Organelles - The Nucleus

The Nucleus is the largest organelle, features include:
  - Nuclear Envelope - two membranes with fluid 
     between them
  - Nuclear Pores - holes that go right through the 
     envelope
             - This allows relative large molecules to pass 
                through
  - Nucleolus - a dense, spherical structure




The nucleus contains almost all of the cell's genetic material. The DNA contains instructions for making proteins. Some of these proteins regulate cell activity.
The nucleus also makes RNA and Ribosomes

Linear Magnification

How to calculate the linear magnification of an image:

It may be easier to remember the equation as: AIM or I AM

The magnification is not measured in anything e.g. If the magnification is 1500 just write: x1500

Staining

A lot of biological material is not coloured, and therefore need to be stained in order to view the details of it.

Staining refers to any process that helps to reveal or distinguish different features.

In light microscopy, they may be dyes. In electron microscopy, they are metal particles or metal salts.

Magnification and Resolution

Magnification: The degree to which the size of an image is larger than the object itself

Resolution: The ability to distinguish two objects as distinct from one another. The higher the resolution, the greater detail that can be seen.

Light Microscope
Magnification: x1500
Resolution: 200nm

Transmission Electron Microscope:
Magnification: x500,000
Resolution: 0.1nm

Scanning Electron Microscope:
Magnification: x100,000
Resolution: 0.1nm

Specification: 1.2.1 Exchange Surfaces and Breathing

Specification: 1.1.3 Cell Division, Cell Diversity and Cellular Organisation

- state that mitosis occupies only a small percentage of the cell cycle and that the remaining 
   percentage includes the copying and checking of genetic information;
- describe, with the aid of diagrams and photographs, the main stages of mitosis:
      - behaviour of the chromosomes
      - nuclear envelope
      - cell membrane 
      - centrioles
- explain the meaning of the term homologous pair of chromosomes
- explain the significance of mitosis for growth, repair and asexual reproduction in plants and 
animals
- outline, with the aid of diagrams and photographs, the process of cell division by budding in yeast
- state that cells produced as a result of meiosis are not genetically identical (details of 
   meiosis are not required)
- define the term stem cell
- define the term differentiation, with reference to the production of erythrocytes (red blood 
   cells) and neutrophils derived from stem cells in bone marrow, and the production of xylem 
   vessels and phloem sieve tubes from cambium
- describe and explain, with the aid of diagrams and photographs, how cells of multicellular 
   organisms are specialised for particular functions, with reference to:
      - erythrocytes
      - neutrophils
      - epithelial cells
      - sperm cells
      - palisade cells
      - root hair cells
      - guard cells 
- explain the meaning of the terms tissue, organ and organ system; 
- explain, with the aid of diagrams and photographs, how cells are organised into tissues, 
   using squamous and ciliated epithelia, xylem and phloem as examples; 
- discuss the importance of cooperation between cells, tissues, organs and organ systems

Specification: 1.1.2 Cell Membranes

- outline the roles of membranes within cells and at the surface of cells; 
- state that plasma (cell surface) membranes are partially permeable barriers; 
- describe, with the aid of diagrams, the fluid mosaic model of membrane structure  
- describe the roles of the components of the cell membrane;
      - phospholipids
      - cholesterol
      - glycolipids
      - proteins
      - glycoproteins
- outline the effect of changing temperature on membrane structure and permeability; 
- explain the term cell signaling; 
- explain the role of membrane-bound receptors as sites where hormones and drugs can 
   bind; 
- explain what is meant by:
      - passive transport (diffusion and facilitated diffusion including the role of membrane proteins)
      - active transport
      - endocytosis
      - exocytosis;
- explain what is meant by osmosis, in terms of water potential. (No calculations of water potential will be required); 
- recognise and explain the effects that solutions of different water potentials can have upon plant and animal cells