OCR A-Level Biology

What is Cell signalling? - answer-When cells communicate by signalling, one cell releases a chemical•This chemical is detected by another cell•The second cell then responds to this signal What are the two Cell signalling systems - answer-There are 2 major systems of communication: Neuronal System• via Network of neurons• Quick signals• Rapid responses Hormonal System•Uses blood to transport signals•Endocrine glands secrete hormones directly into blood•Carried all over the body•recognized by specific target cells•Enables long-term responses to be coordinated•Specific target cells have receptors that have a shape that is complementary to the shape of the hormone What is homeostasis?/ What factors are controlled (5) - answer-Homeostasis is the regulation of internal environments with a certain range Temperature• Blood glucose concentration• Blood salt concentration •Water content• Blood pressure• Blood carbon dioxide partial pressure (blood pH) What is negative feedback? (2) - answer-A response to a change in the body that counteracts or opposes the initial change. eg thermoregulation and Blood sugar regulation What is positive feedback? (1) - answer-Response that causes change to increase,Destabilizes the system, Usually more harmful•Does not lead to homeostasis•Can be useful in •Eg: childbirth (oxytocin )Uterine contractions What are endotherms? - answer-Animals who maintain body temperature through metabolic heat, independent of external temperature eg mammals and birds Advantage and disadvantages of Endotherms (2) - answer-Advantages ○Constant body temperature regardless of external environment ○Activity possible in cooler temperatures○ Able to inhabit cooler parts of the world• Disadvantages:○lot of energy intake used to maintain body temperature ○More food required ○Less energy from food can be used for growth What are ectotherms? - answer-Animals whose body temperature is determined by their environment/ Behavioral changes lizards Advantages and disadvantages of Ectotherms - answer-Advantages Less food used in respiration○ Less food required○ Greater proportion of energy derived from food can be used for growth• disadvantages: ○Less active in cooler temperatures ○May not be capable of activity during cold winters What is Excretion and what is metabolic waste? - answer-Excretion = the removal of metabolic waste products from the body. Metabolic waste = Unneeded byproducts produced as a result of normal metabolism. That need to be removed from the body as they can become toxic in large quantities eg co2 , urea Why does CO2 need to be excreted? - answer-Excess CO2 is toxic•High levels of carbon dioxide Reduce the oxygen carrying capacity of the red blood cells○Combines with haemoglobin to form carbaminohaemaglobin, which has a lower affinity for oxygen why are Nitrogenous compounds such as protein excreted and how? - answer-The body is unable to store amino acids or proteins• its wasteful to excrete amino acids•transported to the liver and deaminated•The removed amine groups initially forms the very toxic ammonia•This is then converted to the less toxic urea, ornithine cycle which is transported to the kidneys for excretion•The remaining keto acid can be directly respired, or converted to a carbohydrate or fat Blood flow in the Liver which type of Blood and how? - answer-Oxygenated Blood from the aorta via Hepatic artery• Deoxygenated Blood from the digestive system via Hepatic portal vein○has digestive products Exit via the hepatic vein •Sinusoids○Oxy and deoxy blood mix in vessels called sinusoids○Join together to form the hepatic(central) vein○Blood flowing by sinusoids come into contact with the liver cells(Hepatocytes) What are Liver Cell called and what are Kupffer cells - answer-Hepatocytes Specialised macrophages• in sinusoids•Break down and recycle old red blood cells•Haemoglobin is broken down into bilirubin○This is the brown pigment in faeces Liver function and diagram (3) - answer-Detoxification of Blood Storage of Glycogen Breakdown of Erythrocytes Production of plasma protein deamination of amino acids kidney function / functional unit of kidney - answer-The kidney's role is to filter blood and remove excess ions/water to produce urine. The functional unit of the kidney is the nephron. Nephron structure (6) - answer-nephrons spread across the cortex and medulla of the kidney. Blood enters the organ via the renal artery and exits via the renal vein. In between, it passes through tiny capillaries that surround the continuous tube constituting the nephron. Function•Filter out waste products Bowman's Capsule-Ultrafiltration ,Filter blood •Proximal Convoluted Tubule (PCT) selective reabsorption Re-absorbs valuable substances, such as glucose• Loop of Henle Creates low water potential in the medulla○Allows water to be reabsorbed•Distal Convoluted Tubule (DCT)○osmoregulation○Varies the amount of water reabsorbed into the Blood Compostion of Nephron - answer-PCT○In the PCT fluid composition is altered by reabsorption 100% sugars, most salts and water○85% of water is reabsorbed• Descending Limb○the water potential decreased Salts added- Water removed•Ascending Limb○In the ascending limb water potential is increased○Salts are removed by active transport•Collecting Duct○In the collecting duct water potential is decreased again- Water removed What is the basement membrane? - answer-Fine mesh of collagen fibers and glycoproteins- Acts as a filter to prevent the passage of molecules with a RMM of over 69,000- Most proteins are held in the capillaries of the glomerulus Epithelial cells of the Bowman's capsule structure How is glomerular filtrate formed - answer-Podocytes-Finger like projections called major processes make gaps between cells Filtrate from blood can pass into the lumen of the Bowman's capsule• High pressure forces some water and solutes through the basement membrane and into the Bowman's capsule•This liquid is now known as the 'glomerular filtrate' What is Selective Reabsroption - answer-high pressure forces water and solutes through the basement membrane and into the Bowman's capsule•This liquid is now known as the 'glomerular filtrate'What is left in the capillary?•Proteins•Blood cells•Molecules bigger than 69,000 RMM will remain in the blood.Selective reabsorption•As fluid moves along the nephron, substances are removed•Sodium-Potassium pumps move sodium ions from the cells lining the PCT into the tissue fluid•This reduced the concentration of sodium ions in the cytoplasm •Sodium ions are transported to cell, with glucose or amino acids, by facilitated diffusion•As gluc and amin acid conc rise , these substances diffuse out into the tissue fluid•Process may be enhanced by the active removal of glucose and amino acids•Tissue fluids substances diffuse into the blood and are carried away•Reabsorption of salts, glucose and amino acids reduced the water potential in cells and increases it in the tubule fluid•Water enter cells• Adapations for selective reabosrption - answer-Microvilli increase surface area• Membrane contains co-transporter proteins that transport glucose and amino acids with sodium ions in facilitated diffusion •Many mitochondria( for ATP generated) How does the loop of Henle reabsorb water - answer-Salts can be transferred from the descending limb to the ascending limb• Increases concentration of salts in the tubule fluid• Salts diffuse out into the surrounding medulla tissue• Medulla tissue has a very low water potential• Amount of water reabsorbed controls water potential of blood Process of water reabsorption - answer-As the fluid moves down, the water potential falls○Water is lost to surrounding tissue fluid○Sodium and chloride ions diffuse into the tubule•As the fluid moves up the ascending limb, the water potential rises○At the base, sodium and chloride ions diffuse out○Sodium and chloride ions are actively transported out○Wall of the ascending limb is impermeable to water○Fluid loses salt, but not water, when moving up the ascending limb Explain the hair pin counter current multiplier - answer-Close arrangement of the ascending and descending limb•Increases the efficiency of salt transfer from the ascending to descending limb•Salt concentrations build up in the surrounding tissue•Movement of salts into the medulla creates a low water potential•Removal of ions from the ascending limb means at the top, urine is dilute•Water is then reabsorbed, according to the needs of the body How is water content of blood controlled - answer-Brain releases antidiuretic hormone •ADH travels to the collecting duct the Cell have membrane bound receptors for ADH•ADH binds to receptors•Aquaporins sent in vesicles to the cell surface membrane•Aquaporins inserted into cell surface membrane•Walls of collecting duct more permeable to water•More water moves into the medulla by osmosis•Water potential of the blood rises back to the set level•Brain stops releasing ADH Causes of Kidney Failure (4) - answer-Diabetes mellitus Heart disease Hypertension Infection what are 3 treatments of Kidney failure - answer-Renal Transplants• •Kidney surgically attached to blood supply and bladder•Patient take immunosuppressant drugs to prevent rejection Dialysis•Waste removed from blood by passing it over a dialysis membrane•Partially permeable membrane allows the exchange of substances between blood and dialysis fluid•Any excess substances diffuse out of the blood and into the dialysis fluid Treatment Haemodialysis•Blood from an artery is passed into a machine and dialyzed•Heparin added to avoid clotting•Performed at a clinic•Three times a week Explain peritoneal dialysis - answer-Uses filter in the abdominal membrane•Permanent tube implanted in the abdomen•Dialysis solution fills space between organs and membrane•Solution drained after several hours•Patient able to walk around•Can be carried out at home Explain Gas Chromatography and Mass Spectrometry - answer-Sample vaporized in the presence of a gaseous solvent•Passed down a long tube lined by an absorption agent•Each substance dissolved differently in the gas•Remains there for a unique and specific length of time•Eventually substance moves out of the gas and is absorbed into the lining•This is then analysed to create a chromatogram•Chromatograms of standard drugs and urine samples are taken, allowing unidentified substances to be easily identified What do sensory receptors do? - answer-Sensory receptors are specialised cell in the body that detect changes in the environment. They work by converting energy — acting as transducers from one form into electrical energy, which relays a signal to another part of the body. what are Pacinian corpuscles and what is the structure - answer-Pressure receptor in skin•Consists of concentric rings surrounding a nerve ending•Pressure causes the rings to apply pressure on the sensory nerve fibre•Nerve fibre detects change in pressure - not constantly applied pressure Advantages of Myleination and its structure - answer-Myelinated neurons can transmit action potentials more quickly than non-myelinated neurons○100-120 m/s•Non-myelinated neurons tend to be slower○2-20 m/s•Myelinated neurons carry signals from sensory receptors, to the CNS and from CNS to effectors•Carry signals over long distances•Enables rapid response to a stimulus by saltatory conduction Generation of nerve impulses (how) - answer-At rest neurones have higher concentration of sodium outside the cell○Steep concentration gradient across cell membrane ○Cell charge is -60mV compared to extracellular environment•Sodium can move into the cell by gated channels○Causing cell to depolarise — become electrically charged•Gated channels stimulated to open by action of synapse•A few channels open — a few sodium ions move into the cell•The membrane depolarises○Becomes less negatively charged compared to the extracellular environment•If the threshold potential is reached (enough sodium ions enter the cell to surpass threshold), this initiates a positive feedback loop ○Threshold is -50mV•More sodium channels open•Cell becomes more depolarised Explain Transmission of nerve impulses along a neuron - answer-Once the electrical impulse has been established, a local current exists in the cytoplasm of the neuron•This local depolarisation triggers neighbouring voltage-gated channels to open•Action potential travels in one direction along the cell What is the refractory period? - answer-immediately after the cell becomes depolarised, it begins to repolarise•When sodium channels open, potassium ion channels open also•Potassium diffuses down the concentration gradient out of the cell •This outflux of positively charged ions make