c9e_answers_active_reading_06

29. Use this figure to explain how the elements of the endomembrane system function together to
secrete a protein and to digest a cellular component. Label as you explain.
See page 108 in your text for the labeled figure.
Nuclear envelope is connected to rough ER, which is also continuous with smooth ER.
Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi
apparatus. Golgi apparatus pinches off transport vesicles and other vesicles that give rise to
lysosomes, other types of specialized vesicles, and vacuoles. Lysosome is available for fusion
with another vesicle for digestion. Transport vesicle carries proteins to plasma membrane for
secretion. Plasma membrane expands by fusion of vesicles; proteins are secreted from cell.
Concept 6.5 Mitochondria and chloroplasts change energy from one form to another
30. What is an endosymbiont?
An endosymbiont is a cell living within another cell.
31. What is the endosymbiont theory? Summarize three lines of evidence that support the model of
endosymbiosis.
The endosymbiont theory states that an early ancestor of eukaryotic cells engulfed an oxygenusing
nonphotosynthetic prokaryotic cell, and over the course of evolution, the host cell and its
endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion. At least
one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of
eukaryotic cells that contain chloroplasts.
Three lines of evidence that support the model of endosymbiosis:
1. Rather than being bound by a single membrane, like organelles of the endomembrane
system, mitochondria and typical chloroplasts have two membranes surrounding them.
2. Like prokaryotes, mitochondria and chloroplasts contain ribosomes, as well as circular DNA
molecules attached to their inner membranes.
3. Also consistent with their probable evolutionary origins as cells, mitochondria and
chloroplasts are autonomous organelles that grow and reproduce within cells.
32. Mitochondria and chloroplasts are not considered part of the endomembrane system, although
they are enclosed by membranes. Sketch a mitochondrion here and label its outer membrane,
inner membrane, inner membrane space, cristae, matrix, and ribosomes.
See page 110 of your text for the labeled figure.
33. Now sketch a chloroplast and label its outer membrane, inner membrane, inner membrane space,
thylakoids, granum, and stroma. Notice that the mitochondrion has two membrane
compartments, while the chloroplast has three compartments.
See page 111 of your text for the labeled figure.
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