Cellular Organelles 3 (College Board AP® Biology)

Lysosomes & Vacuoles

Lysosomes

• Lysosomes are membrane-enclosed sacs which contain hydrolytic enzymes (enzymes that break biological molecules down)

• They have three main roles:

  • To break down waste materials such as worn out organelles

  • Roles within cells of the immune system to destroy pathogens

  • In apoptosis (programmed cell death when a cell is very worn out)

The structure of a lysosome

Large Permanent Vacuoles

• A vacuole is a sac in plant cells surrounded by the tonoplast, a selectively permeable membrane

• The vacuole contents (the cell sap) is chemically different to that of the cytoplasm

  • Thanks to the highly selectively permeable nature of the tonoplast

• Vacuoles have a number of distinct roles

  • As a cellular storage of water, helping to maintain water balance in the plant

  • To keep the cell turgid, by filling with water and exerting pressure on the cell wall, giving the plant's tissues structural strength

  • Some vacuoles contain colored pigments that give the plant its characteristic color

  • Other plant species store bitter/astringent compounds in the vacuole that deter insects/other animals

• They can often be a place where waste products are sequestered (temporarily stored before excretion from the cell)

• A vacuole can sometimes take up most of the inner volume (around 80%) of a plant cell

• Vacuoles in animal cells are not permanent and small

  • Their role in animals is as a temporary store of metabolites or for the transport of substances

The structure of the vacuole