cell structure

• Cells are the building blocks of all

  living things.
• Some organisms are made of only one

  cell – unicellular – e.g. a bacterial cell (

  shown in diagram)
• Some organisms are made of many

  cells – multicellular – e.g. humans are

  made up of over 30 trillion cells!
• Eyepiece

  To magnify the image
• Objective Lens

  To magnify the image
• Stage

  To place the slide on
• Coarse Focus Wheel

  To focus the image coarsely
• Fine Focus Wheel

  To precisely focus the image
• Diaphragm

  To adjust the amount of light
• Condenser

  Focuses light on the object
• Electron microscopes use accelerated

  electrons as a source of illumination
• Components of the cell that are only

  visible using an electron microscope are

  referred to as the cell ultrastructure
• Cells contain a variety of internal

  structures called organelles
• An organelle is a cell component that

  performs specific functions for the cell
• The cell membrane is also called the

  plasma membrane
• the cell memebrane is a phospholipid bilayer – two

  layers of phospholipids with proteins

  embedded.

  The hydrophilic heads of the

  phospholipids face the outside and

  the hydrophobic tails face the inside.

  It is referred to as the fluid mosaic

  model
• The functions of the cell

  membrane include:

  Controls what enters and exits the

  cell ( are selectively permeable)

  Retain the cell contents

  Have receptors on their surface for

  molecules to bind to
• The cytoplasm contains the entire cell

  contents inside the cell membrane except the

  nucleus

  Protoplasm is the cytoplasm and the

  nucleus

  Cytoplasm consists of the cytosol, a jelly like

  substance in which the organelles are

  suspended
• The functions of the cytoplasm

  are:

  Acts as a medium in which most of

  the chemical reactions of the cell

  take place

  The first stage of respiration takes

  place in the cytosol
• Each mitochondrion consists of a smooth

  outer membrane and a folded inner

  membrane

  Contained within mitochondria is

  mitochondrial DNA
• Cells that require a lot of energy will contain

  a lot of mitochondria and cells that require

  very little energy will have fewer

  mitochondria
• The main function of the

  mitochondrion is:

  Site of respiration – produce almost all

  of the energy required by the cell

  Mitochondrion
• The nucleus is a spherical structure

  suspended in the cytoplasm

  It is surrounded by a double membrane –

  nuclear membrane
• The nucleus is the control centre of the

  cell

  It contains chromosomes – these are

  made of protein and DNA

  (deoxyribonucleic acid)

  Your genes are sections of DNA found

  along the chromosomes

  When a cell is not dividing the

  chromosomes are very long and

  interwoven and called chromatin
• Within the nucleus there are one

  or more structures called nucleoli

  These are where ribosomes are

  made

  Cells that contain large numbers

  of ribosomes have numerous

  nucleoli
• Ribosomes are surrounded by a

  membrane

  They are found in the cytoplasm
• Ribosomes are made of ribosomal

  RNA and protein

  They manufacture proteins
• Chloroplasts are surrounded by

  double membrane

  They contain the green pigment

  chlorophyll
• Chloroplasts are the site of

  photosynthesis
• The plant cell wall is made from fibres

  of the polysaccharide called

  cellulose

  The cell wall is fully permeable –

  allows everything to pass through it

  Their function is to support and

  strengthen the cell
• Vacuoles are fluid filled vesicles

  Most animal cells have small

  vacuoles but not all

  Plant cells all have a large

  permanent vacuole

  Vacuoles store food and waste

  materials ( salt, sugar and water)
• Prokaryotic cells do not have a nucleus or

  membrane enclosed organelles
• Eukaryotic cells have a nucleus

  and membrane enclosed organelles
• Plant cell used : Onion cell
• How was the sample obtained: Peel off the inner epidermis of an onion ( only one cell thick) using a

  forceps and cut into small pieces
• Stain : iodine

  Why was a stain used?: To provide contrast and allow the cell structures to be seen clearly
• How did you apply the cover slip? Cover the sample with a cover slip by lowering it gently at a

  450 angle using a mounted needle
• Why did you apply the cover slip in this way? To prevent air bubbles forming
• Results: the nucleus stained darker than the cytoplasm
• Results: the nucleus stained darker than the cytoplasm