Bacteria + Viruses

• A species is a group of organisms that can interbreed and produce fertile offspring.
• Monera are single-celled organisms. They are both autotrophs and heterotrophs. They are prokaryote cells as they have no cell membrane. e.g bacteria
• Animals are complex multi-cellular organisms. They are heterotrophs and feed by ingestion. They reproduce sexually.
• Protists are mainly single-celled organisms. They have membrane-bound organelles and have multiple methods of getting food. They have a nucleus in their cells.
• Fungi are mainly multi-cellular. They are heterotrophs and feed by absorption. They have cell walls made of chitin and have nuclei in their cells. They reproduce asexually using spores.
• Plants are complex multi-cellular organisms. They photosynthesize to make food and reproduce asexually and sexually. They have nuclei in their cells and have a cellulose cell wall.
• Viruses have an outer protein coat and a nucleic acid.
• Viruses can be round, rod-shaped or complex.
• Viruses can be used in genetic engineering and the control of infections.
• Examples of human viruses are AIDS, the common cold, chicken pox, and cold sores.
• The virus attaches to a host cell, and inserts its nucleic acid into the cell’s cytoplasm. The nucleic acid takes over the cell's DNA and makes copies of itself.
• This is the structure of a bacterial cell.

  
• A cell wall surrounds all bacteria. Some bacteria have a gelatinous sheath around the cell wall. Others may have a dry capsule. Motile bacteria have flagella.
• A pathogen is a micro-organism that causes a disease.
• Coccus (round) bacteria cause sore throats and pneumonia.
• Bacillus (rod) bacteria cause tuberculosis and tetanus.
• Spirrilium (spiral) bacteria cause syphillis.
• Bacteria reproduce via binary fission. The cell divides in two, each of which contains a copy of the original DNA.
• This is a diagram of binary fission.

  
• Some bacteria can withstand unfavorable conditions by producing endospores. When conditions become suitable, the endospore absorbs water and breaks down.
• Photosynthetic bacteria have chlorophyll and use sunlight to make their own food. Chemosynthetic bacteria make food using energy from chemical reactions e.g. nitrifying bacteria. These are known as autotrophic bacteria.
• Saprophytes take in food from decaying organic matter. Parasites take in food from a live host and cause harm e.g. tetanus. These are known as heterotrophic bacteria.
• There are three kinds of symbiotic relationships. Mutualism, where both organisms benefit, Commensalism, where one organism benefits and the other is not harmed, and Parasitism, where one organism benefits and the other is harmed.
• Temperature, pH and oxygen concentration are all factors that may affect the growth of bacteria.
• Bacteria usually grow well between 20-30 degrees Celsius. Any lower may slow down the rate of growth.
• Aerobic bacteria require oxygen for respiration.
• Bacteria convert milk to products like cheese and yogurt.
• A substance is sterile if it is free from all microbes.
• Asepsis means excluding microbes from as much of the environment as possible.
• There are four stages in a growth curve for bacteria. Lag, log, stationary and death phase.
• Two methods of food processing are continuous flow processing, and batch food processing.
• In batch food processing a fixed amount of sterile nutrient is added to the micro-organisms in the bioreactor. At the end of processing the bioreactor is cleared out. The product is separated from the rest of the solution and is purified.
• In continuous-flow food processing nutrients are continuously fed into the bioreactor. ​At the same time, the culture medium (containing some micro-organisms) is continually withdrawn. This process can last weeks or months.