One of the most useful sites for science teachers that I have found is Science Class, written by a very experienced science teacher who has generously shared his resources, including practical activities, lesson plans and slideshows.
The Science Spot has a range of lesson starters (PowerPoints) for biology, chemistry and other science classes.

In Year 7 and 8, students are working towards Level 5. The following standards describe what students at Level 5 are expected to achieve:

Science knowledge and understanding
At Level 5, students use the particle model to explain structure and properties of matter, chemical reactions and factors that influence rate. They explain the structure and function of cells and how different cells work together.
Students explain the relationships, past and present, in living and non-living systems, in particular ecosystems, and human impact on these systems. They analyse what is needed for living things to survive, thrive or adapt, now and in the future. They explain how the observed characteristics of living things are used to establish a classification system.
Students use everyday examples of machines, tools and appliances to show how the thermodynamic model describes energy and change, and force and motion. They use time scales to explain the changing Earth and its place in space. Students distinguish ideas about the Universe that have a scientific basis from those that do not. They use physical and theoretical models to investigate geological processes.
Science at work
At Level 5, students demonstrate safe, technical uses of a range of instruments and chemicals, and of procedures for preparation and separation. They design investigations that include measurement, using standard laboratory instruments and equipment and methods to improve accuracy in measurement. They make systematic observations and interpret recorded data appropriately, according to the aims of the study.
Students justify their choice of instruments and the accuracy of their measurements, commenting on the reliability of the procedures, the measurements used, and the conclusions drawn against the prediction or hypothesis investigated. They use appropriate diagrams and symbols when reporting on their investigations.
Students make and use models and images from computer software to interpret and explain observations. In field work, they demonstrate use of basic sampling procedures and represent relationships in ecosystems graphically.
Students use simulations to predict the effect of changes in an ecosystem. They work effectively in a group to use science ideas to make operating models of devices. Students identify, analyse and ask their own questions in relation to scientific ideas or issues of interest.