Cells

Cells

1. Tyoes of cells

   • Eukaryotic Cells
     • Animal Cells
       • Nucleus
         • Contains genetic material that controls the activites of the cell
       • Cytoplasm
         • Gel-like substance where most of the chemical reactions occur. It contains enzymes that control these chemical reactions
       • Mithochondria
         • Where most of the reactions for aerobic respiration takes place
           • Respiration transfers energy that the cell needs to work
       • Ribosomes
         • Where the proteins are made in the cell
       • Cell membrane
         • Hold the cell together and control what goes in and out of the cell
     • Plant Cells
       • Rigid cell wall
         • Made out of cellulose. It supports the cell and strengthens it
       • Permanent vacuole
         • Contains cell sap - a weak solution of sugar and salts
       • Chloroplasts
         • Where photosynthesis takes places - makes 'food' for the plant. It contains a green substace called chlorophyll, which absorbs the sunlight
   • Prokaryotic cells
     • Bacteria
       • Don't have a true nucleus - instead they have a single circular thread of DNA that floats freely in the cytoplasm
       • May contain one or more small rins of DNA called plasmids
       • No chloroplasts or mitochondria

2. Differentiation and specialisation

   • Differentiation is the process by which a cell changes to become specialised for a job. As a cell specialises, the sub-celluar structures change and turn into different types of cells.
     • This allows them to carry out specific funtions.
     • Most differentiation occurs as an organism develops.
     • In animals cells the ability to differentiate is lost at an early stage but plant cells do not lose this ability.
   • Cells that differentiate in mature animals are mainly used for repairing or replacing cells, such as skin or blood cells.
   • Undifferentiated cells are called stem cells.
   • Examples of specialised cells
     • Sperm cells
       • Specialised for reproduction - long tail and streamlined head to help it swim to the egg.
       • Lots of mitochondria to provide energy.
       • Enzymes to digest through the egg cel membrane.
     • Nerve cells
       • Specialises for rapid signalling.
       • Carry electical signals from one part of the body to another.
       • Long and branched connections at their end to connect to other onerve cells and form a network throughout the body.
     • Muscle cells
       • Specialised for contraction.
       • Long and contain lots of mitochondria to generate the energy needed for contraction.
     • Phloem and xylem
       • Specialised for transporting substances.
       • These cells form phloem and xylem tubes which transport substances such as food and water around plants.
         • The cells are long and joined at the end to form tubes
       • Xylem tubes are hollow in the centre and phloem have very few sub-celluar structures so that substances can flow through them.
     • Root hair cells
       • Specialised for absorbing water and minerals.
       • They are on the surface of plant roots, which grow into long "hairs" that stick out into the soil.
         • This gives the plant a large surface area for absorbing water and mineral ions from the soil.

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