AV:  Photosynthesis

AV:  Diversity of Life

LAB 8

PHOTOSYNTHESIS and

DIVERSITY OF LIFE:  A SURVEY OF THE ORGANISMS

Living organisms require energy to synthesize and maintain their protoplasm.  There are only two primary energy sources which may be utilized - chemical energy from the oxidation of organic or inorganic molecules and solar energy.  These forms of energy are not used directly by cells, but are converted to ATP (adenosine triphosphate).  ATP stores energy in its chemical bonds which can be released as needed by the cell.  Thus, ATP is often called the energy currency of the cell.

Man and many other organisms require the chemical energy stored in organic molecules to produce their ATP.  Organisms which require organic nutrients are termed heterotrophs.  The animals, fungi, and protozoa are heterotrophs.

Some living things are able to use the energy of sunlight to produce ATP.  The energy from the ATP can then be used to synthesize sugars from simple raw materials such as carbon dioxide and water.  Organisms which are able to use carbon dioxide to synthesize their own organic compounds are called autotrophs.  The green plants and the algae are the two major groups of autotrophs.

Photosynthesis is the process by which autotrophs utilize sunlight, water, and carbon dioxide to produce simple sugars. Since heterotrophs consume the organic molecules produced by photosynthetic organisms, almost all living things are directly or indirectly dependent on photosynthesis for energy and for food.

The photosynthetic organelles of eukaryotic cells are the chloroplasts.  A single plant cell may contain as many as forty to fifty chloroplasts, while a unicellular alga may contain only one.  The chloroplast contains light-absorbing pigments and the enzymes required to catalyze the reactions of photosynthesis.  The chlorophyll pigments are abundant in the chloroplasts of plants, and give them their characteristic green color.  Chlorophyll a is the primary light-absorbing pigment in photosynthesis.  The yellowish carotenoids act as accessory pigments by absorbing shorter wavelengths of light and passing the energy on to chlorophyll a.  The carotenoids are usually masked by the green chlorophylls.  However, in the fall, the chlorophylls decrease, and the carotenoids provide the golden shades of the autumn leaves.

Photosynthesis is often represented by the following equation:

6CO₂   +   12H₂O -------------->  C₆H_l2O₆   +   6O₂ + 6 H₂O 

^chlorophyll

                                        sun light

                                        enzymes

carbon +   water ^{---------------------->}   sugar   +    oxygen + water

dioxide    

Photosynthesis is not a one-step reaction as the previous equation might suggest.  The photosynthetic process involves many different chemical reactions which are typically divided into two groups: (1) the light reactions which require light and (2) the dark reactions which do not require light.

In the light reactions, solar energy is absorbed by chlorophyll producing energized electrons.  The electrons are then passed through a series of coenzymes to generate ATP.  Photolysis, the splitting of water, also occurs during the light reactions. The hydrogen released in photolysis is transferred to the coenzyme, NADP (nicotinamide adenine dinucleotide phosphate), yielding the reduced coenzyme, NADPH.  The oxygen, released in photolysis, is available to the many organisms which use it in respiration.

In the dark reactions, the ATP and NADPH from the light reactions are used to reduce carbon dioxide to form simple sugars.  These simple sugars can be converted to starch and other complex compounds needed by the alga or plant.

Question l:        List two primary energy sources which may be used by living organisms. 

Question 2:       What is the function of ATP within cells? 

Question 3:       What are heterotrophs? 

Question 4:       List three groups of heterotrophs. 

Question 5:       What is an autotroph? 

Question 6:       List two groups of autotrophs. 

Question 7:       Where does photosynthesis occur within eukaryotic cells?

Question 8:       What is the primary light-absorbing pigment in photosynthesis? 

Question 9:       What is the function of the carotenoids? 

Question 10:     Give the overall equation for photosynthesis. 

Question 11:     List two events which occur during the light reactions. 

Question 12:     List three products of the light reactions. 

Question 13:     What takes place during the dark reactions of photosynthesis? 

OBJECTIVE:

To gain a general understanding of the reactions of photosynthesis, including the conditions required and the products which are formed.

PROCEDURE:

I.        View the videotape on Photosynthesis and participate

in the discussion led by your instructor.

                   II.       Separation of Chloroplast Pigments by Paper Chromatography.

                             NOTE:  YOUR INSTRUCTOR MAY CHOOSE TO SET UP A

DEMONSTRATION OF THIS CHROMATOGRAPH.

The chloroplasts of eukaryotic cells contain two major groups of photosynthetic pigments, the chlorophylls and the carotenoids.  Chlorophyll a, which has a blue-green color, and chlorophyll b, which has a yellow-green color, are the most common chlorophylls. The most abundant carotenoids are the yellow carotenes and the yellow-orange xanthophylls.  When an extract of plant leaves is allowed to dry on a strip of chromatography paper, and the paper is placed in an organic solvent; the chlorophylls and the carotenoids can be separated as the solvent moves up the strip.  The distance moved by each pigment is determined by its attraction for the paper, its solubility in the solvent, and its molecular weight.  Carotenes travel the greatest distance, followed by the xanthophylls, then chlorophyll a and last chlorophyll b.

PROCEDURE:

1.      Obtain a strip of chromatography paper from the front desk.

2.      Using a pencil, draw a line across the strip about one-half inch from one end.  Try not to touch the strip with your fingers.

3.      A chlorophyll extract from spinach leaves is supplied on the front desk.  Using a dropper, streak the extract across the line on the strip of paper.  Allow the extract to dry.  Repeat this procedure until you have added five streaks of the extract to your strip of paper.

4.      Obtain a large test tube and a stopper to fit it from the front desk.

5.      Pour about one centimeter of a solvent, containing ninety parts petroleum ether and ten parts acetone, into the tube.

Note: PETROLEUM ETHER IS HIGHLY FLAMMABLE. KEEP THE TUBE AWAY FROM THE LAMP USED IN THE OTHER EXERCISES.

6.      Carefully insert the end of the strip containing the extract into the tube.  The end of the paper should touch the solvent, but the solvent should not touch the extract.

7.      Stopper the tube and leave it undisturbed until the solvent nears the top of the strip.

8.      Remove the strip from the tube and allow it to dry.

9.      Identify the pigments separated on the chromatogram.

Question 14:     List four groups of pigments found in chloroplasts.

Question 15:     List three factors which determine the distance a pigment will move during paper chromatography. 

Question 16:     Which group of pigments appeared to be most soluble in the solvent? 

Question 17:     Assuming the solubility of all four groups of pigments in the solvent is similar, which group probably has the greatest molecular weight?

DIVERSITY OF LIFE:  A SURVEY OF THE ORGANISMS 

On our planet today, there are roughly 2,000,000 species which have been studied and classified, but it is estimated that millions of other species remain to be discovered.  The number of animal species is much greater than the number of plant species; the insects and the nematodes (roundworms) are especially diverse animal groups.  The other kingdoms in order of descending diversity are fungi, protists and monerans. 

This staggering diversity of life forms on Earth today is the culmination of millions of years of evolution.  Fossils clearly show us that the diversity of life has generally increased through the ages.  Life began in the water and slowly spread to the land and the air.  And, there is a good probability that one species on earth will eventually colonize the depths of the universe.  Perhaps our descendants will discover even greater variety of life forms on other planets. 

Although there is a vast array of different life forms, there is considerable unity at the cellular and molecular level.  Plant and animal cells have a nucleus, ribosomes, mitochondria and certain other organelles.  Also many of the chemical processes of eukaryotic cells (those containing a nucleus bounded by a nuclear membrane) are similar -- cellular respiration, protein synthesis and mitosis occur in all eukaryotic organisms.

In the past, diversity was temporarily diminished by extinctions.  Some were mass extinctions such as the complete removal of all species of dinosaurs at the close of the Mesozoic Era.  Eradication of species continues today at an accelerated pace, primarily as a result of our destruction of habitats in all parts of the world.  Many species are now being exterminated in tropical rainforests at an alarming rate as we burn and cut the forests.  Other species such as the Passenger Pigeon were directly eliminated by relentless hunting. 

When a species is lost, unique genes are lost.  It behooves us to conserve our living resources. Who knows what benefits we would derive from wild plants, animals and microbes?  Many medicinal drugs are derived from wild plants; wild animals provide breeding stock for improving livestock, and even molds (Penicillium for example) have provided us with antibiotics.  There are efforts to preserve our flora and fauna.  Seeds of rare plants are saved in seed banks.  Rare animals are protected in zoos and some reproduce in captivity.  Organizations like the Sierra Club and the Nature Conservancy have done much to establish and protect wilderness and natural areas which are refuges for countless species.  It is our responsibility as stewards of planet earth to preserve as best we can our rich heritage of wildlife.

OBJECTIVES:

1.      To learn the main characteristics and some representative species of the five kingdoms. 

2.      To gain the understanding that the great diversity of life forms on Earth today is the product of millions of years of biological evolution. 

3.      To learn that there is much similarity among organisms at the cellular and molecular levels even though there is great diversity among the species. 

4.      To become aware of relationships among the organisms -- especially the relationship of our species to other organisms. 

5.      To become aware of the importance of preserving the diversity of life as best we can.

PROCEDURE:

While viewing the tape, The Diversity of Life, the students will answer the questions posed in this lab exercise.  When the tape is over, the instructor will ask students to supply these answers and will likely expand upon some of them.  It is also probable that some of these questions will be on a future quiz and/or major lab test.

Question 18:     In the old classification system there were only two kingdoms; what were they? 

Question 19:     What are the five kingdoms used in this tape? 

Question 20:     Prokaryotic organisms are placed in what kingdom?

Question 21:     List the three shapes of bacteria. 

Question 22:     List two examples of blue-green algae (cyanobacteria). 

Question 23:     Give two characteristics of the Kingdom Protista. 

Question 24:     What group of protists are regarded as the most primitive group?

Question 25:     Nonmotile protozoans (can't move themselves) which are all parasitic are the .

Question 26:     Name a protozoan that moves by extending its protoplasm (these extensions are called pseudopodia).

Question 27:     Name one example of a ciliated protozoan.

Question 28:     Organisms which can't make their own food and depend on food from the environment are called .

Question 29:     What kingdom consists of organisms that are mostly multicellular, heterotrophic, and consist of hyphae.

Question 30:     Name a fungus parasitic on corn.

Question 31:     Spore cases are called .

Question 32:     What kingdom consists of multicellular, photosynthetic (autotrophic), eukaryotic organisms?

Question 33:     What are the three major groups of plants? 

Question 34:     Name a green alga that lives in the ocean.

Question 35:     The largest algae are called .

Question 36:     What is the main difference between bryophytes and tracheophytes? 

Question 37:     Mosses and  are bryophytes.

Question 38:     A fern ________ develops from a fern spore.

Question 39:     Name the two classes of seed-producing plants. 

Question 40:     How are pine seed dispersed? 

Question 41:     What group of seed plants produces flowers and fruits which enclose the seeds?

Question 42:     What kingdom consists of eukaryotic, multicellular, hetertrophic, and mostly motile organisms.

Question 43:     What is the simplest group of animals?

Question 44:     Name two coelenterates.

Question 45:     What are the three body layers of a flatworm such as Planaria.

Question 46:     What worms have a circulatory system with "hearts" and a coelom (body cavity completely lined by mesoderm)?

Question 47:     Name three mollusks. 

Question 48:     List four groups of arthropods (the most abundant group of invertebrates). 

Question 49:     Starfishes and  are representative echinoderms.

Question 50:     List three characteristics of the chordates. (Amphioxus and humans are members of this group.) 

Question 51:     What is the most primitive group of vertebrates?

Question 52:     In what way are amphibians dependent on water? 

Question 53:     List 3 groups of modern reptiles. 

Question 54:     Name some early reptiles that are now extinct. 

Question 55:     Name a characteristic that the first birds had that modern birds do not have. 

Question 56:     Provide 3 characteristics of mammals. 

Question 57:     Name 3 species that have been directly exterminated by Homo sapiens and explain why this happened.  (This question does not pertain to the tape; answers can be found in the library or you could consult your lab instructor.)