CLASS NOTES FOR THE ENTIRE IB BIOLOGY CORE SYLLABUS
Topic 1: Statistical analysis
Topic 2: Cells
2.1 Cell theory
2.2 Prokaryotic cells
2.3 Eukaryotic cells
2.4 Membranes
2.5 Cell division
Topic 3: The chemistry of life
3.1 Chemical elements and water
3.2 Carbohydrates, lipids and proteins
3.3 DNA structure
3.4 DNA replication
3.5 Transcription and translation
3.6 Enzymes
3.7 Cell respiration
3.8 Photosynthesis
Topic 4: Genetics [15h]
4.1 Chromosomes, genes, alleles and mutations
4.2 Meiosis
4.3 Theoretical genetics
4.4 Genetic engineering and biotechnology
Topic 5: Ecology and evolution
5.1 Communities and ecosystems
5.2 The greenhouse effect
5.3 Populations
5.4 Evolution
5.5 Classification
Topic 6: Human health and physiology
6.1 Digestion
6.2 The transport system
6.3 Defence against infectious disease
6.4 Gas exchange
6.5 Nerves, hormones and homeostasis
6.6 Reproduction
TOPIC 1: STATISTICAL ANALYSIS
1.1.1 State that error bars are a graphical representation of the variability of data.
Error bars can be used to show either the range of the data or the standard deviation.
1.1.2 Calculate the mean and standard deviation of a set of values.
1.1.3 State that the term standard deviation is used to summarize the spread of
values around the mean, and that 68% of the values fall within one standard deviation
of the mean. For normally distributed data, about 68% of all values lie within ±1
standard deviation (s or σ ) of the mean. This rises to about 95% for ±2 standard
deviations.
1.1.4 Explain how the standard deviation is useful for comparing the means and the
spread of data between two or more samples.
A small standard deviation indicates that the data is clustered closely around the mean
value. Conversely, a large standard deviation indicates a wider spread around the mean.
1.1.5 Deduce the significance of the difference between two sets of data using
calculated values for t and the appropriate tables.
For the t-test to be applied, the data must have a normal distribution and a sample size of
at least 10. The t-test can be used to compare two sets of data and measure the amount of
overlap.
1.1.6 Explain that the existence of a correlation does not establish that there is a
causal relationship between two variables.
TOPIC 2: CELLS
Topic 2.1 – Cell Theory
2.1.1 Outline the cell theory.
Living organisms are composed of cells. Cells are the smallest unit of life. All cells come from
pre-existing cells. There are some interesting exceptions—skeletal muscles and some fungal
hyphae are not divided into cells but have a continuous multinucleate cytoplasm.
Viruses are also problematic. A virus is a non-cellular structure consisting of DNA or RNA
surrounded by a protein coat. It has no cell machinery of its own and is entirely dependent
on host cell cytoplasm for its reproduction.
2.1.2 Discuss the evidence for the cell theory.
17th century microscopic evidence of Hooke and Leeuwenhoek. Later, in the 19th Century,
Schleiden and Schwann recognize the universal importance of the nucleus in a broad range
of cells. 2.1.3 State that unicellular organisms carry out all the functions of life.
Include: metabolism, response, homeostasis, growth, reproduction and nutrition.
2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses,
bacteria, organelles and cells, using the appropriate SI unit.
1000 nm (nanometer) = 1 μm (micrometer), 1000 μm = 1mm
Appreciation of relative size is required, such as molecules (1 nm), thickness of membranes
(10 nm), viruses (100 nm), bacteria (1 μ m), organelles (up to 10 μ m), and most cells (up to
100 μ m). The three-dimensional nature/shape of cells should be emphasized.
All the biological entities in the above list are beyond our ability to perceive directly. They
must be observed through the use of technology such as the light microscope and the
electron microscope.
Advantages of light microscopes:
Real color images instead of monochrome (or digitally enhanced color); easily prepared
sample material; the possibility of observing living material and movement and a larger field
of view.
Advantages of electron microscopes:
Much higher magnification. Light microscopes are limited by the wavelength of visible light
and imperfections in glass lenses. Higher resolution, revealing more detail. EM samples
must be freeze-dried in a vacuum and stained with heavy metals like gold. The processing
kills and may distort cellular material.
2.1.5 Calculate the linear magnification of drawings and the actual size of specimens
in images of known magnification.
Magnification could be stated (for example, ×250) or indicated by means of a scale bar, for
example: 1 μm.
2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting
cell size.
When a cell grows, the volume increases at a much faster rate than the surface area. As any
object grows, its surface to volume ratio decreases. Specifically: the area increases
proportional to length squared whilst volume/mass increases in proportion to length cubed.
A cell relies on a large surface area for exchange of oxygen and other small molecules by
diffusion. Facilitated diffusion and active transport depend on enzymes and protein
channels embedded in membranes. The rate of heat production/waste production/resource
consumption of a cell is a function of its volume, whereas the rate of exchange of materials
and energy (heat) is a function of surface area.
Simple mathematical models involving cubes and the changes in the ratio that occur as the
sides increase by one unit should be considered.
2.1.7 State that multicellular organisms show emergent properties.
Emergent properties arise from the interaction of component parts: the whole is greater than
the sum of its parts.
2.1.8 Explain that cells in multicellular organisms differentiate to carry out
specialized functions by expressing some of their genes but not others.
In multicellular organisms, all the cells contain all the genes. They have the complete
genome but only switch on genes as needed. The cells of a multicellular organism
differentiate to carry out specialized functions by selectively expressing their genes.
A tissue is an integrated ensemble of cells that have a common function. For example, the
animal stomach is made of three bands of muscle tissue and is lined with endothelial tissue
that secretes pepsin, mucus and hydrochloric acid. In plants xylem, phloem and palisade
cells are example of tissues. An organ is a functional anatomical unit composed of several
different types of tissue. Kidneys, ovaries, eyes and leaves are organs. An organ system is a
group of organs that work together. Nervous, excretory, digestive and reproductive systems
are famous examples.
2.1.9 State that stem cells retain the capacity to divide and have the ability to
differentiate along different pathways.
2.1.10 Outline one therapeutic use of stem cells.
This is an area of rapid development. In 2005, stem cells were used to restore the insulation
tissue of neurons in laboratory rats, resulting in subsequent improvements in their mobility.
Any example of the therapeutic use of stem cells in humans or other animals can be chosen.
There are ethical issues involved in stem cell research, whether humans or other animals
are used. Use of embryonic stem cells involves the death of early-stage embryos, but if
therapeutic cloning is successfully developed the suffering of patients with a wide variety of
conditions could be reduced.
Topic 2.2 - Prokaryotic Cells
2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an
example of a prokaryote.
The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella,
ribosomes and nucleoid (region containing naked DNA).
2.2.2 Annotate the diagram from 2.2.1 with the functions of each named structure.
The cell wall maintains the shape of the cell. The plasma membrane facilitates the selective
movement of metabolites in and out of the cell. A mesosome, when present, is an
invagination of the cell membrane that increases the surface area internally for staging
metabolic reactions. The cytoplasm is the generic name for the complex viscous liquid that
holds and suspends various specialized organelles. of specialized function. Ribosomes (70s)
are the main sites for protein synthesis. Naked DNA contains the genetic code which
ultimately controls the cell.
Pili are protein filaments that facilitate cell adhesion and conjugation (swapping plasmids).
Flagella are long, corkscrew-shaped structures that are rotated for rapid locomotion in a
liquid medium.
Prokaryotes show a wide range of metabolic activity including fermentation, photosynthesis
and nitrogen fixation. Although as a group they exhibit a wide repertoire of biochemical
tricks, and come in a range of shapes and sizes, their interior architectures appear similar.
2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli.
2.2.4 State that prokaryotic cells divide by binary fission: Not mitosis (the dance of
chromosomes).
Topic 2.3 - Eukaryotic Cells
2.3.1 Draw and label a diagram of the ultrastructure of a liver cell as an example of an
animal cell.
The diagram should show free ribosomes, rough endoplasmic reticulum (rER), lysosome,
Golgi apparatus, mitochondrion and nucleus. .
2.3.2 Annotate the diagram from 2.3.1 with the functions of each named structure
Ribosomes (80s) are the main sites for protein synthesis. The proteins made by ribosomes
can be used internally, or exported by exocytosis. The rough endoplasmic reticulum is the
portion of the endoplasmic reticulum that is studded with ribosomes. The proteins made in
these ribosomes are packaged in the rough ER and are usually sent outside of the cell. A
lysosome uses hydrolytic enzymes (lysozyme) to digest macromolecules. The Golgi
apparatus receives many of the products of the rough endoplasmic reticulum and it
modifies them. Later these proteins are transported to other destinations in packages of
membrane reticulum called vesicles. A mitochondrion is the site of aerobic cellular
respiration. The membrane-bound nucleus contains the genotype encoded in DNA coiled on
chromosomes. The nucleus also contains a dark region called the nucleolus where
ribosomes are manufactured.
2.3.3 Identify structures from 2.3.1 in electron micrographs of liver cells.
2.3.4 Compare prokaryotic and eukaryotic cells.
Both prokaryotic cells carry out all life functions. Eukaryotic cells also exhibit all metabolic
functions but are often highly specialized. In contrast to eukaryotes, the smaller prokaryotic
cells have no membrane-bound organelles or interconnecting sheets of endoplasmic
reticulum—an internal architecture of membranes that compartmentalize cell functions.
Prokaryotes have a single circular loop of DNA and tiny plasmids rather than the
membrane-bound nuclei, containing DNA combined with histone protein on separate
chromosomes, characteristic of eukaryotes. Prokaryotes have 70S ribosomes, whereas
eukaryotes have 80S ribosomes.
2.3.5 State three differences between plant and animal cells. Plant cells appear more complex than generic animal cells because they are surrounded by
a cellulose cell wall and often have large central vacuoles. The presence of the vacuole
necessitates an inner and outer membrane surrounding the cytoplasm. In addition to
mitochondria, plant cells also contain chloroplasts, the organelles of photosynthesis. The
cellulose cell wall puts certain constraints on mitosis. A cell plate made of cellulose is
formed just before cytokinesis. Plants form spindles but do not have centrioles 2.3.6 Outline two roles of extracellular components. The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the
whole plant up by turgor pressure against the force of gravity. The plant cell wall is
comprised of bands of tough microfibrils made of the polysaccharide cellulose. The CCW
prevents the cell from bursting when water is taken on by osmosis. A fully pumped up plant
cell is turgid. A shrunken plant cell with its blob of cytoplasm separating from the CCW has
undergone plasmolysis. It is important to realize that the CCW is chemically extremely
simple. It has none of the functionality of a living membrane. Rather, it acts as an inert
sponge soaking up indiscriminately whatever ambient solution happens to surrounds it.
Animal cells secrete glycoproteins that form the extracellular matrix. This functions in
support, adhesion and movement
Topic 2.4 – Membranes
2.4.1 Draw and label a diagram to show the structure of membranes.
The diagram should show the phospholipid bilayer, cholesterol, glycoproteins, and integral
and peripheral proteins. Use the term plasma membrane for the membrane surrounding the
cytoplasm. Integral proteins are embedded in the phospholipid of the membrane, whereas
peripheral proteins are attached to its surface.
2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help
to maintain the structure of cell membranes.
The head of the phospholipid molecule is polar and hydrophilic (water-loving). The heads
line up spontaneously to form the outside of the bilayer. The tail of the phospholipid locates
itself inside the membrane. The tail is non-polar and hydrophobic (water-fearing).
2.4.3 List the functions of membrane proteins.
Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-tocell communication, channels for passive transport, and pumps for active transport.
2.4.4 Define diffusion and osmosis.
Diffusion is the passive movement of particles from a region of high concentration to a
region of low concentration. It is important to realize that molecules and ions continue to
bounce around, bump into each other and swap places even when the concentration
gradient is zero; it is just that, at equilibrium, the movement to and fro, statistically
speaking, cancel each other out so that there is no net movement.
Osmosis is the passive movement of water molecules, across a partially permeable
membrane, from a region of lower solute concentration to a region of higher solute
concentration. Solutes are chemicals dissolved in a solvent. In a salt solution NaCl is the
solute and H2O is the solvent.
2.4.5 Explain passive transport across membranes by simple diffusion and facilitated
diffusion.
Passive transport is another name for facilitated diffusion. Materials are transported across
the membrane through protein channels with specific three-dimensional shapes. Facilitated
diffusion is still diffusion. It is powered by kinetic energy—constant, vibrating movements of
chemical particles. It requires no ATP energy from the cell. As long as a concentration
gradient exists, facilitated diffusion will occur.
2.4.6 Explain the role of protein pumps and ATP in active transport across
membranes.
During active transport across membranes, the substance being transported moves against
a concentration gradient. ATP Energy is required because the natural tendency is a net
movement of particles in precisely the opposite direction. Proton pumps are powered by ATP.
Protein pumps are made of protein. They are gated channels that can modify their specific
shapes just in the same way as active sites in enzymes can change shape slightly to allow
induced fit of a substrate.
It is worth mentioning that water cannot be pumped directly by active transport. If water
needs to be transported against a concentration gradient, ions like Na+ or K+ are first
pumped into a region and the water follows passively by osmosis.
2.4.7 Explain how vesicles are used to transport materials within a cell between the
rough endoplasmic reticulum, Golgi apparatus and plasma membrane.
Vesicles are membranous sacs in which materials are stored and transported throughout
the cell. They are pinched off from smooth endoplasmic reticulum or the cell membrane
itself.
2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and
re-form during endocytosis and exocytosis.
Endocytosis is when the plasma membrane engulfs extracellular material forming
membrane-bound vesicles that enter the cytoplasm.
Exocytosis is the movement of material out of a cell. Intracellular material is enclosed
within a vesicle that moves to the plasma membrane and fuses with it, releasing the
material outside.
The cell membrane is fluid. It is in constant motion and can easily repair temporary holes.
Topic 2.5 - Cell Division
2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and
cytokinesis.
Interphase is an active period in the life of a cell when many biochemical reactions occur, as
well as DNA transcription and DNA replication. Chromosomes are replicated during the Sphase. The S-phase is punctuated by two “Gap” phases. Cytokinesis refers to the splitting of
the cell after mitosis.
2.5.2 State that tumors (cancers) are the result of uncontrolled cell division and that
these can occur in any organ or tissue.
2.5.3 State that interphase is an active period in the life of a cell when many
metabolic reactions occur, including protein synthesis, DNA replication and an
increase in the number of mitochondria and/or chloroplasts.
Chromosomes are replicated during the S-phase. The S-phase is punctuated by two “Gap”
phases. Cytokinesis refers to the splitting of the cell after mitosis.
2.5.4 Describe the events that occur in the four phases of mitosis (prophase,
metaphase, anaphase and telophase).
During prophase the stage is set. Chromatin fibers, consisting of exposed DNA and
associated histone proteins, become supercoiled and visible as chromosomes. They become
so tightly wound that they can no longer replicate or provide templates for mRNA. The
chromosomes appear as two identical sister chromatids joined at the centromere. Centrioles
migrate to opposite poles of the cell and form the mitotic spindle. Some of the microtubules
that make up the spindle attach to the centromeres of the chromosomes. The nuclear
envelope breaks down.
In metaphase the chromosomes line up on the cell equator with each sister chromatid
facing opposite poles of the cell.
During anaphase, the centromere replicates and separates, dragging the sister chromatids
apart. These newly separated chromosomes move along the spindle microtubules to opposite
poles, so that each pole of the cell contains a complete set.
In telophase, the microtubules elongate the cell, further separating the two poles.
Fragments of endoplasmic reticulum are used to form new nuclear envelopes.
In this course, the two DNA molecules formed by DNA replication are considered to be sister
chromatids until the splitting of the centromere at the start of anaphase; after this, they are
individual chromosomes.
2.5.5 Explain how mitosis produces two genetically identical nuclei.
During mitosis, pairs of identical chromosomes are pulled to opposite ends of the cell and
become the nuclei of the two daughter cells.
2.5.6 State that growth, embryonic development, tissue repair and asexual
reproduction involve mitosis.
TOPIC 3: THE CHEMISTRY OF LIFE
Topic 3.1 - Chemical Elements and Water
3.1.1 State that the most frequently occurring chemical elements in living things are
carbon, hydrogen, oxygen and nitrogen.
3.1.2 State that a variety of other elements are needed by living organisms, including
sulfur, calcium, phosphorus, iron and sodium.
3.1.3 State one role for each of the elements mentioned in 3.1.2.
Bones and teeth are made of Ca3(PO4)2. Calcium is also necessary for blood clotting and
nerve impulse transmission. Phosphorus is a key component of ATP, phospholipids and
nucleic acids. Iron is a part of the hemoglobin and the cytochromes found in the electron
transport chain of aerobic respiration in mitochondria, and of photosynthesis in
chloroplasts. Sodium ions are essential for muscle contraction, nerve transmissions,
maintaining pH balance, and hydration.
3.1.4 Draw and label a diagram showing the structure of water molecules to show their
polarity and hydrogen bond formation.
3.1.5 Outline the thermal, cohesive and solvent properties of water.
Water has an unusually high specific heat capacity. It heats up and cools down slowly.
Water can absorb large amounts of energy without rapid temperature fluctuations that
could harm cells. It is also a good insulator.
Water has cohesive properties. It binds to itself, due to its polarity. The electro-positive,
hydrogen end of the molecule binds to the negative, oxygen side of another water molecule.
This bond is called a hydrogen bond. A glass of water could be considered one giant entity,
because all of the water molecules inside of it are gently bonded to one another. The
cohesive and adhesive properties of water allows for transport of water through xylem
vessels against gravity in plants.
Since water is a small polar molecule it is a versatile solvent. It is an excellent transport
medium.
3.1.6 Explain the relationship between the properties of water and its uses in living
organisms as a coolant, medium for metabolic reactions and transport medium.
Water has an unusually high specific heat capacity. It heats up and cools down slowly.
Water can absorb large amounts of energy without large temperature fluctuations that could
harm cells. Water is also a good insulator. We use the water in sweat to lower body
temperature. The sweat evaporates carrying the latent heat of evaporation away from the
body.
Water is transparent. This allows aquatic plants to absorb light and perform photosynthesis.
Since the ancestor of all plants originated in the ocean, the transparency of water is a key
aspect of the success of life as we know it.
Since water is a versatile liquid solvent, it is an excellent transport medium.
Topic 3.2 - Carbohydrates, Lipids and Proteins
3.2.1 Distinguish between organic and inorganic compounds.
Compounds containing carbon that are found in living organisms (except
hydrogencarbonates, carbonates and oxides of carbon) are regarded as organic.
3.2.2 Identify amino acids, glucose, ribose and fatty acids from diagrams showing
their structure.
3.2.3 List three examples each of monosaccharides, disaccharides and
polysaccharides.
• glucose, galactose and fructose
• maltose, lactose and sucrose
• starch, glycogen and cellulose.
3.2.4 State one function of glucose, lactose and glycogen in animals, and of fructose,
sucrose and cellulose in plants.
Glycogen is the medium term polysaccharide food store in the liver. Starch is the equivalent
in plants. Cellulose is structural rather than a food source. It is the stuff of cellulose cell
walls. When converted to lignin it forms woody xylem vessels, critical for water transport
and support in larger green plants. Sucrose is the disaccharide commonly translocated in
the phloem vessels.
3.2.5 Outline the role of condensation and hydrolysis in the relationships between
monosaccharides, disaccharides and polysaccharides; between fatty acids, glycerol
and triglycerides; and between amino acids and polypeptides.
When monomers covalently bond to synthesize polymers, a water molecule is released. This
is a condensation reaction. Building large molecules from smaller components requires
ATP energy. We say that anabolic reactions are endergonic.
The reverse process is hydrolysis (“water splitting”) the addition of a water molecule breaks
covalent bonds and polymers are split into their component monomers. Breaking covalent
bonds releases energy. This energy can be harnessed to make ATP from ADP and P. We say
that catabolic reactions are exogonic.
3.2.6 State three functions of lipids.
Include energy storage and thermal insulation. Phospholipids and cholesterol are the main
structural components of membranes. Cholesterol is also the precursor of steroid hormones.
Adipose deposits below the skin are the basis of some female secondary sexual
characteristics
3.2.7 Compare the use of carbohydrates and lipids in energy storage.
Glucose circulating in the blood is available for immediate use. Excess glucose has dire
osmotic consequences. It is converted to insoluble glycogen by insulin as a medium term
source. After the glycogen in the liver reaches a maximum, excess sugars are converted to
lipids and laid down as long term energy stores as adipose deposits under the skin.
Topic 3.3 - DNA Structure
3.3.1 Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and
phosphate.
3.3.2 State the names of the four bases in DNA.
Adenine, Guanine, Thymine, and Cytosine.
3.3.3 Outline how DNA nucleotides are linked together by covalent bonds into a single
strand.
The phosphate group is covalently bonded to the 5’ carbon of the deoxyribose, and the
nitrogenous base is attached to the opposite side.
3.3.4 Explain how a DNA double helix is formed using complementary base pairing and
hydrogen bonds.
The DNA molecule resembles a twisted ladder. Every 10 nucleotides the structure is coiled a
full 360°. The two covalently bonded sugar phosphate backbones form the sides of the
"ladder. The nitrogenous base pairs are covalently bonded to the sugar and form the rungs
of the ladder. The complimentary base pairing allows DNA replication, and is the basis of all
reproduction. A pairs with T and C with G. The bases join by relatively weak hydrogen
bonds.
3.3.5 Draw and label a simple diagram of the molecular structure of DNA.
The story of the elucidation of the structure of DNA illustrates that cooperation and
collaboration among scientists exists alongside competition between research groups. To what
extent was Watson and Crick’s “discovery” of the three dimensional structure of DNA
dependent on the use of data generated by Rosalind Franklin, which was shared without her
knowledge or consent?
Topic 3.4 - DNA Replication
3.4.1 Explain DNA replication in terms of unwinding the double helix and separation
of the strands by helicase, followed by formation of the new complementary strands
by DNA polymerase.
When replication takes place, the enzyme helicase first unwinds the double helix. Next the
two DNA strands are split apart at hundreds, sometimes thousands, of points along the
strand. Each splitting point is an area where replication is occurring called a replication
bubble. In each replication bubble, new DNA is made by attaching free nucleotides to the
original strand (called the template) by base-pairing rules with the help of the enzyme DNA
polymerase. The process results in two identical DNA strands produced from one.
3.4.2 Explain the significance of complementary base pairing in the conservation of
the base sequence of DNA.
The fact that only complementary base pairs can join together ensures that in replication
the newly formed strands are complementary to the old strands, thus conserving precisely
the same base sequence as the original. The human body has up to a hundred trillion cells
all containing the entire genome. The fact that all these cells were derived from a single
zygote is an illustration of the power and fidelity of DNA replication.
3.4.3 State that DNA replication is semiconservative.
Topic 3.5 – Transcription and Translation
3.5.1 Compare the structure of RNA and DNA.
Limit this to the names of sugars, bases and the number of strands. RNA has ribose sugar
while the DNA has deoxyribose. RNA is a single strand while DNA has two strands coiled
into a double helix. Also, the thymine nucleotide of DNA is replaced by uracil in RNA (uracil,
like thymine, attaches to adenine by hydrogen bonds).
3.5.2 Outline DNA transcription in terms of the formation of an RNA strand
complementary to the DNA strand by RNA polymerase.
The synthesis of messenger RNA uses DNA as a template. First, the two strands of DNA are
separated in a specific place. Then, with the help of RNA polymerase, RNA nucleotides
attach to their complimentary bases on one side of the exposed DNA strand. This creates a
single strand of complimentary nucleotide bases. After this is done, the mRNA molecule
separates from the DNA.
3.5.3 Describe the genetic code in terms of codons composed of triplets of bases.
The genetic code for an amino acid is contained in DNA as a series of three nitrogenous
bases. Each of these triplets (codons) codes for a particular amino acid.
3.5.4 Explain the process of translation, leading to polypeptide formation. Include the
roles of messenger RNA (mRNA), transfer RNA (tRNA), codons, anticodons, ribosomes
and amino acids.
After transcription the mRNA strand moves out of the nucleus, through a nucleopore, into
the cytoplasm, where it attaches to a ribosome. In the cytoplasm there are 20 different
transfer RNA (tRNA) molecules, each composed of a short RNA molecule folded into a
specific shape. A tRNA molecule is shaped so that it bonds to a certain amino acid. Each
tRNA molelcule also has an anticodon at the opposite end which compliments a specific
mRNA codon. Once the mRNA attaches to a ribosome, it acts like a conveyor belt.
The tRNA molecules attach to the mRNA according to the complimentary nature of their
bases. For example, a tRNA with the anticodon ACC will carry the amino acid tryptophan.
This tRNA molecule will attach to the codon UGG on the mRNA because UGG compliments
ACC. After two tRNA molecules are attached to the mRNA, they bond covalently and the first
tRNA is released. After this the next tRNA connects and bonds. The process repeats until
the entire polypeptide is synthesized.
The genetic code is universal because it applies to all living organisms.
The DNA code is degenerate because 64 base triplet combinations code for only 20 amino
acids. In other words several triplets code for the same amino acid. For example, UUU and
UUC both code for phenylalanine. Universal refers to the fact that this genetic code occurs
in all living organisms.
3.5.5 Discuss the relationship between one gene and one polypeptide.
Originally, it was assumed that one gene would invariably code for one polypeptide, but many
exceptions have been discovered. Where a theory is suddenly and totally abandoned, to be
replaced by a different theory, this is known as a paradigm shift.
Topic 3.6 - Enzymes
3.6.1 Define enzyme and active site.
An enzyme is a globular protein functioning as a biological catalyst. An active site is the
place on the surface of an enzyme to which substrate or substrates bind.
3.6.2 Explain enzyme–substrate specificity.
The active site has a particular three-dimensional structure that corresponds to a specific
substrate rather like a lock and key.
3.6.3 Explain the effects of temperature, pH and substrate concentration on enzyme
activity.
For all enzymes, there is an optimum temperature at which the maximum amount of
collisions occur in the active sites. As the temperature decreases, there is less movement
and fewer collisions, so enzyme activity decreases. There is a limit to which the enzyme
activity can increase because at a certain temperature the active site is distorted by heat.
Enzyme activity increases with substrate concentration but only up to a certain point. There
is an upper limit to the increase in enzyme activity because at some point all available active
sites are filled.
Enzymes are pH sensitive. Hydrogen ions can interfere with hydrogen bonding and, in
extreme cases, may even break covalent bonds. There is an optimal pH level for each
enzyme.
3.6.4 Define denaturation.
Denaturation is a structural change in a protein that results in the loss (usually permanent)
of its biological properties. Refer only to heat and pH as agents.
3.6.5 Explain the use of lactase in the production of lactose-free milk.
Production of lactose-free milk is an example of an industrial process depending on
biological methods (biotechnology). Lactose intolerance is found in a high proportion of the
human population (for example, in Asia) but more rarely among those of European origin.
Lactose-free milk is produced industrially by passing milk over lactase enzyme bound to an
inert carrier (alginate beads). The enzyme cleaves the lactose disaccharide into glucose and
galactose. These monosaccharides have no lactose ill effects. The nutritionally identical,
converted milk has a slightly sweeter taste.
Topic 3.7 - Cell Respiration
3.7.1 Define cell respiration. Cell respiration is the controlled release of energy from
organic compounds in cells to form ATP.
3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by
glycolysis into pyruvate, with a small yield of ATP.
3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the
cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.
Mention that ethanol and carbon dioxide are produced in yeast, whereas lactate is
produced in humans.
In anaerobic cell respiration, pyruvate is converted into either lactate by lactic acid
fermentation or ethanol and carbon dioxide during alcohol fermentation. This produces no
further yield of ATP. The ethanol and carbon dioxide are produced in yeast whereas lactate
is produced in humans.
3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the
mitochondrion into carbon dioxide and water with a large yield of ATP.
In aerobic respiration, each pyruvate enters the Krebs cycle, a series of chemical reactions
within the mitochondria that produces a very high yield of ATP. Anaerobic respiration of
glucose yields 2 ATP. Aerobic respiration generates more than 30 ATP. Anaerobic
respiration represents only a partial breakdown of glucose. Its end products 3C pyruvate,
2C ethanol and 3C lactic acid still have large amounts of potentially usable energy tapped in
their covalent bonds. The end products of aerobic respiration are, famously, CO2 and H20.
This represents a more complete breakdown.
Topic 3.8 - Photosynthesis
3.8.1 State that photosynthesis involves the conversion of light energy into chemical
energy.
3.8.2 State that light from the Sun is composed of a range of wavelengths (colours).
Reference to actual wavelengths or frequencies is not expected.
3.8.3 State that chlorophyll is the main photosynthetic pigment.
3.8.4 Outline the differences in absorption of red, blue and green light by chlorophyll.
Chlorophyll is a collection of similar pigments that absorb specific wavelengths of visible
light. In general green is reflected. Light in the red and blue ranges is absorbed and powers
photosynthesis.
3.8.5 State that light energy is used to produce ATP, and to split water molecules
(photolysis) to form oxygen and hydrogen.
3.8.6 State that ATP and hydrogen (derived from the photolysis of water) are used to
fix carbon dioxide to make organic molecules.
3.8.7 Explain that the rate of photosynthesis can be measured directly by the
production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in
biomass.
3.8.8 Outline the effects of temperature, light intensity and carbon dioxide
concentration on the rate of photosynthesis.
An increase in temperature causes an increase in photosynthesis. However, at very high
temperatures, the rate of photosynthesis crashes due to the denaturing of key enzymes. The
more light, the more photosynthesis occurs. However, high light intensity can be associated
with overly high temperatures and their previously noted damaging effects. The more carbon
dioxide, the greater the rate of photosynthesis. Carbon dioxide represents less than 0.04% of
the composition of air. In nature, during daylight hours, at moderate temperatures, CO2 it
is the limiting factor for photosynthesis. Phytoplankton and other aquatic plants rely on
dissolved CO2.
TOPIC 4: GENETICS
Topic 4.1 - Chromosomes, Genes, Alleles and Mutations
4.1.1 State that eukaryote chromosomes are made of DNA and proteins.
4.1.2 Define gene, allele and genome.
A gene is a heritable factor that controls a specific characteristic. An allele is one specific
form of a gene, differing from other alleles by one or a few bases only and occupying the
same gene locus as other alleles of the gene. The genome is the whole of the genetic
information of an organism.
4.1.3 Define gene mutation.
Gene mutation is a change in the base sequence of the DNA.
4.1.4 Explain the consequence of a base substitution mutation in relation to the
processes of transcription and translation using the example of sickle-cell anemia.
GAG has mutated to GTG causing glutamic acid to be replaced by valine. This single base
substitution resulting in one amino acid change in the structure of hemoglobin causes
sickle-cell anemia.
The frequency of the sickle-cell allele is correlated with the prevalence of malaria in many
parts of the world. In this case, there is a clear causal link. There has clearly been natural
selection in favoor of the sickle-cell allele in malarial areas, despite it causing severe anemia
in the homozygous condition. Natural selection has led to particular frequencies of the
sickle-cell and the normal hemoglobin alleles, to balance the twin risks of anemia and
malaria.
Topic 4.2 - Meiosis
4.2.1 State that meiosis is a reduction division of a diploid nucleus to form haploid
nuclei.
4.2.2 Define homologous chromosomes.
Homologous chromosomes are pairs of equivalent chromosomes that correspond in size and
centromere position. They contain alleles for the same genes point for point along their
length. One of the homologous chromosomes is inherited from the organism's mother; the
other from the organism's father. Homologous chromosomes line up in pairs during meiosis.
4.2.3 Outline the process of meiosis, including pairing of homologous chromosomes
and crossing over, followed by two divisions, which results in four haploid cells.
Meiosis can be divided into two segments, meiosis I and II. In meiosis I, the chromosomes
meet in homologous pairs. Each chromosome consists of 2 identical sister chromatids,
therefore each homologous pair is a group of 4 chromatids, called a tetrad. Crossing over
refers to the exchange of genetic material between non-sister chromatids during prophase I.
The first division occurs by each of these chromosome pairs segregating, or separating, onto
different sides of the cell. This produces two cells with the diploid number of chromosomes.
Then, the second division occurs in both new cells when the sister chromatids are
separated, pulling apart the chromosome. This produces four cells with the haploid number
of chromosomes.
4.2.4 Explain that non-disjunction can lead to changes in chromosome number,
illustrated by reference to Down syndrome (trisomy 21).
Non-disjunction is when certain homologous chromosomes or sister chromatids fail to
separate. This results in one gamete receiving two of the same type of chromosome and
another gamete receiving no copy. An example is Down's syndrome which results from
trisomy of chromosome 21. This means the individual with the syndrome has received three,
rather than two, copies of chromosome 21.
4.2.5 State that, in karyotyping, chromosomes are arranged in pairs according to their
size and structure.
Karyotyping can be done by using enlarged photographs of chromosomes. Karyotypes can
be used to screen for defective chromosomes in the fetus, so if a problem is found parents
can deal with it early.
4.2.6 State that karyotyping is performed using cells collected by chorionic villus
sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities. There are ethical and social issues associated with karyotyping of unborn fetuses because
this procedure allows parents to abort fetuses with a chromosome abnormality. There is also
evidence that, in some parts of the world, abortion on the basis of gender is carried out.
There are also questions about whether or not national governments should interfere with
personal freedoms, and whether or not they should be able to ban procedures within the
country and possibly also ban citizens travelling to foreign countries where the procedures
are permitted. 4.2.7 Analyze a human karyotype to determine gender and whether nondisjunction
has occurred.
Topic 4.3 - Theoretical Genetics
4.3.1 Define genotype, phenotype, dominant allele, recessive allele, codominant
alleles, locus, homozygous, heterozygous, carrier and test cross.
Genotype: the alleles of an organism.
Phenotype: the characteristics of an organism.
Dominant allele: an allele that has the same effect on the phenotype whether it is present
in the homozygous or heterozygous state.
Recessive allele: an allele that only has an effect on the phenotype when present in the
homozygous state.
Codominant alleles: pairs of alleles that both affect the phenotype when present in a
heterozygote. (The terms incomplete and partial dominance are no longer used.)
Locus: the particular position on homologous chromosomes of a gene.
Homozygous: having two identical alleles of a gene.
Heterozygous: having two different alleles of a gene.
Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in
individuals that are homozygous for this allele.
Test cross: testing a suspected heterozygote by crossing it with a known homozygous
recessive.
4.3.2 Determine the genotypes and phenotypes of the offspring of a monohybrid cross
using a Punnett grid.
The grid should be labeled to include parental genotypes, gametes, and both offspring
genotype and phenotype.
4.3.3 State that some genes have more than two alleles (multiple alleles).
4.3.4 Describe ABO blood groups as an example of codominance and multiple alleles.
The ABO blood groups are an example of multiple alleles of a single gene because this gene
exists in three allelic forms: A, B and O. Type O will only be expressed in the homozygous
form; when combined with A or B alleles it will not be expressed. The blood groups are also
an example of codominance, or the expression of the phenotypic form of both alleles. For
example, a person with both the A and B alleles, carries AB type blood. Both blood group A
and B are fully expressed.
Phenotype: Genotype
O: ii
A: IAIA or IAi
B: IBIB or IBi
AB: IAIB
4.3.5 Explain how the sex chromosomes control gender by referring to the inheritance
of X and Y chromosomes in humans.
Gender in humans is determined by two chromosomes called X and Y because this is the
way they appear on karyotypes. The Y chromosome is tiny and almost entirely lacking in
genetic material. All males have one X chromosome and one Y chromosome. Females have
two X chromosomes. During meiosis females can only produce gametes with an X
chromosome. Males can produce gametes with either an X or a Y chromosome. The male's
gametes, decide gender: the child can have XX (female) or XY (male) chromosomes.
4.3.6 State that some genes are present on the X chromosome and absent from the
shorter Y chromosome in humans.
4.3.7 Define sex linkage.
Sex linkage depends on the fact that certain genes are found on a sex chromosome. Usually
harmful sex-linked phenotypes are due to a recessive sex-linked allele on the X
chromosome. For this reason they are more common in males than females.
4.3.8 Describe the inheritance of color blindness and hemophilia as examples of sex
linkage.
Both color blindness and hemophilia are produced by a recessive sex-linked allele on the X
chromosome. Xb and Xh is the notation for the alleles concerned. The corresponding
dominant alleles are XB and XH.
4.3.9 State that a human female can be homozygous or heterozygous with respect to
sex-linked genes.
4.3.10 Explain that female carriers are heterozygous for X-linked recessive alleles.
Obviously a recessive X-linked gene will only be expressed in the homozygous form. If an Xlinked recessive allele is present in a male, it will always be expressed.
Since females have two X chromosomes but only is actually expressed. The other entire
chromosome is bound up in an inactive structure known as a Barr body.
4.3.11 Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses
involving any of the above patterns of inheritance.
Statisticians are convinced that Mendel’s results are too close to exact ratios to be genuine. We
shall never know how this came about, but it offers an opportunity to discuss the need for
scientists to be truthful about their results, whether it is right to discard results that do not fit
a theory.
4.3.12 Deduce the genotypes and phenotypes of individuals in pedigree charts.
For dominant and recessive alleles, upper-case and lower-case letters, respectively, should
be used. Letters representing alleles should be chosen with care to avoid confusion between
upper and lower case. For codominance, the main letter should relate to the gene and the
suffix to the allele, both uppercase. For example, red and white codominant flower colours
should be represented as CR and Cw, respectively. For sickle-cell anemia, HbA is normal and
Hbs is sickle cell.
There are many social issues in families in which there is a genetic disease, including
decisions for carriers about whether to have children, personal feelings for those who have
inherited or passed on alleles for the disease, and potential problems in finding partners,
employment and health or life insurance. There are ethical questions about whether personal
details about genes should be disclosed to insurance companies or employers. Decisions may
have to be made about whether or not to have screening. These are particularly acute in the
case of Huntington disease.
Topic 4.4 - Genetic Engineering and Biotechnology
4.4.1 Outline the use of polymerase chain reaction (PCR) to copy and amplify minute
quantities of DNA.
4.4.2 State that, in gel electrophoresis, fragments of DNA move in an electric field and
are separated according to their charge and size.
4.4.3 State that gel electrophoresis of DNA is used in DNA profiling
4.4.4 Describe the application of DNA profiling to determine paternity and also in
forensic investigations.
There are a variety of social implications stemming from DNA profiling, such as identity
issues for a child who learns unexpectedly who his or her biological father is, self-esteem
problems for someone who learns he is not a father, problems in relationships where the
male partner learns that he did not father a child, but also relief for crime victims when
those responsible for the crime are identified and convicted, sometimes decades later.
4.4.5 Analyse DNA profiles to draw conclusions about paternity or forensic
investigations.
4.4.6 Outline three outcomes of the sequencing of the complete human genome.
1. Three billion nucleotides represent only 23,500 genes, just a few thousand more than a
nematode worm.
2. No dramatic medical cures are on the horizon a decade after the announcement of the
first draft in 2000. The projected was “completed” in 2003.
3. “Non-coding DNA is not just “junk DNA.”
4. The central dogma of biology is refuted. One gene does not code for one protein (or
poltpeptide).
5. Exon sequences combine in multiple ways. Also lot of, but not all, non-coding DNA has a
complex, interactive, regulatory function.
6. Much non-coding DNA has no known biological function. Epigenetic gene expression is a
wide open frontier.
We can either emphasize the large shared content of the human genome, which is common to
all of us and should give us a sense of unity, or we can emphasize the small but significant
allelic differences that create the biodiversity within our species, which should be treasured. It
is important to stress parity of esteem of all humans, whatever their genome.
The Human Genome Project was an international endeavor, with laboratories throughout the
world collaborating. However, there were also efforts in some parts of the world to gain
commercial benefits from the outcomes of the project. The data from the Human Genome
Project can be viewed in different ways: it could be seen as a complete account of what makes
up a human, if one takes a reductionist view of life, or, alternatively, as merely the chemical
instructions that have allowed a huge range of more significant human characteristics to
develop.
4.4.7 State that, when genes are transferred between species, the amino acid
sequence of polypeptides translated from them is unchanged because the genetic code
is universal.
There is an ethical or moral question here: whether it is right to change the genetic integrity
of a species by transferring genes to it from another species.
4.4.8 Outline a basic technique used for gene transfer involving plasmids, a host cell
(bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase.
The use of E. coli in gene technology is well documented. Most of its DNA is in one circular
chromosome, but it also has plasmids (smaller circles of DNA). These plasmids can be
removed and cleaved by restriction enzymes at target sequences. DNA fragments from
another organism can also be cleaved by the same restriction enzyme, and these pieces can
be added to the open plasmid and spliced together by ligase. The recombinant plasmids
formed can be inserted into new host cells and cloned.
4.4.9 State two examples of the current uses of genetically modified crops or animals.
Examples include salt tolerance in tomato plants, synthesis of beta-carotene (vitamin A
precursor) in rice, herbicide resistance in crop plants and factor IX (human blood clotting) in
sheep milk.
The economic benefits of genetic modification to biotechnology companies that perform it
could be considered. Also mention the possibility that harmful changes to local economies
could result, and the danger that wealth could become more concentrated in a smaller
percentage of the population if expensive but profitable new techniques are introduced. In
this respect, inequalities in wealth may become greater.
4.4.10 Discuss the potential benefits and possible harmful effects of one example of
genetic modification.
This is an opportunity to discuss how we can assess whether risks are great enough to
justify banning techniques and how the scientific community can inform communities
generally about potential risks. Informed decisions need to be made but irrational fears
should not be propagated. Consideration could be given to the paradox that careful research
is needed to assess the risks, but performing this research in itself could be risky.
4.4.11 Define clone.
A clone is a group of genetically identical organisms or a group of cells derived from a single
parent cell.
4.4.12 Outline a technique for cloning using differentiated animal cells.
The 8-cell stage embryo resulting from in vitro fertilization is divided into separate cells.
Each cell is grown into an embryo again and then transferred to surrogate mother animals.
The process can be repeated many times to produce a line of offspring that are genetically
identical. Example: Dolly the sheep.
Ethical questions about cloning should be separated into questions about reproductive
cloning and therapeutic cloning. Some groups are vehemently opposed to both types.
4.4.13 Discuss the ethical issues of therapeutic cloning in humans.
Therapeutic cloning is the creation of an embryo to supply embryonic stem cells for medical
use. Cloning happens naturally, for example monozygotic twins. Some may regard the in
vitro production of two embryos from one to be acceptable. Others would see this as leading
to the selection of those "fit to be cloned" and visions of "eugenics and a super-race."
Perhaps the most pressing question, however, is that of the status and rights of a theoretical
human clone. What is being debated and discussed right now by lawmakers, ethicists and
religious leaders is exactly this. Is a clone its own unique human being? To what extent is
cloning strictly for the purpose of stem cell production or organ harvesting right?
Topic 5: ECOLOGY AND EVOLUTION
Topic 5.1 - Communities and Ecosystems
5.1.1 Define species, habitat, population, community, ecosystem and ecology.
Species: a group of organisms that can interbreed and produce fertile offspring.
Habitat: the environment in which a species normally lives or the location of a living
organism.
Population: a group of organisms of the same species who live in the same area at the same
time.
Community: a group of populations living and interacting with each other in an area.
Ecosystem: a community and its abiotic environment.
Ecology: the study of relationships between living organisms and between organisms and
their environment
5.1.2 Distinguish between autotroph and heterotroph.
Autotroph: an organism that synthesizes its organic molecules from simple inorganic
substances.
Heterotroph: an organism that obtains organic molecules from other organisms.
5.1.3 Distinguish between consumers, detritivores and saprotrophs.
Consumer: an organism that ingests other organic matter that is living or recently killed.
Detritivore: an organism that ingests non-living organic matter. Typical detritivores are
small organisms living on fragments of decaying matter such as earthworms, millipedes,
woodlice and ants. Crabs and other small marine and aquatic crustaceans and also ants
come to mind. Myriad species of protoctista and bacteria are also important.
Saprotroph: an organism that lives on or in nonliving organic matter, secreting digestive
enzymes into it and absorbing the products of digestion. Saprotrophs are the fungi and
certain bacteria.
5.1.4 Describe what is meant by a food chain, giving three examples, each with at
least three linkages (four organisms).
Only real examples should be used from natural ecosystems. A→ B indicates that A is being
“eaten” by B (that is, the arrow indicates the direction of energy flow). Each food chain
should include a producer and consumers, but not decomposers. Named organisms at
either species or genus level should be used. Common species names can be used instead of
binomial names. General names such as “tree” or “fish” should not be used.
5.1.5 Describe what is meant by a food web.
A food web is more complex and more realistic than a linear food chain and it includes a
larger variety of organisms.
5.1.6 Define trophic level.
Trophic levels are based on the division of species in an ecosystem on the basis of their
main nutritional source. The trophic level that ultimately supports all others consists of
autotrophs, or primary producers.
5.1.7 Deduce the trophic level of organisms in a food chain and a food web.
Students should be able to place an organism at the level of producer, primary consumer,
secondary consumer, and so on, as the terms herbivore and carnivore are not always
applicable.
5.1.8 Construct a food web containing up to 10 organisms, using appropriate
information.
5.1.9 State that light is the initial energy source for almost all communities.
5.1.10 Explain the energy flow in a food chain.
Energy losses between trophic levels include material not consumed or material not
assimilated, and heat loss through cell respiration.
5.1.11 State that energy transformations are never 100% efficient.
A transfer of energy art each trophic level as low as 10% is quite typical.
5.1.12 Explain reasons for the shape of pyramids of energy.
A pyramid of energy shows the flow of energy from one trophic level to the next in a
community. The units of pyramids of energy are, therefore, energy per unit area per unit
time, for example, kJ m–2 yr –1.
5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be
recycled.
5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
Decomposers feed on dead organisms and products of living organisms. They secrete
extracellular enzymes on these materials that cause decomposition, and then they absorb
decomposed and digested foods. Examples include many species of bacteria and fungi.
These are essential organisms to an ecosystem, since they cause recycling of materials
between biotic and abiotic parts of the ecosystem. Topic 5.2 – The greenhouse Effect
5.2.1 Draw and label a diagram of the carbon cycle to show the processes involved.
The details of the carbon cycle should include the interaction of living organisms and the
biosphere through the processes of photosynthesis, cell respiration, fossilization and
combustion. Include the saprophytes decomposers. The percentage of C02 in the air is only
0.037%, or 370 ppm. CO2 dissolves in water as HCO3-.
5.2.2 Analyse the changes in concentration of atmospheric carbon dioxide using
historical records.
Data from the Mauna Loa, Hawaii, or Cape Grim, Tasmania, monitoring stations may be
used.
5.2.3 Explain the relationship between rises in concentrations of atmospheric carbon
dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.
Students should be aware that the greenhouse effect is a natural phenomenon. Reference
should be made to transmission of incoming shorter-wave radiation and re-radiated longerwave radiation. Knowledge that other gases, including methane and oxides of nitrogen, are
greenhouse gases is expected.
The greenhouse effect is a naturally occurring phenomenon in the ecosystem of the planet.
It is simply the accumulation of carbon dioxide and other gases such as methane and
nitrogen dioxide in the atmosphere, which traps heat from the sun's radiation and raises
planetary temperatures. Recently, however, increased industry and burning of fossil fuels
have caused the release of excessive amounts of carbon dioxide into the atmosphere. The
planet is now enveloped by a layer of carbon dioxide far thicker than would be there
naturally, which allows the sun radiation to enter our atmosphere, but prevents it from
going out. This causes the trapping of heat into our atmosphere, and the consequent
gradual increase in temperature around the world, hence global warming. This effect is
called the greenhouse effect, since the layer of carbon dioxide around our planet has similar
effects to the glass walls of a greenhouse in causing increased temperature inside.
The greenhouse effect should never be confused with the reduction of the ozone
layer. The ozone (O3) layer is present at about 20 Km above the surface of the earth. It
absorbs ultra violet light that radiates from the sun, thus protecting us from the harmful effects
of these radiations. Increased industry in the last 20 years or so, have caused the breaking of
ozone molecules into oxygen, resulting in a hole in this protective layer. The chemicals
responsible for this effect are a group of chloro-fluoro-carbons (CFCs) that are used in
refrigeration, aerosol cans and other technologies. These compounds are very light and they
escape to the upper layers of the atmosphere, reaching the ozone layer and destroying it. A
hole in the ozone layer is most prominent over the Antarctic.
5.2.4 Outline the precautionary principle.
The precautionary principle holds that, if the effects of a human-induced change would be
very large, perhaps catastrophic, those responsible for the change must prove that it will not
do harm before proceeding. This is the reverse of the normal situation, where those who are
concerned about the change would have to prove that it will do harm in order to prevent
such changes going ahead. If the possible consequences of rapid global warming are
devastating enough, preventive measures are justified even if it is far from certain that rapid
global warming will result from current human activities.
5.2.5 Evaluate the precautionary principle as a justification for strong action in
response to the threats posed by the enhanced greenhouse effect.
Consider whether the economic harm of measures taken now to limit global warming could
be balanced against the potentially much greater harm for future generations of taking no
action now. There are also ethical questions about whether the health and wealth of future
human generations should be jeopardized, and whether it is right to knowingly damage the
habitat of, and possibly drive to extinction, species other than humans. The environmental
angle here is that the issue of global warming is, by definition, a genuinely global one in
terms of causes, consequences and remedies. Only through international cooperation will a
solution be found. There is an inequality between those in the world who are contributing
most to the problem and those who will be most harmed.
5.2.6 Outline the consequences of a global temperature rise on arctic ecosystems.
Effects include increased rates of decomposition of detritus previously trapped in
permafrost, expansion of the range of habitats available to temperate species, loss of ice
habitat, changes in distribution of prey species affecting higher trophic levels, and increased
success of pest species, including pathogens
Topic 5.3 - Populations
5.3.1 Outline how population size is affected by natality, immigration, mortality and
emigration.
In order for a population to be stable in size, natality (birth) + immigration = mortality
(death) + emigration.
5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve.
5.3.3 Explain the reasons for the exponential growth phase, the plateau phase and the
transitional phase between these two phases.
The exponential growth phase is when the population rises quickly because there are no
limiting factors yet and the resources are abundant. The plateau phase begins when the
organism hits its carrying capacity, which is the maximum number of organisms in a
population that can be supported by the ecosystem at a given time. The transitional phase
in between these two phases occurs because this is when the limiting factors in the
environment start to limit the increase, slowing the population increase.
5.3.4 List three factors that set limits to population increase.
Three factors that set limits to population increase are the availability of nutrients, the
number of predators, and the accumulation of waste materials.
Topic 5.4 - Evolution
5.4.1 Define evolution.
Evolution is the cumulative change in the heritable characteristics of a population. If we
accept not only that species can evolve, but also that new species arise by evolution from
preexisting ones, then the whole of life can be seen as unified by its common origins.
Variation within our species is the result of different selection pressures operating in
different parts of the world, yet this variation is not so vast to justify a construct such as
race having a biological or scientific basis.
5.4.2 Outline the evidence for evolution provided by the fossil record, selective
breeding of domesticated animals and homologous structures.
The fossil record provides snapshots of the past that, when assembled, illustrate a
panorama of evolutionary change over the past four billion years. The picture may be
smudged in places and may have bits missing, but fossil evidence clearly shows that life is
old and has changed over time. Fossils or organisms that show the intermediate states
between an ancestral form and that of its descendants are referred to as transitional forms
(“missing links” that are not missing!). There are numerous examples of transitional forms
in the fossil record, providing an abundance of evidence for change over time. In
sedimentary rocks older fossils are always found at the deeper layers.
People have been artificially selecting domesticated plants and animals for thousands of
years. These activities have amounted to large, long-term, practical experiments that clearly
demonstrate that species can change dramatically through selective breeding.
All living things are fundamentally alike. At the cellular and molecular level living things are
remarkably similar to each other. These fundamental similarities are most easily explained
by evolutionary theory: life shares a common ancestor. Organisms that are closely related to
one another share many anatomical similarities. Sometimes the similarities are
conspicuous, as between crocodiles and alligators, but in other cases considerable study is
needed for a full appreciation of relationships. Whales and hummingbirds have tetrapod
skeletons inherited from a common ancestor. Their bodies have been modified and parts
have been lost through natural selection, resulting in adaptation to their respective lifestyles
over millions of years. On the surface, these animals look very different, but the relationship
between them is easy to demonstrate. Except for those bones that have been lost over time,
nearly every bone in each corresponds to an equivalent bone in the other. The bird wing and
whale flipper are homologous structures.
5.4.3 State that populations tend to produce more offspring than the environment can
support.
5.4.4 Explain that the consequence of the potential overproduction of offspring is a
struggle for survival.
5.4.5 State that the members of a species show variation.
5.4.6 Explain how sexual reproduction promotes variation in a species.
Unlike the outright cloning that occurs in asexual reproduction, the offspring in sexual
reproduction are a genetic combination of both parents. During meiosis, a huge variety of
gametes are created because homologous chromosomes are independently assorted. Crossover further increases the variability.
5.4.7 Explain how natural selection leads to evolution.
Greater survival and reproductive success of individuals with favorable heritable variations
can lead to change in the characteristics of a population.
5.4.8 Explain two examples of evolution in response to environmental change; one
must be antibiotic resistance in bacteria.
If a culture of bacteria is treated with an antibiotic, most of the bacteria are killed. A small
number that naturally have genes resistant to the antibiotic, will prevail. It is important to
realize that these bacteria did not "learn" to resist the antibiotic. They had mutated genes
that somehow protected them. These bacteria reproduce and pass on their resistant genes.
This can become a problem when trying to kill a bacterial infection in a patient. New
antibiotics must be developed constantly. The problem is worse when a prescribed course of
antibiotics is not completed.
There are two varieties of the moth Biston betularia, one is black, the other speckled. On a
tree covered in lichens, the peppered moth blends in very well. The black moth is easily seen
by predators. During the industrial revolution when trees began to get covered in sooty
carbon deposits the black moth was better camouflaged. More black moths than speckled
moths evaded predators, allowing them to survive and pass on their melanic genes.
Topic 5.5 - Classification
5.5.1 Outline the binomial system of nomenclature.
The adoption of a system of binomial nomenclature is largely due to Swedish botanist and
physician Carolus Linnaeus (1707–1778). The first name indicates the genus and the
second indicates the species. The genus is written in a capital letter and the species in small
letters. Also the two names are usually printed in italics or underlined when written.
Naming organisms in this way facilitates the process of identification and helps in
overcoming language barriers between scientists.
5.5.2 List seven levels in the hierarchy of taxa—kingdom, phylum, class, order,
family, genus and species—using an example from two different kingdoms for each
level.
5.3 Distinguish between the following phyla of plants, using simple external
recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta.
5.5.4 Distinguish between the following phyla of animals, using simple external
recognition features: porifera, cnidaria, platyhelminthes, annelida, mollusca and
arthropoda.
5.5.5 Apply and design a key for a group of up to eight organisms.
A dichotomous key should be used.
TOPIC 6: HUMAN HEALTH AND PHYSIOLOGY
Topic 6.1 - Digestion
6.1.1 Explain why digestion of large food molecules is essential.
Digestion is necessary because it breaks large food molecules into soluble, smaller
molecules that can be absorbed into the villi of the small intestine and eventually travel
through the blood. Simple molecules can then dissolve in blood plasma and go into
circulation to reach every part of the body.
6.1.2 Explain the need for enzymes in digestion.
At body temperature the rate of digestion would be extremely slow without the catalytic
effect of enzymes.
6.1.3 State the source, substrate, products and optimum pH conditions for one
amylase, one protease and one lipase.
One source of amylase is the salivary glands in the mouth, The substrate is starch and the
product is maltose. The optimum pH is around 7 (neutral).
Pepsin is a protease. Its source is the secretory glands lining the stomach wall. Pepsin
breaks down proteins to polypeptides and amino acids. It is unusual in that its optimum pH
is 2 (strongly acidic).
Lipase is found in the pancreas juice. It converts triglycerides into glycerol and fatty acids.
Its optimum pH is slightly basic (a little higher than 7).
6.1.4 Draw and label a diagram of the digestive system. The diagram should show the
mouth, esophagus, stomach, small intestine, large intestine, anus, liver, pancreas and
gall bladder. The diagram should clearly show the interconnections between these
structures.
6.1.5 Outline the function of the stomach, small intestine and large intestine.
The stomach is where protein digestion begins. The muscular stomach churns and mixes
the food. Like chewing in the mouth, this is physical digestion as opposed to enzymemediated chemical digestion. The stomach is made of protein but it does not digest itself.
Pepsin is secreted as a precursor molecule that is activated only in the acid medium of the
stomach interior. Mucus secreted from the stomach lining also protects the stomach from
the action of its own pepsin.
Chemical digestion is finished off in the duodenal loop, the first part of the small intestine.
Bile from the liver and pancreatic juice meet at a common duct and are squirted onto the
food soon after it leaves the stomach. Pancreatic juice contains trypsin (the final protease
that faces the same self-digestion issue encountered with pepsin), more amylase, maltase,
lipase and nuclease. Bile salts are made in the liver from the breakdown of worn out red
blood cells. Bile is responsible for the brown color of feces. Bile emulsifies fats into droplets.
The droplets present a large surface area for the action of lipase.
The soluble products of digestion are monosaccharides, amino acids, glycerol, fatty acids,
and free nucleotides. The small intestine is about 7 meters long. This alone presents a
large surface area for absorption. Tiny finger-like membrane folds called villi further
increase the surface area.
In the large intestine, or colon, water is reabsorbed and, feces, the solid wastes of the
digestive tract, are consolidated. Feces are egested through the rectum. It is important to
realize that egestion is not really excretion. The lumen of the digestive system is technically
outside the body. The bile component is an interesting exception.
6.1.6 Distinguish between absorption and assimilation.
Absorption is the passage of digested substances through the wall of the intestine into the
blood capillaries. Assimilation is a process by which food is apportioned, used and
incorporated into the body.
6.1.7 Explain how the structure of the villus is related to its role in absorption and
transport of the products of digestion.
A villus is a folded finger-like structure. Villi increase the surface area for absorption. They
contain a network of blood capillaries and a central lymph vessel called a lacteal. The
breakdown products of lipids enter the lymphatic system. All other products enter the blood
capillary network.
Topic 6.2 - The Transport System
6.2.1 Draw and label a diagram of the heart showing the four chambers, associated
blood vessels, valves and the route of blood through the heart. Care should be taken
to show the relative wall thickness of the four chambers.
Neither the coronary vessels nor the conductive system are required in the diagram.
6.2.2 State that the coronary arteries supply heart muscle with oxygen and nutrients.
6.2.3 Explain the action of the heart in terms of collecting blood, pumping blood, and
opening and closing of valves. A basic understanding is required, limited to the
collection of blood by the atria, which is then pumped out by the ventricles into the
arteries. The direction of flow is controlled by atrio-ventricular and semilunar valves.
The secret of the valves lies in their elegant hydrodynamic design which necessitates a oneway flow. As pressure builds up in a chamber, the valve is suddenly forced open and blood
flows through to the next chamber. The abrupt pressure build-up in the new chamber
caused by the influx of blood causes the the valve to slam shut behind it. The “lub-dub”
sound of the heart corresponds to the Atrio-Ventricular, followed by the semi-lunar valves,
closing on the left and right sides simultaneously.
The left ventricle is much larger simply because it has more work to do. The pulmonary
artery on the right side only has to pump blood to the lungs; whereas the aorta on the right
pumps blood to the entire body including the head against gravity and extremities like the
toes and fingertips. Pressures are so intense, when the atrio-ventricular valves close, that
cord-like tendons called “heartstrings” are necessary to prevent the valves from turning
inside out.
6.2.4 Outline the control of the heartbeat in terms of myogenic muscle contraction,
the role of the pacemaker, nerves, the medulla of the brain and epinephrine
(adrenaline).
The heart is made of interconnecting cardiac muscle which is myogenic. Myogenic
referstrange fact that isolated heart muscle contracts spontaneously by itself. It needs no
nerve stimulation. However, isolated heart tissue beats only erratically. It needs the
autonomic nerve connections from the brain to the pacemaker to beat steadily at rest, and
to increase heart rate in response to exercise.
Located in the wall of the right atrium is the sino-atrial node (SAN) also known as the
pacemaker. It spontaneously produces electrical impulses which spread to the two atria
causing them to contract. Similarly, a centrally placed atrio-ventricular node (VAN) picks
up the waves of excitation from the atria and sends a direct message to each ventricle via
the bundle of His and the Purkinje tissue.
The pacemaker receives two nerves from the brain stem. One of these nerves, the
sympathetic nerve, releases noradrenaline, and causes the heart rate to increase. The
parasympathetic nerve releases acetylcholine and lowers the heart rate. In emergency
situations, the hormone adrenaline is released by the adrenal gland and prepares the body
for “fight or flight” increasing the heart rate.
6.2.5 Explain the relationship between the structure and function of arteries,
capillaries and veins.
Arteries carry blood towards organs. Arteries have thick walls and small lumens because
they have to absorb the high pressure coming from the ventricles of the heart. The arteries
are vascular. The pulse rate is a direct measure of the arteries pumping blood in unison
with the heart. Arterial walls are made of connective tissue, elastic and muscle fibers and a
layer of endothelial cells. The elastic tissue allows the arteries to expand and recoil. This
helps push the blood in the circulation.
Veins have thinner walls and larger lumens. They carry blood, at much lower pressures
than the arteries, from the various organs back to the heart. They have thinner layers of
connective, elastic and smooth muscle fibers.
Capillaries are only one cell thick. They consist of only one layer of endothelium. Some
capillaries also have pores that facilitate mass flow of tissue fluid. The thin walls allow
substances to pass in and out of capillaries by diffusion. No cell in the body is more than
1mmm away from as capillary. The total capillary surface area for exchange of materials is
enormous.
6.2.6 State that blood is composed of plasma, erythrocytes, leucocytes (phagocytes
and lymphocytes) and platelets.
6.2.7 State that the following are transported by the blood: nutrients, oxygen, carbon
dioxide, hormones, antibodies, urea and heat.
Topic 6.3 – Defence against infectious disease
6.3.1 Define pathogen: an organism or virus that causes a disease.
6.3.2 Explain why antibiotics are effective against bacteria but not against viruses.
Antibiotics block specific metabolic pathways found in bacteria. Viruses reproduce using the
host cell’s metabolic pathways, which are not affected by antibiotics.
6.3.3 Outline the role of skin and mucous membranes in defense against pathogens.
The waterproof, naturally oily, keratinized, outer layer of the skin is being constantly
renewed. It is significant and very effective barrier against pathogens. It is worth noting how
the various orifices and parts of the body that present a large permeable surface to the
external world ,not covered by the skin, are protected.
The eyes are protected by the blinking reflex. Tears contain lysozyme. The ears are
protected initially by hairs and the strong tympanic membrane. Cerumen (ear wax) also
contains lysozyme. The mouth is a potential entry point for pathogens. The sense of smell
and taste helps us avoid putrid foods. Saliva contains lysozyme. More important is the
vomiting reflex (antiperistalsis) and the fact that the 0.5% HCl in stomach kills many
pathogens. As far as entry through the nostrils is concerned, coughing, and sneezing
provides an immediate short-term protection. Mucus , again containing lysozyme, is wafted
up by the ciliated epithelium lining the bronchioles and trachea to the back of the throat.
The mucus traps pathogens, dust and other particles for swallowing, sterilization. The
mucus (a glycoprotein) is broken down and recycled. Pathogens are sterilized in the stomach
and digested. Waste materials become part of the feces.
The urethra is protected by the one-way flow of sterile, antiseptic urine. The vagina is an
acidic environmental, hostile to most pathogens. It produces and secretes lactic acid
naturally. As in the gaseous exchange system, the female reproductive tract is protected by
mucus containing lysozyme wafted down towards the exterior, by ciliated epithelium. The
anus is a closed sphincter muscle and there is obviously a one-way flow of feces. Finally:
nipples are protected by breast milk which, once again, contains lysozyme.
6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body
tissues.
Phagocytes move and ingest pathogens like Amoeba. They ingest the entire foreign
organisms by phagocytosis. This is a large scale version of endocytosis. One or more
lysosomes attach to a “food vacuole” and release proteolytic enzymes (lysozyme) which digest
the unwelcome guests.
6.3.5 Distinguish between antigens and antibodies.
An antigen is a foreign macromolecule that does not belong to the host organism and that
elicits an immune response. An antibody is produced by the body in response to the
antigen. Antibodies are also called immunoglobulin. They are comprised of 2 heavy and 2
light polypeptide chains.
6.3.6 Explain antibody production.
Many different types of lymphocyte exist. Each type recognizes one specific antigen and
responds by dividing to form a clone. This clone then secretes a specific antibody against the
antigen.
6.3.7 Outline the effects of HIV on the immune system.
The effects of HIV should be limited to a reduction in the number of active lymphocytes and
a loss of the ability to produce antibodies.
6.3.8 Discuss the cause, transmission and social implications of AIDS.
AIDS is caused by HIV, a retrovirus having RNA as its genetic material rather than DNA. It
transcribes its RNA into the host white blood cell DNA using an enzyme called reverse
transcriptase. Acquired Immune Deficiency Syndrome is the final stage of HIV disease. The
immune system fails and opportunistic pathogens cause further harm. It is transmitted by
sexual intercourse, sharing of needles, blood transfusions, accidents causing blood
contamination, cuts in the skin, tattoos and ear piercing with infected needles.
The social implications of AIDS are well known. Cases of AIDS are not evenly distributed in
the world, and consideration could be given to the severe problems in southern Africa.
Cultural and economic reasons for differences in the prevalence of AIDS could be
considered. The moral obligation of those with the technology and the wealth to help others
lacking these things could be discussed. The different methods of transmission of HIV each
carry their own risk.
Topic 6.4 - Gas Exchange
6.4.1 Distinguish between ventilation, gas exchange and cell respiration.
Ventilation is pumping air in and out of the lungs. It provides and constant supply of new
air and brings it into direct content with the respiratory surface. It maintains a high
concentration of oxygen and low concentration of carbon dioxide in the alveoli as we breathe
in and out. Gas exchange occurs between the air, the moist surface of the aveoli, and the
capillaries by diffusion. By contrast cell respiration is the sum total of the chemical
reactions that occur inside the cell resulting in the controlled production of energy in the
form of ATP from food molecules.
6.4.2 Explain the need for a ventilation system.
A ventilation system is needed to maintain high concentration gradients in the
alveoli.
6.4.3 Describe the features of alveoli that adapt them to gas exchange.
Alveoli have all the characteristics of an efficient respiratory surface. There is a large total
surface area, a dense network of capillaries in intimate contact, a thin wall consisting of
only a single layer of flattened epithelial cells separated from one another by a thin
basement membrane, The pleural membrane, which lines the thoracic cavity, secretes a film
of moisture that lubricates and keeps the alveoli moist.
6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs,
bronchi, bronchioles and alveoli. Students should draw the alveoli in an inset diagram
at a higher magnification.
6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and
pressure changes caused by the internal and external intercostal muscles, the
diaphragm and abdominal muscles.
To inhale: the diaphragm contracts and flattens and the external intercostal muscles also
contract and cause the ribcage to expand and move up. Thoracic volume increases, lungs
expand, and the pressure inside the lungs decreases, so that air flows into the lungs in
response to the pressure gradient.
To exhale: the diaphragm relaxes and moves up. In quiet breathing, the external intercostal
muscles relax causing the elasticity of the lung tissue to recoil. In forced breathing, the
internal intercostal muscles and abdominal muscles also contract to increase the force of
the expiration. Thoracic volume decreases making the pressure inside the lungs increase.
Air flows passively out of the lungs in response to the pressure gradient.
Topic 6.5 – Nerves hormones and homeostasis
6.5.1 State that the nervous system consists of the central nervous system (CNS) and
peripheral nerves, and is composed of cells called neurons that can carry rapid
electrical impulses.
6.5.2 Draw and label a diagram of the structure of a motor neuron.
Include dendrites, cell body with nucleus, axon, myelin sheath, nodes of Ranvier and motor
end plates.
6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory
neurons, within the CNS by relay neurons, and from the CNS to effectors by motor
neurons.
6.5.4 Define resting potential and action potential (depolarization and repolarization).
Like firing a gun, nerve impulses are “all or nothing.” They fire or they don’t fire. In order to
fire nerve impulses require certain threshold of stimulation. The strength of the impulse is
constant, regardless of the strength of the stimulus. Squeezing the trigger of a gun very
gently or aggressively has no influence on the speed of the bullet. Nerves make specific
physical connections in the body. Impulses travel rapidly in one direction only, “from A to
B.” Nerve impulses are measured in millivolts; but a dynamite fuse is a better analogy for an
axon nerve than an electrical wire.
6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron.
Nerve impulses involve rapid movement of positively charged ions. The resting potential (70mV) is caused by a chemical concentration gradient established by pumping Na+ and K+
ions selectively across the axon membrane. At rest the exterior of the axon is positive
respect with to the inside. The action potential (+40mV) is the dramatic reversal (and
subsequent restoration) of the resting potential. This depolarization depends on the sudden,
localized opening of gated channels in the axon membrane, allowing N+ ions to rush into the
interior. There is a refractory period as concentration gradients of Na+ and K+ ions are
restored by active transport.
6.5.6 Explain the principles of synaptic transmission
Neurons are situated close together, but they do not touch. The axon of one neuron points
towards the dendrites of the next one. Signals are carried between them by chemical
messengers called neurotransmitters. Neurotransmitters are initially located in vesicles and
are released into the synaptic cleft by exocytosis. The neurotransmitter molecules diffuse
across the gap and attach to specific binding sites embedded in the post-synaptic
membrane of the target axon. The binding action initiates a new action potential. Finally,
the neurotransmitter is removed and recycled. It renters the pre-synaptic neurotransmitter
through channels called re-uptake proteins.
6.5.7 State that the endocrine system consists of glands that release hormones that
are transported in the blood.
6.5.8 State that homeostasis involves maintaining the internal environment between
limits, including blood pH, carbon dioxide concentration, blood glucose concentration,
body temperature and water balance.
The internal environment consists of blood and tissue fluid.
6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting
changes in levels by negative feedback mechanisms.
Homeostasis involves maintaining the internal environment at a constant level or between
narrow limits, including blood pH, oxygen and carbon dioxide concentrations, blood glucose,
body temperature and water balance.
6.5.10 Explain the control of body temperature, including the transfer of heat in
blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering.
If body temperature rises above or falls below 37 degrees Celsius, messages are sent by the
hypothalamus to various parts of the body so the temperature returns to normal. Negative
feedback refers the mechanisms that return the body to the set-point.
Nerve cells beneath the skin called thermoreceptors detect ambient temperature changes
and send messages to the hypothalamus. Hormones are released from the hypothalamus
and make the very short journey to the adjacent pituitary gland. The pituitary gland then
releases a hormone bound for the thyroid-gland which in turn releases thyroxine. Thyroxine
increases the basal metabolic rate of the body, which generates heat. The hypothalamus
also plays a role in transmitting nerve messages to muscles, blood capillaries and sweat
glands. The effect of this is the occurrence of responses such as shivering, vasoconstriction
or vasodilatation and sweating.
6.5.11 Explain the control of blood glucose concentration, including the roles of
glucagon, insulin and α and β cells in the pancreatic islets.
Insulin and glucagon regulate the sugar level in the body. These two hormones are
manufactured in the pancreas and, through the general blood circulation, are carried to the
liver where they perform their functions. Enzymes that convert glucose to glycogen though a
condensation reaction are stimulated by Insulin. Enzymes that hydrolyze glycogen to
glucose are stimulated by glucagon. Receptors in the pancreas are sensitive to the changes
in sugar level, thus releasing the necessary requirements of insulin and glucagon depending
on the needs of the body. The beta cells found in the islets of the pancreas make insulin and
the alpha cells make glucagon.
6.5.12 Distinguish between type I and type II diabetes.
Type 1 diabetes used to be called insulin dependent diabetes or juvenile onset diabetes. In
type 1 diabetes, the pancreas undergoes an autoimmune attack and is rendered incapable
of making insulin. Type 2 diabetes was known as non-insulin dependent diabetes or adult
onset diabetes. In type 2 diabetes, patients can still produce insulin, but do so relatively
inadequately for their body's needs, particularly when insulin resistance develops.
Rates can be particularly high when individuals consume a diet very different to the
traditional one of their ancestors, for example, when having migrated to a new country.
There are genetic differences in our capacity to cope with high levels of refined sugar and fat
in the diet. Humans also vary considerably in how prone they are to become obese
Topic 6.6 - Reproduction
6.6.1 Draw and label diagrams of the adult male and female reproductive systems.
6.6.2 Outline the role of hormones in the menstrual cycle, including FSH (follicle
stimulating hormone), LH (luteinizing hormone), estrogen and progesterone.
The pituitary secretes Follicle Stimulating Hormone (FSH) and a little Leutenizing Hormone
(LH) into the bloodstream which cause the follicles to begin to mature. The maturing follicles
then release another hormone, estrogen. As the follicles ripen over a period of about seven
days, they secrete more and more estrogen into the bloodstream. Estrogen causes the lining of
the uterus to thicken. When the estrogen level reaches a certain point it causes the pituitary to
release a surge of Leutenizing Hormone (LH) which triggers the one most mature follicle to
burst open and release an egg. This is called ovulation.
Between ovulation and menstruation, the follicle from which the egg burst becomes the corpus
luteum (yellow body). As it heals, it produces the hormones estrogen and, in larger amounts,
progesterone which is necessary for the maintenance of a pregnancy. If fertilization and
implantation do not occur, the spiral arteries of the lining close off, stopping blood flow to the
surface of the lining. The blood pools into "venous lakes" which, once full, burst and, with the
endometrial lining, form the menstrual flow. Most periods last 4 to 8 days but this length varies
over the course of a lifetime. Some researchers view menses as the natural monthly cleansing
of the uterus and vagina of sperm and bacteria.
6.6.3 Annotate a graph showing hormone levels in the menstrual cycle, illustrating the
relationship between changes in hormone levels and ovulation, menstruation and
thickening of the endometrium.
6.6.4 List three roles of testosterone in males.
Limit this to pre-natal development of male genitalia, development of secondary sexual
characteristics and maintenance of sex drive. From birth to the age of ten, testosterone level
is very low. It increases sharply dramatically at puberty and stays at high levels until the
age of 40-50, after which it gradually decreases. Secondary sexual characters are voice
change, beard and pubic hair and the building of a muscular physique.
6.6.5 Outline the process of in vitro fertilization (IVF).
Eggs are removed surgically from the ovaries of a woman by a large needle through the wall
of the vagina. They are sucked into a syringe and placed in a glass dish for cleaning and
incubation. Sperms are added and fertilization takes places in vitro (Latin for “in glass”). If
fertilization occurs the developing embryos is monitored and incubated for a few days,
transferred through the vagina to the uterus for implantation. After two weeks the success
of the procedure can be measured with a standard pregnancy test.
6.6.6 Discuss the ethical issues associated with IVF.
There is great variation between human societies around the world in the views held on IVF.
This is the result of cultural and religious diversity. There is little evidence to suggest that
children born as a result of standard IVF protocols are different in any way from children
conceived naturally. There are potential risks in the drug treatments that the woman is given,
and there are concerns about the artificial selection of sperm and the injection of them into the
eggs that occurs with some IVF protocols. The natural selection of sperm with consequent
elimination of unhealthy ones is bypassed, and there is evidence that there are higher rates of
abnormality in the offspring as a result.