This document is a worksheet created by Cambridge Assessment International Education for Cambridge Lower Secondary Science Stage 8. Cambridge Lower Secondary Science includes learning objectives on models and representations because they are central to students' understanding of science.
Gases
Students may become confused by the everyday use of the scientific terms 'pure' and 'purity'. Arrows can be added to show the force exerted by the particles on the walls of the container.
Suggested activities
Explain that the "particles" have a shorter distance to travel before hitting the sides of the tray, so the number of collisions per second is increased. What happens to the gas pressure in the syringe when it is compressed.
Liquids
A particle model diagram can be used with many circles to represent the solvent and fewer differently colored circles (or even a different shape) to represent the solute particles. Particles of some sample substances "stick" to the solvent particles (ie dissolve in the solvent) and move along the paper with them.
Suggested activities
Give students some data on the mass of a solute that dissolves at different temperatures. Place the bottom of the paper in water (make sure the water is lower than the pencil line) and clip the paper to the top of the beaker (or attach it to a pencil resting on the rim of the beaker).
Respiration and the respiratory system
Students may think that only oxygen enters the lungs, whereas air enters the lungs and air. Students may think that oxygen is carried in blood plasma, so it is important to point out that oxygen is carried in red blood cells.
Suggested activities
Ask learners to predict how the temperature of the water in the 'live yeast' flask will compare to the. Mark out a corner of the classroom (to represent an alveolus) and an area next to it (to represent a capillary next to the alveolus). It represents the movement of the blood carrying the oxygen away from the alveolus.
Explain to students that they will build a physical model of the respiratory system to test the analogy. Explain that a key component of the respiratory system is the blood that moves in the circulatory system.
Light and colour
Ray drawings can be used as a model to show what happens to the light. A ray diagram can be used to emphasize that the light travels from the source to the mirror and then to the eye. 8Ps.03 Know that white light consists of many colors and this can be represented by the dispersion of white light using a prism.
Ray diagrams can be used to show how different colors of light (or colors within white light) can be added, subtracted, absorbed, and reflected. A ray diagram can be used to show how light propagates. reflected in our eyes), meaning the object is seen as black.
Suggested activities
Using a beam box (or a lamp with a narrow slit placed in front of it), beware of using electrical equipment near water, direct a beam of light at an angle to the side of the container. Explain that this is an analogy for the movement of light from air to water (or glass). It evokes the idea that the speed of light is slower in glass (or water) than in air.
Can you predict what might happen to the speed of light as it goes from glass to air? There are three primary colors of light (i.e. red, green and blue) and secondary colors of light are formed when two of the primary colors are combined (i.e. magenta, yellow and cyan).
Atomic structure and chemical reactions
Students may think that atoms can be seen under a microscope; they often find it difficult to appreciate how small subatomic particles are. Some students may think that the presence of only protons in the nucleus should cause repulsion. Students may think that the main attraction in an atom is between protons and electrons.
Learners may think that carbon dioxide is two products because there are two separate words. Learners may have heard of microplastics and think they differ in chemical composition from plastics they can see (eg plastic bottles).
Suggested activities
Present the hypothesis that "the electrostatic attraction between the positive charge of protons and the negative charge of electrons holds individual atoms together". Ask the students to put the metals in order, starting with the metal that reacts most strongly with the oxygen in the air. Prove the reactions of sodium, potassium, calcium with water; add a few drops of universal indicator to the water so students can observe the color change caused by the formation of hydroxide.
Ask students to put the metals in order, starting with the metal that reacts most strongly with water. Ask students to rank the metals, starting with the metal that reacts most strongly with water; note that copper should not react with water.
Health
Some students may think that vitamins are only available as supplements and do not realize that they are in food. Students may think that all fats and all sugars are always bad, instead of realizing that they should be consumed in moderation. Students may think that all (or most) of the food we eat is used for energy.
Students may not understand that blood is red because it contains red blood cells; they may think that blood is just a red liquid. Students may think that there are no toxins present that are not visible (or can no longer be seen).
Suggested activities
Discuss how people, seeing biological phenomena (e.g. the ball and socket joint, the hinge joint), are often inspired to invent new technologies (e.g. a ball and socket joint is in cars and the pneumatic ladders of ' a fire engine). Show learners images taken of blood under a microscope and discuss the components of blood; support the learners in identifying red blood cells, white blood cells and plasma. What would happen if a pesticide were used to kill insects at the lower levels of the food web by coating plants.
The pesticide enters a larger organism that ingests the plant/dead insects; however, the level of pesticide may not harm the larger organism. Discuss what might happen to a top predator if they ingest too much of the original toxic substance and their body can't get rid of it - the animal gets sick and/or dies.
Speed, motion and forces
The magnitude and direction of the force are indicated by the length and direction of the arrow, respectively. It can be helpful to always use the same color (or formatting) of the power arrows to clearly distinguish them from arrows indicating movement. They may think that the arrow representing the force describes the direction of motion.
Students may think that the motion must be in the same direction as the force. Explain the scientific definition of the term and provide opportunities for students to use the term correctly.
Suggested activities
For each scenario, ask learners to show what forces (if any) are initially acting on a particular object and then, by choosing a time when the ball is moving, add force arrows to the diagram. They describe, in words, what will happen to the speed of the ball and draw a distance/time graph. Elicit the answer that the force of gravity pulls the ball downwards, while the normal reaction force of the hand pushes upwards with an equal and opposite force; that is why the ball does not move.
Elicit the idea that the forces are now unbalanced, which explains why the ball starts moving. The piece of mat should be long enough for the ball to travel several meters.
Earth and the Solar System
Learners may think that all magnets are made of iron and that the strength of a magnet is based on its physical size. Learners may think the Earth has a giant magnet inside rather than the magnetic field generated by electric currents in the Earth's core. 8Be.01 Identify different ecosystems, habitats, A diagram can be used to represent an ecosystem; Learners may not realize that ecosystems are these.
Students may think that an invasive species actively kills (or poisons) other species, but this is not common. Students may think that the Earth's climate varies only by the amount of carbon dioxide.
Suggested activities
This means the core of the Earth produces the magnetic field that our compasses respond to. Resources: Magnetic compasses, an image of the Earth, a fruit containing a stone, thread 8Be.01 Identify. Show learners a diagram of the 'greenhouse effect' and explain the impact that 'greenhouse gases' (e.g. carbon dioxide, methane, water vapour, nitrogen oxide) have on the Earth's atmosphere, i.e.
Is there a relationship between greenhouse gas levels, atmospheric composition and climate? Explain how the Arctic was not always the polar climate it is now; Scientists have collected samples of the Earth's core that show it once had a tropical climate.
Applications of science
Galaxies also contain stellar dust and gas created when stars explode and the remnants of the universe's origins. You may need to explain to students that our solar system is an example of a planetary system and is called the solar system because the Latin name of the sun is Sol, derived from Solis. In an exothermic reaction, energy is transferred to the environment and the temperature of the environment increases.
Students may think that a magnetic field is a pattern of lines rather than a force field around a magnet. Students may think that strength is a property of the electromagnet rather than the magnetic field it creates.
Suggested activities
An endothermic reaction causes the surrounding temperature to drop (i.e. the products have more energy than the reactants). reaction; it is the temperature of the environment. They attach one end of the wire to the positive terminal (and the other end of the wire to the negative terminal) of a D-cell battery. Does the number of times you wrap the wire around the nail affect the strength of the electromagnet?.
Ask them to plan a study to determine the effect of: i) the voltage and ii) the number of turns of wire around the nail on the strength of the magnetic field generated. Once their plan is approved, they must put it to practice and come to a conclusion on how the voltage and length of the wire affect the strength of the electromagnet.
Plan
Learning Objectives 8Bs.03 Describe how the structure of the human respiratory system relates to its gas exchange function (in terms of the structure of the lungs and the action of the diaphragm and intercostal muscles) and understand the difference between inhalation and exhalation. Students should know before the lesson that the respiratory system consists of the trachea, bronchi, bronchioles, air sacs, lungs, ribs, diaphragm and intercostal muscles. Main activities Explain that students will work in pairs to build a model which is a physical model of the respiratory system.
Ask students to identify which parts of the model correspond to the trachea, lung, diaphragm. Discuss with students how breathing and the effect of the respiratory system is different from breathing.
