QUESTIONS: REVISION
CHAPTER 1: BIOLOGICAL MOLECULES
Question 1: Describe the role of carbohydrates in living organisms.
Answer: Carbohydrates play several important roles in living organisms, including serving as
a source of energy, structural support, and signalling molecules. Glucose is the primary
source of energy for most cells, and is stored in the form of glycogen in animals and starch
in plants. Carbohydrates also play a key role in the structure of cell walls, and some
carbohydrates, such as glycoproteins, are involved in cell signalling.
Question 2: Explain the difference between saturated and unsaturated fatty acids, and
discuss the health implications of each.
Answer: Saturated fatty acids have no double bonds between carbon atoms, whereas
unsaturated fatty acids have one or more double bonds. Saturated fats are typically solid at
room temperature, while unsaturated fats are typically liquid. A diet high in saturated fat has
been linked to increased risk of heart disease, while a diet high in unsaturated fat may help
lower cholesterol levels and reduce the risk of heart disease.
Question 3: Compare and contrast the structures of DNA and RNA.
Answer: Both DNA and RNA are nucleic acids composed of nucleotides. DNA is a
double-stranded helix, while RNA is typically single-stranded. DNA contains the bases
adenine, guanine, cytosine, and thymine, while RNA contains uracil instead of thymine. DNA
is responsible for the storage and transmission of genetic information, while RNA plays a key
role in protein synthesis.
Question 4: Explain the difference between an alpha helix and a beta pleated sheet in
protein structure.
Answer: An alpha helix is a secondary structure of a protein in which the amino acid chain
coils into a helix shape. The structure is stabilised by hydrogen bonds between the amino
acid backbone. A beta pleated sheet is another type of secondary structure in which the
amino acid chain folds back and forth, forming a sheet-like structure. The structure is
stabilised by hydrogen bonds between adjacent amino acid chains. While both structures are
formed by hydrogen bonding, they differ in the direction of the bonds and the resulting shape
of the protein.
Question 5: Describe the function of enzymes in biochemical reactions, and explain how the
structure of an enzyme is related to its function.
Answer: Enzymes are biological catalysts that increase the rate of biochemical reactions by
lowering the activation energy required for the reaction to occur. Enzymes are specific to the
substrates they act upon, and typically work by binding to the substrate to form an
enzyme-substrate complex. The structure of an enzyme is critical to its function, as the
shape of the enzyme's active site must be complementary to the shape of the substrate.
Additionally, the catalytic activity of an enzyme is often influenced by the presence of
cofactors or the regulation of enzyme expression.
Question 6: Discuss the structural and functional differences between globular and fibrous
proteins.
Answer: Globular proteins are typically rounded or globular in shape and are soluble in
water, whereas fibrous proteins are long and thin and are typically insoluble in water.
Globular proteins often have a tertiary or quaternary structure and are involved in functions
such as enzymes, transport, and regulation. Fibrous proteins, on the other hand, often have
a primary or secondary structure and are involved in functions such as support, protection,
and movement. Examples of globular proteins include haemoglobin and enzymes, while
examples of fibrous proteins include collagen and keratin. The differences in structure and
function between globular and fibrous proteins reflect the diverse roles that proteins play in
living organisms.
CHAPTER 2: Cells and Cell structure
Question 1: Describe the structure and function of the plasma membrane in eukaryotic cells.
Answer: The plasma membrane is a thin, flexible layer that surrounds the cell and separates
the interior of the cell from its environment. It is composed of a phospholipid bilayer, which
has hydrophilic heads that face outward and hydrophobic tails that face inward. The
membrane also contains proteins, which can act as channels, receptors, and enzymes. The
function of the plasma membrane is to regulate the movement of molecules in and out of the
cell and to maintain the cell's internal environment.
Question 2: Compare and contrast the cell wall in plant cells and bacterial cells.
Answer: The cell wall in plant cells is composed of cellulose and is located outside the
plasma membrane. It provides support and protection for the cell, as well as contributing to
the structure of tissues and organs. In bacterial cells, the cell wall is composed of
peptidoglycan and is also located outside the plasma membrane. It provides support and
protection for the cell, and is an important target for antibiotics.
Question 3: Describe the structure and function of the nucleus in eukaryotic cells.
Answer: The nucleus is a membrane-bound organelle that contains the genetic material of
the cell in the form of chromosomes. It is composed of a double membrane called the
nuclear envelope, which has pores that allow the passage of molecules in and out of the
nucleus. The nucleus also contains a nucleolus, which is responsible for the production of
ribosomes. The function of the nucleus is to regulate gene expression and control the
activities of the cell.
Question 4: Explain the process of protein synthesis in eukaryotic cells, including the role of
ribosomes, rough endoplasmic reticulum, and Golgi apparatus.
Answer: Protein synthesis begins in the nucleus, where DNA is transcribed into messenger
RNA (mRNA). The mRNA then moves to the cytoplasm, where it is translated into protein by
ribosomes. Ribosomes can be free in the cytoplasm or attached to the rough endoplasmic
reticulum (RER). Proteins synthesised by ribosomes attached to the RER are transported
into the lumen of the RER, where they are modified and folded. Vesicles transport the
modified proteins to the Golgi apparatus, where they are further modified, sorted, and
packaged for delivery to their final destination.
Question 5: Compare and contrast the structure and function of mitochondria and
chloroplasts in eukaryotic cells.
Answer: Both mitochondria and chloroplasts are membrane-bound organelles that produce
energy in eukaryotic cells. Mitochondria produce ATP through aerobic respiration, while
chloroplasts produce ATP through photosynthesis. The structure of mitochondria includes an
outer membrane, an inner membrane with cristae, and a matrix. The structure of
chloroplasts includes a double membrane, thylakoid membranes, and stroma. Chloroplasts
also contain chlorophyll, which is responsible for capturing light energy for photosynthesis.
Question 6: Describe the structure and function of lysosomes in eukaryotic cells.
Answer: Lysosomes are membrane-bound organelles that contain hydrolytic enzymes. They
are responsible for the breakdown of macromolecules, such as proteins, carbohydrates, and
lipids, as well as the degradation of old organelles and foreign substances. Lysosomes are
formed by the Golgi apparatus and are found in most animal cells.
Question 7: Compare and contrast the structures and functions of optical microscopes and
electron microscopes.
Answer: Optical microscopes use visible light to magnify specimens and can produce
images with a resolution of about 0.2 micrometres. They are useful for studying living cells
and tissues, but have limited magnification and resolution. Electron microscopes use a beam
of electrons instead of visible light to magnify specimens and can produce images with a
resolution of up to 0.2 nanometers. They have higher magnification and resolution than
optical microscopes, but require the specimens to be fixed and coated with heavy metals,
and cannot be used to observe living specimens. There are two types of electron
microscopes: transmission electron microscopes (TEMs) and scanning electron microscopes
(SEMs). TEMs use electrons transmitted through the specimen to produce an image, while
SEMs use electrons scattered from the surface of the specimen to produce an image.
Question 8: Compare and contrast the structure and function of prokaryotic and eukaryotic
cells.
Answer: Prokaryotic cells are smaller and simpler in structure than eukaryotic cells. They
lack a nucleus and membrane-bound organelles, and their DNA is circular and located in the
nucleoid region of the cell. Prokaryotic cells have a cell wall, which provides support and
protection for the cell, and may also have pili and flagella for movement. Eukaryotic cells are
larger and more complex in structure than prokaryotic cells. They have a nucleus and
various membrane-bound organelles, including mitochondria, chloroplasts, endoplasmic
reticulum, Golgi apparatus, lysosomes, and vacuoles. Eukaryotic cells have a cytoskeleton,
which provides structural support and is involved in cell movement and division. Both
prokaryotic and eukaryotic cells carry out essential functions such as metabolism, growth,
and reproduction, but they differ in their modes of organisation and complexity.
CHAPTER 3: Enzymes
Question 1: Describe the general structure and mechanism of action of enzymes.
Answer: Enzymes are proteins that act as biological catalysts, speeding up chemical
reactions in cells. They have a specific three-dimensional structure, with a pocket or cleft
called the active site where the substrate binds. Enzymes lower the activation energy
required for a chemical reaction to occur, by orienting the substrate molecules and facilitating
the formation of the transition state. Enzymes themselves are not consumed or changed by
the reaction, and can be used repeatedly.
Question 2: Explain how enzyme activity is affected by changes in temperature and pH.
Answer: Enzyme activity is highly dependent on the temperature and pH of the environment.
At low temperatures, enzyme activity is slow because the kinetic energy of the molecules is
low. At high temperatures, enzyme activity may denature or irreversibly change the structure
of the protein, preventing it from functioning. Each enzyme has an optimal temperature
range, at which it is most active. Similarly, enzymes have an optimal pH range at which they
function best. Changes in pH can alter the charge or shape of the enzyme, affecting its
ability to bind to the substrate.
Question 3: Describe the effects of substrate concentration on enzyme activity.
Answer: Enzyme activity increases with increasing substrate concentration, until a point is
reached where all the active sites are occupied and the rate of reaction plateaus. This point
is called the maximum velocity or Vmax of the reaction. At low substrate concentrations, the
rate of reaction is proportional to the substrate concentration and follows first-order kinetics.
At higher substrate concentrations, the rate of reaction becomes saturated and follows
zero-order kinetics.
Question 4: Explain how enzyme inhibitors can affect enzyme activity.
Answer: Enzyme inhibitors are molecules that bind to the enzyme and reduce its activity.
There are two main types of enzyme inhibitors: competitive inhibitors and noncompetitive
inhibitors. Competitive inhibitors bind to the active site of the enzyme, blocking the substrate
from binding. Noncompetitive inhibitors bind to other parts of the enzyme, changing the
shape or charge of the protein and reducing its activity. Some enzyme inhibitors are naturally
occurring molecules, such as toxins or poisons, while others are used as drugs to treat
diseases.
Question 5: Discuss the importance of enzyme regulation in cell metabolism.
Answer: Enzyme regulation is critical for maintaining the balance and efficiency of metabolic
pathways in cells. Enzymes can be regulated at various levels, including gene expression,
post-translational modification, and allosteric regulation. By controlling the activity of specific
enzymes, cells can adjust their metabolic rates in response to changing environmental
conditions or internal signals. Enzyme regulation also allows cells to avoid the wasteful or
harmful buildup of metabolic intermediates, and to prioritise the use of certain substrates or
pathways over others. Without enzyme regulation, cellular metabolism would be chaotic and
inefficient.
CHAPTER 4: Transport in and out of the cells
CHAPTER 5: Gas exchange
Question 1: Describe the structure and function of the plasma membrane in cells.
Answer: The plasma membrane is a phospholipid bilayer that surrounds all cells, separating
their internal environment from the external environment. The phospholipid bilayer consists
of two layers of phospholipid molecules with their hydrophobic tails facing inward and their
hydrophilic heads facing outward. Embedded in the membrane are proteins that perform
various functions, such as transport of molecules, cell signalling, and cell adhesion. The
plasma membrane is selectively permeable, allowing only certain molecules to pass through.
1. Explain how the surface area to volume ratio affects gas exchange in organisms. (6)
Question 2: Explain the processes of diffusion and osmosis, and give examples of each in
cells.
Answer: Diffusion is the movement of molecules from an area of high concentration to an
area of low concentration, down a concentration gradient. This process occurs
spontaneously and does not require energy. Osmosis is a special case of diffusion in which
water molecules move across a selectively permeable membrane from an area of high
concentration to an area of low concentration. Examples of diffusion in cells include the
movement of oxygen and carbon dioxide across the plasma membrane during respiration
and photosynthesis, and the movement of ions such as potassium and sodium across cell
membranes. An example of osmosis in cells is the movement of water into and out of red
blood cells.
Question 3: Describe the process of active transport and the role of carrier proteins and ATP.
Answer: Active transport is the movement of molecules across a membrane against their
concentration gradient, from an area of low concentration to an area of high concentration.
This process requires energy in the form of ATP (adenosine triphosphate), which is
generated by the cell through cellular respiration. Carrier proteins in the membrane bind to
the molecules being transported, and then use energy from ATP to change shape and move
the molecules across the membrane. Examples of active transport in cells include the
transport of ions such as sodium, potassium, and calcium across cell membranes, and the
uptake of nutrients such as glucose by cells.
Question 4: Explain the importance of exchange surfaces in organisms, and how their
structure is related to their function.
Answer: Exchange surfaces are structures in organisms that allow for the exchange of
materials between the organism and its environment. Examples include the alveoli in the
lungs, the villi in the small intestine, and the gills in fish. These structures have specialised
features such as large surface areas, thin membranes, and a high concentration of transport
proteins, that facilitate the exchange of molecules such as oxygen, carbon dioxide, and
nutrients. The structure of exchange surfaces is related to their function in that they are
designed to maximise the efficiency of exchange while minimising the energy required. For
example, the villi in the small intestine have a large surface area due to their finger-like
projections, which increases the surface area available for absorption of nutrients from food.
The surface area to volume ratio is an important factor in gas exchange in organisms.
Smaller organisms have a higher surface area to volume ratio than larger organisms. This
means that a smaller organism has a larger surface area relative to its volume, which makes
it easier for gases to diffuse across the cell membrane and reach the cells that need them.
For example, single-celled organisms, such as amoeba, have a large surface area to volume
ratio, which enables them to absorb oxygen and release carbon dioxide through their cell
membrane by simple diffusion.
On the other hand, larger organisms, such as mammals, have a lower surface area to
volume ratio, which makes it harder for gases to diffuse across the cell membrane.
Therefore, larger organisms have evolved specialized structures for gas exchange, such as
lungs in mammals.
2. Describe the adaptations of gas exchange in insects with reference to the tracheal
system. (6)
Insects have a highly efficient respiratory system, which is adapted to their small size and
active lifestyle. The respiratory system in insects consists of a network of tubes called
tracheae, which are responsible for gas exchange. The tracheae are lined with a thin layer of
cuticle and are supported by chitin rings that prevent them from collapsing.
Air enters the body through small openings called spiracles, which are located on the
surface of the insect's body. The spiracles are surrounded by muscles that control their
opening and closing, which helps to prevent water loss. The air then diffuses through the
tracheae and reaches the cells where gas exchange occurs.
The tracheal system in insects is highly efficient because it allows for direct diffusion of
gases between the cells and the environment. This eliminates the need for a circulatory
system to transport gases and reduces the energy required for gas exchange.
3. Explain how the structure of leaves in dicotyledonous plants is adapted for gas exchange.
(6)
Dicotyledonous plants have specialised structures in their leaves that are adapted for gas
exchange. These structures include stomata, mesophyll cells, and a network of veins.
Stomata are small openings located on the surface of leaves that allow for the exchange of
gases between the leaf and the environment. They are surrounded by guard cells, which
regulate their opening and closing to prevent water loss.
Mesophyll cells are specialised cells in the leaf that are responsible for photosynthesis. They
contain chloroplasts, which capture light energy and convert it into chemical energy.
The network of veins in the leaf provides support and transports water, nutrients, and gases
to and from the leaf. The veins are surrounded by a layer of parenchyma cells, which help to
maintain the structure of the leaf.
The structure of leaves in dicotyledonous plants is highly efficient for gas exchange because
it provides a large surface area for gas exchange and allows for direct diffusion of gases
between the leaf and the environment.
4. Describe the mechanism of breathing in humans. (6)
The mechanism of breathing in humans involves a series of steps that help in the exchange
of gases between the body and the environment. The process is mainly driven by the
diaphragm, a muscular structure that separates the chest cavity from the abdominal cavity.
When the diaphragm contracts, it moves downwards, increasing the volume of the chest
cavity, which in turn decreases the pressure within the lungs. This causes air to rush in
through the nose or mouth and fill the lungs.
Once the lungs are filled with air, the diaphragm relaxes and moves back up, decreasing the
volume of the chest cavity and increasing the pressure within the lungs. This pressure forces
the air out of the lungs and out of the body through the nose or mouth. The process of
breathing is controlled by the respiratory centre in the brain, which constantly monitors the
levels of oxygen and carbon dioxide in the body and adjusts the breathing rate accordingly.
In addition to the diaphragm, the intercostal muscles between the ribs also play a role in
breathing by expanding and contracting the chest cavity. The process of breathing is
essential for the survival of humans as it ensures that oxygen is supplied to the body's
tissues and carbon dioxide is removed from the body.
Chapter 7: DNA, Genes, Chromosomes.
1. Explain the structure of nucleic acids, including DNA and RNA. (6 marks)
Answer: Nucleic acids are the genetic material that encodes the instructions for the
development and functioning of all living organisms. The structure of nucleic acids is based
on a repeating unit called a nucleotide. A nucleotide consists of a phosphate group, a
5-carbon sugar (either deoxyribose in DNA or ribose in RNA), and a nitrogenous base
(adenine, guanine, cytosine, or thymine in DNA, or uracil in RNA). The nitrogenous bases
are held together by hydrogen bonds. In DNA, two polynucleotide chains are held together
by hydrogen bonds between complementary base pairs, forming a double helix. In RNA,
there is a single polynucleotide chain that can fold upon itself, forming secondary structures.
2. Describe the structure of mRNA and tRNA. (6 marks)
Answer: Messenger RNA (mRNA) is a type of RNA that carries the genetic information from
DNA in the nucleus to the ribosome in the cytoplasm, where it is used to synthesize proteins.
mRNA is a single-stranded molecule that is made up of a sequence of nucleotides, with
each nucleotide containing a sugar, a phosphate group, and a nitrogenous base. The
nitrogenous bases in mRNA are adenine, guanine, cytosine, and uracil.
Transfer RNA (tRNA) is another type of RNA that is involved in protein synthesis. tRNA
molecules have a unique cloverleaf-shaped structure, with a single strand of RNA folding
back on itself to form stem-loop structures. Each tRNA molecule has an anticodon, a
sequence of three nucleotides that is complementary to a codon in mRNA. The anticodon of
tRNA binds to the codon of mRNA, allowing the correct amino acid to be added to the
growing protein chain.
3. Explain the organization of DNA in the eukaryotic nucleus. (6 marks)
Answer: Eukaryotic DNA is organized into structures called chromosomes. A chromosome is
a long, linear molecule of DNA that is tightly coiled around histone proteins. The DNA and
histones together form a complex called chromatin. During cell division, the chromatin
condenses further into visible chromosomes, which are then separated into daughter cells.
In eukaryotic cells, there are typically several different chromosomes, each containing a
different set of genes. The location of a gene on a chromosome is called its locus.
Non-coding DNA, which does not code for proteins, is also present in chromosomes.
Eukaryotic DNA also contains regions called telomeres, which protect the ends of the
chromosomes, and centromeres, which are important for the separation of chromosomes
during cell division.
4. What is a gene? Explain the difference between coding and non-coding genes. (6 marks)
Answer: A gene is a segment of DNA that contains the instructions for making a specific
protein. These instructions are encoded in the sequence of nucleotides in the gene. Genes
are located on chromosomes, and the specific location of a gene on a chromosome is called
its locus.
Coding genes are those that contain the instructions for making a protein. The sequence of
nucleotides in a coding gene is translated into a sequence of amino acids, which make up
the protein. Non-coding genes, on the other hand, do not code for proteins. However, they
may still have important regulatory functions. For example, some non-coding genes produce
RNA molecules that are involved in the regulation of gene expression.
5. Explain the role of DNA replication in cell division.
Answer: DNA replication is the process by which a cell makes an exact copy of its DNA
before cell division occurs. The DNA molecule unwinds, and each strand serves as a
template for the creation of a new complementary strand. The enzyme DNA polymerase
then adds nucleotides to the growing new strand, following the base-pairing rules (A-T, C-G).
This results in two identical DNA molecules, each containing one original strand and one
newly synthesised strand. The two DNA molecules are then separated into two new cells
during cell division. Accurate DNA replication is essential for maintaining the genetic
information of the cell and passing it on to daughter cells.
eventually reaches a terminator sequence that signals the end of the gene. The newly
synthesized mRNA molecule then separates from the DNA template strand and is ready for
translation.
6. Describe the structure and function of a gene.
Answer: A gene is a sequence of DNA that encodes a specific protein or RNA molecule. It is
made up of several different components, including a promoter region that controls when
and where the gene is expressed, a coding region that specifies the sequence of amino
acids in the protein or RNA molecule, and regulatory elements that control the activity of the
gene. The coding region is transcribed into mRNA, which is then translated into a protein.
The protein produced by a gene carries out a specific function in the cell, such as catalyzing
a chemical reaction or transporting molecules across the cell membrane.
3. Discuss the role of ribosomes in protein synthesis. (6 marks)
7. Discuss the significance of the genetic code.
Answer: The genetic code is the set of rules by which the sequence of nucleotides in DNA is
translated into the sequence of amino acids in a protein. Each codon, or three-nucleotide
sequence, specifies a particular amino acid or a start or stop signal for protein synthesis.
The genetic code is universal, meaning that it is the same in all organisms, from bacteria to
humans. This allows scientists to use genetic information from one organism to study the
functions of genes in another organism. The genetic code also has important implications for
genetic engineering and the development of new treatments for genetic diseases.
CHAPTER 8: Protein synthesis
1. Explain the importance of the genetic code in protein synthesis. (6 marks)
The genetic code is the set of rules by which the information in DNA is translated into
proteins. It is important because it allows the sequence of nucleotides in DNA to be
translated into the sequence of amino acids in a protein. The code is universal, meaning that
it is the same in all living organisms, and it is non-overlapping, so each triplet of nucleotides
codes for only one amino acid. The code is also degenerate, meaning that multiple triplets
can code for the same amino acid, providing redundancy and reducing the impact of
mutations. This allows the genetic code to be a reliable method for transmitting genetic
information from generation to generation.
2. Describe the process of transcription in protein synthesis. (6 marks)
Transcription is the process by which a segment of DNA is used as a template to create a
complementary strand of messenger RNA (mRNA). RNA polymerase binds to the promoter
region on DNA and separates the two strands of the double helix. It then adds nucleotides to
the growing mRNA chain, using one strand of DNA as a template. RNA polymerase reads
the DNA sequence and matches the complementary RNA nucleotide to each DNA
nucleotide. The mRNA is synthesized in the 5' to 3' direction, and the RNA polymerase
Ribosomes are organelles found in both prokaryotic and eukaryotic cells that play a crucial
role in protein synthesis. They consist of a large and small subunit, each made up of proteins
and ribosomal RNA (rRNA) molecules. Ribosomes are responsible for reading the
information encoded in mRNA and assembling amino acids into a polypeptide chain
according to the sequence specified by the mRNA. The small subunit of the ribosome binds
to the mRNA, and the large subunit catalyzes the formation of peptide bonds between
adjacent amino acids. The ribosome moves along the mRNA molecule, reading each codon
and adding the appropriate amino acid to the growing polypeptide chain until a stop codon is
reached, at which point the ribosome disassembles and the newly synthesized protein is
released.
4. Explain the role of tRNA in protein synthesis. (6 marks)
Transfer RNA (tRNA) is a type of RNA molecule that plays a crucial role in protein synthesis.
Each tRNA molecule is specific for a particular amino acid, and has a three-nucleotide
sequence called an anticodon that is complementary to a codon in mRNA. The tRNA
molecule binds to the appropriate amino acid and carries it to the ribosome, where it can be
incorporated into a growing polypeptide chain. The tRNA molecule recognizes the
appropriate codon in the mRNA by base-pairing between its anticodon and the codon. Once
the amino acid is incorporated into the polypeptide chain, the tRNA is released and can be
recharged with another amino acid for use in another round of protein synthesis.
5. Describe the process of protein folding
Protein folding is a crucial process for the proper functioning of proteins. The primary
sequence of amino acids determines the protein's final folded structure, which is essential for
its function. The process of protein folding is spontaneous and is driven by the protein's
intrinsic physicochemical properties.
The folding process involves the formation of non-covalent interactions between amino acid
residues, such as hydrogen bonds, van der Waals forces, hydrophobic interactions, and
electrostatic interactions. These interactions lead to the formation of secondary structures,
such as alpha helices and beta sheets, which are further stabilised by hydrogen bonds.
As the protein folds, the hydrophobic residues tend to be buried in the interior of the protein,
while the hydrophilic residues are exposed to the solvent. This process is driven by the
hydrophobic effect, which is the tendency of hydrophobic molecules to avoid contact with
water.
Finally, the protein attains its three-dimensional structure, which is stabilized by disulfide
bonds between cysteine residues and other covalent bonds. The folded protein structure is
essential for its function, and any disruptions in the folding process can lead to protein
misfolding, aggregation, and disease.
In summary, protein folding is a complex process involving the formation of non-covalent
interactions, the burial of hydrophobic residues, and the stabilization of the protein's
three-dimensional structure by covalent and non-covalent bonds.
of genes. The homologous chromosomes then separate and move to opposite poles of the
cell. In the second division (meiosis II), the sister chromatids of each chromosome separate
and move to opposite poles of the cell. This results in the formation of four genetically
diverse haploid daughter cells.
2. How does independent segregation of homologous chromosomes during meiosis result in
genetically diverse daughter cells?
6. Explain the role of amino acid sequence in determining protein folding. (6 marks)
The process of protein folding is essential for the formation of functional proteins. The amino
acid sequence, also known as the primary structure of a protein, is the basis for protein
folding. The primary structure is a linear sequence of amino acids that are joined together by
peptide bonds.
As the protein is being synthesised, the amino acid sequence determines how the protein
will fold. The folding process is guided by the interactions between the different amino acid
residues, which can include hydrogen bonds, electrostatic interactions, and hydrophobic
interactions. These interactions determine the three-dimensional structure of the protein,
known as the tertiary structure.
In some cases, proteins require additional levels of folding to form their functional structure.
These proteins, known as specialized proteins, require the assistance of chaperone proteins
to fold correctly. Specialized proteins, such as antibodies and enzymes, have specific
shapes that are essential for their functions.
The amino acid sequence of a protein is determined by the base sequence of nucleic acids
in DNA. DNA acts as a template for the production of messenger RNA (mRNA), which is
then translated into a sequence of amino acids. Therefore, the sequence of nucleotides in
DNA ultimately determines the sequence of amino acids in the protein and the folding of the
protein.
In conclusion, the amino acid sequence of a protein determines how the protein folds and
ultimately its function. The sequence is determined by the base sequence of nucleic acids in
DNA.
Chapter 9: Genetic Diversity because of Meiosis
1. Explain the process of meiosis and how it results in the formation of genetically diverse
daughter cells.
During meiosis, a single diploid parent cell undergoes two rounds of nuclear division to form
four haploid daughter cells. Meiosis begins with the replication of DNA during interphase. In
the first division (meiosis I), homologous chromosomes pair up and exchange genetic
material in a process called crossing over. This results in the formation of new combinations
During meiosis, homologous chromosomes pair up and separate from each other during the
first division. This separation is random and independent, meaning that the maternal and
paternal chromosomes can end up on either side of the dividing cell. This results in
genetically diverse daughter cells as each daughter cell receives a random combination of
maternal and paternal chromosomes.
3. Explain how crossing over between homologous chromosomes during meiosis leads to
genetic diversity among daughter cells.
Crossing over occurs during meiosis when homologous chromosomes pair up and exchange
genetic material. This results in the formation of new combinations of genes on each
chromosome. As the homologous chromosomes separate during meiosis, each daughter
cell receives a unique combination of maternal and paternal chromosomes. This process
results in genetic diversity among the daughter cells.
4. Describe the chromosomal behaviour in photographs of meiosis.
During meiosis, chromosomes condense and become visible as individual structures. During
the first division, homologous chromosomes pair up and separate from each other, resulting
in the formation of two cells, each with half the number of chromosomes as the parent cell.
During the second division, the sister chromatids of each chromosome separate and move
to opposite poles of the cell, resulting in the formation of four haploid daughter cells. The
chromosomal behaviour in photographs of meiosis shows the progression of these events
and the formation of genetically diverse daughter cells.
5. How does meiosis contribute to genetic diversity in sexually reproducing organisms?
Meiosis is the process by which sexually reproducing organisms produce gametes, which
are the cells that carry genetic information from one generation to the next. Meiosis results in
genetically diverse daughter cells through the independent segregation of homologous
chromosomes and the process of crossing over. These processes result in the formation of
new combinations of genes on each chromosome, leading to genetic diversity among
offspring. This genetic diversity is important for the survival of populations and the evolution
of new species.
Question 6:
Explain how the process of meiosis leads to genetic diversity. (6)
Answer: Meiosis is a process of cell division that produces haploid gametes with unique
combinations of chromosomes. The process of meiosis increases genetic diversity in the
following ways:
1. Independent assortment of homologous chromosomes: During meiosis I, homologous
chromosomes align randomly along the metaphase plate, resulting in a random orientation
of maternal and paternal chromosomes. This means that the daughter cells will receive
different combinations of maternal and paternal chromosomes, resulting in genetic diversity.
2. Crossing over: During prophase I of meiosis, homologous chromosomes pair up and
exchange segments of DNA, resulting in the exchange of alleles between chromosomes.
This results in new combinations of alleles on each chromosome, leading to genetic
diversity.
3. Random fertilisation: During sexual reproduction, gametes from different individuals
combine randomly to form a zygote. This means that the combination of genetic material
from two different individuals is random, resulting in genetic diversity.
Overall, the combination of these three mechanisms leads to a high degree of genetic
diversity in the offspring produced by sexual reproduction.
Question 7:
Describe and explain the behaviour of chromosomes during meiosis. Use photographs to
support your answer. (6)
Answer:
During meiosis, chromosomes undergo a series of complex movements and interactions that
ensure the proper distribution of genetic material to the daughter cells. The process of
meiosis can be divided into two main stages: meiosis I and meiosis II.
In meiosis I, homologous chromosomes pair up and exchange genetic material through a
process called crossing over. This results in genetic recombination, which increases genetic
diversity. The paired homologous chromosomes then separate and migrate to opposite poles
of the cell, resulting in two haploid daughter cells.
In meiosis II, the sister chromatids of each chromosome separate and migrate to opposite
poles of the cell, resulting in four haploid daughter cells.
The behaviour of chromosomes during meiosis can be observed through the use of
microscopy and staining techniques. For example, Giemsa staining can be used to visualize
the condensed chromosomes during metaphase of meiosis I. This reveals the paired
homologous chromosomes aligned along the metaphase plate.
In summary, the behaviour of chromosomes during meiosis involves a series of complex
movements and interactions that ensure the proper distribution of genetic material to the
daughter cells. The use of microscopy and staining techniques can help to visualize and
understand these processes.
Chapter 10: Species and taxonomy
1. Explain the concept of a species. (6 marks)
A species is a group of organisms that share common characteristics and can interbreed to
produce fertile offspring. This concept is based on the biological species concept, which
defines a species as a group of individuals that can breed and produce viable offspring. It
also takes into account the idea that members of a species share a common gene pool and
are reproductively isolated from other species. The concept of a species is important for
understanding biodiversity, conservation efforts, and evolution.
2. Describe the taxonomic hierarchy. (6 marks)
The taxonomic hierarchy is a system of classifying organisms based on their characteristics
and relationships to each other. At the highest level, organisms are classified into three
domains: Archaea, Bacteria, and Eukarya. Within each domain, organisms are further
classified into increasingly specific categories, from kingdom to species. The taxonomic
hierarchy includes the following levels: domain, kingdom, phylum, class, order, family, genus,
and species. Each level represents a group of organisms that share a set of characteristics,
with species being the most specific level of classification. This system is useful for
organizing and understanding the relationships between different organisms and is an
important tool for research in biology and ecology.
3. How does immunology help clarify taxonomic relationships between organisms? (6 marks)
Immunology helps clarify taxonomic relationships between organisms by studying the
immune response of different species to similar pathogens. The immune response is highly
specific to the antigen, or foreign substance, that triggers it. Therefore, the similarities and
differences in the immune response of different species can provide insight into their
evolutionary relationships. For example, if two species have similar immune responses to a
particular antigen, it suggests that they share a common ancestor and are more closely
related. On the other hand, if two species have very different immune responses, it suggests
that they are more distantly related. By studying the immune response of different species,
researchers can gain a better understanding of their evolutionary relationships and the
development of the immune system.
4. How does genome sequencing help clarify taxonomic relationships between organisms?
(6 marks)
Genome sequencing is a powerful tool for clarifying taxonomic relationships between
organisms. By comparing the genomes of different species, researchers can identify
similarities and differences in their genetic makeup. The more similar the genomes, the more
closely related the species are thought to be. This approach has been used to clarify the
relationships between many different groups of organisms, from bacteria to mammals. For
example, genome sequencing has shown that humans and chimpanzees share about 98%
of their DNA, indicating a close evolutionary relationship. Similarly, genome sequencing has
helped to clarify the relationships between different species of bacteria, fungi, and plants. By
studying the similarities and differences in the genomes of different species, researchers can
gain a better understanding of their evolutionary relationships and the processes that have
shaped biodiversity.
5. Why is the concept of a species important for understanding evolution? (6 marks)
The concept of a species is important for understanding evolution because it helps us
understand how new species arise and how they are related to one another. The biological
species concept defines a species as a group of individuals that can breed and produce
viable offspring. This means that when two populations become reproductively isolated from
each other, they can evolve independently and eventually become distinct species. By
studying the patterns of speciation and the relationships between different species,
researchers can gain insights into the mechanisms of evolution and the processes that drive
biodiversity. Additionally, the concept of a species helps us understand the relationships
between extinct and extant species, and can provide clues about the evolutionary history of
life on Earth.
Chapter 11: Biodiversity in a community
1. Explain how genetic diversity can be measured and provide examples of how it can be
used to infer relationships between different organisms. (6 marks)
Genetic diversity can be measured in various ways, such as by examining the base
sequence of DNA or mRNA, or the amino acid sequence of encoded proteins. By comparing
these sequences across different organisms, we can infer their genetic relationships and
evolutionary history. For example, closely related organisms will tend to have similar
sequences, while more distantly related organisms will have more differences. One example
of this is the comparison of the cytochrome c protein across different species, which has
been used to construct evolutionary trees. Another example is the measurement of allele
frequencies in populations, which can help us to understand genetic variation within and
between populations.
2. Define and explain the concept of species richness and how it can be used to measure
species diversity. (6 marks)
Species richness refers to the number of different species present in a given area or
community. It is a simple measure of species diversity that takes into account only the
number of species and not their abundance or distribution. Species richness can be used to
compare the diversity of different communities or areas, and can also be used to track
changes in diversity over time. For example, if a new species is introduced to a community,
the species richness will increase. Conversely, if a species goes extinct, the species
richness will decrease. However, species richness alone does not provide a complete picture
of biodiversity, as it does not account for the relative abundance or distribution of different
species.
3. Describe an index of diversity and how it differs from species richness as a measure of
biodiversity. (6 marks)
An index of diversity is a measure of biodiversity that takes into account both the number of
species and their relative abundance. The most commonly used index of diversity is the
Simpson's Diversity Index, which is calculated by taking the sum of the squared proportions
of each species in a community. This index ranges from 0 (indicating no diversity) to 1
(indicating maximum diversity), and takes into account both the number of species and their
relative abundance. Unlike species richness, which only considers the number of species
present, an index of diversity provides a more comprehensive measure of biodiversity that
takes into account the relative abundance of different species.
4. Explain how human activities can reduce biodiversity and provide specific examples. (6
marks)
Human activities can have a significant impact on biodiversity, leading to the loss of species
and ecosystems. One major cause of biodiversity loss is habitat destruction, which can occur
through deforestation, land-use change, and urbanisation. Another cause is the introduction
of non-native species, which can compete with native species and cause their decline.
Pollution, overfishing, and climate change are other human activities that can negatively
impact biodiversity. For example, overfishing can lead to the collapse of fish populations,
while climate change can cause shifts in ecosystems and the extinction of species that
cannot adapt to changing conditions.
5. How can immunology and genome sequencing help to clarify taxonomic relationships
between organisms? (6 marks)
Immunology and genome sequencing can both provide insights into the evolutionary
relationships between different organisms. Immunology involves the study of the immune
system and the ways in which organisms produce and respond to antibodies. By comparing
the antibodies produced by different organisms, we can infer their genetic relationships and
evolutionary history. Genome sequencing, on the other hand, involves the analysis of an
organism's DNA sequence. By comparing the genomes of different organisms, we can
identify similarities and differences in their genetic makeup, which can help us to infer their
evolutionary relationships.
REQUIRED PRACTICALS:
Required Practical 1: Investigation of the effect of temperature, pH, or substrate
concentration on the rate of an enzyme-controlled reaction
1. Explain how you could investigate the effect of substrate concentration on the rate of an
enzyme-controlled reaction. (6 marks)
To investigate the effect of substrate concentration on the rate of an enzyme-controlled
reaction, you would need to prepare a series of enzyme and substrate solutions of different
concentrations. You could then mix a fixed volume of enzyme solution with each substrate
solution and start a timer to measure the time taken for a fixed amount of product to be
produced. The reaction could be stopped using an appropriate method, such as adding acid
or freezing the mixture, and the amount of product produced could be measured using a
colorimetric assay or other appropriate method. By plotting the results on a graph, you could
then determine the relationship between substrate concentration and reaction rate.
Required Practical 2: Investigation of the effect of solute concentration on the uptake or loss
of water from plant tissue
2. Describe how you could investigate the effect of solute concentration on the uptake or
loss of water from plant tissue. (6 marks)
To investigate the effect of solute concentration on the uptake or loss of water from plant
tissue, you could first obtain a range of plant samples of the same species and size. You
could then prepare solutions of different concentrations of a solute, such as sodium chloride,
and measure the initial mass of each plant sample. Each plant sample could then be
submerged in a solution of a different solute concentration and left for a fixed period of time,
such as 30 minutes. After the time has elapsed, the plant samples could be removed, dried
gently with paper towels, and their final masses measured. By comparing the initial and final
masses, you could determine the amount of water that has been taken up or lost by each
plant sample. By plotting the results on a graph, you could then determine the relationship
between solute concentration and water uptake or loss.
Required Practical 3: Use of chromatography to investigate the pigments present in leaves
3. Explain how you could use chromatography to investigate the pigments present in leaves.
(6 marks)
To use chromatography to investigate the pigments present in leaves, you could first obtain a
range of leaf samples from different plants. A small section of each leaf could be cut and
placed into a small tube containing a small amount of a suitable solvent, such as ethanol or
acetone. The tube could then be placed into a beaker containing a small amount of the same
solvent, allowing the solvent to rise up the tube and separate the different pigments present
in the leaf. Once the solvent has reached the top of the tube, the tube could be removed and
the location of each pigment could be marked. The different pigments could then be
identified by comparing their positions to a standard reference, such as a known set of
pigments or a published chromatogram. By analysing the results, you could then determine
the types and relative amounts of pigments present in each leaf sample.