Seventh Grade Science Final Exam Review Packet

Measurement and Tools of Observation

- Measurement:

- Length: a measure of how long an object is end-to-end

- The base metric unit for length is the meter (m). In 7th grade, we most

typically used the centimeter (cm, 1/100 of a meter) to measure length.

- The tool used to measure length is a ruler.

- Temperature: a measure of the heat energy an object or substance has.

- The base metric units for temperature are degrees Celsius (°C).

- The tool used to measure temperature is a thermometer.

- Mass: a measure of the total amount of matter in an object or substance.

- The base metric unit for mass is the gram (g).

- The tool used to measure mass is a triple beam balance.

- Weight: a measure of the force of gravity on an object

- Weight is determined by multiplying the mass of an object by the force

of gravity.

- Weight changes with gravity; mass does not. For example, you would weigh less on the moon than you do on Earth due to the weaker force of gravity.

However, on the moon, your mass would be the same as it was on Earth.

- Volume: a measure of the amount of space an object or substance takes up. In other words, it’s how big an object or substance is.

- The base metric unit for solid volume is the cubic centimeter (cm3). The base

metric unit for liquid length is the liter. In 7th grade, we most typically used the milliliter (mL, 1/1000 of a liter) to measure liquid volume.

- The tool used to measure liquid volume is a graduated cylinder.

- To measure the solid volume of a rectangular prism, the formula used is as follows: Volume of a rectangular prism = length x width x height

- To find the volume of an irregularly (strangely) shaped object, like a rock, the

water displacement method is used.

- First, pour enough water into the graduated cylinder so that the water

can cover your object, but not so much that it will go higher than the

numbers on the graduated cylinder when you drop your object(s) in. Make note of the starting volume.

- Second, gently drop the object(s) into the water and measure the

combined volume of the water and the object(s). Record this volume.

- Finally, subtract the starting volume of the water from the combined volume of the water and the object(s). The difference is equal to the

volume of the object(s). The unit for solid volume is cm3. However, 1 mL = 1 cm3, so you do not have to change the number of your measurement, just

the unit.

- Density: a measure of the mass of an object in a specific volume of that object. IN OTHER WORDS: It’s how tightly packed the particles are of an object or substance.

- The formula for density is: Density = mass ÷ volume or D = m / V

- In 7th grade, we most typically used the units g/cm3 and g/mL

- Changing the volume of an object does not change its density. This is because when you change the volume, you automatically change the mass. For example, 60

cm3 of iron has a mass of 474.0 g. Using the formula for density we would find

that 474.0 g ÷ 60 cm3 = 7.9 g/cm3.

If we cut the iron in half so that we now only have 30 cm3, then the mass would

also be reduced to 237.0 g. Again, using the formula for density, 237.0 g ÷ 30 cm3 = 7.9 g/cm3.

Iron block: Volume = 60 cm3;

Mass = 474.0 g; Density = 7.9 g/cm3

Iron block (cut in half): Volume = 30 cm3; Mass = 237.0 g; Density = 7.9 g/cm3

- Density and whether an object floats:

- If an object or substance has a density which is less than the density of a liquid, the object or substance will float in that liquid.

- For example: A wood block has a density of 0.7 g/cm3. Water has a

density of 1.0 g/cm3. Since the density of the wood is less than the density of water, the wood would float in the water.

- If an object or substance has a density which is greater than the density of a

liquid, the object or substance will sink in the liquid.

- For example: A piece of copper has a density of 8.9 g/cm3. Water has a density of 1.0 g/cm3. Since the density of copper is greater than the

density of water, the copper would sink in the water.

Scientific Method and Experimental Design - Scientific method:

- The scientific method consists of 6 basic steps:

1) Make observations (quantitative and/or qualitative).

2) Based on observations, recognize a problem or form a question. Conduct

background research about your problem or question.

3) Identify variables and construct a hypothesis (It’s a possible answer to your question or solution to your problem.).

4) Design an experiment and test the hypothesis.

5) Analyze your results.

6) Draw conclusions (Was your hypothesis correct? Do you need to revise your original hypothesis? Is further testing needed?).

- Observations:

- There are two types of observations: quantitative and qualitative.

- QuaNtitative observation: an observation about the Number or amount

of something.

- Examples of quantitative observations: Crystal is 113 centimeters tall. The mass of the rock is 873 grams. The volume of the pool is

2,000,000 liters.

- A qualitative observation is an observation made using your five senses, but is not made using numbers.

- Examples of qualitative observations. I can see the flowers from

the tree are yellow. The sandpaper feels rough. The rock smells like

rotten eggs. The liquid tastes sour. The smaller tuning-fork produced

a high-pitched sound.

- When you make a qualitative observation, you are using your five senses. A good way to remember this is that a quaLitative observation

is about what something Looks like. But remember, a qualitative observation can also be what something sounds, feels, tastes or smells

like.

- Inference vs. observation

- An inference is something that you think you know based on observations and prior knowledge. It is a conclusion based on observation.

- Examples of observations based on the above picture. All of the

following sentences are factual.

- She has curly hair. - She has a choice of eating candy or fruit.

- She is eating candy instead of fruit.

- She is wearing a tank top. - She has brown hair.

- Her eyes are closed.

- Examples of inferences based on the above picture. The following

sentences are not necessarily factual. They are just things someone

might think based on observations.

- Everyone prefers to eat candy instead of fruit.

- She is hungry.

- Identifying a problem or asking a question

- Based on the observations from previous page, there are many questions a

scientist could ask.

- For example: Do people with brown hair like candy? Do people usually eat with their eyes closed? Etc.

- The question we will focus on is: Do people prefer to eat candy instead of

fruit?

- Identifying variables

- Next, variables must be identified.

- Variable: something that might change (in an experiment). There are three types of variables, independent, dependent, and controlled.

- Independent Variable: a variable in an experiment which is

intentionally changed or manipulated by the person conducting the experiment to affect the dependent variable. (It’s the variable I

control).

- If we were to make an experiment regarding our question about candy and fruit, an independent variable could be the

choice of food being presented to people. The person designing

this experiment would be in complete control of giving people the choice of eating fruit or candy.

- Dependent Variable: a variable in an experiment which is measured or studied. The person conducting the experiment cannot precisely

control the dependent variable.

- If we were to make an experiment regarding our question about candy and fruit, the dependent variable could be what

food people choose to eat. The person designing this experiment

would not be in control of what choice people make.

- Controlled variables: variables which are kept constant (they do

not change)

- If we were to make an experiment regarding our question about candy and fruit, controlled variables would be things like

making sure each person has the same type of candy and the

same type of fruit to choose between; making sure that each person is tested at the same time of day; making sure that the

food is presented in the same way to each person.

- Writing hypotheses

- Hypothesis (plural: hypotheses): a suggested explanation for an observation

- Hypotheses are written using the independent and dependent variables.

- Hypotheses are always worded “If…, then…”

- Generally, the independent variable is placed first in a hypothesis

and the dependent variable is placed second.

- For example: If a person is given a choice between eating

candy or fruit, then they will choose to eat candy.

- The first part of the sentence is the independent

variable. The second part of the sentence is an inference

or prediction which refers to the dependent variable.

- Further investigation and/or experimentation can either

support or oppose (not support) the hypothesis.

- Design the experiment

- Using your hypothesis as a framework, design an experiment which will either support or oppose your hypothesis.

- Based on the hypothesis we wrote above, “If a person is given a

choice between eating candy or fruit, then they will choose to eat candy,” a scientist might consider gathering a group of people (let’s

say 10 people) and giving each person a choice of candy or fruit to eat.

- The scientist will keep track of which choice the people in the

experiment made.

- Record results:

- A data table should be used to record information obtained during the experiment.

- In the experiment from the last page, a data table would look

something like this:

Person Candy Fruit

1 X

2 X

3 X

4 X

5 X

6 X

7 X

8 X

9 X

10 X

- Analyze results

- Turn the data gathered into factual statements.

- Based on the data table above, analysis might read like this: When testing 10 subjects to determine if a person would choose to eat candy if given the choice between candy and fruit, it was found that 7 people chose candy and 3 people chose fruit. Each subject was given the same type of candy and the same type of fruit and was tested at the same time of day.

- Draw conclusions

- Refer back to your hypothesis to determine if it was supported or not supported by the results of your experiment.

- Come up with ideas for future experimentation and revise hypothesis if

necessary.

- In the experiment conducted above, a good conclusion might read like this: According to the results of my experiment, my hypothesis, which stated that if a person is given a choice between eating candy or fruit, then they will choose to eat candy, has been supported. For future experimentation, I would like to perform the same experiment using a larger population of people. 500 subjects should be utilized for the next experiment.

Chemistry

- Matter:

- Matter: anything that has mass and occupies space.

- All matter has properties. Properties are the things that distinguish one type of matter from another.

- Properties are things like hardness, color, texture, shape, etc.

- Some matter has characteristic properties. Characteristic properties never

change and are used to identify matter. Examples of characteristic properties are melting point, boiling point and density (at room temperature)

- The particulate nature of matter:

- Matter is made of tiny particles which cannot be seen by the human eye.

- The tiny particles which make up matter are called atoms and molecules.

- Types of matter:

- Matter can be classified into two categories: mixtures and pure substances.

- Mixture: two or more substances that are mixed together but are NOT

chemically combined

- A mixture can always be separated into its separate substances by physical means. For example, sand and iron filings mixed together can

be separated using tweezers or a magnet. Salt and water can be separated by boiling the water.

- The separate substances in a mixture keep their individual

properties. For instance, when sand is mixed with iron filings, the iron filings are not chemically changed. They are still metal, magnetic,

black, etc. The sand is not chemically changed either.

- Heterogeneous mixture: a mixture consisting of visibly different substances or states of matter. Examples include

sand, a mixture of oil and vinegar and a mixture of marbles and rocks.

- Homogeneous mixture: a mixture that is uniform (the same)

throughout the mixture (you can’t see a difference from one location in the mixture to the next). Examples include steel and

salt water

- Solution: a homogenous mixture of at least two substances in which the particles of the substances are

completely and evenly mixed together. An example is Kool-Aid.

- Solvent: a substance which dissolves another substance

in a solution (ex. water is a solvent in Kool-Aid fruit punch).

- Solute: a substance which gets dissolved by another substance in a solution (ex. Kool-Aid drink mix is the solute

in Kool-Aid fruit punch)

- There is almost always more solvent than solute in a solution.

- Pure substance: a substance made of only one kind of matter that has

definite properties (properties that don’t change). Pure substances can be further categorized into elements and compounds.

- Element: a substance that cannot be broken down into other

substances by chemical or physical means. Examples are oxygen, gold and neon.

- All known elements are shown in the periodic table.

- Elements can be categorized into metals, nonmetals and

metalloids.

- Metals: elements which are lustrous (shiny), malleable

and ductile (able to change shape without breaking), and

good conductors of heat and electricity. Examples are silver and iron.

- Nonmetals: elements which do not have the qualities of

metals. Nonmetals appear dull, are brittle (break when their shape is changed) and are poor conductors of heat

and electricity. Examples are hydrogen and sulfur.

- Metalloids: elements which have some properties of metals and some properties of nonmetals. An example is

silicon.

- Compound: a pure substance made of two or more elements that are chemically combined. Compounds are different from mixtures because

the parts that make up a compound change their properties and the parts are difficult to separate (ex: Water – H2O; Table salt – NaCl)

- The properties of a compound are always different from the

properties of the elements that formed the compound. For example, table salt (NaCl) is made by chemically combining the

elements sodium and chlorine. In its elemental form, sodium is a soft, pale-gray metal which reacts explosively with water. In its

elemental form, chlorine is a yellow-green gas which is highly

poisonous. Yet chemically combined, sodium and chlorine form a solid, edible, white crystal known as table salt.

How do we classify matter?

MATTER

PURE SUBSTANCES MIXTURES

HETEROGENEOUS

MIXTURES

HOMOGENEOUS

MIXTURES

SOLUTIONS

ELEMENTS COMPOUNDS

METALS NONMETALS METALLOIDS

- States of matter:

- Matter can exist in three states: solid, liquid and gas.

- Solid: a state of matter which has a definite shape and a definite volume (shape and volume don’t change); it cannot flow and cannot be compressed

- Liquid: a state of matter which has no definite shape but has a definite

volume; it can flow but cannot be compressed

- Gas: a state of matter which has no definite shape or volume; it can flow and can be compressed

- Changes of state:

- Matter can change from one state to another.

- A change of state is brought about by the addition or removal of energy from

matter.

- When energy is added to matter, the particles become more active and spread apart.

- When energy is removed from matter, the particles become less active and

come together.

Solids do not

take the shape

or volume of their

container.

Liquids take

the shape of

their container, but

not the volume.

Gases take the

shape and

volume of their container.

___________________

(Low Energy)

___________________

(Medium Energy)

___________________

(High Energy)

- Every change of state has a name:

- Solid to liquid: Melting

- Liquid to solid: Freezing

- Liquid to gas: Evaporation

- Gas to liquid: Condensation

- Solid to gas: Sublimation

- Gas to solid: Deposition

Subtract

Energy

Add Energy

Add Energy

Subtract Energy

Solid Liquid Gas

- Particles of matter:

- Atom: the smallest part of an element that keeps all of the properties of that element

- Though an atom is the smallest part of an element, it is hardly the

smallest matter. Atoms are made of subatomic particles called protons, neutrons and electrons. Protons and neutrons are found in the nucleus

(center) of the atom and the smaller electrons are found orbiting (circling)

the nucleus.

- Nucleus: the central core of an atom

- Proton: a small, positively charged particle found in the nucleus of

the atom

- Electron: a tiny (smaller than protons and neutrons), negatively charged particle that moves around the nucleus of an atom

- Neutron: a small, neutral (no electrical charge) particle found in the

nucleus of an atom An Atom (of carbon)

- Molecule: a combination of two or more atoms

- A molecule can be a compound or an element.

- If two atoms of the same element are combined, than a molecule is formed that is an element. An example is the oxygen you breathe. A

molecule of the oxygen you breathe is made from two oxygen atoms

(O2). Therefore, since it has two or more atoms, it is a molecule, but since it only contains one kind of element, it is still an element. Below

is a picture of N2. It’s a molecule and an element.

- If two atoms of different elements are combined, than a molecule is

formed that is a compound. An example is water. Water is made from two hydrogen atoms and one oxygen atom (H2O). Therefore, since it

has two or more atoms, it is a molecule, but since it contains more than one kind of element, it is a compound. Below is a picture H2S. It’s

a molecule and a compound.

- The periodic table:

- The periodic table is a chart which provides information about all known elements.

- Each box in the periodic table generally includes the element’s atomic number,

chemical symbol, name, and atomic mass.

- Atomic number: the number of protons in the nucleus of an atom.

- All elements have a different atomic number.

- Every atom of the same element will have the same atomic number. In other words, every single atom of oxygen, no matter where it is

found in the universe, will have an atomic number of 8. Every atom of Titanium will have an atomic number of 22. And so on.

- Only in an electrically neutral atom (an atom with no charge) will the

atomic number also equal the number of electrons.

- When writing a chemical symbol, the first letter written is always uppercase. If

there is a second letter in the symbol, it is lowercase.

- Atomic mass is not something you will concern yourself with in seventh grade. Wait until high school. For now, just focus on the atomic number of an element.

- Period: a horizontal row of elements in the periodic table

- Elements in the same period do not have similar properties.

- Periods are numbered 1-7 from the top of the table down.

- Group: (also called a family) elements in the same vertical column of the periodic table

- Elements in the same group have similar properties. For example, most of

the elements in group 2 explode if placed in water.

- Groups are numbered 1-18 from the left of the table to the right.

- Metals, nonmetals and metalloids:

- As you move along period 4 of the periodic table you will notice that you will encounter thirteen metals, two metalloids and three nonmetals. These

are the three types of elements you can find in the periodic table.

- Metals make up most of the elements. Almost all are solid at room temperature, except for mercury (Hg), which is a liquid.

- Nonmetals make up much of the right side of the periodic table.

Most nonmetals are gaseous at room temperature. However, a few are

solid and bromine is a liquid at room temperature.

- Metalloids are found at the boundary between metals and

nonmetals. There are only seven metalloids.

- Changes of matter:

- Matter can undergo two types of changes: chemical and/or physical.

- Physical change: a change in a substance that does not alter its identity (The original substance does not change into another substance.)

- Physical changes are reversible. This means that matter which has

undergone a physical change can be restored to its original form.

- Examples: All changes of state, like boiling water or melting

butter (remember, you can always reverse a change of state);

tearing paper; breaking glass.

- Chemical change: a change in which one or more substances combine or

break apart to form new substances (the original substance does change into another substance)

- Chemical changes are not reversible. This means that matter which

has undergone a chemical change cannot be restored to its original form by physical means.

- Chemical changes are characterized by a change in color, a change in

temperature, a gas given off and/or a change in smell.

- Examples: Burning paper; pouring acid on metal.

- Another name for a chemical change is a chemical reaction.

- Chemical formulas:

- Chemical formula: the symbolic form of an atom or a molecule. The chemical formula for helium is He. The chemical formula for water is H2O.

- A chemical formula has two parts.

- The symbol(s) are from the periodic table and tell you which

elements are present.

- The subscript(s) tell you how many atoms of an element are in the formula. Subscripts are written after an element’s symbol. If no

subscript is written after a symbol, it means there is only one atom of that element present.

- For example, in the chemical formula CO2, the elements which

are present are carbon and oxygen. There is only one atom of carbon and two atoms of oxygen.

- Chemical equations:

- Chemical equations: a representation of a chemical reaction using symbols and

words. In a chemical equation, the reactants are on the left side and the

products are on the right side. The reactants and the products are separated by an arrow.

- Reactant: a substance which is present at the start of a chemical

reaction

- Product: a substance which is present at the end of a chemical reaction

- Example of a chemical equation:

C12H22O11 C + H2O

Reactant Products

- In word form, this equation would read: When heat is applied to sugar, it yields (produces) carbon and water.

Heat

Traits of Living Things - All living things have several things in common with each other.

- Living things are made of cells.

- Unicellular: made of one cell

- Multicellular: made of more than one cell

- Living things obtain and use energy.

- Organisms require nutrients to produce energy. There are two different

ways in which organisms can get these nutrients.

- Autotrophs: produce their own food.

- Example: A plant performs photosynthesis to make sugar.

- Heterotrophs: consume (eat) their food

-Example: All animals are heterotrophs.

- Living things reproduce.

- Living things can reproduce in two ways, sexually and asexually.

- Asexual reproduction: Reproduction in which one "parent" organism produces offspring with identical genetic material to itself.

Organisms which reproduce in this fashion are genetic clones

- Sexual reproduction: Reproduction in which two "parent" organisms combine genetic material in offspring. Organisms which reproduce in

this fashion are genetically different from their "parents".

- Living things grow and develop.

- Growth: the process by which an organism becomes larger. It is a part of

development.

- Development: the process by which an organism becomes more complex

- Living things respond to their environment to maintain homeostasis.

- Homeostasis: the ability of an organism to maintain a stable internal environment even when the outside environment changes

- Stimulus: any change in the environment that makes an organism

react. Too much or too little water being ingested is an example of this.

- Response: an organism's reaction to a stimulus. Releasing extra

water or feeling thirsty are examples of this.

- Organisms adapt to their environment to survive.

- Adaptation: a change in an organism which helps it better survive in its environment.

- Organisms which are unable to adapt to their environment cannot

maintain homeostasis and eventually die.

Classification of Living Things

- Classification: the process of grouping things based on their similarities

- Taxonomy: the study of how living things are classified

- Living things are classified based on shared characteristics.

- Scientists have developed 6 kingdoms of life. Each kingdom contains

organisms which share some basic traits.

- The six kingdoms of life are animals, plants, fungi, protists,

eubacteria and archaebacteria.

- In 7th grade we only focused on the plant and animal kingdoms.

- Scientists have developed 7 taxa or groupings of living things to help classify

all known organisms. The seven taxa used to classify organisms are kingdom, phylum, class, order, family, genus and species.

- Every organism on Earth fits into one of the six kingdoms, but the

kingdoms are very general, meaning that organisms in the same kingdom only share a small number of characteristics. Each taxon below a kingdom

contains organisms which share more and more specific traits.

- Organisms in the same species share so many characteristics and are so similar that they are able to reproduce with one another and have offspring

which are also able to reproduce.

- In summary, kingdoms contain many organisms which share only a few characteristics with other organisms in the same kingdom. Species contain

only one type of organism that shares many characteristics with organisms

in the same species.

Number of organisms

Kingdom

Phylum

Class Order

Family Genus

Species

Shared characteristics

Lots of organisms

Fewer organisms

Only a few similarities

Lots of similarities

-The scientific name of an organism

- To write the scientific name of an organism, you use the genus name and the

species name.

- The genus gets written first and the first letter is capitalized.

- The species gets written second and it is not capitalized.

- Examples: The scientific name for a human being is Homo sapiens. (Homo is the genus and sapiens is the species.). The scientific name for the

African lion is Panthera leo (Panthera is the genus and leo is the species.).

- Identifying organisms using a dichotomous / taxonomic key.

- A dichotomous key is a tool used to help identify an organism which you are observing. To use a dichotomous key, you read in step 1 two possible descriptions

of a trait which your organism has. Depending on which trait the organism has,

you follow the directions next to the description.

A Dichotomous / Taxonomic Key

1) a. It has a horn or horns Go to 2

b. It does not have horns Go to 3

2) a. It has wings Floopy shmoo b. It does not have wings Flippy floppy

3) a. It has arms Bobbidy boop b. It does not arms Galumphy mop

1 2 3 4

- According to the dichotomous key, organism 1 is a Bobbidy boop because it does not have horns (1b) and it has arms (3a); organism 2 is a Flippy floppy because it

has a horn (1a) and it does not have wings (2b); organism 3 is a Floopy shmoo because it has horns (1a) and it has wings (2a); organism 4 is a Galumphy mop

because it does not have horns (1b) and it does not have arms (3b).

The Cell

- Basic cell information:

- The cell is the basic unit of life. In other words, a cell is the smallest thing

that is still considered to be a living thing.

- All living things are made of cells.

- There are many types of cells and they all have specific jobs.

- Organelles found in both plant and animal cells:

- Cytoplasm: the region between the cell membrane and the nucleus. It is mostly made of water.

- Nucleus: a cell structure that contains genetic material (DNA), the chemical

instructions that direct all the cell’s activities. It can be considered to be the “brain” of the cell.

- Cell membrane: a thin, tough band of protein that that controls which

substances can enter or leave the cell. A cell membrane is said to be semi-permeable.

- Semi-permeable: allowing certain substances to pass through, while

other substances are unable to pass

- Vacuole: a water filled sac inside a cell that acts as a storage area. Vacuoles are usually much larger in plant cells than they are in animal cells.

- Organelles Found Only Plant Cells:

- Cell wall: a rigid (hard) layer of nonliving material that surrounds the cells of

plants and some other organisms; the cell wall is always outside the cell

membrane. Cell walls give plant cells strength and support.

- Chloroplast: a structure found in the cells of plants and some other organisms that captures energy from sunlight and uses it to produce food in a process

called photosynthesis.

- Chloroplasts contain chlorophyll. Chlorophyll is the chemical which gives plants their green color and allows photosynthesis to occur.

Animal Cell

Plant Cell

Cell Membrane

Cell Membrane

Cell Wall

Nucleus

Nucleus

Vacuole

Vacuole

Mitochondria

Mitochondria

Cytoplasm

Cytoplasm

Chloroplast

- Cell division:

- DNA: the genetic material that carries information about an organism

- Chromosome: DNA which has bunched together. Human beings have 46 chromosomes

- Gene: a specific part of a chromosome which controls a specific trait (like eye

color).

- Mitosis: a process of cell division in which one parent cell produces two identical daughter cells. After mitosis is completed, the daughter cells have

the same number of chromosomes that the parent cell had.

Mnemonic device: MiTosis results in Two daughter cells.

- Meiosis: a process of cell division in which one parent cell produces four

daughter cells. After meiosis is completed, the daughter cells have half the

number of chromosomes that the parent cell had.

- Meiosis is only used to produce the sex cells, sperm and ova (eggs).

Mnemonic device: MEiosis has an Extra

round of cell division.

Mitosis

(in humans)

Meiosis

(in humans)

Number of parent cells

1

1

Number of chromosomes in the parent cell

46

46

Number of daughter cells at the end of each process

2

4

Number of chromosomes in each daughter cell

46

23

- DNA replication: the copying of the genetic material that takes place

before mitosis and meiosis can occur.

- Mutation: a mistake in the genetic code which can occur during DNA

replication.

- The cell checks for mutations during mitosis and meiosis, but

sometimes, the mistakes go undetected. If this happens the daughter cells and every cell that comes from the daughter cells will carry this

mistake.

- Some mutations are bad, such as those which cause cancer.

- Cancer: a disease in which cells divide and grow uncontrollably

- Occasionally, a mutation can be beneficial. A beneficial mutation

actually helps and organism. An example of beneficial mutations would be the mutations that led to humans’ opposable thumbs.

Genetics and Heredity

- Traits: a characteristic which an organism can pass on to its offspring

- Heredity: the passing of traits from one generation to the next

- Due to the process of meiosis which produces sex cells with half of the genetic information that a normal cell has, organisms which reproduce sexually are able

to pass some of their genetic information on to their offspring. Organisms which

reproduce sexually receive half of their genetic information from the male “parent” and half from the female “parent.”

- Genetics: the study of heredity

- Dominant gene: a gene which always produces a trait which appears in an

organism whenever the gene for that trait is present. A dominant trait appears when both genes from each parent have the dominant trait OR when one gene

from one parent has the dominant trait and the other gene has the recessive trait.

- Recessive gene: a gene which always produces a trait which only appears when

BOTH genes from each parent have the recessive trait

- Representing genes with symbols.

- Dominant and recessive genes which control the same type of trait use the same letter as a symbol. The letter which is used is representative of

the dominant gene.

- A dominant gene symbol uses a capital letter and a recessive gene symbol uses a lowercase letter.

- Example if a certain plant has a dominant gene for hairy stems and a

recessive gene for smooth stems then the symbols for the genes would be written as such: “H” for the dominant hairy stem gene and

“h” for the recessive smooth stem gene.

- Since every organism possesses two genes for any given trait

several combinations of genes could exist for stems of this particular plant.

- HH – purebred hairy stems. The stems will be hairy and

this plant will only pass on a hairy stem gene to its offspring.

- Hh – will have hairy stems, but is a carrier of the smooth

stem gene. The stems will be hairy and this plant will only pass on a hairy stem gene to its offspring.

- hh – purebred smooth stems. The stems will be smooth

and this plant will only pass on a smooth stem gene to its offspring.

- Allele: a gene with two different variations for the same trait

- Example: the plant described above has two alleles for stems (hairy and smooth). The genes control the same trait, but have different results.

- Genotype vs. phenotype

- Genotype: the combination of genes an organism inherits for a specific trait. –

- Phenotype: the physical trait that the genes actually produce.

- For example, a plant as described above can have a genotype for stems of Hh. The phenotype for the genotype of Hh would be hairy since the hairy stem gene dominates the smooth stem gene.

- A plant can only have a phenotype of a smooth stem if it has a genotype of

hh since the smooth gene is recessive.

- Using Punnett squares to predict the probability of inheritance in offspring.

- A Punnett square shows how the genes from two “parents” might possibly combine in their offspring.

- The “parents’” genes get written on the outside of the square. One parent gets

written along the top, the other parent gets written down the left side. Then, you fill in the squares by matching letters from the top and side. Each square will

have two genes, one from the side and one from the top.

- For example, if two plants reproduce (again using the plants described

earlier in this section), and one plant has a genotype of Hh and the other has a genotype of hh, this is how the Punnett square would look.

- According to this Punnett square, there is a 50% probability that the

offspring of these two plants will have smooth stems (hh appears in 2 out of 4 squares.

- According to this Punnett square, there is a 50% probability that the

offspring of these two plants will have hairy stems (Hh appears in 2 out of 4 squares.

H h

h

h

hh

hh

Hh

Hh

Environmental Science

Ecosystems, Biotic and Abiotic Factors and Food Webs

- Ecosystem: the living and nonliving things in an area that function as a unit:

- Biotic factors: the living things in an ecosystem (plants and animals)

- Population: all of the members of ONE species that live in a specific

area. For example a population would be the squirrels that live in

Westchester; or the ducks that live on the Kensico reservoir.

- Community: all of the different populations that live together in an area

- Habitat: the specific place an organism lives and is provided with the

things it needs to survive

- Abiotic factors: the nonliving things in an ecosystem (water, sunlight, oxygen, temperature, soil)

- Abiotic factors impact the living things in an ecosystem.

- For example, the amount of sunlight and type of soil influence the

plants that can grow in an ecosystem.

- Food web: A food web shows the transfer of energy and nutrients from one organism to another. These organisms are linked together as energy and nutrients pass

through them.

- The source of all energy in most food webs is the sun.

- A food web is made of three types of organisms:

- Producer: an organism that can make its own food. Most plants and some bacteria are producers.

- Consumer: an organism that obtains energy by feeding on other

organisms. A producer can be a carnivore, herbivore or an omnivore. All animals are consumers.

- Decomposer: an organism that breaks down wastes and dead organisms.

Many bacteria and some fungi are decomposers.

- There are different levels of consumers in a food web.

- Producers are at the bottom level in a food web. (Example: Plants)

- 1st level consumers eat producers (Example: a grasshopper eats some grass)

- 2nd level consumers eat 1st level consumers (Example: a mouse eats a

grasshopper)

- 3rd level consumers eat 2nd level consumers (Example: a snake eats a mouse)

- And so on… it is possible for an organism to be part of multiple levels of

consumption depending on what it eats.