| State the type of property that multicellular organisms have [1] | Emergent property |
| Explain why cells differentiate, using examples within your answer [5] | - Every cell with a nucleus contains an organism’s genome \n - Only certain genes are expressed during differentiation \n - Allows different functions by different cells \n - Multicellular organisms are more complex \n - Emergent properties arise \n - So organism is better adapted/suited to its environment \n - E.g. white blood cells, cardiac muscle, epithelial, root hair, guard cell etc |
| Identify two ways in which striated muscle fibres are different [2] | - Long \n - Multinucleated \n - No cell wall \n - No vacuole \n - No chloroplasts |
| Explain how young tadpoles are able to get enough oxygen to their cells without developed gills [2] | - Diffusion of oxygen \n - Short diffusion pathway / large surface area to volume ration |
| Describe how you would prepare and view a sample of cells from this tissue using a light microscope [5] | - Place single layer of cells on slide \n - Add drop of water \n - Place slide on microscope stage \n - Focus using lowest power lens \n - Use larger coarse-focusing knob \n - Use fine-focusing knob to sharpen the image \n - Increase magnification by using higher power lens \n - Only use fine-focusing knob at higher objective powers |
| List 3 differences between prokaryotic and eukaryotic cells [3] | Prokaryotic cells have 70S ribosomes, circular DNA, don’t have nucleus, aren’t compartmentalised and aren’t associated with proteins |
| List 4 processes that scientists believe were required for the first cells to be formed [4] | 1. Simple organic molecules synthesised from inorganic molecules \n 2. Simple molecules assemble into polymers \n 3. Some polymers developed ability to self-replicate \n 4. Formation of membrane around simple molecules / molecules become isolated from surroundings |
| Outline the evidence scientists have provided to explain the origin of eukaryotic cells [4] | - Mitochondria and chloroplasts have similar structure to prokaryotes \n - Both reproduce by binary fission \n - Both have double membranes \n - Both have their own 70S ribosomes \n - Both have circular, non-membrane bound DNA \n - Both transcribe DNA and use mRNA to synthesise their own proteins |
| Outline the experiment Pasteur used to demonstrate cells only come from pre-existing cells [6] | - Falsified concept of spontaneous generation \n - Used culture medium in swan-necked flasks \n - Sterilised to kill pre-existing microorganisms \n - Didn’t show growth because microorganisms couldn’t enter flask \n - Broke neck of flask → showed growth because it was contaminated by air and microorganisms could enter flask |
| Structures not visible with a light microscope | Mitochondria, ribosome \n Endoplasmic reticulum \n Lysosome \n Cell-surface membrane |
| TEM vs SEM | Both are electron microscopes: not live specimens, black and white only \n TEM: thin, 2D \n SEM: thick, 3D |
| Light vs electron microscopes | Light: max 200nm resolution \n Electron: max 0.2nm resolution |