Biology 123 Dr. Raut’s Class
Session 5- 1/28/2015
1. What are the primary functions of the Golgi apparatus?
The Golgi receives products from the ER, modifies them, and then sends them to their
destination. The Golgi will place a chemical identifier onto each product’s vesicle so that the cell
knows where the product needs to go.
2. What do the cis and trans faces do respectively? What are the flattened membranous sacs of
the Golgi called?
The cis-face of the Golgi is typically located near the ER and receives vesicles coming from the
ER. The trans-face allows new vesicles to pinch off and “ships” products. The flattened
membranous sacs are called the cisternae and the inside of these cisternae is called the lumen.
These cisternae are different from the cisternae of the ER in that the cisternae of the Golgi are
separate, while the cisternae of the ER are continuous.
3. What is a lysosome?
A lysosome is a membranous sac full of hydrolytic enzymes that work best in the acidic
environment found in lysosomes. The fact that lysosomes work best in an acidic environment
means they are less active in the neutral pH of the cytoplasm. This means that if one bursts it is
not a big deal, but if many burst the cell can die.
4. What are the three different ways that a lysosome can use its hydrolytic enzymes?
The three different ways that a lysosome can use its hydrolytic enzymes are phagocytosis,
autophagy, and apoptosis, or programmed cell death. Phagocytosis is the process by which the
cell digests food; a lysosome fuses with a food vacuole, releasing its digestive enzymes into the
food vacuole. In autophagy, the lysosome’s hydrolytic enzymes break down old, worn out
organelles. In apoptosis, the lysosomes all burst, killing the cell by self-digestion.
5. Contrast central vacuoles and contractile vacuoles.
A central vacuole is present in a mature plant cell. The central vacuole holds “cell sap,” which
includes storage of inorganic ions. The central vacuole will expand as more water flows into the
cell, helping the cell to expand in size easily.
A contractile vacuole is present in protists that live in hypotonic solutions. The contractile
vacuole will take in water that flows into the cell, until it becomes full. At that point, it will squirt
the water out of the cell.
6. True or false: All cells have the same number of mitochondria.
False! The number of mitochondria are dependent on the metabolic activity of the cell. If the cell
needs more ATP, then the cell will have more mitochondria. For example, muscle cells always
have many mitochondria.
7. Describe the structure of mitochondria? What is the mitochondria’s main function?
A mitochondrion has both an inner and outer membrane, with an intermembrane space in
between them. The inner membrane is folded into cristae. Inside these cristae is the
mitochondrial matrix, which holds mitochondrial DNA and ribosomes. The main function of the
mitochondria is to produce ATP; that is why mitochondria have so many membranes, because
most of cellular respiration happens along these membranes.
8. Describe the structure of the chloroplast? What is the chloroplast’s main function?
Chloroplasts also have an inner and outer membrane with an intermembrane space. They also
have thylakoids, which are flat interconnected sacs. These thylakoids are put into stacks called
granum. The fluid that surrounds the granum is called stroma. A chloroplast’s main function is to
perform photosynthesis.
9. Mitochondria and chloroplasts can multiply independently of the nucleus. What allows these
organelles to function autonomously?
Mitochondria and chloroplasts can function autonomously due to the fact that they have both
their own DNA and their own ribosomes.
10. What are the two different functions of the enzymes in peroxisomes?
Peroxisomes function in breaking down different molecules through removing hydrogens and
therefore oxidizing the compounds. The first enzyme oxidizes the compound and forms
hydrogen peroxide (H2O2). Since hydrogen peroxide is toxic, a second enzyme turns hydrogen
peroxide into water.
11. What are the three different types of fibers in the cytoskeleton?
The three different types of fibers in the cytoskeleton are microtubules, intermediate filaments,
and microfilaments.
12. What are the protein subunits of each of the different fibers?
Microtubules are made out of tubulin, which is a dimer consisting of both alpha and beta tubulin.
Intermediate filaments are made out of a variety of proteins, including keratin. Microfilaments
are made out of actin.
13. What are the functions of microtubules?
Microtubules maintain cell shape, aid in cell motility (flagella and cilia), enable chromosome
movement in cell division (centromere), and assist in organelle movements.
14. What are the functions of intermediate filaments?
Intermediate filaments maintain cell shape, anchor the nucleus and other organelles, and form the
nuclear lamina.
15. What are the functions of microfilaments?
Microfilaments maintain cell shape, change the cell shape, cause muscle contraction, cause
cytoplasmic streaming, help in cell motility (pseudopodia), and help with cell division (cleavage
furrow formation).
16. Draw and label the cell walls of neighboring plant cells.
17. What is the function of the extracellular matrix?
The extracellular matrix supports the cell and also sends the cell signals through the integrins.
18. What are the three glycoproteins present in the extracellular matrix?
The three glycoproteins present in the extracellular matrix are collagen, proteoglycan, and
fibronectin.
19. What do these glycoproteins connect to?
These glycoproteins connect back to integrins, which are proteins that span the entire width of
the plasma membrane, connecting with both the extracellular matrix and the cytoskeleton.
20. What are plasmodesmata?
Plasmodesmata are small membrane lined channels that allow communication between plant
cells. In this instance, communication means the flow of materials.
21. List and describe the three junctions in animal cells.
Tight junctions: do not allow any contact between cells and the membranes are tightly bound
together with proteins so that nothing can seep through, prominent in the lining of the stomach
Desmosomes: do not allow any contact between cells and fasten cells together so that they do not
come apart, prominent in skin and muscle cells.
Gap junctions: Allow materials to flow between cells, similar to plasmodesmata, prominent in
cardiac cells and embryonic cells
22. A growing plant cell elongates primarily by
a. increasing the number of vacuoles.
b. synthesizing more cytoplasm.
c. taking up water into its central vacuole.
d. synthesizing cellulose fibrils in an orientation perpendicular to the axis of cell elongation.
e. producing a secondary cell wall.
23. Which of the following is not a similarity among nuclei, chloroplasts, and mitochondria?
a. They contain DNA.
b. They are bounded by two (or more) phospholipid bilayer membranes.
c. They can divide to reproduce themselves.
d. They are derived from the endoplasmic reticulum system.
e. Their membranes are associated with specific proteins.