Cell walls are a structure of plant cells. They are the outermost layer of the cell and are strong and rigid due to their cellulose content. They allow transmission of water, oxygen and carbon dioxide into and out of the cell, as well as provide protection of the cell contents and support of its structure. Plants and animals both have a cell membrane. On plants, the cell membrane is located within the cell wall. Animal cell membranes are made of cholesterol. Cell membranes are selectively permeable, meaning they allow only certain substances to pass through. The cell membrane functions as protection, support and a gateway for substance transmission.
All cells have a nucleus, nuclear membrane and cytoplasm. The nucleus is a large, oval-shaped structure that controls all functions within the cell. It acts as the brain of the cell. The nuclear membrane protects the nucleus and controls the transmission of substances through its selectively-permeable structure. Cytoplasm is a thick, clear substance found within all cells. Its function is to protect the organelles and provide support to the cell's structure. Centrioles are found in animal cells and are used in cell division.
ER is found in all cells. It attaches to the nucleus and zigzags away from it. There are two types of ER: smooth and rough. Rough ER is found near the nucleus, covered in ribosomes, while smooth ER is further away and lacks ribosomes. The function of ER is to help transfer materials through the cell. Rough ER, in combination with ribosomes, plays a role in protein synthesis. Ribosomes also are found in all cells. They are small organelles that attach to ER, but they also occur throughout the cell. They are composed of ribonucleic acid and are created within the nucleus.
Shaped like a bean, mitochondria are considered the powerhouses of all cells. They break sugar molecules down to produce energy for the cell. Mitochondria have two membranes, a smooth outer membrane, and a rough inner membrane. During the process of energy creation, the mitochondria transfer chemicals across its membranes.
Plant vacuoles are large, while animal vacuoles are small. They are sacs filled with fluids. These fluids consist of food, water and waste. The reason for plant vacuoles to be larger is the greater need for food storage in plants. While vacuoles store the cell's various fluids, vesicles are smaller and often serve as transports within the cell. If one of the other organelles needs food or water, the vesicles run the needed supplies to their destination.
Vesicles often transfer fluids to and from the Golgi apparatus, or Golgi body. Appearing like stacks of ribbon, Golgi bodies receive fluids from vesicles and determine where they should be distributed to. New vesicles pinch off of the Golgi body and move to their final destination.
Lysosomes are small, round organelles. They are surrounded by a semipermeable membrane. Lysosomes are uncommon in plants. The role of the lysosome is to break down food molecules. They also serve as clean up of old cell parts, digesting them and turning them into food or waste.
Chloroplasts are only found in plants. Chloroplasts are responsible for photosynthesis, converting light energy into chemical energy. Chloroplasts contain the green pigment chlorophyll. Two membranes surround each chloroplast: an outer membrane and an inner membrane.