Animal and Plant Cell Structure and Function

Once students have investigated the cell as the basic unit of life, they focus on how eukaryote cells are systems, made up of smaller, interacting parts that contribute to the overall functioning of the cell. The cells of plants and animals share certain similarities, but they also have differences. It is these differences that result in the unique characteristics of each kind of organism.

• Within a eukaryotic cell, there are special structures called organelles that are responsible for particular functions.
• The cells of plants and animals have different structures to perform the specific functions of each organism.
• The nucleus tells all of the other organelles what to do. This is possible because the nucleus contains the cell’s DNA. DNA is an instruction manual for how the cell should look and what it should do.

• Why do eukaryotes have a nucleus?
• Why are proteins important for cells?
• How are the proteins that make up all organelles made?
• Why do eukaryotic cells have mitochondria?
• What is the function of the chloroplasts in plant cells?
• How do plant cells function differently from animal cells?
• Why don’t animal cells need a cell wall?

Misconception: Human cells are completely different from other animal cells, plant cells, and prokaryotic cells.

Fact: All cells, whether human, plant, or prokaryote, share certain similarities. All cells must perform essential life functions, and all cells share certain parts, including a cell membrane and cytoplasm.

Misconception: Individual cells do not need water to function.

Fact: Because cells are living things, cells need water to survive.

Animal : a kingdom of eukaryotic organisms that eat other organisms for energy, breathe oxygen, and undergo growth and reproduction

Chloroplasts : organelles in plant cells that use sunlight, carbon dioxide, and water to produce oxygen molecules and food for the plant through a process called photosynthesis; contain chlorophyll, which gives plants their green color

Function : the normal action of something or how something works

Mitochondria : organelles that are the power centers of the cell; combine sugar from food with oxygen from respiration to produce molecules the cell uses for energy (ATP)

Oucleus : a membrane-bound organelle that holds an organism’s genetic material (DNA)

Organelle : small parts that carry out specific functions in a cell

Organism : a complete living thing that has the ability to carry out all functions for life

Plant : a kingdom of eukaryotic organisms; includes organisms that contain chloroplasts in their cells to capture energy from sunlight for growth and development

Proteins : large, complex molecules that play many important roles in the cell

A Cell’s Structure and Function

Cells come in many different shapes and sizes. However, all cells, both eukaryote and prokaryote, have certain things in common. For example, all cells have cytoplasm and a cell membrane. The cell membrane is a protective membrane that surrounds a cell and selects what molecules can enter and exit the cell.

Ribosomes are structures in both prokaryotes and eukaryotes that build proteins according to the cell’s DNA. Genetic instructions from the DNA travel through the nuclear membrane to reach the ribosomes. Ribosomes then use the information in DNA to build proteins. Each cell builds proteins for its own uses, including for growth and repair. Ribosomes are the smallest and most common organelles in a cell. In eukaryotes, ribosomes either float freely throughout the cytoplasm or are attached to an organelle called the endoplasmic reticulum (pronounced en-doh-PlAZ-mik-ri-TIK-yuh-luhm).

The endoplasmic reticulum (ER) is a network of membranes where many proteins are built because many ribosomes attach themselves to it. The part of the ER that has ribosomes attached to it is called rough endoplasmic reticulum. Smooth endoplasmic reticulum has no ribosomes attached to it. Because of its role in making proteins, the ER is located near the cell nucleus.

The Golgi (pronounced GOHL-jee) complex is a series of membranes that adjusts the shape of proteins and transports them to their place in the cell. The Golgi complex transports proteins by wrapping them in vesicles—small sacs that bud off from a membrane.

Plant vs. Animal Cells

Animal cells and plant cells share most of the same organelles because they are both eukaryotes, but there are some differences. The following are organelles that differ between a plant cell and an animal cell:

Vacuole

Vacuoles are sac-like organelles that store water for the cell. Vacuoles in animal cells are small and float freely in the cytoplasm. Plants cells contain a larger central vacuole. Up to ninety percent of a plant cell may be taken up by the central vacuole. This vacuole fills with water and waste from the cell. A plant wilts if its cells lose water in their central vacuoles.

Chloroplasts

Chloroplasts are only found in plant cells. Chloroplasts contain a green pigment called chlorophyll. This pigment gives plant cells their green color. It also absorbs sunlight, which begins a process of turning carbon dioxide and water into a kind of sugar called glucose, which plants use for energy, growth, and development. Animals do not have chloroplasts and so they must eat other organisms for energy and nutrients.

Cell Wall

A cell wall is a stiff, shell-like wall that surrounds the cell membrane of plant cells and helps plants stand up. Plant cell walls are made of cellulose, which is a type of sugar molecule. Animals often have skeletons (or exoskeletons in the case of insects) to help support them. Because animal cells are not confined by a rigid cell wall, they have developed more kinds of cells, especially those that enable movement.

Centrosome

In this lesson, students develop animal and plant cell models to investigate the phenomena of how the different parts of a cell contribute to how the cell functions as a whole and then analyze single-celled organisms with microscopes. Students apply what they know about plant and animal cells and their observations of single-celled organisms to figure out the relationship between the phenomena of structure and function in a cell.