2. plants and water Flashcards
water use in plants
Water is vital for plant survival, supporting essential processes such as photosynthesis, nutrient transport, and maintaining structural integrity
What is transpiration? What are the 2 steps?
the process by which water is absorbed by plant roots from the soil, moves through the plant, and is released as water vapor through small openings called stomata on the leaves and stems.
First step- Evaporation then diffusion
How are leaves adapted to prevent water loss?
Stomata regulation, waxy cuticle, trichomes, shape
Number of stomata per square mm?
100-1000
How do stomata open and close? The role of sucrose(afternoon) and potassium(morning)
Stomata open and close through the actions of guard cells, which surround the stomatal pore. The movement of water into and out of these guard cells, regulated by ion transport and osmotic changes, controls the opening and closing of the stomata. Toward the end of the day or during stress, sucrose levels decrease, facilitating stomatal closure
Guard cell walls – arrangement of microfibrils?
Radial microfibril arrangement controls the direction of guard cell expansion.
the differential thickness of the inner and outer cell walls causes guard cells to bend outward when turgid, leading to stomatal opening.
What is a circadian rhythm?
internal process that regulates various physiological and biochemical activities on a roughly 24-hour cycle, even in the absence of external cues like light or temperature. These rhythms are driven by the plant’s internal biological clock and help synchronize the plant’s activities with the day-night cycle.
What is photoperiodism? What controls this? (Phytochrome)
Photoperiodism: Plant response to day length, controlling flowering, dormancy, and other processes.
Phytochrome: The light-sensitive pigment that helps plants measure day and night length through two forms (Pr and Pfr).
Water conduction – the Cohesion-Adhesion-Tension Theory
water Uptake by Roots: Water is absorbed from the soil into the root hairs by osmosis. This water then enters the xylem, the plant’s main water-conducting tissue.
Cohesion: Water molecules form a continuous column from the roots to the leaves due to their cohesive properties, as they stick together through hydrogen bonds.
Adhesion: Water molecules adhere to the walls of the xylem vessels, helping maintain the upward flow of water against gravity.
Tension from Transpiration: As water evaporates from the stomata in the leaves (during transpiration), it generates tension (negative pressure) in the xylem. This tension pulls more water upward from the roots, maintaining a constant supply of water to the leaves.
Water Transport to the Leaves: The combination of cohesion, adhesion, and tension allows water to move through the plant’s vascular system, providing essential moisture for photosynthesis and maintaining cell turgidity.
Xylem embolisms – what are these? Implication for flowers?
air blockages that interfere with water transport in plants. For flowers, these embolisms can lead to wilting, reduced lifespan, and impaired reproductive functions. In cut flowers, preventing embolisms through proper cutting techniques can help extend their freshness and longevity.
