Biology Unit 1.5 Cell Structure

• All living cells contain some sort of DNA, this varies between eukaryotic cells and prokaryotic cells
• The presence of DNA means that a new cell can be formed from an old cell, as genetic material is able to be stored and transferred
• Cytoplasm is found within the boundary of a cell
• The plasma membrane surrounds the cell and encloses all the cell contents
• In all cell types, the plasma membrane has two layers and this is called a bilayer
• The cell structure of organisms determines whether they are prokaryotic or eukaryotic
• Prokaryotes have the simplest cell structure, being the first organisms to evolve on Earth and have been classified into two domains: bacteria or archaebacteria
• Bacteria or Eubacteria - 'true' bacteria, includes commonly known bacteria
• Archaebacteria or Archaea - typically found in extreme environments such as high temperatures and salt concentrations and include methanogens
• Prokaryotic cells are small
• Prokaryotes have cells that lack a nucleus 
• The cytoplasm of prokaryotic cells is not divided into compartments, it lacks membrane-bound organelles
• Prokaryotic ribosomes are structurally smaller (70S)
• Prokaryotes do not have a nucleus, but they do have genetic material
• DNA in prokaryotes is located in the nucleoid
• Plasmids are small loops of DNA that are separate from the main circular DNA molecule
• Prokaryotic cytoplasm is very similar to the cytoplasm of any other cell and is the site of many cellular reactions
• The cell membrane of prokaryotes is composed of a lipid bilayer
• Most prokaryotes have a cell wall containing a glycoprotein
• The cell wall acts as protection, maintains the shape of the cell and prevents the cell from bursting
• Some bacteria are able to be classified because of their cell wall structure
• Eukaryotic cells have a more complex ultrastructure than prokaryotic cells
• The cytoplasm of eukaryotic cells is divided up into membrane-bound compartments called organelles
• The compartmentalisation of the cell is advantageous as it allows optimal conditions to be maintained for certain processes, and enzymes and substrates to be localised and therefore available at higher concentrations
• Animal cells contain centrioles and microvilli
• Plant cells have a cellulose cell wall, large permanent vacuoles and chloroplast
• In complex multicellular organisms, eukaryotic cells become specialised for specific functions
• Metabolism - all the enzyme-catalysed reactions occurring in a cell, including cell respiration
• Reproduction - the production of offspring. It may be sexual or asexual
• Homeostasis - the ability to maintain and regulate internal conditions within tolerable limits, including temperature
• Growth - the permanent increase in size
• Response - (or sensitivity), the ability to respond to external or internal changes (stimuli) in their environment. Thus improving their chance of survival
• Excretion - the disposal of metabolic waste products, including carbon dioxide from respiration
• Nutrition - the acquisition of energy and nutrients for growth and development, either by, absorbing organic matter or by synthesising organic molecules (e.g. photosynthesis)
• Mitochondria are present to provide energy through respiration
• The cell membrane controls movement of materials in and out of the cell to maintain homeostasis
• Ribosomes are present to produce proteins for growth and repair, in addition enzymes for vital cell functions
• Vacuoles are used for digestion purposes and also to store waste substance
• Cilia or flagella are used for movement of the organism in response to changes in the environment 
• Eukaryotic cells exist in three kingdoms, animal, plat and fungal