Answer:
Explanation:
### C) Three Roles of Active Transport
1. **Nutrient Uptake in Plants**: Active transport is crucial for the uptake of essential nutrients, such as mineral ions, from the soil into plant roots. These nutrients are often present in lower concentrations in the soil compared to the plant cells, requiring energy to move them against the concentration gradient.
2. **Maintaining Cell Homeostasis**: Active transport helps in maintaining the proper balance of ions within cells, such as sodium and potassium ions in animal cells. The sodium-potassium pump, for example, actively transports sodium out of the cell and potassium into the cell, which is essential for maintaining cell potential and overall cellular function.
3. **Removal of Waste Products**: Cells use active transport mechanisms to remove toxic substances or waste products from inside the cell to the outside environment. For example, the kidneys use active transport to remove urea and other waste products from the blood, concentrating them in the urine.
### Dandelion Stem Experiment
**a) Account for the appearance of the pieces in solutions L₁ and L₂:**
- **Piece in L₁**: If L₁ is a hypertonic solution (higher solute concentration than the dandelion cells), the cells in the stem piece lose water through osmosis, leading to plasmolysis. The cell membrane pulls away from the cell wall, causing the piece to become flaccid or shriveled.
- **Piece in L₂**: If L₂ is a hypotonic solution (lower solute concentration than the dandelion cells), the cells absorb water through osmosis, causing the cells to become turgid. This results in the stem piece swelling or stiffening due to the pressure of the turgid cells against the cell walls.
**b) Significance of the Biological Process Involved (Plasmolysis):**
- **Plasmolysis** is the process where plant cells lose water in a hypertonic environment, causing the cell membrane to detach from the cell wall. This process is significant as it demonstrates the effects of osmotic pressure on cells. It is also a critical survival mechanism for plants, allowing them to manage water loss in stressful environments and avoid permanent damage by reducing metabolic activity when water is scarce.