Transcript BioUT.4.1.Characteristics of Life

Characteristics of Life
Biology 20
Life Has Organization
• Life processes maintain the organization but
upon death and organism breaks apart from
the simplest to the most complex and include:
– Atoms  molecules  cell organelles  cells
(smallest unit of life)  tissue  organs 
organ systems  organism
Life Acquires Materials and Energy
• Living things acquire nutrient molecules
that can be used as building blocks or for the
organisms structure
• Molecular bond energy is used in cell
metabolism.
Homeostasis means “Staying the
Same”
• The internal environment of an organism
stays relatively constant compared to the
external environments; for example
– Body temperature fluctuates only slightly
during a variable day
Life Responds to Stimuli
• Living things often respond to external
stimuli by moving, whether an animal
detects an energy and runs or plant leaves
track the movement of the sum
• Behaviors are directed toward minimizing
injury, acquiring food, and reproducing.
Life Reproduces
• During reproduction, a copy of its hereditary
information (genes) is passed on.
• Unicellular organisms may reproduce asexually by
dividing into two cells, each of which has the same
genes and structures as the single parent.
• Multicellular organisms may reproduce sexually.
Each parent contributes one-half of the total
number of genes to an offspring, which then has
characteristics of both parents and may not
resemble either one exactly.
Life Grows and Develops
• Growth is recognized by an increase in size
and often in the number of cells.
• Human development includes all changes
that take place between conception and death.
Life Adapts
• Adaptations are modifications that make an
organism suited to its way of life; for example,
hollow bones in birds reduce weight and permit
flying.
• Adaptations are selected by evolution, the process
where characteristics of species change through
time. When new variations arise that allow certain
members of the species to capture more resources,
survive in higher numbers and have more offspring
than poorly adapted members. Evolution explains
the diversity and unity of life.
Structure of the Ecosystem
• Population – all the members of one species found in a
specific area at the same time.
• Community – a group or population of both plants and
animals that live together. (Biotic only)
• Ecosystem – consists of various interactions among
populations and with the physical environment. (Biotic and
Abiotic)
• Biosphere – the narrow band around the Earth in which life
can exist.
– Upper boundary is higher atmosphere
– Lower boundary extends into soil and
ocean bottoms
Humans Threaten the Biosphere
• Humans modify existing ecosystems for their own
purposes.
• Increases in human populations threaten more ecosystem
stability and diversity.
• Loss of stable and diverse ecosystems in turn threatens
human populations; for example, destruction of the world’s
rain forest may lead to increased carbon dioxide in the
atmosphere, which in turn may increase the average daily
temperature.
Biodiversity
• From perhaps 80 million species, fewer than 2
million have been destroyed.
• Extinction, which occurs naturally, has increased
from human’s alteration of the environment,
development, pollution and overfishing.
• Modern extinction rates from human activities
could exceed the five natural mass extinctions in
geological history.
Tropical Rain Forest Destruction
• Even if you do not believe in a species existing for its own
sake, the extinction of species reduces resources available to
humans for food, clothing, medicines and other raw
materials.
– Rain forests constitute an area similar to the USA
– Each year an area of rain forest 1/3 the size of Alberta is lost
– Social, economic and political forces encourage poor people to convert
rain forest into smaller farms, followed by logging, mining and
cattle ranching.
– Harvest of natural forest products might
be an economic alternative that would
save this ecosystem.