Exam Tip: If a question asks you to "Explain the difference," remember to use the word "because." For example: "Breathing is mechanical because it involves the physical movement of air, whereas respiration is chemical because it involves releasing energy from nutrients".
The Components of Blood
Once oxygen is absorbed in the lungs, it must be transported around the body by the blood. Blood is not just a red liquid; it is a complex mixture of different components, each with a specific job:
- Plasma: The liquid part of the blood that carries nutrients, hormones, and waste products.
- Red Blood Cells: These cells are specialized to carry oxygen from the lungs to the rest of the body.
- White Blood Cells: These are part of your immune system and help fight infections.
- Platelets: These are small cell fragments that help the blood clot when you have a cut, preventing excessive bleeding.
Unit 2: Properties of Materials
The second unit shifts from biology to chemistry, focusing on how substances dissolve and how we can separate them in a lab.
Dissolving and Solutions
When you mix a solid into a liquid, you are often creating a solution. To describe this accurately, you need to know three specific terms:
- Solute: The substance that is being dissolved (e.g., salt or sugar).
- Solvent: The liquid that does the dissolving (e.g., water).
- Solution: The final mixture of the solute and the solvent.
The "strength" of a solution is described by its concentration. A dilute solution contains a small amount of solute relative to the solvent, while a concentrated solution contains a large amount of solute.
Solubility and Saturation
Solubility is a measure of how much of a substance can dissolve in a particular solvent. It is important to note that temperature plays a huge role here: generally, as the temperature of the solvent increases, the solubility of the substance also increases.
If you keep adding solute to a solvent, you will eventually reach a point where no more can dissolve, no matter how much you stir. At this point, the solution is described as a saturated solution.
Experimental Skills: Variables and Chromatography
Science is about more than just facts; it is about how we test those facts.
Planning an Investigation
When designing an experiment, you must identify three types of variables to ensure the test is fair:
- Independent Variable: The factor that you intentionally change (e.g., the temperature of the water).
- Dependent Variable: The factor that you measure (e.g., how much salt dissolves).
- Control Variables: The factors you keep exactly the same to ensure a fair test (e.g., the volume of water used).
You should also define your range (the minimum and maximum values of your independent variable) and your interval (the step size between those values).
Paper Chromatography
Paper chromatography is a laboratory technique used to separate mixtures, such as different colors found in ink.
In this process, a sample is placed on chromatography paper and dipped into a solvent. As the solvent moves up the paper, it carries the different components of the mixture at different speeds. The resulting pattern of colored spots is called a chromatogram. By looking at a chromatogram, you can tell if a substance is pure (it will only show one spot) or a mixture (it will show multiple spots).
Final Study Tips for Success
To ensure you are ready for your exam, follow these proven study strategies:
- Visualize: Don't just read text. Draw the respiratory system or a particle diagram of a solution from memory.
- Active Recall: Use flashcards for terms like diffusion, respiration, and breathing to ensure you don't mix them up.
- Analyze the Marks: If a question is worth 2 marks, you must provide two distinct points or a reason using "because".
- Teach to Learn: Try explaining the difference between a solute and a solvent to a friend or family member. If you can teach it, you know it.
