Layman D. Biology Demystified: A Self-Teaching Guide

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CHAPTER

Patterns of Life

Chapter 1, The Coming of Biology, brought home to you some of the

fundamental concepts of the modern ‘‘study of life.’’ Prominent among

these concepts was the notion of Biological Order – a particular pattern

associated with living things. Recall that the spotted body pattern of a

giraﬀe was used to symbolize Biological Order within the individual organ-

ism. And a spider in its web represented Biological Order extending out-

ward beyond the organism. This elegantly simple visual pattern suggested a

criss-crossing network of linkages existing among various living things in

the external environment.

The Pyramid of Life (Levels of Biological

Organization)

Now it is time to consider still another pattern, one well-known to the

Ancient Egyptians. Of course, you have already guessed it! It is the distinctly

pointed-and-sloped pattern of the pyramid:

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The pyramid shape consists of a number of horizontal levels, stacked one

upon the other. This stacked pyramid is sometimes used in biology to help

model the various levels of biological organization. A level of biological orga-

nization represents a certain degree of size and complexity of body structures,

as well as the inter-relationships between them and other non-body struc-

tures. In biology, a Pyramid of Life can be identiﬁed. This Pyramid consists

of 12 stacked horizontal levels of biological organization (Figure 2.1, A).

Observe that these levels are numbered from bottom-to-top (Levels I–XII).

Level XII, the peak of the Pyramid of Life, is the largest and most complex.

This position at the top or peak symbolizes the fact that Level XII contains

all the other levels of biological organization below and within it. Further,

each of the other levels likewise contains the lower levels closer to the broad

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CHAPTER 2 Patterns of Life 19

(B)

Fig. 2.1 The pyramid of life: The 12 levels of biological organization.

(C)

base of the Pyramid. The farther one goes up in the Pyramid, the greater is

the size and complexity of the biological patterns encountered.

‘‘Why is this diagram called the Pyramid of Life?’’ you may well ask. The

reason is that life begins at a certain level of the Pyramid (Level V), and then

continues upward through each of the higher levels of biological organization

(Levels VI–XII). As Figure 2.1 (B) shows, the 12 Pyramid levels are as

follows: subatomic (sub-ah-TAH-mik) particles, atoms, molecules, organelles

(OR-gah-nels), cells, tissues, organs, organ systems, organism, population,

community, and ecosystem (E-koh-sis-tem). Figure 2.1 (C) labels and tags

certain levels in special ways. For example, Level V (cells) is labeled as

‘‘The Life-line.’’ This indicates that the cell is the lowest living level of bio-

logical organization. All levels above this ‘‘Life-line,’’ therefore, also include

living things. Note, too, that the spotted giraﬀe (Biological Order) icon

appears alongside Levels I–IX. This is because the giraﬀe, as an organism

(Level IX), includes all the lower levels (organ systems down to subatomic

particles) within it. Finally, observe that the spider in its web icon occurs

beside Levels X–XII. The explanation is that a population, community, and

ecosystem are all above the organism level of the Pyramid.

THE CHEMICAL LEVEL OF ORGANIZATION

Not speciﬁcally mentioned, yet, is the chemical level of biological organiza-

tion. The chemical level includes the lowest three levels of the Pyramid

(Figure 2.2). Speciﬁcally, this includes subatomic particles, atoms, and mole-

cules.

The most important of these is the atom. An atom is the simplest form of a

chemical element, or primary type of matter. A carbon (C) atom, for instance,

is the simplest form of the element carbon. The four most common elements

(atoms) found in the human body are carbon (C), oxygen (O), hydrogen (H),

and nitrogen (N). [Study suggestion: Remember the four letters, COHN, as in

the slang expression, ‘‘Don’t COHN me, Man! Tell me the truth!’’]

The subatomic level is the one immediately ‘‘below’’ (sub-) the entire atom.

This level consists of three main types of subatomic particles: protons

(PROH-tahns), neutrons (NEW-trahns), and electrons (e-LEK-trahns).

Each proton has an electrical charge of þ1, while each neutron (as its

name suggests) is electrically ‘‘neutral’’ (neither positively nor negatively

charged).

Together, a certain number of protons and neutrons make up the nucleus

(NEW-klee-us) or central ‘‘kernel’’ (nucle) of the atom. And orbiting very

rapidly around this nucleus are one or more negatively-charged electrons.

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The carbon atom, for example, contains 6 protons and 6 neutrons within its

nucleus. Orbiting around it is a total of 6 electrons. Since the number of

positively charged protons in the nucleus always equals the number of nega-

tively charged electrons rapidly orbiting around the nucleus, the net charge of

any atom is 0. Thus, the carbon atom, which has a nucleus of charge þ6

(from the six protons), and a cloud of electrons with a charge of 6, has a net

(overall) charge of 66 ¼ 0. [Study suggestion: As shown in Figure 2.2,

visualize the atom as being a hard gumball – the nucleus – surrounded by

a sticky cloud of cotton candy, representing the movements of all the elec-

trons orbiting around the nucleus.]

Lying just above the atom level is the molecule. A molecule is a com-

bination of two or more atoms held together by chemical bonds. A chemical

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Fig. 2.2 The chemical level of biological organization.

bond is a linkage created by the sharing or transfer of electrons between the

outer surface clouds of atoms. For example, a C–C (carbon–carbon) bond

(Figure 2.2) can be visualized as resulting from the linkage of two gumballs.

Each gumball (nucleus of a C atom) is surrounded by a sticky (electron)

cloud of cotton candy. When the two clouds are smashed together, and

then pulled apart slightly, a chemical bond or sticky connection is made

between them.

If one or more carbons and other types of atoms are bonded together in a

string or ring shape, an organic molecule results. A very simple organic (car-

bon-containing) molecule is CO

– carbon dioxide (die-OX-eyed). This mole-

cule is the one usually excreted as a waste product by the metabolism of our

human body cells.

Our cells typically consume the oxygen (O

) molecule in the process of

making energy. Obviously, O

is classiﬁed as an inorganic molecule, because

it does ‘‘not’’ (in-) contain any C atoms.

Carbon atoms easily bond together with one another, making long C–C

chains. Quite often, hydrogen (H) atoms bond to the sides of these carbon

atoms. The resulting molecules are called hydrocarbons (HIGH-droh-kar-

buns) – literally, ‘‘hydrogen (hydr) and carbon’’ molecules. Most of the

organic molecules making up human, animal, and plant bodies include

large numbers of hydrocarbons.

When a molecule becomes very ‘‘big’’ (macro-), it is described as a macro-

molecule (MAK-roh-mall-uh-kyewl). One of the most important macromole-

cules in all living things is the DNA molecule. (Chapter 4 will provide much

more information about chemical bonding, DNA, and other types of macro-

molecules essential for biology.)

ORGANELLES

Located just above the macromolecules (the top of the chemical level), are the

organelles. The word, organelle, literally means ‘‘little organ.’’ Hence, an

organelle is a ‘‘little organ’’-like structure that carries out speciﬁc functions

within the cell. The cell, like an individual atom, contains a central ‘‘kernel’’

or nucleus. In the case of the cell, however, the nucleus is a rounded, kernel-

like organelle. [Study suggestion: Picture an oval kernel of corn.] The cell

nucleus of all humans, plants, and animals holds a large amount of the

macromolecule, DNA. Genes (jeans) are particular sections of a DNA mole-

cule. Their chief function is directing protein synthesis (the making of pro-

teins) within the cell. (Chapter 5 will discuss all the major organelles and

other components of the cell in more depth.)

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Cells to Organism: Where the Pyramid Comes

to Life

So far, we have been discussing the lowest levels of biological organization.

Remember that the chemical level includes subatomic particles, atoms, and

molecules. And just beyond the macromolecules lie the organelles. Finally,

recall that the cell level begins ‘‘The Life-line,’’ because it is the lowest living

level of biological organization. It is now appropriate for us to ask, ‘‘Just

what is it that we mean, by living level?’’ For an answer, just go back to

Chapter 1, and review the section on the characteristics of living things.

These are the characteristics that ﬁrst appear in the Pyramid at the cell

level, and then continue upward through the entire organism.

TISSUES

Right above the cell is the tissue level. A tissue is a collection of similar cells,

plus the intercellular (in-ter-SELL-yew-lar) material located ‘‘between’’ them.

There are four basic or primary types of tissue (Figure 2.3). These are epithe-

lial (eh-pih-THEE-lee-al) tissue, muscle tissue, connective tissue, and nervous

tissue. By basic or primary, it is meant that all of the speciﬁc types of tissues

found in living things (especially humans and animals) are modiﬁcations or

specializations of these four types.

Epithelial denotes something present ‘‘upon’’ (epi-) the ‘‘nipples’’ (theli),

such as the nipples in humans and related animals (like a bear, monkey, or

your family cat or dog). Epithelial tissue is a covering and lining tissue. It

covers body surfaces in general, and lines cavities within the body interior.

Epithelial tissue, for example, forms the outermost layer of the human skin.

As evident from Figure 2.3, A, epithelial tissue is almost entirely cellular in

nature, with little or no intercellular material between its cells. Connective

tissue (Figure 2.3, B), in great contrast, includes a lot of intercellular material

between its cells. Frequently, this intercellular material contains long, slender

rods – connective tissue ﬁbers. Such ﬁbers help connective tissue do its main

job, which is to directly or indirectly connect body parts together. The fear-

some teeth in the jaw of a shark, for instance, are ﬁrmly anchored into their

sockets by connective tissue ﬁbers. Nevertheless, these teeth sometimes break

oﬀ, and then re-grow. Muscle tissue (Figure 2.3, C) consists of long, slender,

muscle ﬁbers. These muscle ﬁbers are actually cells that contract or shorten,

thereby creating body movements. Nervous tissue (Figure 2.3, D) is the

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major tissue for communication and control within the body’s internal envir-

onment. (The internal environment is everything deep in from the surface of

the skin.) The nervous tissue largely does its communicating by means of

neurons (NUR-ahns), the nerve cells. Neurons (nerve cells) within the nervous

tissue inform the brain when the body has been damaged, usually resulting in

the sensation of pain.

ORGANS

In line above the tissues are the organs. An organ is a collection of two or

more of the basic body tissues, which together perform some special function.

The heart, for instance, is an organ with special muscle in its thick walls that

allows it to carry out the function of pumping the blood. The heart contains

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Fig. 2.3 The basic or primary types of body tissues.

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connective tissue valves in its chambers, which are lined with modiﬁed epithe-

lial cells. And various nerves supply the heart wall, serving either to speed it

up or slow it down, whenever particular conditions arise.

ORGAN SYSTEMS

An organ system is a collection of two or more organs, which together per-

form some complex body function. Consider the cardiovascular (kar-dee-oh-

VA-skew-lar) or circulatory (SIR-kyew-lah-tor-ee) system. (Examine Figure

2.4.) The cardiovascular (circulatory) system mainly involves the ‘‘heart’’

(cardi) and its attached blood ‘‘vessels’’ (vascul), through which the blood

is pumped in a ‘‘little circle’’ (circul). The complex function performed by this

system is the carrying of blood and its contained nutrients (such as oxygen

and glucose) towards the body tissues, followed by the removal of waste

products (such as carbon dioxide) from the body tissues.

Life beyond the Organism: Populations,

Communities, and Ecosystems

Life does not stop with the individual body. There are still several levels of

biological organization lying beyond the organism (but including it).

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Fig. 2.4 An overview of the cardiovascular (circulatory) system.

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POPULATIONS

Of course, male and female organisms of the same species (SPEE-sheez) or

‘‘kind’’ can breed with one another. The result of such breeding is a popula-

tion. A population consists of a group of individuals of the same species that

live together in the same place. A population of human beings, for example,

consists of individuals of the species Homo sapiens (HOH-moh SAY-pea-enz)

– literally ‘‘men’’ (Homo) who are ‘‘wise’’ (sapiens), living and breeding

together.

COMMUNITIES

Found above the population level is the community level. A community

consists of all the organisms (including those of diﬀerent species) living

and potentially interacting with each other in the same area. An interacting

group of Homo sapiens and various species of plants, animals, birds, and

insects, for instance, could make up a particular forest community.

ECOSYSTEMS

Perched at the peak of the Pyramid of Life is the ecosystem. An ecosystem

includes both the living organisms in a biological community as well as the

non-living factors present in their physical environment. A forest community

like the one just described, for example, could include rivers, waterfalls, and

scenic gorges.

SUMMARY

We have now deﬁned and discussed all 12 levels of biological organization.

And when we talk about biological organization, we essentially mean

Biological Order. Each of the 12 levels in the Pyramid of Life, then, repre-

sents a particular pattern and complexity of Biological Order. If one of these

levels becomes disturbed, such that its pattern is broken, then many other

levels in the Pyramid may also become disturbed. Consequently, Biological

Disorder may ﬁrst occur within only a single level of biological organization.

But this initial state of disorder may eventually disturb either higher or lower

levels within the Pyramid. Therefore, Biological Disorder can rapidly spread

through many levels, like a series of falling dominoes. The result – sickness or

death of the organism! (Later chapters will explore some of these ‘‘falling

dominoes,’’ using speciﬁc examples.)

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