OCR A-Level Biology - Modules 1-4 – Questions and Answers

OCR A-Level Biology - Modules 1-4 – Questions and Answers "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" 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" "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" "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 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+" "which ions are responsible for increasing the pH of a solution? - Correct answer OH-" "why do different organisms have different haemoglobin activities? - Correct answer depending on the organism's needs and environment, the structure of haemoglobin will vary and affect the oxygen affinity" "what is meant by partial pressure of oxygen? - Correct answer the measure of oxygen concentration" "how does oxyhaemoglobin form? - Correct answer 4 oxygen molecules will load onto a haemoglobin molecule when there is a high partial pressure - this is known as a high affinity for oxygen" "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" "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" "explain the shape of the oxygen dissociation graph - Correct answer "S" shaped: - at a low partial pressure, haemoglobin has a low affinity for oxygen because it is hard for the O2 molecule to reach the haem group in the centre of the blood cell - when partial pressure rises, the diffusion gradient of oxygen into haemoglobin steeply rises, when one oxygen molecule has bound to a haem group the haemoglobin undergoes a conformational change to make it easier for the second and third oxygen molecules to associate - when the haemoglobin molecule starts to become saturated it is harder for the fourth oxygen molecules to bind which is why the graph begins to level off - it is difficult to achieve 100% saturation even at high partial pressures" "explain the Bohr effect - Correct answer when tissues respire they produce CO2 which raises the partial pressure of carbon dioxide and makes the blood more acidic and causes oxygen to unload more readily as haemoglobin can take up the H+ ions to form haemoglobonic acid so that acidity does not affect the cell's activity" "explain the Bohr shift to the right - Correct answer the oxygen dissociation curve shifts to the right when carbon dioxide levels increase and more oxygen is released form the blood (because the lower the saturation of haemoglobin with oxygen, the more oxygen released)" "how do vesicles move through a cell? - Correct answer by the cytoskeleton" "what are elastic fibres especially important for? - Correct answer expiration" "what is a closed circulatory system? - Correct answer one in which the blood/transport system does not leave the vessels in which it flows" "what is the advantage of having a double closed circulatory system? - Correct answer - oxygen can be delivered to respiring cells more quickly - blood can be transported quickly at a high pressure as the heart gives blood an extra push between the lungs ad the rest of the body" "what is an open circulatory system? - Correct answer one in which the blood is not contained in vessels but rather flows freely in the body cavity" "why are open circulatory systems sufficient for smaller organisms? - Correct answer - they have a high SA:VOL ratio - blood doesn't have to travel far - open circulatory systems rely on diffusion and the diffusion pathway in small organisms is short" "why is the pulmonary system essential for humans? - Correct answer - allows blood to pumped at low pressure to avoid damage to the lungs - allows blood to pumped at high pressure to the rest of the body to meet nutrients and oxygen demands in respiring cells" "what are the three domains? - Correct answer bacteria, eukaryota, archaea" "what are the five kingdoms? - Correct answer Animalia, protoctista, plantae, fungi, prokaryotae" "how are capillaries adapted to their function? - Correct answer - one endothelial cell thick which reduces diffusion pathway - small diameter creates a large SA:VOL ratio for rapid diffusion - narrow lumen reduces the rate of blood flow which leaves time for diffusion to occur - endothelial cells are flattened to create a short diffusion pathway - have fenestrations in the wall to allow tissue fluid to move out" "what is the function of capillaries? - Correct answer to allow the exchange of material between blood and tissue" "what is tissue fluid? - Correct answer - plasma without plasma proteins with dissolved nutrients and oxygen - that bathes tissue cells - allows the transference of nutrients and oxygen from blood to tissue and the waste products of the tissue back to the blood" "describe how tissue fluid forms - Correct answer - at the arteriole end of the capillary, there is a high hydrostatic pressure due to the activity of the heart - the hydrostatic pressure is greater than the osmotic effect (oncotic pressure) which forces fluid and dissolved substances out through the fenestrations between endothelial cells - plasma proteins and red blood cells are too large to fit through - at the venous end of the capillary the hydrostatic pressure is much less than the osmotic effect (blood has far more dissolved solutes and proteins in it which makes its water potential lower than that of the tissue fluid) and therefore some tissue fluid will diffuse back into capillaries via osmosis - other tissue fluid will diffuse into lymph vessels via the pores by osmosis" "describe the composition of blood - Correct answer - red blood cells - white blood cells - platelets - proteins - water - dissolved solutes" "describe the composition of tissue fluid - Correct answer - NO RED BLOOD CELLS - very few white blood cells (macrophages to fight bacteria in tissues) - NO PLATELETS - very few (proteins secreted from tissue cells or hormones that leave the capillary and bind to receptors on the tissue) - water - dissolved solutes (far less oxygen as tissue will absorb it via diffusion for respiration)" "what happens to tissue fluid once it has served its purpose? - Correct answer some drains back into the capillaries, some drains into lymphatic vessels" "what is the difference between lymphatic fluid (lymph) and tissue fluid? - Correct answer location; surrounding cells/tissue = tissue fluid in lymph vessels = lymph" "how can blood be separated out into plasma and erythrocytes? - Correct answer spin it in a centrifuge to separate according to density" "what is the benefit of having a lymphatic system? - Correct answer it's part of the immune system and protects us from infection" "what is important about lymph? - Correct answer it contains lymphocytes which are produced in the lymph nodes which detect and destroy bacteria" "why does lymph contain less oxygen and more carbon dioxide than blood? - Correct answer the tissue fluid has delivered most of the oxygen from the blood to the respiring cells and collected metabolic waste from respiration before entering the lymph vessels via osmosis" "which is the only vein that does not carry deoxygenated blood to the heart? - Correct answer pulmonary vein" "what is the function of veins? - Correct answer to carry deoxygenated blood back to the heart?" "how are veins adapted to their function? - Correct answer - valves prevent backflow - large lumen and little elastic/muscular tissue allow low pressure and least flow resistance" "what is the function if the coronary arteries? - Correct answer as the heart is a muscle, it too needs a blood supply to receive the necessary oxygen and nutrients - coronary arteries supply this blood" "why do the atria have relatively thin walls? - Correct answer they only ump blood a short distance to the ventricles which means weak contractions" "why does the right ventricle have a thinner wall than the left? - Correct answer - right ventricle undergoes weaker contractions at a lower pressure as it only pumps blood through the pulmonary system which is nearby - left ventricle undergoes stronger contractions at a higher pressure to pump blood to the rest of the body ad overcome the resistance of systemic circulation" "define resolution? - Correct answer the ability to distinguish between two points that are close together" "define magnification? - Correct answer the size of the image compared to the actual size" "why can it be said that cytokinesis is a separate process to mitosis? - Correct answer cytokinesis is a division of the cytoplasm whereas mitosis is a division of the nucleus and its genetic material" "how are the alveoli adapted for gas exchange? - Correct answer - single layer of thin, flat epithelial cells creates a sort diffusion pathway - high SA:VOL ratio for rapid diffusion of oxygen and carbon dioxide - they have lots of capillaries that carry the O2 away and the CO2 in the alveoli to maintain a concentration gradient - permeable to gases - surfactant lowers surface tension within the alveoli to prevent them from collapsing" "what is the function of valves in the heart? - Correct answer to ensure that the blood flows in the right direction" "how do valves open and shut? - Correct answer - if the pressure behind the valve is greater, it opens - if the pressure in front of the valve is greater, it is forced shut" "explain the pressure in the veins - Correct answer transports deoxygenated blood back to the heart at lower pressure" "what is the function of the arteries? - Correct answer to carry oxygenated blood away from the heart to respiring tissues" "how are the arteries adapted to their function? - Correct answer - thick muscular walls containing elastic fibres help the arteries to withstand high pressure - narrow lumen and thick walls maintain high pressure along the vessel and smoothes the pressure created by the surges of the heart - muscular tissue can contract and dilate to alter the diameter of the lumen and control blood flow to certain organs" "what is atrial systole? - Correct answer - atria contract - atrial pressure increases - AV valves are forced open - blood flows into ventricles" "what is ventricular systole? - Correct answer - ventricles contract - ventricular pressure increases - AV valves are forced shut - SL valves are forced open - blood flows into the arteries" "why are valves not needed in the arteries? - Correct answer blood is being carried away from he heart at such a high pressure that backflow is virtually impossible" "describe the function of cellulose - Correct answer Cell wall in plants" "explain the need for staining specimens in light microscopy and electron microscopy - Correct answer - the majority of the biological material in a cell is colourless - stain makes organelles visible - allows you to distinguish between different organelles - images produced by an electron microscope start off in black and white and colour is added by a specialised computer program afterwards" "state the function of the nucleolus - Correct answer houses cell's genetic material in the form of DNA which codes for protein synthesis" "where are ribosomes produced? - Correct answer in the nucleolus" "describe the role of haemoglobin carrying oxygen around the body - Correct answer - a haemoglobin molecule has four subunits - each subunit has a polypeptide and a haem group - each haem group has an iron (Fe2+) ion prosthetic group - therefore red blood cells can hold up to four oxygen molecules around the blood stream" "what is a cofactor? - Correct answer an inorganic non-protein molecule that help the enzyme and substrate to bind together" "what is a coenzyme? - Correct answer an organic non-protein molecule that participates in the reaction and is changed by it - they often act as carriers by moving chemical groups between different enzymes" "name a source of coenzymes - Correct answer vitamins" "what are prosthetic groups? - Correct answer a tightly bound cofactor" "what happens during prophase mitosis? - Correct answer - chromosomes condense and shorten - centrioles move to opposite ends of the cell - the spindle fibres form - nuclear envelope breaks down" "what happens during metaphase mitosis? - Correct answer - chromosomes align along the centre of the cell - chromosomes attach to the spindle fibre by the centromere - metaphase check point ensures that the chromosomes are attached to the spindle fibre before mitosis occurs" "the heart beat creates a 'lub-dub' sound, what is responsible for the first component of this sound? - Correct answer the closing of the AV valves" "what are light microscopes useful for? - Correct answer viewing whole cells and tissues" "what are TEM useful for? - Correct answer viewing organelles" "what are laser scanning confocal microscopes useful for? - Correct answer an object at a certain depth within a cell" "why is facilitated diffusion passive? - Correct answer - molecules have their own kinetic energy - they move down a concentration gradient" "why can't glucose pass through plasma membranes by diffusion? - Correct answer - glucose is too large a molecule - phospholipid molecules act as a barrier" "which two nitrogen-containing bases are purines and which are pyrimidines? - Correct answer - adenine and guanine are purines - thymine and cytosine are pyrimidines" "what are the differences between purines and pyrimidines? - Correct answer purines are larger as they have two rings in their structure whereas pyrimidines only have one" "how do bacteria cells divide? - Correct answer by binary fission" "What is the material in the cell wall of bacteria called? - Correct answer Peptidoglycan" "Use the cohesion-tension theory to explain how water travels up from the roots to the leaves - Correct answer - water evaporates from the top of the plant via the stomata during transpiration - this creates a tension in the xylem - water molecules are pulled up the xylem by tension in a column as the hydrogen bonding between them makes them cohesive" "Why do plants need to uptake water? - Correct answer - to use as a reactant in photosynthesis - to support leaves and shoots by keeping cells rigid - cools leaves by evaporation - it transports dissolved minerals around the plant" "How is water loss reduced by leaves? - Correct answer They have a waxy cuticle on their surface to prevent water vapour escaping through the epidermis. They also have fewer stomata on top" "What is water potential? - Correct answer a measure of water molecule concentration" "name one feature of animal cells that is not present in plant cells - Correct answer centrioles" "define the term tidal volume - Correct answer the volume of air inhaled and exhaled in each breath during regular breathing" "define the term vital capacity - Correct answer the maximum volume of air that can be inhaled and exhaled in one breath" "where does oxygen bind to haemoglobin - Correct answer - haemoglobin has a high affinity for oxygen - it binds to oxygen in the alveoli in the lungs to form oxyhaemoglobin - transports oxygen to respiring tissue and offloads it" "describe how hydrocarbonate ions are produced in erythrocytes - Correct answer - carbon dioxide diffuses into the erythrocytes and combines with water with the aid of carbonic anhydrase enzymes - carbonic acid forms - this dissociates into H+ and HCO3- ions" "what is the effect of the Bohr shift? - Correct answer - reduces the affinity of HB to oxygen - haemoglobonic acid forms - which prevents the build of H+ ions (therefore not affecting the activity of cells) - this alters the shape of haemoglobin so that oxygen is more easily offloaded to areas of high CO2 concentration" "why is the genetic code considered to be degenerate? - Correct answer a single amino acid can be coded for by more than one codon" "why is it essential that the genetic material in a cell replicates before it can divide? - Correct answer - so that each daughter cell receives a full set of genetic information" "what stimulates the division of a cell? - Correct answer reproduction growth repair" "what is meant by 'homologous chromosomes'? - Correct answer - a pair of chromosomes containing a paternal and a maternal chromatid joined together by the centromere - same length - carry the same genes at the same loci - homologous pairs pair up during meiosis" "what is the function of squamous tissue? - Correct answer - allows the passage of material by diffusion - found in the lungs, alveoli, lining of the heart" "what is the function of ciliated tissue? - Correct answer - secrete mucous and bat away dust/mircroorganisms - found in the respiratory tract/fallopian tubes" "state the function of the Golgi body - Correct answer - receives proteins from the RER - modifies and packages proteins into labeled vesicles - makes lysosomes" "what causes the fluctuating pressure along the aorta? - Correct answer - systole increases the pressure - diastole decreases the pressure" "what is the term used to describe the number of fluctuations in the aorta per minute? - Correct answer heart rate" "how do root epidermal cells absorb minerals form the soil? - Correct answer - by active transport - cells have many mitochondria - cells have many carrier proteins in the cell membrane - have hairs on cells which increases surface area - thin cell wall" "why can residual volume not be breathed out? - Correct answer - trachea/bronchi are held open by cartilage - thorax cannot be completely compressed - bronchioles/alveoli held open by elastic fibres" "why is sampling important? - Correct answer - it saves time and money - gives a representation of a population" "how are species richness and evenness measured in a habitat? - Correct answer simpson's index" "why can't ions pass through plasma membranes by diffusion? - Correct answer the ion and the water molecules around it can interact with the polar phospholipid head but no the hydrophobic tail" "generally, how does having more intermediate values improve the outcome of an experiment? - Correct answer - conclusions can be determined more accurately - patterns can be spotted - anomalous results can be spotted" "what shape are sieve tube elements? - Correct answer angular/hexagonal" "suggest two sources of natural substances - Correct answer - plants - microorganisms" "how does pH affect enzyme activity? - Correct answer extreme pH (low or high) interferes with the ionic/hydrogen bonds and alters the tertiary structure and changes the shape of the active site so that the specific substrate no longer fits - the enzyme becomes denatured" "why are vaccinations an example of active immunity? - Correct answer - when a person is vaccinated, they produce antibodies - this activates lymphocytes in clonal selection -" "give three properties of fibrous proteins - Correct answer - insoluble - strong - unreactive" "explain how complementary base pairing allows the replication of DNA - Correct answer - A pairs with T, C pairs with G - A-T = 2 hydrogen bonds, C-G = 3 hydrogen bonds - purines can only bind with pyrimidines because they're different sizes"