Chapter 1 Section 2

Imagine that you are in California standing next to a giant redwood tree. You have to bend your head way back to see the top of the tree. How do you thing redwoods grow so large? How do they carry out all the functions necessary to stay alive? We will be using this example to learn about tiny cells, structures found in plant cells and the differences between the tiny cells in plants and animals. Think about this….

Animal and Plant Cells Tiny cell structures, called organelles, carry out specific functions within the cell. Similar to the way your stomach, lungs, and heart have different functions in your body, each organelle has a different function within the cell. Organelles

Entering a plant’s cell is a bit difficult. You must first pass through the cell wall. A cell wall is a rigid layer of nonliving material that surrounds the cells of plants and some other organisms. The cell wall is made of a tough, yet flexible, material called cellulose. Think of a stalk of celery and you will have a good idea of what cellulose is. Celery contains a lot of cellulose. The cells of animals and some other organisms lack cell walls. The plant’s cell wall helps protect and support the cell. This is why the giant redwood trees can grow so tall. Although the cell wall is stiff, many materials, including water and oxygen, can pass through the cell wall easily. Cell Wall

As you pass through the cell wall, the next structure you encounter is the cell membrane. All cells have cell membranes. In cells with cell walls, the cell membrane is located just inside the cell wall. In other cells, the cell membrane forms the outside boundary that separates the cell from its environment. One of the cell membrane’s main functions is to control what substances come into and out of a cell. Everything the cell needs, from food to oxygen, enters the cell through the cell membrane. Harmful waste products leave the cell through the cell membrane. You can think of a cell membrane like a window screen. The screen keeps insects out of a room but allows air to enter and leave. Cell Membrane

The large oval structure inside the cell is called the nucleus and it acts as the cell’s brain. You can think of the nucleus as the cell’s control center, directing all of the cell’s activities The nucleus is surrounded by a nuclear membrane. Just as the cell membrane protects the cell, the nuclear membrane protects the nucleus. Materials pass in and out of the nucleus through small openings, or pores in the nuclear membrane. Nucleus

Plant Cell

Animal Cell

The nucleus knows how to direct the cell through the thin strands floating directly ahead in the nucleus. These strands are called chromatin. They contain the genetic material, the instructions that direct the functions of a cell. For example, the instructions in the chromatin ensure that leaf cells grow and divide to form more leaf cells. The genetic material is passed on to each new cell when an existing cell divides. Chromatin

Just outside the nucleus is the cytoplasm, the region between the cell membrane and the nucleus. The fluid in the cytoplasm is constantly moving. Many cell organelles are found in the cytoplasm. The organelles function to produce energy, build and transport needed materials and store and recycle waste. Organelles in the Cytoplasm

Mitochondria are rod shaped structures or organelles. Mitochondria are called the “powerhouses” of the cell because they produce most of the energy the cell needs to carry out its functions. Muscle cells and other very active cells have large numbers of mitochondria. Mitochondria

Farther into the cytoplasm is a maze of passageways called the endoplasmic reticulum. These passageways carry proteins and other materials from one part of the cell to another. Ribosomes – Attached to the outer surface of the endoplasmic reticulum are small grain-like bodies called ribosomes. Other ribosomes are found floating in the cytoplasm. The ribosomes release some proteins through the wall of the endoplasmic reticulum. From the interior of the endoplasmic reticulum, the proteins will be transported to the Golgi bodies. Endoplasmic Reticulum and Ribosomes

Golgi bodies look like a flattened collection of sacs and tubes. They can be thought of as a cell’s mailroom. The Golgi bodies receive proteins and other newly formed materials from the endoplasmic reticulum, package them, and distribute them to other parts of the cell. The Golgi bodies also release materials outside the cell. Golgi Bodies

The green structures floating in the cytoplasm are called chloroplasts. Only the cells of plants and some other organisms have these structures. Chloroplasts capture energy from the sunlight and use it to produce food for the cell. It is the chloroplasts that give plants their green color. Chloroplasts

The large, round, water-filled sac floating in the cytoplasm is called a vacuole. The vacuole is the storage area of the cell. Most cells have one large vacuole. Vacuoles store food and other materials needed by the cell. They can also store waste products. Most of the water in plant cells are stored in the vacuoles. When the vacuoles are full of water, they make the cell plump and firm. Without water in the vacuoles, the plant wilts. Vacuoles

Lysosomes are small round structures that contain chemicals that break down large food particles into smaller ones. Lysosomes also break down old cell parts and release the substances so they can be used again. You can think of lysosomes as the cell’s clean up crew. Lysosomes

The plant and animal cells that you just learned about are very different from the bacterial cell. Bacterial cells are smaller than plant and animal cells. While a bacterial cell does have a cell wall and a cell membrane, it does not contain a nucleus. Specialized Cells In many celled organisms, the cells are often very different. Think of the differences in you body. You have skin, bones, muscles, blood, a brain, a liver, a stomach, and so on. Each of these body parts carries out a different function. The structure of each kind of cell is suited to the unique function it carries out within the organism Bacterial cells