LATEST Biology A level OCR 100% (400+ QUESTIONS WITH VERIFIED SOLUTIONS 2023/2024

What is the MAIN role of membranes and what are the other roles? - ANSWER - COMPARTMENTALISATION -site of chemical reactions -cell signalling -cell adhesion How do cell membranes compartmentalise? - ANSWER Membranes are hydrophobic layers that separate different regions of substances dissolved in water. This hydrophobic layer acts as a barrier preventing the movement of hydrophilic molecules from one region to another. It keeps one compartment separate from another. What are the 3 examples of membrane compartmentalisation? - ANSWER -separate contents of the cell from the environment -separate different areas of the cell from each other (organelles) -separate different areas within organelles How are cell membranes sites of chemical reactions? - ANSWER Some enzymes or electron carriers involved in aerobic respiration or photosynthesis have to be in particular positions relative to each other in order to work. Being membrane bound allows these organelles to be maintained. What is cell signalling and how are cell membranes involved in cell signalling? - ANSWER Cell signalling is where one cell releases a chemical which causes a response in another cell. Glycoproteins are often the receptors on cells that detect the presence of the chemical and cause changes to the cell. What is cell adhesion and how are cell membranes involved in cell adhesion? - ANSWER The binding of a cell to a particular surface or substrate particularly the extracellular matrix of another cell. Some types of glycoproteins perform this role. What are the 5 components of membranes? - ANSWER -phospholipids -glycolipids -proteins -glycoproteins -cholesterol Fill in the blanks: Membranes are a ______ ______. The membrane is ______ layers of ______ that is about ______ nm thick in total. Each layer has the hydrophilic ______ ______ of the ______ pointing out of the membrane and the hydrophobic ______ pointing into the centre of the membrane. - ANSWER Membranes are a PHOSPHOLIPID BILAYER. The membrane is TWO layers of PHOSPHOLIPIDS that is about 7 nm thick in total. Each layer has the hydrophilic PHOSPHATE HEADS of the PHOSPHOLIPID pointing out of the membrane and the hydrophobic TAILS pointing into the centre of the membrane. Explain the fluid mosaic model of membrane structure. - ANSWER The term fluid refers to the fact that the phospholipids are free to move with the layer relative to each other. The term mosaic refers to the fact that proteins of various shapes and sizes are embedded in the membrane resembling a patchwork. What is a membrane protien? - ANSWER Proteins embedded within membranes. They can be intrinsic or extrinsic proteins depending on the way they are associated with the membrane. What are intrinsic proteins? - ANSWER Transmembrane proteins are embedded through both layers of the membrane. What are 3 examples of intrinsic proteins. - ANSWER -Channel proteins -Carrier proteins -Glycoproteins What are extrinsic proteins? - ANSWER Peripheral proteins are present in one side of the membrane. What are 2 examples of extrinsic proteins? - ANSWER -Enzymes -Proteins that bind cytoskeleton to membrane What is the function of channel proteins? - ANSWER Intrinsic proteins that allow the passive movement of polar molecules down their concentration gradient each channel is specific for a specific molecule or ion. The molecule provides a hydrophilic channel through the membrane. What is the function of carrier proteins? - ANSWER Intrinsic proteins that allow either passive or active movement of polar molecules or ions down their concentration gradient or the active transport of polar or ions against their concentration gradient. Transport involves the shape of the protein changing. What are glycoproteins and what are their functions? - ANSWER Proteins with attached carbohydrate chains of varying lengths and shapes. They play a role in cell adhesion as well as receptors for chemical signals. What are receptors and what are their functions? - ANSWER Usually glycoproteins, they detect the presence of an extra cellular chemical that causes a response in the cell. What are glycolipids and what are their functions? - ANSWER Lipids with an attached carbohydrates chain. They are cell markers or antigens ad are involved in the recognition of self and non self by immune system. What are 3 polysaccharides that are storage molecules and how are they suited for this? - ANSWER Amylose, amylopectin and glycogen What are phospholipids? - ANSWER the molecule that allow the membrane to hold its form and generate a hydrophobic barrier between one side of the membrane an the other What are the two main types of cells and what is the difference between them? - ANSWER Eukaryotic cells (have a nucleus and membrane bound organelles) and Prokaryotic cells (without a nucleus or membrane bound organelles) What does cell ultrastructure describe? - ANSWER The structures that cells are made of. State whether cell walls are present in animals/plants/both, describe the structure and the function. - ANSWER Cell wall are present in plants only Cell walls are a layer of cellulose(chitin in fungi) outside the plasma membrane that may have holes in that join to adjacent cells called plasmodesmata. It allows the cell to become turgid by preventing bursting. It is freely permeable. Plasmodesmata allow the movement of substances between cells. State whether centrioles/centrosomes are present in animals/plants/both, describe the structure and the function. - ANSWER Centrioles/ centrosomes are present in animals only.