Biology The Study of Life
Recognizing life’s characteristics and the methods used to study life provide a basis for understanding the living world.

Principles of Life Science
Living things do not exist in isolation; they are all functioning parts in the delicate balance of nature. All living things depend upon other living and nonliving things in a variety of ways and for a variety of reasons.

Characteristics of Life
• Organization
• Homeostasis
• Reproduction
• Growth and Development
• Response to a Stimulus

Organisms in nature possess unique features that allow biologists to identify them as living rather than nonliving. They are as follows:

#1 Organization
• All living things are organized into Cells
• Unicellular – one celled organisms.
Ex. Paramecium, amoeba, stentor
•
• Multicellular – more than one cell.
Ex. Humans, sponges
• Cells are not found in nonliving things.

#2 Homeostasis
• Regulate external and internal conditions.
• Get energy from food.

• Use Energy

#3 Ability to Reproduce
Reproduction – is the ability to produce a new organism of the same type. It is not essential for the survival of an individual organism, but it is essential for the continuation of a species (a group of organisms that can interbreed and produce fertile offspring in nature).

Asexual – One cell splits into two new cells.
Ex. Paramecium, sponges, strawberry runner, spider plants and other simple organisms usually undergo asexual reproduction.
There are two classifications of reproduction: Asexual and Sexual

#4 Reproduction
Sexual Reproduction – two different cells join to form one new individual. New individual is different from either parent.
Fertilization – union of the egg and sperm.
Zygote – new cell formed as a result of fertilization. Most complex organisms reproduce in this way.

#5 Growth and Development
• Two Basic Kinds of Growth:
Increasing the number of cells.
Increasing the size of the cells.
• Development: cycle of changes living things go through as they grow.
Aging process – part of cycle.
Death – end of the cycle.

#6 Respond to Environment
• Stimulus – a change in the environment
o Ex. light shines in eyes.
• Response – reaction to the change.
o Ex. pupils get smaller.
• Vital to any organism
o Escape predators
o Find food
o Move to light
o Move away from toxins
o Find a mate

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