All cells have a cell membrane that separates the inside of the cell from its environment. The cytoplasm is a jelly-like fluid and DNA, which is the cells genetic material. The first category is eukaryotic cells. They have organelles, which include the nucleus and other special parts. Eukaryotic cells are more advanced complex cells. They can be found in plants and animals. The second category are prokaryotic cells. They do not have a nucleus or membrane enclosed organelles. They do have genetic material but it is not contained within a nucleus. Prokaryotic cells are always one celled, or unicellular organisms such as bacteria. Organelles are the specialized parts of a cell that have unique jobs to perform. The organelle known as the nucleus is the control center of the cell. The nucleus contains DNA or genetic material. Our DNA dictates what that cell is going to do and how and when it is going to do it. Chromatin is the tangled, spread out form of DNA found inside the nuclear membrane. When a cell is ready to divide, DNA condenses into structures known as chromosomes. The nucleus also contains a nucleolus, which is a structure where ribosomes are made. After ribosomes leave the nucleus, they will have the important job of synthesizing proteins. Outside the nucleus, the ribosomes and the rest of the organelles float around the cytoplasm. A vesicle is a membrane bound container, a vacuole is an example of a vesicle and they have the ability to move material around. Ribosomes can wander around freely within the cytoplasm and some even attach to the endoplasmic reticulum. The rough ER has ribosomes attached to it, while the smooth ER does not. The ER is a membrane enclose passageway for transporting materials such as the proteins synthesized by ribosomes. Proteins and other materials emerge from the ER in small vesicles where the Golgi apparatus (Golgi body) receives these vesicles. As proteins move through the Golgi body, they are customized into forms that the cell can use. The Golgi body does this by folding the proteins into usable shapes. They also have the ability to add other materials onto the proteins such as lipids or carbohydrates. Vacuoles are sac-like structures that store different materials. In a plant cell, the central vacuole stores water. The cytosol is a dissolved material, its fluid and it contains solutes inside it. Picture it as the aqueous part of the cytoplasm. There are concentration gradients within the cell, which tells us that the cytosol is complex. Lysosomes are garbage collectors that take in damaged or worn out cell parts. They are filled with enzymes that break down this cellular debris. We also have the centriole, which is part of what’s called the centrosome. It is important in positioning within the cell. The centrioles can be found in pairs and move towards the opposite ends of the poles of the nucleus when cell division takes place. The mitochondrion is an organelle that is the powerhouse for both animal and plant cells. During cellular respiration, the mitochondria make ATP molecules that provide the energy for all the cells activities. Cells that need more energy have more mitochondria. Meanwhile, the cell maintains its shape through a cytoskeleton. The cytoskeleton includes the thread-like microfilaments, which are made of protein, and microtubules, which are thin hollow tubes. Plants are photoautotrophic and they capture sunlight for energy. They have cells with an organelle known as the chloroplast, which is where photosynthesis takes place. It is green because it has a green pigment called chlorophyll. Plant cells also have a cell wall outside of their cell membranes that shape, support, and protect the plant cell. Animal cells never have a cell wall. There tons of unique structures that some cells have. In humans, the respiratory tract is lined with cells that have cilia. These microscopic hair-like projections move in waves to help trap inhaled particles in the air and expels them when I cough. Another unique feature in some cells is flagella. Some bacteria have flagella and its flagellum is a little tail that can help a cell move or propel itself. The only human cell that has a flagellum is a sperm cell.