Comprehensive Year 8 Science and Healthy Living Study Notes

Fundamentals of Healthy Living and Nutrition

Healthy living is defined as a lifestyle that maintains fitness, energy, and a reduced susceptibility to disease. This lifestyle is built upon three fundamental rules: consuming a balanced diet, engaging in regular exercise, and ensuring a minimum of $8$ hours of sleep per day. Specific lifestyle choices, such as smoking or consuming alcohol, are explicitly excluded from a healthy lifestyle. Food is necessary for three primary biological reasons: growth, tissue repair, and energy production. Different food items provide varying levels of nutrients. For instance, an egg is categorized as a rich source of proteins and fats, containing minor amounts of vitamins and minerals, but it is considered a very poor source of carbohydrates. Therefore, a variety of foods must be consumed to obtain a complete nutrient profile.

Nutrients are categorized into several key groups, each with specific biological roles. Carbohydrates, found in staples like bread, pasta, and potatoes, serve as the body's primary energy source. Proteins, found in meat, chicken, fish, eggs, and nuts, are essential for cell repair and the creation of new cells, making them critical for growth and development in children, adolescents, and pregnant women. Fats, located in dairy products, olives, and oils, provide energy storage, insulation for warmth, and maintenance of healthy skin and hair. While essential, excessive fat intake can lead to health complications. Minerals, primarily sourced from vegetables, are necessary for many functions, including the development of healthy bones and teeth. Vitamins, found in fruit, facilitate growth, development, immunity, and digestion. Deficiencies in vitamins and minerals can lead to specific conditions such as night blindness, scurvy, and anaemia.

Additional dietary components include fibre and water. Fibre, found in green leafy vegetables, is necessary for maintaining a healthy digestive system. Water is considered a vital resource, as the human body consists of approximately $60\%$ water. While a human can survive for multiple weeks without food, survival is limited to between $5$ and $7$ days without water. Nutritional requirements vary based on life stages and lifestyles. For example, individuals undergoing puberty, pregnant women, and athletes like heavyweight lifters require higher amounts of energy or protein compared to sedentary office workers. A balanced diet consists of carbohydrates, proteins, fats, vitamins, and minerals in appropriate proportions. Malnutrition arises from an inadequate or unbalanced diet, absorption problems, or medical conditions. Starvation is a severe form of malnutrition, while obesity—excessive body fat resulting from overconsumption of fatty foods or lack of exercise—is also categorized as a form of malnourishment. Obesity increases the risk of heart disease, heart attacks, and diabetes.

Human Anatomy: Digestion and Respiration

The digestive system is responsible for breaking down food into smaller molecules for cellular use. For example, complex carbohydrates like bread are broken down into glucose, and meat is broken down into protein. The process begins in the mouth, where mechanical breakdown by teeth and chemical breakdown by saliva occur. Food is then pushed through the oesophagus via peristalsis into the stomach. In the stomach, enzymes continue chemical breakdown, and hydrochloric acid kills microbes. The small intestine continues chemical breakdown and serves as the primary site for nutrient absorption into the blood. The large intestine absorbs water from undigested material and stores faeces until they are removed through the anus.

The respiratory system facilitates breathing, specifically the inhalation of oxygen ( $O_2$ ) and the exhalation of waste gases like carbon dioxide ( $CO_2$ ). Atmospheric air enters the nose, where it is filtered by cilia and moistened by mucus. It travels through the pharynx and the trachea (held open by cartilage rings) into the bronchi tubes, then to bronchioles, and finally to the alveoli (air sacs). Gas exchange occurs in the alveoli, which are surrounded by capillaries. Oxygen diffuses through the thin walls into the blood, while carbon dioxide moves from the blood into the alveoli. Breathing mechanics rely on the diaphragm and rib cage. During inhalation, the diaphragm contracts and moves downward, and the ribs move upward and outward, increasing chest volume and sucking air in. During exhalation, these muscles relax, the chest volume decreases, and air is pushed out.

Smoking severely impacts respiratory health, with over $80\%$ of lung cancer cases attributed to the habit. Cigarette smoke contains irritants that paralyse cilia, leading to mucus and toxin accumulation. Three primary harmful chemicals in tobacco smoke are Nicotine (the addictive component), Tar (a sticky substance that coats the lungs), and Carbon Monoxide (a poisonous gas). Long-term exposure to these chemicals causes irreversible damage to lung structures.

Biological Energy and Circulation

All living organisms must perform seven vital functions: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. Respiration is defined as a chemical reaction occurring in all cells to release energy from glucose. It is distinct from breathing, which is the mechanical process of gas exchange. The chemical equation for aerobic respiration is: $\text{Glucose} + \text{Oxygen} \rightarrow \text{Water} + \text{Carbon Dioxide} + (\text{Energy})$

The circulatory system acts as the body's transport network, delivering glucose and oxygen to cells and removing waste products. The system comprises the heart (a muscular organ roughly the size of a fist that pumps blood), arteries (vessels carrying blood away from the heart), veins (vessels carrying blood toward the heart), and capillaries (the site of gas and nutrient exchange). Human adults typically possess between $5$ and $6$ litres of blood. The components of blood include Red Blood Cells (transport $O_2$ and $CO_2$ ), White Blood Cells (part of the immune system to fight infection), Platelets (responsible for blood clotting and repair), and Plasma (a watery fluid containing nutrients).

The pulse, which averages $72$ beats per minute in adults, represents the frequency of the heart's contraction and can be felt in the neck or wrist. During physical exercise, the pulse and breathing rates increase because the body requires more energy. To meet this demand, the heart beats faster and blood travels quicker to deliver increased amounts of glucose and oxygen to the cells for respiration, while also removing the increased output of carbon dioxide.

Elements, Compounds, and Mixtures

All matter is composed of atoms, which are the smallest particles of an element. Atoms consist of a central nucleus with electrons orbiting around it. Materials can be solid, liquid, or gas, and may be natural (like wood) or synthetic (like plastic). An element is a pure substance made of only one type of atom. There are $92$ naturally occurring elements, each represented by a chemical symbol and listed in the Periodic Table. Examples include Hydrogen ( $H$ ), Sodium ( $Na$ ), Iron ( $Fe$ ), and Oxygen ( $O$ ). A molecule is formed when two or more atoms are joined together, such as $O_2$ or $H_2O$ . Compounds consist of two or more different types of atoms chemically bonded, such as salt ( $NaCl$ ), glucose ( $C_6H_{12}O_6$ ), and rust ( $Fe_2O_3$ ).

The Periodic Table organizes elements into vertical columns called groups, where elements share similar chemical properties. Elements are broadly classified into metals and non-metals. Metals (except for Mercury, which is liquid) are typically solid, shiny, conductive of heat and electricity, malleable, and ductile. Non-metals may be solids, liquids, or gases; they are generally dull, brittle, and poor conductors (with the exception of graphite, a form of carbon). Mixtures consist of substances that are physically combined but not chemically joined, meaning the process is reversible. Air is a primary example of a mixture of gases, composed of approximately $78\%$ Nitrogen, $21\%$ Oxygen, and $1\%$ Carbon Dioxide and other gases.

Oxygen ( $O_2$ ) is a non-metal element molecule produced in nature by plants during photosynthesis. In a laboratory, it can be produced through the decomposition of Hydrogen Peroxide ( $H_2O_2$ ) into water and oxygen. Manganese (IV) oxide is often used as a catalyst—a substance that increases the reaction rate without being consumed. The chemical test for oxygen involves placing a glowing splint in the gas; if oxygen is present, it will relight the splint.

Chemical Reactions and Physical Changes

Changes in matter are classified as physical or chemical. Physical changes are generally reversible, produce no new substances, and the components retain their properties (e.g., melting ice). Chemical changes are irreversible, forming new substances with entirely new properties. Indicators of chemical changes include gas production, effervescence, color changes, temperature changes, pH changes, the appearance of a precipitate, or the production of light and sound. Scientists use word equations to describe these reactions, where an arrow indicates an irreversible change. For example, during combustion, a fuel reacts with oxygen to produce an oxide: $\text{Carbon} + \text{Oxygen} \rightarrow \text{Carbon Dioxide}$

Separation of Mixtures

Mixtures can be separated using various techniques based on the physical properties of their components. Solubility refers to the ability of a substance (the solute) to dissolve in a liquid (the solvent) to form a solution. Common solvents include water. To dissolve substances faster, one can stir the mixture, heat the solvent, or use smaller solute particles.

Filtration: Separates an insoluble solid from a liquid. The solid left behind is the residue, and the liquid passing through is the filtrate.
Evaporation: Separates a soluble solid from a liquid by heating the solution until the liquid evaporates, leaving the solid behind.
Simple Distillation: Separates a solvent from a solution or two liquids with different boiling points. The liquid is evaporated, then cooled and condensed in a separate container, allowing for the recovery of both the liquid and the solid residue. Pure water boils at exactly $100^\circ\text{C}$ .
Chromatography: Separates dissolved substances, such as ink pigments, based on their solubility and molecular size. More soluble substances with smaller molecules travel further up the chromatography paper.
Magnetism: Uses a magnet to separate magnetic substances (like iron) from non-magnetic ones (like sulfur).

Light and Sound Physics

Light travels as a wave in straight lines at a speed of $300,000,000\,\text{m/s}$ . Objects are classified as luminous (emitting their own light, like the sun) or non-luminous (reflecting light). Reflection occurs when light hits an object. Smooth, shiny surfaces reflect light regularly, producing clear images, while rough, dull surfaces scatter light, creating diffused images. Shadows form when an opaque object blocks light traveling in a straight line. Materials are categorized by how much light they allow through: transparent (clear), translucent (semi-transparent), or opaque (no light passage). The human eye functions like a camera; light passes through the cornea and lens (which focuses the image), through the iris (which controls light levels), onto the retina (which contains rods for black/white and cones for color). The retina produces an inverted electrical message sent to the brain via the optic nerve.

Sound is produced by vibrations traveling through a medium (solid, liquid, or gas) as longitudinal waves consisting of compressions and rarefactions. Sound cannot travel through a vacuum, as demonstrated by the Bell Jar experiment, where removing air particles causes sound to fade. Sound travels fastest in solids and slowest in gases. Humans use the ear to detect sound, which is measured in decibels. The ear also provides a sense of balance. Hearing can be damaged by infections, physical trauma like a torn eardrum, or noise pollution (excessive noise from transport or machinery). Noise pollution can be mitigated by using hearing protection, following noise laws, and keeping volumes low.

Microbiology and Health

Microbes are microscopic organisms categorized into bacteria, viruses, and fungi. They can be beneficial or harmful (pathogens). An example of a beneficial microbe is yeast, a unicellular fungus that respires anaerobically to turn sugar into alcohol and carbon dioxide through fermentation: $\text{Sugar} \rightarrow \text{Alcohol} + \text{Carbon Dioxide} + (\text{Energy})$ Lactic acid bacteria are used to produce cheese and yoghurt, while gut bacteria assist in digestion. Harmful microbes cause infectious diseases, which spread via contact, body fluids, droplets, air, contaminated food/water, or insect bites. Specific examples include the common cold (virus), food poisoning (salmonella bacteria), and athlete's foot (fungus). HIV is a virus that causes AIDS by destroying the immune system.

The body defends itself through natural barriers: skin (which clots using platelets and fibrinogen to form scabs), nose hairs, stomach acid (hydrocloric acid), and tears. The immune system utilizes white blood cells to digest microbes or produce antibodies and antitoxins. Immunity can be acquired naturally through exposure, through breast milk (antibodies passing from mother to baby), or through vaccines (small doses of dead microorganisms). Antiseptics are used on the body, disinfectants on surfaces, and antibiotics are drugs used specifically to kill bacteria. Misuse of antibiotics can lead to bacterial resistance.

Forensic Science and Forces

Forensic science is the application of scientific principles to solve crimes, largely based on Locard's Principle, which states that "every contact leaves a trace." Evidence includes fingerprints (unique to individuals), DNA, toxicology (fluid testing), bite marks (matched by teeth types: incisors for cutting, canines for tearing, and molars/premolars for grinding), and trace evidence like fibers or hair. Chemical identification in forensics often uses flame tests; for example, sodium produces an orange flame and magnesium produces a white flame. The fire triangle—heat, fuel, and oxygen—defines the requirements for combustion.

Forces, measured in Newtons ( $N$ ) using a Newton meter, are interactions that involve a push, pull, or turn. On Earth, a mass of $1\,\text{kg}$ exerts a weight of $10\,N$ . Friction is a force that opposes movement. It is helpful for braking, walking, and generating warmth, but unhelpful when it causes wear in machinery or makes objects difficult to move. Friction is increased by rough surfaces or specialized equipment (like weightlifter's powder) and decreased by smoothing surfaces, streamlining (reducing air resistance/drag), or using lubrication (oil/grease).

Climate Change and Environment

Most electricity in Malta is generated by thermal power stations burning fossil fuels (coal, oil, gas). Combustion releases energy along with harmful gases like sulfur dioxide, nitrogen oxides, and carbon dioxide. The presence of $CO_2$ is confirmed if lime water turns milky. These gases can react with atmospheric water to produce acid rain, which damages structures and ecosystems. The Greenhouse Effect is a natural process where gases trap heat to keep the Earth habitable; however, increased $CO_2$ levels lead to global warming and changing climate patterns.

A carbon footprint measures the total $CO_2$ produced by an individual's activities (e.g., using transport or electricity). Energy sources are classified as non-renewable (fossil fuels, nuclear) or renewable (solar, wind, biofuel). Renewable sources are generally non-polluting but may be intermittent or expensive to install. Biofuels are considered carbon-neutral because the plants consumed the same amount of CO2 during growth that is released during burning. Pollution affects the land (pesticides, landfills), sea (sewage, plastics), and air. Environmental protection strategies include sustainable practices and the "Three R's": Reduce waste, Re-use items, and Recycle materials.