Biology, Eighth Edition (Raven)

Chapter 4: Cell Structure

Lysosomes

How do cells dispose of unwanted organic material? Although food has been broken down into individual molecules by the time it reaches a cell, cells still need to deal with larger complexes of organic material. Intracellular digestion is carried out by organelles called lysosomes. There are several contexts in which cells need to carry out digestion. They include the recycling of cellular organelles and the breakdown of viruses and other cellular invaders. Single-celled organisms such as amoebas use lysosomes to digest their food as they have no process for extracellular digestion. Lysosomes are analogous to the human stomach. The pH within a lysosome is very acidic and the enzymes within work most effectively in this environment. The components of a lysosome have evolved specific conformations that make them resistant to break down by the enzymes within the lysosome.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Lysosomes are membrane-bound vesicles that arise from the

		A)	nucleus.
		B)	mitochondria.
		C)	endoplasmic reticulum.
		D)	Golgi apparatus.
		E)	cell membrane.

2.	The lysosome contains ________ enzymes.

		A)	photosynthetic
		B)	anabolic
		C)	hydrolytic
		D)	melancholic
		E)	alcoholic

3.	Which of the following cells will be expected to contain the most active lysosomes?

		A)	brain cell
		B)	skin cell
		C)	kidney cell
		D)	intestinal cell
		E)	phagocytosing white blood cell

4.	Lysosomes function in the destruction and recycling of old organelles.

		A)	True
		B)	False

5.	The enzymes found in the lysosomes were formed in the endoplasmic reticulum.

		A)	True
		B)	False