Teachers are reminded, prior to reading this section, that the syllabus is the definitive prescribed material.
It is hoped that this section will help promote professional teaching methods as distinct from textbook methodology. This section could be used as a class guide through the syllabus. It is not intended to be a text for students as it contains both non-prescribed and prescribed material.
To assist and support you in class preparation:
- The preamble to each subunit gives a broad insight into the central ideas of the syllabus depth of treatment.
- The suggested `texted' and practical detail should be used as suggestions to support you in:
Depth of prescribed and non-prescribed material you wish to use.
Methodology practice to include practical activities.
Suggested resources.
Time parameters.
Special attention in class preparation should be given to the use of 18 class periods for non prescriptive material at Ordinary level.
You may wish to use the non-prescribed activities and resources marked by an asterisk * or use other materials such as DART.
PREAMBLE TO SUB-UNIT 2.1: CELL STRUCTURE
- The cell is the smallest unit of living matter that exhibits the characteristics of life.
- All cells have structures in common to carry out basic life processes.
- Structural similarities and differences exist between cells of different organisms of all the major groups.
- Where a nucleus exists, the gene expression which leads to the phenotype begins in this organelle. This has led scientists to consider the nucleus as the control centre of the eukaryotic cell. A parallel system of control, though not yet confirmed, is thought to exist in prokaryotic cells.
Higher Level Extension - There are two major types of cells: · eukaryotic cells have a membrane-bound nucleus and other organelles · prokaryotic cells do not have such a membrane-bound nucleus and organelles.
MANDATORY ACTIVITIES
MICROSCOPY
Students should:
- Be familiar with and use the light microscope.
- Prepare and examine one plant cell - unstained and stained - using the light microscope (×100, × 400).
- Prepare and examine one animal cell - unstained and stained - using the light microscope (×100, × 400).
CELL STRUCTURE / SUGGESTED CLASS PERIODS: 9 O L , 9 H L
2.1.1 MICROSCOPY
DEPTH OF TREATMENT
Ageneral introduction to the microscope.
Specific reference to the light microscope and the transmission electron microscope.
2.1.2 CELL STRUCTURE AND FUNCTION
DEPTH OF TREATMENT
Components of the cell under the light microscope and their functions:
Plant cells: cell wall, cytoplasm, nucleus, vacuole, chloroplast.
Animal cells: cytoplasm, nucleus.
In both cases indicate the position and function of the cell membrane.
ACTIVITIES
Start with a hand lens and develop a familiarity with and procedural use of the light microscope.
Examine the microscopic structure of any one animal cell and any one plant cell e.g. own cheek cells, onion cells, elodea leaf, potato tissue, moss leaf; to observe, draw and identify the following:
- the existence of cells
- simple structures to include in plant cells: cell wall, cytoplasm, nucleus, vacuole, chloroplast; in animal cells: cytoplasm, nucleus. In both cases indicate the position of the plasma membrane.
The advantage and use of simple stains to facilitate observation e.g. Methylene blue or I2/KI dilute solution.
*Visual identification of the listed cell ultra structures as illustrated by use of published electron micrographs.
SUGGESTED RESOURCES
Hand lenses Microscopes
Boxes of glass slides Boxes of cover slips Forceps
I2/KI solution stain ** (** Health caution) Methylene blue stain, droppers, filter paper
Projector and slides
2.1.3 CELL ULTRA STRUCTURE
DEPTH OF TREATMENT
Identification and function of cell membrane, mitochondrion, chloroplast, nucleus, nuclear pores, ribosomes, DNA.
HIGHER LEVEL EXTENSION
H.2.1.4 PROKARYOTIC AND EUKARYOTIC CELLS
DEPTH OF TREATMENT
Existence and definition: eukaryotic cells have a membrane-bound nucleus and other organelles prokaryotic cells do not have such a membrane-bound nucleus and organelles.
PREAMBLE TO SUBUNIT 2.2: CELL METABOLISM
- Cellular activities require energy. Ultimately all of this energy comes from the sun. Some energy from sunlight is trapped in carbohydrates and other biomolecules. (Subsequently these biomolecules are broken down to release energy for use by the cell).
- Metabolism is the collective term for reactions that take place within living cells. The reactions of metabolism are catalysed by enzymes.
- The activity of enzymes is based upon
(i) active site(s)
(ii) a suitable environment. - Enzymes mediate the release of energy particularly in respiration.
- Enzymes are essential in the energy transfer process of photosysnthesis.
- A dynamic balance exists between cells and their environment through cell membranes (i) in controlling the passage of materials in and out of cells (ii) in recognising foreign particles (iii) in sensing.
- Movement of water has specific significance for cell shape and activity.
Higher Level Extension - Enzyme activity is "specific" for one reaction or one type of reaction.
- Adenosine triphosphate (ATP) has a special role as an intermediary in the trapping and transferring of energy for cell activities. NAD/NADP+ has a special role as an intermediary in the trapping and transferring of electrons and hydrogen ions for cell activities.
MANDATORY ACTIVITIES
LABORATORY ACTIVITIES AND INVESTIGATIONS
Students should:
- Investigate the effect of pH on the rate of one of the following: amylase, pepsin or catalase activity.
- Investigate (a) the effect of temperature on the rate of one of the following: amylase, pepsin or catalase activity and (b) the effect of denaturation by heat application on the activity of one enzyme (part (b) for H.L. only).
- Prepare one enzyme immobilisation and examine its application
- Investigate the influence of light intensity or carbon dioxide concentration on the rate of photosynthesis.
- Prepare and show the production of alcohol by yeast.
- Conduct any activity to demonstrate osmosis.
CELL METABOLISM / SUGGESTED CLASS PERIODS: 24 OL, 32 HL
2.2.1 CELL METABOLISM
DEPTH OF TREATMENT
Definition of "metabolism".
2.2.2 SOURCES OF ENERGY
DEPTH OF TREATMENT
Solar energy
Sunlight is a source of energy capable of being absorbed by cellular pigments e.g. chlorophyll.
Cellular energy
Cell sources of energy capable of release by metabolic processes in cells.
ACTIVITIES
*Investigate by designing and carrying out experiments to show:-
- that light is a form of energy e.g. movement of lightmeter needle
- that plants are a source of energy e.g. burn a nut to show energy conversion
or - show that heat is evolved from germinating peas.
SUGGESTED RESOURCES
Lightmeter.
Peanut, mounted needle, test tube, ignition source, test tube clamp.
Vacuum flasks, peas, cotton wool,
thermometers.
2.2.3 ENZYMES
DEPTH OF TREATMENT
Definition of enzyme to refer to protein nature and folded shape.
Role in plant and animal, special reference to their role in metabolism:
Amylase, pepsin or catalase as examples of enzymes involved in chemical breakdown.
Other enzymes, such as potato phosphorylase, are involved in synthesis.
Effect of pH and temperature range on enzyme activity.
ACTIVITIES
*The activity of catalase on hydrogen peroxide solution.
*The presence of urease in melon seeds or beans.
*The activity of amylase on starch, or pepsin on protein.
*The anabolic activity of potato phosphorylase on glucose 1 phosphate.
Investigate the effect of pH on the rate of amylase or pepsin or catalase activity.
Investigate the effect of temperature on the rate of any one of the following: amylase, pepsin or catalase activity. Contemporary Issues & Technology
Bioprocessing with immobilised enzymes procedure,advantages and use in bioreactors.
Procedure: beads prepared using sodium alginate, enzymeand calcium chloride solutions.
Advantages: gentle procedure, easily recovered, reusable.Use in bioreactors.
ACTIVITIES
Prepare one enzyme immobilisation and examine its application.
SUGGESTED RESOURCES
Enzyme, sodium alginate, calcium chloride, enzyme substrate, beakers, syringes or droppers, stirring rods, sieve, thermometer, graduated cylinders.
SUGGESTED RESOURCES
Sticks of celery or liver, knife, large graduated cylinder, hydrogen peroxide solution.
Melon seeds, soya beans or jack beans, powdered urea, pH meter.
2% diastase (amylase) or pepsin (protease) solution (fresh and boiled), starch suspension or protein source, biuret solutions, iodine solution, thermometer, test tubes, petri dishes, pipette or syringe. Starch or milk-agar plates, or hydrogen peroxide, cork borer, diastase, protease or catalase solution.
Potatoes, glucose 1-phosphate, iodine solution, blender, muslin, ice, distilled water, pipette.
Buffer solutions: pH 4, pH 7, pH 10, distilled water, timer.
Liver or celery, pestle and mortar, buffer (pH as required) centrifuge, distilled water, substrate (H202), refrigerator, waterbath at 20°C and 40°C, test solutions.
ICT facility
2.2.4 PHOTOSYNTHESIS
DEPTH OF TREATMENT
Photosynthesis definition, the overall sequence of reactions as represented by the equation: 6CO2+ 6H2O + light/chlorophyll C6H12O6 + 6O2.
A simple treatment of photosynthesis as follows:
Chlorophyll in chloroplasts traps sunlight energy. This trapped energy splits water to release electrons, protons and oxygen. These electrons are passed to chlorophyll, the protons are released to a general pool of protons. The oxygen is either released to the atmosphere or it may be used within the cell. Electrons from chlorophyll are used with protons from the pool of protons to reduce carbon dioxide to form a carbohydrate Cx(H2O)y
Location of chlorophyll within cells.
Identify the sources of light, carbon dioxide and water for photosynthesis in leaf cells.
2.2.5 RESPIRATION
DEPTH OF TREATMENT
Definition and role of aerobic respiration, the overall sequence of reactions as represented by the equation: C6H12O6+ 6O2 6CO2+ 6H2O + energy.
Respiration may occur as a one or two-stage process:
- the first stage does not require oxygen and releases a small amount of energy;
- the second stage does require oxygen and releases a large amount of energy.
Anaerobic respiration may occur in the presence of oxygen but does not use oxygen. It is therefore a first-stage process. The products of anaerobic respiration are lactic acid or alcohol and carbon dioxide. Refer to fermentation.
Aerobic respiration uses oxygen and is described as a two-stage process.
Cellular location of the first and second-stage process. The first stage process occurs in the cytosol (the cytoplasm minus the organelles). The second stage process occurs in the mitochondrion.
Contemporary Issues & Technology
Examine the role of micro-organisms in industrial fermentation and include bioprocessing with immobilisedcells: procedure, advantages and use in bioreactors.
Procedure: beads prepared using sodium alginate, yeast cells and calcium chloride solutions in industrialfermentation of alcohol. Advantages: gentle procedure, easily recovered, reduction in filtration procedure,reusable. Use in bioreactors.
Contemporary Issues & Technology
Human intervention: Use of artificial light and carbondioxide enrichment to promote crop growth in greenhouses.
ACTIVITIES
*Conduct an experiment to demonstrate the release of carbon dioxide by respiring cells; the release of heat energy from respiring cells e.g. germinating peas or barley or yeast fermentation.
Prepare and show the production of alcohol by yeast.
SUGGESTED RESOURCES
Germinating peas or barley, limewater, vacuum flasks, cotton wool, thermometers.
Yeast, sugar solution, conical flasks, thermometers.
Yeast, sugar solution, flasks, tubing, test tubes, Iodoform test solutions, lime-water or bicarbonate indicator.
ACTIVITIES
To investigate the influence of light intensity or carbon dioxide concentration on the rate of photosynthesis.
*Design and carry out an investigation to demonstrate the need for any one of the following in photosynthesis: chlorophyll, light or carbon dioxide.
SUGGESTED RESOURCES
Elodea, test tubes, buffer solution, warm water, sodium hydrogen carbonate solution(s), lamps of different wattage, or 1 lamp at different distances away from plant, timer, or use of computer interfacing.
2.2.6 MOVEMENT THROUGH CELL MEMBRANES
DEPTH OF TREATMENT
Selective permeability of cell membranes, surrounding the cells and within the cells.
Diffusion definition, passive transport e.g. movement of oxygen and carbon dioxide.
Osmosis a special case of diffusion the movement of water across biological membranes by a form of diffusion.
Definition of "turgor".
Simple explanation of how plant cells remain turgid:
plant cells containing more concentrated solution than their surroundings water flows in, vacuoles collect this water and the cells swell against their restraining cell walls.
Plant cells containing less concentrated solution than their surroundings water flows out of the vacuole and the cell shrinks.
Contemporary Issues & Technology
Describe the application of high salt or sugar concentrationin food preservation.
HIGHER LEVEL EXTENSION
H.2.2.7 ENZYMES (EXTENDED STUDY)
DEPTH OF TREATMENT
Active site theory to explain enzyme function, its flexibility, 3D molecules with variable domains and "specificity".
Enzymes are proteins whose activity is affected by: environmental pH, temperature. Explain the term "optimum activity" under specific conditions applied to pH range.
Heat denaturation of protein.
ACTIVITIES
*Any simple experiment to demonstrate diffusion.
Design and carry out an investigation to demonstrate osmosis e.g. cell models made from Visking tubing using starch or glucose.
*Design and carry out an investigation into the response of plant cells to different concentrations of saline or sucrose solutions e.g. using living beetroot cells or tulip petals or rhubarb epidermis.
*A piece of wilted lettuce placed in water becomes crisp as the individual cells expand like inflated balloons.
SUGGESTED RESOURCES
Visking tubing, water, starch suspension, glucose solution, iodine solution, syringe, clip.
Beetroot cells, rhubarb epidermis, microscopes, microscope slides, cover slips, forceps, mounted needle, scissors, dropper, filter paper, 3% salt solution, sucrose solution. Lettuce
ACTIVITIES
Investigate the effect of denaturation on the activity of one enzyme by heat application.
SUGGESTED RESOURCES
Starch agar plates or milk agar plates liver or celery cork borer diastase or protease solution incubator at 37°C fridge
oven Iodine/KI solution hydrogen peroxide distilled water water baths timer.
H.2.2.8 ROLE OF ADENOSINE TRIPHOSPHATE (ATP) AND NICOTINAMIDE ADENINE DINUCLEOTIDE (NAD/NADP+)
DEPTH OF TREATMENT
In order for photosynthesis and respiration to occur (both high energy reactions) the role of ATP and NAD/NADP+needs to be understood.
Word structure of ATP.
Adenosine triphosphate has a special role in the trapping and transferring of energy for cell activities.
ADP +ATP + H2O, energy in.
ATP + H2OADP +, energy out.
Role of NAD/NADP+
Nicotinamide adenine dinucleotide has a special role in trapping and transferring electrons and hydrogen ions in cell activities.
H.2.2.9 PHOTOSYNTHESIS (EXTENDED STUDY)
DEPTH OF TREATMENT
Photosynthesis is a two-stage process:
- the first stage, driven by light energy, is called the light stage or light-dependent stage;
- the second stage is dependent upon the products of the light stage, does not require light and is called the dark stage or lightindependent stage.
In the light stage, light energy is absorbed and then passed on from one pigment molecule to other pigment molecules in the chloroplast until it reaches a reaction centre chlorophyll molecule.
From here energised electrons enter two pathways:
- they return to chlorophyll releasing their surplus energy for the formation of ATP
- two electrons are trapped by NADP+forming NADP-.
This leaves the chlorophyll molecules electron deficient.
These are replenished from the splitting of water into 2H+, electrons and oxygen
H+ ions from a pool of H+ions are attracted to NADPto form NADPH.
In the dark stage NADPH supplies H+ ions and electrons (reducing power) which are used to convert CO2to carbohydrates, Cx(H2O)y.
The energy to achieve this conversion comes from ATP.
ADP and NADP+return to the light stage to be re-used.
H.2.2.10 RESPIRATION (EXTENDED STUDY)
DEPTH OF TREATMENT
The first-stage process, referred to as glycolysis, converts a six-carbon carbohydrate to pyruvate with the release of ATP.
Under anaerobic conditions:
- the pyruvate molecule is converted or reduced to alcohol and carbon dioxide
or - the pyruvate molecule is reduced to lactic acid.
In the second-stage process, under aerobic conditions, a series of reactions occurs:
- the pyruvate molecule is broken down to one molecule of carbon dioxide and a two-carbon acetyl group, Acetyl Co-enzyme A
- this Acetyl Co. A enters a series called Krebs Cycle and leaves it later as CO2 and H2O
- during this cycle an electron transport system operates to remove electrons from the substrate intermediates
- electrons from the cycle are transferred through an electron transport chain
- ultimately these are transferred to oxygen which combines with hydrogen to form water
- the energy released by these electrons through the chain is used in the production of ATP molecules.
(Further biochemical references not required).
PREAMBLE TO SUB-UNIT 2.3: CELL CONTINUITY
- Mitosis is a form of cell replication in which the chromosome number remains constant in each of two identical cells generated from one.
- Meiosis, a second form of cell division associated with reproduction, halves the number of chromosomes to form parental half cells (n), sex cells or gametes.
- In single-celled organisms mitotic division allows the organism to reproduce. In multicellular organisms mitosis is primarily for growth and repair.
- Cell continuity involves growth, synthesis and reproduction. It can be summarised in a cycle called the "cell cycle". The cell cycle describes a cell's state of non-division (interphase) and division (mitosis) See Fig. 1.
- During mitosis the genetic material divides and the cytoplasm, organelles and biomolecules are partitioned into two cells.
- The process of meiosis is important in multicellular organisms for the purposes of:
(a) maintaining the parental chromosome number by gamete or haploid cell production in sexual reproduction
(b) introducing variation in the species by exchange of genetic material between homologous chromosomes. - Cancer is a group of disorders in which certain cells lose normal regulation over both the mitotic rate and the number of divisions they undergo. This results in uncontrolled multiplication of abnormal cells.
Higher Level Extension - The process of mitosis, a continuous process, is arbitrarily divided into four stages for convenience of description.
2.3 CELL CONTINUITY / SUGGESTED CLASS PERIODS: 3 OL, 4 HL
2.3.1 CELL CONTINUITY AND CHROMOSOME
DEPTH OF TREATMENT
Explanation of the terms "cell continuity" and "chromosome".
2.3.2 HAPLOID, DIPLOID
DEPTH OF TREATMENT
Definition of
"haploid number"
"diploid number".
2.3.3 THE CELL CYCLE
DEPTH OF TREATMENT
The cell cycle describes the cell's activities in the state of non-division (interphase) and division (mitosis).
2.3.4 MITOSIS
DEPTH OF TREATMENT
Definition of "mitosis".
Simple treatment, with the aid of diagrams, to show chromosome behaviour (names of stages or chromosome parts are not required).
Just before the cell divides, chromosomes become visible in the nucleus (short, thick and duplicated). The nuclear membrane disappears, and fibres are formed to which the chromosomes attach. Chromosomes are pulled apart to opposite ends of the cell. A nuclear membrane forms around each set of chromosomes and the cell divides in two. Each new daughter cell now contains the same number of chromosomes as the parent cell.
2.3.5 FUNCTION OF MITOSIS
DEPTH OF TREATMENT
In single-celled organisms, mitosis allows the organisms to multiply.
In multicellular organisms, mitosis is primarily for growth.
2.3.6 MEIOSIS
DEPTH OF TREATMENT
Definition of "meiosis".
ACTIVITIES
*Mixed card illustrations of mitosis to be placed in correct sequence and drawn.
SUGGESTED RESOURCES
Card illustrations
Contemporary Issues & Technology
Cancer
Professional discretion should be shown whendealing with this sensitive topic.
Defined as:
a group of disorders in which certain cells losenormal regulation over both the mitotic rate and thenumber of divisions they undergo. This results in theuncontrolled multiplication of the abnormal cells.Two possible causes.
2.3.7 FUNCTIONS OF MEIOSIS
DEPTH OF TREATMENT
Functions of meiosis in multicellular organisms:
- to maintain parental chromosome number by gamete or haploid cell production in sexual reproduction
- to introduce variation in the species by re-arrangement of genetic material.
HIGHER LEVEL EXTENSIONH.
2.3.8 STAGES OF MITOSIS (EXTENDED STUDY)
DEPTH OF TREATMENT
Detailed study with the aid of labelled diagrams of the stages of mitosis:
Prophase recognised by the presence of condensed chromosomes, disappearance of nuclear membrane and formation of spindle.
Metaphase presence of a fully formed spindle apparatus with chromosomes located at the equator of the cell.
Anaphase centromeres split, chromosomes pulled back to each end of the cell.
Telophase chromosomes are positioned within new nuclei. Cleavage furrow formation in animal cells, cell plate formation in plant cells.
ACTIVITIES
*Examine suitably prepared plant or animal cells to show various stages of mitosis.
SUGGESTED RESOURCES
Film strips or slides of cell mitosis, projector, microscope.
PREAMBLE TO SUB-UNIT 2.4: CELL DIVERSITY
- Groups of similar cells are arranged into tissues, modified to perform specialised functions. When tissues are therefore discussed, function takes a special position of emphasis.
- Organs are made up of several different tissues each of which contributes to the overall function of the organ as a whole within an organism.
- Several organs working in conjunction form an organ system.
CELL DIVERSITY / SUGGESTED CLASS PERIODS: 3 OL, 3 HL
2.4.1 TISSUES
DEPTH OF TREATMENT
Definition of a "tissue".
Exemplify using four tissue types, two each from a plant and an animal.
Contemporary Issues & Technology
Tissue culture:
Explanation: a technique in which individual cells are grown and divide in a bath of sterile nutritive fluid whichoften contains hormones and growth substances.
Reference to any two applications: cancer research, plant breeding, routine analysis of chromosome karyotypes.
2.4.2 ORGANS
DEPTH OF TREATMENT
Definition of an "organ".
Exemplify by using two kinds of organs, one each from a plant and an animal.
2.4.3 ORGAN SYSTEMS
DEPTH OF TREATMENT
Definition of an "organ system".
Exemplify using any two animal organ systems.
ACTIVITIES
*Broad introduction to organ systems. (For detailed structure see Unit Three the human).
ACTIVITIES
*Visual recognition of three selected tissue types from both plants and animals.
SUGGESTED RESOURCES
A selection of plant and animal tissues.
ACTIVITIES
*Visual recognition of any three organs of plant or animal, to include naming of tissue components.
SUGGESTED RESOURCES
PREAMBLE TO SUB-UNIT 2.5: GENETICS
- Given the wide-ranging diversity of organisms, classification is an attempt, initially, to have an orderly system of cataloguing organisms and also an attempt to assemble related organisms.
- Characteristics result from heredity and environment.
- Heredity is the transmission of characteristics controlled by a genetic code contained within the chromosome structure.
- The genetic code controls the life processes within cells e.g. simple concept of protein synthesis: DNA sends out an instruction on how to link amino acids together to form proteins: DNA RNA protein.
- Students should therefore develop an appreciation and understanding of: The structure and role of DNA. The Mendelian concept of a gene. Expression of genes in the life of organisms. Transmission of genetic information from generation to generation. The influence of the environment and other factors in gene expression.
- Today's uniqueness in species represents the accumulated changes of a life process which is still changing, albeit slowly.
- Evolutionary theory tries to trace or link common origins for many of today's highly specialised organisms.
- Modern technological developments of genetics have led to an increasing influence of genetics on human life commercial, social and ethical that needs or demands informed debate.
Higher Level Extension - The science of genetics developed from the studies of Gregor Mendel who expressed his findings in two laws:-
(i) The Law of Segregation
(ii) The Law of Independent Assortment. - Diploid organisms inherit pairs of genes on pairs of homologous chromosomes. The two genes segregate from each other at meiosis so each gamete formed after meiosis has an equal chance of receiving one or other gene but not both.
- Further studies on nucleic acid structure and function, including protein synthesis, will enhance the student's knowledge of this topic.
Special Note: While differentiation should be made between probabilities and certainties when teaching genetics, particular attention should be paid to this when considering sensitive aspects of human inheritance.
MANDATORY ACTIVITY
LABORATORY INVESTIGATION
Students should:
- Isolate DNA from a plant tissue.
2.5 GENETICS / SUGGESTED CLASS PERIODS: 27 OL, 36 HL
2.5.1 VARIATION OF SPECIES
DEPTH OF TREATMENT
Diversity of organisms that necessitates sub-classification to species level.
Definition of "species". Refer also to the uniqueness or individuality found within species.
ACTIVITIES
*Visit fieldwork site, zoo, natural history museum, botanic garden to observe the diversity of species.
*Identify differences within species: tongue rolling, hair colour, skin colour, leaf shape, flower colour etc.
Show results by histogram.
2.5.2 HEREDITY AND GENE EXPRESSION
DEPTH OF TREATMENT
Definition and example of "heredity" and "gene expression".
2.5.3 GENETIC CODE
DEPTH OF TREATMENT
Definition and role of a "gene".
Chromosome structure
Refer to DNA and protein nature.
2.5.4 DNA STRUCTURE, REPLICATION AND PROFILING
DEPTH OF TREATMENT
Simple structure of DNA:
DNA is a very long molecule. It consists of two strands. The two strands are linked together by paired bases. There are four different bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). Each base can only link with one other type, A with T and C with G.
Coding and non-coding structures.
Triplet base code.
Chromosome sequence of coding and non-coding (junk DNA) sequences.
RNA as a complementary structure to DNA. Refer to Uracil (U). Function of messenger RNA (mRNA) in protein synthesis.
Replication of DNA involving the opening of the helix followed by the synthesis of complementary nucleic acid chains alongside the existing chains to form two identical helices.
Contemporary Issues & Technology
DNA profiling: definition, any two applications e.g. forensic and medical.
Stages involved:
- cells are broken down to release DNA
- DNA strands are cut into fragments using enzymes
- fragments are separated on the basis of size
- the pattern of fragment distribution is analysed.
Genetic Screening: diagnostic test(s) to identify the presence or absence of changed genes (detail of process not required).
ACTIVITIES
Isolate DNA from a plant tissue.
SUGGESTED RESOURCES
Blender, sharp knife, chopping board, water bath at 60°C, ice in a jug, thermometer, beakers, coffee filter papers, onion, washing-up liquid, sodium chloride, distilled water, glass rod, syringe, boiling tube, protease enzyme, ice cold 95% ethanol.
OTHER SUGGESTED RESOURCES
DNA model, video, CD, ICT.
2.5.5 PROTEIN SYNTHESIS
DEPTH OF TREATMENT
DNA contains a code for proteins. This code is transcribed to mRNA.
The transcribed code goes to a ribosome.
The code is translated and the amino acids are assembled in the correct sequence to synthesise the protein.
The protein folds into its functional shape.
2.5.6 GENETIC INHERITANCE
DEPTH OF TREATMENT
Gamete formation and function in plants and animals
in sexual reproduction cells that transmit genes from one generation to another are called sex cells or gametes. During meiosis the diploid number of chromosomes (2n) is reduced to one set and gametes are formed. This single set is called the haploid number (n).
Definition of the following terms:
fertilisation
allele
homozygous and heterozygous
genotype
phenotype
dominance
recessive
incomplete dominance
Study of the inheritance to the first filial generation (F1) of a single unlinked trait in a cross involving:
homozygous parents
heterozygous parents
Genotype for each parent.
Representation of possible gametes resulting from meiotic separation or division of each parent cell.
Prediction of genotype(s) of the first filial generation (F1) using Punnett square.
Relation of phenotype(s) to genotype(s).
Sex determination
the control of maleness and femaleness by genes located on sex chromosomes designated X and Y. A human male body cell has one X and one Y chromosome. A human female body cell has two X chromosomes. However bird, butterfly and moth females are XY and their males are XX.
Prediction of sex by genetic cross mechanism using Punnett square.
ACTIVITIES
*Place photographic or simulated models at different work stations in the laboratory to exemplify each of the terms, accompanied by test card questions and problems.
*Perform simulations to investigate different crosses using Punnett squares.
*Class project on sex ratio differential throughout the human life cycle. Communicate the results in a clearly written report.
SUGGESTED RESOURCES
Test cards and questionnaires
ACTIVITIES
*Design or play a game to help understand protein synthesis.
2.5.7 CAUSES OF VARIATION
DEPTH OF TREATMENT
Variation from: sexual reproduction and mutations.
Mutations
characteristics of mutant alleles e.g. random occurrence, low frequency.
Types of mutation:
gene mutation e.g. sickle-cell anaemia
chromosome mutation e.g. by number change in Down's syndrome.
2.5.8 EVOLUTION
DEPTH OF TREATMENT
Definition of "evolution".
Broad outline of Darwin and Wallace Theory of Natural Selection.
Evidence from any one source:
- fossil studies of any one anatomical characteristic
- comparative studies of the embryos of fish, tortoise, chick, rabbit, human
- any plant or animal adaptation e.g. from aquatic to terrestrial life genetics.
2.5.9 GENETIC ENGINEERING
DEPTH OF TREATMENT
Genetic engineering defined as the manipulation and alteration of genes. Process involves some or all of the following:
isolation, cutting (restriction), transformation (ligation), introduction of base sequence changes, expression.
Contemporary Issues & Technology
Study any two agents responsible for increasedmutation rates e.g. chemicals, radiation.
Contemporary Issues & Technology
Three applications of genetic engineering:one plant, one animal, one microorganism.
SUGGESTED RESOURCES
Games, videos, ICT.
HIGHER LEVEL EXTENSION
H.2.5.10 ORIGIN OF THE SCIENCE OF GENETICS
DEPTH OF TREATMENT
Work of Gregor Mendel leading to the expression of his findings in two laws.
H.2.5.11 LAW OF SEGREGATION
DEPTH OF TREATMENT
Law of Segregation:
each cell contains two factors for each trait, these factors seperate during the formation of gametes so that each gamete contains only one factor from each pair of factors. At fertilization the new organism will have two factors for each trait, one from each parent.
H.2.5.12 LAW OF INDEPENDENT ASSORTMENT
DEPTH OF TREATMENT
Law of Independent Assortment:
members of one pair of factors separate independently of members of another pair of factors at gamete formation.
H.2.5.13 DIHYBRID CROSS
Study of the inheritance to the second filial generation (F2) of two unlinked traits using the Punnett square technique.
Definition of "linkage".
Explanation of change in 1:1:1:1 probability for a dihybrid heterozygote crossed with a dihybrid recessive organism. (Knowledge of crossing over is not required).
Definition of "sex linkage". Common sex-linked traits: red-green colour blindness, haemophilia.
Non-nuclear inheritance: existence of DNA in non-nuclear components of a cell e.g. mitochondrial and chloroplast DNA.
ACTIVITIES
*Communicate the work of Gregor Mendel in a clearly written report.
ACTIVITIES
*Perform simulations to investigate Punnett square technique. Examination of cross to F2 generation.
H.2.5.14 NUCLEIC ACID STRUCTURE AND FUNCTION (EXTENDED STUDY)
DEPTH OF TREATMENT
DNA
Nucleotide structure:
one deoxyribose sugar, one phosphate, one of four named nitrogenous bases.
Specific purine and pyrimidine couples - complementary base pairs.
Hydrogen bonding.
Double helix.
H.2.5.15 PROTEIN SYNTHESIS (EXTENDED STUDY)
DEPTH OF TREATMENT
Process of protein synthesis:
Enzymes unwind the DNA double helix.
Transcription RNA nucleotide bases bond with one strand of exposed DNA. The enzyme RNA polymerase assembles these bases to form mRNA. mRNA, therefore, has a series of bases that are complementary to those in DNA.
mRNA moves into the cytoplasm. Each three base sequence of mRNA carries a genetic code or codon that specifies a starting codon, a particular amino acid or a stop codon.
Ribosome subunits (rRNAs) attach to the mRNA. These subunits form the ribosome, the site of protein synthesis.
Free-floating tRNAs with their attached amino acids, within the cytoplasm, are attracted by their `binding site' to complementary mRNA already attached to the ribosome. This ensures the amino acids are aligned in a sequence determined by the codons of the mRNA.
Aligned amino acids bond to form links of the new protein molecule.
tRNAs continue to move to the ribosome, until a stop codon on the mRNA is reached. The protein is released when the mRNA code sequence is complete and the protein is synthesised.
ACTIVITIES
*Use of a computer programme, video or biokits.
SUGGESTED RESOURCES
Video, ICT.
ACTIVITIES
*Use simulated modes to demonstrate the process of protein synthesis.
Communicate the result in a clearly written report.
SUGGESTED RESOURCES
Models, ICT, video.