Biology - Topic 1

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  • Created by: Rianne
  • Created on: 10-04-13 16:39

CELLS AND MICROSCOPY

All animals and plants are made of cells. Animal and plant cells have features in common, such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall, and often have chloroplasts and a permanent vacuole. Note that cells may be specialised to carry out a particular function.

  • Animal Cell
  • 4 THINGS ANIMAL AND PLANT CELLS HAVE IN COMMON:
  • Nucleus - Cotains DNA that controls what the cell does.
  • Cytoplasm - Gel-like substance where most of the chemical reactions happen
  • Cell membrane - Holds the cell together and controls what goes in and out
  • Mitochondria - The are where most of the reactions for respiration take place. Respiration releases energy that the cell needs to work.
  • Plant Cell
  • 3 EXTRAS THAT ONLY THE PLANT CELLS HAVE:
  • Rigid cell wall - Made of cellulose, gives support for the cell
  • Large vacuole - Contains cell sap, a weak solution of sugar and salts
  • Chloroplasts - Where photosynthesis occurs. They contain a green substance called chlorophyll.

Bacterial Cells Have No Nucleus

Using electron microscopes we now know that bacteria have a cell wall. This is similar to a plant cell wall but is more flexible. Bacteria do not have a nucleus. They do have two types of DNA – plasmid and chromosomal. The chromosomal DNA carries most of the genetic information. Plasmid DNA forms small loops and carries extra information. Some bacteria have a flagellum – a whip like tail. This helps the bacteria to move itself along. When we talk about these flagellum tails in multiple bacteria, we call them flagella.

  • Bacterial cells are alot smaller than plant cells and have these features:
  • Chromosomal DNA (one long circular chromosome) controls the cell's activities and replication. It floats free in the cytoplasm (not in a nucleus)
  • Plasmids are small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for things like drug resistance, and can be passedbetween bacteria.
  • The flagellum is a long, hair-like structure thatrotates to make the bacterium move.
  • The cell is supported by a cell wall

Cells are studied using microscopes

  • Microscopes let us see things that we cant see with the naked eye
  • Light microscopes were invented in the 1590's. They let us see things like nuclei, chloroplasts and mitochondria.
  • Electron microscopes were invented in the 1930s. they let us see much smaller things in more detail like the internal structure of mitochondria and chloroplasts, and even tinier things like plasmids.
  • You need to be able to calculate magnification.Magnification is how much bigger the image is than the specimen (the sample you're looking at)
  • Its calculated by using this formula:
  • Magnification = length of image ÷ length of specimen

DNA - A DOUBLE HELIX OF PAIRED BASES

  • A DNA molecule has two strands coiled together in the shape of a double helix ( two spirals)
  • The two strands are held together by chemicals called bases. There are four different bases  - 
  • Adenine

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