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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
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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
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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.
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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).
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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
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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).
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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.
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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.
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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
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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
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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%
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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V-Shaped Valley
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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.
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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.
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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.
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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).
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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.
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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
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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.
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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)
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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