8
UNIT ONE
5.
Pressure
is an application of force on an object
or substance. For example, the force acting on the
outside of a land organism due to the weight of air
above it is called
atmospheric pressure.
In humans,
this pressure plays an important role in breathing.
Similarly, organisms living under water are subjected
to
hydrostatic pressure
—a pressure a liquid exerts—due
to the weight of water above them. In complex animals,
such as humans, heart action produces blood pressure
(another form of hydrostatic pressure), which keeps
blood fl
owing through blood vessels.
Although the human organism requires water, food, oxy-
gen, heat, and pressure, these factors alone are not enough
to ensure survival. Both the quantities and the qualities of
such factors are also important.
Table 1.4
summarizes the
major requirements of organisms.
Homeostasis
Most of the earth’s residents are unicellular, or single-celled.
The most ancient and abundant unicellular organisms are
the bacteria. Their cells do not have membrane-bound organ-
elles. Some unicellular organisms, however, consist of cells
that have organelles as complex as our own. This is the case
TABLE
1.2
|
Organ Systems
Organ System
Major Organs
Major Functions
Integumentary
Skin, hair, nails, sweat glands, sebaceous glands
Protect tissues, regulate body temperature, support sensory receptors
Skeletal
Bones, ligaments, cartilages
Provide framework, protect soft tissues, provide attachments for
muscles, produce blood cells, store inorganic salts
Muscular
Muscles
Cause movements, maintain posture, produce body heat
Nervous
Brain, spinal cord, nerves, sense organs
Detect changes, receive and interpret sensory information, stimulate
muscles and glands
Endocrine
Glands that secrete hormones (pituitary gland, thyroid gland,
parathyroid glands, adrenal glands, pancreas, ovaries, testes,
pineal gland, and thymus)
Control metabolic activities of body structures
Cardiovascular
Heart, arteries, capillaries, veins
Move blood through blood vessels and transport substances
throughout body
Lymphatic
Lymphatic vessels, lymph nodes, thymus, spleen
Return tissue F
uid to the blood, carry certain absorbed food molecules,
defend the body against infection
Digestive
Mouth, tongue, teeth, salivary glands, pharynx, esophagus,
stomach, liver, gallbladder, pancreas, small and large intestines
Receive, break down, and absorb food; eliminate unabsorbed material
Respiratory
Nasal cavity, pharynx, larynx, trachea, bronchi, lungs
Intake and output of air, exchange of gases between air and blood
Urinary
Kidneys, ureters, urinary bladder, urethra
Remove wastes from blood, maintain water and electrolyte balance,
store and transport urine
Reproductive
Male: scrotum, testes, epididymides, ductus deferentia, seminal
vesicles, prostate gland, bulbourethral glands, urethra, penis
±emale: ovaries, uterine tubes, uterus, vagina, clitoris, vulva
Produce and maintain sperm cells, transfer sperm cells into female
reproductive tract
Produce and maintain egg cells, receive sperm cells, support
development of an embryo and function in birth process
TABLE
1.3
|
Characteristics of Life
Process
Examples
Process
Examples
Movement
Change in position of the body or of a body part;
motion of an internal organ
Digestion
Breakdown of food substances into simpler forms that
can be absorbed and used
Responsiveness
Reaction to a change inside or outside the body
Absorption
Passage of substances through membranes and into
body F
uids
Growth
Increase in body size without change in shape
Circulation
Movement of substances in body F
uids
Reproduction
Production of new organisms and new cells
Assimilation
Changing of absorbed substances into di²
erent
chemical forms
Respiration
Obtaining oxygen, removing carbon dioxide, and
releasing energy from foods (some forms of life do
not use oxygen in respiration)
Excretion
Removal of wastes produced by metabolic reactions
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