Contractile vacuoles
A) are generally found in protists that inhabit salt water.
B) help in the excretion of excess salt.
C) prevent cells from bursting as a result of the influx of excess water.
D) allow organisms to avoid dehydration by absorbing water from the environment.

C

Relaying a message from a membrane receptor to a molecule that performs a specific function within a cell is called
A) signal transduction.
B) inhibition.
C) competition.
D) selective permeability.

A

Plasma membranes are selectively permeable. This means that
A) anything can pass into or out of a cell as long as the membrane is intact and the cell is healthy.
B) the plasma membrane allows some substances to enter or leave a cell more easily than others.
C) glucose cannot enter the cell.
D) plasma membranes must be very thick.

B

Which of the following examples is classified as a metabolic pathway?
A) protein synthesis
B) osmosis
C) cell lysis
D) passive diffusion

A

The transfer of a phosphate group to a molecule or compound is called
A) carboxylation.
B) ionization.
C) phosphorylation.
D) hydrogenation.

C

The active site of an enzyme is
A) the region of a substrate that is changed by an enzyme.
B) the highly changeable portion of an enzyme that adapts to fit the substrates of various reactions.
C) the region of an enzyme that attaches to a substrate.
D) the region of a product that detaches from the enzyme.

C

The enzymes of the citric acid cycle are located in the
A) cytoplasm.
B) outer mitochondrial membrane.
C) nucleus.
D) matrix and inner mitochondrial membrane.

D

) During chemiosmosis,
A) energy is released as H+ ions move freely across mitochondrial membranes.
B) ATP is synthesized when H+ ions move through a channel in ATP synthase.
C) a concentration gradient is generated when large numbers of H+ ions are passively transported from the matrix of the mitochondrion to the mitochondrion's intermembrane space.
D) H+ ions serve as the final electron acceptor.

B

Photoautotrophs
A) make sugar by using organic raw materials.
B) produce organic molecules from inorganic molecules.
C) eat other organisms that use light energy to make food molecules.
D) include only the green plants.

A

What is the likely origin of chloroplasts?
A) mitochondria that had a mutation for photosynthesis
B) photosynthetic prokaryotes that lived inside eukaryotic cells
C) prokaryotes with photosynthetic mitochondria
D) eukaryotes that engulfed photosynthetic fungi

B

________ cells in leaves are specialized for photosynthesis.
A) Companion
B) Mesophyll
C) Sclerenchyma
D) Tracheid

B

CO2 enters and O2 escapes from a leaf via
A) stomata.
B) thylakoids.
C) grana.
D) stroma.

A

A redox reaction involves the transfer of
A) oxygen.
B) water.
C) an electron.
D) carbon dioxide.

C

The light reactions occur in the ________, while the Calvin cycle occurs in the ________.
A) stroma . . . thylakoid membranes
B) stroma . . . nucleus
C) cytoplasm . . . thylakoid membrane
D) thylakoid membranes . . . stroma

D

Carbon fixation
A) occurs when carbon atoms from CO2 are incorporated into an organic molecule.
B) supplies the cell with ATP.
C) occurs during the light reactions.
D) provides the cell with a supply of NADPH molecules.

A

The energy that excites P680 and P700 is supplied by
A) electrons passing down the electron transport chain.
B) ATP.
C) photons.
D) NADPH.

A

Which of the following cells has the greatest surface-to-volume ratio?
A) bacterium
B) human red blood cell
C) human muscle cell
D) ostrich egg

A

Plasma membranes are permeable to
A) large hydrophilic molecules such as starch.
B) small ions such as Na+.
C) nonpolar molecules such as CO2.
D) hydrophilic molecules such as glucose.

C

Unlike animal cells, plant cells have ________ and ________. Unlike plant cells, animal cells have ________.
A) chloroplasts . . . cell walls . . . centrioles
B) centrioles . . . chloroplasts . . . cell walls
C) chloroplasts . . . cell walls . . . a nucleus
D) centrioles . . . cell walls . . . large central vacuoles

A

The fluid mosaic model describes the plasma membrane as consisting of
A) a phospholipid bilayer with embedded carbohydrates.
B) two layers of phospholipids with cholesterol sandwiched between them.
C) carbohydrates and phospholipids that can drift in the membrane.
D) diverse proteins embedded in a phospholipid bilayer.

D

Aquaporins
A) allow water to cross the plasma membrane via facilitated diffusion.
B) allow water to cross the plasma membrane against its concentration gradient.
C) allow for the active transport of water.
D) are found in all cells.

A

The process of a white blood cell engulfing a bacterium is
A) osmosis.
B) receptor-mediated endocytosis.
C) pinocytosis.
D) phagocytosis.

D

When an enzyme catalyzes a reaction,
A) it lowers the activation energy of the reaction.
B) it raises the activation energy of the reaction.
C) it acts as a reactant.
D) it is used once and discarded.

A

Which of the following statements regarding enzyme function is false?
A) An enzyme's function depends on its three-dimensional shape.
B) Enzymes are very specific for certain substrates.
C) Enzymes are used up when they catalyze a chemical reaction, so must be synthesized for each new chemical reaction.
D) Enzymes emerge unchanged from the reactions they catalyze.

C