This pages gives outline details of the content of the topic together with essential questions and student skills and applications. Helpful for revision.

1.1 Introduction to cells

Cell theory

• According to cell theory, living organisms are composed of cells.
• Organisms consisting of only one cell carry out all functions of life in that cell. e.g. Paramecium, Chlorella.
• Identifying the characteristics of living things (Mr H. Gren - metabolism, response, , homeostasis, growth, reproduction, excretion & nutrition)
• Surface area to volume ratio is important in the limitation of cell size.
• Multicellular organisms have properties that emerge from the interaction of their cellular components. (Emergent properties)
• Specialized tissues can develop by cell differentiation in multicellular organisms.
• Differentiation involves the expression of some genes and not others in a cell.
• Stem cells can divide and differentiate along different pathways in embryonic development which makes stem cells useful for therapeutic uses (e.g. Stargart's disease).
• There are ethical concerns about the use of embryo stem cells.

Calculating magnification and size

• Calculate the magnification of an electron microscope image from a scale bar?
• Calculate specimen size using a scale bar?
• Calculate specimen size using magnification?

1.2 Ultrastructure of cells

• Know and be able to draw the simple structure of Prokaryote cells
• Know and draw the compartmentalised structure of Eukaryotic cells.
• Understand that the resolving power of electron microscopes is between 10µm and 1nm
• whereas light microscopes resolve details between 1mm and 1µm.

1.3 Membrane structure & 1.4 function

Membrane structure

• Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
• Membrane proteins are diverse in terms of structure, position in the membrane and function.
• Cholesterol is a component of animal cell membranes.
• Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.
• Can you draw a diagram of the fluid mosaic model.
• Can you explain how evidence from electron microscopy led to the proposal of the Davson-Danielli model.
• Can you outline the evidence which led to the falsification of the Davson-Danielli model and support of the Singer-Nicolson model.

Membrane transport

• Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
• The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
• Know how the structure helps the function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
• Understand why tissues (or organs) waiting to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
• Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)

1.5 The origin of cells and 1.6 cell division

• The first cells must have arisen from non-living material.
• The origin of eukaryotic cells can be explained by the endosymbiotic theory.
• Mitosis is division of the nucleus into two genetically identical daughter nuclei.
• Chromosomes condense by supercoiling during mitosis.
• Cytokinesis occurs after mitosis and is different in plant and animal cells.
• Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.(including G1, S, G2)
• Cyclins are involved in the control of the cell cycle.
• Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.