Name: _______________________________ Period: _____ Date: ___________
Directions: Read the following paragraphs. Highlight the important information and answer the questions that
The organ systems in an organism work together to maintain homeostasis, the body’s tendency to keep
an internal balance. Homeostasis is the process by which an organism’s internal environment is kept in
equilibrium, or stable, in spite of changes in the external environment.
1. What word is most closely associated with homeostasis? (circle the answer)
growth stability temperature energy
Your body has other ways of maintaining homeostasis. When you need food, your brain sends signals to
make you feel hungry. A stimulus is something inside or outside an organism’s body that causes the organism
to react. An organism’s response is the action or change in behavior that occurs as a result of the stimulus.
Hunger is an internal stimulus – one that comes from inside your body.
The sight or smell of food is an external stimulus- one that comes from outside your body. Eating the
food is your response to both stimuli. If the food that you eat is bad, the stimulus, you can vomit to get the bad
food out of your system, the response. All organisms respond to stimuli. For example, earthworms respond to a
bright light by moving away from it. The leaves of a plant respond to light by growing towards it.
2. Give your own example of an external stimulus and an internal stimulus.
External - ______________________________________________________________________
Internal - ______________________________________________________________________
Stress is the reaction of your body and mind to threatening, challenging, or disturbing events. Stress
upsets homeostasis and your body reacts in specific ways. Initially your body releases adrenaline into your
blood. Adrenaline acts as an internal stimulus that gives you bursts of energy and causes many other responses
in your body. Your breathing quickens which sends more oxygen to your muscles and the extra oxygen causes
your heart to beat faster. Your pupils will also become wider which can help you see better.
The fight or flight response also helps you in a stressful situation. It prepares your body to fight the
source of stress or to take flight and escape. The stressor could be a social studies test or a barking dog.
4. How is homeostasis important to the survival of an organism?
5. A cat sees a dog beginning to chase it. Is the stimulus internal or external? ______________________
How will the cat’s body probably respond to this stimulus?
Integumentary System (skin)
If an adult’s skin were stretched out flat, it would cover an area larger than 1.5 square meters – about
the size of a twin sized mattress! The integumentary system takes a wide variety of forms in animals across the
world. Just think about the differences in the skin of a fish, a frog, a lizard, a bird, and a mammal. Scales, slime,
feathers, and hair are all parts of the integumentary system for animals. Your parts include the basic types of
skin, hair, fingernails, oil, and sweat glands. Did you know your skin makes up over fifteen percent of your body
weight and is the largest organ in your body? Yes, your skin is considered an organ. You may think your skin is
nothing but a covering for your body, but it performs several major functions for your body.
The skin covers the body and prevents the loss of water. It protects the body from injury and infection.
The skin also helps to regulate body temperature, eliminate wastes, gather information about the
environment, and produce vitamin D.
When you perspire, or sweat, on a hot day, your body is responding to environmental conditions and
helping itself maintain a stable body temperature. The perspiration, or sweat, evaporates and it absorbs heat
from your body which helps to cool you down. Other animals have different ways of maintaining body
temperature. For example, dogs pant to remove excess heat and reptiles, such as lizards, warm their bodies by
lying in the sun.
6. What are the functions of the skin?
7. How does perspiration, sweating, help regulate body temperature?
The digestive system has three main functions. First, it breaks down food into molecules the body can
use. Then, the molecules are absorbed into the blood and carried throughout the body. Finally, wastes are
eliminated from the body. Absorption is the process by which nutrient molecules pass through the wall of the
digestive system into your blood.
The path of digestion starts in the mouth where food is broken down physically (by your teeth) and
chemically (with saliva). It then travels down the esophagus to your stomach. Your stomach digests most of
your food mechanically (breaking it into smaller pieces), but some chemical digestion occurs too. Your stomach
releases the food to your small intestines where most chemical digestion takes place. This is also where all of
the nutrients are absorbed into your blood. The waste products of digestion and water then enter the large
intestine where the water is absorbed into your body and the waste is eliminated.
There are three other organs that aid in digestion, but food does not pass through them. They are the
liver (which produces bile), the gall bladder (which stores the bile), and the pancreas (which produces
chemicals called enzymes that help break down food).
8. The digestive system is sometimes said to be an assembly line in reverse. What are some similarities and
differences between your digestive system and an assembly line?
9. Where does most chemical digestion take place? ___________________
10. Where does most mechanical digestion take place? ___________________
Skeletal systems come in many forms. You have a skeleton inside of your body (endoskeleton) made up
of bones. Insects and crustaceans have skeletal systems on the outside or their bodies (exoskeletons) that are
made of hard plates.
Your skeletal system has five major functions. It provides shape and support, enables you to move,
protects your internal organs, produces blood cells, and stores certain minerals until your body needs them. In
your body, the skeleton works very closely with the muscular system to help you move. Muscles connect to
your skeleton by tendons and they contract and move the skeleton along. A place where two bones meet to
help you move is called a joint. Joints allow your bones to move in different ways. There are two types of joints
in your body. Immovable (like your skull) and movable (like your elbow).
Your skeletal system is made up of cartilage and calcified bone that work together. Marrow inside of
your bones helps produce the cells inside of your blood. Both red blood cells and white blood cells are created
in your bones.
11. What are bones made up of?
12. What cells are your bones responsible for creating?
Muscles control movement in your body. We have about 600 muscles in our body. Some muscles, like
your heart beating, are not under your control. We call these muscles involuntary muscles. Muscles that
you can control, such as smiling, are called voluntary muscles.
Your body has three types of muscle tissue – skeletal muscle, smooth muscle, and cardiac muscle.
Skeletal muscles are voluntary and are attached to your bones by tendons. They help you move. Smooth
muscles are involuntary and are found inside many internal organs such as your stomach and blood
vessels. The cardiac muscle is involuntary and is only found in your heart.
Muscles in your body can only contract, they cannot extend, and therefore they must work in pairs.
While one muscle contracts, the other muscles returns to its original length.
13. How do voluntary and involuntary muscles differ in their function?
14. If your smooth muscles had to be consciously controlled (you had to think about what to do), what
problems do you think you would have in your daily life?
15. What are the three types of muscles? Give your own examples of where each type can be found.
________________________ -- ______________________________________________
________________________ -- ______________________________________________
________________________ -- ______________________________________________
Forces and the Muscular System
Our muscular system helps us move objects by force. The simplest forces are pushes and pulls. A force
can start an object that is at rest into motion, or it can slow down, speed up, or change the direction of an
object that is already moving. At other times, a force can have no effect at all. In this case, the force may
be canceling out the effect of another force.
Sometimes forces are applied in the same direction and sometimes they are applied in different
directions. The net force is the combination of all forces acting on an object. If the forces are going in the
same direction, we add them together. If they are going in opposite directions, we subtract them from
each other. The object moves in the direction of the greatest force.
The size of a force is measured in the unit of Newtons (N). A Newton is mass (kg) x acceleration (m/s2).
The abbreviation is written with a capital letter because it is named after Sir Isaac Newton.
When the object has moved a distance as a result of the force – work has been done. The formula for
work is: Work = Force x distance and the unit of measurement is Joules (J). If an object does not move then
no work has been done on the object.
In the space below the picture (A) calculate the Net Force, (B) tell which direction the box is moving and (C) if
any work is done on the box.
16. 17. 18.
A. Net Force = ___________ A. Net Force = ___________ A. Net Force = ___________
B. Direction = ___________ B. Direction = ____________ B. Direction = ____________
C. Work done? ___________ C. Work done? ___________ C. Work done? ___________
The circulatory system touches every organ and system in your body. The system is connected to all of
your body's cells so that it can transport oxygen efficiently. When you breathe, the circulatory system carries
oxygen to your cells and carries carbon dioxide back to the lungs.
The main functions of the circulatory system are to carry needed substances to cells and carry waste
products away from cells. The circulatory system and its fluids are super important to your digestive system
that has absorbed nutrients from your food into the bloodstream. It also carries white blood cells that help
fight disease. Guess what? Hormones created by your endocrine system are sent through the body by the
19. Why other systems to does the circulatory systems work with?
The main parts of your circulatory system are the heart, blood vessels, and blood. You happen to have a
four-chambered heart while other organisms may have one, two, or three chambers. The heart is the pump for
the system. As blood is pumped from the heart, it passes through a system of arteries and then capillaries.
Capillaries are very small and have thin walls to allow easier passage of compounds including nutrients,
glucose, carbon dioxide, and waste products to and from the cells. After the capillaries, your blood passes
through veins. The veins lead the circulatory fluids back to the heart. That's it; the system is complete (and
20. What path of blood vessels would blood take as it leaves the heart to get back to the heart?
heart - __________________- _________________-cells - _________________-__________________- heart
Your respiratory system is all about exchanging gases with the environment. Some animals such as
amphibians are able to exchange gases through their moist skin. Fish have gills while mammals, birds, and
reptiles have lungs. Your respiratory system is made of your nose and mouth, a tube called the pharynx,
another tube called the trachea, and your two lungs. Inside your lungs are small sacs called alveoli that are
surrounded by tiny capillaries. Oxygen and carbon dioxide pass back and forth through these in an exchange of
Animals need oxygen (O) to survive. In fact, all organisms need oxygen to complete the process to
burning glucose for fuel in the mitochondria of the cell. The respiratory systems main functions are to bring
oxygen into your body and remove carbon dioxide and water. Remember, the products of cellular respiration
are carbon dioxide and water. Your respiratory system helps your body get rid of that carbon dioxide. While
you have lungs, fish have gills that serve as the location for that transfer of gases. Whatever animal you study,
oxygen is taken in and carbon dioxide let out.
21. What is the difference between breathing and respiration?
22. If you exhale onto a mirror, the mirror will become clouded with a thin layer of moisture. Explain why
The excretory system is very important to your body and only has a few parts. In a similar way to
removing solid waste from your body, you must also get rid of fluids. The main functions of the excretory
system are to collect wastes produced by cells and remove that waste from the body. You know the results of
the excretory system as urine. If wastes were not taken away, they would pile up and make you sick. Excretion
helps maintain homeostasis by keeping the body’s internal environment stable and free of harmful materials.
Urine is the result of the excretory system balancing the amount of water and salts in your body. We
said the system is small. Your two kidneys are the main organs involved in the excretory system. Other parts
include the ureters (which carry urine to the bladder), bladder (stores urine), and urethra (where urine leaves
the body). Once the urine passes through your urethra, that's it, it's out of your body. The kidneys pull harmful
molecules out of your bloodstream and leave the ones that are good for you.
The kidneys are also key players in the hydration (water) levels for your body. Let's say you are in the
desert and you haven't been drinking much water. Chemical signals are sent to your kidneys to reabsorb as
much water as possible. The result is less urine creation and your body loses less water. A normal day has you
creating about one and a half liters of fluid.
You have three other organs that are also involved in excretion, but not of urine. The lungs help to
remove carbon dioxide and water. The skin excretes water and some chemical wastes when it perspires. And
the liver helps to break down some wastes before they can be excreted.
23. What two ways can the excretory system help to maintain homeostasis in your body?
24. What are the three other organs of excretion in the excretory system?
Diseases are everywhere. You may have heard about tuberculosis, SARS, AIDS, malaria, or something as
simple as the flu. All of those diseases can kill you, escpecially if you did not have an immune system. Your
immune system protects the cells of your body from bacteria, viruses, and poisons you encounter every day.
Your immune system is relatively invisible, compared to the organs in other systems, and made of many
different types of immune cells.
You know when your immune system is at work because of the symptoms you might have. Fever,
swelling, and a runny nose are all examples of symptoms during an immunological response. There are also
genetic problems with immune systems. Something as simple as an allergic reaction happens because an
individual cannot properly tolerate certain allergens. Inflammation and hay fever occur. Normal individuals can
destroy those allergens, but people who are "allergic" cannot defend themselves. You could have allergies to
animals, food, or plants. Some allergic reactions are so extreme they can kill.
25. Do you know anyone who suffers from severe allergies? How does it affect their lives?
Since you're reading this page, we figure you've got a nervous system. If you were an insect you would
also have a nervous system, but it would be a lot simpler. Even animals that don’t have complex systems like
our have simple systems called nerve nets that help them move.
Your nervous system is divided into two parts. Your central nervous system includes your brain and
your spinal cord. Your peripheral nervous system is made up of a network of neurons that leaves your spinal
cord and reaches your organs, muscles, and the rest of your body. The neurons in both systems work together
to help you think, survive, and change the world around you.
26. What two parts is your nervous system divided into?
The nervous system has several main functions. It receives information about what is happening both
inside and outside your body. It also directs the way in which your body responds to this information and helps
to maintain stable internal conditions.
Animals are able to sense what is going on in their surroundings and do something in reaction to that
input. If you see a bike that might hit you, you jump out of the way. In that example, your nervous system was
involved in many ways. Your eyes saw the bike, your brain figured out the bike might hit you, and your brain
told your muscles to make your legs jump out of the way. You sensed and then acted.
The nervous system also senses activity inside of your body. Most of the nervous system response
inside of your body is not in your control. Your body automatically senses and reacts to stimulus. Think about
eating your lunch. As you eat, your nervous system triggers the start of digestion and release of many
hormones and enzymes throughout your body.
27. Give a situation when you’re nervous system acted to help you not get hurt.
28. While sitting in the dark you hear a balloon pop. Explain how your body would reactant to this? (How
would you feel? What organs would be affected?)
The human body has two systems that regulate its activities. One is the nervous system and the other is the
endocrine system. The endocrine system controls many of the body’s daily activities as well as long term
changes such as development.
The endocrine system is made up of glands which are organs that produce chemicals. There are many
different glands spread throughout the body and they release their chemicals directly into the bloodstream.
The chemical that they release is called a hormone. Hormones can turn on, turn off, speed up, or slow down
activities in different organs and tissues.
The hypothalamus, a tiny part of the brain near the middle of your head, links the endocrine system to
the nervous system. Nerve messages control sleep, hunger, and other things. Through nerve impulses and
hormones, the hypothalamus plays an important role in maintaining homeostasis. The pituitary gland
communicates with the hypothalamus. In response to a nerve impulse or hormone signal from the
hypothalamus, the pituitary releases its hormone to tell the other glands what to do. The pituitary gland also
regulates the growth from infancy to adulthood.
29. How do the hypothalamus and the pituitary gland interact?
When organisms reproduce, their traits are passed from parents to their offspring. This happens in
sexual reproduction and asexual reproduction.
In sexual reproduction the offspring are considered diverse and they receive genes from two parents.
When things are diverse that means they are different and they do not look the same. Special cells, called
sperm and egg cells are used in sexual reproduction. In sexual reproduction, cells from two organisms must
unite to form a cell that develops into a new organism. In humans, a sex cell called a sperm is produced in the
testes of a male. This cell must unite with an egg cell that is made in the ovaries of a female. When a sperm and
egg cell unite, then you have fertilization. Half of the DNA, found in chromosomes, comes from the mother and
half from the father. Once fertilized, the egg cell begins to divide to make more cells. These new cells specialize
and take on different functions. After about 40 weeks (for humans), a fully developed baby is born.
30. What are the sex cells called in males and females?
In asexual reproduction the offspring are usually considered uniform and they look just alike. The
offspring of an asexually reproducing organism receives genes from only one parent so they are genetically
identical. This is done without a sperm and egg. The offspring is exactly like the parent. Asexual reproduction
can occur through binary fission, budding, and regeneration.
31. Give an example of an organism that reproduces asexually.
The passing of traits, or characteristics, from parents to offspring (one generation to the next) is called
heredity. Genetics is the study of heredity. These traits are carried on DNA; this is the genetic material that is
found in the nucleus. DNA is just like a blueprint for the cells of an organism, it tells the cell how to put
together materials to produce certain traits. Genes are segments, or parts, of DNA that carry instructions for
the traits of an organism. Genes are located on chromosomes in the nuclei, or center, of cells. Each type of
organism has a fixed number of chromosomes. Humans have 46 (23 pairs). Your genes determine your traits.
Some genes control more than one trait, and some traits are controlled by more than one gene.
32. What is heredity?
33. Where is genetic material found in the cell?
Gregor Mendel is the “father” of genetics. He did many early experiments with heredity and set the
stage for genetics. One popular study that he did was using pea plants. All organisms have a set of genes that
determine their traits. These genes occur in pairs and each gene in a pair is known as an allele.
An organism’s appearance (the way it looks/what you can see) is its phenotype. Ex. hair color, eye color,
height. The code that is written on the genes and expressed with letters is known as the genotype. Ex. TT, Tt,
tt. Alleles are usually written using letter. The dominant alleles are expressed with capital letters and the
recessive alleles are expressed or shown with lower case letters. The dominant allele is always expressed when
present. The recessive allele is only expressed when the dominant allele is not present.
An organism that carries two dominant (TT) or two recessive (tt) alleles for a given trait is known as pure
for that trait and we call those purebred or homozygous. When an organism carries both a dominant allele and
a recessive (Tt) allele for a certain trait it is called a hybrid or heterozygous. Just like a hybrid car that uses both
gas and electricity, this gene would carry a dominant and a recessive allele.
34. Who is the father of genetics?
35. When is a recessive allele expressed?