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
Exam Tip
It is important to note that both lysosomes and vacuoles are bound by a membrane, and that these membranes are highly selectively permeable. This enables the plant to compartmentalize their contents effectively.
