BIO 122
Unit 1: The Nature of Life
Life is a complex phenomenon that can be studied at different levels, from the molecular to the
ecological. In this unit, we will explore the fundamental characteristics of life, the basic
principles of biology, and the levels of organization in living organisms.
1.1 Characteristics of Life
All living organisms share certain characteristics that distinguish them from non-living matter.
These characteristics include:
● Cellular Organization: All living organisms are composed of one or more cells, which are
the basic units of life. Cells can be either prokaryotic (lacking a true nucleus) or
eukaryotic (containing a true nucleus).
● Reproduction: Living organisms have the ability to reproduce, either sexually or
asexually, to pass on their genetic material to the next generation.
● Metabolism: Living organisms carry out various chemical reactions to obtain and use
energy to carry out their life processes. This includes processes such as respiration,
digestion, and photosynthesis.
● Homeostasis: Living organisms maintain a stable internal environment, despite changes
in the external environment. This is achieved through feedback mechanisms that regulate
various physiological processes.
● Growth and Development: Living organisms grow and develop throughout their lifespan,
undergoing changes in their structure and function.
● Response to Stimuli: Living organisms can respond to stimuli from their environment,
such as light, temperature, and chemicals, through various physiological and behavioral
responses.
● Evolution: Living organisms exhibit genetic changes over time, resulting in the diversity
of life on Earth. This is due to the process of evolution through natural selection, as
proposed by Charles Darwin.
1.2 The Scientific Method
Biology is a science that relies on the scientific method, a systematic approach to investigating
Unit 1: The Nature of Life
Life is a complex phenomenon that can be studied at different levels, from the molecular to the
ecological. In this unit, we will explore the fundamental characteristics of life, the basic
principles of biology, and the levels of organization in living organisms.
1.1 Characteristics of Life
All living organisms share certain characteristics that distinguish them from non-living matter.
These characteristics include:
● Cellular Organization: All living organisms are composed of one or more cells, which are
the basic units of life. Cells can be either prokaryotic (lacking a true nucleus) or
eukaryotic (containing a true nucleus).
● Reproduction: Living organisms have the ability to reproduce, either sexually or
asexually, to pass on their genetic material to the next generation.
● Metabolism: Living organisms carry out various chemical reactions to obtain and use
energy to carry out their life processes. This includes processes such as respiration,
digestion, and photosynthesis.
● Homeostasis: Living organisms maintain a stable internal environment, despite changes
in the external environment. This is achieved through feedback mechanisms that regulate
various physiological processes.
● Growth and Development: Living organisms grow and develop throughout their lifespan,
undergoing changes in their structure and function.
● Response to Stimuli: Living organisms can respond to stimuli from their environment,
such as light, temperature, and chemicals, through various physiological and behavioral
responses.
● Evolution: Living organisms exhibit genetic changes over time, resulting in the diversity
of life on Earth. This is due to the process of evolution through natural selection, as
proposed by Charles Darwin.
1.2 The Scientific Method
Biology is a science that relies on the scientific method, a systematic approach to investigating
