1. Multicellular Organisms

• Inside the nucleus we find long threadlike structures. These are called chromosomes.
• Every species of living organisms has a characteristic number of chromosomes called its Chromosome Complement.
• A cell that has two matching sets of chromosomes are known as diploid.
• Normal body cells contain two matching sets of chromosomes, so they are diploid. However, sex cells only contain a single set of chromosomes so they are haploid.
• New cells always need to be produced in order to replace damaged cells and allow growth to take place.
• The process of producing new cells is Mitosis.
• Mitosis provides new cells for growth and repair of damaged cells while maintaining the diploid chromosome complement.
• Mitosis Stage 1: At the beginning of mitosis, the cell prepares itself for diffusion. The DNA of the cell is duplicated, creating two cells of each strand of DNA called a chromosome.
• Mitosis stage 2: The chromosomes shorten and thickens and are seen as a pair of chromatids.
• Mitosis stage 3: The nucleus breaks down and the chromosomes line up along the equator of the cell. The spindle fibres attach to the chromosomes.
• Mitosis stage 4: The pair of chromatids are pulled apart and the chromatids move to opposite ends of the cell. Duplicate copies of the cells DNA are now on each side of the cell and are ready to divide.
• Mitosis stage 5: The cytoplasm divides between the new cells. The cell pinches in the middle and divides into two genetically identical daughter cells.
• Stem cells are unspecialised cells. This means that they have the potential to become different type of cell.
• Stem cells can divide in order to self renew and are involved in growth and repair.
• Cells can be specialised to perform a certain function. This can lead to the formation of tissues and organs.
• Groups of organs work together to form systems.
• Hierachy in systems

  Cells > Tissues > Organs > Systems