Cells and Miocroscopy - B1

an organism is a living thing. unicellular organisms are made of only one cell, where multicellular organisms are made of many cells.

• nucleus - controls the activities of a cell and contains DNA
• cytoplasm - site of most chemical reactions
• cell membrane - controls the movement of substances in and out of a cell
• mitochondria - where energy is released in respiration (the site of respiration)
• ribosomes - site of protein synthesis
• cell wall - strengthens the cell
• chloroplasts - absorbs light to make food in photosynthesis
• vacuole - a store of cell sap

in eukaryotic cells, the DNA is inside a nucleus

in prokaryotic cells, the DNA is not inside a nucleus, and instead, there is a single loop of DNA. there may also be plasmids, which are rings of DNA.

each specialised cell has adaptations, which are features that enable the cell to perform a particular job.

• sperm cell - 
  • streamlined shape and tail allows it to swim
  • many mitochondria release a lot of energy for respiration
• nerve cell / neurone - 
  • long body allows info to be passed for long distances
  • branches allow info to be passed to many cells at a time
• muscle cell - 
  • many mitochondria release energy through respiration very quickly 
  • filaments allow contraction and relaxation

each specialised cell has adaptations, which are features that enable the cell to perform a particular job.

• root hair cells
  • hair like projection increases surface area which leads to faster absorption 
  • many mitochondria releases energy for transport of water and mineral ions
• xylem - 
  • lignin strengthens the walls, and is waterproof to prevent leaks
  • hollow tube allows water to travel through without nucleus or vacuole in the way
• phloem - 
  • tubes formed from living cells joined end to end
  • pores allow sugar to move through in either direction

as an organism develops, cells differentiate and their structures change to enable them to carry out different functions. they become specialised.

• in animals, most cells differentiate at a very early stage in development
• in plants, cells can differentiate throughout the life of the plant

some cells do not differentiate and remain unspecialised. these cells are called stem cells. a stem cell has the possibility to differentiate into any type of cell, or to reproduce to form new stem cells.

light microscope:

• low magnification
• low resolution
• readily available and cheaper
• cannot see some organisms or microorganisms

electron microscope:

• high magnification
• high resolution
• expensive
• enables cells to be studied in more detail 
• allows bacteria and subcellular structures to be seen
• has improved the scientific understanding of cells because of this

image size = magnification * real size

micrometres are 1000* bigger than nanometres