Name _______________________
Due 4.21.2010
Ch 5 & 8 homework- KEY
Ch 5
1.
Describe the difference between diffusion and facilitated diffusion. (1)
Facilitated diffusion involves the use of transport proteins to cross a membrane. Diffusion is the random movement of molecules down a concentration gradient.
2.
Draw the structure of ATP. Where is the energy stored in this molecule? Is ATP a form of kinetic energy or potential energy? How do you know? (1)
Energy is stored in the bonds between the Phosphate groups. This is a type of potential energy because it is in a chemical bond.
1

3.
Describe the action of enzymes (how they work to catalyze a reaction). How do they affect E a
?
Be sure to include active site and induced fit (1). **Hint: drawing a picture is sometimes easier
Enzymes work to catalyze reactions. They are protein molecules with a specific shape that fits with a specific substrate. One ach enzyme is an active site, which is the binding site for a substrate. It is this site that makes the enzyme specific to a particular substrate. Once a substrate has bound to the active site on the enzyme, a small change in shape occurs called the induced fit. This allows the enzyme to slightly reposition the substrate for reactions. Overall, enzymes lower the energy of activation.
4.
Define hypotonic, hypertonic and isotonic. What happens to an animal cell placed in a hypertonic solution? A hypotonic solution? A plant cell in an isotonic solution? (1.5)
Hypertonicity
A hypertonic solution contains a greater concentration of solutes than the solution on the other side of the membrane.
A cell placed in a hypertonic solution will shrink
Hypotonicity
A hypotonic solution contains a lesser concentration of solutes than the solution on the other side of the membrane.
A cell placed in a hypotonic solution will swell
Isotonicity
Isotonic solutions contain equal concentrations of solutes on either side of the membrane. Nothing will happen to the cell.
In an isotonic solution, a plant cell is flacid
2

5.
Describe how competitive, non-competitive and feedback inhibition work. (1.5)
Competitive inhibition is when an inhibitor physically blocks the active site of an enzyme preventing the substrate from binding.
Noncompetitive inhibition is when an inhibitor attached in a place other then the active of a n enzyme changing the shape of the enzyme and preventing the substrate from binding.
Feedback inhibition- this type of inhibition is when the product from the reaction accumulates and acts as an inhibitor, preventing the enzyme from working.
6.
How do the components and structures of cell membranes relate to the function of the membrane? (1)
Cell membranes are made of phospholipids and proteins. The hydrophobic/hydrophilic properties of the phospholipids create a membrane that is hydrophobic on the interior and hydrophilic on the interior.
This prevents polar molecules from crossing the membrane.
The imbedded proteins in the membrane serve a variety of functions including transport, cell communication, structural support , and junction formation. Membrane proteins also act as enzymes and receptors. The presence of these proteins allows the cell to control and regulate activity and the intake/output of substances across its membrane.
7.
The sodium concentration is ten times less than the concentration in the surrounding fluid.
What mechanism would a cell use to move sodium out of the cell? (.5)
Active transport
3

8.
Describe the process of phosphorylation (.5)
Phosphorylation is the transfer of a phosphate group from one molecule of ATP to a molecule of ADP.
The covalent bond between the phosphate groups is broken, which released energy.
9.
Compare and contrast phagocytosis, pinocytosis and receptor-mediated endocytosis. Why would receptor-mediated endocytosis be beneficial to a cell? (1)
Phagocytosis is the process of cellular eating, where a cell intakes food particles. Pinocytosis is the process of cellular drinking, where a cell intakes fluids and receptor mediated endocytosis is when a cell takes in specific particles. The benefit of receptor mediated endocytosis would be so the cell can control what is and is not allowed into the cell at a particular time.
10.
Most of the functions of a cell membrane are performed by (.5)
A) glycolipids.
B) proteins.
C) phospholipids.
D) cholesterol.
E) nucleotides.
11.
Osmosis can be defined as (.5)
A) the diffusion of water.
B) the diffusion of nonpolar molecules.
C) active transport.
D) the diffusion of a solute.
E) endocytosis.
4

Ch 8
1.
Describe what happens in each phase of mitosis (3) ***Pictures may help, but DO NOT copy and paste pictures, draw your own) a.
Interphase b.
Prophase c.
Metaphase d.
Anaphase e.
Telophase f.
Cytokenesis
Interphase - Synthesizes new organelles and molecules. Growth phase. Chromosomes duplicated. Not individually distinguished. Loosely packed chromatin. Contains nucleoli indicating cell is making proteins
Prophase- Chromatin fibers more tightly coiled and folded. Form discrete chromosomes. Nucleoli disappear. Duplicated chromosomes appear. Joined together at centromere. Mitotic spindle begins to form in cytoplasm, Made from microtubule fibers growing from centromeres
ProMetaphase- Nuclear envelope fragments disappears. Microtubules emerge from centrosomes at poles and reach chromosomes. Chromosomes tightly condensed. Kinetochore appears.
Metaphase- Mitotic spindle fomed, Chromosomes at metaphase plate, Centromeres of chromosomes lined up
Anaphase- Two centromeres of each chromosome come apart. Sister chromatids separated. Poles move further apart, elongating cell. Complete collection of chromosomes at each pole
Telophase- Nuclear envelope forms, chromatin fibers uncoil. Nucleoli re-appear. Reverse of prophase
Cytokenesis- Cleavage furrow, pinching cell in two
5

2.
What is the difference between mitosis and meiosis (.5)
Mitosis is the process in which somatic cells divide. Meiosis is the process in which haploid gametes are formed.
3.
Why do cells divide? (.5)
To make more cells. To grow new tissues and organs, to replace old and dying cells.
4.
What is the advantage of organizing DNA into chromosomes? (.5)
A large amount of information can be coiled, folded and stored in a very small place. Chromosome structure decreases the amount of space needed to house the DNA
5.
Compare and contrast mitosis and meiosis (1)
Meiosis is essentially two mitosis processes with only one chromosome duplication. Mitosis duplicates the chromosomes and divides into two. Meiosis duplicates the chromosomes, divided into two and then divides again. The process of Mitosis results in 2 diploid cells where as meiosis results in 4 haploid cells.
Mitosis is used to duplicate somatic cells and meiosis is used to create more sex cells.
6.
Explain how growth factors control cell division (1)
Growth factors control the cell cycle. They are required at each stage to trigger and coordinate events.
In the absence of growth factors, the cell cycle will not continue.
6

7.
How is ‘chromatin’ different than a ‘chromosome? (.5)
Chromatin is a relax version of a chromosome. When these fibers coil more tightly, they become chromosomes.
8.
Describe “crossing over” (1)
Crossing over is when there is an exchange of corresponding segments of homologous chromosomes. It occurs during prophase 1 of meiosis
9.
How does independent assortment lead to genetic diversity? (1)
Independent assortment is the random separating of chromosomes during meiosis. This is a random process. The chromosomes are then reunited during sex in a completely random way, leading to a variety of possible combinations.
10.
Describe how cytokinesis differs in plants and animals (1)
In plants cytokinesis happens by vacuoles containing cell wall material gathering at the middle of the cell and forming a cell plate. They fuse together an d eventually fuse with the cell wall, creating two new cells.
In animals cytokinesis happens via cleavage. A cleavage furrow appears, which is a shallow groove on the cell surface. Microfilaments form a ring at the site and contract deepening the furrow and splitting the cell in two new cells.
7