OCR A-Level Biology - Modules 1-4 Exam Solution.

why do specimens need to be thin when observing them under a light microscope? - correct answer to allow light to pass through identify and explain the starch test - correct answer add iodine dissolved in potassium iodide solution to the sample - positive test = blue-black - negative test = orange-brown why is the structure of the plasma membrane often referred to as the fluid mosaic model? - correct answer - the continuous bilayer is 'fluid' as the phospholipid molecules are constantly moving - protein molecules are scattered through the bilayer like a mosaic why is cell signalling important? - correct answer so that cells can communicate with each other how do cells communicate? - correct answer - one cell releases a messenger molecule by exocytosis - the molecule travels in the blood to another cell - messenger molecule is detected by another cell as it binds to the receptor on the plasma membrane why is cell signalling specific? - correct answer different receptors are specific to different molecules what does cell signalling initiate? - correct answer a physiological response what is the approximate size of eukaryotic cells? - correct answer 10-100 µm state the defining features of eukaryotic cells - correct answer - nucleus - membrane-bound organelles describe the process of protein synthesis - correct answer - in the nucleus, DNA coding is copied onto a molecule of mRNA - in ribosomes in the RER, amino acids are assembled into polypeptide chains with mRNA and tRNA - the polypeptide chain is folded and modified in the RER and transported to the Golgi body in labelled vesicles - Golgi body modifies and packages the protein and transports it to the plasma membrane for secretion - vesicle fuses with the plasma membrane and is secreted what is the function of the cytoskeleton? - correct answer it allows eukaryotic and prokaryotic cells to move, retain a structured shape and transport organelles what is the function of microfilaments? - correct answer responsible for cell movement and contract to aid with cell division what is the function of microtubules? - correct answer - form part of the spindle fibre during cell division - scaffold-like structures that determine the shape of the cell what is the function of intermediate fibres? - correct answer to give mechanical strength how does blood circulation help to maintain a concentration gradient of oxygen? - correct answer blood is constantly taking away oxygen and bringing in more carbon dioxide what happens during inspiration? - correct answer - diaphragm contracts (flattens) which presses down on the digestive organs and allows room for the lungs to fill with air - intercostal muscles contract which moves the ribs up and out - volume of thorax increases and therefore pressure in the lungs decreases which forces air to rush in what happens during expiration? - correct answer - diaphragm relaxes (domes) and pushes against the lungs - intercostal muscles relax which moves the ribs down and outwards - volume of the thorax decreases and therefore pressure in the lungs increases and forces air out is expiration active or passive? - correct answer both; normal expiration is passive as inspiration muscles relax, however forced breathing can be active as the abdominal muscles depress the rib cage to forcefully decrease the volume of the thorax why is cartilage essential in the trachea? - correct answer it acts as a support column because its 'C' shape allows the pipe to stay open and not collapse under high pressure what are the inner tissues of the trachea? - correct answer glandular connective elastic fibres smooth muscle ciliated epithelium what is the lumen in the trachea formed from? - correct answer the ciliated epithelium which tissues are present in arteries and veins? - correct answer endothelium connective tissue walls smooth muscle what are the functions of the smooth muscle and elastic fibres in the trachea? - correct answer to allow the lumen to dilate and narrow: - larger volumes of air can enter the lungs during exercise - trachea can constrict when there are toxic substances in the air why is it important that the smooth muscle and elastic fibres work together in the trachea? - correct answer - muscles cannot reverse contraction on their own - when muscles contract, elastic fibres deform and stretch, they then recoil when energy has stopped being applied to contraction why are ciliated epithelial and goblet cells important in the trachea? - correct answer - goblet cells secrete mucus which traps dust and microorganisms in the inhaled air, preventing them from reaching the alveoli - ciliated cells beat the mucus away from the lungs which prevents infection what happens to haemoglobin after the first oxygen molecule has bound to it? - correct answer it undergoes a conformational change to make it easier for the other oxygen molecules to bind to it what is the name of the compound that forms one oxygen ha bound to haemoglobin? - correct answer oxyhaemoglobin what is the function of haemoglobin? - correct answer to transport oxygen around the body in which type of cell is haemoglobin found? - correct answer red blood cell where does haemoglobin bind to oxygen? - correct answer in the lungs why does a graph of an oxygen dissociation curve plateau at around 8 kPa partial pressure? - correct answer haemoglobin molecules become the limiting factor; there could be an oxygen excess how is oxygen released from haemoglobin? - correct answer in respiring tissues there is a low partial pressure of oxygen and a high concentration of carbon dioxide which lowers the pH and brings about a conformational change in the haemoglobin molecule, allowing it to release the oxygen - which means that there is a decreased % saturation of oxygen which ions does carbonic acid dissociate into? (H₂CO₃) - correct answer H+ and HCO3- which ions are responsible for lowering the pH of a solution? - correct answer H+