Homework 1 (q3)
Name___________________________________
Balanced forces acting on an object do not change the object’s motion. When equal forces are exerted in opposite
directions, the net force is zero. In the figure, when two people push on the car with equal force in opposite
directions, the forces cancel out. The car does not move. In science we call these forces balanced. Unbalanced forces
can cause an object to start moving, stop moving, or change direction. Unbalanced forces acting on an object result in a
change in the object’s motion.
Matching:
_______1. When equal forces are exerted in opposite directions are
a. mass
_______2. When motion is produced the forces are
b. balanced.
_______3. Balanced forces have a net force of
c. zero.
_______4. Unbalanced forces produce
d. motion.
_______5. Force of gravity
e. weight
_______6. Measures with a triple beam balance
f. unbalanced.
Muscles and bones act together to form levers. A lever is a rigid rod (usually a length of bone) that turns about a pivot
(usually a joint). Levers can be used so that a small force can move a much bigger force. This is called mechanical
advantage.
1. What is mechanical advantage?_______________________________________.
2. Where do bones pivot?________________. What works like a lever in our bodies?______________________
Muscle cells contract when they receive messages from the nervous system. Because muscle cells can only contract, not
extend, skeletal muscles must work in pairs. While one muscle contracts, the other muscle in the pair relaxes to its
original length. As the biceps contracts, the triceps on the back of the upper arm relaxes and returns to its original
length. Then, to straighten the elbow, the triceps muscle contracts. As the triceps contracts to extend the arm, the
biceps relaxes and returns to its original length.
3. Describe how the muscles in your upper arm work together to bend and straighten your arm.________________
_______________________________________________________________________________________________
Muscles are connected to bones by tough, cord-like tissues called tendons, which allow the muscles to pull on bones. They can
only contract (shorten or tighten) When the specified muscle shortens, it pulls on the corresponding bone. Upon receiving the
signal to relax, the muscle opposing the contracted muscle will then act to extend the movable bone back to its original
position. Muscle cells are packed with thousands of mitochondria for energy. Mitochondria organelles that release energy.
When the temperature drops some organism will hibernate to conserve energy. Muscle cells sleep during hibernation.
3. Why do all skeletal muscles always work in pairs? _______________________________________________________
4. Muscles (push/pull) on bones. Muscles work (alone/ in pairs). To straighten the elbow, the triceps muscle (relaxes/contracts). 5.
5. Muscle cells are filled with thousands of organelles called (mitochondria/ tissue). Organelles are (larger/smaller) than
a cell. When the (food supply/temperature) drops some organism will hibernate to conserve energy.
1. Circle the lowest level at which symbiosis can occur.
2. Place an X on the lowest level which includes millions of stars.
Many-celled organisms (only)
Element, Compound  ,Organelle , Cell  , Tissue  , Organ, Organ system , Organism, Population,
Community, Ecosystem, Biome, Earth, Solar system, Galaxy, Universe.
3. Draw a square around the lowest level at which asexual reproduction can occur.
1. List three things that are LESS complicate and/or smaller than an organism. ___________,____________,__________
2. List two things that are larger or more complicated than our solar system. ________________, ________________
3. List three things that are LESS complicate and/or smaller than a cell. ___________,____________,__________
4. Only _______-_______ed organisms have tissues, organs, or organ systems. Bacteria and germs cannot form
_________, organs, or organ system because they unicellular. Bacteria do not have specialized cells.
Example of specialized…….
……cells that obtain energy.
……cells for sexual reproduction.
……cells that absorb water and nutrients.
……cells that protect from infection.
……cells that contract or shorten.
Producers
Leaf cells (photosynthesis)
Flower cells
Root cell
Bark cells
-none-
Consumers
Stomach cells (digestion)
Egg cell
Stomach cells
Skin cells
Muscle cells
2. Why do leaf cells look different that root cells?_________________________________________________________
3. ________________ do not have specialized cells. _________ cells specialize in photosynthesis. Stomach cells
specialize in ______________. Skin cells specialize to protect the body from ___________. Producers do not have cells
_______ or shorten. List a cell that specializes in sexual reproduction. _____________________________
In a many-celled organism, the cells are often quite different from each other and are specialized to perform specific
functions. Contrast, for example, the nerve cell and red blood cells. Nerve cells are specialized to transmit information
from one part of your body to another, and red blood cells carry oxygen throughout your body.
4. What is the function of the red blood cell?____________________________________________________________
5. Could a red blood cell move through your blood vessels if it looked like a nerve cell?__________________________
6. Why does a nerve cell look different than a red blood cell? _______________________________________________
__________________________________________________________________________________________________
In many celled organisms, the cells are often quite different from each other. The structure of each kind of cell is suited
to the function it carries out in the organism. A red blood cell is small and doughnut-shaped so that it can move in small
places. A nerve cell is long so that it can carry a message like a telephone wire.
Each cell looks different because it has a different function.
1. Circle the image that has a structure and function which is most like that of a red blood cell.
2. Place an X on the image which has a function and structure which is most like that of a nerve cell.
3. Cells have different structures because they have different ______________________________.
1. If organism hibernating is a responding variable, what is the manipulated variable? a. food supply b. temperature
A force is a push or a pull. Forces are described not only by how strong they are, but also by the direction in which they act. When
two forces are exerted in the same direction, they add together. When forces are exerted in opposite directions, they are
subtracted. The overall force on an object is called the net force.
200 N
100 N
100 N
100 N
1. Would you add or subtract the forces on the box to the left?
2. What is the net force? ______________N
3. Will the box move?__________, right or left?___________
1. Would you add or subtract the forces on the box to the left?
2. What is the net force? ______________N
3. Will the box move?__________ , right or left?____________
Bacterial cells are usually much smaller than plant or animal cells. While a bacterial cell does have a cell wall and a cell
membrane, it does not contain almost none of the organelles found in plant or animal cells. Bacteria do not specialize.
2. How are bacterial cells different than animal or plant cells._______________________________________________
Only the cells of plants have green organelles called chloroplasts. Chloroplasts capture energy from sunlight and use it to produce
glucose for the cell. Chloroplasts make leaves green.
3. What are chloroplasts? ________________________________________________________________________