Cellular Respiration

Question 1

Life requires energy.

Answer 1

In almost all ecosystems, energy ultimately comes from the sun.

Question 2

In photosynthesis,

Answer 2

some of the energy in sunlight is captured by chloroplasts,
atoms of carbon dioxide and water are rearranged, and
glucose and oxygen are produced.

Question 3

In cellular respiration

Answer 3

glucose is broken down to carbon dioxide and water and
the cell captures some of the released energy to make ATP.
Cellular respiration takes place in the mitochondria of eukaryotic cells.

Question 4

Respiration, as it relates to breathing, and cellular respiration are not the same.

Answer 4

Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO2.
Cellular respiration is the aerobic (oxygen requiring) harvesting of energy from food molecules by cells.

Question 5

Cellular respiration is an exergonic process

Answer 5

that transfers energy from the bonds in glucose to form ATP.
Cellular respiration
produces up to 32 ATP molecules from each glucose molecule and
captures only about 34% of the energy originally stored in glucose.
Other foods (organic molecules) can also be used as a source of energy.

Question 6

The energy necessary for life

Answer 6

is contained in the arrangement of electrons in chemical bonds in organic molecules.

Question 7

An important question is how do cells extract this energy?

Answer 7

When the carbon-hydrogen bonds of glucose are broken, electrons are transferred to oxygen.
Oxygen has a strong tendency to attract electrons.
An electron loses potential energy when it “falls” to oxygen.

Question 8

redox reaction

Answer 8

The movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction,
the loss of electrons from one substance is called oxidation,
the addition of electrons to another substance is called reduction,
a molecule is oxidized when it loses one or more electrons, and
reduced when it gains one or more electrons.

Question 9

A cellular respiration equation is helpful to show the changes in hydrogen atom distribution.

Answer 9

Glucose - loses its hydrogen atoms and becomes oxidized to CO2.
Oxygen - gains hydrogen atoms and becomes reduced to H2O.

Question 10

Enzymes are necessary to oxidize glucose and other foods

Answer 10

NAD+
is an important enzyme in oxidizing glucose,
accepts electrons, and
becomes reduced to NADH.

Question 11

electron transport chain

Answer 11

There are other electron “carrier” molecules that function like NAD+.
They form a staircase where the electrons pass from one to the next down the staircase.
These electron carriers collectively are called the electron transport chain.
As electrons are transported down the chain, ATP is generated.

Question 12

Cellular respiration consists of a sequence of steps that can be divided into 3 stages.

Answer 12

Stage 1 – Glycolysis
Stage 2 – Pyruvate oxidation and citric acid cycle
Stage 3 – Oxidative phosphorylation (Electron Transport Chain)

Question 13

Stage 1: Glycolysis

Answer 13

occurs in the cytosol,
begins cellular respiration, and
breaks down glucose into 2 molecules of a 3-carbon compound (pyruvate).

Question 14

Stage 2: The citric acid cycle

Answer 14

takes place in mitochondria,
oxidizes pyruvate to a two-carbon compound, and
supplies the third stage with electrons.

Question 15

Stage 3: Oxidative phosphorylation(Electron Transport Chain)

Answer 15

involves electrons carried by NADH and FADH2,
shuttles these electrons to the electron transport chain embedded in the inner mitochondrial membrane,
involves chemiosmosis, and
makes ATP via oxidative phosphorylation associated with chemiosmosis.

Question 16

In glycolysis,

Answer 16

a single molecule of glucose is enzymatically cut in half through a series of steps,
two molecules of pyruvate are produced,
two molecules of NAD+ are reduced to two molecules of NADH, and
a net of two molecules of ATP is produced.

Question 17

The pyruvate formed in glycolysis is transported from the cytoplasm into a mitochondrion where

Answer 17

the citric acid cycle and
oxidative phosphorylation will occur.
2 molecules of pyruvate are produced for each molecule of glucose that enters glycolysis.
Pyruvate does not enter the citric acid cycle but undergoes some chemical grooming
a carboxyl group is removed and given off as CO2,
the two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH,
coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, and
acetyl CoA enters the citric acid cycle.

Question 18

The citric acid cycle is also called the Krebs cycle

Answer 18

completes the oxidation of organic molecules, and generates many NADH and FADH2 molecules.
During the citric acid cycle
the two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate,
citrate is degraded back to the four-carbon compound,
two CO2 are released, and
1 ATP, 3 NADH, and 1 FADH2 are produced.
Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose.
Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is
2 ATP,
6 NADH, and
2 FADH2.

Question 19

The Electron Transport Chain

Answer 19

Electrons from NADH and FADH2 travel down the electron transport chain to O2.
Oxygen picks up H+ to form water.
Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space.
In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.

Question 20

Fermentation is a way of harvesting chemical energy that does not require oxygen.

Answer 20

Fermentation
takes advantage of glycolysis,
produces two ATP molecules per glucose, and
reduces NAD+ to NADH.
The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+.

Question 21

lactic acid fermentation

Answer 21

Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which
NADH is oxidized to NAD+ and pyruvate is reduced to lactate.
Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.