Plants growing in cracks is an example of biological weathering, but it's not the direct action of the plant itself that causes the weathering. Here's a breakdown:

How plants contribute to biological weathering:

1. Root Growth: Plant roots, seeking water and nutrients, grow into cracks and crevices. As they grow larger, they exert pressure on the surrounding rock, widening the cracks.

2. Chemical Secretion: Some plants secrete acids from their roots to help dissolve minerals from the soil, making them more accessible. These acids can also slowly dissolve the rock itself, further widening cracks.

3. Water Retention: Plants act as sponges, absorbing and retaining water. This water can seep into cracks and freeze during cold temperatures. As the water freezes, it expands, putting pressure on the rock, causing it to crack further.

How this relates to weathering:

Weathering is the breakdown of rocks, soil, and minerals through contact with the Earth's atmosphere, water, and biological organisms. The processes described above, initiated by plant growth, contribute to the physical and chemical breakdown of rock, which is a core component of weathering.

Important Note: While plants can play a role in weathering, the process is often slow and gradual. Other weathering agents, like wind, rain, and temperature fluctuations, also play a significant role in shaping the Earth's surface.