25. Which organelle of the cell structure is responsible for intracellular digestion? What is the chemical content of those organelles?

Intracellular digestion occurs through the action of lysosomes. Lysosomes contain digestive enzymes (hydrolases) that are produced in the rough endoplasmic reticulum and stored in the Golgi apparatus. Lysosomes are hydrolase-containing vesicles that detach from the Golgi apparatus.

26. Why are lysosomes known as “the cleaners” of cell waste?

Lysosomes carry out autophagic and heterophagic digestion. Autophagic digestion occurs when residual substances of the cellular metabolism are digested. Heterophagic digestion takes place when substances that enter the cell are digested. Lysosomes enfold the substances to be broken down, forming digestive vacuoles or residual vacuoles, which later migrate toward the plasma membrane, fusing with it and releasing (exocytosis) the digested material to the exterior.

• Cell Structure Review – Image Diversity: lysosomes

27. What are the morphological, chemical and functional similarities and differences between lysosomes and peroxisomes?

Similarities: lysosomes and peroxisomes are small membranous vesicles that contain enzymes and enclose residual substances of an internal or external origin to break them down. Differences: lysosomes have digestive enzymes (hydrolases) that break down substances to be digested into smaller molecules whereas peroxisomes contain enzymes that mainly break down long-chain fatty acids and amino acids, and which inactivate toxic agents including ethanol. In addition, within peroxisomes, the enzyme catalase is present. It is responsible for the oxidation of organic compounds by hydrogen peroxide (H₂O₂) and, when this substance is present in excess, it is responsible for the breaking down of the peroxide into water and molecular oxygen.