Year 10 Science Comprehensive Exam Study Guide

DNA Structure and Genetic Material

DNA Nucleotides:
- DNA (Deoxyribonucleic Acid) is composed of nucleotides.
- A single nucleotide consists of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base (Adenine, Thymine, Cytosine, or Guanine).
- In a DNA molecule, four nucleotides bond together where the sugars and phosphates form the backbone via covalent bonds, and nitrogenous bases pair across the center (A with T, C with G) via hydrogen bonds.
Role of DNA:
- DNA acts as the blueprint for life, carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms.
Mutations:
- Mutations are changes in the DNA sequence.
- The result of mutations can vary from being neutral (no effect) to beneficial or harmful (causing genetic disorders or diseases).

Karyotypes and Chromosomal Anomalies

Normal Human Karyotype:
- A normal human karyotype consists of $46$ chromosomes in total, arranged into $23$ pairs.
- Pairs $1$ through $22$ are autosomes.
- The $23^{rd}$ pair consists of sex chromosomes ( $XX$ for females and $XY$ for males).
Identifiable Anomalies:
- Karyotypes allow for the identification of chromosomal abnormalities such as:
  - Aneuploidy: An abnormal number of chromosomes (e.g., Trisomy $21$ , also known as Down Syndrome, where there is an extra copy of chromosome $21$ ).
  - Monosomy: Missing a chromosome (e.g., Turner Syndrome, $XO$ ).
  - Structural abnormalities: Deletions, duplications, or translocations of chromosome segments.

Modes of Inheritance

Complete Dominance:
- Definition: A form of inheritance where the dominant allele completely masks the effect of the recessive allele in the heterozygous condition.
- Example: Pea plant height; Tall ( $T$ ) is dominant over short ( $t$ ). A $Tt$ plant is tall.
Incomplete Dominance:
- Definition: A form of inheritance in which the heterozygous phenotype is a blend or intermediate between the two homozygous phenotypes.
- Example: Snapdragons where crossing a Red flower ( $RR$ ) and a White flower ( $WW$ ) results in Pink flowers ( $RW$ ).
Co-dominance:
- Definition: A form of inheritance where both alleles in a heterozygote are expressed equally and independently in the phenotype.
- Example: ABO blood groups (specifically type $AB$ ) or roan coat color in cattle where both red and white hairs are present.

Cell Division: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Purpose	Growth, tissue repair, and asexual reproduction	Production of gametes (sperm and eggs) for sexual reproduction
Number of Divisions	$1$	$2$
Number of Daughter Cells	$2$	$4$
Haploid or Diploid	Diploid ( $2n$ )	Haploid ( $n$ )
Genetic Variation?	No (genetically identical)	Yes (genetically unique due to crossing over and independent assortment)

Genetic Terminology and Zygosity

Key Definitions:
- Gene: A segment of DNA that codes for a specific protein or trait.
- Allele: An alternative form of a gene.
- Genotype: The genetic makeup of an organism (e.g., $AA$ , $Aa$ , or $aa$ ).
- Phenotype: The physical expression or observable characteristics of a genotype.
- Dominant Allele: An allele that is expressed even if only one copy is present ( $A$ ).
- Recessive Allele: An allele that is only expressed if two copies are present ( $a$ ).
- Homozygous: Having two identical alleles for a particular gene (e.g., $AA$ or $aa$ ).
- Heterozygous: Having two different alleles for a particular gene (e.g., $Aa$ ).
- Hemizygous: Having only one copy of a gene or chromosome (usually referring to genes on the X chromosome in males, $XY$ ).
Zygosity Table:
- Heterozygous dominant: Genotype $Aa$
- Homozygous dominant: Genotype $AA$
- Heterozygous: Genotype $Aa$

Genetic Tools and Testing

Punnett Squares:
- Autosomal Monohybrid Cross: A cross between two heterozygous individuals ( $Aa \times Aa$ ) results in a phenotypic ratio of $3:1$ (Dominant:Recessive) and a genotypic ratio of $1:2:1$ ( $AA:Aa:aa$ ).
- Sex-Linked Inheritance: Inheritance of genes located on the sex chromosomes (usually the X). For example, a color-blind male ( $X^b Y$ ) and a carrier female ( $X^B X^b$ ).
Pedigree Charts:
- Information determined: Patterns of inheritance (autosomal vs. sex-linked, dominant vs. recessive) and the probability of offspring inheriting a trait.
- Common Symbols:
  - Square: Male
  - Circle: Female
  - Shaded: Affected individual
  - Unshaded: Unaffected individual
  - Horizontal line between symbols: Marriage/Mating
  - Vertical line leading down: Offspring
Genetic Testing:
- Predictive Testing: Testing asymptomatic individuals to determine their risk of developing a genetic disorder later in life.
- Diagnostic Testing: Testing used to identify or confirm a specific genetic or chromosomal condition in a symptomatic individual.
- Ethical Considerations: Privacy of genetic data, potential for discrimination (insurance or employment), the psychological impact of results, and the ethics of testing minors for adult-onset conditions.

Physics: Scalar and Vector Quantities

Scalar Quantities: Described by magnitude (size) only. Examples include distance, speed, mass, and time.
Vector Quantities: Described by both magnitude and direction. Examples include displacement, velocity, acceleration, and force.

Physics: Motion Formulae and Graphs

Formulae:
- Average Velocity ( $v_{av}$ ): $v = \frac{s}{t}$ (where $s$ is displacement and $t$ is time).
- Acceleration ( $a$ ): $a = \frac{\triangle v}{\triangle t} = \frac{v - u}{t}$ (change in velocity over change in time).
Unit Conversions:
- To convert between $m/s$ and $km/s$ (as per transcript):
  - $1000 \text{ m/s} = 1 \text{ km/s}$ .
  - From $m/s$ to $km/s$ : divide by $1000$ .
  - From $km/s$ to $m/s$ : multiply by $1000$ .
Distance-Time Graphs:
- Gradient: Represents the speed/velocity of the object.
- Straight horizontal line: Indicates the object is stationary (distance not changing over time).
- Straight sloped line: Indicates constant speed.
- Calculating Distance: Read the final value on the y-axis for total distance travelled from the start.
Velocity:
- Positive Velocity: Motion in the positive (forward) direction.
- Negative Velocity: Motion in the negative (backward) direction.

Physics: Forces and Newton's Laws

Mass vs. Weight:
- Mass: The amount of matter in an object, measured in kilograms ( $kg$ ). It remains constant regardless of location.
- Weight: The force of gravity acting on an object, measured in Newtons ( $N$ ).
- Calculation: $W = m \times g$
  - On Earth: $g \text{ (acceleration due to gravity)} \thickapprox 9.8 \text{ m/s}^2$ .
  - On the Moon: $g$ is significantly lower (approx. $1.6 \text{ m/s}^2$ ), making weight much lower than on Earth despite mass staying the same.
Newton’s Laws of Motion:
- First Law (Law of Inertia): An object will remain at rest or move at a constant velocity unless acted upon by an unbalanced external force.
- Second Law ( $F = ma$ ): The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
- Third Law: For every action, there is an equal and opposite reaction.
Balanced Forces: When forces are balanced, the net force is zero ( $F_{net} = 0$ ), resulting in no change in motion (the object stays at rest or continues at a constant velocity).
Force Diagrams:
- Car: Includes Thrust (forward), Friction/Drag (backward), Weight (downward), and Normal Force (upward).
- Parachute: Includes Weight (downward) and Air Resistance/Drag (upward).

Chemistry: Atomic Structure and the Periodic Table

Atomic Mass vs. Relative Atomic Mass:
- Atomic Mass: The mass of a single atom (approx. protons + neutrons).
- Relative Atomic Mass ( $A_r$ ): The weighted average mass of the isotopes of an element relative to $1/12^{th}$ the mass of a carbon-12 atom.
Phosphorus ( $P$ ):
- Element Symbol: $_{15}^{31}P$
- Bohr Model: Nucleus with $15$ protons and $16$ neutrons. Electrons arranged in shells.
- Electron Configuration: $2, 8, 5$
Periodic Table Groups and Properties:
- Alkali Metals (Group 1): Highly reactive, soft, silvery metals.
- Halogens (Group 17): Very reactive non-metals.
- Noble Gases (Group 18): Extremely stable, inert (unreactive) gases with full outer shells.
- Metals: Lustrous, malleable, ductile, good conductors of heat/electricity.
- Non-metals: Dull, brittle, poor conductors.
- Metalloids: Properties intermediate between metals and non-metals.
Flame Tests:
- Mechanism: When heat is applied, electrons absorb energy and jump to higher energy levels (excited state). As they fall back to lower energy levels (ground state), they release energy as light of a specific wavelength/color.
- Potassium: Applying heat to potassium creates a purple (lilac) light.

Chemistry: Bonding and Formulas

Bond Types:
- Covalent Compounds: Formed when non-metal atoms share electrons.
- Ionic Compounds: Formed by the electrostatic attraction between oppositely charged ions (cations and anions) after the transfer of electrons.
Prefixes for Covalent Naming:
- One: Mono-, Two: Di-, Three: Tri-, Four: Tetra-, Five: Penta-, Six: Hexa-, Seven: Hepta-, Eight: Octa-, Nine: Nona-, Ten: Deca-.
Ionic Formula Table:

Name	Cation	Anion	Formula
Calcium Nitrate	$Ca^{2+}$	$NO_3^-$	$Ca(NO_3)_2$
Aluminium Bromide	$Al^{3+}$	$Br^-$	$AlBr_3$
Lead(II) Iodide	$Pb^{2+}$	$I^-$	$PbI_2$
Sodium Hydroxide	$Na^+$	$OH^-$	$NaOH$
Magnesium Phosphate	$Mg^{2+}$	$PO_4^{3-}$	$Mg_3(PO_4)_2$
Zinc Hydroxide	$Zn^{2+}$	$OH^-$	$Zn(OH)_2$

Valency: The combining power of an element, determined by the number of electrons it must lose, gain, or share to reach a stable outer shell.

Chemistry: Chemical Reactions

Reactivity of Metals:
- Reaction: $Mg + 2HCl \rightarrow MgCl_2 + H_2$
- Explanation: Because Magnesium ( $Mg$ ) is higher on the reactivity series than Hydrogen, it displaces the hydrogen from the hydrochloric acid to form Magnesium Chloride and Hydrogen gas.
Collision Theory and Reaction Rates:
- Temperature: Increasing temperature gives particles more kinetic energy, leading to more frequent and more energetic collisions.
- Surface Area: Increasing surface area exposes more particles for collision, increasing the rate.
- Concentration: Higher concentration means more particles in a given volume, increasing collision frequency.
- Catalyst: Lower the activation energy required for a reaction without being consumed, providing an alternative reaction pathway.
Reaction Types:
- Synthesis: $A + B \rightarrow AB$
- Decomposition: $AB \rightarrow A + B$
- Single Replacement: $A + BC \rightarrow AC + B$
- Neutralisation: $Acid + Base \rightarrow Salt + Water$
- Precipitation: Two soluble salts react to form an insoluble solid ( $precipitate$ ).
- Combustion: Reaction with oxygen to produce heat; e.g., $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$ .
- Redox: Reduction-Oxidation reactions involving the transfer of electrons.
- Solubility Table Purpose: Used to predict whether a precipitate will form during a chemical reaction.

Key Science Skills: Experimental Design

Definitions:
- Independent Variable (IV): The variable that is deliberately changed in an experiment (e.g., Temperature).
- Dependent Variable (DV): The variable that is measured or observed (e.g., Time for reaction).
- Controlled Variable (CV): Variables kept the same to ensure a fair test (e.g., Concentration of reactants, volume of solution).
- Precision: How close experimental results are to one another.
- Accuracy: How close the experimental results are to the true or accepted value.
Experiment: Sodium Thiosulfate and Hydrochloric Acid:
- Equation: $Sodium \text{ } thiosulfate + hydrochloric \text{ } acid \rightarrow sodium \text{ } chloride + sulfur + sulfur \text{ } dioxide + water$
- Mechanism: As sulfur ( $s$ ) is produced, the solution becomes cloudy. The reaction is complete when the black cross under the flask is obscured.
- Raw Data:
  - $20^\text{o}C$ : $95 \text{ s}$
  - $30^\text{o}C$ : $78 \text{ s}$
  - $40^\text{o}C$ : $62 \text{ s}$
  - $50^\text{o}C$ : $49 \text{ s}$
  - $60^\text{o}C$ : $38 \text{ s}$
  - $70^\text{o}C$ : $30 \text{ s}$
- Discussion: The data shows that as temperature increases, the time for the reaction decreases, indicating an increased rate of reaction due to higher kinetic energy and collision frequency.
Improvements:
- To improve Precision: Repeat trials and calculate an average; use more precise measuring equipment (e.g., electronic sensors instead of human eyes for the black cross).
- To improve Accuracy: Ensure all controlled variables are strictly maintained; calibrate equipment.