Chapter 36 Flashcards
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What are the dual habitats of plants and why are they significant?
Plants inhabit two distinct environments: above ground (shoots) and below ground (roots). This dual habitat is significant because it allows plants to acquire essential resources from both environments. Shoots capture sunlight and CO₂ for photosynthesis, while roots absorb water and minerals from the soil. This adaptation was crucial for the colonization of land by plants, enabling them to thrive in diverse terrestrial ecosystems
How did early algal ancestors and nonvascular plants adapt to their environments?
Early algal ancestors absorbed water, minerals, and CO₂ directly from the surrounding water, with all cells being close to resources. Nonvascular early plants grew photosynthetic shoots above shallow freshwater and developed adaptations such as waxy cuticles to minimize water loss and few stomata for gas exchange. These adaptations allowed them to survive in environments where water was not always readily available.
What role did the development of roots and shoots play in plant evolution?
The development of roots and shoots was pivotal in plant evolution. Roots anchored plants and absorbed water and minerals, while shoots allowed plants to grow taller and capture more sunlight. This led to increased photosynthetic efficiency and the ability to support larger, more complex plant structures. The evolution of vascular systems (xylem and phloem) enabled efficient long-distance transport of water, minerals, and photosynthetic products, further supporting plant growth and diversification.
Describe the adaptations in shoot architecture that enhance light capture.
Shoot architecture adaptations that enhance light capture include:
Stem Length and Thickness: Tall stems avoid shading by neighboring plants, and thick stems support vascular flow and mechanical stability.
Branching Patterns: Branching allows for better sunlight harvesting by spreading leaves over a larger area.
Leaf Diversity: Large leaves in rainforests maximize light capture, while small leaves in arid or cold regions reduce water loss.
Phyllotaxy: The arrangement of leaves on stems (alternate, opposite, or whorled) minimizes shading and maximizes light exposure.
Leaf Orientation: Horizontal leaves maximize light capture in low-light environments, while vertical leaves reduce overheating in intense sunlight.
What is the significance of the leaf area index (LAI) in plants?
The leaf area index (LAI) is the ratio of total upper leaf surface area to the ground area covered by the plant. It is significant because it indicates the plant’s ability to capture sunlight for photosynthesis. An optimal LAI ensures efficient light capture without excessive self-shading. Excessive LAI can lead to self-pruning, where shaded leaves die and fall off, reducing the plant’s overall photosynthetic capacity.
How do root architecture and mutualistic associations enhance resource acquisition?
Root architecture and mutualistic associations enhance resource acquisition in the following ways:
Adaptive Root Growth: Roots grow through nutrient-poor patches and branch in nutrient-rich pockets, optimizing nutrient uptake.
Mycorrhizae: Symbiotic relationships with fungi (mycorrhizae) increase the surface area for water and phosphate absorption, improving nutrient uptake and plant growth.
What are the three pathways for resource movement in plants?
The three pathways for resource movement in plants are:
Apoplast Route: Movement through cell walls and extracellular spaces.
Symplast Route: Movement through the cytoplasm connected via plasmodesmata.
Transmembrane Route: Movement across cell membranes and cell walls repeatedly.
Explain the role of proton pumps in solute transport across plant cell membranes.
Proton pumps actively transport H⁺ ions out of the cell, creating a proton gradient across the membrane. This gradient generates a membrane potential, which drives the uptake of nutrients through cotransport mechanisms. For example, the proton gradient facilitates the uptake of nitrate (NO₃⁻) and sucrose into the cell. Proton pumps also help regulate cell pH and maintain ion homeostasis.
What is water potential and how does it predict water movement in plants?
Water potential (Ψ) is a measure of the potential energy of water in a system and predicts the direction of water movement. It is determined by solute potential (ΨS) and pressure potential (ΨP). Water moves from regions of higher water potential to regions of lower water potential. In plants, water potential gradients drive the movement of water from the soil into roots, through the plant, and out through the leaves via transpiration.
Describe the cohesion-tension mechanism for the ascent of xylem sap.
The cohesion-tension mechanism explains the upward movement of water (xylem sap) from roots to leaves. Transpiration creates a negative pressure (tension) in the leaf air spaces, pulling water from the xylem. Water molecules are cohesive (stick together) due to hydrogen bonding, forming a continuous column in the xylem. Adhesion (water molecules sticking to xylem walls) helps counteract gravity. This mechanism relies on the physical properties of water and the structure of the xylem.
How do stomata regulate water loss and gas exchange in plants?
Stomata are pores on the leaf surface that regulate water loss and gas exchange. Guard cells control the opening and closing of stomata. When guard cells take up potassium ions (K⁺), they become turgid and open the stomata, allowing CO₂ to enter for photosynthesis and water vapor to exit. When guard cells lose K⁺, they become flaccid and close the stomata, reducing water loss. Environmental factors such as light, CO₂ concentration, and water availability influence stomatal behavior.
What is the role of aquaporins in water transport in plants?
Aquaporins are membrane proteins that facilitate the rapid diffusion of water across cell membranes. They increase the efficiency of water movement in response to osmotic gradients. Aquaporins can be regulated by factors such as cytosolic pH and calcium ion (Ca²⁺) concentrations, ensuring that water transport is responsive to the plant’s needs and environmental conditions.
Explain the process of bulk flow in the xylem and phloem.
Bulk flow is the movement of water and solutes together due to pressure differences. In the xylem, bulk flow is driven by the negative pressure created by transpiration, pulling water and minerals from roots to leaves. In the phloem, bulk flow is driven by positive pressure generated by the active loading of sugars into sieve-tube elements, creating a pressure gradient that moves phloem sap from sources (e.g., leaves) to sinks (e.g., roots, fruits)
How do plants adapt to minimize water loss in arid environments?
Plants in arid environments have several adaptations to minimize water loss:
Reduced Leaf Surface Area: Smaller leaves or modified structures like spines reduce transpiration.
Thick Cuticles: A thick, waxy cuticle reduces water loss through the leaf surface.
CAM Photosynthesis: CAM plants open their stomata at night to reduce water loss while still allowing CO₂ uptake for photosynthesis.
Deep Root Systems: Extensive root systems access deeper water sources.
What is the significance of the proton gradient in ATP synthesis during photosynthesis?
The proton gradient across the thylakoid membrane is crucial for ATP synthesis during photosynthesis. As electrons move through the electron transport chain, protons are pumped into the thylakoid space, creating a high concentration of protons. This gradient drives protons back into the stroma through ATP synthase, providing the energy needed to convert ADP and inorganic phosphate (Pi) into ATP. This process, known as photophosphorylation, is essential for providing the energy required for the Calvin cycle.
