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Why are not all plants adapted to the sun, and what do they produce to cope with it?
Some plants are not adapted to the sun because they can get “sunburnt.” These plants produce anthocyanins, which are dark pigments that help neutralize reactive oxygen species (ROS).
What are the inputs of the carbon-fixing reaction?
CO₂, ATP, NADPH
What are the outputs of the carbon-fixing reaction?
Sugars
Where does the carbon fixing reaction take place?
In the storma of chloroplasts
What molecule is the starting and ending point of the Calvin Cycle, and why is it called a cycle?
The starting and ending molecule of the Calvin Cycle is RuBP (ribulose bisphosphate). It is called a cycle because RuBP is regenerated at the end of the process.
What are the three phases of the Calvin Cycle?
Carbon fixation! Reduction, regeneration
Carbon fixation
RuBP is converted to 2 molecules of 3-PGA using rubisco.
Reduction
3-PGA is reduced to G3P (PGAL) using ATP and NADPH.
Regeneration
5 G3P molecules and 3 ATP regenerate RuBP.
What happens during photorespiration and when does it occur?
Photorespiration occurs when CO₂ is scarce, and rubisco uses oxygen instead of CO₂, leading to the production of glycolate and 1 PGA. This process slows plant growth and requires energy to recover carbon.
Which three organelles are involved in photorespiration, and what role do they play?
• Chloroplast: Consumes oxygen.
• Peroxisome: Consumes oxygen and detoxifies glycolate.
• Mitochondrion: Releases CO₂.
What role do oils and fats play in plants, and what is unique about their energy content?
Oils and fats are stored in plants in the form of triacylglycerols. They have a high proportion of C-H bonds, meaning they contain more chemical energy compared to carbohydrates. Additionally, they contain a high proportion of unsaturated fatty acids.
Transitory starch
Made in leaves during photosynthesis and degraded at night for energy and metabolism.
Storage starch
Stored for long periods in non-photosynthetic tissues, such as seeds and grains, to provide energy during dormancy or germination.
How is fixed carbon stored in plants?
Fixed carbon is stored as either starch or sucrose:
Starch
Insoluble and stored in plastids, provides energy during periods without photosynthesis (e.g., at night).
Sucrose
A disaccharide used for transport in plants and stored in vacuoles or collected in roots, nectaries, and fruits.
What are the three types of photosynthesis
C3, c4, CAM
C3 photosynthesis
Used by most plants and crops, uses only the Calvin cycle, suited for cooler temperatures, and cannot avoid photorespiration.
C4 photosynthesis
Used by 50% of grasses, concentrates CO₂ in bundle sheath cells, avoids photorespiration, and is suited for warmer environments.
CAM photosynthesis
Used by succulents like cacti, stomata stay closed during the day to conserve water, CO₂ is fixed at night, and converted for use during the day.
Why do some plants produce pigments like anthocyanins in response to sun exposure?
Anthocyanins are produced to protect plants from sun damage by neutralizing reactive oxygen species (ROS) generated by excessive sunlight. These pigments help prevent cellular damage.
Why is the Calvin Cycle considered a cycle, and what role does RuBP play in this process?
The Calvin Cycle is considered a cycle because it regenerates RuBP at the end of the process, allowing the cycle to continue. RuBP is crucial because it initially captures CO₂ for carbon fixation.
How does photorespiration negatively affect plant growth, and why does it occur under certain conditions?
Photorespiration slows plant growth because it consumes energy and releases fixed carbon as CO₂ without producing sugar. It occurs when rubisco binds to oxygen instead of CO₂, usually under conditions of low CO₂ concentration and high oxygen levels.
How do C4 photosynthesis pathways help plants adapt to hot, dry environments?
concentrate CO₂ in bundle sheath cells, reducing photorespiration and increasing efficiency in warm climates.
How do CAM photosynthesis pathways help plants adapt to hot, dry environments?
fix CO₂ at night when stomata are open, conserving water by keeping stomata closed during the hot day.
How does the structure and function of starch and sucrose differ in plants, and what are their roles?
• Starch is a storage molecule that is insoluble and used for long-term energy storage, especially in seeds and grains.
• Sucrose is a soluble sugar used for transport within the plant and stored in vacuoles in tissues like roots, nectaries, and fruits for immediate energy use.
Why is photorespiration considered wasteful, and what mechanisms have plants evolved to minimize its effects?
Photorespiration is wasteful because it consumes energy and releases CO₂ without producing sugar. Plants have evolved mechanisms like C4 and CAM photosynthesis to minimize photorespiration by concentrating CO₂ near rubisco or temporally separating CO₂ fixation from sugar production.
In what ways do plants balance the need for CO₂ uptake with water conservation, especially in arid environments?
Plants in arid environments, like CAM plants, balance CO₂ uptake and water conservation by opening stomata at night to take in CO₂, which is stored for
What role do mycorrhizae play in plant-fungi interactions?
Mycorrhizae form mutualistic relationships with plants, where the fungal mycelium connects to plant roots, helping with nutrient and water absorption, while the plants provide sugars and lipids to the fungi.
endomycorrhizae
(arbuscular mycorrhizae) penetrate the cell walls of plant roots and are found in about 70% of plants.
Ectomycorrhizae
form an external sheath around plant roots without penetrating the cell walls.
What do plants provide to the fungi in a mycorrhizal relationship?
Plants provide sugars and lipids to the fungi in exchange for the resources they receive.
What do fungi provide to plants in a mycorrhizal relationship?
Fungi provide water, nutrients (such as phosphorus and nitrogen), and protection from pathogens.
How do mycorrhizae benefit plants in terms of pathogen protection?
Mycorrhizal fungi can help protect plants from soil pathogens by enhancing the plant’s defense mechanisms and creating a physical barrier against harmful organisms.