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.

The 64 codons in the genetic code give rise to the same amino acids in nearly all organisms, There is very little variaion. If the genetic code had evolved several times in the history off life, there would be many differences.

Chromosomes condense by supercoiling during mitosis. This makes the chromosomes visible.

The DNA replicates during interphase, not prophase.

The mitotic shows the speed of cell division, which can be used as a tool to identify cancer.

It is calculated by dividing the number of cells doing mitosis by the total number of cells.

Cell A is swollen turgid, it is in a hypotonic solution or an isotonic solution.

The cells B, C and D show increasing signs of plasmolysis, and so they must be in hypertonic solutions.

Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)

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

Multicellular organisms have properties that emerge from the interaction of their cellular components. (Emergent properties)

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.

Calculate specimen size using magnification?

First change the size measurement into µm units = 20000µm

Then divide by the magnification. 20000 / 3000 = 20 / 3 = 6.6 µm

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.

The 64 codons in the genetic code give rise to the same amino acids in nearly all organisms.
There is very little variation. This is evidence for a single common origin of life.

Differences in the frequency of amino acid use reflects the different genes in the two organisms.

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.

A fungal hypha has many nuclei in a hypha but no cross walls to divide the hypha into cells.

The lack of a membrane bound nucleus (nucleoid) classifies a cell as prokaryotic.

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.

Protein channels cross the membrane to allow hydrophilic substances to pass through the membrane.

The saline drip must be isotonic to human blood to not cause water gain or loss from tissues.

The first cells must have arisen spontaneously from non-living matter, probably in volcanic vents, but the universal nature of cell ultrastructure and of the genetic code makes it likely that this only happened once.