BIOLOGY CAPT REVIEW

1. BIOLOGY CAPT REVIEW

2. D 27. Describe significant similarities and differences in the basic structure of plant and animal cells.

3. D 27. Describe significant similarities and differences in the basic structure of plant and animal cells. Structures found in both plant and animal cells

4. D 27. Describe significant similarities and differences in the basic structure of plant and animal cells. Differences Between Plant and Animal Cells

5. D 28. Describe the general role of DNA and RNA in protein synthesis. • DNA (deoxyribonucleic acid) – hereditary material which makes up chromosomes and is located in the cell’s nucleus. It contains all of the information necessary to reproduce the cell and synthesize proteins. • REPLICATION - DNA is copied during the cell cycle in a process called replication. During replication, the DNA molecule separates into two strands and produces two new complementary strands following base pairing rules: A-T; C-G (adenine –thymine and cytosine –guanine). Each strand of the DNA serves as a template for the new strand.

6. D 28. Describe the general role of DNA and RNA in protein synthesis.

7. D 28. Describe the general role of DNA and RNA in protein synthesis. Protein synthesis requires two processes: transcription and translation. Transcription – A section of DNA is copied into a complementary sequence in mRNA. • Two strands of DNA unwind and separate (occurs in the nucleus) • One strand is used as a template to form a strand of messenger ribonucleic acid (mRNA). • In RNA, the nucleotide, thymine (T) is replaced with uracil (U). (Base pairing is A-U and C-G) • The enzyme, mRNA polymerase, uses nucleotides in the nucleus to translate the DNA information into mRNA. • mRNA passes through a nuclear pore and attaches to a ribosome in the cytoplasm. Ribosomes are made up over 50 proteins and are the site of protein synthesis.

8. D 28. Describe the general role of DNA and RNA in protein synthesis. Translation - Transfer RNA (tRNA) is used to translate the nucleic acid code into the correct amino acid sequence. The amino acids are linked together to form the specific protein. (Occurs in the cytoplasm). • Each of the 20 amino acids has one or more specific codons consisting of a triplet of nucleotides. Codons are located on the mRNA. (Example: codon = CGU) • The tRNA has a three letter sequence called an anticodon. The anticodon on the tRNA recognizes the corresponding codon on the mRNA. An enzyme in the ribosome detaches the amino acid from the tRNA and links it with the growing protein chain. (So, if the codon is CGU then the anticodon is GCA and the corresponding amino acid is arginine). • The process continues until the entire sequence in the protein is complete.

9. D 29. Describe the general role of enzymes in metabolic cell processes. Metabolism is all of the cell’s activities including the breakdown of food, the elimination of wastes and the synthesis of necessary chemicals. Enzyme is a protein that serves as a catalyst in a chemical reaction. (Catalyst is a substance that speeds up the rate of a chemical reaction and which is not used up in the process). • Most chemical reactions in living things require enzymes. • Enzymes break down molecules and build other molecules. • Each reaction requires a specific enzyme. • Refer to the next slide to examine the specific enzymatic reaction of the sugar, sucrose. The substrate, sucrose, binds to the active site in the enzyme, sucrase, forming an enzyme-substrate complex. The substrate, sucrose, is changed into the products, glucose and fructose.

10. D 29. Describe the general role of enzymes in metabolic cell processes.

11. D 29. Describe the general role of enzymes in metabolic cell processes. • Enzymes speed up chemical reactions in cells. Without enzymes, reactions would occur too slowly – resulting in the death of living things. • Notice in the graph below how the addition of an enzyme lowers the activation energy in the reaction. This action speeds up the reaction.

12. D 30. Explain the role of the cell membrane in supporting cell functions

13. D 30. Explain the role of the cell membrane in supporting cell functions Cell Membrane – exterior part of an animal cell; located inside the cell wall in a plant cell • Selectively permeable - membrane allows some chemicals to pass through it but not others. • Cell Membrane Structure • Three major parts – phospholipidbilayer, proteins and carbohydrates • Phospholipid has a tail and a head. The tail is made up of a long fat molecule consisting of carbon and hydrogen atoms. The head is made up of a phosphate group (PO₄⁻³). In water (cells are mostly water inside and outside) the phosphate head aligns to the outside pointing towards the water and the long lipid tail is directed inward away from the water. • Protein molecules are embedded in the phospholipidbilayer and short chain carbohydrates are bonded to both the phosphates and the proteins on the outside of the membrane. • Cell Membrane Functions • Diffusion - Certain molecules can cause the phospholipids to separate slightly creating a channel that allows molecules to cross the membrane. Movement is always from areas of higher concentrations to areas of lower concentration. (No energy required) • Active transport – energy requiring process that moves materials across the membrane against a concentration gradient. Process is carried out by special transport proteins.

14. D 31. Describe the similarities and differences between bacteria and viruses. Bacterium Virus

15. D 31. Describe the similarities and differences between bacteria and viruses.

16. D 32. Describe how bacterial and viral infectious diseases are transmitted, and explain the roles of sanitation, vaccination and antibiotic medications in the prevention and treatment of infectious diseases. Infectious Disease • Infectious disease is a disease caused by a virus or bacterium that can be spread from one organism to another. • Humans are the main source of viruses or bacteria which spread disease to other humans • Other sources of viruses and bacteria include food, and nonliving things such as water and soil. Disease Transmission • Direct contact – including shaking hands, kissing, sexual activity • Indirect contact • In the air --sneezing, coughing • Sharing objects – toothbrushes or toys • Vectors – disease carrying animals that pass the disease through a bite. • Mosquitoes, flies, rabid animals.

17. D 32. Describe how bacterial and viral infectious diseases are transmitted, and explain the roles of sanitation, vaccination and antibiotic medications in the prevention and treatment of infectious diseases Sanitation - is the hygienic means of promoting health through prevention of human contact with the hazards of wastes. Hazards can be either physical, microbiological, biological or chemical agents of disease. • Sewage and water treatment plants help reduce/destroy the disease producing organisms in human waste and water ; reducing chances of the spread of disease. • Cleaning up dumpsites removes breeding sites for mosquitoes- such as old tires and reduces the number of rodents. • Personal cleanliness kills and removes bacteria from the skin (especially important is hand washing); as well as careful washing of dishes and countertops before and after preparing food.

18. D 32. Describe how bacterial and viral infectious diseases are transmitted, and explain the roles of sanitation, vaccination and antibiotic medications in the prevention and treatment of infectious diseases. Vaccinationor immunization is the introduction of a dead, weakened or synthetic form of a pathogen into the body to stimulate the body to produce chemicals that will cause the body to become immune. • Decreases the risk of getting the disease or decreases its severity • Only a very slight chance of contracting (getting) the disease • Often used to treat viral diseases – chicken pox, measles • Best methods to prevent viral diseases –hand scrubbing, covering mouth when coughing or sneezing and avoiding contact with anyone who has a viral infection Antibiotic -drug used to kill or inhibit the growth of bacteria • Antibiotics completely ineffective against viruses • Used mostly as a cure for a disease such as strep throat • Used also in the prevention of infections such as antibiotic creams applied to cuts before bacteria can grow. • Overuse of antibiotics, has produced “superbugs” – which are bacteria no longer affected by common antibiotics

19. D 33. Explain how bacteria and yeasts are used to produce foods for human consumption. Bacteria respire anaerobically (without oxygen) to produce lactic acid through a process called fermentation. The fermentation process is used to create a variety of foods. • Cheese Production • Bacteria are added to milk where they begin lactic acid fermentation, changing lactose (milk sugar) into lactic acid. The acid causes the mild to curdle (clump) and this curd is then made into cheese. (The flavor of many cheeses ,brie and blue cheese, is produced by the addition of simple fungi – ie molds). • Sour Cream and Yogurt • Fermentation of cream or milk with bacteria • Sauerkraut and Pickles –fermentation of sugar by bacteria in cabbage and cucumbers

20. D33. Explain how bacteria and yeast are used to produce foods for human consumption. Yeast is a dried form of a single-celled fungus. Yeast respire anaerobically to produce alcohol, ethanol, and the gas, carbon dioxide. Yeast cells in the dry form are dormant, but when placed in a moist environment, they rapidly begin to grow and multiply. • Bread-Making • Carbon dioxide formed during fermentation caused bubbles to form in the dough and the dough rises. The ethanol that is formed evaporates during baking. • Alcoholic Beverages • Yeast used in fermenting fruit and vegetables to produce beer, wine and other alcoholic beverages.

21. D 34. Describe, in general terms, how the genetic information of organisms can be altered to make them produce new materials. Mutations– permanent changes in the genetic sequence. • May occur when the wrong nucleotide is inserted into the growing nucleic acid and this change will be passed on as cells multiply. • In other cases, a molecule resembling a nucleotide is inserted which makes it impossible for the nucleic acid to replicate. This change cannot be passed onto future generations of cells. • Many of these mutations occur naturally. • Some mutations are harmful and result from mutagens. • Mutagens - chemicals and radiation (including UV light from the sun) which cause mutations resulting in genetic damage and disease. • Some mutations are beneficial. • Natural genetic mutations are the driving force of evolution allowing the beneficial traits to accumulate through natural selection.

22. D34. Describe, in general terms, how the genetic information of organisms can be altered to make them produce new materials. Transgenic Organisms - Organisms that carry a gene or genes from another organism. Genetic Engineering is the process of creating a transgenic organism by introducing desirable traits into plants and animals using recombinant DNA (rDNA) technology. • Recombinant DNA(rDNA) molecules are DNA sequences that result from the use of laboratory methods (molecular cloning) to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms. • Recombinant DNA is possible because DNA molecules from all organisms share the same chemical structure; they differ only in the sequence of nucleotides within that identical overall structure. Consequently, when DNA from a foreign source is linked to host sequences and then introduced into the host organism, the foreign DNA is replicated along with the host DNA. • Recombinant DNA is made in the laboratory by taking a strand of DNA from the host and chemically adding or inserting a fragment of DNA from another source. • New DNA may be inserted in the host genome by first isolating and copying the genetic material of interest using molecular cloning methods to generate a DNA sequence, or by synthesizing the DNA, and then inserting this construct into the host organism. • An organism that is generated through genetic engineering is considered to be a genetically modified organism (GMO).

23. D34. Describe, in general terms, how the genetic information of organisms can be altered to make them produce new materials.

24. D34. Describe, in general terms, how the genetic information of organisms can be altered to make them produce new materials. Examples of GMO’s - • Plants • Corn, soybeans, cotton – developed to produce their own insecticides and herbicides. • Peanuts being developed which will not cause an allergic reactions. • Other plants now produce vitamins and other nutrients that are not found in the original plant. • Other plants have been made so they can grow in different environments. • Animals • Many animals carry altered genes that make them more resistant to disease. • Animals modified to grow faster – ex. salmon • Other animals have been engineered to produce complex molecules used in medicines. • Bacteria • Genetically engineered to produce medicines, to protect crops from frost damage and clean up oil spills.

25. D 35. Explain the risks and benefits of altering the genetic composition and cell products of existing organisms. Scientists do not agree on whether all genetically engineered plants and animals are good or bad. Some benefits to GMO’s discussed in D 34. US government is trying to control the manufacture and distribution of genetically modified (GM) plants and animals. • Potential Risks • Plants are the most difficult to control since pollen blows in the wind and can pollinate non-GM species. • Bees and butterflies cannot tell the difference between non-GM and GM plants and therefore may pollinate non-GM plants with pollen from GM plants. • Hardier GM plants maybe good in some places but in other places may drive out the native species. • Plants that produce insecticide to give a better crop yield may also kill beneficial insects such as bees and butterflies. • Plants with a resistance to bacteria might actually pass this trait to bacteria making them tolerant to antibiotics. • Plants that produce vitamins and other dietary supplements may cause physical problems or diseases that develop in humans over a lifetime. • Benefits • Food crops or herds that grow bigger and faster could ease the world food shortage. • Food containing a gene against yellow fever and malaria could save millions of livers each year.

26. D 36. Explain how meiosis contributes to the genetic variability of organisms.

27. D 36. Explain how meiosis contributes to the genetic variability of organisms. Meiosis – process of forming gametes (sex cells, eggs and sperm). This process reduces the number of chromosomes by half and is also referred to as reduction division. Meiosis involves 2 cell divisions – • Meiosis I • Replicated homologous chromosomes pair up at the cell equator. (The lining up of maternal and paternal homologous pairs at the equator is random; thus contributing to genetic variability in the sex cells). • Homologous chromosomes may swap sections of DNA in a process called crossing-over. (The more crossing-over that occurs, the greater the genetic variability). • The cells divide into 2 daughter cells which have a different genetic make-up from the original cell. • Meiosis II • Each of the 2 daughter cells divides leaving each new cell with only half of the original number of chromosomes. These are the gametes. • In humans, each sperm cell contains 23 chromosomes and each egg cell contains 23 chromosomes. When the human egg and human sperm combine, a zygote forms which contains 46 chromosomes. (Zygote formation also increases genetic variability since any two gametes may combine).

28. D 36. Explain how meiosis contributes to the genetic variability of organisms. Mitosis – Stage in the cell cycle where the nucleus divides into 2 new nuclei and one copy of the DNA is distributed to into each daughter cell. The 2 daughter cells are genetically identical. • Mitosis occurs as an organism grows. Comparison of Mitosis and Meiosis

29. D 37. Use the Punnett Square technique to predict the distribution of traits in mono- and di-hybrid crossings. Punnett Square - A chart that shows all the possible genetic combinations that can result from the combination of an egg and a sperm. Traits – Characteristics of an organism such as eye or hair color, which are controlled by the alleles inherited from the parents. • Each trait is determined by two alleles, each represented by a letter • Each parent contributes one allele Allele – an alternative form of a single gene for a particular trait. • Dominant allele – represented by an upper case letter; indicates the trait that will always show up when this allele is present. (For example: B represents the allele for brown eyes and b represents the allele for blue eyes. Brown eyes – BB or Bb) • Recessive allele –represented by a lower case letter; trait is masked by the presence of a dominant allele and trait will only occur when a double dose of the recessive allele is present. (Blue eyes – bb) Phenotype – the visible trait Genotype – organism’s genetic makeup

30. D 37. Use the Punnett Square technique to predict the distribution of traits in mono- and di-hybrid crossings. Monohybrid Cross – shows the predicted results from the genetic cross of a single gene. Example – A man with brown eyes (BB or Bb) has a child with a woman with blue eyes (bb). What are the chances of the baby having blue eyes? Brown eyes? Genotype for all offspring is Bb; therefore all (100%) of the offspring will have brown eyes. Genotypes are Bb and bb; therefore, each offspring has a 50% chance of having brown eyes and a 50% chance of having blue eyes.

31. D 37. Use the Punnett Square technique to predict the distribution of traits in mono- and di-hybrid crossings. Di-Hybrid Cross: Study of the inheritance patterns for organisms differing in two traits. Example – In hair color, brown (H) is dominant over blond (h); and brown eyes (B) is dominant over blue eyes (b). If a brown eyed (Bb) and brown haired male (Hh) has a baby with a brown-eyed (Bb) and brown haired female (Hh). What are the chances of the offspring having brown hair or blond hair with brown eyes or blue eyes?

32. D 37. Use the Punnett Square technique to predict the distribution of traits in mono- and di-hybrid crossings. Of the 16 possibilities – Each offspring will have the following probability of having the two traits. 9/16 = brown eyed with brown hair 3/16 = brown-eyed with blond hair 3/16 = blue-eyed with brown hair 1/16 = blue-eyed with blond hair

33. D 38. Deduce the probable mode of inheritance of traits (e.g., recessive/dominant, sex-linked) from pedigree diagrams showing phenotypes Pedigree Diagrams – trace the inheritance of a trait through several generations. Grandparents Parents Child A Child B Child C KEY Male Blue-Eyed Male Deceased Male Female Blue-Eyed Female Deceased Female

34. D 38. Deduce the probable mode of inheritance of traits (e.g., recessive/dominant, sex-linked) from pedigree diagrams showing phenotypes Refer to pedigree chart on previous slide • Using eye color (D37) the blue-eyed grandmother must have the two alleles bb and is homozygous (both alleles are the same). • Grandfather must have the alleles Bb since one daughter has blue eyes. • Three sons must be heterozygous (two alleles are different) with Bb. • Child A is homozygous (bb) receiving her two recessive genes from her blue-eyed father and recessive mother. • Child C’s parents must have both been heterozygous (Bb). • It is not possible to determine whether Child B’s father was BB or Bb. Note: If the pedigree diagram is used to follow a disease, the shaded individuals will have the disease and display the symptoms of that disease. Sex-linked Traits – characteristics determined by genes located on the X and Y chromosomes which are passed from parent to child on a sex chromosome. (Sex-linked traits may be dominant or recessive). • Since males (XY) have only one X chromosome, any allele on the X chromosome will be expressed even if it is recessive. • Females will be carriers of a recessive sex linked trait if one X chromosome carries the recessive allele and the other X chromosome carries the dominant allele. If sex linked trait is ominant; only 1 dominant allele on one X-chromosome is required to produce the trait. • Females will possess the recessive sex linked trait when each X chromosome carries the recessive allele

35. D 38. Deduce the probable mode of inheritance of traits (e.g., recessive/dominant, sex-linked) from pedigree diagrams showing phenotypes Color Blindness – sex linked trait controlled by a recessive allele on the X chromosome. (A person with this trait cannot distinguish between red and green). • A female who receives only one recessive allele for red-green color blindness will not have the trait; but she will be a carrier. • Female must have the recessive allele on both X chromosomes in order to be color blind. • A male who receives one recessive allele will be colorblind.

36. D 39. Describe the difference between genetic disorder and infectious diseases. Genetic disorders – diseases or physical deformities caused by errors in the genetic code or by prolonged exposure to radiation. • Specific to an individual and can only be passed to that person’s offspring. • Genetic disorders may be either dominant or recessive. • A person only needs one copy of a dominant disease gene to display symptoms of the disease or the deformity. • A person with a recessive disorder will not show any signs of the disease or deformity if he is heterozygous (Aa), but can pass the trait(s) onto his offspring. This individual is a carrier of the trait. • Recessive disorder can only be displayed if the genotype is homozygous recessive (aa). • Sex linked disorders discussed in D 38. • There is no cure at this time in the US since gene therapy is banned; however, there are some treatments for some disorders.

37. D 39. Describe the difference between genetic disorder and infectious diseases. Genetic Disorders

38. D 39. Describe the difference between genetic disorder and infectious diseases. Infectious diseases - also known as transmissible diseases or communicable diseasescause illness in the individual as indicated by specific symptoms of the disease. • Result from the infection, presence and growth of pathogenic agents in an individual. • Pathogenic agents are organisms that cause disease and may be bacteria, viruses or fungi. • Transmitted or spread from person to person through personal contact or through air or water. • Cures exist for many infectious diseases through treatment with antibiotics, antiviral drugs or antifungal medications.

39. D 40. Explain how the processes of genetic mutation and natural selection are related to the evolution of species. Adaptation is an inherited trait that helps an organism to better survive in its environment. • Adaptations in nature can include size, beak shape, coloring or flower shape, enzyme efficiency and many more. • Adaptation may occur through random genetic mutations or in response by existing traits to a change in the environment. • Sometimes the physical changes caused by the mutation are harmful or fatal and do not get passed to the offspring of the next generation. • Other mutations may be beneficial that allow the organism to better survive and reproduce, passing the new trait to future generations. • Adaptations may be beneficial, neutral or harmful.

40. D 40. Explain how the processes of genetic mutation and natural selection are related to the evolution of species. Natural Selection is the gradual, nonrandom process by which traits become either more or less common in a population based on the reproductive success of the individuals. (survival of the fittest) • Key Aspects of Darwin’s Theory of Evolution 1.Individuals in a population show variations and these variations can be inherited. 2. Organisms have more offspring than can survive, and surviving organisms compete for limited resources. 3. Individuals best suited to their environment survive and reproduce most successfully. 4. Any genetic variation that increases the reproductive success of that organism has a greater chance of getting passed onto future generations. Natural Selection is the key mechanism of evolution. Evolution– process by which modern organisms have descended from ancient organisms due to natural selection.

41. D 40. Explain how the processes of genetic mutation and natural selection are related to the evolution of species.Darwin’s Finches

42. D 41. Explain how the current theory of evolution provides a scientific explanation for fossil records of ancient life forms. Fossilsare the preserved parts or the impressions of parts of ancient organisms. • Scientists have found that rocks of different ages preserved different combinations of fossils and these combinations succeeded one another in a regular order. • Simpler fossils are found in the lower (older)rock layers. • Complex fossils are found in the upper(more modern) rock layers. Fossil Record – shows how species have changed over time and provides a history of life on Earth. • Two classes of traits used in studying fossils • Derived traits: newly evolved features found only in recent parts of a lineage. • Ancestral traits: characteristics found only in more ancient forms. • Over 95% of all species that once existed are now extinct. (Cockroach and the horseshoe crab still exist and originated before the dinosaurs). Evolutionary History of a Species • Determined by knowing the ages of fossils and observing the appearance and disappearance of certain traits.

43. D 41. Explain how the current theory of evolution provides a scientific explanation for fossil records of ancient life forms.Cladogram – Diagram showing the evolutionary relationships among groups using derived traits.

44. D 42. Describe how structural and behavioral adaptations increase the chances for organism to survive in their environments. Adaptation is an inherited trait or characteristic that allows a species to better survive in its environment. • Structural adaptations are changes in the anatomy of a species that increase its chances of reproducing. • Development of wings and the ability to fly . This allowed birds rapid means of fleeing predators, searching for food and migrating to various climates. • Ability of cacti and camels to store water allows them to live in areas with little water. • Behavioral adaptations are genetic (instinct) or learned traits and are an animal’s way of responding to a stimulus (a change in the environment that has a direct effect on that animal). • Opossum “plays dead” when cornered by an enemy, hoping it will be ignored by the predator. • Snakes and lizards (cold blooded animals) lie in the sun or on a dark colored rock to keep warm. • Penguins group in a circle to protect their young and keep them warm. • Many birds have specific calls or songs to attract a mate, mark a territory or call alarm.

45. D43. Describe the factors that affect the carrying capacity of the environment. Carrying Capacity - largest number of individuals that a specific environment can support. Limiting Factor – something that causes population growth to decrease. • Density dependent limiting factors are factors that occur when a population becomes too large and dense. • Competition for food, water, space, sunlight • Birds competing for nesting sites • Predation due to predator - prey relationships • Sea urchins (prey) for sea otters (predator) – When there is a large number of prey, predator population increases. As prey population declines, little or no food for predator and its population decreases. • Similar situations for sea otters (prey) and killer whales (predator); rabbits (prey) and coyotes(predator). • Parasitism and Disease • Larval (caterpillar) sphinx moth attacked by a parasitic wasp. Wasp inserts its eggs under the caterpillar’s skin. After hatching, the wasp larvae feed on the insides of the caterpillar –eventually killing it.

46. D43. Describe the factors that affect the carrying capacity of the environment. Predator-Prey Graph Wolf and Moose Populations on Isle Royale

47. D43. Describe the factors that affect the carrying capacity of the environment. • Density independent limiting factors – factors that affect all populations regardless of population size. • Human Activities • Damming rivers and clear-cutting forests • Unusual weather, natural disasters, seasonal cycles • Drought, hurricanes, tornadoes, severe winters

48. D 44. Explain how change in population density is affected by emigration, immigration, birthrate and death rate and relate these factors to the exponential growth of human populations. Population density is the number of people residing in a square mile. (It is a measure of how close together people are living in a specific area). • Population density will increase or decrease depending on how many people are added to it or removed from it. • Emigration is the movement of people away from an area, decreasing the population density. • Immigration is the movement of people into an area, increasing the population density. • Birth rate is the number of live births per 1,000 of the population per year. This is affected by the number of children each woman has and her age when she begins to have them. • Death rate the number of deaths per 1,000 of the population per year. • If the death rate is greater than the birth rate, then population density decreases. If the death rate is less than the birth rate, then the population density will increase.

49. D 44. Explain how change in population density is affected by emigration, immigration, birthrate and death rate and relate these factors to the exponential growth of human populations. Demographics is the study of human populations. • Prior to 1500 AD, the human population remained fairly constant with a high birth rate and high death rate. Limiting factors kept populations low – food was scarce, diseases rampant and lack of shelter. • After 1500 AD, the human population began growing. Agriculture and industry made life easier and safer. Improved sanitation, medicine and healthcare reduced the death rate and increased longevity. Birth rates remained high. • With advances in medicine and agriculture, human population experienced exponential growth. • Today, human population continues to grow exponentially. • Medical advancements, energy use, technology and continued improvement in nutrition have increased survival rates . These factors explain most of the recent human population explosion. • People live much longer today than they did just several decades ago.

50. D 44. Explain how change in population density is affected by emigration, immigration, birthrate and death rate and relate these factors to the exponential growth of human populations.