Edexcel Biology Additional Science Revision

Additional Science Revision

BIOLOGY

TOPIC 1;

Cells and Microscopy;

-Organelles are tiny structures that carry out specific jobs, for example the nucleus and mitochondria.

-Nucleus contains DNA that controls what the cell does.

-Cytoplasm is a gel-like substance where most of the chemical reactions happen.

-Cell Membrane holds the cell together and controls what goes in and out.

-Mitochondria is where most chemical reactions for respiration take place (respiration releases energy that is needed for the cell to work).

-Rigid Cell Wall is made of cellulose and gives support for the cell.

-Large Vacuole contains cell sap which is a weak solution of sugar and salts.

-Chloroplasts are were photosynthesis occurs, they contain chlorophyll.

-Bacterial cells have NO nucleus and are a lot smaller than plant and animal cells. The cell is supported by a cell wall.

-They contain Chromosomal DNA which controls the cell’s activities and replication

-Plasmids which are small loops of extra DNA that aren’t part of the chromosome. Plasmids contain genes for things like drug resistances and can be passed between bacteria.

-Flagellum (flagella) which is a long, hair-like structure that rotates to make the bacterium move.

-Microscopes are used to learn about the structure and the function of cells of which organisms are made.

-In light microscopes, light passes through a specimen and then through magnifying lenses so you see the object much bigger than it actually is, these were invented in the 1590s and lets us look at things such as nuclei, chloroplasts and mitochondria.

-in the 1930s the electron microscope was invented. This uses a beam of electrons to magnify specimens up to about 2million times. They also produce very clear images.

-Light microscopes show us that bacteria do not have a nuclei whereas Electron microscopes show us that bacterial cells contain two types of DNA.

-Magnification is how much bigger the image is than the sample you’re looking at.

Magnification= length of image / length of specimen

DNA;

-Gene is a section of a molecule of DNA that codes for a specific protein

-a DNA molecule has two strands coiled together in the shape of a double helix

-the strands are held together by bases, there are four different bases (Adenine, Cytosine, Guanine and Thymine)

-the bases are paired A-T and C-G and they are paired by weak hydrogen bonds

-the order of the bases in DNA contains the information needed to form the proteins for body cells.

-In the 1950s Maurice Wilkins and Rosalind Franklin were studying the structure of DNA using X-Rays. They worked out that DNA had a helical structure by directing beams of x-rays onto purified DNA, from the patterns they could work out how the groups of atoms in the DNA molecule were arranged.

-James Watson and Francis Crick used these ideas as well as the knowledge of the base pairs to make a model of the DNA molecule where all the pieces fitted…