Your Body and How It Works Body Organization: A Closer Look at a Human Cell

A Closer Look at a Human Cell

Since a cell is the basic building block of the human body, maybe we should take acloser look at a human cell. If we want to know everything possible about our wonderful"machine," we need to understand how a human cell is put together and what the differentparts do.

There are four basic parts of a human cell. Beginning in the middle, the cell has anucleus. The nucleus is a dense, ball-shaped part that is usually found near the center ofthe cell. The nucleus controls the activities of the cell. It also controls the cell's ability toreproduce. Finally, the nucleus has hereditary information in it. The nucleus of the cell hasthe information that determines if a person will have blue eyes or green eyes, brown hairor black hair, big feet, little hands, and so on. Sometimes, this information is called thegenes.

All around the nucleus is the nuclear membrane. This membrane has the job ofkeeping all the parts of the nucleus inside the nucleus. We do not want genes runningaround where they are not supposed to be!

The next basic part of a cell is called the cytoplasm. This is a jelly-like material thatis all around the outside of the nucleus. Cytoplasm is alive. It is made of water, salts, andother materials. Smaller cell parts, called organelles, can be found inside the cytoplasm.

The final basic part of the cell is the cell membrane. This membrane surrounds theentire cell. It is thin and flexible. Like the cytoplasm, the cell membrane is alive. The cellmembrane keeps the cell together. It also controls movement of material in and out of thecell.

There are two kinds of movement that the cell membrane allows. The first kind ofmovement is called diffusion. Diffusion is movement from an area with many particles toan area with fewer particles. Food particles and oxygen molecules diffuse through the cellmembrane into the cell. Waste products diffuse out of the cell through the cell membrane.

The other kind of movement is known as osmosis. Osmosis is a special kind ofdiffusion for fluids. Water moves through the cell membrane by osmosis.

A cell can have several smaller parts called organelles. The organelles are impor-tant for the life activities of the cell. They are controlled by the nucleus. One type of or-ganelle is the mitochondria, which release the energy the cell needs to perform its activi-ties. Vacuoles are also organelles, and they transport material through the cytoplasm inthe cell. Ribosomes and endoplasmic reticulum are responsible for forming and trans-porting protein in the cell.

Scientists have spent a lot of time studying human cells. The study of cells is calledcytology. Scientists have learned a lot about how cells work. However, they still havemore to learn.

Mitochondrion-.......~~~9~~~

Nucleus ---tf-':-~"'+fItf(9C

Cytoplasm

Nuclear Membrane L--'C~_ Vacuole......-- .......•-~~~~===~,Ribosomes

Endoplasmic Reticulum

© Mark Twain Media, Inc., Publishers 6

Your Body and How It Works Body Organization: A Closer Look at a Human Cell

Name: _ Date: _

Questions

1. What is the basic unit of the human body?

2. What are the four basic parts of a human cell?

3. What is the job of each part you listed for question #2?

4. What is diffusion?

5. What is osmosis?

6. What organelles are responsible for releasing energy in a cell?

7. What does a vacuole do?

8. What organelles are responsible for forming and transporting protein in a cell?

9. What is a cytologist?

10. Label the parts of the following diagram.

a. _

_ f.

~M'W"- ------- d.b. _ ~~~~#===-- e.c. _

---------- g.

© Mark Twain Media, Inc., Publishers 7

Your Body and How It Works Body Organization: A Closer Look at a Human Cell

Name: _ Date: _

Vocabulary Review

Write a good definition for each of the following words.

1. Cell membrane: _

2. Cytology: _

3. Cytoplasm: _

4. Diffusion: _

5. Endoplasmic reticulum: _

6. Genes: _

7. Mitochondria: _

8. Nuclear membrane: -----------------------------------------------9. Nucleus: _

10.0rganelles: _

11. Osmosis: _

12. Ribosomes: _

13. Vacuoles: _

© Mark Twain Media, Inc., Publishers 8