2.2 Cell Structure and Function Study Guide

2.2 Cell Structure and Function (Bio.2.2)

Explore this Phenomenon

The pictures above show different types of cells. The cell types look different, even though they all have to perform the same functions to stay alive.

1. What do you think causes the cells to look different?
2. What are three questions you could investigate to figure out why cells look different

Bio.2.2 Cell Structure and Function

Ask questions to plan and carry out an investigation to determine how (a) the structure and function of cells, (b) the proportion and quantity of organelles, and (c) the shape of cells result in cells with specialized functions. Examples could include mitochondria in muscle and nerve cells, chloroplasts in leaf cells, ribosomes in pancreatic cells, or the shape of nerve cells and muscle cells. (LS1.A)

The structures in a cell affect how it functions. As you read this chapter, pay attention to the different structures in cells, and how these structures affect the cell’s function.

Cell Structure: What are cells made of?

A close-up view of a spider web? Some sort of exotic bacteria? What do you think this is?

This is actually a nerve cell, the cell of the nervous system. This cell carries signals from one part of your body to another. Why are nerve cells shaped like this? Why aren’t all cells shaped like this?

Understanding the structure and function of cells is essential to understanding how living organisms work. To understand why cells have different structures, you need to first understand the basic components of the cell, which include the:

• Cell membrane
• an area for DNA
• cytoplasm

The Plasma Membrane and Cytoplasm

All cells have a cell membrane. The cell membrane is a double layer of specialized lipids, known as phospholipids, along with many special proteins. The function of the cell membrane is to control what moves in and out of the cell.

The cell membrane is semipermeable, which means that some molecules molecules can go through the cell membrane while others can't. Without a cell membrane, a cell would be unable to maintain a stable internal environment separate from the external environment.

Cells also share an internal fluid-like substance called the cytoplasm. The cytoplasm is composed of water and other molecules, including enzymes that speed up the cell’s chemical reactions

The Nucleus and Chromosomes

The nucleus is a membrane-enclosed structure that contains most of the genetic material, or DNA, of the cell. The nucleus is surrounded by a membrane, which controls which molecules go in and out of the nucleus.

Inside the nucleus are the chromosomes, which consist of DNA that is wrapped in special proteins. The genetic information on the chromosomes is stored, made it available to the cell when necessary, and also duplicated when it is time to pass the genetic information on when a cell divides. All the cells of a species carry the same number of chromosomes. For example, human cells each have 23 pairs of chromosomes. Each chromosome in turn carries hundreds or thousands of genes that encode proteins that help determine traits as varied as tooth shape, hair color, or kidney function.

Not all cells have a nucleus. The DNA in bacterial cells is not enclosed in a membrane.

The Other Organelles

Cells contain organelles, which are specialized structures. Each organelle has a different function. See the table below for a list of organelles and their functions.

Plant Cells

Plant cells differ in some ways from animal cells. Use the table above to identify organelles that are found in plant cells but not in animal cells. Consider the functions of these organelles. How does having a different structure affect the function of plant cells?

First, plant cells are unique in having a large central vacuole that holds a mixture of water, nutrients, and wastes. A plant cell's vacuole can make up 90% of the cell’s volume. In animal cells, vacuoles are much smaller.

Second, plant cells have a cell wall, animal cells do not. A cell wall gives the plant cell strength, rigidity, and protection. Although bacteria and fungi also have cell walls, a plant cell wall is made of a different material.

Third, plant cells have chloroplasts. These organelles convert light energy from the sun into chemical energy that can be stored and used by cells.

Examples of Various Structure and Function

All cells have to carry out some functions to stay alive. For example, cells must all be able to take in energy and reproduce. Cells may also have specialized functions. For example, nerve cells must be able to send signals, and muscle cells must be able to contract. Cells may have different structures to enable them to perform their function. How do the structures and function of the following types of cells compare?

• Plant cell vs. Animal cell
• Nerve cell vs. Muscle cell
• Normal blood cell vs. Sickle blood cell
• Prokaryote vs. Eukaryote

Putting It Together

The pictures above show different types of cells. The cell types look different, even though they all have to perform the same functions to stay alive.

1. How have your ideas about what causes the cells to look different changed?
2. Based on your understanding of cell structure and function, predict the function of cells with various structures. For example, what might be a function of a cell that contains high numbers of mitochondria?