Comprehensive Year 7 Science Study Guide

Introduction to Science and Laboratory Safety

A hazard is defined as something that has the potential to cause harm or damage to a person or the environment. In the laboratory, hazard symbols are utilized to provide a universal, immediately recognizable warning regarding the dangers of specific chemicals, regardless of the language spoken by the user. These symbols include 'Flammable,' 'Irritant,' 'Corrosive,' 'Hazardous to the Environment,' 'Toxic,' and 'Health Hazard.' To ensure safety during practical work, several rules must be strictly followed: students must always wear safety goggles to protect their eyes, stand up during experiments, and avoid running in the lab. Long hair must be tied back with a bobble to prevent it from catching fire or touching chemicals. Any breakages or spills must be reported to a teacher immediately, and all equipment must be properly stored at the end of the session.

The Bunsen burner is a primary piece of equipment used to heat solutions and can produce different types of flames based on the air hole position. When the air hole is fully shut, less oxygen enters the burner, resulting in a yellow 'Safety Flame.' This flame is easier to see and is used when the burner is not actively heating something. When the air hole is fully open, more oxygen enters, creating a 'Roaring Flame.' This flame is blue, much hotter, and is used to heat substances quickly. Basic specialized equipment includes the beaker, which is multipurpose for holding and heating liquids; the measuring cylinder, used for measuring the precise volume of liquids; the test tube and boiling tube; the conical flask; and the crucible with a lid for heating solids. Supporting apparatus includes the tripod, gauze mat, heat-proof mat, retort stand with boss head and clamp, funnel, clay pipe triangle, and Petri dish.

Scientific Variables and Data Interpretation

In scientific investigations, variables are categorized into three types: the independent variable is the one that the experimenter deliberately changes; the dependent variable is the one that is measured as a result of those changes; and control variables are those that are kept exactly the same to ensure a fair test. An experiment is considered 'repeatable' if the original experimenter repeats the investigation using the same method and equipment and obtains similar results. It is 'reproducible' if a different person conducts the experiment and produces the same results. To ensure results are reliable, a practical should be repeated at least three times, and a mean average should be calculated. Precision refers to the closeness of multiple measurements to each other, while accuracy refers to how close a measurement is to the true or accepted value.

Data collected in science can be categoric (words like 'red' or 'rough'), discrete (numeric data that can only have specific values, like shoe size or number of people), or continuous (numeric data that can have any value within a range, such as temperature, height, or time). When recording data in a table, the independent variable is placed in the first column and the dependent variable in the second, with units included only in the brackets of the headings. On a graph, the independent variable is plotted on the x-axis and the dependent variable on the y-axis. Points should be plotted with a sharp pencil, and an anomalous result is identified as one that lies far from the line of best fit or smooth curve. A prediction is a statement describing what an investigator thinks will happen, while a hypothesis is the starting point for an investigation that provides an idea or explanation to be tested.

Cells and Biological Organisation

All living organisms can be identified by the seven life processes, summarized by the acronym MRS GREN: Movement (altering position), Respiration (releasing energy from food), Sensitivity (responding to environmental changes like light or sound), Growth (increasing in size), Reproduction (producing offspring), Excretion (getting rid of waste products), and Nutrition (absorbing chemicals from food, soil, or air). Organisms are organized into a hierarchy from smallest to largest: cells, tissues (a group of cells of one type working together), organs (a group of different tissues working together), organ systems, and the whole organism. Organisms made of only one cell are called unicellular, such as bacteria (e.g., Salmonella) or fungi (e.g., yeast), while those made of many cells are multicellular.

Microscopes are used to magnify cells that are too small to see with the naked eye. The total magnification is calculated by the formula: $\text{Total Magnification} = \text{Eyepiece Lens} \times \text{Objective Lens}$. Animal and plant cells share common structures: the nucleus, which contains DNA/genetic material and controls cell activities; the cytoplasm, a jelly-like substance where chemical reactions occur; the cell membrane, which controls what enters and leaves the cell; ribosomes, where proteins are made; and mitochondria, where respiration occurs to release energy. Plant cells have three additional structures: a cell wall made of cellulose for shape and support; a permanent vacuole filled with cell sap for rigidity; and chloroplasts, which contain chlorophyll to absorb light for photosynthesis.

Specialized Cells and Microscopic Study

Specialized cells have structural adaptations to perform specific functions. Sperm cells have a long tail for movement to carry DNA to the egg. Egg cells have a large cytoplasm with food stores for the developing embryo. Red blood cells lack a nucleus to provide more room for oxygen and contain haemoglobin for transport; they also have a large surface area. Muscle cells contain many mitochondria to release the energy needed for contraction. Ciliated epithelial cells possess hair-like cilia that waft to move mucus out of the lungs or move eggs through the reproductive system. Root hair cells in plants have a large surface area to absorb water; they do not have chloroplasts because they are located underground. Palisade leaf cells are packed with chloroplasts to maximize photosynthesis.

The Particle Model and States of Matter

Matter exists in three states: solid, liquid, and gas. Solids are dense, cannot flow, and cannot be compressed; their particles are arranged in a regular pattern, packed closely together, and vibrate in fixed positions. Liquids are also dense and cannot be compressed, but they can flow; their particles are close together but arranged randomly and can move over each other. Gases have low density, can flow, and are easily compressed because their particles are far apart, moving quickly in random directions with only weak forces of attraction. Liquids and gases are collectively known as fluids because they can flow.

Changes of state occur when energy is added or removed, causing particles to rearrange. Melting is the transition from solid to liquid at the melting point (e.g., $0\,^\circ\text{C}$ for water). Freezing is the transition from liquid to solid. Boiling and evaporation involve liquid turning into gas; boiling occurs at a specific boiling point (e.g., $100\,^\circ\text{C}$ for water), while evaporation is slower and occurs only at the surface. Condensing is the transition from gas to liquid. During a change of state, the temperature of a substance stays the same on a heating or cooling curve because the energy is being used to break or form bonds between particles rather than changing the temperature.

Pressure in Solids and Fluids

Pressure is the effect of a force acting over a specific area. In solids, pressure is calculated using the formula: $\text{Pressure} = \frac{\text{Force}}{\text{Area}}$. A small surface area concentrates force, resulting in high pressure (e.g., a drawing pin sinking into wood), while a large surface area spreads the force, resulting in low pressure. In fluids (liquids and gases), pressure is caused by particles colliding with surfaces. The pressure in a container can be increased by reducing the volume, increasing the number of particles, or increasing the temperature (which gives particles more energy to move and collide).

Atmospheric and liquid pressure are influenced by gravity. At sea level, the air pressure is approximately $101\,k\text{Pa}$ because of the weight of the air particles above pushing down. At higher altitudes, like the top of Mount Everest ($8,850\,m$), the pressure drops to approximately $31\,k\text{Pa}$ because there are fewer particles above. Similarly, in the ocean, water pressure increases with depth because the weight of the water above increases, leading to more frequent and forceful particle collisions.

Forces, Friction, and Magnetism

Forces are pushes or pulls measured in Newtons ($N$) using a Newton meter. They can change an object's speed, shape, or direction. Forces are represented on diagrams using arrows to show size and direction. Contact forces require physical touch and include air resistance, friction, upthrust (the upward force in liquids), and tension. Non-contact forces act at a distance and include gravity, magnetic force, and electrostatic force. Friction acts between surfaces sliding over each other and always opposes movement; it can be reduced by polishing or adding lubricants like oil or water. Drag is a type of friction that occurs in fluids (air or water resistance).

Magnetism is a non-contact force caused by magnets. Every magnet has a magnetic field, the region where a force acts on magnetic materials like iron, nickel, and cobalt. The field is strongest closest to the poles. Like poles (North-North or South-South) repel each other, while opposite poles (North-South) attract. Electrostatic force, often called 'static,' allows objects to attract or repel each other without touching.

Mass, Weight, and Gravitational Fields

Mass is the amount of matter in an object, measured in kilograms ($kg$), and remains constant regardless of location. Weight is a force caused by gravity acting on mass, measured in Newtons ($N$). Every object has a gravitational field around it. On Earth, the gravitational field strength is approximately $10\,N/kg$. Weight is calculated using the formula: $\text{Weight (N)} = \text{Mass (kg)} \times \text{Gravitational Field Strength (N/kg)}$. For example, an object with a mass of $70\,kg$ has a weight of $700\,N$ ($70\,kg \times 10\,N/kg$) on Earth. Forces often act in pairs; when they are equal in size but opposite in direction, they are 'balanced' and do not change the object's motion. If they are unequal, they are 'unbalanced,' leading to a change in speed, direction, or shape.

Human Reproduction and Development

Human reproduction involves four life stages: childhood, adolescence, adulthood, and old age. During adolescence, hormones trigger puberty, making the body physically ready for reproduction. The male reproductive system includes the testes (where sperm gametes are made and stored), the scrotum, the sperm duct, the urethra, and the penis. The female system includes the ovaries (where egg/ovum gametes are produced), the oviducts (fallopian tubes), the uterus (womb), the cervix, and the vagina. The menstrual cycle lasts approximately $28$ days and involves the thickening of the uterus lining, ovulation (release of an egg around day $14$), and menstruation (shedding of the lining if no fertilisation occurs).

Fertilisation occurs when the nucleus of a sperm cell fuses with the nucleus of an egg cell, typically in the oviduct. The resulting fertilised egg divides to form an embryo, which then undergoes implantation into the uterus lining. The baby develops as a foetus inside an amniotic sac filled with amniotic fluid for protection. The placenta acts as an exchange organ, allowing oxygen, glucose, and nutrients to diffuse from the mother’s blood to the foetus, and waste products like carbon dioxide to diffuse back. Toxic substances like nicotine and alcohol can also cross the placenta. In humans, the gestation period is nine months. Birth occurs in three stages: the breaking of the amniotic sac ('waters breaking'), the contraction of the uterus to push the baby out, and the delivery of the placenta ('after-birth').

Plant Reproduction and Seed Dispersal

Flowers are the reproductive organs of plants. The male part is the stamen, consisting of the anther (produces pollen) and the filament. The female part is the carpel (or pistil), consisting of the stigma (where pollen lands), the style, and the ovary (contains ovules). Pollination is the transfer of pollen from an anther to a stigma, facilitated by insects or wind. Insect-pollinated flowers often have brightly coloured petals and nectaries to attract animals. Wind-pollinated plants rely on the wind to carry their pollen. Fertilisation occurs when a pollen tube grows down the style and the pollen nucleus joins the ovule nucleus.

Following fertilisation, the ovules develop into seeds and the ovary develops into a fruit. Before germination (growth), seeds must be dispersed to reduce competition for light, water, and space. Methods of seed dispersal include wind (seeds with wings or parachutes), animals (seeds eaten or hooked onto fur), self-propulsion (exploding pods), and water (floating seeds).

Elements, Compounds, and Mixtures

An element is a substance made of only one type of atom, and all known elements are organized in the Periodic Table. An atom is the smallest part of an element. A molecule consists of two or more atoms joined together, while a compound is a substance made of different elements strongly joined by a chemical reaction. A mixture contains different substances that are not chemically joined and can be separated. Solutions are mixtures where a solid (solute) dissolves into a liquid (solvent). If a substance dissolves, it is soluble; if not, it is insoluble. Solubility is the maximum mass of solute that can dissolve in a specific volume of solvent, often increasing with temperature.

Separation Techniques in Chemistry

Various methods exist to separate mixtures based on physical properties. Filtration separates an insoluble solid from a liquid; the solid remains in the filter paper as the 'residue,' while the liquid passes through as the 'filtrate.' Evaporation separates a soluble solid from a liquid by heating the solution until the liquid disappears, leaving crystals behind. Simple distillation separates a solvent from a solution based on boiling points; the liquid evaporates, is cooled in a condenser, and collected as a pure liquid. Chromatography separates dissolved substances, such as dyes in ink, based on their different solubilities in a solvent. In chromatography, a pencil line is used because pencil lead is insoluble and will not interfere with the results. A pure substance will only produce one spot on a chromatogram, whereas an impure substance (mixture) will produce multiple spots. Impurities can alter the physical properties of a substance, such as changing its boiling point.