The whole chloroplast is some ten times larger than a mitochondrion, and it stacks of membranes inside are called grana . These grana are composed of many individual membrane sacs called thylakoid membranes. Each thylakoid membrane has special proteins that hold molecules of the green pigment chlorophyll . This chlorophyll is responsible for trapping the energy of the light to use in driving the production of carbohydrates in photosynthesis. We shall learn more of this process later in the term.
Animals lack chloroplasts.
Finally in our brief tour of cell structure and function, let us remember that all processes described here produce waste materials, and this leads us to one more distinction between plants and animals. Typically animals use various processes to dump their wastes to the environment. Single-celled animals may use vesicular transport to rid themselves of waste by exocytosis. Higher animals concentrate wastes through a urinary system and then urinate periodically in the environment. Since a plant produces great food for an animal to eat, you might not be surprised to find that plants hold their toxic wastes.