Science 20 - Unit D Living Systems

Transcription

1 Science 20 - Unit D Living Systems Chapter 1 - The biosphere of Life an ecosystem is an area of land or water that includes all the organisms living in the area all the non-living factors affecting those organisms (e.g. water supply most ecosystems are considered to be open systems an open system is one where there is both an exchange of energy and of matter with the surroundings abiotic factors physical, non-living parts of the environment e.g. soil ph, temperature human effect on abiotic factors use of fertilizers to improve soil nutrients pollution of water supply in some cases, this makes the water less suited for aquatic life in other cases, this makes the water too suited for aquatic life harmful algal bloom - depletes the supply of oxygen and nutrients in the water for other organisms reduction of water supply biotic factors living organisms in the environment e.g. interspecies competition, presence of soil micro-organisms human effect on biotic factors hunting use of insecticides & herbicides deforestation displacement and domestication of animals habitat the particular area where an organism grows and thrives an organism s ideal habitat is one with the combination of biotic and abiotic factors that best meets its needs Water: uses internal transport makes up most of our blood main ingredient in tree sap (phloem) solvent - dissolves all ionic compounds and some molecular compounds photosynthesis - required for a plant to convert sun energy into chemical energy nutrient - needed by our bodies and other living organisms to stay hydrated habitat - provides a habitat for aquatic animals shelter - some animals live use snow and ice for shelter weather & climate results in clouds, rain, snow, fog determines if an area will have temperate climate or more variation ecology: the study of the interactions of living organisms with each other and with the physical environment the study of biotic and abiotic factors in an ecosystem a population refers to all of the individuals of the same species living in the same place at the same time a community includes all the species that occupy a given area at a certain time a study of a community only includes the study of living organisms

2 Biomass the mass of all the living organisms occupying a habitat includes all plants and animals living above ground root systems of plants bacteria in the air and soil any animals, insects or plant life living underground or underwater Interactions in biological communities interspecific interactions interspecific interactions occur between members of two different species three types: predator-prey relationships one benefits, one is harmed One organism kills and feeds on another organism The organism doing the killing is the predator The organism being killed is the prey predator and prey populations tend to go in cycles as prey populations increase, the number of predators increases shortly thereafter, and vice versa as prey evolve, predators must evolve with them, or risk losing a food source interspecific competition both are harmed Interspecies competition occurs when members of two different species compete both species must rely on the same resources there must be limited access to resources symbiotic relationships one benefits, the effect on the other varies close relationship between individuals of different species that live together there are three types of symbiotic relationships mutualism where both partners benefit from the relationship example: the relationship between the flowering plants and their pollinators when pollination is carried out by bees, the bees benefit by getting nectar the plant benefits by getting its pollen dispersed to other plants commensalism when one partner benefits, and the other is unaffected example: the clownfish lives in a type of coral called an anemone normally the anemone stings predators and digests it with enzymes it secretes from its tentacles the clownfish is immune to the anemone s sting because of a special mucus secreted by its skin the clownfish benefits from having the protection of the anemone, but the anemone is largely unaffected by the clownfish parasitism one partner benefits at the expense of the other the partner who benefits is called the parasite, while its victim is referred to as the host they will never completely wipe out a population, because that would also cause the parasite to become extinct parasites include all viruses, and some worms, bacteria, and insects less developed areas are more susceptible due to contaminated drinking water, lower standard of living, and poorer nutrition intraspecific interactions intraspecific interactions occur between members of the same species e.g. intraspecific competition (e.g. for mating partners)

3 Roles of organisms in an ecosystem Producers organisms using light energy to synthesis sugars through photosynthesis produce organic compounds that will serve as food for other organisms rely on sunlight, water and nutrients from the soil and air Consumers organisms that rely upon producers as a source of food primary consumers (herbivores) rely directly on producers for food only eat green plants, algae or plankton secondary consumers - feed on primary consumers tertiary consumers - feed on secondary consumers carnivores - organisms that kill and eat other animals omnivores - will feed on both plants and animals depending on availability and opportunity scavengers - an animal that feeds on dead and decaying animals it did not kill itself decomposers organisms that break down decaying organic matter into simpler molecules return organic material into inorganic nutrients in the soil play a critical role in the cyclic nature of the ecosystem Energy flow in an ecosystem First Law of Thermodynamics energy can be changed from one form to another, but it cannot be created or destroyed. in order for an ecosystem to persist energy must flow from one form to another energy flows into an ecosystem in the form of solar energy most energy flows out of an ecosystem in the form of heat energy storage after the sun s energy is converted by photosynthesis, the energy is stored in chemical bonds sugars, starches, fats and proteins are complex organic compounds that store energy in their chemical bonds when an organism digests its food, it breaks these bonds and releases usable energy Energy pyramid an energy pyramid divides up all the species in an ecosystem based on their energy source each step in the energy pathway corresponds to a level on the pyramid called a trophic level energy conversions are never very efficient moving from one level to another results in most of the energy being lost as waste only about 10% of the energy available to one level is passed on to the next level the rest of the energy (90%) isn t destroyed it is lost to the environment as heat each trophic level requires a greater volume of food to obtain the necessary energy A biomass pyramid compares the dry mass of all organisms for each level A pyramid of numbers compares the number of individuals in each trophic level Other graphic organizers Food chains show the flow of energy from producer through to all levels of consumers Food webs give a more detailed account of the interactions between species food webs are made of several food chains that overlap or interconnect

4 Flow of energy vs. flow of matter Energy flows into an ecosystem from the sun escapes from the ecosystem in the form of heat survival of an ecosystem depends on a continual input of new energy from the sun Matter (elements & compounds) also moves through the trophic levels of an ecosystem however, matter can move in either direction - matter is recycled. hydrologic cycle (water cycle) the movement of water through an ecosystem the most influential non-living component of an ecosystem processes that add water to the atmosphere - increases the humidity evaporation cellular respiration transpiration processes that use water from the atmosphere condensation (cloud formation) photosynthesis Impacts on the water cycle wildfires - the total amount of water in that ecosystem is reduced through industry, humans remove fresh water from the environment and return polluted, lower quality water back deforestation (clear-cutting) has a similar impact to a wildfire biogeochemical cycles the movement of elements and compounds between living and non living components Carbon cycle all life on Earth has carbon as its building blocks producers taken in CO 2(g) for photosynthesis all living organisms return CO 2(g) to the atmosphere by cellular respiration carbon is stored in various reservoirs such as fossil fuels, animal fossils, calcium carbonate in the oceans carbon sink a system that removes carbon dioxide from the atmosphere (e.g. photosynthesis) carbon source a system that adds carbon dioxide to the atmosphere (e.g. combustion of fossil fuels) human impact on the carbon cycle burning fossil fuels increases atmospheric carbon dioxide carbon was previously trapped in the Earth in the form of fossil fuels increase in atmospheric CO 2 is a cause of global warming and has resulted in climate change deforestation reduces trees that could be absorbing carbon dioxide from the atmosphere Oxygen cycle the oxygen cycle is essentially the reverse of the carbon cycle processes that produce carbon dioxide take in oxygen combustion cellular respiration processes that take in carbon dioxide release oxygen photosynthesis Human impact on the oxygen cycle ozone layer about 10km above the Earth s surface is a layer of oxygen called ozone (O 3(g)) when pollutants like CFCs are released into the atmosphere, they react with the oxygen in ozone this makes the ozone layer thinner and less able to filter the sun s UV radiation wildfires not only takes in oxygen as it burns also removes oxygen-producing vegetation

5 Nitrogen cycle nitrogen is a critical element in biological structures because it forms the basis for both protein and DNA the atmosphere is composed of 78% nitrogen (N 2(g)) because of its triple bond, nitrogen molecules are very stable and hard to break apart plants cannot get usable nitrogen from the atmosphere because it takes too much energy Nitrogen fixation the process of bacteria converting nitrogen gas into ammonia Nitrification convert the ammonia into nitrate and nitrite ions that are usable for the plant this step is done by nitrifying bacteria Denitrification requires a third type of bacteria, denitrifying bacteria, convert excess nitrates back into atmospheric nitrogen gas Natural impacts on the nitrogen cycle Lightning - converts nitrogen gas into nitrates Wildfires break down complex nitrogen compounds into smaller compounds like nitrates and ammonia a wildfire has the same effect as nitrogen fixation the heat from a fire makes the soil more livable for nitrogen fixing bacteria plants that thrive in soils with a high nitrogen content are the first to grow back after a wildfire Human impact on nitrogen cycle fertilizers the main ingredient in most fertilizers is nitrogen over-reliance on fertilizers can pollute water sources industry some emissions from smokestacks and car exhaust also produce nitrogen compounds Humans have an effect on an ecosystem by habitat fragmentation breaking a continuous habitat into smaller, separate habitats fragmentation can occur by roads, natural gas pipelines, power lines and clear cutting impact of habitat fragmentation interspecific relationships are affected because the two species may be physically isolated cleared areas may help support one species, which causes a shift in the balance in the ecosystem habitat destruction the permanent alteration of a habitat clear-cutting is the most significant example of habitat destruction when a habitat is destroyed, a large number of species are affected habitat destruction is the leading cause of species endangerment and extinction species at risk categories from likely to become threatened in the future to already wiped out worldwide Vulnerable - species likely to become threatened in the future Threatened - species likely to become endangered if the factors aren t reversed Endangered - species is threatened by imminent extinction throughout the area Extirpated - species no longer exists in the area, but still exists elsewhere Extinct - species no longer exists anywhere mass extinction have only occurred 5 or 6 times in Earth s history (600 million years) have previously been due to natural phenomena such as meteors colliding with Earth now due to human activity loss of biodiversity the variety of ecosystems, species, and genetic diversity in an area typically, an ecosystem with more species and genetic diversity is better able to adapt to change as species become extinct, or genetically limited, the entire ecosystem is affected introduction of an invasive species a new species is introduced into an ecosystem; the species thrives, and expands in population species takes over and threatens the area s biodiversity could be unintentional (e.g. organisms stow away on a ship container) could be intentional

6 attempt to expand biodiversity (e.g. give a region new food options) biological control - governments introduce new species to try to control other damaging species Economy vs. Ecology Though as humans we rely on both systems to maintain our quality of life, the goals of the two systems are often in opposition in terms of: Timeframe, use of the physical environment and in how they measure success Chapter 2 - Changing Populations Primary Succession: the process of changing - in successive stages - an environment from an area of bare rock and few species to a complex community It starts with a pioneer species usually a simple, hardy plant that will invade a barren ground (often include fern, lichen, moss, bacteria) the pioneer species pave the way for future life by changing the original habitat bacteria and lichen produce acid which breaks down the rock when these beginning species die and decay their remains add to the formation of humus humus is the organic component of soil Succession Continues once there is a humus-rich soil, grasses can begin to grow. grass roots grow into small cracks eroding away at the rock it produces shade and so mosses and lichen die off climax Community: the stable community that results from the process of succession Aquatic succession Water first collects in a basin from rain fall, but this water is poor in nutrients algae begin to colonize the water, which provides food for frogs, insects, salamanders, etc., which will then lay their eggs in the water Fish eggs and plant seeds may be carried to the water by birds Sediment will be carried to the dugout by the streams/rivers that fill it, and this sediment will collect at the bottom forming an aquatic soil, for plants to grow in. Cattails and reeds may begin to flourish around the outer edges of the aquatic ecosystem. As there is increased vegetation around the aquatic ecosystem, a terrestrial ecosystem begins to develop. Secondary Succession The Destruction Often times an ecosystem can be destroyed by natural causes such as severe storms, tornado s, or even fires When a fire occurs, it may destroy the ecosystem, but the soil that had developed during primary succession will remain. With the remaining soil, and very few organisms left to survive, an ecosystem must develop again. the process is much faster then primary succession, as humus rich soil already exists secondary succession will lead to the climax community much faster then primary succession Human impact on succession: we now realize that forest fires are an important part of ecosystem protection and renewal. forest harvesting logging companies are required by law to practice reforestation programs, where they must replant a certain number of trees ecologists argue that this interferes with the naturally occurring secondary succession. sustainable development is development that meets the needs of the present without compromising the needs of the future Overgrowth in Human Populations problems will occur such as overcrowding, outbreaks in disease, water, food and housing shortages and pollution and waste accumulation these effects can result in the collapse of an entire civilization

7 Exponential Growth Bacteria are single-celled organisms that reproduce by splitting in two, and a population that grows exponentially this means that it continues to grow at a faster and faster rate the doubling time is the amount of time it takes for a population to double in size growth will continue until a limiting factor slows or stops the population s expansion, e.g. scarcity of resources, predators, disease exponential curves When exponential growth is graphed, the shape of the line is like the letter J (J-curves) species that are able to grow exponentially: have short life spans reproduce often produce numerous offspring do little to care for young only occurs in some organisms, and only under ideal conditions - most often in micro-organisms (e.g. bacteria), small animals (e.g. insects), certain plants (e.g. weeds) Factors that increase population size births immigration (movement into the population) Factors that decrease population size deaths emigration (movement out of the population) If all four of these factors can occur in a population, it is an open population If artificial conditions prevent immigration and emigration, the population is said to be closed Population Explosions & Crashes a population explosion is a sudden exponential growth in a population most ecosystems cannot tolerate exponential population growth for very long a population crash is a rapid drop in population size due to limiting factors Carrying capacity While some populations will alternate between explosions and crashes, most will find an equilibrium the carrying capacity of a population is the maximum number of individuals that can be sustained in an ecosystem the curve for a population that is being limited by its carrying capacity is called an S-curve Thomas Malthus was a scientist working in the late 1700s he wrote an essay warning of the dangers of exponential growth in human populations he noted that the supporting resources (e.g. food supply) were not growing at the same rate human population growth for most of its history, the human population has been stable or grown very slowly explosive growth of the human population is linked with advancements in medicine and science human population is not currently growing in a sustainable way If we continue at this rate of growth, scientists estimate we will see the 9-billion mark in the next 40 years

8 why do snails make a good study in adaptation? slow moving, common to find the remains of hundreds of generations of snails in one small area they adapt readily to changing environments, why they have been around for 500 million years Fossil Record Biologists will study the morphology of a species to observe how adaptations have occurred to a species Morphology is the detailed shape and form on an animal Thousands of generations can be studied by looking at the fossil record of the species The fossil record provides a record of all life on earth throughout history Changes in Populations Some changes to a species are slight changes that occur gradually. This is called gradualism Sudden and major changes to the morphology of a species that occur more rapidly are called punctuated equilibrium Genetics Changes in physical characteristics of animals represent a change in their genetic code. A genetic change in one individual is passed on to its offspring Subtle changes in genetics account for variation within a species Major changes in genetics lead to the development of a whole new species Genes (the basic unit of inheritance) are sets of instructions encoded in the DNA molecule Each cell in an organism has two sets of genes - one from each parent. This causes the offspring to have a mix of traits, leading to variation within a species Variation is a difference in the frequency of genes and traits among individual organisms within a population Mutations can sometimes lead to beneficial traits, that will aid in the organisms survival. Adaptations are any structural trait or behavioral trait that improves an organism s change of success at surviving and reproducing in a particular environment Charles Darwin In 1831, naturalist Charles Darwin voyaged around the world, studying and observing a huge variety of organisms, recording the enormous variety and adaptations He arrived at the Galapagos Islands (off the coast of South America), and found that in each distinct region of the islands, there were distinct climactic conditions Finches were found covering the entire set of islands, but in each region, the finches had distinct variations. The finches in each region appeared to have very different beaks, each adapted to the food types available in that region The finches best suited to consume available food would survive and breed, passing on genetic traits the lead to many difference finch species after several generations From his observations, Darwin deduced his Theory of Evolution the nature of a population gradually changes form over time Darwin believed evolution was driven by Natural Selection, based on three key observations Observation 1: Organisms usually produce more offspring than can survive Observation 2: There is variation among individuals with respect to any trait in a population Observation 3: Organisms within a population compete for limited resources also known as survival of the fittest, natural selection presumes two things: there is a genetic basis for variation of traits rates of survival differ with each trait Jean-Baptiste Lamark offered the idea that species change due to the environment, or due to some desire to change He proposed that giraffe s had long necks because they stretched their necks as far as possible to reach more vegetation. Offspring would therefore have longer necks Today we understand that changes only occur due to genetic variations, and not because of desire or environmental factors Inheritance of acquired characteristics Lamarckism Lamarck postulated that features acquired during the lifetime of an individual can be passed on to future generations

9 Evidence of evolution homologous structures similar structures with similar functions in different species (e.g. human hand, bat wing) vestigial structures structures present in a species with no discernible function, leftover from previous ancestor e.g. The human tailbone (coccyx) - thought to be remnants of a human tail