Section 1: The Sonoran Desert & Biodiversity

BIO 1108 Exam 3

What two countries share the Sonoran Desert?

The southwestern United States and northwestern Mexico.

Why is the Sonoran Desert a good model for studying ecological adaptations?

It exhibits extreme temperature and water limitations, requiring diverse plant adaptations for survival and providing insights into how life persists under stress.

How does rainfall influence plant growth in the Sonoran Desert?

Summer is too hot (~95°F) for most plant growth, spring is too dry, and winter provides the best growing season—especially for annuals that complete their life cycle in one season.

What are annual vs. perennial plants in the Sonoran Desert?

Annuals germinate, grow, reproduce, and die in one growing season; perennials (like saguaros and mesquite) survive for years, adapting to water scarcity through resource storage and structural adaptations.

How is climate change altering the Sonoran Desert?

Increasing temperature, decreasing total rainfall, and more episodic precipitation patterns (fewer but more intense storms), leading to floods, droughts, and stressed ecosystems.

What percentage of Earth's biomass is made up of plants?

80% (bacteria: 13%, fungi: 2%, animals: 0.36%, humans: 0.01%).

What molecule makes up most of a plant’s biomass (besides water)?

Cellulose, made primarily of carbon derived from CO₂ in the air.

Who proved that plant mass comes from air and not soil?

Jan van Helmont (1600s) through his willow tree experiment.