Pasteur's famous experiments with swan neck flasks showed that broth kept in a flask where no dust could settle in the nutrient medium, and thus no living cells could get in, would not go mouldy.

This disproved the theory of spontaeous generation.

Cholesterol is a component of animal cell membranes. Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.

Students are expected to be able to identify organelles from microscope images of cells. The nucleus is distinctive because it is about 10µm in size, and it has black dots in it, chromatin, and sometimes one or more dark patches within the nuclear membrane. It also has a double membrane, not often easily visible.

The resolving power, or resolution, is the ability to separate objects, to produce separate images of two objects.

According to cell theory, living organisms are composed of cells.
Cells come from pre-existing cells and cells are the smallest using of life.

Calculate the magnification of an electron microscope image from a scale bar?

Convert the ruler measurement to the same units written on the scale bar, in this case 25mm is 25000µm

then divide the ruler measurement 25000 by the number on the scalebar, 25.

Remember MR H GREN. These letters represent the seven characteristics of living things.

Stem cells can differentiate and become specialised cells.
They often take on the features of the cells around them.
Rod cells, cone cells, and erythrocytes are specialised cells and cannot differentiate.

Many transmembrane proteins are involved in transport of molecules across membranes. These can either provide a sort of molecular pore through which ions or molecules can pass (facilitated diffusion), or they can use ATP to actively move molecules, even against the concentration gradient (active transport).These are just two examples, transport can also occur by simple diffusion through the phospholipid bilayer, or by endocytosis.

Facilitated diffusion does not require energy from ATP so this process is active transport. It can move sodium ions against the concentration gradient, but this is not always the case.

Endocytosis is the process where a substance is surrounded by the plasma membrane which forms a vesicle inside the cell that then moves into the cytoplasm, separating from the plasma membrane.

Comment: The multicellular condition allows for differentiation into cells of different types and also replacement of cells when injured or damaged.

Comment: There are approximately 8 cells across a diameter so 250/8 = 33 μm.
Beware of the units, mm are 1000 times bigger than µm.

There are actually four types of membrane transport which are required in DP Biology, Simple diffusion, facilitated diffusion, osmosis and active transport.

The ribosome is too small to be seen in the electron microscope, the other organelles were seen in the light microscope before the electron microscope was invented.

White blood cells engulf bacteria by endocytosis, the intake of solid particles by a cell membrane.

Ribosomes on the RER manufacture protein. This is packaged in vesicles by the Golgi Body and moves to the surface of the cell where the vesicle and plasma membrane fuse and exocytosis of the protein occurs.

Pasteur demonstrated that broth would go cloudy only when air was allowed to contact the broth, bringing microbes. He disproved Spontaneous Generation.