The Nature of Life Science — Reading Comprehension

Biology is the branch of science focused on studying living things and their interactions. In every habitat on Earth, from the deepest oceans to the highest mountains, life demonstrates remarkable diversity and complexity. Scientists use life science to seek answers to questions about what it means to be alive, how living things function, and how they change over time.

Characteristics of Life
To determine whether something is alive, scientists use a set of key characteristics. Living things, or organisms, are organized into cells, which are the smallest units of life. This organization allows them to perform complex functions. All living things undergo metabolism, the chemical processes that provide energy for growth and activity. They maintain homeostasis, keeping their internal environment stable even when surroundings change. Organisms grow by increasing in size or cell number, and they reproduce, passing genetic information to offspring. Living things respond to stimuli—for example, plants bend toward light, and animals flee from danger. Over generations, populations of organisms adapt to their environments, a process called adaptation.

Distinguishing Living and Nonliving Things
Nonliving things, such as rocks or water, may share some features with living things but lack the full set of characteristics. For instance, fire grows, moves, and needs fuel, yet it does not have cells, does not reproduce, and does not maintain homeostasis. Viruses present a special case. They contain genetic material and can evolve, but they cannot reproduce or carry out metabolism on their own. Scientists debate whether viruses are truly alive or exist at the boundary between living and nonliving. Research in 2020 showed that some giant viruses have genes for metabolic processes, but they still depend on host cells for reproduction. This shows how our understanding of life can change with new discoveries.

Systems, Interactions, and the Diversity of Life
Life science also studies how living things interact with each other and with nonliving elements in their environment. For example, plants use photosynthesis to convert sunlight into food, supporting animals that eat them. Bacteria help decompose dead matter, recycling nutrients. These interactions form ecosystems, where the balance between organisms and their environment is vital for survival. Quantitative studies estimate that Earth is home to over 8.7 million species, from microscopic bacteria to towering trees and large animals. This tremendous diversity results from billions of years of evolution, adaptation, and interaction.

Life science not only helps us understand what it means to be alive but also provides tools to address environmental, health, and technological challenges. For example, studying how bacteria adapt to antibiotics guides the development of new medicines, and understanding ecosystems helps us protect endangered species. The investigation of life's boundaries, such as whether viruses are alive, continues to shape scientific thinking and advances our knowledge of biology.

Interesting Fact: The tardigrade, or "water bear," can survive extreme conditions—freezing, boiling, or even the vacuum of space—demonstrating the incredible adaptability of life.

What is the main focus of biology?

Which of the following is NOT a characteristic of living things?

What does homeostasis mean in living things?

Which example from the passage shows a living thing responding to a stimulus?

Why do scientists debate if viruses are alive?

What is an ecosystem?

What is the main reason fire is not considered alive?

Which statement best describes adaptation?

True or False: All living things must be able to reproduce and respond to stimuli.

True or False: Scientists' understanding of what is considered alive can change with new discoveries.