Cells

All living things are made up of cells. The structures of different types of cells are related to their functions. Animal cells and plant cells have features in common, such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant and algae cells also have a cell wall, and often have chloroplasts and a permanent vacuole. Bacterial and yeast cells have different structures to animal and plant cells. Dissolved substances pass into and out of cells by diffusion. Animal and plant cells Function of cells which animal and plant cells have in common Nucleus - contains genetic material, which controls the activities of the cell. Cytoplasm - most chemical processes take place here, controlled by enzymes Cell membrane - controls the substances into and out of the cell Mitochondria - most energy is released by respiration here. Ribosomes - protein synthesis happens here.   Plant cells have extra parts: Extra parts of plant cells Cell wall - strengthens the cell Chloroplasts - contain chlorophyll, which absorbs light energy for photosynthesis Permanent vacuole - filled with cell sap to help keep the cell turgid Make sure you can label diagram of animl and plant cells.   Bacterial cells A bacterium is a single celled organism. A bacterial cell has a different structure to an animal or plant cell. It has cytoplasm, a membrane and a surrounding cell wall, but the genetic material in a bacterial cell is not in a distinct nucleus. Yeast Yeast is a single celled organism. Like bacterial cells, yeast cells have cytoplasm and a membrane surrounded by a cell wall. But unlike bacterial cells yeast cells have a nucleus.   Specialised cells Cells may be specialised for a particular function. Their structure will allow them to carry this function out. Here are some examples: Leaf cell - Absorbs light energy for photosynthesis - packed with chloroplasts, regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight. Root hair cell - Absorbs water and mineral ions from the soil - long 'finger-like' process with very thin wall, which gives a large surface area. Sperm cell - fertilises an egg cell - female gamete - the head contains information and an enzyme to help penetrate the egg cell membrane. The middle section is packed with mitochondria for energy. The tail moves the sperm to the egg. Red blood cells - Contains haemoglobin to carry oxygen to the cells - thin outer membrane to let oxygen diffuse through easily. Shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin.   Diffusion Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allow this to happen.  Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. This is how the smell of cooking travels around the house from the kitchen, for example. Two example of diffusion fown concentration gradients Gut - digested food product - gut cavity - blood in capillary of villus  Lungs - oxygen - alveolar air space - blood circulating around the lungs. Remember, particles continue to move from a high to a low concentration while there is a concentration gradient. In the lungs, the blood will continue to take in oxygen from the alveolar air spaces provided the concentration of oxygen there is greater than in the blood. Oxygen diffuses across the alveolar walls into the blood, and the circulation takes the oxygen rich blood away.