Biology Unit 3 & 4
Testosterone is a small steroid hormone that is important in cell signaling. Which of the following indicates where testosterone enters a cell and why it is able to cross at that point?
1, because testosterone is nonpolar and can diffuse through the membrane.
Various materials are transported into or out of the cells by diffusion. Which of the following cube-shaped cells would be most efficient in removing waste by diffusion?
10um
What is essential for diffusion?
A concentration gradient
Which of the following is required for osmosis to occur?
A solute concentration gradient
Simple diffusion and facilitated diffusion are related in that both
Depend on a concentration gradient
Which statement BEST explains why enzymes bind to specific substrates?
Different amino acid sequences cause variations in the shapes of an enzyme's active sites.
What happens during end product inhibition of the pathway shown below?
Enzyme I is inhibited by substance Z.
Enzymes have the ability to facilitate the reaction of many substrate molecules. Which choice below best describes why enzymes have this ability?
Enzymes are reusable.
Cells in the adrenal gland produce the hormone epinephrine and store it in vesicles. To release epinephrine these vesicles are carried to the plasma membrane and fuse with it. What process is occurring?
Exocytosis
In the diagram below, macromolecules are being transported to the exterior of a cell. What is the name of this process?
Exocytosis
Which pair of characteristics is correct for the cellular processes of exocytosis and endocytosis?
Exocytosis - Secretion of cellular materials; Endocytosis - Vesicles are moved away from the plasma membrane
When a substance moves across the plasma membrane along a concentration gradient at a rate faster than would be expected by simple diffusion alone but without the expenditure of energy, the process is best described as
Facilitated Diffusion
Illustration 1 shows sugar that has formed a bond by the action of an enzyme. Illustration 2 shows the enzyme, and Illustration 3 shows the enzyme after the addition of heat. How does the addition of heat affect the ability of an enzyme to help the sugar molecules form a bond?
Heat changes the enzyme so that the sugar molecules can no longer bond.
The diagram below shows a model of a biological membrane. What do labels I, II and III illustrate?
I = Glycoprotein, II = Integral protein, III = Hydrophilic phosphate head
The diagram below shows a channel protein in a membrane. Which parts of the surface of the protein would be composed of polar amino acids?
I and II only
Which evidence falsifies the Davson-Danielli model? I. The presence of globular proteins within the phospholipid bilayer II. Non-polar amino acids cause proteins to remain embedded in membranes III. Membrane proteins remain in a fixed position inside a membrane
I and II only
Which statements are characteristics of diffusion through membranes? I. Polysaccharides can be transported II. It can be facilitated by special channels III. It is affected by concentration gradients
II and III only
What is lactase used for?
It improves the digestion of milk by some people.
Glucose is absorbed through protein channels in the plasma membrane of epithelium cells in the small intestine. Which characteristics of glucose prevent its diffusion through the phospholipid bilayer?
It is polar and therefore hydrophilic.
If ATP breakdown (hydrolysis) is inhibited, which of the following types of movement across cell membranes is also inhibited?
Passage of a solute against its concentration gradient.
Which of the following components of the cell membrane is responsible for active transport?
Protein
In an experiment the effect of changing pH on an enzymatic reaction is tested. Which could be a dependent variable in this kind of experiment?
Rate of formation of product
Oxygen is a small, nonpolar molecule. How does oxygen enter cells?
Simple Diffusion
Which of the following processes requires the expenditure of ATP?
Sodium-potassium pump
If red blood cells cultured in an isotonic medium are placed in distilled water, they will most likely
Swell
According to the induced fit model of enzyme function, which of the following statements is correct?
The binding of the substrate changes the shape of the active site slightly.
Paramecia are unicellular protists that have contractile vacuoles to remove excess intracellular water. In an experimental investigation, paramecia were placed in salt solutions of increasing osmolarity. The rate at which the contractile vacuole contracted to pump out excess water was determined and plotted against osmolarity of the solutions, as shown in the graph. Which of the following is the correct explanation for the data?
The contraction rate decreases as the osmolarity increases because the amount of water entering the paramecia by osmosis decreases.
The graph below shows enzyme activity plotted against temperature. What is happening at point I?
The enzyme is being denatured.
The graph below shows the effect of substrate concentration on enzyme activity. What conclusion can be drawn about section X of the graph?
The enzyme is saturated and is working at its maximum reaction rate.
The graph below shows energy changes during a chemical reaction that occurs without a catalyst.What would change if the reaction was catalysed by an enzyme?
The maximum energy level (II) would be lower, speeding up the reaction.
What is facilitated diffusion?
The passive movement of a particle across a cell membrane via a channel protein.
The graph below shows the effect of changing the substrate concentration on an enzyme-controlled reaction. What is the correct interpretation of these data?
The rate of reaction increases up to a point and then remains constant.
What is an active site?
The sequence of amino acids responsible for the catalytic activity of enzymes.
What determines the specificity of an enzyme for its substrate?
The structure of the enzyme's active site
Enzymes act as catalysts in biochemical reactions. In the diagram, which represents a catalyst?
Y
Which condition is indicated by lines Y and Z?
Y = competitive inhibitor present; Z = non-competitive inhibitor present
Catalase is an enzyme that speeds up the decomposition of hydrogen peroxide into water and oxygen. Students conducted two investigations to determine the ideal conditions for the function of catalase. One investigation compared catalase activity at different values of pH. The other investigation compared catalase activity at different temperatures. According to the data in the graphs, which pH and temperature combination provides the BEST conditions for catalase to function?
pH 7 and 37°C
