Use your understanding of natural selection to describe how the following trait might have evolved:
Plants have pores on the surfaces of their leaves that allow carbon dioxide into the leaf (for photosynthesis), but also allow water to escape. Land plants have guard cells surrounding these pores that actively regulate the size of the pore and will make the pore smaller in dry conditions. The ancestors of land plants did not have guard cells.
I understand what natural selection is but I don't know how this trait may have evolved.
the pores in their leaves?
To understand how this trait might have evolved, let's break it down using the principles of natural selection:
1. Variation: Initially, in the ancestors of land plants, there was likely a variation in the structure of the pores on the surfaces of their leaves. Some individuals may have had larger pores, while others may have had smaller ones.
2. Environmental Pressures: The environment plays a crucial role in natural selection. In land plants, one of the challenges they faced was the need to regulate water loss through the leaf pores. In drier conditions, there was a selective pressure for plants to minimize water loss and prevent dehydration.
3. Differential Fitness: In dry conditions, individuals with larger, unregulated pores would experience excessive water loss, reducing their fitness. On the other hand, individuals with smaller, regulated pores might have had an advantage by conserving water and maintaining proper hydration.
4. Heredity: Traits that contribute to better survival and reproduction tend to be passed on to the next generation. In this case, individuals with smaller, regulated pores would have been more likely to survive and produce offspring who inherited these traits.
5. Accumulation of Adaptive Traits: Over time, the individuals with the advantageous trait of smaller pores would have become more prevalent in the population, leading to an accumulation of this adaptive trait through generations.
6. Evolution of Guard Cells: As plants with smaller pores had a selective advantage, mutations could have occurred in some individuals that resulted in the development of specialized cells, called guard cells, around the leaf pores. These guard cells allowed for active regulation of the pore size, enabling plants to adjust the opening based on the prevailing conditions.
7. Increased Fitness: Plants with guard cells that could control pore size would have gained an even greater advantage in regulating water loss. The individuals possessing this new trait would have better fitness and survival in a variety of environmental conditions, leading to its further spread in the population.
Through this process of natural selection, the trait of having guard cells to regulate pore size on the surfaces of leaves could have evolved in land plants as an adaptation to balance efficient photosynthesis with water conservation in varying environmental conditions.