What is a defining feature of the tundra biome?

The defining feature of the tundra biome is the presence of long, cold winters. This characteristic is central to the tundra's climate and ecosystem. Tundra regions, typically found in high-latitude areas near the Arctic and Antarctic, experience harsh winters that can last up to nine months. During this time, temperatures can drop well below freezing, which significantly influences the types of plants and animals that can survive there.

The cold conditions result in a short growing season, which allows limited vegetation to thrive, such as mosses, lichens, and hardy plants. Additionally, the permafrost layer—permanently frozen ground—further shapes the tundra ecosystem by restricting root growth. Thus, the long, cold winters not only define the climatic conditions of the tundra but also play a crucial role in the overall biodiversity and physical characteristics of the region.

The other options do not accurately reflect the tundra's primary features; for instance, the tundra is not characterized by very hot summers or significant human habitation, and its vegetation is not diverse compared to other biomes like forests or grasslands.