9700 · 14.2
Homeostasis in plants
Just like animals, plants need to keep their internal conditions stable to survive and thrive. This is called homeostasis, and for plants, it mainly involves carefully managing their water levels, temperature, and carbon dioxide intake. Without this delicate balance, plants couldn't photosynthesise, grow, or even stand upright.
Need to know
What you need to know
- **Light Intensity:** In light, guard cells actively pump K+ ions in, decreasing their water potential. Water enters by osmosis, making them turgid and bowing outwards, opening the stoma. In darkness, K+ ions leave, guard cells become flaccid, and the stoma closes.
- **Carbon Dioxide Concentration:** Low internal CO2 (due to high photosynthetic rates) signals stomata to open wider to increase CO2 uptake. High internal CO2 causes stomata to close.
- **Water Availability:** When water is scarce, roots produce **abscisic acid (ABA)**. This hormone is transported to the leaves, triggering guard cells to release K+ ions, become flaccid, and close the stomata, conserving water. This response overrides light and CO2 signals.
- **Temperature:** Very high temperatures can induce stomatal closure to prevent excessive water loss, even if it reduces CO2 uptake.
Explanation
Plants' Internal Balance
- Grasp why stable water potential is non-negotiable for plants.
- Understand how stomata are the plant's 'gatekeepers' for water and CO2.
- Learn the roles of different plant structures and hormones in regulation.
- Practise explaining these mechanisms in detail for exam success.