Multicellular organisms

• Give the way cells organise into organisms 


  Groups of the same specialised cell are organised into tissues, different tissues working together to perform a function are organised into organs, different organs working together to perform a function are organised into organ systems. All the organ systems together are an organism.
• explain why multicellular organisms need specialised cells 


  Large, multicellular organisms have a small surface area:volume ratio, and internal cells have no contact with the external environment. Therefore cells need to be specialised to gather nutrients and excrete waste products.
• Describe and explain the organelles involved in the release of a protein from a cell


  The nucleus contains the DNA that is transcribed into mRNA. The mRNA travels out of a nuclear pore and is translated by a ribosome attached to endoplasmic reticulum, producing a protein. The protein is 'pinched off' the rER inside a vesicle, that travels to and fuses with the Golgi apparatus. The Golgi apparatus process and packages the protein into a vesicle, again this is 'pinched off' from the Golgi apparatus. The vesicle fuses with the cell surface membrane and the protein is released outside the cell.
• explain why a cell involved in secreting proteins would have a large amounts of mitochondria and Golgi vesicles 


  Many mitochondria release energy in the form of ATP for protein synthesis and the movement of vesicles. The many Golgi vesicles contain the protein to be released from the cell, and will travel to the cell membrane where they fuse with it to be released by exocytosis.
• Glycoproteins are produced by cells. one is a polypeptide with lactose attached. Describe how lactose is formed and where it would be attached to the polypeptide to form a glycoprotein 


  Glucose and galactose would undergo a condensation reaction to form a glycosidic bond joining the monosaccharides into lactose. Lactose would be added to the polypeptide at the Golgi apparatus.
• describe how the rough ER and Golgi apparatus are involved in the secretion of enzymes 


  Rough endoplasmic reticulum has ribosomes that produce proteins through protein synthesis. The Golgi apparatus modifies proteins, packages them into vesicles and transports them to the cell surface membrane, where they fuse so the contents can be secreted
• compare and contrast the Golgi body and smooth ER


  They are both single membrane organelles. They can both package and transport molecules. The Golgi body is a series of separate flattened sacs, whereas the smooth endoplasmic reticulum are interconnected tubes.

  The smooth endoplasmic reticulum can synthesis lipids, the Golgi apparatus does not. The Golgi apparatus can form lysosomes, the smooth endoplasmic reticulum does not.
• Explain the advantage of a cell having large amounts of mitochondria 


  Can perform large amounts of aerobic respiration to make large amounts of ATP/release large amounts of energy.
• explain the advantage of a cell having large amounts of ribosomes/ rough ER


  Can perform large amounts of protein synthesis to make large amounts of proteins.