GCSE Online Classes

  Microscopes Microscopes are useful for showing detail at cellular and sub-cellular level and are used to observe objects that are too  s mall to see with the naked eye. There are two main types of microscope – the  Light Microscope  (like the ones you will use in your school or college) and the  Electron Microscope  which has higher magnifications and resolution than a Light Microscope (used by scientists). The Light Microscope 1 The Eye piece 2 Objective lenses of different magnifications 3 The Iris 3 The Light source. Comparing light and electron microscopes Common units used in microscopy Magnification and resolution Magnification is the measure of how many times a given object under a microscope has been made larger. To calculate the magnifying power of a microscope you need to use the below formula: Magnification = size of the image / size of the real object An example question you may be asked could be: A light microscope produces an image of a cell...

Enzymes are large proteins that act as biological catalysts. Enzymes speed up chemical reactions, in living cells these reactions include: photosynthesis, protein synthesis and respiration. Enzymes Enzymes are specific, i.e. one reaction will be catalysed by one enzyme. Enzymes can be denatured by high temperatures and or extreme changes in PH level. Enzymes have an optimum PH at which they will work, which will vary by activity. Enzymes have an optimum temperature at which thy work, for many enzymes this is body temperature (37⁰C) Enzymes have and active site, which is formed by the precise folding of the enzyme molecule. Enzyme Activity In synthesis reactions enzyme molecules work by colliding with substrate molecules, forcing them to break up and join with others. This is known as lock and key theory. Excessive heat vibrates the atoms in the protein molecule this will denature the enzyme by putting strain on the bonds and breaking them. High temperatures will change the shape of the...

Cell division and cell enlargement is used by multicellular organisms to grow and reproduce. Plants can also grow via differentiation into branches, leaves, etc. From the moment of fertilisation cell division begins, when the zygote replicates itself exactly through mitosis. Later in its life cycle an organism may use cell division to produce sex cells (gametes) in a different type of division called meiosis. The stages of cell division make up the cell cycle of an organism. Chromosomes Chromosomes are found in the nucleus of eukaryotic cells. Chromosomes exist as pairs called homologues and are made of DNA and carry a large number of genes. For the exact duplication of cells is it essential that all of the genetic material is duplicated. Chromosomes form a key part of a sequence of events that ensures the genetic code is transmitted exactly and appears in the new daughter cells. DNA replication DNA replication occurs during the cell cycle; the genetic material is doubled and then divi...

  Stem cells are found in plants and animals. They are   unspecialised   or   undifferentiated   (meaning they have the potential to become almost any type of cell).  Once the cell is fully specialised, it will possess sub-cellular organelles specific to the function of that cell. Embryonic stem cells are more flexible in terms of what they can become compared to stem cells found in the bone marrow of adults. Plant cells retain their ability to  differentiate  (specialise) throughout their life, whereas Animal cells are mainly restricted to repair and replacement in later life. Stem cells can be used to treat humans.  Therapeutic cloning  can be used to treat diabetes. Embryonic stem cells (that can specialise in any type of cell) are produced with the same genes as the person who needs the treatment, when these cells are put into the body they are not usually rejected. The benefits of using stem cells Stem cells left over from IVF treat...

The Cell Biology section of Revision Science for GCSE Biology (9-1) covering: Structure of Cells, Organisation and Differentiation, Microscopy and Microorganisms, Cell Division and Metabolism – Respiration and Enzymes. Cell Differentiation and Stem Cells Cell Division Enzymes and Metabolism Microscopy and Microorganisms Organisation and Differentiation Osmosis and Diffusion Plant Cells vs. Animal Cells Proteins and Amino Acids Respiration and Metabolism Structure of Cells