in photosynthesis, and how is it linked to photosynthetic rate?
Answer
Nitrogen is a major component of rubisco and chlorophyll, both essential for photosynthesis. The maximum (light saturated) rate of photosynthesis is correlated with the leaf nitrogen content—higher nitrogen generally leads to higher photosynthesis rates.
24
Question
What are macronutrients and micronutrients in plants, and how do they affect plant growth?
Answer
Macronutrients are elements plants need in large amounts, while micronutrients are needed in smaller, often trace amounts. The availability of these nutrients directly affects plant survival, growth, and reproduction.
25
Question
How can plants adapt their leaves to minimize water loss in response to environmental conditions?
Answer
Plants can modify leaf features such as increasing cell wall thickness, reducing stomatal size, altering the density of the vascular system, and producing hairs, wax, or resins to reduce water loss.
26
Question
What changes occur in plant root and leaf structure when soil water is low?
Answer
Plants allocate more carbon to roots to explore deeper and larger soil volumes, and reduce leaf area exposure by producing smaller and thicker leaves to minimize water loss through transpiration.
27
Question
How do wetland plants adapt to anaerobic or flooded soil conditions?
Answer
Some wetland plants accumulate ethylene in their roots, which stimulates cells to self-destruct and form gas-filled chambers called aerenchyma. These chambers help facilitate oxygen transport within the plant under flooded conditions.
28
Question
Why is excess water stressful to plants, and what similarity does it share with water deficiency symptoms?
Answer
Excess water fills soil pores causing root 'drowning' and forcing roots into anaerobic respiration, which limits oxygen availability. Symptoms of excess water stress are similar to those caused by insufficient water, affecting plant function.
29
Question
How does root mass relate to a plant's ability to exploit nutrient resources, especially in low-nutrient environments?
Answer
A greater root mass allows plants to access more nutrients from the soil. In low-nutrient environments, plants can compensate by increasing root production to improve nutrient uptake.
30
Question
How do nutrient availability and a plant's growth rate influence each other?
Answer
Nutrient availability affects a plant's uptake of nutrients, which influences its growth rate. Conversely, a plant's growth rate determines its nutrient demand, creating a direct relationship between nutrient availability and plant growth.