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CMT SCIENCE REVIEW Sage Park Middle School C1. Describe the properties of common elements, such as oxygen, hydrogen, carbon, iron and aluminum. Matter is anything that has both volume and mass. Everything is made up of matter. An element is matter consisting of only one kind of atom. The type of element is determined by the number of protons. Protons are positively charged particles found in the nucleus of an atom. Electrons are very small, negatively charged particles that travel around in space outside the nucleus. In an element, the number of protons is equal to the number of electrons. It is the number and the arrangement of the electrons that determines the chemical and physical properties of the element. The third kind of particle in an atom is the neutron. Neutrons have no charge (they are neutral) and only change the mass of the atom. They do not change the kind of element nor its chemical and physical properties. The periodic table is used to organize the elements by their physical and chemical properties and by the number of protons in each element. The number of protons in each element (the atomic number) is equal to the whole number in the box for each element. The number of protons is equal to the Windsor Public Schools Windsor, CT 06095 January 2008 Page 1 of 53 CMT SCIENCE REVIEW Sage Park Middle School number of electrons in the atom. The number of neutrons can be found by subtracting the number of protons from the mass of the atom (not shown in the above chart). Protons and neutrons have relative masses of one (1). Electrons are so small that they have very, very little mass and really do not contribute to the mass of the atom. Each element, and every other kind of matter, has characteristic properties that are specific to that element or kind of matter. These include density, melting and boiling points, solubility, electric conductivity, magnetic attraction among others. Hydrogen (symbol H) is the first element, is a non-metal with one proton and one electron. The mass of a hydrogen atom is 1 so there are no neutrons in hydrogen. Atomic mass - #protons = #neutrons 1 – 1 proton = 0 neutrons Hydrogen is a gas, which is lighter than air and is extremely flammable. It combines explosively with oxygen and burns, giving off a great amount of energy. This energy is used in the rocket motors of the space shuttle. 2H2 + O2 Î 2H2O + Energy In nature, hydrogen exists as a diatomic molecule (two or more atoms bonded together) with the formula H2. Note that oxygen is also a diatomic molecule. Carbon (C) is element number six is a non-metal with a mass of 12. Each atom of carbon has six protons, six electrons and six neutrons. In nature, pure carbon can be found in a variety of different forms: diamonds, which are clear and extremely hard, soot which is soft and black and formed when wood or gasoline is incompletely burned, and graphite which is soft and is the black in pencil lead. Carbon is essential for all life and everything that is living or was living contains carbon. Carbon can form as many as four bonds with other atoms including other carbon atoms to form long chains or rings. Carbon forms the basis of petroleum products (gasoline, oil, waxes, etc.), all plastics and carbon dioxide which increases global warming and which plants use to make food. Oxygen (O) is element number eight with a mass of sixteen. Each oxygen atom contains eight protons, eight neutrons and eight electrons. Oxygen is a clear, odorless, diatomic (two atoms bonded together) non-metallic gas. It is the most Windsor Public Schools Windsor, CT 06095 January 2008 Page 2 of 53 CMT SCIENCE REVIEW Sage Park Middle School common element (46.6%) on the Earth’s surface and is essential for all animal life. The air in the atmosphere is approximately 21% oxygen. Plants give off oxygen in photosynthesis. Oxygen is also necessary for combustion (burning). When carbon burns, it combines with oxygen gas to form carbon dioxide. C + O2 Î CO2 Aluminum (Al) is the most abundant metal on the Earth’s surface (8.13%). It has an atomic number of thirteen and a mass of twenty-seven. This means that it has thirteen protons, thirteen electrons and fourteen neutrons. Aluminum is a silvery, non-magnetic, lightweight, yet strong metal and is used in construction, toys (aluminum frames for bicycles) and containers (soda cans). Like all metals, aluminum is a conductor of electricity. Note that the aluminum atom has three electrons in its outer ring (shell). The electrons in the outermost shell of any atom are called valence electrons and it is these electrons that determine the chemical properties of the atom. The three electrons mean that aluminum can form three bonds with other atoms. Iron (Fe) derives its chemical symbol from the Latin name for iron, ferrum. Its atomic number is 26 and it has a mass of 56 meaning that an iron atom has 26 protons, 26 electrons and 30 neutrons. It is the second most abundant metal on the Earth’s surface and the most abundant metal if the Earth’s core in included. Iron is a shiny, silvery colored solid that is easily molded into different shapes. It is a magnetic and a good conductor of electricity. It can be mixed with carbon to form steel. Iron is found in most construction and machinery and also in blood. Iron oxidizes (combines with oxygen) to form the common chemical rust. Windsor Public Schools Windsor, CT 06095 January 2008 Page 3 of 53 CMT SCIENCE REVIEW Sage Park Middle School C2. Describe how the properties of simple compounds, such as water and table salt, are different from the properties of the elements of which they are made. Atoms of different elements can combine to form a compound. A compound is a substance that is made up of two or more elements. When different atoms combine, the resulting compound can have very different chemical and physical properties from the original atoms. In a chemical reaction, the atoms rearrange themselves to form a new substance. However, since no atoms are created or destroyed, the mass is the same at the beginning and the end of the reaction. An atom of sodium can combine with an atom of chlorine to form the compound sodium chloride, table salt. Sodium (Na, from the Latin name natrium) is a soft, yellowish gray metal that reacts violently with water. Chlorine (Cl) is a yellowishgreen diatomic gas that is highly poisonous. Together they form sodium chloride (NaCl) that is a colorless to white crystal that is necessary for life. Hydrogen and oxygen are both colorless and odorless diatomic gases. However, when two atoms of hydrogen combine with one atom of oxygen they form water (H2O) that is a liquid at room temperature. Elements can react to form compounds that contain different amounts or ratios of the individual elements. For example, carbon (C) and oxygen (O) can form either carbon dioxide (CO2) or carbon monoxide (CO). Hydrogen (H) and oxygen (O) can form water (H2O) or hydrogen peroxide (H2O2) and carbon and hydrogen can for methane (natural gas, CH4) or octane (gasoline, C8H18). Windsor Public Schools Windsor, CT 06095 January 2008 Page 4 of 53 CMT SCIENCE REVIEW Sage Park Middle School C3. Explain how mixtures can be separated by using the properties of the substances from which they are made, such as particle size, density, solubility and boiling point. A mixture is a combination of two or more substances that have not combined chemically such as chocolate chips in ice cream. A solution is a mixture that looks the same everywhere. An example of a solution is table salt dissolved in water. All mixtures can be separated into their individual parts using one or more techniques based on their physical properties. Particles can be separated by their size. A window screen allows air (very small particles) to pass through but keeps the bugs (large particles) out. A sieve or strainer can be used to separate larger objects from smaller ones. The same technique can be used on an atomic level. A semipermeable membrane will allow small compounds to pass through while larger compounds cannot. Iron can be separated from a mixture because it is attracted to a magnet. Density (measured in g/cm3) can be determined by dividing the mass in grams by the volume in cubic centimeters. Density can also be used to separate substances. If a mixture of sawdust and sand is placed in water, the less dense sawdust will float on top and the denser sand will sink. A strainer can be used to collect the sawdust and the water can be carefully poured off the sand. In an oil and vinegar salad dressing the less dense oil will float on top of the more dense water. Even after extensive shaking these two layers will reform and the oil could be siphoned from the top or the water drained from the bottom. In a solution, one or more substances are dissolved in another. The substance that is dissolved is called the solute, and the substance it is dissolved into is called the solvent. The amount (grams) of solute that is dissolved in a specific volume of solvent is the solubility. The more grams of solute that can be dissolved, the higher the solubility. Soluble and non-soluble (more commonly called insoluble) substances can easily be separated by filtering or filtration. This is because the insoluble particles tend to clump together forming larger sized particles while those remaining in solution remain separated and are much smaller. A teabag or coffee filter is good example. Here the paper in the bag or the filter has very small holes that allow the dissolved substances to pass through while the much larger tealeaves or coffee grounds cannot. A mixture of sugar and sand can be separated in the same manner. Water is added to the mixture until all of the sugar dissolves and then filtered. The insoluble sand remains in the filter while the sugar can be recovered by evaporating off the water. Solubility is not limited to solids and liquids. Gases can also dissolve in water to form solutions. Soda is a solution of carbon dioxide (CO2) in sugar water with a little added flavor. When the cold bottle of soda is opened, the carbon dioxide, which has been dissolved under pressure, begins to come out of solution in the form of little bubbles (carbonation). As the soda warms up, more and more of Windsor Public Schools Windsor, CT 06095 January 2008 Page 5 of 53 CMT SCIENCE REVIEW Sage Park Middle School these bubbles form and are separated from the liquid until the soda goes totally flat. This is because the solubility of all gases decreases as the temperature goes up. On the other hand, the solubility of solids in liquids usually increases as the temperature goes up. The boiling point of a substance is the temperature at which the liquid turns into a gas. For water this is 100oC. A solution of two liquids, say rubbing alcohol (isopropanol) and water can be separated by the differences in their boiling points in a process called distillation. A mixture of water and isopropanol (boiling point 80oC) is carefully heated. When the temperature of the solution reaches 80oC, the isopropanol begins to boil but the water does not. All of the isopropanol will boil off before the temperature again increases. The vapors can be condensed (turned back into liquid) recovering pure isopropanol while pure water remains in the heating vessel. The boiling point (going from a liquid to a gas) of a substance is the same temperature as the condensation point (going from a gas to a liquid). Air is a solution of two gases, oxygen and nitrogen, that can be separated by their relative boiling/condensation points. If a sample of air is cooled to a very low temperature, liquid oxygen will form (condensation point –183oC) leaving gaseous nitrogen (condensation point –196oC). Windsor Public Schools Windsor, CT 06095 January 2008 Page 6 of 53 CMT SCIENCE REVIEW Sage Park Middle School C4. Describe how abiotic factors, such as temperature, water and sunlight, affect the ability of plants to create their own food through photosynthesis. Temperature, water and sunlight are abiotic factors, meaning that they are not alive (a means not and biotic means living). However, all three are necessary for plants to live and grow. Plants make their own food in the process of photosynthesis. In photosynthesis (photo means light and synthesis means to make) plants take carbon dioxide from the air and water from the ground and use the energy in sunlight to produce glucose (a sugar) and give off oxygen gas. CO2 + H2O + sunlight energy Î C6H12O6 (glucose) + O2 During photosynthesis, the pigment chlorophyll absorbs the sunlight and energy in the sunlight is converted to chemical energy in the glucose, which the plant uses for food. Chlorophyll is also the chemical that gives plants their green color. The oxygen produced is used by animals and combines with food (mostly sugars) to produce energy, water and carbon dioxide in respiration. Note that respiration is the reverse of photosynthesis. C6H12O6 + O2 Î CO2 + H2O + energy The plant’s roots absorb water from the ground and carry nutrients into the plant that are needed for growth. Without these nutrients and the water needed in photosynthesis, the plant will die. Water comprises some of the mass of the growing plant, but most of the mass of a plant comes originally from the carbon dioxide in the air. All chemical reactions go faster with an increase in heat or higher temperature. In photosynthesis, the higher the temperature, the faster the reaction will proceed, the more glucose is produced for food and the faster the plant will grow. At low temperatures the production of glucose can be very slow, and in extremely cold conditions, the water in the plant can freeze destroying the plant cells and the plant will die. In temperate or cooler climates a drop in temperature stops photosynthesis causing the leaves to change color and drop off in preparation for winter. Windsor Public Schools Windsor, CT 06095 January 2008 Page 7 of 53 CMT SCIENCE REVIEW Sage Park Middle School C5. Explain how populations are affected by predator-prey relationships. The plants and animals that live together in the same environment are called a community. In any community there are various animals that eat other animals (carnivores, meat eaters). The animals that eat other animals are also called predators and the animals they eat are called prey. In a balanced community, the number of prey eaten by the predators will be the same as the number of prey that are born in the same time period. Thus, the number of predators and prey remains the same. If the number of prey eaten is greater than the birthrate, then there is less food for the predators and they will starve and/or go to another community where there is more food available. If the prey’s birthrate is greater than the number of prey needed for food, then their population will increase and their number could overrun the community. In that case, either more predators will enter the community and/or the birthrate/survival rate of the predators will increase bring the relative numbers of predators and prey back into balance. Windsor Public Schools Windsor, CT 06095 January 2008 Page 8 of 53 CMT SCIENCE REVIEW Sage Park Middle School C6. Describe common food webs in different Connecticut ecosystems. Terrestrial Food Web A food chain shows the order of what eats what. In more scientific terms, it traces the energy pathway from one organism to another. All food chains begin with a producer. A producer is always some kind of plant as plants are the only organisms that can make their own food (see C4). In the above chart, the oak and the pine trees are producers. Any creature that directly eats a producer is called a primary consumer (mouse or insect). Consumers can eat different types of food. Herbivores are consumers that eat only plants; carnivores eat only meat; and omnivores eat both plants and meat. Anything that eats a primary consumer is a secondary consumer (bird, hawk, snake, salamander, etc.). Thus, one food chain in this chart could be: Sun light Î Oak acorn Î mouse Î hawk All food chains end with the death and the decomposition of the last consumer by bacteria and fungi (decomposers). The decomposers break down the organic matter and return nutrients to the environment to be used by other organisms. A Windsor Public Schools Windsor, CT 06095 January 2008 Page 9 of 53 CMT SCIENCE REVIEW Sage Park Middle School food web is a combination of many overlapping food chains in a specific ecosystem. Two more examples of food webs common to Connecticut are found in ponds/wetlands and marine areas. Pond Food Web Marine Food Wed Windsor Public Schools Windsor, CT 06095 January 2008 Page 10 of 53 CMT SCIENCE REVIEW Sage Park Middle School C7. Describe the effect of heating on the movement of molecules in solids, liquids and gases. All matter (anything having both mass and volume) can exist in three main phases or states: solid, liquid and gas. Phase or state of matter Solid Liquid Gas Physical Definition Keeps is own shape, does not fill container Takes shape of container, does not fill it completely Takes shape of container, fills it completely All matter is made up of atoms and molecules. All atoms and molecules attract each other and the greater the attraction the denser (closer) they become. All atoms and molecules are in constant motion and the greater the temperature, the more freely and faster they are moving. In a solid, the particles are packed tightly together and their attraction for each other is great enough to keep them rigidly in place. The only motion they can have is vibration. In a liquid, the particles have more energy. This energy is enough to overcome some of the attractions among the particles and they can move around each other and flow. This lack of rigidity allows a liquid to take the shape of a container. Lastly in a gas, the particles have enough energy to break all of the attractions among them and separate completely from each other. This total separation allows a gas to spread out and fill any shape or size container. Imagine a block of ice at –20oC that is slowly being heated at a constant rate. (The amount of heat absorbed during a given time is the same.) The temperature of the block of ice will gradually increase. This is because the more energy the particles have the more they can vibrate. Temperature is the measure of how much the particles are vibrating. So, the more heat is added, the more the Windsor Public Schools Windsor, CT 06095 January 2008 Page 11 of 53 CMT SCIENCE REVIEW Sage Park Middle School particles will vibrate, and the more they vibrate, the more the temperature goes up. This continues until the amount of vibration is great enough to break some of the attraction among the particles and ice will begin to melt. Melting is the change from a solid to a liquid, and the temperature at which this occurs is the melting point (for water this is 0oC). Even though more heat is added during the melting process, the temperature will remain constant and does not change. All of the added heat goes to overcome the attractions among the particles. When the block of ice has completely changed into liquid water, the added heat again goes to increasing the amount of vibrations and the temperature begins to rise again. The temperature continues to rise at a constant rate until the amount of vibrations is so great that the remaining attractions among the particles can be totally overcome and the particles separate completely. The liquid water turns into gaseous water (water vapor or steam). The process of going from a liquid to a gas is called vaporization. The temperature at which vaporization occurs is the boiling point (for water this is 100oC). For the same reasons mentioned above, the temperature remains constant until the liquid has been totally converted to gas. When a substance is changing phases the temperature is constant, and when the temperature is changing, the phase of the substance does not change. The reverse can also occur. The process of changing a gas into a liquid is called condensation and the temperature at which this occurs is the condensation point (for water it is 100oC). Note that the condensation point is always the same as the boiling point. Likewise, freezing is the process of turning a liquid into a solid and the freezing point (the temperature at which this happens) is always the same as the melting point. There is another type of phase change that can occur under special circumstances. Sublimation is the process of changing a solid directly into a gas. This occurs in a home freezer to keep it frost-free. Windsor Public Schools Windsor, CT 06095 January 2008 Page 12 of 53 CMT SCIENCE REVIEW Sage Park Middle School C8. Explain how local weather conditions are related to the temperature, pressure and water content of the atmosphere and the proximity to a large body of water. Weather is the condition of the atmosphere at a given place and time. There are four major factors, which govern the weather. They are: heat energy from the Sun, temperature, air pressure and water content in the atmosphere. Energy from the Sun is absorbed by the land and water on the Earth’s surface. Some of this is reflected and radiated into the lower atmosphere causing it to warm. The longer the sunlight hours the warmer the air becomes which is one reason why the air is warmer in the summer than in the winter. (See C29) Air pressure is a measure of the weight of a column of air pressing down on the Earth’s surface. The air pressure is measured with a barometer. Like most matter, air is affected by changes in temperature. When air cools it reduces in volume and becomes denser (high pressure). The denser the column of air, the higher the pressure. When air is heated, it expands and the pressure decreases (low pressure). The less dense a column of air, the lower the pressure. Large areas of air that have the same conditions are called air masses. When a high pressure air mass is next to a low pressure air mass, air flows from the high pressure area to the low pressure area causing wind. The greater the difference in the two air pressures the greater the force and speed of the wind. Humidity is the amount of water in the air. Water evaporates more easily when the temperature is higher. This is why warmer low pressure areas are more humid and why hot summer days can be very muggy and uncomfortable. Cold, high pressure areas contain very little water vapor and the air is very dry. The mass of a molecule of nitrogen or oxygen, the major components of the atmosphere, is greater than that of a molecule of water. So, when a molecule of water vapor displaces a molecule of nitrogen or oxygen in the air, the total mass of that air sample decreases and the air pressure goes down. Thus, the more humidity in the air, the lower the air pressure and the easier it is for more water to vaporize causing the humidity to increase even more. The location of an air mass also affects the humidity. In desert areas such as the Sahara or the southwest US, the air can get extremely hot but there is no water to evaporate so the humidity remains very low causing ‘dry-heat.’ Most land masses heat up very rapidly during the day and cool quickly during the night. Water on the other hand, heats up very slowly but it is also very slow to cool down. Proximity to a large body of water also keeps the climate (the average weather over an area during a long period of time) relatively moderate. This is because the water changes temperature only very slowly, whereas in very dry areas away from large bodies of water, temperature changes can vary drastically over very short periods of time. Windsor Public Schools Windsor, CT 06095 January 2008 Page 13 of 53 CMT SCIENCE REVIEW Sage Park Middle School C9. Explain how the uneven heating of the Earth’s surface causes winds. (Also see C8.) Some areas of air heat up faster than others. The greater the temperature of the air, the more it expands and the air pressure decreases. Likewise, the cooler the air, the more it contracts and becomes more dense, and the air pressure increases. Air flows from regions of high pressure to regions of low air pressure causing wind. The greater the differences in air pressure, the greater the speed and the force of the wind. For example, air masses coming out of northern Canada tend to be cold with high air pressure, while air masses coming to Connecticut from the south tend to be much warmer with low air pressure. When these two air masses collide, a wind is produced from the high to the low pressure area. Because of the differences in humidity in these air masses storms also can be produced. Winds can also be produced by the different rates of heating and cooling of land and water. During the day, for land near an ocean or a large body of water, the land heats up hotter and faster than the nearby water. The warm land heats the air above it causing the air to rise and the air pressure over the land decreases. The air pressure over the cooler water is now greater than the air pressure over the land. This difference in air pressures causes wind to blow from the water onto the land. This is called a sea breeze. At night, the land cools quickly and the air pressure over the land increases. Over the water, which cools much slower than the land, the air pressure is now less than that over the land. Wind now flows from the land over the water in what is called a land breeze. Windsor Public Schools Windsor, CT 06095 January 2008 Page 14 of 53 CMT SCIENCE REVIEW Sage Park Middle School C10. Explain the role of septic and sewage systems on the quality of surface and ground water. Every day millions of gallons of wastewater are produced in towns such as Windsor. Wastewater contains human waste, dirt, soap, bacteria and bits of food. What happens to it after it goes down the drain? The wastewater leaves the home, and in urban and suburban areas, it travels through a series of pipes which increase in size as they run under the streets and eventually carry the wastewater to a treatment plant where it is cleaned. First, there is a series of physical steps. The solid materials are allowed to settle and are removed. Any floating oil and scum is removed by skimming. The second stage of the cleaning process involves the use of both biological and chemical agents. Bacteria are used to break down any remaining particulate matter into very small pieces called sludge. The sludge is removed by filtration. This material can be recycled as fertilizer or it can be dried and burned for use as fuel in power plants. In the final step, chemicals, called disinfectants, are added to remove and destroy any remaining waste material. The clean water is then released into rivers or the public water supply. Windsor Public Schools Windsor, CT 06095 January 2008 Page 15 of 53 CMT SCIENCE REVIEW Sage Park Middle School In rural areas where the houses are far apart, most houses have their own source of water, a well, and a way of cleaning up the wastewater. A septic tank is a large concrete or steel tank that is buried in the ground. Wastewater from the house flows into the septic tank where the particulate matter sinks to the bottom as sludge. A harmless bacteria is sometimes added to the tank to help break down the solid material into tiny pieces. Additional wastewater displaces the water already in the tank where it runs through a pipe into the drain field, also called a leach field. This drain field consists of one or more perforated pipes, buried in gravel and sand, that allow the water to slowly run into ground. The water is continuously filtered by the soil until it reaches the groundwater. This water also supplies many nutrients to the plants living over the drain field. Over a few years, the sludge in the bottom fills the septic tank and it has to be removed. Windsor Public Schools Windsor, CT 06095 January 2008 Page 16 of 53 CMT SCIENCE REVIEW Sage Park Middle School C11. Explain how human activity may impact resources in Connecticut, such as ponds, rivers and the Long Island Sound ecosystems. An ecosystem is the collection of all living and nonliving things in a specific environment. Aquatic (water) ecosystems are extremely susceptible to damage from pollution. Most of the water pollution in Connecticut, and the rest of the world, is caused by man. As human populations grew more land was needed for houses and farming. Plants and trees that stabilized the soil were removed and sediments (rocks, sand and dirt) could be washed into rivers, lakes, ponds or the Sound (oceans). As these sediments settle to the bottom, where they block sunlight to plants and can destroy animal species that live on the bottom. Eventually, large amounts of sediment can clog and completely block rivers and streams. Fertilizers used in farming can also get washed into these ecosystems. The fertilizer can causes a rapid growth in algae that blocks sunlight to plants living on the bottom and use up all the dissolved oxygen in the water causing the animal species to die. The number of landfills (garbage dumps) is growing throughout the United States. Many toxic chemicals are released or produced in landfills which, if the landfill is not constructed properly, can seep into the ground water (large amounts of water under the Earth’s surface) eventually polluting the lakes, Sound, etc. Other hazardous chemicals are dumped directly into rivers and the Sound from factories, towns and mines. Oil spills from oil tankers pollute the water, the banks and the beaches as well as killing aquatic birds. Sewage (human waste, soap, small pieces of food, etc.) is often released into rivers and the Sound both by accident and intentionally. Water treatment plants are often too small to purify all the sewage they receive and the excess is diverted into the rivers. Flooding can cause a large increase of sewage getting into the water ecosystems. With this pollution also comes a rapid growth of harmful bacteria that can be dangerous for animals and humans alike. Many factories and especially nuclear power plants use water from rivers and the Sound for cooling. While this water is not polluted with chemicals it does contain thermal (heat) pollution. This heat raises the temperature of the rivers or the Sound. Plant and animal species that require colder water can no longer exist and are often replaced with species that normally live in much warmer or tropical climates. There is presently a proposal to lay a series of large electrical cables from Connecticut to New York. These cables would be buried deep under the water of Long Island Sound. The dredging would destroy many of the oyster and lobster beds off the coast. There is also some controversy about the effects of the magnetic field on wildlife that is produced from electric cables. Windsor Public Schools Windsor, CT 06095 January 2008 Page 17 of 53 CMT SCIENCE REVIEW Sage Park Middle School Man can also affect the ecosystem by either over or under hunting. Many years ago Connecticut had a wolf population that fed on deer and other animals. The wolves were killed or scared off and the deer population exploded. Fewer people now hunt and hunting areas are limited. Today deer can be found in suburban areas and occasionally in the cities eating gardens, creating traffic hazards and spreading disease. Too much killing of a certain species also can have drastic effects. Over-fishing of specific kinds of fish has decreased the breeding population to a point where abundant numbers may never again be achieved. This is the case of what has happening to cod and most types of shark. Windsor Public Schools Windsor, CT 06095 January 2008 Page 18 of 53 CMT SCIENCE REVIEW Sage Park Middle School C12. Explain the relationship among force, distance and work, and use the relationship (W = FxD) to calculate work done in lifting heavy objects. A force (F) can be defined as a push or a pull. Work (W) occurs when a force moves an object over a distance (D). These three things are mathematically related by the equation: W=FxD Work = Force times Distance To do the same amount of work there needs to be a large force over a short distance, or a smaller force over a greater distance. In the diagrams below, the D2 D1 height of each ramp is the same and it takes the same amount of work to push a box up each ramp. It is easier however, to push the box up the first ramp because it is less steep. However, the distance the box needs to be pushed is greater, D1>D2. The less force, the greater the distance over which that force must be exerted. Note: No actual calculations will be needed on the CMT. Windsor Public Schools Windsor, CT 06095 January 2008 Page 19 of 53 CMT SCIENCE REVIEW Sage Park Middle School C13. Explain how simple machines, such as inclined planes, pulleys and levers, are used to create mechanical advantage. A simple machine is an instrument or a device that makes work easier. It does this by using less force over a greater distance to move an object. In addition to changing the amount of force used, some simple machines change the direction of the applied force. An inclined plane is a ramp and is the only simple machine that does not move. The longer the ramp, the less steep and the easier it is to move an object. Less force is needed over a longer distance. (See C12.) A wedge is an inclined plane that moves. Here a force is exerted on the wide end of the wedge and is transferred to the sides causing an object to split or two adjacent objects to move apart. The narrower the wedge, the easier it is to use as the distance it moves, the length of the wedge, is much less than the distance the object moves, the width of the wedge. This is why a sharp knife cuts better than a dull one. A screw is an inclined plane wrapped around a cylinder or a circular ramp. As the screw (the lid) is turned through a large distance, the object (the jar) is pulled up the screw only a short ways. A wheel and axle has a shaft, the axle, at right angles to the center of a wheel. A force applied to the wheel gets transferred to the axle and increased. In a doorknob, the force or effort is applied to the knob through a large distance. The force is magnified and changes direction as it is transferred to the bolt. In a bicycle wheel a force is applied to the axle by the pedals. The force is transferred Windsor Public Schools Windsor, CT 06095 January 2008 Page 20 of 53 CMT SCIENCE REVIEW Sage Park Middle School to the outside of the wheel causing it to go around faster and increasing the distance it moves. A lever consists of a stiff bar, a pivot (formally called a fulcrum), a weight or load and an applied force or effort. There are three kinds or classes of levers that differ only in the relative placements of these four things. The force is decreased as the fulcrum is moved closer to the load. A pry bar or a seesaw is an example of a first class lever. If the fulcrum is closer to one end of the bar, a small effort moving a large distance can result in heavy object moving a short distance. A wheelbarrow is a second class lever allowing a person to move the handles a long distance and lifting a heavy object a short distance. One type of third class lever is a baseball bat. The hands and arms of the batter move a relatively short distance while the end of the bat moves a much greater distance. The last of the simple machines is the pulley. A pulley is a grooved wheel and an axle. A rope goes around the wheel and can lift objects when a force is exerted on the other end of the rope. Like the lever there are three major kinds of pulleys. A fixed or non-movable pulley has the load attached to one end of the rope while the other end is pulled down lifting the object upwards. The direction of the force is changed but the amount of force needed to raise the object remains the same. In a movable pulley, one end of the rope is held secure while the other end of the rope is pulled in the same direction as the object and the pulley moves along the length of the rope. Since the stationary end of the rope is supporting half the mass of the object, only half as much force is needed to lift the load. A block and tackle uses two or more pulleys in a single system. The more pulleys, the more rope is needed, but the force needed to lift the object is decreased as the length of rope used is increased. Windsor Public Schools Windsor, CT 06095 January 2008 Page 21 of 53 CMT SCIENCE REVIEW Sage Park Middle School Mechanical advantage is a measure of how effective a machine is. No machine is totally perfect. In machines, some force is converted to friction with the loss of energy to heat. Energy can also be lost by incomplete combustion of fuels in an engine. While machines make work easier, they also result in energy loss and the mechanical advantage is always less than 100% Windsor Public Schools Windsor, CT 06095 January 2008 Page 22 of 53 CMT SCIENCE REVIEW Sage Park Middle School C14. Describe how different types of stored (potential) energy can be used to make objects move. Kinetic energy is the energy in an object in motion. Potential energy is the stored energy in an object based on its position or shape. Each of these two types of energy can be converted (changed) into the other. A ball held at the top of a steep hill has potential energy due to the height of the hill and gravity. This energy is converted into kinetic energy when the ball is allowed to roll down the hill, reaching its maximum kinetic energy at the bottom of the hill. Likewise, it takes kinetic energy to stretch or compress a spring and this energy is stored in the spring as potential energy until the spring is released. Energy stored in chemical bonds (chemical energy) can be converted to kinetic energy in all animals and plants. Plants store energy in starch (sugar) while animals store their chemical energy in fat and glycogen (sugar). When needed, this stored energy can be converted, through a number of complicated steps, into kinetic energy and motion. Chemical energy stored in a battery can by converted into moving an object when the battery is allowed to transform its chemical energy into electrical energy to run a motor. Theoretically, when one form of energy is transformed into another form, the total amount of energy in the system is conserved, stays the same. In the real word this is not absolutely true. When the ball rolls down the hill, some of its energy is transformed into heat by friction and it lost. If this experiment is done in a skateboard half-pipe, the ball would not be able to reach its initial height without adding energy. Windsor Public Schools Windsor, CT 06095 January 2008 Page 23 of 53 CMT SCIENCE REVIEW Sage Park Middle School C15. Describe the basis structures of an animal cell, including nucleus, cytoplasm, mitochondria and cell membrane, and how they function to support life. Plant and animal cells have many similarities. Each is surrounded by a cell membrane that allows some materials to pass through but not others. The membrane is filled with a gel-like substance called cytoplasm. All cells contain membrane-enclosed structures called organelles. Located near the center of the cell is the nucleus that contains the genetic information to produce new cells and control the cell’s functions. Protecting the outside of the nucleus is the nuclear membrane and inside the nucleus is the nucleolus that produces ribosomes. Ribosomes are attached to the endoplasmic reticulum as well as scattered throughout the cytoplasm. Together they produce proteins, fats and other essential products for the cell. Vacuoles are liquid-filled storage vessels for food and waste products. Golgi bodies move the products formed in the endoplasmic reticulum around or out of the cell. Mitochondria, found throughout the cytoplasm, react oxygen with food to produce the cell’s energy. There are some major differences between plant and animal cells. Animal cells tend to be round or oblong while plant cells are more angled or rectangular. Plant cells also contain two structures what are not found in animal cells. The first is the cell wall that provides protection for the cell while giving it shape and support. The second are chloroplasts that contain chlorophyll to produce the cell’s food through photosynthesis. Windsor Public Schools Windsor, CT 06095 January 2008 Page 24 of 53 CMT SCIENCE REVIEW Sage Park Middle School C16. Describe the structures of the human digestive, respiratory and circulatory systems, and explain how they function to bring oxygen and nutrients to the cells and expel waste materials. The digestive system consists of many different interconnected organs. These include the mouth, the esophagus, the liver, the stomach, the large and small intestines, the gallbladder and the pancreas. As one eats, food is placed in the mouth and it is cut, torn or ground into smaller pieces; this is called mechanical digestion. As a person chews, saliva is released. Saliva contains an enzyme (a substance that speeds up a chemical reaction) that begins to break down the food into much smaller pieces in the process of chemical digestion. The saliva also makes it easier to swallow. The food then passes down the esophagus, a tube leading from the mouth to the stomach. Muscles in the esophagus squeeze the sides of the tube together pushing the food down in the process of peristalsis. In the stomach, both mechanical and chemical digestion occurs. Muscles in the stomach churn the food while acids and enzymes further break down the food by chemical digestion. The food then travels into the small intestine. Three organs aid the digestive process although the food never enters them. The acids and the enzymes in the stomach are made in the pancreas as is a chemical used to neutralize these acids before they pass into the small intestine. The liver makes a chemical to aid in the digestion of fats called bile that is stored in the gallbladder. Most digestion occurs in the small intestine. The lining of the small intestine is covered with finger-like structures called villi that greatly increase the surface area. The villi are full of blood vessels that can absorb nutrients into the blood stream. Not all of the food is digested. The remains pass through to the large intestine where the water is absorbed and solid waste is formed. This waste passes through the rectum and is excreted out the anus. Windsor Public Schools Windsor, CT 06095 January 2008 Page 25 of 53 CMT SCIENCE REVIEW Sage Park Middle School The respiratory system is responsible for bringing oxygen (air) into the body and expelling carbon dioxide (CO2) from the body into the air. To breathe, chest muscles contract and lift the rib cage up and outward. The diaphragm is a large muscle that pulls the bottom of the chest cavity lower. These two actions increase the volume of the chest cavity and cause air to be sucked into the body. The air can enter through the nose where small hairs and mucus filter out dirt and dust. Air can also enter through the mouth but there is no filtering system. The air travels down the throat (pharynx) and into the windpipe (trachea). The trachea divides into two smaller tubes, the bronchi (bronchus- singular) that go into the lungs. Inside the lungs, the bronchi continue to divide up into smaller and smaller tubes. The small tubes are covered with tiny air sacs called alveoli (alveolus- singular) which look like bunches of grapes. The alveoli are covered with very thin blood vessels called capillaries that are only one cell thick. Oxygen molecules in the air pass through the alveoli into the capillaries that are connected to larger blood vessels that allow oxygenated blood to flow throughout the body. At the same time, carbon dioxide that is dissolved in the blood passes through the capillaries and into the alveoli. At this point the diaphragm moves up and the chest muscles relax decreasing the volume of the chest cavity and the remaining air and carbon dioxide are exhaled. Every cell in the body requires food (nutrients) and oxygen to function. The system that is responsible for this is the circulatory system. The circulatory system consists of blood vessels, blood and the heart. The blood vessels are flexible tubes that carry the blood to every cell in the body. The large arteries (red) carry oxygenated blood from the lungs, back to the heart and from there to the rest of the body. The arteries get smaller and smaller until they form capillaries that can only pass one blood cell at a time. The oxygen and food nutrients pass through the capillary wall into the individual cells and carbon dioxide is passed into the capillaries that are now called veins (blue). The veins get larger and larger until they reach the heart and the lungs. Windsor Public Schools Windsor, CT 06095 January 2008 Page 26 of 53 CMT SCIENCE REVIEW Sage Park Middle School The heart is a large muscle that pumps the blood and keeps it flowing throughout the body. Blood enters the heart into the right atrium. From there it passes through a valve into the right ventricle where it goes through another valve and to the lungs. The oxygenated blood returns to the heart through the left atrium into the left ventricle where it is pumped out the aorta into the rest of the body. Blood is a mixture of liquids and solids that transports oxygen and food nutrients to the cells and removes carbon dioxide and other soluble wastes. Blood contains about 50% liquid called plasma. The plasma is mostly water that carries dissolved nutrients and waste products around the body. There are three kinds of solids mixed with the plasma. The red blood cells deliver oxygen to the cells and remove carbon dioxide. The white blood cells play an important roll in fighting infection and disease and the platelets work to help the red blood cells to clump up and form clots to stop bleeding. The excretory system removes both solid and liquid wastes from the body. Undigested material moves into the large intestine and the water is removed. The remaining solid waste moves through the rectum and is excreted through the anus. (See diagram of digestive system above.) Liquid waste is removed from the blood by the kidneys. It then travels through thin tubes called ureters and is collected in the urinary bladder. The collected liquid waste, called urine, contains water and dissolved salt, urea and other substances. The urine is finally excreted through the urethra. Windsor Public Schools Windsor, CT 06095 January 2008 Page 27 of 53 CMT SCIENCE REVIEW Sage Park Middle School C17. Explain how the human musculo-skeletal system supports the body and allows movement. All mammals, including humans, have two organ systems working together that provide support for the body and allow it to move. The skeletal system consists of bones and cartilage, a hard but flexible tissue. The skeletal system has five major functions: 1) it provides support for the body and gives it shape, 2) it protects the internal organs, 3) it produces both red and white blood cells, 4) it stores minerals such as calcium and phosphorous, and 5) it allows the body to move. The place where two or more bones come together is called a joint. Most joints allow one bone to move relative to another. These bones are held together by tough connective tissue called ligaments. Some joints, such as those in the skull, are not meant for movement and contain no ligaments. There are four types of movable joints. Type of Joint Examples Pivot Joint Neck, elbow Wrist, ankle, spine Knee, elbow, Hinge Joint fingers, toes Ball and Socket Shoulder, hips Gliding Joint Hinge Joint Type of Movement Bones rotate around each other Bones slide over each other Bones move back and forth Bones move in a circle, or rotate Ball and Socket Joint Windsor Public Schools Windsor, CT 06095 January 2008 Gliding Joint Page 28 of 53 CMT SCIENCE REVIEW Sage Park Middle School Pivot Joint There is a fifth major type of joint called a solid joint and it is very strong but it is non-moveable. This joint is found in the skull and at the very base of the spine. The muscular system is made up of three different types of muscles. The cardiac muscle is found only in the heart and allows it to beat or move. Smooth muscle is found in many internal organs and allows those organs to expand or contract. The movement of these muscles is involuntary. The skeletal muscles that control movement are voluntary muscles and are controlled by the individual. These muscles are attached to the bones by connective tissue, similar to ligaments, called tendons. Many of the joints in the body rely on a pair of muscles to function. When a person begins to move, the brain sends a nerve impulse causing one muscle in the pair to contract and the other to relax. Another signal from the brain relaxes the first muscle and contracts the second, causing the joint to straighten. Windsor Public Schools Windsor, CT 06095 January 2008 Page 29 of 53 CMT SCIENCE REVIEW Sage Park Middle School C18. Describe how folded and faulted rock layers provide evidence of the gradual up and down motion of the Earth’s crust. Rock layers form horizontally. Over millions of years changing pressure in the Earth’s crust cause these horizontal layers to bend, wrinkle and curve either up or down. This squeezing of the rock layers is called folding. An upward fold is called an anticline and a downward fold is called a syncline. As land wears away the lower layers become visible on the surface. Pressure inside the Earth can cause the lock layers to crack or break forming a fracture. With more changes in pressure, different sections of rock layers move up, down or sideways. This movement of one rock layer segment relative to another is called a fault. The movement along a fault, known as an earthquake, releases the pressure. After an earthquake, the layers are stable until the pressure builds again. In a normal fault, the movement is vertical with the two layers pushing away from each other. A reverse fault also has vertical movement but the rock layers are pushed together. A thrust fault is a reverse fault that occurs on a lower angle. In a strike slip fault the movement is horizontal. Windsor Public Schools Windsor, CT 06095 January 2008 Page 30 of 53 CMT SCIENCE REVIEW Sage Park Middle School 19. Explain how glaciation, weathering and erosion create and shape valleys and floodplains. The Earth’s surface is constantly changing form due to erosion, deposition and weathering, which wear down or build up the surface. Weathering is the process of physically or chemically breaking down rock into small particles called sediments. Erosion is the process of moving weathered soil and rocks by gravity, water, wind or ice. Deposition is the process of depositing (putting down) new layers of dirt and rocks. Weathering can occur by physical, chemical or biological processes. Chemical weathering occurs when certain substances dissolve in water (such as acid rain) and react with certain types of rocks. Biological weathering is caused by roots breaking up rocks or soils. Physical weathering can be caused by repeated freezing and thawing of water in cracks in soil or rock. However, flowing water is responsible for most of the erosion and deposition. Water flows downhill due to the force of gravity. Water moving over the land is called runoff, and as it flows, it picks up small pieces of rocks and dirt. The runoff forms tiny grooves in the soil called rills. As this erosion continues, the grooves enlarge to form gullies. The gullies continue to enlarge and join together forming a stream. Gullies differ from streams in that they only contain water after a rain or snowmelt, while streams contain water all or most of the time. The streams then flow into each other. A small stream that flows into a larger one is called a tributary. Smaller rivers flow into larger ones. The drainage basin is the total land area that collects the water for a river. Many rivers begin high up in the mountains. The steep slope causes the water to flow rapidly increasing the amount of erosion over a small area. Over time V-shaped valleys or canyons are formed. At the base of the mountain the slope of the land decreases, the water flow loses speed and the river broadens. The resulting valley widens and becomes shallower. In times of heavy flooding these wide, shallow valleys may be several kilometers wide. While in normal times, the river will run in a relatively small channel near the middle of the broad valley. These broad valleys are called flood plains. Windsor Public Schools Windsor, CT 06095 January 2008 V-Shaped Valley Page 31 of 53 CMT SCIENCE REVIEW Sage Park Middle School Glaciers are large masses of slowly moving snow and ice. Glaciers can erode the land surface by plucking and abrasion. The massive weight of a glacier is often enough to crush the rock of the surface. Plucking is the process of picking up loose rock into the ice. Many of these rocks become embedded to the bottom of the glacier which will scratch and wear away the surface land much like sandpaper on wood in a process called abrasion. Many glaciers form in high mountain riverbeds. Small valley glaciers can become tributaries to larger ones and form a river of ice. As with rivers, glaciers slow down and spread out as the slope of the land decreases. The abrasion now covers a much wider area and the resulting valley becomes a flood plain as the glacier melts and retreats. The rock and dirt carried down with the glacier are deposited as the glacier melts. Windsor Public Schools Windsor, CT 06095 January 2008 Page 32 of 53 CMT SCIENCE REVIEW Sage Park Middle School Wind can also cause erosion by lifting up small particles of soil and rock and depositing them in other areas. In some windy canyons these small particles can also wear down larger rocks by abrasion. However, most winds are not strong enough to pick up particles as large as a grain of sand so the effect of erosion is very small. Windsor Public Schools Windsor, CT 06095 January 2008 Page 33 of 53 CMT SCIENCE REVIEW Sage Park Middle School C20. Explain how the boundaries of tectonic plates can be inferred from the location of earthquakes and volcanoes. The Earth consists of five major layers. At the center is the solid metallic inner core above which is the liquid metallic outer core. The mantle consists of molten and solid rock with the lower mantle being totally molten and the upper layer basically solid. The liquid portion of the mantle is called magma. The asthenosphere consists of a mixture of molten and solid rock with the consistency of putty. The lithosphere is the top layer and is made up of the upper solid portion of the mantle and the crust. The lithosphere is broken up into a number of pieces called plates. These plates float on top of the asthenosphere. The magma is constantly moving from the hotter region in the lower mantle towards the cooler region just under the crust and then falling back towards the center forming convection currents. These currents in the mantle just under the lithosphere cause the plates to move and rub against each other. The plates can move towards each other (convergent boundary), away from each other (divergent boundary) or slide past each other (transform boundary). The pressure between two plates builds and earthquakes occur to relieve the pressure. (See C18.) Most earthquakes occur at these plate boundaries although some do occur in the middle of a plate. (See map next page.) Likewise, when two plates meet, a vent or a fissure can form allowing magma to reach the surface of the Earth. This is a volcano. The molten (melted) magma is called lava when it reaches the surface. Most volcanoes are found where plates are colliding although some are found at boundaries that are puling apart. Most of the world’s volcanoes are found in a circle going up the west coast of the Americas and down the east coast of Asia called the Ring of Fire. (See map next page.) Mountains are usually found at a convergent plate boundary where two plates Come together and rock and dirt are pushed up. Divergent plates can cause a rift which will produce mountains as the side erodes away. Windsor Public Schools Windsor, CT 06095 January 2008 Page 34 of 53 CMT SCIENCE REVIEW Sage Park Middle School Windsor Public Schools Windsor, CT 06095 January 2008 Page 35 of 53 CMT SCIENCE REVIEW Sage Park Middle School C21. Describe how freezing, dehydration, pickling and irradiation prevent food spoilage caused by microbes. Most foods are chemically quite stable. Spoilage only occurs when microscopic organisms, bacteria, yeast and mold, grow on them, producing toxins (poisons) and decomposing the foods. These microscopic organisms are usually bacteria, single cell organisms without a cell nucleus. Food can be preserved in many different ways but all methods either kill the bacteria or severely slow their ability to reproduce. Temperature is a most commonly used factor to preserve food. At room temperature (22oC) many foods will spoil quite rapidly but when put into a refrigerator they can remain fresh for many days. This is because the temperature inside the refrigerator (usually 0o-5oC) is cold enough to stop or greatly slow down the bacteria’s ability to reproduce and release toxins. Freezing the food will reduce the number of multiplying bacteria even more. Placing food in a freezer (-10oC) will stop the large majority of bacteria from growing. Rapidly frozen bacteria can remain dormant (not operating, inactive) for long periods of time, only to become active again when the food is thawed. Bacteria which are frozen slowly in a commercial process are usually destroyed. This is because the initial formation of ice crystals in the cell can destroy the structure of the cell. Eventually, the cells burst since the volume of water increases when it is frozen. Heating some foods will also help preserve them. In the process of pasteurization, milk, dairy products, beer and wine can be heated to a relatively low temperature that kills most of the bacteria without damaging the taste or nutritional value of the food. Food can also be preserved by dehydration. Dehydration is the process of removing water. Like all other life forms, bacteria need water to survive. If enough water is removed from the food, the bacteria will die. This dehydration or drying is usually used on fruit and meat. Beef jerky, salted fish, raisons and apricots are a few examples. Pickling is the process of storing food in a solution of acetic acid (vinegar). An acid solution prevents the bacteria from growing and reproducing especially in the absence of air. Pickling is often used for meat, eggs and vegetables. Examples include cucumbers, onions and sauerkraut (literally sour cabbage). Windsor Public Schools Windsor, CT 06095 January 2008 Page 36 of 53 CMT SCIENCE REVIEW Sage Park Middle School C22. Calculate the average speed of a moving object and illustrate the motion of objects in graphs of distance over time. The average speed, or simply speed of an object, is how far it can travel over a period of time. For example, the speed of a car is 40 miles per hour. Average speed = distance traveled total time The speed can be calculated and/or described using a line graph with distance measured on the y-axis and time measured on the x-axis. On the graph on the left the straight line indicates that the object is traveling at a constant speed. The steeper the slope, the faster the speed. Note that at the origin, zero distance and zero time, the object is not in motion. The average speed can be calculated from any point on the line. Average speed = 50 m = 10 m/sec 5 sec Other information can also be learned from a distance-time graph. On the graph to the right, an object at rest moves at a constant speed for the first four seconds (red line). The object then stops for three seconds as indicated by a horizontal line. Then, it returns to its initial position at a faster constant speed. In this graph an object is moving with varying speeds. It accelerates to a constant speed, slows down and comes to rest. Windsor Public Schools Windsor, CT 06095 January 2008 Page 37 of 53 CMT SCIENCE REVIEW Sage Park Middle School 23. Describe the qualitative relationship among force, mass and changes in motion. Inertia is the tendency of an object to resist a change in motion. According to Newton’s First Law of Motion, an object at rest will remain at rest and an object in motion will continue at the same speed and direction unless acted upon by an unbalanced force. Three terms are needed to understand motion. Speed is the distance traveled by an object over a specific time. This is different from velocity which is the speed and direction of travel. Finally, acceleration is a change in an object’s speed and/or direction. A ball on a playing field will remain motionless until someone kicks it and will remain moving in a straight line until gravity (an unbalanced force pulling downwards) pulls it back to Earth. An object on the backseat of a moving automobile will remain there until the car comes to a rapid stop, when it suddenly flies forward due to inertia. A person in a moving car remains seated vertically until the car makes a sudden sharp turn (a force on the car but not the passenger) and that person tends to remain traveling in a straight line and leans over in the direction opposite the force. Newton’s Second Law of Motion states that the force (a push or a pull) of an object is equal to the product of its mass and its acceleration. The motion of an object is dependent upon the action of an unbalanced force, which in turn is dependent upon the mass and the direction of the object applying the force. For example, large rubber ball is moving in a straight line when it is hit from behind by a beach ball. The beach ball applies a force to the rubber ball relative on its mass and velocity, and the speed of the rubber ball increases slightly. Now replace the beach ball with a bowling ball with the same speed. The bowling ball is much heavier than the beach ball and imparts a much larger force causing a large change in the rubber ball’s velocity. The same concept holds if the collision is not Windsor Public Schools Windsor, CT 06095 January 2008 Page 38 of 53 CMT SCIENCE REVIEW Sage Park Middle School from directly behind. The beach ball will change the direction of the rubber ball a small amount while the bowling ball, with a much greater force, will greatly alter the direction of the rubber ball. Windsor Public Schools Windsor, CT 06095 January 2008 Page 39 of 53 CMT SCIENCE REVIEW Sage Park Middle School C24. Describe the forces acting on an object moving in a circular path. Any object traveling in a circular path involves two major forces. One force, the centripetal force, is always towards the center of the circle. If this were the only force involved then the object in motion would not travel in a circular path but in a straight line towards the center of the circle. However, the second force, the centrifugal force, is at right angles with the centripetal force. This is because of Newton’s First Law of inertia that says, an object in motion will continue in its motion unless acted upon by an outside (unbalanced) force. The path of an object in motion is a straight line, the centrifugal force. The unbalanced force is the centripetal force pulling the object towards the center of the circle. As the object tries to move in a straight line it is constantly pulled towards the center and the resulting motion is circular. Planetary motion works in a similar way. The planet’s inertial motion is forward, but gravity pulls the planet inward toward the central object. The result is the familiar elliptical orbit for the planet or moon. (See C28) Windsor Public Schools Windsor, CT 06095 January 2008 Page 40 of 53 CMT SCIENCE REVIEW Sage Park Middle School C25. Explain the similarities and differences in cell division in somatic and germ cells. Somatic cells are body cells that do not give rise to new individuals. They produce exact copies of themselves in a process called mitosis. In mitosis the DNA is replicated and the cell divides into two daughter cells, each with the exact same DNA as the parent cell. The two cells are genetically identical. Mitosis occurs as an organism grows. In the initial step of mitosis, the chromosomes replicate producing exact copies of themselves The chromosomes then move to the cell’s equator where they separate and move towards the poles of the cell. Finally the cell splits into two identical daughter cells. This allows each cell to carry the same genetic information as the previous generation. Germ cells are cells from which new organisms form in a process called meiosis. Meiosis is the 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 two consecutive cell divisions. In the first, the chromosomes replicate and then pair up at the cell equator At this stage, crossing over, the swapping of genetic material from one chromosome to another, occurs. The cell splits into two daughter cells which have a different genetic make-up from the original cell. In the second division, each of the two daughter cells divides leaving each new cell with only half of the original number of chromosomes. These are the gametes. When two gametes combine, one from the mother and one from the father, the original number of chromosomes is restored. In meiosis, how the chromosomes line up at the equator of the cell is a random process and gametes with different combinations of chromosomes are formed. Windsor Public Schools Windsor, CT 06095 January 2008 Page 41 of 53 CMT SCIENCE REVIEW Sage Park Middle School The amount of crossing over will also vary so that the probability of having identical gametes is rare. Variety in the embryos is also increased in that any two gametes can combine to form an embryo. This is why siblings rarely look exactly alike. In humans, each gamete contains 23 single chromosomes. The number of chromosomes is usually symbolized by n. A cell with n chromosomes is called a haploid cell. When a human egg and sperm combine the total number of chromosomes doubles to 2n or 46. Cells with 2n chromosomes are called diploid cells or zygotes. Windsor Public Schools Windsor, CT 06095 January 2008 Page 42 of 53 CMT SCIENCE REVIEW Sage Park Middle School MITOSIS MEIOSIS One cell division occurs No crossing over occurs Two cells are produced, each with 2n chromosomes, diploid Daughter cells are identical Occurs only in body cells Involved in cell growth and repair Two different cell divisions occur Crossing over does occur Four haploid cells formed each with n chromosomes, haploid Daughter cells all different Occurs only in reproductive cells Gamete production providing genetic variation due to crossing over Windsor Public Schools Windsor, CT 06095 January 2008 Page 43 of 53 CMT SCIENCE REVIEW Sage Park Middle School C26. Describe the structure and function of the male and female human reproductive systems, including the process of egg and sperm production. The male reproductive system has two functions: 1) to produce sperm cells, and 2) to deliver the sperm into the female’s reproductive system. Sperm cells are made in two glands called the testes. Sperm cells need to be kept cooler than the normal internal body temperature, so the testes are surrounded by a sac of skin, the scrotum, which is outside the body to stay cool. The sperm cells travel from the testes through a thin tube called the sperm duct (vas deferens) and through the urethra. Other glands add fluids to mix with the sperm cells forming semen. The semen can then be passed to the female reproductive system. When a boy reaches an age of 13-16, his reproductive organs begin to mature. At puberty the testes begin to produce the male sex hormone testosterone. This hormone produces muscles, facial and body hair, and deepens the voice. The female reproductive system is responsible for the production of eggs and developing a fetus. The egg cells are made in the ovaries and a woman is born with thousands of times more eggs than she will ever use. Once a month an egg cell is released into the fallopian tube (oviduct), where tiny hair-like cells push it along into the uterus. The uterus is a thick walled, muscular organ. It is in the uterus that a fertilized egg attaches and the fetus (unborn baby) develops. Like the testes, the ovaries are glands that also produce hormones. When a girl reaches the age of 10-14, her ovaries begin to produce estrogen and progesterone, the female sex hormones. Estrogen enlarges the breasts, widens the hips and produces body hair. Progesterone aids the woman’s body to prepare the uterus to implant a fertilized egg if she becomes pregnant. Windsor Public Schools Windsor, CT 06095 January 2008 Page 44 of 53 CMT SCIENCE REVIEW Sage Park Middle School C27. Describe how genetic information is organized in genes on chromosomes, and explain sex determination in humans. Chromosomes are long, string-like structures made of DNA and proteins, which carry all the genetic information needed to produce another cell or individual. The information is contained in a coded sequence of four nucleotide bases (A, T, C and G). A section of a chromosome that contains information for a specific trait is called a gene. Sometimes two or more genes are needed to produce a trait and these genes can be any place on a single chromosome or even on different chromosomes. Human beings have a total of forty-six chromosomes arranged in twenty-three pairs. Chromosome pair #23 contains the two sex chromosomes. Of the twentythree pairs, these are the only two that look totally different from each other The X chromosome is for female and the Y chromosome is for male. (See C25 for the formation of the germ cells and meiosis.) An egg from the female only contains an X chromosome while the sperm from the male can contain either and X or a Y chromosome. If the male sperm carries an X chromosome then the child will be female. If the sperm carries the Y chromosome then the child will be a boy. All females are XX and all males are XY. During meiosis there is an equal chance of receiving an X or a Y chromosome from the father, although in reality, there are slightly more boys born than girls. While most of the traits in any species are inherited, some physical traits can be caused by the environment. For example, a person’s physical appearance can directly reflect his/her eating and exercising habits. Windsor Public Schools Windsor, CT 06095 January 2008 Page 45 of 53 CMT SCIENCE REVIEW Sage Park Middle School C28. Explain the effect of gravity on the orbital movement of planets in the solar system. Newton’s First Law states that an object in motion will continue to travel in a straight line unless it is acted upon by an unbalanced outside force. Since the planets do not travel in a straight line it can be concluded that there must be some outside force either pulling on or pushing the planets. That outside force is gravity. Newton’s Law of Gravity states that every physical object that has mass, also has a force of attraction, gravity, for every other piece of matter. This (centripetal) force is proportional to the mass of the object. That is, the larger the mass of the object, the greater the force of gravity. Gravity is also affected by the distance between the two objects; the greater the distance the smaller the attractive force (inversely proportional). Since the sun is so massive it has a much greater effect on the planets than the planets’ gravity has on the sun. (There is a little effect but it is extremely small.) So the sun’s gravity is the force that pulls the planets from their straight-line inertia and causes their elliptical orbits. Since the planetary orbits are not circular but slightly squished ellipses, the planets do not travel around the sun at a constant velocity. Since the force of gravity decreases with increasing distance they travel faster when they are closer to the sun, and slower when they are further away. The same explanation can be used for the more massive planets and their much smaller moon(s). See C24. A year is the time it takes an object to complete one revolution around the sun. For Earth this is approximately 365 days. The planets closer to the sun move faster and their years are shorter, while those planets that are further away and move slower through space will have longer years. Windsor Public Schools Windsor, CT 06095 January 2008 Page 46 of 53 CMT SCIENCE REVIEW Sage Park Middle School C29. Explain how the regular motion and relative position of the sun, Earth and moon affects the seasons, phases of the moon and eclipses. The Earth travels around the sun in a slightly squashed circular orbit (the path an object takes going around another object) called an ellipse. An imaginary flat surface containing the path of the Earth and the sun is called the orbital plane. The Earth is tilted by 23.5o on its axis. The axis passes through the North and South Poles and always points in the same direction. During the summer in the northern hemisphere, the Earth’s axis is pointed towards the sun and the sun’s rays strike the surface of the Earth at close to a ninety-degree angle. This concentration of light energy causes the northern hemisphere to heat up. Because the Earth’s orbit is not quite circular, the distance from the sun to the Earth changes, and on the first day of summer in Connecticut, the Earth is at its farthest distance from the sun. In winter in the northern hemisphere, the sun is at its closest distance from the Earth but the Earth’s axis is pointed away from the sun. In winter, the sun’s rays hit the Earth’s surface at an angle and are more spread out causing the Earth to cool. The opposite is true for the southern hemisphere. When the Earth’s axis is pointed towards the sun during summer for the northern hemisphere, it is pointed away from the sun in the southern hemisphere causing winter. When it is winter in the northern hemisphere it is summer in the southern hemisphere. It is important to remember that it is the direction of tilt in the Earth’s axis and not the distance between the Earth and the sun that causes the seasons. Windsor Public Schools Windsor, CT 06095 January 2008 Page 47 of 53 CMT SCIENCE REVIEW Sage Park Middle School The moon orbits the Earth in a very slightly elliptical orbit every 27.3 days. The moon does not give off any light of its own but merely reflects the light from the sun. As the moon orbits the Earth, it appears to change shape or phase. During moon’s trip around the Earth there are eight major lunar phases caused by the amount of reflected light it is possible to see from Earth. While the moon’s trip around the Earth takes only 27.3 days, but the average month on Earth is about thirty days. This is because the Earth is also moving around the sun and it takes approximately three extra days for the moon to regain its original position as seen from Earth. Windsor Public Schools Windsor, CT 06095 January 2008 Page 48 of 53 CMT SCIENCE REVIEW Sage Park Middle School The moon’s orbital plane is at a small angle (5.2o) to the Earth’s orbital plane so that the sun, Earth and moon are rarely in a straight line. When the sun’s rays strike an object it casts a shadow. The Earth and the moon also cast shadows in space. On the rare occasion when the moon is in the Earth’s orbital plane (ecliptic plane), the three objects can line up in a straight line and the shadow from the middle object will fall over the third object. In a solar eclipse the moon casts a shadow on the Earth. Because the moon is so small the shadow is only visible to a very small area on Earth. A solar eclipse is also very short, a few minutes, because the moon quickly moves out of the straight line. In a lunar eclipse, the Earth casts a shadow on the moon. Because the Earth is much larger than the moon the entire moon can be in its shadow and the eclipse will last for up to a few hours. Note that a solar eclipse can only occur with a new moon and a lunar eclipse can only occur with the full moon. Windsor Public Schools Windsor, CT 06095 January 2008 Page 49 of 53 CMT SCIENCE REVIEW Sage Park Middle School Solar Eclipse Lunar Eclipse Ocean tides on Earth are caused by the moon and the sun. Although the sun is much more massive than the moon, it is also much farther from the Earth, so the tides are mostly caused by the gravitational effects of the moon. There are two high tides on opposite sides of the Earth at all times that move as the Earth rotates. One high tide is caused by the water being pulled directly towards the moon. Remember that the force of gravity is inversely related to the distance between two objects. In the diagram, the distance between the moon and the ocean (A) is less than that to the Earth (C). Therefore, the effect of the moon’s gravity is stronger on the ocean and it is pulled away from the Earth. The distance between the moon and the Earth (C) is less than the distance between the moon and the other ocean (B). Now the effect of Windsor Public Schools Windsor, CT 06095 January 2008 Page 50 of 53 CMT SCIENCE REVIEW Sage Park Middle School the moon’s gravity is greater on the Earth and it is pulled away from the water, causing the second tidal bulge on the opposite side of the Earth. Windsor Public Schools Windsor, CT 06095 January 2008 Page 51 of 53 CMT SCIENCE REVIEW Sage Park Middle School C30. Explain how beam, truss and suspension bridges are designed to withstand the forces that act on them. Bridges are elevated structures used to transport objects between two points. All bridges are subject to a number of forces. A force can be thought of as a push or a pull on an object. These forces can have different strengths (magnitudes) and act in different directions. The total net force is the combination of the individual forces. Forces in the same direction are added together, while opposite forces are subtracted. When the net total force is zero, then all the forces cancel out each other and they are in balance. A bridge must support its own weight (dead load) plus the forces of those objects crossing over or on the bridge such as ice, snow and wind (live load). In a bridge, the load force is in balance with the supporting force of the structure. The two most important forces acting on bridges are compression (pushing together) and tension (pulling apart). The design of the bridge structure determines how these two forces are distributed. The simplest type of bridge is the beam bridge. A beam bridge is a long, narrow deck supported at each end by the ground or a pier. The force pushing down on the span causes it to bend. The top side of the span compresses which causes tension in the bottom of the span, which stretches. Too much force on the top of the bridge will cause it to break. Since the forces cannot be transferred away from the span, beam bridges are used only for short distances. A truss bridge uses a series of interlocking triangles to support the flat span. When a load is on the bridge the forces are distributed over the entire network of triangles giving the bridge extra strength. Windsor Public Schools Windsor, CT 06095 January 2008 Page 52 of 53 CMT SCIENCE REVIEW Sage Park Middle School An arch bridge each piece of the arch is supported by the piece below it. When a load is applied to the bridge the forces are transferred down the sides of the arch into the supports. The supports push back, preventing the ends of the bridge from moving apart and keeping the bridge stable. This means that the span is less likely to deform or break. In a suspension bridge, heavy cables are strung through towers and are anchored into the ground at each end of the bridge. The deck is suspended from the cables. The load presses down on the deck, but the compression force is transferred into the cables and eventually into the towers and the ground. This makes the suspension bridge the best type to cover large distances. Windsor Public Schools Windsor, CT 06095 January 2008 Page 53 of 53