LIFE SCIENCE CONCEPT NOTES (WEEK 1 & 2)
WEEK 1
Introduction to LIFE SCIENCE: The Evolving Concept of Life
Biology is a science that deals with all forms of life, including their classification,
physiology, chemistry, and interactions. The term was introduced in Germany in 1800s
and popularized by the French naturalist Jean-Baptiste de Lamarck as a means of
encompassing the growing number of disciplines involved with the study of living forms.
Where did life begin?
Theory of Special creation, in accordance with the Book of Genesis, that every species
was
individually created by God in the form in which it exists today and is not capable
of undergoing any change.
Cosmozoic Theory (Panspermia Theory) – the idea proposed by Richter in 1865 and
supported by
Arrhenius (1908). According to this theory, life has reached the planet Earth from
other heavenly bodies such as meteorites, in the form of highly resistant spores
of some microorganisms. The spores of some microorganisms are called
cosmozoa or panspermia because they are preserved inside meteorites coming
to the earth from the outer space. These meteorites struck the barren earth to
release the cosmozoa and they developed into different creatures on the earth.
Theory of Spontaneous Generation also known as Abiogenesis, the idea that life
arose from
nonlife more than 3.5 billion years ago on Earth. Abiogenesis proposes that the
first life-forms generated were very simple and through a gradual process became
increasingly complex.
Biogenesis Theory, life is derived from the reproduction of other life, was presumably
preceded by abiogenesis, which became impossible once Earth’s atmosphere assumed
its present composition.
Primordial Soup Theory
 According to primordial soup theory proposed by Alexander Oparin and John
Haldane, life started in a primordial soup of organic molecules.
 Some form of energy from lightning combined with the chemicals in the
atmosphere to make the building blocks of protein known as the amino acids.
Coacervate theory, it is expressed by the Russian biochemist A.I. Oparin in 1936
suggesting that the origin of life was preceded by the formation of mixed colloidal units
called coacervates. These are particles composed of two or more colloids which might
be protein, lipid or nucleic acid. He proposed that while these molecules were not living,
they behaved like biological systems in the ancient seas.
They were subject to natural selection in terms of constant size and chemical properties
, there was a selective accumulation of material and they reproduced by fragmentation.
Miller-Urey hypothesis. The first hypothesis where lightning could have operated the
synthesis reactions in the Earth’s early atmosphere was tested by in 1953. It provided the
first evidence that organic molecules needed for life could be formed from inorganic
components. Some scientists support the RNA world hypothesis, which suggests that the
first life was self-replicating RNA.
Fossil Evidence
 Fossil evidence indicates that life on Earth appeared about 3.5 billion years ago in
the oceans
 Provided protection from Ultraviolet (UV) rays
 Allowed multidirectional movement
 Served as a medium for essential chemical reactions.
 Anaerobic prokaryotes
Early forms of life
 The first forms of life are believed to have appeared some 3.5 billion years ago.
 Photosynthetic organisms are organisms who make their own food by utilizing
the energy from the sun and the carbon dioxide in the atmosphere. The process
of photosynthesis produced more oxygen that changed the Earth’s early
atmosphere, allowed oxygen-breathing organisms to exist.
 Cyanobacteria (blue-green algae) are the first photosynthetic organisms to form.
The Early Life
The formation of planets did not use up all the materials orbiting the sun, so the
early Earth received shower of meteorites and was struck by many asteroids. These
extraterrestrial materials and the recurring volcanic eruptions paved the way for the
formation of Earth’s land, seas, and atmosphere.
It is still a matter of discussion, but geological evidence suggests that the early
Earth began with little or no free Oxygen (O2)—had O2 been present iron oxidation (rust
formation) in most ancient rocks would have been observed, but no such sign of oxidation
was found. Had O2 been present, small organic compounds would have broken apart as
quickly as they formed due oxidation reactions.
We know that water is essential to life because molecules that are parts of lifesustaining processes would have to be dissolved in water. The Earth’s lithosphere did not
exist then, but it was covered by molted rock, hence water was in the form of vapor. But
as evidence from ancient rocks suggests, Earth had cooled down 4.3 billion years ago
causing pools of water to arise.
Organic Monomers
Chemists thought that organic molecules were only made by living organisms and
it possessed a special vital force. But in the early 1900s, a chemist was able to make urea
the organic molecule found in urine. Then another was able to synthesized and amino
acid called alanine. The synthesis of these molecules showed the possibility that organic
molecules can be formed synthetically.
In the present, there are three (3) main hypotheses that explain the mechanism on
how the organic monomers came about in early Earth. These mechanisms are not
mutually exclusive and might have set off simultaneously contributing to the formation of
the simple organic compounds in Earth’s early seas—where early life could have started.
Extraterrestrial Materials
At present, meteorites that fall to Earth are often analyzed and was found out that
some contains amino acids, sugars, and nucleotide bases. These compounds (or their
precursors) have been found in gas clouds that surrounds nearby star. Thus, the third
hypothesis—that early life may have been brought about by the extraterrestrial
materials that fell on the early Earth received—was created. This hypothesis suggests
that materials from space carried with them organic monomers that were formed from
outer space.
WEEK 2
UNIFYING THEMES OF LIFE
In this lesson, you will learn about the unifying themes of life. As we know, all known
organisms share certain general properties. To a large degree, these properties define
what we meant by life.
All organisms share common characteristics that guide us in defining what we mean by
life. The unifying themes of life on the other hand refers to all the basic ideas that
apply to all organisms. It give us an idea of how each of these themes contributes to
the connection and interaction of living organisms and their environment.
Regulation and Homeostasis - One unique characteristic of living things is the ability to
use energy and matter to ensure survival. Plants obtain energy from sunlight by means
of photosynthesis while humans and animals released energy from food through cellular
respiration. They are also capable of maintaining body’s internal environment through
homeostasis.
Energy Processing/ Acquisition and use of energy – (Metabolism) is the set of lifesustaining chemical processes that enables organisms transform the chemical energy
stored in molecules into energy that can be used for cellular processes.
Growth and Development - is the increase in size and volume by converting food to
become a part of the body cells.
 Intussusception – growth from within the cells exhibited by living things.
 Accretion – growth by external addition of substances exhibited by nonliving things
Response to the environment / Ability to respond to stimuli - Organisms change their
behavior in response to changes in the surrounding environment. Responses occur in
definite patterns and make up the behavior of an organism.
Evolutionary adaptation/ evolution and adaptation - Certain responsive processes
allow organisms to react to changes in their surroundings. These responses include
movement (mobility), irritability, individual adaptation, and evolution.
 Mobility is movement of animals from one place to another (locomotion)
 Irritability is the ability of an organism to respond appropriately against a stimulus
or external factors such as light, sound, temperature, pressure, food sources, or
presence chemical substances.
 Adaptation is the ability of an organism to adjust to changes in the environment
which happens more slowly than responding to stimulus. Ex. Camouflage
Development and Reproduction - All living things undergo defined stages in their life
cycle called development which starts with birth and ends in death. Living things have
also ways of making sure that their species survive through reproduction (sexual or
asexual) which is a process by which genetic information is passed on from one
generation to another. This way, the characteristics of parents are transmitted from
parents to offspring (heredity).
High degree of organization - Living things exhibit a high degree of organization from
molecular to cellular level. For multicellular organisms such as plants and animals, the
level of organization is more complex. Group of cells from tissues and different tissues
form organs, organs comprise organ systems of an organism
Diversity and Unity - The organism interacts with other organisms of the same kind
known as population, while populations sharing their habitat compose a community. The
communities exist in an environment affected by both living and nonliving components
known as ecosystem.