Semester 1 Exam Revision Summary

DNA the Molecule

  • DNA Structure:

    • Double Helix: DNA is structured as a double helix, resembling a twisted ladder.

    • Nucleotides: The building blocks of DNA. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base.

    • Sugar-Phosphate Backbone: The sides of the DNA ladder are formed by alternating sugar and phosphate groups.

    • Double-Stranded: DNA consists of two strands that are antiparallel.

    • Complementary Base Pairing: Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G). If you know the number of one base, you can calculate the number of its complementary base. For example, if a DNA sample has 20% Adenine, it will have 20% Thymine, and therefore 30% Cytosine and 30% Guanine (A=TA=T and C=GC=G).

  • Identifying Base Sequences:

    • Given one strand of DNA, you can determine the sequence of the complementary strand using the base pairing rules (A with T, and C with G).

  • Chromosomes:

    • Chromosomes are structures within cells that contain DNA.

    • They're located in the nucleus of eukaryotic cells.

  • Relationship between DNA, Genes, and Chromosomes:

    • DNA is the molecule that carries genetic information.

    • Genes are specific segments of DNA that code for particular traits or proteins.

    • Chromosomes are made of DNA and contain many genes.

  • Cells Containing Genetic Information:

    • Most cells in the body contain genetic information in the form of chromosomes. Red blood cells are an exception as they lack a nucleus in mammals.

  • DNA Mutation:

    • A DNA mutation is a change in the DNA sequence.

    • Mutations can be caused by various factors such as radiation, chemicals, or errors during replication (e.g., UV radiation).

Making New Cells

  • Mitosis and Meiosis:

    • Mitosis: Cell division that results in two identical daughter cells. Important for growth and repair.

    • Meiosis: Cell division that results in four genetically different daughter cells (gametes). Important for sexual reproduction.

  • Stages of Mitosis & Meiosis:

    • Be able to describe and identify the stages of mitosis (prophase, metaphase, anaphase, telophase) and meiosis (prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II) on diagrams.

  • When Cell Division Occurs:

    • Mitosis occurs during growth, repair, and asexual reproduction.

    • Meiosis occurs during the formation of gametes (sperm and egg cells) for sexual reproduction.

  • Number of Daughter Cells:

    • Mitosis produces two daughter cells.

    • Meiosis produces four daughter cells.

  • Diploid and Haploid:

    • Diploid: A cell containing two sets of chromosomes (2n). Most somatic (body) cells are diploid.

    • Haploid: A cell containing one set of chromosomes (n). Gametes (sperm and egg cells) are haploid.

    • Gametes are haploid to ensure that when they fuse during fertilization, the resulting zygote has the correct diploid number of chromosomes.

  • Sex Determination:

    • In humans, sex is determined by the X and Y chromosomes.

    • Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

  • Chromosome Inheritance:

    • An equal number of chromosomes is passed on from each parent to offspring. One set from the mother and one set from the father.

Characteristics & Inheritance

  • Allele Combinations:

    • Homozygous Recessive: Two recessive alleles (e.g., rr).

    • Homozygous Dominant: Two dominant alleles (e.g., RR).

    • Heterozygous: One dominant and one recessive allele (e.g., Rr).

  • Types of Inheritance:

    • Dominant/Recessive: One allele masks the effect of the other.

    • Incomplete/Co-dominant: Neither allele is completely dominant, resulting in a blended (incomplete) or shared (co-dominant) phenotype.

  • Punnett Squares:

    • Use Punnett squares to predict the genotypes and phenotypes of offspring from different parental genotypes.

    • Example: If both parents are heterozygous (Rr), the Punnett square would predict:

      • RR (25%): Homozygous dominant

      • Rr (50%): Heterozygous

      • rr (25%): Homozygous recessive

  • Carrier of a Disease:

    • A carrier is an individual who has one copy of a recessive allele for a disease but does not express the disease phenotype because they also have a dominant, non-disease allele.

  • X and Y Chromosomes:

    • The X chromosome is larger and contains more genes than the Y chromosome.

    • The Y chromosome primarily contains genes related to male sex determination.

  • Karyotype:

    • A karyotype is a display of an individual's chromosomes, arranged by size and shape.

    • It can be used to identify chromosomal abnormalities.

  • Common Chromosomal Abnormalities:

    • Down syndrome (Trisomy 21): An extra copy of chromosome 21.

    • Turner syndrome (XO): Females with only one X chromosome.

    • Klinefelter syndrome (XXY): Males with an extra X chromosome.

  • Sex-Linked Disorders:

    • Determine the genotypes of individuals with sex-linked disorders, such as hemophilia or color blindness.

    • These disorders are typically carried on the X chromosome.

  • Pedigree Analysis:

    • Interpret a pedigree chart to determine the genotypes and phenotypes of individuals.

    • Determine if individuals are carriers of a specific trait or disease.

Global Systems

  • Weather vs. Climate:

    • Weather: The short-term atmospheric conditions at a specific time and place.

    • Climate: The long-term average of weather conditions in a region.

  • Global Warming:

    • The increase in Earth's average surface temperature due to the increase in greenhouse gases in the atmosphere.

  • Impacts of Global Warming and Climate Change:

    • Rising sea levels.

    • More frequent and intense heatwaves.

    • Changes in precipitation patterns.

    • Increased ocean acidification.

    • Disruptions to ecosystems and biodiversity.

  • Greenhouse Effect and Enhanced Greenhouse Effect:

    • Greenhouse Effect: The natural process by which certain gases in the atmosphere trap heat, keeping the Earth warm enough to support life.

    • Enhanced Greenhouse Effect: The increase in the concentration of greenhouse gases due to human activities, leading to increased warming.

Forensic Science

Crime Scene

  • Crime Scene Unit (CSU) Specialists and Roles:

    • Crime Scene Investigators: Document and collect evidence.

    • Forensic Scientists: Analyze evidence in the lab.

    • Photographers: Document the scene.

    • Evidence Technicians: Manage and preserve evidence.

  • CSU Search Methods:

    • Grid search

    • Spiral search

    • Quadrant or zone search

    • Line search

  • Physical vs. Trace Evidence:

    • Physical Evidence: Tangible objects (e.g., weapons, documents).

    • Trace Evidence: Small, often microscopic evidence (e.g., hair, fibers).

  • Fingerprints:

    • Fingerprints are left on surfaces due to the transfer of oils and sweat from the fingers.

    • Collection methods vary depending on the surface (e.g., dusting and lifting for smooth surfaces, chemical treatments for porous surfaces).

  • Evidence for Time of Death:

    • Core Body Temperature (Algor Mortis): The body cools at a predictable rate after death (1.5oC1.5^o C per hour until it reaches ambient temperature).

    • Presence of Bacteria: Bacteria in the body begin to decompose tissues after death.

    • Insects (Forensic Entomology): Insect life cycles can help estimate time of death.

    • Decomposition Process: The body undergoes predictable stages of decomposition.

  • Blood Splatters:

    • Blood spatter patterns can indicate the type of weapon used, the direction of impact, and the position of the victim and perpetrator.

Victims and Suspects

  • Ante-Mortem and Post-Mortem:

    • Ante-Mortem: Occurring before death.

    • Post-Mortem: Occurring after death.

  • Autopsy:

    • An autopsy is a post-mortem examination to determine the cause of death.

    • Pathologists: Perform autopsies.

    • Toxicologists: Analyze body fluids and tissues for the presence of drugs or poisons.

  • Rigor Mortis:

    • The stiffening of muscles after death due to the depletion of ATP.

    • It starts a few hours after death, peaks around 12 hours, and disappears after 36-48 hours.

  • Autoradiogram Interpretation:

    • Autoradiograms are used in DNA fingerprinting to match a suspect's DNA to evidence from a crime scene.

The Periodic Table

Atoms and Elements

  • Structure of an Atom:

    • An atom consists of a nucleus and electrons.

    • The nucleus contains protons and neutrons.

    • Electrons orbit the nucleus in shells.

  • Components of the Nucleus:

    • Protons (positive charge).

    • Neutrons (no charge).

  • Charge of Subatomic Particles:

    • Protons: +1

    • Neutrons: 0

    • Electrons: -1

    • Nucleus: Positive (due to protons)

    • Atom: Neutral (number of protons = number of electrons)

  • Electron Shells:

    • Electrons are arranged in shells around the nucleus.

    • The first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and the third shell can hold up to 8 electrons.

  • Electron Configuration:

    • The arrangement of electrons in the shells of an atom.

    • Example: Sodium (Na) has 11 electrons, so its electron configuration is 2, 8, 1.

    • The electron configuration can be used to determine the position of an atom in the periodic table (group and period).

  • Atomic Number:

    • The number of protons in the nucleus of an atom.

    • It determines the element's identity.

  • Ions:

    • Atoms that have gained or lost electrons, resulting in a net charge.

    • Cations: Positive ions (lost electrons).

    • Anions: Negative ions (gained electrons).

  • Ionic Charge:

    • Determined by the number of electrons gained or lost to achieve a stable outer shell.

    • Atoms tend to gain or lose electrons to achieve a full outer shell (8 electrons, except for hydrogen (2)).

Arranging the Elements

  • Period and Group Relationship:

    • The period number corresponds to the number of electron shells.

    • The group number (for main group elements) corresponds to the number of outer shell electrons.

  • Periodic Table and Electron Configuration:

    • Use the position of an element in the periodic table to determine its electron configuration.

    • Use the electron configuration of an element to determine its position in the periodic table.

Family Groupings

  • Main Groups (Families) of Elements and Key Characteristics:

    • Alkali Metals (Group 1): Highly reactive, form +1 ions.

    • Alkaline Earth Metals (Group 2): Reactive, form +2 ions.

    • Halogens (Group 17): Highly reactive nonmetals, form -1 ions.

    • Noble Gases (Group 18): Inert (unreactive), have a full outer electron shell.

Scientific Method

  • Independent Variable: The variable that is manipulated or changed by the researcher.

  • Dependent Variable: The variable that is measured or observed in response to the changes in the independent variable.

  • Hypothesis: A testable prediction or explanation of the relationship between two or more variables.

  • Errors:

    • Random Errors: Unpredictable errors that affect the precision of measurements. Can be minimized by taking multiple measurements and calculating an average.

    • Systematic Errors: Consistent errors that affect the accuracy of measurements. Can be minimized by calibrating instruments and using control groups.

  • Conclusion: A summary of the findings of the experiment and whether the hypothesis was supported or rejected.

  • Graphing Data:

    • Title: Describes the data being presented.

    • Axes Labels: Clearly labeled with units.

    • Units: Appropriate units for each axis.

    • Line of Best Fit: A line or curve that represents the trend in the data.