CELL BIOLOGY TOPIC 1 CHANTELLE

• Cells are grouped due to their structures

  • Eukaryotic cells
  • Prokaryotic cells
  • Plant and animal cells
  • Bacteria cells
• These cells are much smaller
• They have


  • Cell membrane
  • Cytoplasm
  • Genetic material in a nucleus
• They have


  • Cell membrane
  • Cytoplasm
  • Genetic material but NO nucleus
  • A single DNA loop
  • Sometimes plasmids
• Just a way to group cells based on similarities and differences

  Eukaryotic vs Prokaryotic cells

  
• Plasmid is not always present
• Flagella also not always present and these help to move around the bacteria
• Prokaryotic cells can be 100 times smaller than eukaryotic cells
• Cytoplasm


  Liquid gel (thick liquid) that organelles are in and where which most of the chemical reactions take place
• Cell membrane


  Controls the passage of substances into and out of the cell
• Nucleus


  Controls the activities of the cell. Contains genetic material
• Mitochondria


  Where most energy is released in aerobic respiration
• Ribosome


  Where protein synthesis occurs
• Plants have some extra features as follows

  • Chloroplast (Plant cells)
  • Cell wall (Plant cells)
  • Permanent vacuole (Plant cells)

  
• Chloroplast (Plant cells)


  Contains chlorophyll. Photosynthesis occurs here to produce food for the plant

  
• Cell wall (Plant cells)

  Contains cellulose to strengthens the cell to give it support
• Permanent vacuole (Plant cells)


  Filled with cell sap to keep cell rigid for support as it presses hard against the cell wall

  
• When biologists talk about the size of cells and the structures within them, they are dealing with very small numbers
• Very small (or very big) numbers are represented using standard form – this helps to avoid confusion
• Cells are the basic building blocks of all living organisms
• Tissue


  A group of cells with a similar structure and function
• Organs


  Aggregations of tissues performing specific functions. Example of an organ is stomach
• Organ system


  Organs that work together to form organisms. Example of an organ system is the digestive system
• Organism


  Made up of lots of cells working together
• You, as a human being, are made from trillions of cells, but only of about 250 different types
• Specialised cell


  A cell that has a particular structure and composition of subcellular structures
• Structural differences between different types of cells enable them to perform specific functions within the organism
• Differentiation


  The process by which cells specialise
• Sperm Cell


  • The head contains a nucleus which contains half the normal number of chromosomes (haploid, no chromosome pairs)
  • The acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg's nucleus
  • The mid-piece is packed with mitochondria to release energy (via respiration) for the tail
  • The tail rotates, propelling the sperm cell forwards (allowing it to move/swim)
• Muscle Cell


  • There are three different types of muscle in animals: skeletal, smooth and cardiac (heart)
  • All muscle cells have layers of protein filaments in them. These layers can slide over each other causing muscle contraction
  • Muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction
  • Contains stores of glycogen (glucose stores) that can be broken down and used for respiration to release energy
  • Skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison
• Nerve Cell


  • Has a cell body where most of the cellular structures are located and most protein synthesis occurs
  • Lots of dendrites to form connections to many nerve cells
  • Extensions of the cytoplasm from the cell body form dendrites (which receive signals) and axons (which transmit signals), allowing the neurone to communicate with other nerve cells, muscles and glands
  • The axon (the main extension of cytoplasm away from the cell body) is covered with a fatty sheath, which speeds up nerve impulses. Carries the electrical impulse. Axons can be up to 1m long in some animals
  • Gaps between nerve endings called synapses enable electrical impulses to pass between cells as a chemical message

  
• Plant Cell - Xylem cells

  • No top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
  • Cells are essentially dead, without organelles or cytoplasm, to allow free passage of water
  • Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant

  
• Plant Cell - Phloem cells


  • Made of living cells (as opposed to xylem vessels which are made of dead cells) which are supported by companion cells that have mitochondria to provide them with energy
  • Cells are joined end-to-end and contain holes in the end cell walls (sieve plates) forming tubes which allow sugars and amino acids to flow easily through (by translocation)
  • Cells also have very few subcellular structures to aid the flow of materials

  
• Plant Cell - Root hair cells


  • Root hair to increase surface area (SA) so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
  • Thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
  • Large Permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient. Helps increase the speed of water uptake by osmosis
  • Mitochondria for active transport of mineral ions

  
• All animal and plant cells are unspecialised in the early stages of development
• Unspecialised cells


  They can differentiate into any type of specialised cells so as to perform specific functions within the organism
• Most types of animal cells differentiate at an early stage
• Many types of plant cells retain the ability to differentiate throughout life
• Cells become specialised very early in development in animals
• Almost all of the cells in a multicellular organism will contain the same genetic information but depending on what role on particular cell needs to have, only some of the total sum of genes in a particular cell are used to control its development