A cell is the smallest structural and functional unit of an organism, typically microscopic and containing cytoplasm and a nucleus enclosed in a membrane.
Plant cells do not have a cell wall or chloroplasts but plant cells do. Animal cells are round and irregular in shape, while plant cells have a fixed, rectangular shape.
1. Bone cells are responsible for creating new arms for the growth of bones.
2. Muscle cells contain protein filaments that slide past one another, producing a contraction that allows us to produce force and motion.
3. Nerve cells transmit messages from one part of the body to another.
4. White blood cells defend against infection, while red blood cells carry oxygen throughout the body and take carbon dioxide out of the body.
In multicellular organisms, cells are organized into tissues, organs, and organ systems. For example, your brain is made up of mostly nerve tissue, which consists of nerve cells that relay information to other parts of your body. Your brain is made of different kinds of tissues that function together. For example, the brain also has blood vessels that carry the blood that supplies oxygen to your brain cells. Your brain is part of your nervous system, which directs body activities and processes.
1. The digestive system consists of the mouth, the salivary gland, the epiglottis, the esophagus, the stomach, the liver, the gallbladder, the pancreas, the small intestine, the large intestine, and the rectum. You put food in your mouth, then saliva is released by the salivary glands to break down starches, starting chemical digestion. Your epiglottis closes off your windpipe, and the food travels down your esophagus and into your stomach. Here, most chemical and mechanical digestion occur. At this point, the food is a thick liquid that is released into the small intestines in increments. In the small intestine, most chemical digestion and nutrient absorption take place. Once the food enters, bile is released from the gallbladder to help break up large fat particles. Here the pancreas also releases digestive enzymes that break down carbohydrates, proteins, and fats. The water and undigested food that is left moves from the small intestine into the large intestine. Here the water is absorbed into the bloodstream and the remaining material is ready for elimination. The end of the large intestine is the rectum. Here, the waste material is compressed into solid form. It then exits the body from the anus.
2. The cardiovascular system, or circulatory system, is made up of the heart, the blood vessels, and the blood. The heart pumps blood throughout the body through blood vessels. The blood vessels, made up of arteries, capillaries, and veins, take blood from the heart to the lungs and back to the heart. They also take blood from the heart to the whole body, then back to the heart. This is how the blood travels throughout the body.
3. The nose, the pharynx, the trachea, the bronchus, and the lungs make up the respiratory system. Air enters the body through the nose or the mouth. Nose hairs trap large particles from entering the system. From the nose, air enters the pharynx, which helps warm and moisten the air. Then it moves into the trachea which produces mucus. Air moves from the trachea into the left and right bronchi, which take air into the lungs. The trachea and bronchi also warm and moisten the air. Inside the lungs, the bronchi branch into smaller and smaller tubes. At the end of these small tubes are the alveoli. Here, gasses can move between air and blood.
As you can imagine, all three of these systems interact. For example, the water and nutrients from the digestive system get absorbed into the bloodstream, which is part of the cardiovascular system. Another example would be gasses going from the respiratory system to the cardiovascular system in the alveoli.
A Paramecium is a genus of unicellular protozoa, commonly studied as a representative of the ciliate group. They are widespread in freshwater, brackish and marine environments, and are often very abundant in stagnant basins and ponds. It is just like other unicellular organisms, and uses many of the same things to survive, such as cilia and vacuoles.