Unformatted text preview: 7/16/2020 The Characteristics of Life | Biology for Majors I Biology for Majors I
Module 1: Introduction to Biology The Characteristics of Life 1/12 7/16/2020 The Characteristics of Life | Biology for Majors I List the de ning characteristics of biological life
Biology is the science that studies life, but what exactly
is life? This may sound like a silly question with an
obvious response, but it is not always easy to de ne life.
For example, a branch of biology called virology studies
viruses, which exhibit some of the characteristics of
living entities but lack others. It turns out that although
viruses can attack living organisms, cause diseases, and
even reproduce, they do not meet the criteria that
biologists use to de ne life. Consequently, virologists
are not biologists, strictly speaking. Similarly, some
biologists study the early molecular evolution that gave
rise to life; since the events that preceded life are not
biological events, these scientists are also excluded
from biology in the strict sense of the term.
From its earliest beginnings, biology has wrestled with
these questions: What are the shared properties that
make something “alive”? And once we know something
is alive, how do we nd meaningful levels of
organization in its structure? LEARNING OBJECTIVES List the properties of life
Order the levels of organization of living
things 2/12 7/16/2020 The Characteristics of Life | Biology for Majors I Properties of Life
All living organisms share several key characteristics or
functions: order, sensitivity or response to the
environment, reproduction, growth and development,
regulation, homeostasis, and energy processing. When
viewed together, these characteristics serve to de ne
life.
Order Organisms are highly
organized, coordinated
structures that consist of
one or more cells. Even
very simple, single-celled
organisms are
remarkably complex:
inside each cell, atoms Figure 1. A toad represents a highly
organized structure consisting of
cells, tissues, organs, and organ
systems. make up molecules; these
in turn make up cell organelles and other cellular
inclusions.
In multicellular organisms (Figure 1), similar cells form
tissues. Tissues, in turn, collaborate to create organs
(body structures with a distinct function). Organs work
together to form organ systems.
Sensitivity or Response to Stimuli 3/12 7/16/2020 The Characteristics of Life | Biology for Majors I Organisms respond to diverse stimuli. For example,
plants can bend toward a source of light, climb on
fences and walls, or respond to touch (Figure 2).
Even tiny bacteria can
move toward or away
from chemicals (a process
called chemotaxis) or
light (phototaxis).
Movement toward a
stimulus is considered a
positive response, while
movement away from a
stimulus is considered a Figure 2.The leaves of this sensitive
plant (Mimosa pudica) will instantly
droop and fold when touched. After
a few minutes, the plant returns to
normal. (credit: Alex Lomas) negative response.
Watch this video to see how plants respond to a
stimulus—from opening to light, to wrapping a tendril
around a branch, to capturing prey.
Reproduction Single-celled organisms reproduce by rst duplicating
their DNA, and then dividing it equally as the cell
prepares to divide to form two new cells. Multicellular
organisms often produce specialized reproductive
germline cells that will form new individuals. When
reproduction occurs, genes containing DNA are passed
along to an organism’s o spring. These genes ensure 4/12 7/16/2020 The Characteristics of Life | Biology for Majors I that the o spring will belong to the same species and
will have similar characteristics, such as size and shape.
Growth and Development Organisms grow and
develop following speci c
instructions coded for by
their genes. These genes
provide instructions that
will direct cellular growth
and development,
ensuring that a species’
young (Figure 3) will grow Figure 3. Although no two look
alike, these puppies have inherited
genes from both parents and share
many of the same characteristics. up to exhibit many of the
same characteristics as its parents.
Regulation Even the smallest organisms are complex and require
multiple regulatory mechanisms to coordinate internal
functions, respond to stimuli, and cope with
environmental stresses. Two examples of internal
functions regulated in an organism are nutrient transport
and blood ow. Organs (groups of tissues working
together) perform speci c functions, such as carrying
oxygen throughout the body, removing wastes,
delivering nutrients to every cell, and cooling the body.
Homeostasis In order to function properly, cells need to have 5/12 7/16/2020 The Characteristics of Life | Biology for Majors I appropriate conditions
such as proper
temperature, pH, and
appropriate concentration
of diverse chemicals.
These conditions may,
however, change from
one moment to the next.
Organisms are able to
maintain internal
conditions within a Figure 4. Polar bears (Ursus
maritimus) and other mammals
living in ice-covered regions
maintain their body temperature by
generating heat and reducing heat
loss through thick fur and a dense
layer of fat under their skin. (credit:
“longhorndave”/Flickr) narrow range almost
constantly, despite environmental changes,
through homeostasis (literally, “steady state”)—the
ability of an organism to maintain constant internal
conditions. For example, an organism needs to regulate
body temperature through a process known as
thermoregulation. Organisms that live in cold climates,
such as the polar bear (Figure 4), have body structures
that help them withstand low temperatures and
conserve body heat. Structures that aid in this type of
insulation include fur, feathers, blubber, and fat. In hot
climates, organisms have methods (such as perspiration
in humans or panting in dogs) that help them to shed
excess body heat.
Energy Processing All organisms use a source of energy for their metabolic
activities. Some organisms capture energy from the sun
and convert it into chemical energy in food 6/12 7/16/2020 The Characteristics of Life | Biology for Majors I (photosynthesis); others use chemical energy in
molecules they take in as food (cellular respiration). Figure 5. The California condor (Gymnogyps californianus) uses chemical
energy derived from food to power ight. California condors are an
endangered species; this bird has a wing tag that helps biologists identify
the individual. Levels of Organization of Living Things
Living things are highly organized and structured,
following a hierarchy that can be examined on a scale
from small to large. The atom is the smallest and most
fundamental unit of matter. It consists of a nucleus
surrounded by electrons. Atoms form molecules. A
molecule is a chemical structure consisting of at least two atoms held together by one or more chemical
bonds. Many molecules that are biologically important
are macromolecules, large molecules that are typically
formed by polymerization (a polymer is a large molecule
that is made by combining smaller units called
monomers, which are simpler than macromolecules). An
example of a macromolecule is deoxyribonucleic acid
(DNA) (Figure 6), which contains the instructions for the
structure and functioning of all living organisms. 7/12 7/16/2020 The Characteristics of Life | Biology for Majors I Some cells contain aggregates
of macromolecules surrounded
by membranes; these are
called organelles. Organelles
are small structures that exist
within cells. Examples of
organelles include mitochondria
and chloroplasts, which carry
out indispensable functions:
mitochondria produce energy to
power the cell, while
chloroplasts enable green
plants to utilize the energy in
sunlight to make sugars. All
living things are made of cells; Figure 6. All molecules,
including
this
DNA
molecule, are composed of
atoms.
(credit:
“brian0918 ″/Wikimedia
Commons) the cell itself is the smallest
fundamental unit of structure and function in living
organisms. (This requirement is why viruses are not
considered living: they are not made of cells. To make
new viruses, they have to invade and hijack the
reproductive mechanism of a living cell; only then can
they obtain the materials they need to reproduce.) Some
organisms consist of a single cell and others are
multicellular. Cells are classi ed as prokaryotic or
eukaryotic. Prokaryotes are single-celled or colonial
organisms that do not have membrane-bound nuclei or
organelles; in contrast, the cells of eukaryotes do have
membrane-bound organelles and a membrane-bound
nucleus. 8/12 7/16/2020 The Characteristics of Life | Biology for Majors I In larger organisms, cells combine to make tissues,
which are groups of similar cells carrying out similar or
related functions. Organs are collections of tissues
grouped together performing a common function.
Organs are present not only in animals but also in
plants. An organ system is a higher level of organization
that consists of functionally related organs. Mammals
have many organ systems. For instance, the circulatory
system transports blood through the body and to and
from the lungs; it includes organs such as the heart and
blood vessels. Organisms are individual living entities.
For example, each tree in a forest is an organism.
Single-celled prokaryotes and single-celled eukaryotes
are also considered organisms and are typically
referred to as microorganisms.
All the individuals of a species living within a speci c
area are collectively called a population. For example, a
forest may include many pine trees. All of these pine
trees represent the population of pine trees in this forest.
Di erent populations may live in the same speci c area.
For example, the forest with the pine trees includes
populations of owering plants and also insects and
microbial populations. A community is the sum of
populations inhabiting a particular area. For instance, all
of the trees, owers, insects, and other populations in a
forest form the forest’s community. The forest itself is an
ecosystem. An ecosystem consists of all the living things
in a particular area together with the abiotic, non-living
parts of that environment such as nitrogen in the soil or 9/12 7/16/2020 The Characteristics of Life | Biology for Majors I rain water. At the highest level of organization (Figure 7),
the biosphere is the collection of all ecosystems, and it
represents the zones of life on earth. It includes land,
water, and even the atmosphere to a certain extent. PRACTICE QUESTION From a single organelle to the entire biosphere,
living organisms are parts of a highly structured
hierarchy. Figure 7. The biological levels of organization of living things are
shown. From a single organelle to the entire biosphere, living
organisms are parts of a highly structured hierarchy. (credit
“organelles”: modi cation of work by Umberto Salvagnin; credit
“cells”: modi cation of work by Bruce Wetzel, Harry Schaefer/
National Cancer Institute; credit “tissues”: modi cation of work
by Kilbad; Fama Clamosa; Mikael Häggström; credit “organs”:
modi cation of work by Mariana Ruiz Villareal; credit
“organisms”: modi cation of work by “Crystal”/Flickr; credit
“ecosystems”: modi cation of work by US Fish and Wildlife
Service Headquarters; credit “biosphere”: modi cation of work
by NASA) 10/12 7/16/2020 The Characteristics of Life | Biology for Majors I Which of the following statements is false?
a. Tissues exist within organs, which exist
within organ systems.
b. Communities exist within populations,
which exist within ecosystems.
c. Organelles exist within cells, which exist
within tissues.
d. Communities exist within ecosystems,
which exist in the biosphere.
Show Answer Check Your Understanding
Answer the question(s) below to see how well you
understand the topics covered in the previous section.
This short quiz does not count toward your grade in the
class, and you can retake it an unlimited number of
times.
Use this quiz to check your understanding and decide
whether to (1) study the previous section further or (2)
move on to the next section. 11/12 7/16/2020 The Characteristics of Life | Biology for Majors I Previous Next 12/12 ...
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