Topic 1-cell biology

• Organisms can be _ or _


  Prokaryotes or eukaryotes
• Eukaryotes 


  Eukaryotes are organisms made up of eukaryotic cells

  They are complex, include all animals and plant cells
• Prokaryotes 


  Prokaryotes are smaller and simpler than eukaryotes

  E.g bacteria
• Subcellular structures


  The different parts of a cell
• Subcellular structures found in most animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Nucleus


  • Contains genetic material that controls the activities of the cell
• Cytoplasm


  Gel-like substance where most of the chemical reactions happen
• Cell membrane


  Holds the cell together and controls what goes in and out
• Mitochondria


  Where most of the reactions for aerobic respiration take place
• Ribosomes


  Where proteins are made in the cell
• Additional subcellular structures found in plant cells

  • Rigid cell wall
  • Permanent vacuole
  • Chloroplasts
• Rigid cell wall


  Made of cellulose, supports and strengthens the cell
• Permanent vacuole


  Contains cell sap, a weak solution of sugar and salts
• Chloroplasts


  Where photosynthesis occurs, contain chlorophyll
• Bacterial cells are much smaller than plant and animal cells
• Bacterial cells don't have a 'true' nucleus, instead they have a single circular strand of DNA that floats freely in the cytoplasm
• Bacterial cells may also contain one or more small rings of DNA called plasmids
• Bacterial cells don't have a cell membrane, cytoplasm, chloroplasts or mitochondria
• Cells of algae (e.g. seaweed) also have a rigid cell wall and chloroplasts
• Microscopes can see very tiny objects, so it's useful to write numbers in standard form
• Standard form


  Where very big or small numbers with lots of zeros are changed into something more manageable
• Stains are used to highlight objects in a cell by adding colour to them
• Differentiation

  The process by which a cell changes to become specialised for its job
• Most differentiation occurs as an organism develops
• In most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised
• Lots of plant cells don't ever lose the ability to differentiate
• The cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin or blood cells
• Stem cells


  Undifferentiated cells
• Examples of specialised cells

  • Sperm cells
  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Phloem and xylem cells
• Sperm cells


  • Have a long tail and streamlined head to help it swim to the egg, lots of mitochondria to provide energy, enzymes in head to digest egg cell membrane
• Nerve cells


  • Long to cover more distance, have branched connections at ends to connect to other nerve cells
• Muscle cells


  • Long to have space to contract, contain lots of mitochondria to generate energy for contraction
• Root hair cells


  • Grow into long "hairs" that stick out into the soil, giving the plant a big surface area for absorbing water and mineral ions
• Phloem and xylem cells


  • Form tubes to transport substances such as food and water around plants, are long and joined end to end, xylem cells are hollow, phloem cells have very few subcellular structures
• Chromosomes are coiled up lengths of DNA molecules
• Each chromosome carries a large number of genes that control the development of different characteristics
• Body cells normally have two copies of each chromosome, one from the organism's 'mother' and one from its 'father'
• Cell cycle


  A series of stages that body cells in multicellular organisms go through to divide and produce new cells
• Mitosis


  The stage of the cell cycle when the cell divides
• Multicellular organisms use mitosis to grow or replace cells that have been damaged