Mitochondria and Chloroplasts Questions and Answers

11.

State whether the following is true or false.
An uncoupling agent that makes the inner membrane leaky to protons will increase ATP production.

A.False only at small scales
B.True
C.False
D.True only at large scales

Answer: C

It collapses the gradient, so the protons return without passing through the synthase and their energy is released as heat instead. Brown fat uses exactly this trick deliberately to warm the body. The heat is generated without any shivering or muscular work.

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12.

Brown adipose tissue generates heat rather than ATP because its mitochondria contain

A.no functioning electron transport chain at all
B.an unusually small number of cristae inside
C.none of the citric acid cycle enzymes
D.an uncoupling protein in the inner membrane

Answer: D

The protein lets protons leak back without turning the synthase, so the energy of the gradient escapes as warmth. Newborn mammals and hibernators rely on the arrangement. The tissue is brown because it is packed with iron-rich mitochondria.

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13.

The flattened membrane sacs inside a chloroplast are called

A.thylakoids
B.cristae folds
C.matrix sacs
D.porin channels

Answer: A

Stacks of them form the grana, and the pigment systems that capture light are embedded in their membranes. Cristae are the corresponding folds in a mitochondrion and carry a different set of proteins. The two organelles solve the same problem of membrane area in different ways.

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14.

The fluid surrounding the thylakoids within a chloroplast is the

A.intermembrane space
B.stroma
C.matrix
D.cytosol

Answer: B

It contains the enzymes of carbon fixation together with the chloroplast's own DNA and ribosomes. The mitochondrial equivalent is called the matrix, and the two names should not be exchanged. Both compartments hold the organelle's own genome and protein-making machinery.

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15.

The light-dependent reactions of photosynthesis occur in the

A.cytosol of the cell
B.outer chloroplast membrane
C.thylakoid membranes
D.stroma of the chloroplast

Answer: C

Chlorophyll and the electron carriers sit within those membranes, and protons are pumped into the thylakoid lumen as electrons pass along. The reactions of carbon fixation happen outside them in the stroma. Separating the two stages lets each proceed in its own chemical environment.

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16.

The Calvin cycle, which fixes carbon dioxide, takes place in the

A.thylakoid lumen
B.thylakoid membrane
C.intermembrane space
D.stroma

Answer: D

Its enzymes, rubisco among them, are dissolved in the stroma and consume the ATP and NADPH made by the light reactions next door. The two stages are linked by those products rather than by light itself. Rubisco is the most abundant protein on Earth by mass.

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17.

State whether the following is true or false.
The Calvin cycle can proceed in darkness provided ATP and NADPH are available.

A.True
B.False
C.True only at large scales
D.False only at small scales

Answer: A

It requires no light directly, which is why it was long called the dark reaction, though in practice its supply of ATP and NADPH depends on the light reactions. The older name misleads by suggesting it happens only at night.

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18.

Assertion (A): The Calvin cycle is no longer called the dark reaction.
Reason (R): The name suggested that it occurs at night, whereas it runs chiefly in daylight.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both are true and the reason gives the objection: the cycle needs no light itself but depends completely on products the light reactions supply, so it is most active when the sun is shining. The modern name light-independent reactions avoids that confusion.

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19.

In a chloroplast, protons accumulate during the light reactions in the

A.intermembrane space
B.cytosol of the cell
C.thylakoid lumen
D.stroma outside the thylakoids

Answer: C

The gradient therefore runs across the thylakoid membrane, with the lumen acidic. In a mitochondrion the corresponding gradient sits across the inner membrane instead. The principle is the same in both organelles even though the geometry differs.

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20.

Consider the following statements comparing the two organelles.
1. Both are bounded by a double membrane.
2. Both contain their own DNA and ribosomes.
3. Both generate ATP by substrate-level phosphorylation only.

A.3 only
B.1 only
C.All of them
D.1 and 2 only

Answer: D

The first two are correct and are among the reasons for thinking both descended from bacteria. The third is wrong, since each makes ATP chemiosmotically using a proton gradient. Substrate-level phosphorylation contributes only a small part of the total.

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