CHAPTER 14
REVIEW QUESTIONS
14.1
C6H12O6 + 2ATP + 6H2O + 38ADP + 38P + 6O2 2ADP + 2P + 6CO2 + 12H2O + 38ATP
14.2
Within cells glucose undergoes a series of chemical reactions. The complete breakdown of
glucose results in the formation of two small molecules, carbon dioxide and water. At various
stages in the metabolism of glucose, energy is released. This energy is used to bond a
phosphate group to ADP to form ATP. ATP is able to transport and release this chemical-bond
energy to cell reactions requiring energy.
14.3
During the first phase of respiration – glycolysis, which occurs in the cytoplasm – a molecule
of glucose is converted to 2 molecules of pyruvic acid, releasing a net of 2 ATP molecules and
hydrogen which become attached to carrier molecules. If oxygen is present the pyruvic acids
and oxygen move into the mitochondrion. The pyruvic acid is completely broken down to
carbon dioxide and water releasing a further 34 ATP molecules in two processes – the Krebs
citric acid cycle and the electron transport chain.
14.4
a.
b.
14.5
Carbohydrates are the first substance to undergo respiration to produce energy. Starch (plants)
or glycogen (animals) is converted to glucose, which enters the glycolysis phase.
If all the carbohydrate reserves are depleted lipids break down to glycerol and fatty acids. The
glycerol can the enter the glycolysis phase.
Once lipid reserves are used up, protein can break down to amino acids, conversions of which
can produce either pyruvic acid or acetylCoA which enters the Krebs cycle.
If no oxygen is present the pyruvic acid cannot enter the Krebs cycle. In plant cells the pyruvic
acid is converted to (d) carbon dioxide and (e) ethyl alcohol, whilst in animal cells it is
converted to (f) lactic acid.
14.6
Both aerobic and anaerobic respiration involve the chemical conversion of glucose with the
release of energy which is transferred to ATP molecules. Anaerobic respiration occurs in the
cell cytoplasm and has a low energy yield. The aerobic phase of respiration occurs in the
mitochondrion with a high energy yield. Anaerobic respiration does not require the presence of
oxygen but aerobic respiration does. Anaerobic respiration is energy-inefficient whilst aerobic
respiration is energy-efficient.
14.7
Complete anaerobes can only perform anaerobic respiration and are adapted to permanently
oxygen-deficient habitats. They may be poisoned by even a small concentration of oxygen.
Partial anaerobes, on the other hand, are normally aerobic and thrive in the presence of
oxygen, They can, however, survive anaerobically for short periods of time if oxygen is absent
or in short supply.
14.8
Transcription: production of mRNA from the DNA template of the gene for the particular
protein.
Translation: interaction between mRNA, the ribosome and tRNAs in forming the polypeptide
chain.
Aerobic phase in the mitochondrion – the last, electron transport phase in the process.
Electrons from hydrogen atoms produced in previous reactions are transferred to a
coenzyme chain. The electrons, which have a high potential energy, release bundles of
energy as they pass from one coenzyme to the next. This energy is used to convert ADP
to ATP, producing a total of 32 ATP molecules for each original glucose molecule. At
the end of the chain the low energy electrons combine with hydrogen ions and oxygen to
form water.
14.9
a.
b.
c.
d.
e.
f.
g.
h.
DNA contains the codes or instructions for the amino acid sequence in synthesis of
proteins.
A gene is the particular part of the DNA that codes for a specific protein (i.e. the
code).
mRNA is an RNA molecule with complimentary base sequences of the DNA code for
a particular protein.
tRNA is a small piece of RNA which becomes loosely bound to a specific amino acid
in the cytoplasm. It is used to transport amino acids to specific sites on the mRNA.
Amino acid: a monomer of the polypeptide chain that forms the primary structure of
a protein.
Endoplasmic reticulum is the membranous, tubular organelle within the cytoplasm
involved in the synthesis of chemicals.
Polypeptide chain is a sequence of amino acids that forms the primary structure of a
protein.
Golgi apparatus is a membrane-bound organelle within the cytoplasm responsible for
completion of the conversion of the polypeptide chain to the protein, often by the
addition of carbohydrates.
14.10
B: DNA – ribosomes – endoplasmic reticulum – Golgi apparatus – cell membrane.
14.11
DNA replicates.
Nuclear membrane disintegrates.
Spindle forms.
Chromosomes line up at the equator of the spindle.
Chromatids separate.
Chromosomes move to the ends of the spindle.
Nuclear membranes form.
14.12
Centrioles.
14.13
Cell plate.
14.14
If the DNA does not replicate, then mitosis will result in daughter cells only having half the
DNA compliment and thus an incorrect number of chromosomes. Since each chromosome
lines up independently on the spindle fibres, some daughter cells may finish up with most of
the chromosomes and the other with few; the types of chromosomes distributed amongst the
daughter cells would be random. Overall species integrity would be destroyed and the ensuing
cells would not function according to the species requirements, if they in fact survived.
14.15
a.
b.
Mitosis: before haploid or diploid, after the same as the original number. Meiosis: before
diploid, after haploid.
Mitosis: growth, tissue repair; meiosis reproduction. (In algae and plants that exhibit
alternation of generations, meiosis is used in asexual formation of spores and mitosis in
formation of gametes in sexual reproduction.)
14.16
The offspring would have double the chromosome compliment which may disrupt normal gene
function and lead to death or change in species characteristics.
14.17
They separate, with one of each pair going to a daughter cell during meiosis I.
14.18
In mitosis the single pairs of chromatids (formed by the replication of chromosomes) line up
on the spindle. Separation of the two chromatids into the two daughter cells ensures that each
cell has the same number and type of chromosome as the original cell. In meiosis I, tetrads of
chromatids (formed from the replication and pairing of homologous chromosomes) line up on
a spindle thread. The first nuclear division therefore reduces the numbers of chromatid pairs
but ensures that each cell has the same types of chromosomes. The second nuclear division is
essentially the same as mitosis in that the chromatids become separated. Four daughter cells
are therefore formed, each with half the number but the same types of chromosomes.
14.19
a.
b.
c.
d.
Mitosis.
Meiosis.
Mitosis.
Meiosis.
14.20
In both divisions, daughter cells containing the same types of chromosomes as the original cell
are formed and replication of the chromosomes (forming chromatids joined at the centromere)
occurs before the process begins. In mitosis there is a single nuclear division, the chromatid
pairs join joins the spindle fibre at the centromere which results in the separation of the
chromatids into daughter cells. The two daughter cells therefore have the same number of
chromosomes as the original cell. Thus mitosis can occur in either haploid or diploid cells. In
meiosis, tetrads of homologous chromatids link with the spindle fibre. Two divisions are
required – one to separate the tetrads and the next to separate the chromatids. Thus four
daughter cells are formed, each with half the number of chromosomes. Only cells with pairs of
chromosomes, therefore, can undergo meiosis.
14.21
The different wavelengths of energy released by the sun as radiant energy.
14.22
The shorter the wavelength the greater the energy level.
14.23
It is absorbed by particles in the upper atmosphere or is reflected or radiated back into space.
14.24
The pigments of chlorophyll only absorb a few wavelengths of solar radiation.
14.25
An absorption spectrum shows the wavelengths absorbed by a pigment. An action spectrum
shows the effectiveness of particular wavelengths of light in stimulating a specific process.
14.26
To convert radiant energy to chemical bond energy in the formation of glucose.
14.27
a.
Light-dependent reactions occur on the grana.
Light-independent reactions occur in the stroma.
b.
In the light-dependent reactions, light energy is absorbed by chlorophyll molecules,
exciting electrons to such higher energy levels that they escape their molecules and are
passed from one co-enzyme to another along a chain. During this time some of their
energy is used in the formation of ATP. At the end of the co-enzyme chain, the now low
energy electrons are trapped by the electron-deficit chlorophyll molecules.
Simultaneously, water is split. The hydrogen is transported to the stroma and oxygen is
released.
In the light-independent reactions, carbon dioxide enters a complex chemical cycle (the
Calvin-Benson Cycle) in which 2 PGAL molecules are formed with an input of energy
(from ATP) and hydrogen (from the hydrogen carrier). The 2 PGAL molecules undergo a
further series of reactions to form glucose.