2.1.1 Outline the cell theoryThe cell theory states that:1. All living things are composed of cells (or cell products)2. The cell is the smallest unit of life3. Cells only arise from pre-existing cells

2.1.2 Discuss the evidence for the cell theoryMicroscopes: Microscopes have increased man's ability to visualise tiny objects All living things when viewed under a microscope have been found to be made of cells and cell products (e.g. hair) Note:Certain types of cells do not conform to the standard notion of what constitutes a cell Muscle cells contain multiple nuclei Fungal hyphae consist of multiple cells that share a continuous cytoplasm

Light vs Electron Microscopes

Experimental Evidence: Cells removed from tissues can survive independently for short periods of time Nothing smaller than a cell has been found to be able to live independently Experiments by Francesco Redi and Louis Pasteur have demonstrated that cells cannot grow in sealed and sterile conditionsHistory of the Cell Theory

2.1.3 State that unicellular organisms carry out all the functions of lifeUnicellular organisms (such as amoeba, paramecium, euglena and bacterium) are the smallest organisms capable of independent life.All living things share 7 basic characteristics: Movement: Living things show movement, either externally or internally Reproduction: Living things produce offspring, either sexually or asexually Sensitivity: Living things can respond to and interact with the environment Growth: Living things can grow or change size / shape Respiration: Living things use substances from the environment to make energy Excretion: Living things exhibit the removal of wastes Nutrition: Living things exchange materials and gases with the environment

2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units

Relative sizes: Unit Conversion Table:

A molecule = 1 nm Cell membrane thickness = 7.5 nm Virus = 100 nm (range: 20 - 200 nm) Bacteria = 1 - 5 um Organelles = allele B > allele C)

4.3.4 Describe ABO blood groups as an example of codominance and multiple allelesWhen assigning alleles for codominance, the convention is to use a common letter to represent dominant and recessive and use superscripts to represent the different codominant alleles I stands for immunoglobulin (antigenic protein on blood cells) A and B stand for the codominant variants

The ABO gene has three alleles: IA, IBand i IAand IBare codominant, wherease i is recessive (no antigenic protein is produced) Codominance means that both IAand IBalleles will be expressed within a given phenotype

The genotypes and phenotypes of the ABO blood groups are:

The ABO Blood Group System

4.3.5 Explain how sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humansHumans have 23 pairs of chromosomes for a total of 46 (excluding instances of aneuploidy)The first 22 pairs are autosomes - each chromosome pair possesses the same genes and structural featuresThe 23rd pair of chromosomes are heterosomes (or sex chromosomes) and determine gender Females are XX - they possess two X chromosomes Males are XY - they posses one X chromosome and a much shorter Y chromosome

The Y chromosome contains the genes for developing male sex characteristic - hence the father is always responsible for determining gender If the male sperm contains the X chromosome the growing embryo will develop into a girl If the male sperm contains a Y chromosome the growing embryo will develop into a boy In all cases the female egg will contain an X chromosome (as the mother is XX)

Because the X and Y chromosomes are of a different size, they cannot undergo crossing over / recombination during meiosisThis ensures that the gene responsible for gender always remains on the Y chromosome, meaning that there is always ~ 50% chance of a boy or girl

4.3.6 State that some genes are present on the X chromosome and absent from the shorter Y chromosome

The Y chromosome is much shorter than the X chromosome and contains only a few genes Includes the SRY sex-determination gene and a few others (e.g. hairy ears gene)

The X chromosome is much longer and contains several genes not present on the Y chromosome Includes the genes for haemophilia and red-green colour blindness

In human females, only one of the X chromosomes remains active throughout life The other is packaged as heterochromatin to form a condensed Barr body This inactivation is random and individual to each cell, so heterozygous women will be a mosaic - expressing both alleles via different cells

4.3.7 Define sex linkageSex linkage refers to when a gene controlling a characteristic is found on a sex chromosome (and so we associate the trait with a predominant gender) Sex-linked conditions are usually X-linked, as very few genes exist on the shorter Y chromosome

4.3.8 Describe the inheritance of colour blindness and haemophilia as examples of sex linkage Colour blindness and haemophilia are both examples of X-linked recessive conditions The gene loci for these conditions are found on the non-homologous region of the X chromosome (they are not present of the Y chromosome) As males only have one allele for this gene they cannot be a carrier for the condition This means they have a higher frequency of being recessive and expressing the trait Males will always inherit an X-linked recessive condition from their mother Females will only inherit an X-linked recessive condition if they receive a recessive allele from both parents

When assigning alleles for sex-linked traits the convention is to write the allele as a superscript to the sex chomosome (usually X) Haemophilia:XH= unaffected ; Xh= affected Colour Blindness:XA= unaffected ; Xa= affected

Male and Female Genotypes for a Sex-Linked Condition

4.3.9 State that a human female can be homozygous or heterozygous with respect to sex-linked genesAs human females have two X chromosomes (and therefore two alleles for any given X-linked gene), they can be either homozygous or heterozygousMales only have one X chromosome (and therefore only one allele) and are hemizygous

4.3.10 Explain that female carriers are heterozygous for X-linked recessive alleles An individual with a recessive allele for a disease condition that is masked by a normal dominant allele is said to be a carrier Carriers are heterozygous and can potentially pass the trait on to the next generation, but do not suffer from the defective condition themselves Females can be carriers for X-linked recessive conditions because they have two X chromosomes - males (XY) cannot be carriers Because a male only inherits an X chromosome from his mother, his chances of inheriting the disease condition from a carrier mother is greater

4.3.11 Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritanceAutosomal Dominance / Recessive Choose a letter where the upper and lower case forms are easily distinguishable (e.g. E/e, A/a, B/b) Use the capital letter for the dominant allele and the lower case letter for the recessive allele Example:

Codominance Choose a letter to denote the general trait encoded by the gene (capital = dominant, lower case = recessive) Use different superscript letters (capitals) to represent the different codominant alleles Example:

X-linked Recessive Use a capital "X" to denote the X chromosome Choose a superscript letter to represent the trait (capital = dominant, lower case = recessive) Example:

4.3.12 Deduce the genotype and phenotype of individuals in pedigree chartsA pedigree is a chart of the genetic history of a family over several generations Males are represented as squares, while females are represented as circles Shaded symbols means an individual is affected by a condition, while an unshaded symbol means they are unaffected A horizontal line between a man and woman represents mating and resulting children are shown as offshoots to this line

Autosomal Dominance All affected individualsmusthave at least one affected parent If two parents are unaffected, all offspringmustbe unaffected (homozygous recessive) If two parents are affected, theymayhave offspring who are unaffected (if parents are heterozygous)

Autosomal Recessive If two parents show a trait, all childrenmustalso show the trait (homozygous recessive) An affected individualmayhave two normal parents (if parents are both heterozygous carriers)

X-Linked Recessive If a female shows the trait, so must all sons as well as her father The disorder is more common in males

Identifying Modes of Inheritance

4.4.1 Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA

PCR is a way of producing large quantites of a specific target sequence of DNAIt is useful when only a small amount of DNA is avaliable for testing E.g. crime scene samples of blood, semen, tissue, hair, etc.

PCR occurs in a thermal cycler and involves a repeat procedure of 3 steps:1. Denaturation:DNA sample is heated to separate it into two strands2. Annealing:DNA primers attach to opposite ends of the target sequence3. Elongation:A heat-tolerant DNA polymerase (Taq) copies the strands

One cycle of PCR yields two identical copies of the DNA sequence A standard reaction of 30 cycles would yield 1,073,741,826 copies of DNA (230)

4.4.2 State that, in gel electrophoresis, fragments of DNA can move in an electric field and are separated according to their sizeGel electrophoresis is a technique which is used to separate fragments of DNA according to size

Samples of fragmented DNA are placed in the wells of an agarose gel The gel is placed in a buffering solution and an electrical current is passed across the gel DNA, being negatively charged (due to phosphate), moves to the positive terminus (anode) Smaller fragments are less impeded by the gel matrix and move faster through the gel The fragments are thus separated according to size Size can be calculated (in kilobases) by comparing against a known industry standard

4.4.3 State that gel electrophoresis of DNA is used in DNA profiling DNA profiling is a technique by which individuals are identified on the basis of their respective DNA profiles Within the non-coding region of an individual's genome, there exists satellite DNA - long stretches of DNA made up of repeating elements called short tandem repeats (STRs) These repeating sequences can be excised to form fragments, by cutting with a variety of restriction endonucleases (which cut DNA at specific sites) As individuals all have a different number of repeats in a given sequence of satellite DNA, they will all generate unique fragment profiles These different profiles can be compared using gel electrophoresis

DNA Profiling Using STR Analysis

4.4.4 Describe the application of DNA profiling to determine paternity and also in forensic investigation A DNA sample is collected (blood, saliva, semen, etc.) and amplified using PCR Satellite DNA (non-coding) is cut with specific restriction enzymes to generate fragments Individuals will have unique fragment lengths due to the variable length of their short tandem repeats (STR) The fragments are separated with gel electrophoresis (smaller fragments move quicker through the gel) The DNA profile can then be analysed according to need

Two applications of DNA profiling are: Paternity testing (comparing DNA of offspring against potential fathers) Forensic investigations (identifying suspects or victims based on crime-scene DNA)

4.4.5 Analyse DNA profiles to draw conclusions about paternity or forensic investigationsPaternity Testing: Children inherit half of their alleles from each parent and thus should possess a combination of their parents allelesForensic Investigation: Suspect DNA should be a complete match with the sample taken from a crime scene if a conviction is to occur

Paternity Test Forensic Investigation

4.4.6 Outline three outcomes of the sequencing of the complete human genomeThe Human Genome Project (HGP) was an international cooperative venture established to sequence the 3 billion base pair (~25,000 genes) in the human genomeThe outcomes of this project include: Mapping:We now know the number, location and basic sequence of human genes Screening:This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic disease conditions Medicine:With the discovery of new proteins and their functions, we can develop improved treatments (pharmacogenetics and rational drug design) Ancestry:It will give us improved insight into the origins, evolution and historical migratory patterns of humans

With the completion of the Human Genome Project in 2003, researcher have begun to sequence the genomes of several non-human organismsIn Situ Hybridisation

4.4.7 State that, when genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because thegenetic code is universalThe genetic code is universal, meaning that for every living organism the same codons code for the same amino acids (there are a few rare exceptions)This means that the genetic information from one organism could be translated by another (i.e. it is theoretically transferable)Current Examples of Transgenic Modification

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 ligase1. DNA Extraction A plasmid is removed from a bacterial cell (plasmids are small, circular DNA molecules that can exist and replicate autonomously) A gene of interest is removed from an organism's genome using a restriction endonuclease which cut at specific sequences of DNA The gene of interest and plasmid are both amplified using PCR technology

2. Digestion and Ligation The plasmid is cut with the same restriction enzyme that was used to excise the gene of interest Cutting with certain restriction enzymes may generate short sequence overhangs ("sticky ends") that allow the the two DNA constructs to fit together The gene of interest and plasmid are spliced together by DNA ligase creating a recombinant plasmid

3. Transfection and Expression The recombinant plasmid is inserted into the desired host cells (this is called transfection for eukaryotic cells and transformation for prokaryotic cells) The transgenic cells will hopefully produce the desired trait encoded by the gene of interest (expression) The product may need to subsequently be isolated from the host and purified in order to generate sufficient yield

Treating Haemophilia via the Isolation of Human Factor IX Clotting Protein from Transgenic Sheep Milk

4.4.9 State two examples of current uses of genetically modified crops or animalsCrops1. Engineering crops to extend shelf life of fresh produce Tomatoes (Flavr Savr) have been engineered to have an extended keeping quality by switching off the gene for ripening and thus delaying the natural process of softening of fruit2. Engineering of crops to provide protection from insects Maize crops (Bt corn) have been engineered to be toxic to the corn borer by introducing a toxin gene from a bacterium (Bacillus thuringiensis)

Animals1. Engineering animals to enhance production Sheep produce more wool when engineered with the gene for the enzyme responsible for the production of cysteine - the main amino acid in the keratin protein of wool2. Engineering animals to produce desired products Sheep engineered to produce human alpha-1-antitrypsin in their milk can be used to help treat individuals suffering from hereditary emphysema

4.4.10 Discuss the potential benefits and potential harmful effects of one example of genetic modificationExample:Maize introduced with a bacterial gene encoding a toxin to the European Corn Borer (i.e. Bt Corn)

Potential Benefits Allows for the introduction of a characteristic that wasn't present within the gene pool (selective breeding could not have produced desired phenotype) Results in increased productivity of food production (requires less land for comparable yield) Less use of chemical pesticides, reducing the economic cost of farming Can now grow in regions that, previously, may not have been viable (reduces need for deforestation)

Potential Harmful Effects Could have currently unknown harmful effects (e.g. toxin may cause allergic reactions in a percentage of the population) Accidental release of transgenic organism into the environment may result in competition with native plant species Possibility of cross pollination (if gene crosses the species barrier and is introduced to weeds, may have a hard time controlling weed growth) Reduces genetic variation / biodiversity (corn borer may play a crucial role in local ecosystem)

4.4.11 Define cloneA 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 cellsSomatic Cell Nuclear Transfer (SCNT) is a method of reproductive cloning using differentiated animal cells A female animal (e.g. sheep) is treated with hormones (such as FSH) to stimulate the development of eggs The nucleus from an egg cell is removed (enucleated), thereby removing the genetic information from the cell The egg cell is fused with the nucleus from a somatic (body) cell of another sheep, making the egg cell diploid An electric shock is delivered to stimulate the egg to divide, and once this process has begun the egg is implanted into the uterus of a surrogate The developing embryo will have the same genetic material as the sheep that contributed the diploid nucleus, and thus be a clone

Different Uses of Cloning

4.4.13 Discuss the ethical issues of therapeutic cloning in humans Refer to Topic 2.1.10 for an outline of uses for therapeutic cloning in humans

Arguments for Therapeutic Cloning May be used to cure serious diseases or disabilities with cell therapy (replacing bad cells with good ones) Stem cell research may pave the way for future discoveries and beneficial technologies that would not have occurred if their use had been banned Stem cells can be taken from embryos that have stopped developing and would have died anyway (e.g. abortions) Cells are taken at a stage when the embryo has no nervous system and can arguably feel no pain

Arguments Against Therapeutic Cloning Involves the creation and destruction of human embryos (at what point do we afford the right to life?) Embryonic stem cells are capable of continued division and may develop into cancerous cells and cause tumors More embryos are generally produced than are needed, so excess embryos are killed With additional cost and effort, alternative technologies may fulfil similar roles (e.g. nuclear reprogramming of differentiated cell lines)6.1.1 Explain why digestion of large food molecules is essentialMost food is solid and in the form of large complex molecules which are insoluble and chemically inert (not readily usable) As food was synthesised by other organisms, it contains materials not suitable for human tissue - these need to be separated and removed Large molecules need to be broken down into smaller molecules that can be readily absorbed across membranes and into cells Small molecules can be reassembled into new products (e.g. amino acids can be reassembled to make new proteins)

6.1.2 Explain the need for enzymes in digestion Enzymes are biological catalysts which speed up the rate of a chemical reaction (e.g. digestion) by lowering the activation energy Enzymes allow digestive processes to occur at body temperature and at sufficient speed to meet the organism's survival requirements Enzymes are specific for a given substrate and so can allow digestion of certain molecules to occur independently of others

6.1.3 State the source, substrate, product and optimal pH conditions for one amylase, one protease and one lipase

6.1.4 Draw and label a diagram of the human digestive systemThere are two major groups of organs that comprise the human digestive system: Alimentary Canal:Contains organs through which the food actually passes (esophagus, stomach, small intestine, large intestine, etc.) Accessory Organs:Organs that assist in digestion but no food passes through them (liver, pancreas, gall bladder, salivary glands, etc.)

Alimentary Canal Accessory Organs

6.1.5 Outline the function of the stomach, small intestine and large intestineStomach The stomach acts as a temporary storage tank and is where protein digestion begins The stomach contains gastric glands which secrete digestive juices for chemical digestion Acids create a low pH environment (pH~1-2) that denatures proteins, while proteases like pepsin hydrolyse large proteins The stomach also releases a hormone (gastrin) that regulates stomach secretions The mechanical action of the stomach (churning) also promotes digestion by mixing the food The stomach turns food into a creamy paste called chyme

Small Intestine The small intestine is where usuable food substances (e.g. nutrients) are absorbed into the bloodstream The pancreas and gall bladder (via the bile duct) both secrete substances into the small intestine to aid in digestion The small intestine is lined with smooth muscle to allow for the mixing and moving of digested food products (via segmentation and peristalsis) It also contains small pits (crypts of lieberkuhn) that secrete intestinal juices The small intestine contain infoldings called villi, to increase surface area and optimise the rate of absorption

Large Intestine The large intestine absorbs water and dissolved minerals from the indigestible food residues, and by doing so converts what remains from a fluid state into a semi-solid faeces The faeces is stored in the rectum and eliminated out the anus

6.1.6 Distinguish between absorption and assimilation

Absorption:The movement of a fluid or dissolved substances across a membraneAssimilation:The conversion of nutrients into fluid or solid parts of an organismHint:Absorption is taking it into something, assimilation is making it a part of something

6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of products of digestionMicrovilli:Greatly increase the surface area of the villus, allowing for a greater rate of absorptionRich capillary networks:Help to maintain a concentration gradient for absorption by rapidly transporting absorbed products awaySingle epithelial layer:Ensures minimal diffusion distancebetween the intestinal lumen and capillary networkLacteals:Absorb lipids from the intestine into the lymphatic system (which are later reabsorbed back into normal circulation)Intestinal crypts:Located between villi and release juices that act as a carrier fluid for nutrientsMembrane proteins / mitochondria:High amounts to enable active transport into cells (contents then passively diffuse into bloodstream)

Features of a Villus

6.2.1 Draw and label a diagram of the heart showing the four chambers, associated blood vessels, valves and the route of the blood through the heart Valves and Direction of Blood Flow Heart Chambers and Vessels

6.2.2 State that coronary arteries supply heart muscle with oxygen and nutrients The heart is a muscle that must continually contract in order to pump blood around the body Coronary arteries form a network of vessels around the heart and supply the cardiac tissue with oxygen and nutrients (i.e. glucose) These are required to produce the necessary energy via aerobic respiration - if a coronary artery is blocked, a heart attack may occur

6.2.3 Explain the action of the heart in terms of collecting blood, pumping blood and opening and closing valvesBlood returning from all parts of the body (except lungs) enter theright atriumvia thevena cava- this blood is relatively deoxygenatedThe blood passes from the right atrium to theright ventricleand then via thepulmonary arteryto the lungs (where blood is reoxygenated)The blood returns to theleft atriumvia thepulmonary veinand passes through theleft ventricleto theaorta, where it is pumped around the body

The heart valves maintain the one-way flow of blood: When the atria contract, atrioventricular (AV) valves open Blood flows from the atria and into the ventricles When the ventricles contract, the AV valves close and semilunar valves open This forces blood out of the ventricles and into the arteries As arterial pressure rises, the semilunar valves close, ensuring the one-way flow of blood

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 contraction of the heart tissue (myocardium) is myogenic, meaning the signal for cardial contraction arises within the heart muscle itself Within the wall of the right atrium are a specialised plexus of nerves called the sinoatrial node (SAN) The sinoatrial node initiates contraction of the cardiace muscle and acts as a pacemaker, regulating normal sinus rhythm It stimulates atria to contract and, when excitation reaches the junction between atria and ventricles, stimulates another node (atrioventicular node) The atrioventricular node (AVN) sends signals via the Bundle of His to Purkinje fibres, which cause ventricular contraction This sequence always ensures their is a delay between atrial and ventricular contractions, resulting in two heart sounds ('lub dub')

Myogenic Control of the Heart Beat

The pacemaker is under autonomic control from the brain, specifically the medulla oblongata (brain stem) Sympathetic nerves speed up heart rate by releasing a neurotransmitter (noradrenaline) to increase the rate of myocardial contraction Parasympathetic nerves splow down heart rate by releasing a neurotransmitter (acetylcholine) to decrease the rate of myocardial contraction Additionally, the heart rate may be increased by the chemical release of the hormone adrenaline into the blood (from the adrenal gland)

6.2.5 Explain the relationship between the structure and function of arteries, capillaries and veinsArteries Arteries carry blood at high pressure (80 - 120 mm Hg) They have a narrower lumen (to maintain high pressure) surround by a thick wall made of two layers The middle layer (tunica media) contains muscle and elastin to help maintain pulse flow (it can contract and stretch) The outer layer (tunica adventitia) contains collagen prevents the artery rupturing due to the high pressure blood flow

Veins Veins carry blood under low pressure (