Year 8 Science Comprehensive CAT3 Revision Guide

Human Body Systems and Biological Organization

• Levels of Biological Organization:

  • Cell: The basic building block of life. Cells divide so the body can grow and repair itself.

  • Tissue: A group of similar cells working together to do a job.

  • Organ: A structure made of different tissues working together (like the heart or stomach).

  • System: A group of organs working together (like the digestive system).

  • Organism: A complete living thing.

  • Why Large Organisms Need Systems: Large animals cannot get food and oxygen directly to every cell by simple diffusion, so specialized systems carry materials around.

• Essential Food Components:

  • Carbohydrates: Provide main energy for cells.

  • Proteins: Needed for growth and repairing tissues.

  • Fats/Lipids: Used for long-term energy storage and keeping warm (insulation).

  • Vitamins & Minerals: Small amounts needed to keep bodily functions healthy.

  • Water: Essential liquid for dissolving and moving substances in chemical reactions.

  • Fiber: Keeps food moving through the digestive track.

• The Human Digestive System:

  1. Mouth: Teeth chew food into smaller pieces; saliva begins breaking down starch into simple sugars.

  2. Oesophagus: Muscular tube pushing food down to the stomach using wave-like movements called peristalsis.

  3. Stomach: Muscular bag that churns food, uses acid to kill germs, and uses enzymes to break down protein.

  4. Small Intestine: Digestion is finished using bile and enzymes; nutrients are absorbed into the blood through small projections called villi.

  5. Large Intestine: Soaks up excess water from undigested food.

  6. Rectum & Anus: Stores remaining waste (faeces) and releases it.

  • Extra Organs (Food does not pass inside them):

  • Liver: Makes bile to break fats into tiny drops so enzymes can work faster.

  • Gallbladder: Stores bile.

  • Pancreas: Makes digestive enzymes and sends them to the small intestine.

• The Human Circulatory System:

  • Double Loop System:

  • Loop 1 (Lungs): Right side pumps blood without oxygen to the lungs to pick up oxygen and drop off carbon dioxide.

  • Loop 2 (Body): Left side pumps oxygen-rich blood under high pressure to all parts of the body.

  • Blood Vessels:

  • Arteries: Carry blood away from the heart under high pressure (thick, stretchy walls).

  • Veins: Carry blood back toward the heart under low pressure (thinner walls, contain valves to stop backflow).

  • Capillaries: Very thin vessels (one cell thick) where oxygen, nutrients, and waste swap between blood and cells.

  • Heart Structure:

  • Flow path: $\text{Vena Cava} \rightarrow \text{Right Atrium} \rightarrow \text{Right Ventricle} \rightarrow \text{Pulmonary Artery} \rightarrow \text{Lungs} \rightarrow \text{Pulmonary Veins} \rightarrow \text{Left Atrium} \rightarrow \text{Left Ventricle} \rightarrow \text{Aorta} \rightarrow \text{Body}$

  • The left ventricle has a thicker wall because it has to pump blood to the entire body.

• Respiratory System and Breathing:

  • Pathway: $\text{Nose/Mouth} \rightarrow \text{Trachea} \rightarrow \text{Bronchi} \rightarrow \text{Bronchioles} \rightarrow \text{Alveoli}$

  • Gas Exchange in Alveoli: Oxygen moves from tiny air sacs (alveoli) into red blood cells. Carbon dioxide moves out of the blood into alveoli to be breathed out.

  • Breathing vs. Respiration:

  • Breathing: The physical movement of air in and out of the lungs.

  • Respiration: The chemical reaction inside cells that turns glucose and oxygen into energy:       $\text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water} + \text{energy}$

• Excretory System:

  • Removes waste from the body. The liver turns spare protein into urea.

  • Pathway: $\text{Renal Artery} \rightarrow \text{Kidneys} \rightarrow \text{Ureters} \rightarrow \text{Bladder} \rightarrow \text{Urethra}$

  • Kidneys: Filter urea, water, and extra salts out of the blood to make urine. They reabsorb $100\%$ of useful glucose back into the blood.

Scientific Skills and Investigation Methodology

• Investigation Steps: Question $\rightarrow$ Hypothesis $\rightarrow$ Variables $\rightarrow$ Method $\rightarrow$ Results Table $\rightarrow$ Graph $\rightarrow$ Conclusion $\rightarrow$ Evaluation.

• Variables:

  • Independent Variable: The one factor you CHANGE on purpose.

  • Dependent Variable: What you MEASURE to get your result (must have units).

  • Controlled Variables: Factors you KEEP THE SAME so it is a fair test.

  • Recitation: "I CHANGE the independent variable, I MEASURE the dependent variable, and I KEEP controlled variables the same."

• Hypothesis: A testable prediction.

  • Structure: "If I (change independent variable), then (dependent variable) will (go up/down/stay same), because (science reason)."

• Fair Testing, Reliability, and Accuracy:

  • Valid Test: Fair test where only one variable is changed.

  • Reliable Results: Repeating tests gives results close to each other. Repeat at least 3 times, calculate the mean, and ignore outliers (mistakes).

  • Accurate Measurement: Measurement is close to the true value (read at eye level, zero scale first).

• Calculating Mean: $\text{Mean} = \frac{\text{Sum of valid repeats}}{\text{Number of valid repeats}}$

• Risk Assessment: Uses three columns: Hazard (thing that hurts), Risk (what could happen), and Control (how to stay safe).

• Graphs:

  • Bar Graph: Used when independent variable is a category (names, colors).

  • Line Graph: Used when independent variable is a continuous number (time, length, mass).

  • Rules: Independent variable on $x$-axis (across), dependent on $y$-axis (up), clear labels with units, even scale, sharp pencil points, line of best fit.

Energy Transfers, Transformations, and Conservation

• Energy Basics: Measured in Joules ($\text{J}$).

• Transfer vs. Transformation:

  • Transfer: Same form of energy moves from one place to another.

  • Transformation: Energy changes from one form into a different form.

• Law of Conservation of Energy: Energy cannot be created or destroyed. Total energy in always equals total energy out. "Lost" energy just turns into unwanted heat or sound spreading into the air.

• Efficiency Formula: $\text{Efficiency (\%)} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \times 100$

• Sankey Diagrams: Scale flowcharts where the arrow width shows the amount of energy.

Thermal Energy and Heat Transfer Mechanisms

• Heat Flow: Heat always moves from hotter places to colder places.

• Conduction: Heat passing through solids by vibrating particles bumping into neighbors. Metals are good conductors; wood, plastic, and trapped air are insulators.

• Convection: Heat moving through liquids or gases. Warm fluid expands, becomes lighter (less dense), and rises. Cooler fluid drops down to replace it, forming a convection current.

• Radiation: Heat traveling as infrared waves without needing particles. Dark matte surfaces absorb heat best; shiny light surfaces reflect heat.

Chemical Changes and Reaction Dynamics

• Physical Change: Easy to reverse, no new substances formed (e.g., melting ice, dissolving sugar).

• Chemical Change: Hard to reverse, rearranges atoms to form brand new substances.

  • Signs: Color change, gas bubbles/fizzing, temperature change, glowing/sound, or a solid precipitate forming.

• Conservation of Mass: Total mass of reactants equals total mass of products because atoms are not created or destroyed.

• Reaction Types:

  • Exothermic: Releases heat (gets warmer).

  • Endothermic: Takes in heat (gets colder).

Geology: Minerals, Rocks, and Plate Tectonics

• Minerals vs. Rocks:

  • Mineral: A single pure solid with its own crystal shape.

  • Rock: A mixture of mineral grains stuck together.

• Mohs Hardness Scale: Rated from $1$ (softest, talc) to $10$ (hardest, diamond). A harder mineral scratches a softer one.

• Three Rock Families:

  • Igneous: Formed when molten rock cools. Underground (slow cooling) = large crystals. Surface (fast cooling) = tiny crystals.

  • Sedimentary: Formed from layers of squashed and cemented pieces, often contains fossils.

  • Metamorphic: Rocks altered by intense underground heat and pressure without melting.

• Plate Tectonics: Giant crust plates floating on the mantle driven by convection currents.

  • Convergent: Plates collide (mountains, volcanoes).

  • Divergent: Plates pull apart (new rock forms).

  • Transform: Plates slide past each other (causes earthquakes).