Science at key stage 3    (Year 7)

• Review pupils' knowledge of the organs of plants and humans, asking them to name, identify and show where these organs are found by using models and/or by labelling diagrams. Ask questions about the roles these organs play in the life of the organism, and the nature of important life processes.
• Challenge pupils to consider what the organs of the body are made of, and introduce the idea of tissues. Show images of a range of organic structures, eg on video, CD-ROM, OHT slides. Ask pupils to make inferences about the structure of living things from this evidence.

• Ask pupils about using magnifying glasses and microscopes to make detailed observations, and find out what they understand about magnification.
• Demonstrate the correct use of the microscope to make observations under low magnification. Help pupils to use a prepared slide of newsprint, eg the letter 'e', to practise placing and focusing slides.
• Help pupils make slides of common objects, eg sand, newsprint, tissue paper, hair. Encourage them to record observations in clear drawings, eg by showing them prepared drawings and asking them to identify what is clear and unclear in them. Establish through questioning why it is important to include the level of magnification.

• Show pupils evidence of the early observations made by Robert Hooke and others to illustrate how the development of the microscope changed the way in which scientists viewed the structure of living things. Ask pupils to find out how ideas developed. Provide opportunities for pupils to read different types of text, reminding them of ways of identifying key points, and to discuss findings in groups before reporting back to the whole class, eg using flow charts or a series of annotated diagrams.
• Introduce the term 'cell' and show pictures and/or three-dimensional models of a range of cell types from animals and plants. Help pupils to prepare slides of pieces of plant material, eg leaf surface, petals, root, squash, potato and tomato scrapings, onion epidermis. Establish that plant material is made of cells. Ask pupils to describe these cells.
• Provide opportunities for pupils to make their own slides of cheek cells as well as to observe prepared slides of human cells. Ask pupils to suggest ways in which these cells are similar to and different from plant cells. Demonstrate by drawing around a single cell in the photograph, or by drawing a cell which you can see and then showing this particular cell to a pupil, to help to focus their perception and observations.

• Show, and help pupils to make, three-dimensional models of plant and animal cells, eg using small plastic bags filled with cellulose paste to represent cytoplasm, with suitable objects to represent the nucleus (plant cells can also be made if the bags are squeezed into boxes).
• Ask pupils to identify what plant and animal cells have in common and how they are different, and help them relate the models to cells they have observed, and to drawings, diagrams, and photographs of cells. Establish that the diagrams represent a 'view' of the cell from one aspect.
• Provide pupils with secondary sources of information about cells, eg CD-ROMs which allow virtual reality cell exploration, such as a voyage through a cell. Ask them to produce an account, eg 'My journey through a cell'. Compare accounts of plant and animal cells to begin to identify differences between them.
• Review the parts of the cells, with pupils identifying that plant and animal cells contain cytoplasm, cell membrane and nucleus, and that plant cells also have a cell wall, almost always a vacuole and often chloroplasts.

• Present pupils with a collection of pictures, models, CD-ROMs of specialised cells, eg epithelial cell, root hair, pollen, palisade cell, neurone, sperm, egg, red blood cell. Ask them to classify each cell as plant or animal in origin, giving reasons, and to label the parts of the cells which they can identify.

• Review with pupils pictures, models or CD-ROMs of some specialised cells, eg epithelial cell, root hair, pollen, neurone, sperm, egg, red blood cell. Provide information about the role of each type of cell and ask pupils to match these to each cell.
• Show pupils how to use secondary sources to find out more about specialised cells in plants and animals, and how to present this information as a report on a cell type. Use this activity as an opportunity to emphasise that cells are dynamic systems rather than static structures.

• Introduce the concept of a tissue, naming examples relating to specialised cells previously observed. Use the analogy of a house to explain the organisation of tissues, showing that different materials are used to make different parts, and that these parts make the whole. Help pupils to model this, using building sets to make the equivalent of tissues, and using these to build a house or an organ of their choice.
• Show pupils a dissection, eg of a hen's leg, to illustrate the different types of tissue in a complex structure.
• Show pupils a privet leaf as an example of a plant organ, explaining that it is made from different types of cell organised into tissues.
• As an alternative some pupils could provide cartoons or drawings to show and explain how various tissues make up an organ.

• Ask pupils how they think new cells are made, and discuss different ideas that may arise.
• Provide plant material to illustrate active cell division, eg filamentous green algae, budding yeast, broad bean roots, for microscope examination under low magnification. Ask pupils to suggest how they might identify cells that are making new cells, and to locate and identify cells that may have recently divided, giving reasons.
• Using these observations and secondary sources of evidence, eg photographs or video images of dividing cells, help pupils to sequence photographs of cell division. Prompt them with questions, eg Why does the nucleus divide first? Consolidate by providing pupils with diagrams of the same process to sequence and annotate.

• Ask pupils what they remember about pollination and sexual reproduction in plants. Extend their ideas about pollen and ovule by establishing that these are the male and female reproductive cells of plants, and help them to observe pollen and ovules under the microscope at low magnification. Describe the process of fertilisation in plants as the transmission of information within a nucleus of the pollen grain to the ovule, and the combination of the nuclei of ovule and pollen grain to form a new cell. Prepare slides of pollen grains, eg from lilies, in 10% sugar solution and help pupils to observe the growth of pollen tubes. Establish that the new cell grows to form a seed, making new cells by division.

• Remind pupils of their observations of pollen tubes and explain that they are going to find the sugar concentration that is best for pollen tube growth. Help them to frame a question for investigation. Suggest an appropriate range of sugar concentrations and discuss with pupils the control of variables and the sort of observations which would provide the information needed to answer the question.
• Explain issues relating to sampling in biological investigations, eg sufficient sample size to account for variables that cannot be controlled or to provide reliable data.
• Help pupils to collect and present data relating to the number of germinated grains, in a sample of approximately 20, from each sugar concentration.
• Ask pupils to produce an account of their investigation in which the importance of sampling is clearly explained.

• Provide images or video sequences of different specialised cells and of division and growth, eg early stages of a human embryo, together with short descriptions, and ask pupils, in groups, to match image and description. Discuss with them the examples that they have difficulty agreeing on. Ask them to use their work to help them make a summary sheet about the unit.