cell structure

• Describe the plasma membrane

  found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells --> made mainly of lipids and protein
• function of the plasma membrane

  controls which substances move in/out of the cell + has receptor molecules so it can respond to chemicals e.g. hormones
• describe the cell wall

  A rigid structure that surrounds plant cells. It's made mainly of cellulose
• function of the cell wall

  supports plant cells
• describe the nucleus

  large organelles surrounded by a nuclear envelope (double-membrane) which contains many pores. It contains chromatin (DNA and protein) and a nucleolus
• function of the nucleus

  controls the cell's activities by controlling transcription of DNA - contains instructions to make proteins. The pores allow substances in/out of the nucleus. The nucleolus makes ribosomes
• Describe lysosomes

  A round organelle surrounded by a membrane, with no clear internal structure
• function of lysosomes

  contains digestive enzymes - separated from the cytoplasm by the membrane + used to digest invading cells or to break down worn out components of the cell
• describe ribosomes

  very small organelle in the cytoplasm or attached to the RER - made up of proteins and RNA - not membrane-bound
• function of ribosomes

  protein synthesis
• Describe the rough endoplasmic reticulum (RER)

  a system of membranes enclosing a fluid-filled space - the surface is covered with ribosomes
• function of the RER

  Folds and processes proteins that have been made at the ribosomes
• describe the smooth endoplasmic reticulum (SER)

  Similar to rough endoplasmic reticulum but with no ribosomes
• function of SER

  Synthesises and processes lipids
• describe vesicles

  A small fluid-filled sac in the cytoplasm, surrounded by a membrane.
• function of vesicles

  transports substances in and out of the cell and between organelles
• Describe the Golgi Apparatus

  A group of fluid-filled membrane-bound flattened sacs. Vesicles are often seen at the edges of the sacs.
• function of golgi apparatus

  processes and packages new lipids and proteins and makes lysosymes
• describe mitochondria

  long and thin - have a double membrane - the inner one is folded to form structures called cristae. inside is the matrix which contains enzymes involved in respiration
• function of mitochondria

  Site of aerobic respiration where ATP is produced and is found in large numbers in very active cells that require a lot of energy
• Describe chloroplasts

  small, flattened structure found in plant cells - double membrane and inside membranes called thylakoid membranes, these membranes are stacked in some places to form grana, which are linked together by lamellae - thin flat pieces of thylakoid membrane
• function of chloroplasts

  site of photosynthesis - some parts of photosynthesis happens in the grana, and some parts happen in the stroma (thick fluid in chloroplasts)
• describe centrioles

  Small, hollow cylinders made of microtubules - found in all animal cells and some plant cells
• function of centrioles

  involved in cell division
• describe cilia

  small hair-like structures found on the surface membrane of some animal cells
• function of cilia

  The microtubules allow the cilia to move. This movement is used by the cell to move substances along the cell surface.
• describe flagellum

  They stick out from the cell surface and are surrounded by the plasma membrane - they have 2 microtubules in the centre and 9 pairs around the edge
• function of flagellum

  microtubules contract to allow movement, flagella are used like outboard motors to propel cells forward
• what is the plasmodesma

  pore at the boundary between cells
• what is the tonoplast

  membrane that surrounds the vacuole
• what is the middle lamella

  boundary between cells
• describe the synthesis, modification and transport of proteins out of the cell

  1) mRNA attaches to a ribosome attached to the RER, the ribosomes makes the protein

  2) protein is pinched off in a transport vesicle and travels towards the golgi apparatus

  3) vesicle fuses with the golgi apparatus, releasing the protein which is processed and packaged

  4) its then pinched off in a secretory vesicle and travels towards the plasma membrane

  5) vesicle fuses with the plasma membrane which opens to release the protein --> exocytosis
• Prokaryotes

  • Small cells - less than 2 micrometres
  • DNA is circular
  • No nucleus
  • Cell wall made of a polysaccharide
  • No membrane-bound organelles e.g. mitochondria
  • Flagella made of flagellin, in a helix shape
  • Small ribosomes (70s) compared to 80s
• Eukaryotes

  • Large cells - about 10-100 micrometres
  • DNA is linear
  • Nucleus
  • Animals: no cell wall, Plants: cellulose cell wall, Fungi: chitin cell wall
  • Membrane-bound organelles
  • Flagella made of microtubules, in a 9+2 formation