Cell theory and organisation (Edexcel A level Biology B)

This detailed lesson introduces the 3 main principles of the cell theory and describes how cells are organised into tissues, organs and organ systems. The engaging PowerPoint and accompanying resources have been designed to cover points 2.1 (i) & (ii) of the Edexcel A-level Biology B specification.

The cell theory is introduced at the start of the lesson and the 1st principle is immediately discussed to ensure that students are aware that all living organisms are made of cells. This principle is discussed with relation to viruses to enable students to understand that the lack of cell structure in a virus is one of the reasons that they are not considered to be living. The second principle states that the cell is the basic unit of structure and organisation and this leads into the main part of the lesson where specialised cells and their groupings into tissues are considered. Students are challenged to compare an amoeba against a human to get them to focus on the difference in the SA/V ratio. This acts as an introduction into the process of differentiation and a recognition of its importance for multicellular organisms. Students will discover that a zygote is a stem cell which can express all of the genes in its genome and divide by mitosis. Time is then taken to introduce gene expression as this will need to be understood in the later topics of the course. Moving forwards, the lesson uses the process of haematopoiesis from haematopoietic stem cells to demonstrate how the red blood cell and neutrophil differ significantly in structure despite arising from the same cell along the same cell lineage. A series of exam-style questions will not only challenge their knowledge of structure but also their ability to apply this knowledge to unfamiliar situations. These differences in cell structure is further exemplified by the epithelial cells of the respiratory tract and students will understand why the shape and arrangement of these cells differ in the trachea and alveoli in line with function. The link between specialised cells and tissues is made at this point of the lesson with these examples of epithelium and students will also see how tissues are grouped into organs and then into organ systems. The third principle states that cells arise from pre-existing cells and this will be demonstrated later in topic 2 with mitosis and meiosis.