cell biology

• plant and animal (eukaryotic) cells have a cell membrane, cytoplasm and a nucleus containing DNA
• bacterial cells (prokaryotic) cells are much smaller in comparison to eukaryotic cells
• prokaryotic cells have a cytoplasm and cell membrane surrounded by a cell wall
• in prokaryotic cells genetic material is not enclosed in a nucleus, it is a single loop of DNA and there may be one or more small rings of DNA called plasmids
• a eukaryotic cell is 10 to 100 micrometers (µm)
• a prokaryotic cell is less than 1 micrometer (µm)
• eukaryotic cells:

  • cell membrane
  • cytoplasm
  • nucleus
  • DNA is nucleus bound
  • some cells (plant cells) have cellulose cell wall
• prokaryotic cells:

  • cell membrane
  • cytoplasm
  • DNA is free-flowing
  • plasmids
  • cell wall made of peptidoglycan
• • 1 metre = 1000 mm
  • 1mm = 1000 micrometers
  • 1 micrometer = 1000 nanometers
• • all plant and animal cells have a nucleus
  • nucleus contain genetic information (needed to form new cells) and controls cell activity
• • all plant and animal cells have a cytoplasm
  • cytoplasm is a gel-like substance composed of water and dissolved solutes, and its where chemical reactions in the cell occur. It also supports the internal cell structures in it
• • all plant and animal cells have a cell membrane
  • cell membrane controls have can enter and exit the cell, and holds the cell together
• • all plant and animal cells contain mitochondria
  • mitochondria is the site of aerobic respiration, releasing energy for the cell
• • all plant and animal cells contain ribosomes
  • ribosomes are the site of protein synthesis (process in which cells make proteins) and found in the cytoplasm
• • plant cells have a cell wall made from cellulose (a polymer of glucose)
  • the cell wall strengthens the cell and protects it
• • plant cells have a permanent vacuole
  • the permanent vacuole contains cell sap and is found within the cytoplasm.
  • it us used for storage of certain molecules (like salts and sugars) and improves the cells rigidity
• • plant cells have chloroplasts
  • chloroplasts contain chlorophyll which absorbs light needed for photosynthesis and the enzymes needed for photosynthesis
  • chloroplasts are the site of photosynthesis
• • bacterial cells contain cytoplasm
  • the cytoplasm is the gel-like substance where chemical reactions in the cell occur
• • bacterial cells contain a cell membrane
  • the cell membrane controls what enters and exits the cell and holds the cell together
• • bacterial cells contain a cell wall made from peptidoglycan
  • the cell wall strengthens the cell and protects it
• • bacterial cells have a flagellum
  • the flagellum allows the bacterial cell to swim and enables movement
• • bacterial cells have a slime capsule
  • the slime capsule provides protection
• • bacterial cells have plasmids
  • plasmids provide genetic variation and used as a vector in genetic modification
• a specialised cell is a cell that has a particular structure and composition of sub-cellular structures to allow it to perform specific functions
• cells undergo differentiation to become specialised
• most animal cells can only differentiate once, early on in life
• many cells in plants retain the ability to differentiate as the dont fully undergo differentiation, so can change throughout the plants life
• sperm cell:

  • specialised to carry the male DNA to the egg cell for reproduction
  • has a streamlined head and long tail for efficient swimming
  • many mitochondria which release energy through aerobic respiration to move and burrow in the egg cell
  • acrosome (head) has digestive enzymes which break down the outer layers of the membrane of the egg
  • the tail rotates which propels the cell forwards, allowing it to swim
• muscle cell:

  • specialised to contract for movement
  • layers of myosin and actin (protein filaments) which slide over each other which causes the muscle to contract
  • many mitochondria to release energy through aerobic respiration to provide enough energy for contraction
  • can store glycogen to be used for aerobic respiration
• nerve cell:

  • specialised to transmit electrical signals quickly around the body from one place to another
  • has an axon which is long, so electrical impulses can travel long distances
  • lots of dendrites from the cell body allow the nerve cell to form many connections and communicate with other nerve cells, muscles and glands
  • the axon is covered in a fatty sheath which speeds up nerve impulses
  • many mitochondria to release enough energy through respiration to convert electrical impulses into chemical neurotransmitters which allow impulses to pass through synapses
• root hair cells:

  • specialised to take up water through osmosis and mineral ions through active transport
  • have a large surface area to volume ratio so more water can move in through osmosis, creates a larger concentration gradient
  • thinner walls than other plant cells to create a shorter diffusion pathway so water can move into the cell more easily
  • permanent vacuole which contains cell sap which is more concentrated that soil water, maintaining a concentration gradient
  • lots of mitochondria to release enough energy through aerobic respiration for active transport
• xylem cells:

  • specialised to transport water and mineral ions from the roots to the shoots through transpiration
  • lignin which strengthens the wall and makes the tube waterproof which prevents cells from decaying or rotting
  • no top and bottom between cells to form continuous hollow tubes which water can easily be drawn up through, through transpiration
• phloem cells:

  • specialised to transport products of photosynthesis (glucose, dissolved sugars and amino acids) to all parts of the plant
  • cells have sieve plates at their end to allow sugars to move
  • have companion cells around them which provides phloem cells with energy and essential substances
  • have very few subcellular structures to aid the flow of materials
• cell differentiation is the process by which cells become specialised and so are able to carry out specific functions which are essential for survival
• in mature animals, cell division is mainly restricted to repair and replacement
• as a cell differentiates, it acquires different subcellular structures to enable it to carry out a specific certain function, this makes it specialised
• development of microscopy:

  • light microscopes were first developed (in the 17th century)
  • these light microscopes allowed us to develop our first understanding of cells
  • over time, the design of the microscope evolved to increased magnification and resolution to enhance specimen visualisation
  • the first electron microscope was developed, which allowed scientists to see smaller organelles such as mitochondria
• electron microscope:

  • higher magnification
  • higher resolution
  • can study cells in finer detail which enable scientists to see and understand organelles
  • specimen must be dead
  • can created 3D images
  • uses electron beams
• light microscope:

  • more commonly used
  • cheaper than electron
  • live specimen can be used
  • uses light and lenses to form an image
• image = actual x magnification