How Come We Have Different Cells?

Certain cells become different types of cells (differentiation), and they all play a certain role that is useful to organisms.

Cell Differentiation

After meiosis, you have either sperm cells or egg cells. Eventually, one of those sperm or egg cells may combine and form a zygote, or the beginning of a new life. As soon as the sperm donates DNA from the father to the the DNA of the mother (that’s in the egg), the cell begins to divide. In other words, two haploid cells (n) combined to form one diploid cell (2n). Now, this zygote is undergoing mitosis.

Organs of the Human Body

Soon, this bag of cells will begin to differentiate, or become different types of cells. Different types of cells are called tissues, such as muscle tissue, cardiac tissue (that makes up your heart) and nervous tissue (making up nerves, brain and spinal cord). Tissues can be organized into organs (such as the heart, skin, brain and liver) and then organs can be grouped into organ systems (such as the nervous system).

If your body didn’t start to produce different types of cells, then you would just be a 140-or-so-pound ball of living cells that couldn’t really do much of anything. It would be just about as boring as it sounds. But because the purpose of life is to make more life, we need to have a reproductive system that is made up of the organs like ovaries and testicles. Also, we need to be able to eat so that we can get nutrients for our reproductive system; therefore, we need a digestive system that includes organs like the mouth, stomach and anus.

A dividing zygote

You can see that for every need, there is a system of organs that is responsible for taking care of that need. Since we have a skeletal system, we can walk around; our nervous system allows us to communicate among all the different parts of our body. What is most interesting, however, is the fact that all of these systems come from two simple cells that combine to form a zygote: a sperm and an egg.

Cell differentiation means that all of these cells – heart, skin, bones, nerves, ovaries – essentially come from one zygote. This zygote has to divide enough times and make enough changes each time so that all of these different cells can be made. Even though mitosis produces two cells that have the same DNA, these two cells may not look or act the same!

Students in a school can all be presented with the same lunch, not every student will do the same thing with the lunch. Some students will say, “Eww, this looks disgusting,” and choose to eat chips instead. Other students will say, “Well, I guess I could eat this,” and still others will say, “Wow, this looks great!” In other words, different people had different reactions to the same lunch. In the same way, the different cells that your body produces have different reactions to the same DNA. Over time, all of the different cells in your body will be produced. After a cell has been differentiated, it usually can’t turn into any other type of cell. For example, a nerve cell will always be a nerve cell; a heart cell will always be a heart cell.

1. What is cell differentiation?
2. What is the difference between a cell that is haploid and a cell that is diploid?
3. Identify five organ systems and the problems that they solve.
Put it together
4. Make a diagram to show the relationship between cells, tissues, organs and organ systems.
5. Like the lunch story in the passage, what is another case where people have different reactions to the same thing? Explain!
Think about it
6. Imagine that you could add a whole new function on to your body. What would it be? Design an organ system that has at least three organs. Give names to everything!
7. Define the four major roles of the biotic part of the ecosystem in your own words.
8. State how new cells come about.
9. In which cells does mitosis happen?
10. What is the difference between diploid and haploid?
Cell Differentiation
  1. Pick an organ system and identify at least four organs in the system.
  2. For each organ, figure out the tissue(s) that are needed for the organ.
  3. Draw a diagram with a sketch of the system that contains the organs and sketches of the organs. Include “Tissue Cards” for each tissue that is needed for each of the organs that you chose.
Lung Capacity


Balloon Diameter in Centimeters
Column A: Vital Capacity Column B: Expiratory Reserve Column C: Tidal Volume
Trial #1 cm cm cm
Trial #2 cm cm cm
Trial #3 cm cm cm
Trial #4 cm cm cm
Trial #5 cm cm cm
Row 6: Average cm cm cm
Row 7: RadiusDivide Row 6 by 2 cm cm cm
Row 8: CubeRow 7 x Row 7 x Row 7 cm3 cm3 cm3
Row 9: Lung volumeMultiply Row 8 by 3.14 cm3 cm3 cm3
  1. Stretch a balloon several times. Take as deep a breath as possible. Then exhale all of the air that you can into the balloon and pinch the balloon closed to prevent air from escaping.
  2. Measure and record the diameter of the balloon in Column A, by placing the balloon on the table next to a ruler that is placed on the table vertically. This is your vital capacity.
  3. Deflate the balloon and run four more trials. Record the diameter of the balloon for each trial.
  4. Exhale normally. Without inhaling, put the balloon in your mouth and exhale all the air still left in your lungs. This is your expiratory reserve.
  5. Measure and record the diameter of the balloon in Column B. Run four more trials, recording the diameter of the balloon for each trial.
  6. Take in a normal breath. Exhale into the balloon only as much air as you would normally exhale. Do not force your breathing. This is your tidal volume.
  7. Record the diameter of the balloon in Column C. Run four more trials and record each balloon diameter.
  8. Calculate the average for each column in row 6.
  9. Divide the average by two in row 7. This gives you the average radius.
  10. Cube the radius in row 8.
  11. Multiply the cube by pi (3.14) in row 9. This gives you the lung volume.
  12. Define:
    1. Vital capacity
    2. Expiratory reserve
    3. Tidal volume
Type Male Female
Vital capacity 5000 cm3 4000 cm3
Expiratory reserve 1200 cm3 1000 cm3
Tidal volume 525 cm3 475 cm3

Average adult lung volumes measured with a spirometer

  1. Respond to the table above:
    1. How does your average vital capacity compare to the value obtained by spirometer?
    2. Why might these numbers not agree?
    3. How could you improve the accuracy of this experiment without using a spirometer?
  2. A close relationship between height and vital capacity exists. Complete this chart using your height for Column A and one of the following factors for Column B: 20 for females, 22 for female athletes, 25 for males, 29 for male athletes. Your height in inches multiplied by 2.54 will give you your height in centimeters.
Column AYour Height in Centimeters Column BFactor Column CCalculated Vital Capacity (A x B)
  1. Are your calculated and experimental values the same? Explain.
  2. What is your breathing rate (how many times you breathe) for one minute?
  3. Calculate how much air (in cm3) you inhale in one minute.
A-Mazing Plants

Most plants depend on sunlight to provide energy through photosynthesis. Many plants have adaptations that help them maximize, or take full advantage of, their exposure to the sun. Perhaps you have noticed a plant at home that seems to reach toward the light. If you moved that plant to a new location, you may have seen it grow in a different direction to capture more light in the new spot. This process is called phototropism.


  • paper cup
  • cardboard shoe box
  • potting soil
  • 2 cardboard dividers
  • 4 bean seeds
  • masking tape
  • scissors


In this lab, you will build a maze with a plant on one end and a light source at the other. You will observe the plant over time to see how it responds. To make sure that the plants grow, you will first place the planted seeds in full sun.

  1. Add potting soil to the cup until it is about three-quarters full. Use the tip of a pencil to make four holes about 1 cm deep in the soil. Plant the seeds and cover them with a thin layer of soil.
  2. Water the soil until it is moist. Set the cup near the window.
  3. Cut a hole about 5 cm in diameter at one end of the shoe box. Tape two cardboard dividers inside the box as shown in the diagram. Put the cover on the box and store it in a safe place.
  4. Observe the cup each day. Once the seedlings have broken the surface of the soil, place the cup in the box. Place it at the beginning of the maze, away from the hole. Put the lid on the box. Put the box near the window, with the hole facing the sun.
  5. Over the next 2 weeks, open the box every 2 to 3 days to water and observe the seedlings. CAUTION: Do not remove the cup to water the plants. Record what you observe.


Analyze and Conclude

  1. Summarize what happened to the seedlings.
  2. What stimulus did the seedlings respond to? What was happening within the cells of the plant to cause this response?

Build Science Skills

What adaptive advantage does the growth pattern you observed give a plant? What situation in a natural setting does this activity model?