Layman D. Biology Demystified: A Self-Teaching Guide

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Homeostasis versus Ecological Relationships

Chapter 1 introduced the concepts of both homeostasis and ecology. Recall

that homeostasis is a relative constancy of some particular aspect of the

body’s internal environment. The maintenance of a relative constancy of

glucose level within the bloodstream was cited as a deﬁnite instance of home-

ostasis. Such conditions of homeostasis are especially important within the

group of organisms called mammals (MAM-als) – animals with ‘‘breasts’’

(mamm) used to give milk to their young. Thus, cats, dogs, monkeys, and

human beings are all mammals in which the blood glucose concentration is

tightly regulated within a state of homeostasis. The glucose in the blood

eventually becomes glucose within the breast milk, which in turn provides

vital nutrition for the nursing youngsters.

The S-shaped pattern of homeostasis indicates a type of up-and-down

balance within the body’s internal environment. Homeostasis is therefore

restricted to the organism level and below, within the Pyramid of Life.

Chapter 1 also discussed the idea of ecology – a ‘‘study of the household

aﬀairs’’ or relationships between diﬀerent organisms and the total external

environment. Such ecological (e-koh-LAHJ-ih-kal) relationships also repre-

sent a type of balance. But this balance exists at the levels of biological

organization lying beyond the organism. That is, ecological relationships

exist at the population, community, and ecosystem levels. Consider, for

example, a so-called ‘‘population balance.’’ This phrase represents the idea

that, when the number of births occurring within a certain population equals

the number of deaths in that population, over, say, a period of one year, then

that population is ‘‘balanced’’ or ‘‘stable.’’ It is neither greatly increasing nor

greatly decreasing in size over time. This rough balance in the number of

births versus deaths of particular organisms (such as humans) also greatly

inﬂuences the surrounding environment. A stable human population essen-

tially means a fairly stable consumption of food and water, as well as a stable

excretion of waste products into the external environment.

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Quiz

Refer to the text in this chapter if necessary. A good score is at least 8 correct

answers out of these 10 questions. The answers are listed in the back of this

book.

1. A level of biological organization represents:

(a) Some level of complexity below an organism

(b) A particular layer within an Ancient Egyptian pyramid

with the inter-relationships between them and various non-body

structures

(d) An almost complete lack of Biological Order

2. The lowest living level of biological organization is:

(a) The organelle

(b) The cell

(d) The ecosystem

3. The chemical level of organization includes:

(a) Organelles, cells, and communities

(b) Subatomic particles, atoms, and organs

(d) Every living level of biological organization

4. The cell nucleus represents the:

(a) Organelle level

(b) Tissue level

(d) Molecule level

5. A molecule is a combination of two or more atoms held together by:

(a) Chemical bonds

(b) Genes

(d) Electron–proton connections

6. A tissue is best deﬁned as:

(a) The smallest living level of biological organization

(b) A collection of similar cells, plus the intercellular material between

them

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themselves

(d) A collection of similar cells, not including anything else

7. A collection of two or more organs, which together perform some

complex body function:

(a) Organism

(b) Tissue

(d) Population

8. Snowshoe hares, bobcats, and arctic foxes all living in the same cold

northerly area make up:

(a) A population

(b) A community

(d) An ecosystem

9. An ecosystem:

(a) Exists at a level below the community

(b) Only focuses upon the members of a particular population

(d) Never can be more complex than the organisms it contains

10. Ecological relationships are similar to homeostasis in that they:

(a) Can always be diagrammed in an S-shaped pattern

(b) Represent a relative constancy of the mammal’s internal

environment

(d) Maintain a rough balance or equilibrium over time

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The Giraﬀe ORDER TABLE for Chapter 2

(Key Text Facts About Biological Order Within An Organism)

1. ____________________________________________________________

2. ____________________________________________________________

3. ____________________________________________________________

4. ____________________________________________________________

5. ____________________________________________________________

The Spider Web ORDER TABLE for Chapter 2

(Key Text Facts About Biological Order Beyond the Individual Organism)

1. ____________________________________________________________

2. ____________________________________________________________

3. ____________________________________________________________

4. ____________________________________________________________

5. ____________________________________________________________

The Broken Spider Web DISORDER TABLE for Chapter 2

(Key Text Facts About Biological Disorder Beyond the Individual

Organism)

1. ____________________________________________________________

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CHAPTER

Evolution: From Dawn

to Darwin

Chapter 2 discussed The Pyramid of Life, and within it the various levels of

biological organization. Recall that life begins at the cell level. It is now

appropriate for us to ask, ‘‘Okay, we know what life is. But where did it

come from? And did life forms always look the way they do on present-day

Earth?’’

Important Theories about the Origin of Life

Before life, and even before the planet Earth, the Universe or Cosmos

(KAHZ-mohs) began as a ‘‘Big Bang.’’ About 15 billion years ago, one or

more huge, noisy ‘‘Bangs’’ (explosions) of dying stars created giant clouds of

dust and gas. Out of such swirling clouds came our ‘‘sun’’ (sol) and the solar

(SOH-lar) system of planets orbiting around it. The creation of our solar

system was an important example of Cosmic (KAHZ-mik) Order – a pattern

of organization that occurs within the Universe.

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The third planet from the sun – the Earth – appeared approximately 4.5

billion years ago. In the beginning, the Earth had a boiling-hot surface of

liquid rock. But even at this early stage, carbon, hydrogen, and many other

chemicals necessary for life, already existed.

As the planet cooled, a thin crust of hard rock formed upon the surface.

Frequent eruptions of volcanoes forced gases out above this surface crust,

thereby creating the atmosphere. The atmosphere is a 1-mile-thick blanket of

gases surrounding the Earth. The early atmosphere contained water (H

molecules in the form of water vapor, which was belched out by the volca-

noes. Eventually, the surface cooled, and the water fell as rain. The rain

pooled and ﬁlled vast surface canyons, giving rise to the ﬁrst oceans. In

addition, the cooling triggered the creation of oxygen (O

) molecules.

Somewhere between 4 billion and 3.5 billion years ago, life probably began

within the oceans. Biologists sometimes poetically call this great event the

Dawn of Life. Figure 3.1 diagrams A TIME-CLOCK FOR ORDER. Notice

that the CLOCK starts things oﬀ at midnight, representing 5 bya (billion

years ago). As the hand of the CLOCK turns, the number of years from the

present-day Earth decreases step-by-step from 5 bya. Each mark on the clock

face represents a time span of 0.25 bya or 250 mya (million years ago). The

numbers 4, 3, 2, and 1, consequently, represent 1 billion years ago, each. The

appearance of the Earth, for instance, is marked about half-way between 5

and 4 (or 4.5 billion years ago). The Time-Clock sounded an alarm, in a

sense, and woke up the Earth, at approximately 4 bya. The alarm rang out

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Fig. 3.1 A Time-Clock for order.

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loudly, because it announced the Dawn of Life. And ever since this dramatic

time, Biological Order has been present. It has continuously been reﬂected

within the living things of our world.

SPONTANEOUS GENERATION: LIFE COMING OUT OF

NOWHERE

One of the theories attempting to explain the appearance of living things (and

their associated Biological Order) is spontaneous generation. According to

this theory, life is ‘‘produced’’ (generated) ‘‘automatically’’ (spontaneously)

from non-living things. For many centuries, it was commonly assumed that a

living ﬁsh, for instance, could arise ‘‘spontaneously’’ from the mud in the

bottom of a lake! And people naively thought that rotten meat was somehow

‘‘spontaneously’’ transformed into swarms of living ﬂies!

A scientist named Francesco Redi (REH-dee) threw doubt upon the

Spontaneous Generation Theory in the 1600s. Redi demonstrated that

when rotting meat is covered with a mesh, no ﬂies come out of it. Yet,

numerous people still believed that spontaneous generation produced the

great variety of micro-organisms (MY-kroh-or-gan-izms) – ‘‘tiny organisms,’’

such as bacteria.

Another scientist, Louis Pasteur (pas-STER), ﬁnally showed (in the mid-

1800s) that micro-organisms did not spontaneously generate. Pasteur boiled

a rich broth and kept it in a glass ﬂask with a curved neck for well over a

year. The curved neck prevented any micro-organisms from reaching the

broth, so the broth remained clear and free of micro-organisms. If any

micro-organisms had spontaneously generated within the broth, they

would have turned the broth cloudy.

THE MODERN THEORY OF BIOGENESIS

After Pasteur’s experiment, the old idea of spontaneous generation gave way

to the modern Theory of Biogenesis (buy-oh-JEH-neh-sis). Biogenesis is the

theory that ‘‘life’’ (bio) is ‘‘produced’’ (genesis) only from other things that

are already alive. Two living male and female human beings, for instance, can

mate and produce oﬀspring that are also alive.

But our present-day observations about biogenesis still don’t answer the

question, ‘‘How did the very ﬁrst life come into being on our planet?’’ Most

evidence seems to point to a primordial (pry-MORE-dee-al) soup on the sur-

face of the early Earth. Primordial means ‘‘ﬁrst in order’’; that is, existing ﬁrst

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before other things. The basic idea is that a primordial soup of complex

organic compounds existed within the early oceans. Under the right condi-

tions, such as the input of lots of energy from lightning striking the water and

volcanoes spewing hot lava, these complex organic chemicals combined

together and acquired a membrane around themselves. After this, they some-

how became alive. Perhaps these ﬁrst primitive micro-organisms were a spe-

cies of ancient bacteria. According to the Theory of Biogenesis, these ancient

bacteria eventually gave rise to all other living things on our planet.

Dinosaurs Help Make A Fossil Record

We will probably never know for sure exactly how life began – Why? The ﬁrst

living things (such as primitive bacteria) left behind no fossil record. Soft-

bodied micro-organisms, such as the ancient bacteria, had no hard parts.

Hence, their remains were rarely preserved.

Fossil means ‘‘to dig.’’ Thus, the fossil record consists of the remains of

ancient living things that have been preserved and ‘‘dug’’ up. With no hard

body parts preserved, then, the ﬁrst living creatures essentially left no fossils

to be ‘‘dug’’ up later!

Nevertheless, many ancient soft-bodied bacteria created stromatolites

(stroh-MAT-uh-lights) – ‘‘layered rocks.’’ Even today, huge mounds of bac-

terial colonies live in shallow ocean water. Fine particles of dirt, calcium, and

other minerals in the seawater, collect as sediment upon the colonies. This

sediment eventually arranges into thin ‘‘layers’’ (stromas) streaking through

each bacterial mound. As the layers or stromas become calciﬁed (hardened

with calcium sediment), they turn into layered rocks.

Figure 3.2 shows such a stromatolite. Among the oldest-known fossils are

narrow, ﬁlament (‘‘thread’’)-shaped bacteria, preserved within ancient stro-

matolite rock from Western Australia. They are about 3.5 billion years old.

THE FIRST LIVING ORGANISMS: TINY GREEN THREADS

WITHOUT ANY ‘‘KERNELS’’

In the living stromatolites found on present-day Earth, the bacteria are usually

bluish-green in color. This green color indicates that they engage in photosynth-

esis (FOH-toe-sin-theh-sis). Photosynthesis is the use of ‘‘light’’ (photo)to

‘‘place (things) together’’ (synthesis). Speciﬁcally, photosynthesis is the process

whereby certain types of organisms (usually green) use the energy in sunlight to

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3, Order

make sugar molecules for themselves. Thus, the ﬁrst ancient bacteria probably

looked like tiny bluish-green threads or ﬁlaments. Further, each of these

ancient, threadlike, green bacteria cells lacked a nucleus.

In Greek, the word part for ‘‘nucleus’’ or ‘‘kernel’’ is kary (KAIR-ee).

Consequently, these ancient threadlike bacteria are often called prokaryotes

(proh-KAIR-ee-oats). The reason for this name is that, being extremely

ancient, the prokaryotes probably appeared ‘‘before’’ (pro-) other types of

more advanced cells having a ‘‘nucleus’’ (kary).

CELLS WITH NUCLEI: IN COME THE ‘‘KERNELS’’

For well over a billion-and-a-half years, it appears that the prokaryotes

(photosynthetic cells without nuclei) were alone on this planet. All that

time, however, these tiny green cells produced abundant amounts of oxygen

) molecules, since oxygen is one of the main by-products of photosynthesis.

The prokaryotes accomplished the critical task of making Earth’s atmosphere

capable of sustaining aerobic (air-OH-bik) metabolism. This is the type of

metabolism that ‘‘pertains to’’ (-ic) ‘‘oxygen-or-air-using’’ (aer) ‘‘life’’ (ob).

The stage was thus set for the appearance of more complex cells, many of

which had aerobic metabolisms dependent upon a ready supply of oxygen.

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Fig. 3.2 Ancient bacteria and their rocky stromatolite.

About 2.1 billion years ago, numerous eukaryotes (yew-KAIR-ee-oats)

evolved from the prokaryotes. Each eukaryote cell has a ‘‘good’’ (eu-)

‘‘nucleus’’ (kary) surrounded by its own membrane. In addition, the eukar-

yote cell contains numerous other organelles, each enclosed within its own

individual membrane. Besides the nucleus, another very important mem-

brane-covered organelle is the mitochondrion (my-toe-KAHN-dree-un). The

mitochondrion carries out most of the aerobic (oxygen-using) metabolism

within the eukaryote cell.

Figure 3.3 provides a summary of the above information. It shows that

there are two basic types of cells – prokaryotes (cells without a nucleus) and

eukaryotes (cells having a nucleus and other organelles surrounded by mem-

branes). Further, we see that the major examples of prokaryotes now in

existence are the bacteria. The cells of nearly all other organisms besides

bacteria, in contrast, are eukaryotes. (A detailed discussion of cell anatomy

and physiology will be provided in Chapter 5.)

UNICELLULAR ORGANISMS EVOLVE INTO

MULTICELLULAR ONES

So far, we have traced the development of life up to 2.1 billion years ago.

Both the ancient prokaryotes and eukaryotes had a critical characteristic in

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Fig. 3.3 The two basic types of cells: Prokaryotes versus eukaryotes.