Year 7 science revision

3. A substance made of one type of atom only.
5. A large mass at the centre of a solar system (if there are other bodies present) that produces heat and light.
6. Allows light to pass through but is not completely clear.
9. The total mass of reactants before a reaction is equal to the total mass of products after a reaction because no atoms can be created or destroyed so the mass must remain unchanged
11. A substance containing two or more different elements.
13. The process of burning by heat.
14. The change of state from a solid to a gas.
15. Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium.
17. A group of similar cells that carry out the same function.
18. A substance formed in a chemical reaction.
19. The organs responsible for gas exchange in mammals, birds, reptiles and amphibians.
20. A group of different tissues that work together to carry out a particular function.
25. Where photosynthesis happens.
26. The number of waves produced each second.
27. Force exerted over an area.
28. The Earth's only natural satellite

1. Force that resists one object moving through or over something.
2. The force acting on an object due to the pull of gravity from a massive object like a planet.
3. Reaction in which energy is given out to the surroundings.
4. When the total force in opposite directions are equal in magnitude.
7. A pair of muscles that act on a joint. As one contracts, the other one relaxes.
8. The movement of particles from an area of high concentration to an area of low concentration.
10. Sound with a frequency greater than 20,000 Hz (20 kHz).
12. Gives out light.
16. The smallest part of an element that can exist.
21. The maximum height of a wave from the middle of the wave to its crest or trough.
22. A collection of two or more atoms held together by chemical bonds.
23. The jelly like substance where the chemical reactions in a cell take place.
24. A push or a pull. The unit of force is the newton (N).