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ISSUE #4: Life is Us: A New Perspective in Teaching Biology or the Life Sciences

CONVENER(S): Ijya C. Tulloss

PARTICIPANTS: Karen Kuse, Wendy Chan, Jane Ward


The session was a presentation of the ten themes of biology as listed in most modern day college textbooks and how we as Montessorians can translate these concepts into hands-on activites or projects. The aim was to see life science in a broader view as opposed to seeing it as a dicchotomy of botany and zoology. Another aim was to up[date our knowledge especially on recent scientific happenings and new developments that impact our lives now and may have greater impact in the future.

After introducing the first key experience of sorting objects as living and non-living, a discussion and ann inquiry is made as to what makes one classify things as living or non-living. Any idea is accepted as it is taken to be an index of one's developmental stage or cuurrent thinking. From this inquiry the group agrees on teh main characteristics of living things:

 1. movement
 2. respiration
 3. sensitivity
 4. circulation
 5. growth
 6. reproduction
 7. excretion
 8. food and nutrition

The ten themes may then be introduced as follows:

Theme one: Life occurs in many levels in hierarchical fashion.

 A group of cells, which are the smallest unit of life,  is a tissue like the heart tissue.  
 A group of tissues form an organ, an example is the heart.
 A group of organs functioning together is an organ system.  An organ with the arteries, veins and capillaries form the circulatory system.
 A group of organ systems is an organism.  An elephant is an organism, so is a tree.
 A group of organisms living together is a population.  When the population count is low, the population is considered endangered, in danger of becoming extinct.
 A group of populations living in the same area is a community, the meadow is an example.
 A collection of communities make an ecosystem - the everglades, the rain forest, etc are a few examples.
The whole earth where life is found is called a biosphere.

Projects: draw or collect pictures to depict the hierarchy of life. In this theme, life organizes and integrates the components as it moves to the next level so that a higher functioning becomes possible.

Theme two: The smalles unit of life is the cell. The first concept to impress students is that cells are so small and why cells have to be small. The key is to have as much surface available for the different acitvities to take place within a cell . This means a cell needs to have the greatest surface to volume ratio.

By taking a cell as a cube for mathematical computaion purposes:

If a cell has the dimension of one unit, its volume is teh cube of 1 or 1. Its surface is six times the area of each face or 6 times the square of 1 or 6x1=6.

The surface to volume ratio is 6/1 = 6.

If the cube has a dimension of two units, each volume is the cube of 2 or 8, its surface area is 6x the sqaure of 2 or 6x4=24. The surface to volume ratio is 24/8 = 3.

With a cube of a dimension of 3 unites, volume is 27, surface area is 6x9 = 54. Surface to volume ratio is 54/27 = 2.

Thus we can see that the bigger the dimension, the the smalller the surface to volume ratio. Therefore, the cell has to be smalll.

The second concept is that all cells have the DNA, the cytoplasm to provide the fluid medium for the cell to funciton and a cell membranee to define the outer limits of the cell. Basically there are two kinds of cells: the prokaryotic cell, one without a nuclear membrane and the eukaryotic cell, one with a nuclear membrane isolating the nuclues from the rest of the cell.

Students can study pictures of prokaryotic cell, plant cell and an animal ceell, learn the different parts and function of each part of the cell and then make a model out of found items.

Theme three: the continuity of life is made possible through the transfer of inheritable characteristics through the DNA, deoxyribonucleic acid.

The first concept is: life begets life. A pig can only have a pig for a progeny, etc. The second concept is to find out how these characteristics are encoded and passed on through the DNA. The DNA is a double helix capable of unwinding itself and then reforming itself into two new daughter molecules by each half picking up the complementary nitrogenous base needed to complete itself. This explains how inheritable characcteristics are passed on.

Structurally, DNA is like a ladder whose backbone is an alternating chain of sugar and ribose sugar molecules. The ribose in also connected to one of the four bases (A, T, G, C). The four bases are as follows:

 A stands for adenine.
 T stands for thymine.
 G stands for guanine.
 C stands for cytosine.

Each base always pairs with its complement: A pairs up with T, G pairs up[ with C.

The base pairs are linked to each other through hydrogen bonding, they form the rungs of the ladder.

The DNA stays in the nucleus. Its long chain of nucleotides ( sugar + base+ phosphate) codes for protein synthesis, a sequence of three nucleotides code for a specific amino acid. There are only 20 essential amino acids and any sequence of 3 from 4 bases yield 64 possible combinations. We have more than enough combinations to code for all the amino acides. The DNA unzips portion of its molecule and replicates that segment known as messenger RNA. The messenger RNA goes into the cytoplasm and act as a template for the assembling of the amino acids it was coded for with the help of enzymes and transfer RNA. Teh amino acids assembled then interact to form peptide bonds or connect together to form proteins. Thus DNA since it codes for protein synthesis, and proteins form the tissues, DNA is considered to have the instructions for life.

Theme four: Form follows function. The shape and architecture of any given part of an organism is so designed to fulfill its function. For example, if the function of a leaf is to catch as much sunlight from the sun, its design is to have its blade broad and opened. To help the leaf in its function is the petiole which enables the leaf to turn and follwo the sun. If the flower's function is to atttract pollinators, it therefore has to be either colorful or attractive or exude fragrance. The placement of the leaf on the tree is such that its tip directs water caugght from the rain to the eddge of the root or where its root hairs are.

The shape of fish is streamlined to facilitate swimming or cutting across the waters. The webbed feet of ducks enables it tgo swim using its webbed feet as paddles. Birds' feathers are coated with oil to keep it waterproof. The colors of butterflies sometimes mimic other objects to keep away its predators to make them blend with their environment for defense.

Theme five: organisms interact with their environment in order to support life.

Consider a horse, an animal which exhales carbon dioxide as a product of its respiration. It does not need carbon dioxide. The plant through photosynthesis uses this carbon dioxide along with water from the environment in presence of sunlight and its own chlorophyll, produces its main product, sugar, and its by-product, oxygen. Oxygen is then utilized by animals in respiration. Plants are eaten by animals. Waste products off animals fertilize the soil which then promotes plant growth. it shows a cycle where both living and non-living things interact to create a viable living system.

Theme six: An organism has regulatory mechanism to maintain balancee and homeostatis. When one is exerting in a vigorous activity, one needs more oxygen, thereby causing to increase breathing to take in more oxygen, increase heart rate to ppump oxygen around body. One also gets hot. As one sweats, it cools the body down through evaporation of water through sweat glands which takes heat along with the process. This makes one thirsty to take in water to replace the water loss.

The same balancing, self-regulatory activities can be seen in how the body produces and uses insulin to act on excess sugar to maintain blood sugar concentration.

In a marine environment, the corals absorb excess salt to form its skeleton thus reduccing the salinity of the sea to make life for several marine animals to flourish.

Theme seven: the unity and diversity of life is seen throughout the biosphere. As one surveys diversity of life forms, one can notice that it can be classified from the simple to the complex. Since the botanist, Carl Lenaeous, introduced the binomial nomenclature of naming plants using the name of the genus and the species, scientists have been trying to catalog organisms. Now we classify organisms into five kingdooms. Representing the prokaryotes or kingdom monera with the thumb, protists with the little finger, the fungi with the ring finger, the plants with the middle finger, the animals with the index finger, life on earth indeed is in our hands.

Each kingdom is further subdivided into phylum, phylum into class, class into orders, order into families, family into genus, and genus into species.

Activity: reproduce charts using pictures or original drawings or represent with models of plants or animals. Discover how seemingly unrelated organisms are really part of the same family (rice and bamboo belong to the grass family).

Theme eight: evolution is the mechanism whereby the diversity of life forms came into being from ancestor organisms.

 One  knows different breeds of dogs and how one breeds two different breeds to produce a new one, a hybrid.  Similarly new varieties of roses are produced through artificial cross-pollination. We then say that a new life form evolved through selection artificially done by man.  How about when things are left to nature, would such changes occur?

Before the industrial revolution, the population of light colored moth was prevalent. Being light colored, when resting on a light colored bark of the tree, it would remain invisible to its bird predator.

With the advent of Industrial revolution, tree barks became black from being coated with the smoke products of industrial waste. The light colored moth would be more visible on adark background. Its number decreased. Meanwhile, black colored moth which from time to time appeard on scene the became more successful in its survival and therefore in the survival of its progenies. Its number increased through natural selection. Natural selection of the factors already inherent in the organism but was given more expression in order to address environmental conditions increases the chance ffor survival of the organism and therefore of the population.

Evolution says that organisms do not change within a lifetime, it is the resulting population over a period of time through natural selection that changes.

With this theory, one can indeed theorize that life all sprung from a single species, each one evolving on to another, and again to another in a continuous fashion which one can then represent as atree or ladder of life. The more closely the organisms are related, closer they are in the tree of life representation. The evidence for this theory can be reconstructed through the fossils disccovered in different layers of sedimentary rocks. An organism adapts accordingly in order to meet its neeeds to survive. Such amazing correclation was formulated by Charles Darwin in his observation and analysis of the animal life in Galapagos Islands.

Theme nine: the process of science includes obsedrvation, collection of date, formulation of hypothesis, testing the hypothesis and drawing out conclusions. The process of inquiry and rigorous application of the scientific method thus described is responsible for the prodducts of science, the facts and knowledge we have gained through the work of the people in the past.

We teach our children the process of inquiry, to encourage intellectual honesty, patience, to value truth and to test results through repeated trials to make sure that what we obtain indeed is accurate.

Theme ten: The technology of science takes basic science into various applications to benefit mankind. It is possible that with the discovery of the sequence of DNA we can move into a new age where treatment or cancer is not through surgery or radiation but through treating the DNA. Along with this new knowledge comes ethical considerations to make. What do you do when a child is diagnosed early to develope an incurable disease in early adulthood? These and other dilemma will face us as we advance in the applications of science through technology.

It is therefore important to treach our students to value life, to develop compassion for all that lives along with a broad knowledge of sciences so that decisions in future will be based on sound knowledge and a loving heart.

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Last edited February 14, 2003 1:10 pm USA Pacific Time (diff)