KEY IDEA #1 SIMILARITIES AND DIFFERENCES AMONG LIVING ORGANISMS

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1 KEY IDEA #1 SIMILARITIES AND DIFFERENCES AMONG LIVING ORGANISMS LIVING VERSUS NONLIVING Living things carry out almost all the life processes or activities. These life processes include digestion, respiration, circulation, excretion, locomotion, immunity, coordination, and synthesis. Non-living things are incapable of carrying out at least one or more of the life processes. The sum of the energy used in all the life processes represents the metabolism of the organism. Homeostasis The ability to carry on the life processes allow a living thing to maintain dynamic equilibrium or homeostasis with their surroundings. Homeostasis is a state of balance or steady state between a living thing and its environment. Homeostasis in an organism is constantly threatened. Failure to respond effectively to a failure of homeostasis can result in disease or death. ORGANIZATION LEVELS Levels of Organization Living things have different levels of organization. The simplest level of organization is that of the cell. A group of cells with a similar function is called a tissue. Groups of tissues working together to perform a common function are called organs. An example of this would include the nervous, muscle, and other tissues which make up the heart. Groups of organs working together to perform a common function are referred to as a system or organ system. The blood vessels, blood, and the heart are organs which work together to form the circulatory system. Many different systems function together to allow a complex organism to function. Homeostasis All the components of the living things, from the cells and the organelles within them to the organ systems of complex organisms must interact to maintain a balanced internal environment within the organism. Organisms possess many control mechanisms to detect internal and external changes and make changes to correct any deviations. This maintenance of a stable internal environment by an organism is called homeostasis. Homeostasis in an organism is constantly threatened. Failure to respond effectively can result in disease or death. Cell Theory All organisms contain one or more cells which are capable of carrying on the life activities needed by the organism. This idea is often referred to as the cell theory. CELL STRUCTURE Parts of the Cell Theory The cell is the unit of structure in all living things. The cell is the unit of function in all living things. All cells come from preexisting cells.

2 A few exceptions to this theory exist. Viruses lack typical cellular structure. There also is some question as to how the first cell arose. In general, the cell theory holds true for most living things, however. Cell Organelles Cells have particular structures that perform specific jobs. These cell structures are called organelles and perform the actual work of the cell. These organelles are formed from many different molecules. Some functions carried out by organelles include the transport of materials, energy capture and release, protein building, waste disposal, and information storage. Single celled organisms also have organelles similar to those in more advanced organisms to complete their life processes. Many enzymes are needed for the chemical reactions involved in cellular life processes to occur. A Typical Animal Cell Some Cell Organelles Cell Organelle nucleus mitochondrion endoplasmic reticulum ribosome cell membrane food vacuole contractile vacuole chloroplast cell wall Function control center of the cell contains DNA which directs the synthesis of proteins by the cell carries on the process of cell respiration converting glucose to ATP energy the cell can use transport channels within the cell found on the endoplasmic reticulum and free within the cell responsible for the synthesis of proteins for the cell selectively regulates the materials moving to and from the cell stores and digests food pumps out wastes and excess water from the cell found in plant cells and algae carries on the process of photosynthesis surrounds and supports plant cells

3 Cell Membrane The cell membrane or plasma membrane performs a number of important functions for the cell. These functions include the separation of the cell from its outside environment, controlling which molecules enter and leave the cell, and recognition of chemical signals. The cell membrane consists of two layers of phospholipids with proteins embedded within these layers. The surface of the cell contains molecules which recognize (receptors) other molecules which may attach to the outside of the cell. Cell Membrane Structure Membrane Processes The processes of diffusion and active transport are important in the movement of materials in and out of cells. Diffusion Diffusion or passive transport is the movement of materials from a region of higher to a region of lower substance concentration. The diagram at the right shows the movement of molecules from higher concentration on side A to a lower concentration on side B. Active Transport In active transport, molecules move from a region of lower concentration to a region of higher concentration. As this process does not naturally occur, the cell has to use energy in the form of ATP to make active transport occur.

4 Cell Chemistry Many organic and inorganic substances dissolved in cells allow necessary chemical reactions to take place in order to maintain life. Large organic food molecules such as proteins and starches must initially be broken down through the life process of digestion in order to enter cells. Organic Molecules and Digestive End Products Organic Molecule carbohydrates proteins lipids (fats) Digestive End Product(s) simple sugars (glucose) amino acids fatty acids and glycerol LIFE PROCESSES Humans and other complex organisms require many different organ systems to carry on the activities required for life. These life activities or processes include digestion, respiration, reproduction, circulation, excretion, movement, coordination, and immunity. It is important to realize that cell organelles are involved in many of these life processes, as well as the organ systems of complex organisms. Life Processes Digestion Circulation Movement (locomotion) Excretion Respiration Reproduction Immunity Coordination Synthesis breakdown of food to simpler molecules which can enter the cells the movement of materials within an organism or its cells change in position by a living thing removal of waste products by an organism (wastes may include carbon dioxide, water, and urea in urine and sweat) process which converts the energy in food to ATP (the form of energy which can be used by the cells) the making of more organisms of one's own kind -- not needed by an individual living thing but is needed by its species the ability of an organism to resist disease causing organisms and foreign invaders the control of the various activities of an organism (mostly involves the nervous system and endocrine glands in complex animals) the production of more complex substances by combining two or more simpler substances

5 CELLULAR COMMUNICATION Cell Membrane Receptors Cell Membrane Receptors Many cell membranes have receptor molecules on their surface. These receptor sites play an important role in allowing cells and organs to communicate with one another. Hormonal Regulation Hormones provide a primary way for cells to communicate with each other. A hormone is a chemical messenger with a specific shape that travels through the bloodstream influencing another target cell or target organ. Upon reaching the cell the hormone is targeted for, the hormone often activates a gene within a cell to make another necessary compound. One example of this is provided by the pituitary gland. This gland at the base of the brain makes a hormone called LH (luteinizing hormone). This hormone travels through the bloodstream and stimulates the ovary to produce yellow tissue that produces the hormone progesterone, which maintains the thickness of the uterus lining. The graphic below illustrates how this kind of hormonal regulation can work in a plant cell. Animal cell hormonal regulation involves a similar mechanism. A Hormonal Feedback Mechanism The animation at the right illustrates how a hormone can bind to receptors on a cell membrane and trigger that cell to produce a needed compound. Nervous Regulation Nerve cells or neurons also allow cells to communicate with each other. Neuron communications are one way organism can detect and respond to stimuli at both the cellular and organism level. This detection and response to stimuli helps to maintain homeostasis in the cell or organism. Neurons may stimulate other nerve cells or muscle cells, thus causing the later to contract and produce movement.

6 Structure and Function of a Nerve Cell Structures and their Functions 1. dendrite -- neuron branch which detects stimuli (changes in the environment) 2. cyton -- body of the neuron where normal metabolic activities occur 3. axon -- longest dendrite covered by a myelin sheath which provides electrical insulation -- carries nerve message or impulse to the end brushes 4. end brushes -- release nerve chemicals called neurotransmitters which stimulate adjacent dendrites on the next neuron or a muscle cell Any change in nerve or hormone signals will change the communication between cells and organs in an organism and thus may cause problems for organism s stability and ability to maintain homeostasis.

7 KEY IDEA #2 HOMEOSTASIS IN ORGANISMS PHOTOSYNTHESIS The energy for life comes primarily from the Sun. Photosynthesis is the major way the energy of the Sun is converted to sugars which provide for the energy needs of living systems. Plants and many microorganisms use solar energy to combine the inorganic molecules carbon dioxide and water into energy-rich organic compounds such as glucose sugar and release oxygen to the environment. A Representation of Photosynthesis The overall process of photosynthesis in a plant or algal cell is shown in the graphic below. Plants use water and the energy provided by sunlight to combine carbon dioxide into glucose sugar with oxygen being released as a waste product. chloroplasts: organelles that carry on photosynthesis in green plant cells chlorophylls: the variety of green pigments within the chloroplasts RESPIRATION In all organisms, organic compounds such as glucose can be used to make other molecules. These molecules include proteins, DNA, starch, and fats. The chemical energy stored in bonds can be used as a source of energy for life processes.

8 Stored energy is released when chemical bonds are broken during cellular respiration and new compounds with lower energy bonds are formed. Cells usually transfer this energy temporarily in phosphate bonds of a high-energy compound called ATP. (adenosine triphosphate) Equations for Cell Respiration glucose + oxygen carbon dioxide + water + 36 ATP The energy from ATP is then used by the organism to obtain, transform, and transport materials, and to eliminate wastes. water + ATP ADP + P + Energy (ATP-ase) Note: ADP is adenosine diphosphate. This reaction is reversible and ADP can be converted back to ATP in cellular respiration. Types of Reactions Hydrolysis: reaction in which large molecules are broken down into smaller molecules. Chemical digestion is an example of a hydrolysis reaction Synthesis: the combining of simpler molecules to form a more complex molecule Biochemical processes, both breakdown (hydrolysis) and synthesis, are made possible by enzymes. Enzymes and other molecules, such as hormones and antibodies, have specific shapes that influence both how they function and how they interact with other molecules. ENZYME STRUCTURE AND FUNCTION catalyst: inorganic or organic substance which speeds up the rate of a chemical reaction without entering the reaction itself. enzymes: organic catalysts made of protein. most enzyme names end in -ase enzymes lower the energy needed to start a chemical rx. (activation energy), thus speeding the reaction How do enzymes work? substrate: molecules upon which an enzyme acts. The enzyme is shaped so that it can only lock up with a specific substrate molecule. enzyme substrate > product

9 Lock and Key Theory Each enzyme is specific for one and ONLY one substrate (one lock - one key) active site: part of the enzyme that fits with the substrate Note that the active site has a specific fit for this particular substrate and no other. Since the enzyme may unhook from the substrate, it may be reused many times. Factors Influencing Enzyme Activity ph: the optimum (best) in most living things is close to 7 (neutral). High or low ph levels usually slow enzyme activity Temperature: strongly influences enzyme activity optimum (best) temperature for maximum enzyme function is usually about C. reactions proceed slowly below optimal temperatures above 45 C. most enzymes are denatured (change in their shape so the enzyme active site no longer fits with the substrate and the enzyme can't function)

10 Concentrations of Enzyme and Substrate When there is a fixed amount of enzyme and an excess of substrate molecules the rate of reaction will increase to a point and then level off. This leveling off occurs because all of the enzyme is used up and the excess substrate has nothing to combine with. If more enzyme is available than substrate, a similar reaction rate increase and leveling off will occur. The excess enzyme will eventually run out of substrate molecules to react with. FAIRLURE OF HOMEOSTASIS: DISEASE Some Causes of Disease Living organisms which cause disease are known as pathogens. Some viruses, bacteria, fungi, and parasites are examples of living things which are pathogens causing disease. Other factors may be involved which contribute to or cause the body to develop disease. Some of these factors include heredity, exposure to poisonous (toxic) substances, poor nutrition, organ failure or malfunction, and poor personal behavior and choices. Smoking, obesity, and over consumption of alcoholic beverages would be a few examples of poor personal choices which may have immediate or long term consequences for our health. Immunity and Disease Immunity describes the ability of an organism to resist foreign organisms or invaders which enter its body. The immune system is designed to protect against microscopic organisms (bacteria, viruses) and foreign substances which enter an organism from outside its body. The immune system also protects from many cancer cells which arise within our bodies. An antigen is any foreign substance which invades the body of an organism, while a pathogen is a living antigen (such as viruses or bacteria) which invade an organism. Many different kinds of white blood cells exist which are able to help the body fight foreign invaders in various ways. These various ways include: engulfing (eating) invaders (phagocytes are white blood cells doing this) producing antibodies (chemicals which destroy or neutralize antigens) (lymphocytes are the kind of white blood cells which produce antibodies) marking antigens for attack and killing by other white blood cells

11 Below are graphics of two different categories of white blood cells in action: Lymphocyte White Blood Cell Function Phagocytic White Blood Cells in Action It is important to note that an antibody has a specific shape to destroy a specific antigen. Immune System Memory and Vaccinations When organisms are exposed to disease, they make specific antibodies which destroy that antigen during their first exposure to it. This first exposure to a disease and our making of antibodies in reaction to this to defend ourselves is sometimes called the primary immune response. Our immune system has a memory. This means that if we ever are exposed to that same particular disease antigen again, our immune system has a memory and will make antibodies so rapidly in response to another exposure that we will not get the disease. Our immune memory is sometimes called the secondary immune response. Immune System Memory

12 Vaccinations use dead or weakened microbes or parts of them to stimulate the primary immune response or first production of antibodies. Using dead or weakened microbes has the advantage of not making the organism sick as they would become if they caught and recovered from a disease. Because the vaccine has stimulated the immune system, the organism will now have a memory to subsequent exposures to that disease causing antigen. Allergies and Auto-immune Diseases In allergies, the body's immune system produces chemicals in response to normally harmless substances which do not trouble other individuals. These chemicals make people with allergies feel sick. In auto-immune diseases, the body's immune system for usually unknown reasons may attack and destroy some its own cells. Some kinds of arthritis and degenerative diseases result from auto-immune diseases. AIDS, Cancer, and Disease Research Some viral diseases damage the immune system which leaves it unable to cope with many antigens and other infectious agents. AIDS is a viral disease which destroys the ability of the immune system to produce antibodies, so the afflicted individual is unable to cope with infections and cancer cells which arise within the body. Cancer is a group of diseases resulting from gene mutations which cause cells to divide uncontrollably. Exposure of cells to certain chemicals and radiation appears to increase the chance of mutations and thus cancer. Biological research is constantly ongoing to find knowledge about diagnosing, preventing, treating, controlling and curing diseases in plants and animals. The human genome project has provided a great deal of information of the genetic basis of many diseases. FEEDBACK MECHANISMS Homeostasis is the maintenance of a stable internal state within an organism. Homeostasis is also known as steady state. Organisms must respond and maintain homeostasis in relation to many factors. Stimulus and Response

13 Organisms detect changes in their environment and respond to these changes in a variety of ways. These changes may occur at the cellular or organism level. The graphic above shows the response of a human to being struck on the knee with a hammer. Change in the environment is called a stimulus. In this situation, the stimulus is the being struck with the hammer. A response is the manner in which the organism reacts to the stimulus. The knee jerk reflex which is pictured at the right is the response of this individual to being hit with this hammer. Feedback Mechanism Examples Feedback mechanisms have evolved in living things as a mechanism by which they maintain homeostasis or dynamic equilibrium. A feedback mechanism occurs when the level of one substance influences the level of another substance or activity of another organ. An example of a feedback mechanism in humans would be the increase in heart rate and respiratory rate which occurs in response to increased exercise or other increased muscle cell activity. Some other examples of feedback mechanisms in living things appear below. Temperature Homeostasis Humans maintain a relatively constant body temperature of about 37 C. when we "heat up" we sweat if possible the evaporation of this perspiration returns the body to its original temperature

14 Blood Sugar Regulation Homeostasis by Plants The pancreas is an endocrine gland which produces hormones which regulate blood glucose (sugar) levels An increase in blood sugar level triggers the release of the hormone insulin by the pancreas the hormone insulin lowers blood sugar level restoring the body to its original blood glucose level in two major ways: it increases the ability of body cells to take in glucose from the blood it converts blood glucose to the compound glycogen -- this compound is also called animal starch and is stored in our liver and muscles Maintenance of Water plants need to regulate water loss and carbon dioxide intake for photosynthesis and other life activities when plants do not keep enough water in their cells, they wilt and die stomate: a microscopic hole in a plant leaf which allows gases to enter and leave and water vapor to leave as well. Stomata is the plural of stomate. guard cells: open and close the stomate. the ability of the guard cell to close during periods of limited water availability for the plant allows the plant to maintain water homeostasis

15 KEY IDEA #3 GENETIC CONTINUITY DNA STRUCTURE AND FUNCTION DNA provides the set of coded instructions required by every organism for specifying its traits. The DNA molecule also provides for a reliable way for parents to pass their genetic code from one generation to the next. Heredity refers to this passage of these instructions from one generation to another. DNA is a double stranded molecule, which has the shape of a twisted ladder. This shape is called an alpha helix. The sides of this twisted ladder are composed of alternating phosphate and deoxyribose sugar units, while the rungs of the ladder are composed of pairs of nitrogenous bases. These bases are called adenine (A), thymine (T), guanine (G), and cytosine (C). These bases exist in pairs on the rungs of the ladder with A always pairing with T and G pairing with C. This principle is sometimes called complementary base pairing. (The saying G CAT provides a means of remembering this idea.) Structure of the DNA molecule Location of DNA

16 GENE-CHROMOSOME MODEL Hereditary information is contained The Gene Chromosome Model in genes, which are composed of DNA, located in the chromosomes of each cell. Chromosomes are found in the nucleus of each cell. Each gene carries a separate piece of information. An inherited trait of an individual can be determined by one genes, but is usually determined by the interaction of many different genes. A single gene can influence more than one trait. A human cell contains many thousands of different genes coding for many different traits. Changes in the sequence of the DNA molecule and therefore the gene are called mutations. A mutation may change the manner in which a trait is expressed by an organism. ASEXUAL VERSUS SEXUAL HEREDITY Asexual Heredity Every organism requires a set of coded instructions for specifying its traits. For offspring to resemble their parents, there must be a reliable way to transfer information from one generation to the next. Heredity is the passage of these instructions from one generation to another. The DNA molecule provides the mechanism for transferring these instructions. In asexually reproducing organisms, all the genes come from a single parent. As asexually produced offspring are produced by the cell division process of mitosis, all offspring are normally genetically identical to the parent. Sexual Heredity In sexually reproducing organisms, the new individual receives half of the genetic information from its mother through the egg and half from its father from his sperm. Sexually produced offspring resemble, but are not identical to, either of their parents. Some reasons for these variations between sexually reproduced offspring and their parents include crossing over when gametes are formed in each parent and genetic recombination, which is the combining of the genetic instructions of both parents into a new combination in the offspring when fertilization occurs. Genetic Recombination Note that two of the four offspring in the punnett square at the right have a completely different genetic makeup than that of either parent

17 The processes of crossing over and genetic recombination will result in offspring exhibiting variation from the original parents. The variations shown between different sexually produced offspring provide the driving force for the process of natural selection. Heredity and Environment The characteristics of an organism can be described in terms of combinations of traits. Traits are inherited, but their expression can be modified by interactions with the environment. Examples of this include the lack of color in completely shaded grass, even though it still possesses the genetic makeup to appear green and the change in fur color of returning fur in a shaven Himalayan hare at cold temperatures. Effect of Cold on Himalayan Hare Fur Color The application of an ice pack to a region of shaved hair results in black hair growing back instead of the original white color. The many body cells in an individual can be very different from one another, even though they are all descended from a single cell and thus have identical genetic instructions. This is because different parts of these instructions are used in different types of cells, influenced by the cell s environment and past history. Poor health habits can have an adverse effect on the development and expression of many genes in human cells, resulting in sickness or even death. Mutation A mutation is a change in the genetic material of an organism. Mutations which occur in non sex cells of sexually reproducing organisms will not be passed on to the offspring, Mutations although they may result in disease or death for the organism involved. One possible consequence of a mutation in a non sex cell is uncontrolled mitotic cell division or cancer. Mutations which occur in sex cells or gametes may be passed to the offspring. Along with crossing over and genetic recombination, mutation provides for a source of variation in sexually reproducing individuals.

18 PROTEIN SYNTHEIS DNA In all organisms, the coded instructions for specifying the characteristics of the organism are carried in DNA. The genetic code is contained in the four nitrogenous bases of DNA; adenine, guanine, cytosine, and thymine. These bases are often indicated only by using their beginning letters A, G, C, and T. Each individual DNA strand serves as a template or model for the formation of other DNA molecules by replication. RNA DNA codes for the formation of RNA in the nucleus of the cell. RNA is short for another kind of nucleic acid called ribonucleic acid. RNA is very similar in structure to DNA except for three small differences. These differences include the fact that RNA is a single stranded molecule, lacks the base thymine (T) as it is replaced by the base uracil (U), and its five carbon sugar ribose has one more oxygen atom than the sugar in DNA. Three different types of RNA exist, mrna or messenger RNA, trna or transfer RNA, and rrna or ribosomal RNA. Protein Synthesis Cells store and use coded information. The genetic information stored in DNA is used to direct the synthesis of the thousands of proteins that each cell requires. The chemical and structural properties of DNA are the basis for how the genetic information that underlies heredity. DNA is encoded in the sequence of nitrogenous bases which directs the formation of proteins in the cell. How does this process work? First, the DNA code is copied on to the mrna (messenger RNA) codon. A codon is a sequence of three nitrogenous bases. This process is called transcription. This mrna codon is then carried from the nucleus out to the ribosome. Messenger RNA attaches to another kind of RNA called trna (transfer RNA). Transfer RNA attaches to amino acids and carries them to the ribosome. This assembly of amino acids due to the code provided to RNA by the original DNA molecule is what produces proteins for the cell. Remember a protein is a long molecule formed from amino acid subunits. In summary, the code of DNA directs the synthesis of RNA, which in turn directs the making of proteins on the ribosomes. This is sometimes referred to as being the central dogma or idea of biology. There are 64 possible combinations of triplets (sequences of 3 nitrogenous bases) which code for the 20 different possible amino acids. As the DNA of different organisms and most individuals (except for identical twins) is different, this means the proteins produced by different humans and other organisms exhibit differences. It is these differences which make us unique individuals. The work of the cell is carried out by the many different types of molecules it assembles, mostly proteins. Protein molecules are long, usually folded chains made from 20 different kinds of amino acids in a specific sequence. This sequence influences the shape of the protein. The shape of the protein, in turn, determines its function. Offspring resemble their parents because they inherit similar genes (DNA sequences) that code for the production of proteins that form similar structures and perform similar functions.

19 Protein Synthesis Cell Regulation Cell functions are regulated. Regulation occurs both through changes in the activity of proteins and through the selective expression of individual genes, as humans and other organisms have genes which direct the expression of other genes. This regulation allows cells to respond to their environment and to control and coordinate cell growth and division. GENETIC ENGINEERING Selective Breeding For thousands of years new varieties of cultivated plants and domestic animals have resulted from selective breeding for particular traits. Some selective breeding techniques include artificial selection, where individuals with desirable traits are mated to produce offspring with those traits. A variation of this process traditionally used in agriculture is inbreeding, where the offspring produced by artificial selection are mated with one another to reinforce those desirable traits. Hybridization is a special case of selective breeding. This involves crossing two individuals with different desirable traits to produce offspring with a combination of both desirable traits. An example of this are Santa Gertrudis cattle, which were developed by breeding English shorthorn cattle, which provided for good beef, but lacked heat resistance, with Brahman cattle from India which were highly resistant to heat and humidity. The Santa Gertrudis breed of cattle has excellent beef, and thrives in hot, humid environments.

20 Genetic Engineering In recent years new varieties of farm plants and animals have been engineered by manipulating their genetic instructions to produce new characteristics. This technology is known as genetic engineering or recombinant DNA technology. Different enzymes can be used to cut, copy (clone), and move segments of DNA. An important category of enzyme used to cut a section of a gene and its DNA from an organism is known as a restriction enzyme. When this piece of DNA, which has been cut out of one organism, is placed in another organism, that section of gene will express the characteristics that were expressed by this gene in the organism it was taken from. An Example of Genetic Engineering Knowledge of genetics, including genetic engineering, is making possible new fields of health care. Genetic engineering is being used to engineer many new types of more efficient plants and animals, as well as provide chemicals needed for human health care. It may be possible to use aspect of genetic engineering to correct some human health defects. Some examples of chemicals being mass produced by human genes in bacteria include insulin, human growth hormone, and interferon. Substances from genetically engineered organisms have reduced the cost and side effects of replacing missing human body chemicals. While genetic engineering technology has many practical benefits, its use has also raised many legitimate ethical concerns. Other Genetic Technologies Cloning involves producing a group of genetically identical offspring from the cells of an organism. This technique may greatly increase agricultural productivity. Plants and animals with desirable qualities can be rapidly produced from the cells of a single organism. Genetic mapping, which is the location of specific genes inside the chromosomes of cells makes it possible to detect, and perhaps in the future correct defective genes that may lead to poor health. The human genome project has involved the mapping of the major genes influencing human traits, thus allowing humans to know the basic framework of their genetic code Knowledge of genetics is making possible new fields of health care. Genetic mapping in combination with genetic engineering and other genetic technologies may make it possible to correct defective genes that may lead to poor health. There are many ethical concerns to these advanced genetic technologies, including possible problems associated with the cloning of humans. Another down side to genetic mapping technologies it is possible that some organizations may use this genetic information against individuals.

21 KEY IDEA #4 REPRODUCTION AND DEVELOPMENT ASEXUAL REPRODUCTION Reproduction and development are necessary for the continuation of any species. Asexual reproduction is a method of reproduction with all the genetic information coming from one parent. Some Methods of Asexual Reproduction 1. binary fission -- involves an equal division of both the organism cytoplasm and nucleus to form two identical organisms -- the diagram of the protist at the right is example of this 2. budding -- involves one parent dividing its nucleus (genetic material) equally, but cytoplasm unequally -- the diagram of a yeast at the right is an example of this 3. sporulation (spore formation) -- is reproduction involving specialized single cells coming from one parent -- the diagram of mold spores being formed at the right is an example of this Asexual reproduction is sometimes called cloning. Cloning is the production of identical genetic copies. All forms of asexual reproduction are variations of the cell division process of mitosis. Mitosis is associated with asexual reproduction, as well as growth and repair in sexually reproducing organisms.

22 MITOSIS Mitosis is the method used for cell division and reproduction in cells not involved in sexual reproduction. This process starts with one replication (copying of the chromosome material) and one division of the chromosome material. This results in the chromosome numbers in the two cells produced being the same as in the parent cell. This process is represented in the graphic which follows. An Overview of the Process of Mitosis Key Results of Mitosis 1. The same chromosome number is retained from generation to generation Each daughter cell receives an exact copy of the chromosomes of the parent cell. (clones) SEXUAL REPRODUCTION The process of sexual reproduction involves two parents. Both parents normally contribute one gamete or sex cell to the process. This process assures that the genetic information given to the offspring will be obtained equally from each parent. The female gamete is called the egg or the ovum and the male gamete is called a sperm. These gametes are formed in specialized reproductive structures called gonads. The sperm is much smaller than the egg, but is capable of moving on its own power using a whip-like tail called a flagellum. Sperm and Egg (fertilization) The sperm and egg unite in a process called fertilization. This process forms a single celled structure called a zygote which contains the complete genetic information to develop into a complete new organism having characteristics

23 Process of Fertilization This zygote will then divide by mitosis and form the specialized cells, tissues, and organs of the organism. This development of specialized structures from the zygote is called differentiation. Meiosis The process of meiosis produces gametes or sex cells. While some parts of this cell division process are similar to the asexual cell division process of mitosis, there are several key differences. Meiosis produces gametes, while mitosis produces other cell types. The process of meiosis halves the chromosome number from the original parent cell in the four cells it forms. It does this by having two cell divisions forming four cells, where mitosis has only one cell division forming two cells. Both processes start out with one doubling or replication of the chromosome material. The graphic below will help to visually illustrate some of the key events of meiosis. Process of Meiosis Another important way that meiosis differs from mitosis is the exchange of chromosome pieces, which occurs in the first division of this process. This exchange of chromosome pieces is called crossing over. Crossing over assures that the cells produced as a result of meiosis will be different from and exhibit variations from the parent cell that produced them. This process is chiefly responsible for the variations seen in members of the same species of sexually reproducing organisms. These variations are the driving force for the process of natural selection.

24 The process of crossing over and how it produces variation when these chromosomes are recombined in the process of fertilization is illustrated in the graphic below. Crossing Over and Genetic Recombination Comparative Reproduction and Development Different organisms possess different adaptations for reproduction and development. Organisms which spend their lives or a large proportion of their lives in the water tend to lay their eggs in great numbers (thousands) in the water and wait for the male of the species to release sperm near them to fertilize them. The fertilization which occurs in the water in this case outside the body of the organism is called external fertilization. These young organisms then develop outside the mother in the water once this has occurred, which is called external development. A disadvantage of this process is that the eggs and developing young have little or no parental protection. Many fish and amphibians like frogs undergo fertilization and development in this manner. Reptiles and birds engage use the process of internal fertilization to fertilize their eggs. In this situation, the male of the species inserts his sperm inside the female, who then lays her fertilized eggs outside her body. The process of development is then external. Reptiles and especially birds tend to lay fewer eggs and provide much more parental protection for their

25 developing young. Organisms (with some exceptions) which use the process of internal fertilization tend to spend much of their lives on land. Mammals like humans have both their fertilization and initial stages of development occur within the female organism. This is referred to as internal fertilization and internal development. These organisms tend to release very few eggs, but those eggs and the developing organism are very well protected by one or both parents. HUMAN REPRODUCTIVE SYSTEM Male System The structure and function of the human male reproductive system, is very similar to that of many other mammals. The male system is designed to make sperm or male gametes and is adapted to provide for the delivery of these gametes to the female to allow for fertilization. Male Reproductive System 1. testes -- produces sperm and the hormone testosterone 2. scrotum -- pouch enclosing the testes keeping the sperm at an optimum temperature for development 3. vas deferens -- tube carrying sperm away from the testes 4. prostate gland -- the largest of several glands which add lubricating and other fluids to the sperm (this combination of sperm and fluids is called semen) 5. urethra -- tube through the penis carrying sperm to the outside of the body 6. penis -- adaptation for internal fertilization of the female Female System The structure and function of the human female reproductive system, is very similar to that of many other mammals. It is designed to produce female gametes or eggs, allow for internal fertilization, support the internal development of the embryo and fetus, and provide nutrition through milk for the newborn.

26 Female Reproductive System 1. ovary -- (females have two of these) -- produce female gametes or eggs and the hormone estrogen 2. oviduct (fallopian tube) -- carries the egg away from the uterus -- internal fertilization normally occurs here 3. uterus -- implantation and development of the embryo and fetus before birth occurs here 4. vagina or birth canal -- entry point for sperm from the male and exit tube for the baby when it is born Endocrine Interactions Human reproduction and development are influenced by factors such as gene expression, hormones, and the environment. The reproductive cycle in both males and females is regulated by several different hormones. Some of these hormones include: testosterone -- estrogen -- progesterone -- produced by the testes in the male and stimulates the development of male secondary sex characteristics (like facial hair and deeper voice). produced by ovaries in the female and stimulates the development of female secondary sex characteristics (wider hips and mammary glands) as well as starting the thickening of the uterus lining in preparation for a possible pregnancy after the egg is released by the female each month. produced by yellow tissue called corpus luteum in the empty ovarian follicle (place in ovary producing and releasing the egg) -- this hormone maintains the thickness of the uterus lining in case fertilization occurs and development of a fetus occurs.

27 In human females of reproductive age, these hormones interact in a cyclic pattern called the menstrual cycle. This pattern of events repeats itself on average every 28 days unless a pregnancy or other disruption occurs. A graphic representation and written description of the stages of the human menstrual cycle is provided below. Human Menstrual Cycle Note the influence of the hormone progesterone in beginning the thickening of the uterus lining and the role of the hormone estrogen in maintaining the thickness of that lining. Ovulation or release of the egg occurs at the midpoint of this cycle, while the uterine lining thins and is shed (menstruation) when the level of estrogen begins to decline to a large extent. Menstrual Cycle Stages 1. follicle stage (10-14 days average duration) production of ova/eggs occurs in tiny cavities in the ovary called follicles enlarging follicle produces estrogen which causes the uterus to get ready for embryo implantation (uterus thickens its lining) 2. ovulation (1 day) follicle enlarges and ruptures ovary wall egg is released to the oviduct (usually only 1 is released at a time) 3. corpus luteum stage (10-14 days average duration) yellow tissue fills the follicle after ovulation called the corpus luteum "yellow body" secretes progesterone which maintains the thickness of the uterus in case a pregnancy occurs 4. menstruation (3-5 days average duration) periodic shedding of the thickened lining of the uterus which occurs if fertilization does not occur

28 DEVELOPMENT Initial Development and Differentiation The processes of gamete production, fertilization, and development follow an orderly sequence of events. Zygotes contain all the information necessary for growth, development, and eventual reproduction of the organism. The zygote, which is a fertilized egg consisting of one cell, will begin to divide rapidly by mitosis forming the early developing human embryo. Fertilization and the initial stages of this mitotic cell division occur in the oviduct. The early embryo is migrates down the fallopian tube and completes most of its development in the wall of the uterus. Fertilization and Initial Development of the Embryo The embryo will eventually develop into a three cell layered structure. This structure is called a gastrula and will eventually differentiate to form the specialized cells. Differentiation means that the cells will develop specific jobs and develop into specific tissues in the maturing organism. An example of this is that the outer cell layer of the developing gastrula will develop into the skin and nervous system of a mature human organisms. Most multicellular animals undergo a similar pattern of development and differentiation. The placenta is a combination of maternal and fetal tissue which allows for the exchange of materials with the fetus and mother. Needed materials such as food and oxygen diffuse through the placenta to the fetus, while wastes from the fetus diffuse to the mother. The umbilical cord is a fetal structure containing blood vessels which allows materials to be carried between the fetus and placenta in both directions. The amniotic fluid surrounds the fetus and helps to provide a shock absorber to protect the fetus against mechanical injury in the event the mother is shaken or injured in some manner. Fetal Development Development is a highly regulated process After this small cluster of cells called the gastrula forms in humans, tissues begin to form. In humans, the embryonic development of essential organs occurs in early stages of pregnancy. During the first three months of human development, organs begin to form. The human embryo is usually referred to as a fetus when human like features become visible in its structure. All organs and body features are developed

29 by the end of the sixth month. During the last three months of pregnancy, organs and features develop well enough to function after birth. The embryo (or fetus) may encounter risks from faults in its genes and from its mother's exposure to environmental factors such as inadequate diet, use of alcohol, tobacco, drugs, other toxins, or infections. While the patterns of development discussed previously hold true for humans, these developmental patterns vary between different plants and different animals. Aging is a complex series of developmental changes which occur with the passage of time. This process is influenced by both heredity and the environment. This process eventually leads to the death of the organism. Reproduction and development are subject to environmental impact. Human development, birth, and aging should be viewed as a predictable pattern of events. Fetal Development in the Uterus REPRODUCTIVE TECHNOLOGIES Reproductive technology has medical, agricultural, and ecological applications. In many instances, these technologies have progressed at a faster rate than the ethical considerations resulting from these technologies. Some of these techniques include birth control methods used to block the process of fertilization. Many technologies now exist to enhance the process of fertilization and development in humans and other organisms. Hormone therapy can cause increased egg production. Surgery can open blocked fallopian tubes in females and the vas deferens in males. In vitro fertilization (test-tube babies) is a widely used technique to aid infertile couples, allowing them to have children where this otherwise would not be possible. KEY IDEA #5 EVOLUTION

30 NATURAL SELECTION Natural selection is the evolutionary process which selects the variation(s) of organisms best suited for a particular environment. Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life, as well as for the molecular and structural similarities observed among the diverse species of living organisms. The degree of kinship between organisms or species can be estimated from the similarity of their DNA sequences; this similarity often closely matches organisms' or species' classification based on anatomical similarities. Theory of Natural Selection 1. Overproduction: Within a population more offspring are born than can possibly survive. 2. Competition: Since the number of individuals in a population tends to remain constant from generation to generation due to limited resources, a struggle for survival occurs. 3. Survival of the Fittest: The individuals who survive are the ones best adapted to exist in their environment due to the possession of variations that best suit them to their environment. This genetic variability within a species is chiefly due to mutation and genetic recombination.the variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions. 4. Reproduction: Variations assist or hinder individuals in their struggle for survival. The best adapted individuals survive and reproduce, passing on the favorable variations to their offspring. 5. Speciation: As time and generations continue, adaptations are passed on and new species may evolve from a common ancestor. Small differences between parents and offspring can accumulate in successive generations so that descendants become very different from their ancestors. An adaptation is a variation which assists an organism or species in its survival. Biological adaptations include include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment. Some characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase. Behaviors have evolved through natural selection. The broad patterns of behavior exhibited by organisms have evolved to ensure reproductive success. Modern Examples of Natural Selection 1. Peppered moth:

31 two varieties of peppered moth existed, a light colored and a dark colored one as industrialization and coal burning increased, the environment in England where these moths lived became dirtier the dark colored variety of the moth blended into the trees and increased in numbers, while the light colored moth was less adapted and decreased in numbers 2. Insecticides kill insects not resistant to the insecticide, while insects resistant to the insecticide live to reproduce. The insecticide acts as a selecting agent. 3. Bacteria not resistant to an antibiotic are killed by it, while resistant bacteria live to reproduce. The antibiotic is a selecting agent for these bacteria. EVOLUTION AND EXTINCTION Evolution does not necessarily mean long term progress is going to go in a certain direction. Evolutionary changes often appear to be like the growth of a bush. Some branches survive from the beginning with little or no change, many die out altogether, and others branch out repeatedly, sometimes giving rise to more complex organisms. Direction of Evolution. Note the divergence of the various groups from a common ancestor and the fact that some branches became extinct. Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. The fossil record indicates that many organisms that lived long ago are extinct. Extinction of a species is common; most of the species that have lived on earth no longer exist. The Fossil Record Fossils are direct or indirect remains of organisms preserved in media such as sedimentary rock, amber, ice, or tar. Fossils have been found that indicate organisms existed well over 3 billion years ago. These organisms were simple, single-celled organisms. About a billion years ago, increasingly complex multi-cellular organisms began to evolve. The higher up you go in an undisturbed rock stratum (rock layer), the younger the rock layers become and therefore it is believed the fossils within these layers, as compared to lower rock layers.

32 Relative Dating of Undisturbed Sedimentary Rock and its Fossils Upper strata generally contain fossils of younger, more complex organisms, whereas, the lower strata contain fossils of simpler life forms. This means there is a tendency toward increasing complexity in life forms over time. When comparing fossils in undisturbed strata, fossils can be found in upper strata which, although different from fossils in lower strata, resemble those fossils. This suggests links between modern forms and older forms, as well as divergent pathways from common ancestors. Classification Biological classification is based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on structural similarities and evolutionary relationships. The species is the most fundamental unit of classification. This is a group of organisms which are close enough in their evolutionary relationship to be capable of successful reproduction and having fertile offspring. MUTATIONS Mutations are any changes in genetic material. Mutations can be caused by such agents as radiation and chemicals. When they occur in sex cells, the mutations can be passed on to offspring. Mutations occurring in other cells can be passed on to other body cells only. The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience. Some Types of Chromosome Mutations

33 Inversion: chromosome pieces are attached upside down Duplication: involves copying an extra section of chromosome Translocation: chromosome pieces moved Addition and deletion: chromosome is added or removed Either changes in chromosomes or genes on chromosomes changes the genetic which contributes to sources of variation. Some Other Sources of Genetic Variability In addition to mutation, other sources of the variation seen in sexually reproducing offspring include crossing over and genetic recombination during fertilization (union of egg and sperm). In crossing over, which occurs in the production of sex cells or gametes in meiosis, there is an exchange of chromosome pieces between the chromosome pairs associated with each other in this process. Mutations, crossing over, and genetic recombination ensure that no two gametes formed as the result of sexual reproduction will be exactly the same. As a consequence, the offspring formed as a result of sexual reproduction will exhibit variations. Some of these variations will be better suited for survival than others, thus driving the process of biological evolution.

34 Crossing Over and Genetic Variation VARIATION Sources of Variation 1. The exchanging and recombining of genes during meiosis and fertilization result in a great variety of new possible gene combinations from that of the parents. 2. Mutations are random changes in the genes or DNA of sex cells may result in new gene combinations creating variation in the offspring formed from these. Only mutations that occur in sex cells can be passed on to the offspring. Mutations which occur in other cells can be passed on to other body cells only. The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience. Variation and Evolution Evolution is the consequence of the following factors: 1. the potential for a species to increase its numbers 2. the genetic variability of offspring due to mutation and recombination of genes 3. a finite supply of the resources required for life 4. the ensuing selection by the environment of those offspring better able to survive and leave offspring. Some characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase.

35 An Example of Variation Driving Natural Selection Natural selection favors longer necks better chance to get higher leaves. Favored character passed on to next generation. Original group exhibits variation in neck length. After many generations, the group is still variable, but shows a general increase in neck length. The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions. The great diversity of organisms is the result of billions of years of selection for favorable variations that has filled available niches of our planet with life forms.

36 KEY IDEA #6 ECOLOGY ECOLOGICAL ORGANIZATION Ecology is the study of the interactions of living things with each other and their physical environment. The living things on earth may be organized into four different levels of ecological organization. These levels of organization are indicated in the table below. Levels of Ecological Organization A Representation of A Community 1. population 2. community 3. ecosystem 4. biosphere all the members of one species in an area all the members of the different interacting species in an area all the members of a community plus the abiotic (physical) factors influencing them entire region of the earth where living things may be found This is a community of many different organisms which could exist on milkweed. The community contains many organisms of different species in one location. ABIOTIC VERSUS BIOTIC FACTORS Abiotic factors are those non-living physical and chemical factors which affect the ability of organisms to survive and reproduce. Abiotic factors vary in the environment and determining the types and numbers of organisms that exist in that environment. Factors which determine the types and numbers of organisms of a species in an ecosystem are called limiting factors. Many limiting factors restrict the growth of populations in nature. An example of this would include low annual average temperature average common to the Arctic restricts the growth of trees, as the subsoil is permanently frozen.

37 Biotic factors are all the living things or their materials that directly or indirectly affect an organism in its environment. This would include organisms, their presence, parts, interaction, and wastes. Factors such as parasitism, disease, and predation (one animal eating another) would also be classified as biotic factors. Some Abiotic Factors Some Biotic Factors light intensity temperature range type of soil or rock ph level (acidity or alkalinity) water availability dissolved gases level of pollutant animals plants parasitism disease predation Carrying capacity is the maximum number of organisms the resources of an ecosystem can support. The carrying capacity of the environment is limited by the available abiotic and biotic resources (limiting factors), as well as the ability of ecosystems to recycle the residue of dead organisms through the activities of bacteria and fungi. NUTRITIONAL INTERACTIONS Energy flows through ecosystems in one direction, typically from the Sun, through photosynthetic organisms including green plants and algae, to herbivores to carnivores and decomposers. Green plants and algae are called autotrophs or producer organisms, as they capture solar energy to make sugars in the process of photosynthesis. Herbivores or primary consumers use the producer organisms to provide them with their food. Carnivores are secondary consumers as they eat the primary consumers as their source of food. Some organisms are capable of functioning as primary consumers (eating plant material) and as secondary consumers (eating animal material). These organisms are called omnivores. Humans are examples of omnivores. All consumers are examples of heterotrophic organisms, as they can not make their own food using the sun, but depend upon the ingestion of other organisms for their nutrition. A predator is a type of carnivore that kills its food. The organism the predator feeds upon is called its prey. A wolf and rabbit would provide an example of a predator/prey relationship. Scavengers feed upon organisms that other organisms have killed. A crow feeding off dead carrion in the highway would be an example of scavenger in this instance.

38 Competition occurs when two different species or organism living in the same environment or habitat use the same limited resources such as food, water, space, light, oxygen, or minerals. A resource which restricts the growth of a population is sometimes called a limiting factor. The more similar the requirements of the organisms involved, the more intense their competition will become. If two different species compete for the same food source, reproductive site, water, or other limiting factor, one species may be eliminated. This establishes one species per niche in an ecosystem. A niche refers to an organism s role, especially its feeding role, in a community. This allows different species to coexist and helps to contribute to the overall stability of the ecosystem. Symbiotic Relationships Close living associations are called symbiotic relationships. Parasitism is an example of such a relationship. In this situation, the parasite feeds upon the tissues or fluids or another organism, but usually does not kill the organism it feeds upon, as this would destroy its food supply. The organism the parasite feeds upon is called the host organism. An example of this sort of relationship would be fleas on a dog or athlete's foot fungus on a human. Types of Symbiosis parasitism: the parasite benefits at the expense of the host mutualism: both organisms benefit from the association commensalism: one organism is benefited and the other is unharmed Other Relationships Some organisms such as certain pathogenic bacteria may cause disease in other organisms. Decomposer organisms use the energy of dead organisms for food and break them down into materials which can be recycled for use by other organisms. Bacteria of decay and many fungi are examples of decomposer organisms. Food Chains If an ecosystem is to be self-sustaining it must contain a flow of energy. One way of representing the flow of energy through the living components of an ecosystem is through the use of a food chain. A food chain indicates the transfer of energy from producers through a series of organisms which feed upon each other.

39 A Food Chain The algae and floating plants are the producers in this food chain. The aquatic crustaceans are the primary consumers which eat the producers. Note that the arrows in the food chain point to the organisms which are doing the eating. Thus the arrows in the food chain represent the flow of energy through the ecosystem. Fish are secondary consumers eating the primary consumers. A food chain may also contain third level or other consumers as indicated by the raccoons in this food chain. Food Webs In a natural community, the flow of energy and materials is much more complicated than illustrated by any one food chain. A food web is a series of interrelated food chains which provides a more accurate picture of the feeding relationships in an ecosystem, as more than one thing will usually eat a particular species. A Food Web Energy flow in a food web also starts with the producer organisms through the various levels of consumer organisms as in a food chain. Energy Pyramids An energy pyramid provides a means of describing the feeding and energy relationships within a food chain or web. Each step of an energy pyramid shows that some energy is stored in newly made structures of the organism which eats the preceding one. The pyramid also shows that much of the energy is lost when one organism in a food chain eats another. Most of this energy which is lost goes into the environment as heat energy. While a continuous input of energy from sunlight keeps the process going, the height of energy pyramids (and therefore the length of food chains) is limited by this loss of energy.

40 An Energy Pyramid The picture at the left is an energy pyramid. Producer organisms represent the greatest amount of living tissue or biomass at the bottom of the pyramid. The organisms which occupy the rest of the pyramid belong to the feeding levels indicated in each step. On average, each feeding level only contains 10% of the energy as the one below it, with the energy that is lost mostly being transformed to heat. MATERIAL CYCLES Water Cycle The atoms and molecules on the Earth cycle among the living and nonliving components of the biosphere. Some of the water molecules which are used in photosynthesis are returned to the environment. The change of water from the liquid to the gas state is called evaporation, while the water lost to the atmosphere by the activities of plants is referred to as transpiration water loss. This water vapor eventually condenses to form clouds, and is returned to the earth as precipitation. This process is called the water cycle. The processes of cell respiration and excretion also releases some water to the environment as well. The Water Cycle

41 Carbon-Oxygen Cycle Carbon dioxide molecules are used in the process of photosynthesis to form energyrich organic sugar compounds. These carbon dioxide molecules are returned to the environment by the process of cell respiration, when the energy from these compounds is eventually released by cells. Some carbon is also returned to the environment by the decomposition of dead organisms. The Carbon-Oxygen Cycle Oxygen is required by many living things to release the energy in their food in the process of aerobic cellular respiration. Oxygen is released to the environment as a waste product of the process of photosynthesis. Other compounds, such as nitrogen, are cycled in the environment when organisms synthesize proteins from simpler compounds and then return these nitrogen compounds to the environment when they die and decompose. Role of Decomposers The number of organisms any environment can support is the carrying capacity of the environment. Carrying capacity is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms through the activities of decomposers such as bacteria and fungi. BIODIVERSITY The Need for Biodiversity As a result of evolutionary processes, there is a diversity of organisms and a diversity of roles in ecosystems. Biodiversity refers to the differences in living things in an ecosystem. Increased biodiversity increases the stability of the ecosystem as it provides for more genetic variation among species. A great diversity of species increases the chance that at least some living things will survive in the face of large changes in the environment.

42 Human Influences on Biodiversity When humans alter ecosystems either by removing specific organisms, serious consequences may result. Human beings are part of the Earth s ecosystems. Human activities can, deliberately or accidentally, change the equilibrium in ecosystems. Humans are destroying other species as a result of population growth, consumption, and technology. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is especially threatening current global biodiversity. An example of a human activity which has decreased biodiversity is the use of monoculture in modern agricultural practices. Monoculture involves planting one variety of a species over a huge area. This leaves this area more vulnerable to predation or disease and the loss of many or all species. Uses of Biodiversity In addition to the aesthetic beauty added to the world by many different organisms, biodiversity also ensures the availability of a rich variety of genetic material that may lead to future agricultural or medical discoveries with significant value to humankind. As diversity is lost, potential sources of these materials may be lost with it. ECOLOGICAL SUCCESSION Ecosystem Stability The interrelationships and interdependencies of organisms affect the development of stable ecosystems. The types of animal communities found in an ecosystem is dependent upon the kinds of plants and other producer organisms in that ecosystem. Succession The environment may be altered in substantial ways through the activities of humans, other living things, or when natural disasters occur, such as climate changes and volcanic eruptions. Although these changes are sometimes occur very quickly, in most cases species replace others gradually, resulting in long-term changes in ecosystems. These gradual long term changes in altered ecosystems are called ecological successions. Ecosystems tend to change with time until a stable system is formed. The type of succession which occurs in an ecosystem depends upon climatic and other limitations of a given geographical area. A Typical New York State Succession

43 Pioneer organisms are the first organisms to reoccupy an area which has been disturbed by a disruption. Typical pioneers in a succession include grasses in a plowed field or lichens on rocks. These pioneer organisms modify their environment, ultimately creating conditions which are less favorable for themselves, but establishing conditions under which more advanced organisms can live. Over time, the succession occurs in a series of plant stages which leads to a stable final community which is very similar to the plant community which originally existed in the ecosystem. This final stable plant community is called a climax community. This community may reach a point of stability that can last for hundreds or thousands of years. It has been observed that when natural disasters occur, such as a floods or fires, the damaged ecosystem is likely to recover in a series of successional stages that eventually result in a stable system similar to the original one that occupied the area. A Typical New York State Succession This chart represents a typical succession which is observed in New York State. The annual grasses represent the pioneer or first organisms in this succession. The beech-maple forest would represent a typical Northern New York climax community. The climax community will last hundreds or thousands of years unless again disrupted. A forest containing oak and/or hickory trees would be a more typical Southern New York climax community.