Question
11. Explain the how water is transported in the plant. 12. Describe how sugar is transported in the plant. 13. Control Systems: a. What kind of phototropism do the roots in plants display? b. What are the two types of gravitropism and which plant organs display them?
Solution
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Ivan
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Answer
11. **Water Transport in Plants:**Water transport in plants primarily occurs through the xylem, a specialized vascular tissue. The process relies on several key factors:* **Transpiration:** Water evaporates from the stomata (small pores) on the leaves, creating a negative pressure (tension) that pulls water upwards. This is the main driving force for water movement.* **Cohesion:** Water molecules stick to each other due to hydrogen bonding. This allows them to form a continuous column within the xylem.* **Adhesion:** Water molecules also adhere to the walls of the xylem vessels, further aiding in upward movement.* **Root Pressure:** While less significant than transpiration, root pressure can push water upwards from the roots, especially in smaller plants and at night when transpiration is low. This pressure is generated by the active transport of minerals into the root xylem, which draws water in by osmosis.In essence, water is pulled upwards from the roots to the leaves, like a straw, driven by the evaporative power of transpiration.12. **Sugar Transport in Plants:**Sugar transport in plants occurs through the phloem, another specialized vascular tissue. This process is called translocation.* **Source to Sink:** Sugars (primarily sucrose) are transported from areas of production (sources), such as leaves where photosynthesis occurs, to areas of storage or utilization (sinks), such as roots, fruits, and developing leaves.* **Pressure Flow Hypothesis:** This is the most widely accepted model for phloem transport. It proposes that sugar is actively loaded into the phloem at the source, creating a high solute concentration. This draws water into the phloem from the xylem by osmosis, increasing the pressure. At the sink, sugar is unloaded, and water moves back into the xylem, lowering the pressure. This pressure difference drives the flow of sugar solution from source to sink.13. **Control Systems:**a. **Root Phototropism:** Roots generally display **negative phototropism**. This means they grow away from light. This adaptation helps them efficiently explore the soil for water and nutrients.b. **Gravitropism:** There are two types of gravitropism:* **Positive Gravitropism:** Roots exhibit positive gravitropism, meaning they grow downwards in the direction of gravity. This ensures they anchor the plant and access water and nutrients in the soil.* **Negative Gravitropism:** Shoots exhibit negative gravitropism, meaning they grow upwards against the force of gravity. This allows them to reach sunlight for photosynthesis.