IB Biology Notes

• Unit 1: Cell Biology
  • 1.1 Introduction to Cells
    • 1.1.1 Living organisms are composed of cells.
    • 1.1.2 Unicellular organisms carry out all functions of life.
    • 1.1.3 Cell Surface to volume is an important limitation to cell size.
    • 1.1.4 Multicellular organisms have properties that emerge due to the interaction of their cellular components.
    • 1.1.5 Specialized tissues can develop by cell differentiation in multicellular organisms.
    • 1.1.6 Differentiation involves the expressions of some genes and not others in a cell’s genome.
    • 1.1.7 The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
    • 1.1.8 Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
    • 1.1.9 Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
    • 1.1.10 Use of stem cells to treat Stargardt’s disease and one other named condition.
    • 1.1.11 Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a newborn baby and from an adult’s own tissues.
    • 1.1.12 Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells. Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs. (Practical 1)
    • 1.1.13 Looking for trends and discrepancies- although most organisms conform to cell theory, there are exceptions.
    • 1.1.14 Ethical implications of research- research involving stem cells is growing in importance and raises ethical issues.
  • 1.2 Ultrastructure of Cells
    • 1.2.1 Prokaryotes have a simple cell structure without compartmentalization.
    • 1.2.2 Eukaryotes have a compartmentalized cell structure.
    • 1.2.3 Electron microscopes have a much higher resolution than light microscopes.
    • 1.2.4 Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of the leaf.
    • 1.2.5 Prokaryotes divide by binary fission.
    • 1.2.6 Drawings of the ultrastructure of prokaryotic cells based on electron micrographs.
    • 1.2.7 Drawings of the ultrastructure of eukaryotic cells based on electron micrographs.
    • 1.2.8 Interpretations of electron micrographs to identify organelles and deduce the function of specialized cells.
    • 1.2.9 Developments in scientific research follows improvements in apparatus- the invention of the electron microscopes led to greater understanding of cell structure.
  • 1.3 Membrane Structure
    • 1.3.1 Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
    • 1.3.2 Membrane proteins are diverse in terms of structure, position in the membranes and function.
    • 1.3.3 Cholesterol is a component of animal cell membranes.
    • 1.3.4 Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.
    • 1.3.5 Drawing of the fluid mosaic model.
    • 1.3.6 Analysis of evidence from electron microscopy that led to the proposal of the Davidson-Danielli model.
    • 1.3.7 Analysis of the falsification of the Davison-Danielli model that led to the Singer-Nicolson model. NOS 1 Using models as representations of the real world-there are alternative models of membrane structures.
    • 1.3.8 Falsification of theories with one theory being superseded by another-evidence falsified the Davison-Danielli model.
  • 1.4 Membrane Transport
    • 1.4.1 Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
    • 1.4.2 The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
    • 1.4.3 Structure and function of the sodium-potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
    • 1.4.4 Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
    • 1.4.5 Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)
    • 1.4.6 Experimental design- accurate quantitative measurements in osmosis experiments are essential.
  • 1.5 Origin of Cells
    • 1.5.1 Cells can only be formed by division of pre-existing cells.
    • 1.5.2 The first cells must have arisen from non-living material.
    • 1.5.3 The origin of eukaryotic cells can be explained by the endosymbiotic theory.
    • 1.5.4 Evidence from Pastuer’s experiments that spontaneous generation of cells and organisms does not now occur on Earth.
    • 1.5.5 Testing the general principles that underline the natural world- the principles that cells only come from pre-existing cells needs to be verified.
  • 1.6 Cell Division
    • 1.6.1 Mitosis is division of the nucleus into two genetically identical daughter nuclei.
    • 1.6.2 Chromosomes condense by supercoiling during mitosis.
    • 1.6.3 Cytokinesis occurs after mitosis and is different in plants and animal cells.
    • 1.6.4 Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.
    • 1.6.5 Cyclins are involved in the control of the cell cycle. U 6 Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumors.
    • 1.6.6 The correlation between smoking and incidence of cancers.
    • 1.6.7 Identification of phases of mitosis in cells viewed with a microscope or in a micrograph.
• Unit 2: Molecular Biology
  • 2.1 Molecules to Metabolism
    • 2.1.1 Molecular biology explains living processes in terms of the chemical substances involved
    • 2.1.2 Carbon atoms can form four covalent bonds allowing a diversity of stable compounds to exist
    • 2.1.3 Life is based on carbon compounds including carbohydrates, lipids proteins and nucleic acids
    • 2.1.4 Metabolism is the web of all the enzyme-catalyzed reactions in a cell or organism
    • 2.1.5 Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions
    • 2.1.6 Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers
    • 2.1.7 Urea as an example of a compound that is produced by living organisms but can also be artificially synthesized
    • 2.1.8 Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalized amino acid
    • 2.1.9 Identification of biochemical such as sugars, lipids, or amino acids from molecular drawings
    • 2.1.10 Falsification of theories- the artificial synthesis of urea helped to falsify vitalism.
  • 2.2 Water
    • 2.2.1 Water molecules are polar and hydrogen bonds form between them.
    • 2.2.2 Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.
    • 2.2.3 Substances can be hydrophilic or hydrophobic.
    • 2.2.4 Comparison of the thermal properties of water with those of methane.
    • 2.2.5 Use of water as a coolant in sweat.
    • 2.2.6 Modes of transport of glucose, amino acids, cholesterol, fats. Oxygen, and sodium in blood in relations to their solubility in water.
    • 2.2.7 Use of theories to explain natural phenomena- the theory that hydrogen bonds form between water molecules explain the properties of water.
  • 2.3 Carbohydrates and Lipids
    • 2.3.1 U 1 Monosaccharide monomers are linked together by condensation reactions to form disaccharides and polysaccharide polymers.
    • 2.3.2 Fatty acids can be saturated, monounsaturated and polyunsaturated.
    • 2.3.3 Unsaturated fatty acids can be cis or trans isomers.
    • 2.3.4 Triglycerides are formed by condensation from three fatty acids and one glycerol.
    • 2.3.5 Structure and function of cellulose and starch in plants and glycogen in humans
    • 2.3.6 Scientific evidence for health risks of trans fat and saturated fatty acids.
    • 2.3.7 Lipids are more suitable for long term energy storage in humans than carbohydrates.
    • 2.3.8 Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids.
    • 2.3.9 Use of molecular visualization software to compare cellulose, starch and glycogen.
    • 2.3.10 Determination of body mass index by calculation or use of a nomogram.
    • 2.3.11 Evaluating claims- health claims made about lipids in diets need to be assessed.
  • 2.4 Proteins
    • 2.4.1 Amino Acids are linked together by condensation to form polypeptides.
    • 2.4.2 There are 20 different amino acids in polypeptides synthesized on ribosomes.
    • 2.4.3 Amino Acids can be linked together in any sequence giving a huge range of possible polypeptides.
    • 2.4.4 The amino acid sequence of polypeptides is coded for by genes.
    • 2.4.5 A protein may consist of a single polypeptide or more than one polypeptide linked together.
    • 2.4.6 The amino acid sequence determines the three-dimensional conformation of a protein.
    • 2.4.7 Living organisms synthesize many different proteins with a wide range of functions.
    • 2.4.8 Every individual has a unique proteome.
    • 2.4.9 Rubisco, insulin immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions.
    • 2.4.10 Denaturation of proteins by heat or by deviation of pH from the optimum.
    • 2.4.11 Drawing molecular diagrams to show the formation of a peptide bond.
    • 2.4.12 Looking for patterns, trends, and discrepancies- most but not all organisms assemble proteins from the same amino acids.
  • 2.5 Enzymes
    • 2.5.1 Enzymes have an active site to which specific substrates bind.
    • 2.5.2 Enzyme catalysis involves molecular motion and the collision of substrates with the active site.
    • 2.5.3 Temperature, pH and substrate concentration affect the rate of activity of enzymes.
    • 2.5.4 Enzymes are denatured.
    • 2.5.5 Immobilized enzymes are widely used in industry.
    • 2.5.6 Methods of production of lactose-free milk and its advantages.
    • 2.5.7 Design of experiments to test the effect of temperature, pH, and substrate concentration on the activity of enzymes.
    • 2.5.8 Experimental investigation of a factor affecting enzyme activity. (Practical 3)
    • 2.5.9 Experimental design-accurate, quantitative measurements in enzyme experiments require replicates to ensure reliability.
  • 2.6 Structure of DNA and RNA
    • 2.6.1 The nucleic acids DNA and RNA are polymers of nucleotides
    • 2.6.2 DNA differs from RNA in the number of strands present, the base composition and the type of pentose
    • 2.6.3 DNA is double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complimentary base pairs.
    • 2.6.4 Crick and Watson’s elucidation of the structure of DNA using model making.
    • 2.6.5 Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons, and rectangles to represent phosphates, pentoses and bases.
    • 2.6.6 Using models as representation of the real world- Crick and Watson used model making to discover the structure of DNA.
  • 2.7 DNA Replications, Transcription and Translation
    • 2.7.1 The replication of DNA is semi-conservative and depends on complimentary base pairing.
    • 2.7.2 Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.
    • 2.7.3 DNA polymerase links nucleotides together to form a new strand, using a pre-existing strand as a template.
    • 2.7.4 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
    • 2.7.5 Translation is the synthesis of polypeptides on ribosomes.
    • 2.7.6 The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
    • 2.7.7 Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
    • 2.7.8 Translation depends on complimentary base-pairing between codons on mRNA and anticodons on tRNA.
    • 2.7.9 Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR).
    • 2.7.10 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
    • 2.7.11 Use a table of the genetic code to deduce which codons corresponds to which amino acids.
    • 2.7.12 Analysis of Messelson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.
    • 2.7.13 Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence.
    • 2.7.14 Deducing the DNA base sequence for the mRNA strand.
    • 2.7.15 Obtaining of evidence for scientific theories- Messelson and Stahl obtained evidence for the semi-conservative replication of DNA.
  • 2.8 Cell Respiration
    • 2.8.1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.
    • 2.8.2 ATP from cell respiration is immediately available as a source of energy in the cell.
    • 2.8.3 Anaerobic cell respiration gives a small yield of ATP from glucose.
    • 2.8.4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
    • 2.8.5 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
    • 2.8.6 Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
    • 2.8.7 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
    • 2.8.8 Assessing the ethics of scientific research- the use of invertebrates in respirometers experiments
  • 2.9 Photosynthesis
    • 2.9.1 Photosynthesis is the production of carbon compounds in cells using light energy.
    • 2.9.2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.
    • 2.9.3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.
    • 2.9.4 Oxygen is produced in photosynthesis from the photolysis of water.
    • 2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
    • 2.9.6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate photosynthesis.
    • 2.9.7 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
    • 2.9.8 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
    • 2.9.9 Design an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
    • 2.9.10 Separation of photosynthetic pigments by chromatograph. (Practical 4)
    • 2.9.11 Experimental design- controlling relevant variables in photosynthesis experiments is essential.
• Unit 3: Genetics
  • 3.1 Genes
    • 3.1.1 U 1 A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.
    • 3.1.2 gene occupies a specific position on a chromosome.
    • 3.1.3 The various specific forms of a gene are alleles.
    • 3.1.4 Alleles differ from each other by one or only a few bases.
    • 3.1.5 New alleles are formed by mutation.
    • 3.1.6 The genome is the whole of the genetic information of an organism.
    • 3.1.7 The entire base sequence of human genes was sequenced in the Human Genome Project.
    • 3.1.8 The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin.
    • 3.1.9 Comparison of the number of genes in humans with other species.
    • 3.1.10 Use of a database to determine differences in the base sequence of a gene in two species.
    • 3.1.11 Developments in scientific research follow improvements in technology-gene sequencers are used for the sequencing of genes.
  • 3.2 Chromosomes
    • 3.2.1 U 1 Prokaryotes have one chromosome consisting of a circular DNA molecule.
    • 3.2.2 Some prokaryotes also have plasmids but eukaryotes do not.
    • 3.2.3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
    • 3.2.4 In a eukaryote species there are different chromosomes that carry different genes.
    • 3.2.5 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.
    • 3.2.6 Diploid nuclei have pairs of homologous chromosomes.
    • 3.2.7 Haploid nuclei have one chromosomes of each pair.
    • 3.2.8 The number of chromosomes is a characteristic feature of member of a species.
    • 3.2.9 A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.
    • 3.2.10 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.
    • 3.2.11 Cairns’ technique for measuring the length of DNA by autoradiography.
    • 3.2.12 Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens, Paris japonica.
    • 3.2.13 Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascarsis equorum.
    • 3.2.14 Use karyograms to deduce sex and diagnose Down Syndrome in humans.
    • 3.2.15 Use of databases to identify the focus of a human gene and its polypeptide product.
    • 3.2.16 Developments in research follow improvements in techniques- autoradiography was used to establish the length of DNA molecules in chromosomes.
  • 3.3 Meiosis
    • 3.3.1 One of diploid nucleus divides by meiosis to produce four haploid nuclei.
    • 3.3.2 The halving of the chromosomes number allows a sexual life cycle with fusion of gametes.
    • 3.3.3 DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.
    • 3.3.4 The early stages of meiosis involved pairing of homologous chromosomes and crossing over followed condensation.
    • 3.3.5 Orientation of pairs of homologous chromosomes prior to separation is random.
    • 3.3.6 Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number .
    • 3.3.7 Crossing over and random orientation promotes genetic variation.
    • 3.3.8 Fusion of gametes from different parents promotes genetic variation.
    • 3.3.9 Non-disjunction can cause Down syndrome and other chromosome abnormalities.
    • 3.3.10 Studies showing age of parents influences chances of non-disjunction.
    • 3.3.11 Description of methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks.
    • 3.3.12 Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid cells.
    • 3.3.13 Making careful observations- meiosis was discovered by microscope examination of dividing germ-line cells.
  • 3.4 Inheritance
    • 3.4.1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
    • 3.4.2 Gametes are haploid so contain only one allele of each gene.
    • 3.4.3 The alleles of each gene separate into different haploid daughter nuclei during meiosis.
    • 3.4.4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.
    • 3.4.5 Dominant alleles mask the effect of recessive alleles but co-dominant alleles have joint effects.
    • 3.4.6 Many genetic diseases in human are due to excessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles.
    • 3.4.7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to to their location on sex chromosomes.
    • 3.4.8 Many genetic diseases have been identified in humans but most are very rare.
    • 3.4.9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
    • 3.4.10 Inheritance of ABO blood groups.
    • 3.4.11 Re-green color blindness and hemophilia as examples of sex-linked inheritance.
    • 3.4.12 Inheritance of cystic fibrosis and Huntington’s disease.
    • 3.4.13 Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
    • 3.4.14 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
    • 3.4.15 Comparison of predicted and actual outcomes of genetic crosses using real data.
    • 3.4.16 Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
    • 3.4.17 Making quantitative measurements with replicates to ensure reliability, Mendel’s genetic crosses with peas plants generated numerical data.
  • 3.5 Genetic Modification and Biotechnology
    • 3.5.1 Gel electrophoresis is used to separate proteins or fragments of DNA according to size.
    • 3.5.2 PCR can be used to amplify small amounts of DNA.
    • 3.5.3 DNA profiling involves comparison of DNA.
    • 3.5.4 Genetic modification is carried out by gene transfer between species.
    • 3.5.5 Clones are groups of genetically identical organisms, derived from a single original parent cell.
    • 3.5.6 Many plants species and some animal species have natural methods of cloning.
    • 3.5.7 Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells.
    • 3.5.8 Methods have been developed for cloning adult animals using differentiated cells.
    • 3.5.9 Use of DNA profiling in paternity and forensic investigations.
    • 3.5.10 Gene transfer in bacteria using plasmids makes use of restriction endonucleases and DNA ligases.
    • 3.5.11 Assessment of potential risks and benefits associated with genetic modification of crops.
    • 3.5.12 Production of clones embryos produced by somatic-cell nuclear transfer.
    • 3.5.13 Design of an experiment to assess one factor affecting the rooting of stem-cuttings.
    • 3.5.14 Analysis of examples of DNA profiles.
    • 3.5.15 Analysis of data on risks to monarch butterflies of Bt crops.
    • 3.5.16 Assessing risks associated with scientific research- scientists attempt to assess the risks associated with genetically modified crops or livestock.

Practice