Cell Structure and Function

Cell Structure and Function

The Cell

What do you think? Read the two statements below and decide

whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you've read this lesson, reread the statements to see if you have changed your mind.

Before

Statement

After

3. Different organisms have cells with different structures.

4. All cells store genetic information in their nuclei.

Key Concepts

? How are prokaryotic cells and eukaryotic cells similar, and how are they different?

? What do the structures in a cell do?

Cell Shape and Movement

Cells come in many shapes and sizes. The size and shape of a cell is part of the function of the cell. Some cells, such as human red-blood cells, can be seen only by using a microscope. The cells can pass easily through small blood vessels because of their small size. Their disk shapes are important for carrying oxygen. Nerve cells have parts that jut out. These projections on nerve cells can send signals over long distances. Some plant cells are hollow. These hollow cells make up tubelike structures that can carry water and dissolved substances to parts of the plant.

The size and shape of a cell make it possible for the cell to carry out its functions. The parts that make up a cell have their own functions as well. A cell's parts are like the players on a football team who perform different tasks on the playing field. A cell is made up of different parts that perform different functions to keep the cell alive.

3TUDY#OACH

Use Prior Knowledge Before you read this lesson, look at the figures and headings to learn what the lesson is about. Write what you know about the cell on a piece of paper. As you read the lesson, fill in what you learned about the cell.

ACADEMIC VOCABULARY

function (noun) the purpose for which something is used

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Reading Essentials

Cell Structure and Function 23

Visual Check

1. Describe the location of

the cell wall.

Mitochondrion Ribosome

Plant Cell

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Central vacuole

Cytoskeleton

Vesicle

Reading Check 2. Describe What are cell membranes made of?

Visual Check 3. Identify Circle the names of two parts in the animal cell that are also found in the plant cell.

Genetic material Nucleus Nucleolus

Nuclear membrane

Chloroplast

Cell wall

Cell membrane Golgi apparatus

Cell Membrane

All cells have some parts, or structures, in common. One of these structures is a cell membrane. A cell membrane is a flexible covering that protects the inside of a cell from the environment outside the cell. You can see the cell membrane in both drawings on this page. Cell membranes are made of proteins and phospholipids.

Smooth endoplasmic reticulum

Animal Cell

Centriole

Lysosome

Cell membrane

Rough endoplasmic

reticulum

Vesicle

Genetic material Nucleus Nucleolus Nuclear envelope

Golgi apparatus

Ribosome

Cytoskeleton Mitochondrion

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

24 Cell Structure and Function

Reading Essentials

Cell Wall

Every cell has a cell membrane. But some cells also have a cell wall. Plant cells, fungal cells, bacterial cells, and some protists have cell walls. A cell wall is a stiff structure outside the cell membrane. A cell wall protects a cell from viruses and other harmful organisms. In some plant and fungal cells, the cell wall helps the cell keep its shape and gives it support.

Cell Appendages

If you look at a cell using a microscope, you might see structures on the outside of the cell. These appendages might look like hairs or long tails. They often help a cell move. Flagella (fluh JEH luh) (singular, flagellum) are long and taillike. They whip back and forth to move the cell. Cilia (SIH lee uh) (singular, cilium) are short, hairlike structures. They can move a cell or move molecules away from a cell. The cilia in your windpipe move harmful particles away from your lungs.

Cytoplasm and the Cytoskeleton

The fluid inside a cell is made of water, salts, and other molecules and is called the cytoplasm. The cytoplasm contains a cell's cytoskeleton. The cytoskeleton is made of threadlike proteins that are joined together. The cytoskeleton is a framework that gives a cell its shape and helps it move.

Cell Types

Microscopes helped scientists discover that cells can be grouped into two types. There are prokaryotic (proh ka ree AH tihk) cells and eukaryotic (yew ker ee AH tihk) cells.

Prokaryotic Cells

The genetic material in a prokaryotic cell is not surrounded by a membrane. Look at the drawing below. Prokaryotic cells also do not have many of the cell parts other cells have. Most prokaryotic cells are unicellular organisms and are called prokaryotes.

Reading Check

4. Describe the structure

of the cytoskeleton.

DNA Ribosome Cytoplasm

Flagellum

Cell membrane

Cell wall

Capsule

Visual Check

5. Name three parts of a

prokaryotic cell.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Reading Essentials

Cell Structure and Function 25

Key Concept Check 6. Compare and Contrast How are

prokaryotic cells and eukaryotic cells the same? How are they different?

SCIENCE USE V. COMMON USE

envelope Science Use an outer covering Common Use a flat paper container for a letter

Reading Check 7. Contrast smooth ER and rough ER.

Eukaryotic Cells

The cells of plants, animals, fungi, and protists are eukaryotic cells. The genetic material of eukaryotic cells is surrounded by a membrane. Every eukaryotic cell also has organelles--other parts that are surrounded by a membrane and have specialized functions. Eukaryotic cells are usually larger than prokaryotic cells.

Cell Organelles

The organelles of eukaryotic cells have different functions in the cell. Organelles help a cell carry out different functions at the same time. These functions include getting energy from food, storing information, and getting rid of waste material.

The Nucleus

The largest organelle inside most eukaryotic cells is the nucleus. The nucleus is the part of a eukaryotic cell that directs cell activities and contains genetic information stored in DNA.

DNA is in structures called chromosomes. The number of chromosomes in a nucleus is different for different species of organisms.

The nucleus also contains proteins and an organelle called the nucleolus (new KLEE uh lus). The nucleolus makes ribosomes, organelles that help produce proteins. Two membranes form the nuclear envelope that surrounds the nucleus. The nuclear envelope has many pores. Certain molecules, such as ribosomes and RNA, move into and out of the nucleus through these pores.

Manufacturing Molecules

You learned that proteins are important molecules in cells. Proteins are made of small organelles called ribosomes. A ribosome is not surrounded by a membrane. Ribosomes are in the cytoplasm of a cell. Ribosomes can be attached to an organelle called the endoplasmic reticulum (en duh PLAZ mihk ? rih TIHK yuh lum), or ER. ER with ribosomes on its surface is called rough ER. Rough ER is where proteins are produced. ER without ribosomes on its surface is called smooth ER. It makes lipids such as cholesterol. Smooth ER also helps remove harmful substances from a cell.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

26 Cell Structure and Function

Reading Essentials

Processing Energy

All living things must have energy to survive. Cells process some energy in specialized organelles called mitochondria (mi tuh KAHN dree uh) (singular, mitochondrion). Most eukaryotic cells contain hundreds of mitochondria. Some cells in a human heart can contain 1,000 mitochondria.

ATP A mitochondrion is surrounded by two membranes. Chemical reactions within mitochondria release energy. This energy is stored in high-energy molecules called ATP-- adenosine triphosphate (uh DEH nuh seen ? tri FAHS fayt). The energy in ATP molecules is used by the cell for growth, cell division, and transporting materials.

Chloroplasts The cells of some organisms, such as plants and algae, contain organelles called chloroplasts (KLOR uh plasts). Chloroplasts are membrane-bound organelles that use light energy and make food, a sugar called glucose, from water and carbon dioxide in a process called photosynthesis (foh toh SIHN thuh sus). The sugar has stored energy that can be used when the cells need it.

Processing, Transporting, and Storing Molecules

The Golgi (GAWL jee) apparatus is an organelle that looks like a stack of pancakes. It gets proteins ready for their specific jobs. It then packages the proteins into tiny membrane-bound, ball-like structures called vesicles. Vesicles are organelles that transport substances to other parts of the cell. Some vesicles in an animal cell are called lysosomes. Lysosomes help break down and recycle different parts of the cell.

Some cells also have structures called vacuoles (VA kyuh wohlz). Vacuoles are organelles that store food, water, and waste materials for a cell. A plant cell usually has one large vacuole. Some animal cells have many small vacuoles.

Make a half-book to record information about cell organelles and their functions.

Cell Organelles and Their Functions

Reading Check 8. Identify the types of cells that contain chloroplasts.

Key Concept Check 9. Explain the function of

the Golgi apparatus.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Reading Essentials

Cell Structure and Function 27

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