Grade 12 Biology unit 2: Microorganisms

The chapter says microorganisms are too small to be seen clearly by the unaided eye. Micro means very small, so you need a microscope to see them.

Most bacteria reproduce by asexual division, called binary fission. The DNA copies itself, the two DNA molecules separate, and the cell divides into two genetically identical daughter cells.

The three main bacterial shapes are cocci, bacilli and spirochaetes. Hyphae are the thread-like filaments of fungi, not a bacterial shape.

Gram-positive bacteria keep the purple crystal violet stain. This happens because their thick peptidoglycan layer holds the stain.

Table 2.1 says Gram-positive cell walls are thicker, at 20-80 nm. The 8-11 nm range belongs to Gram-negative cell walls, which are thinner.

The chapter lists the steps in order: heat fix, primary stain (crystal violet), add a mordant (Gram's iodine), decolorize with ethanol or acetone, then counterstain with safranin. Gram's iodine is the mordant.

Table 2.1 shows that Gram-negative cell walls have an outer membrane, and Gram-positive cell walls do not. Teichoic and lipoteichoic acids belong to Gram-positive walls, and a thick peptidoglycan layer is typical of Gram-positive walls.

The chapter says archaea are prokaryotic, single-celled and have no membrane-bound nucleus. They lack true peptidoglycan in their cell walls, and their membrane lipids have branched hydrocarbon chains.

The chapter describes methanogens as the archaea that generate methane. They are strictly anaerobic and live in places such as waterlogged soils and lake sediments. Extreme halophiles, hyperthermophiles and psychrophiles are other groups, but they are not named for making methane.

The chapter says the photosynthetic organism (usually an alga or cyanobacterium) provides energy from light and carbohydrates. The fungus supplies minerals and protection. Fungi lack chlorophyll, so they cannot make it.