2.1

• All living organisms are made of cells, which are of several different types, some sharing common features.
• Humans are made up of eukaryotic cells.
• All eukaryotic cells contain a nucleus and membrane-bound organelles.
• A more detailed structure of cells, called the ultrastructure, can be obtained by using a microscope.
• The nucleus is surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus.
• The nucleus also contains chromatin and a nucleolus which is the site of ribosome production.
• Rough endoplasmic reticulum is a series of flattened sacs enclosed by a membrane with ribosomes on the surface.
• RER folds and processes proteins made on the ribosomes.
• Smooth endoplasmic reticulum is a system of membrane-bound sacs.
• Golgi apparatus is a series of fluid-filled, flattened & curved sacs with vesicles surrounding the edges.
• Golgi apparatus processes and packages proteins and lipids.
• Golgi apparatus also produces lysosomes.
• The cytoskeleton of the cell plays an important role in providing mechanical strength as well as aiding transport within cells and enabling cell movement.
• Proteins are produced on the ribosomes.
• Proteins which are produced on the surface of RER are folded and processed in the RER.
• The proteins are then transported from the RER to the Golgi apparatus in vesicles.
• They are then modified in the Golgi apparatus.
• Golgi apparatus packages proteins into vesicles to be transported around the cells where they’re required.
• Some of the proteins such as extracellular enzymes leave the cell by exocytosis.
• Cell wall in prokaryotic cells is a rigid outer covering made of peptidoglycan.
• Capsule in prokaryotic cells is a protective slimy layer which helps the cell to retain moisture and adhere to surfaces.
• Plasmid in prokaryotic cells is a circular piece of DNA.
• Flagellum in prokaryotic cells is a tail-like structure which rotates to move the cell.
• Pili in prokaryotic cells are hair-like structures which attach to other bacterial cells.
• Ribosomes in prokaryotic cells are the site of protein production.