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175 Cards in this Set
- Front
- Back
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Give examples of materials that are exchanged. |
- Respiratory gases - Nutrients - Excretory products (eg, urea) - Heat |
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What kind of adaptations do animals have to minimise heat loss? |
- Small ears (smaller surface area) - Long fur (to trap a layer of air to keep warm) |
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What kind of adaptations do animals have to maximise heat loss? |
- Large ears (larger surface area) - Panting (to increase evaporation) |
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Why does the process of diffusion happen quicker in very small organisms? |
They have a large SA:V ratio. |
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What is Fick's law? |
SA x Concentration^n Gradient -------------------------------------------- Length of diffusion pathway |
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What features do exchange surfaces need to allow effective transfer of materials by diffusion or active transport? |
- Large SA:V ratio - Thin so diffusion pathway is short - Partially permeable - Movement of external(eg, air, water)/internal (eg, blood) medium to maintain a concentration gradient |
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Describe gas exchange in singe-celled organisms. |
Oxygen is absorbed by diffusion across the cell surface. Carbon dioxide produced by respiration diffuses out across the cell surface. Cell walls are completely permeable so do not provide a barrier to diffusion. |
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What is the trachea of an insect supported by? |
Kept open by circular bands of chitin (structural protein). |
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What feature do insects have that allows gas exchange? |
Tracheal system has air tubles throughout the body which open to the environment via spiracles. The open spiracles allow gas exchange but also water loss. |
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How are insects adapted to reduce water loss? |
They have a small SA:V ratio and waterproof coverings (cuticle) on their body surfaces. The spiracles also close to prevent dehydration. |
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Use Fick's law to explain how the insect gas exchange system is adapted to make diffusion of gases more efficient. |
- Oxygen delivered directly to respiring cells, short diffusion pathway. - Trachea branched out to increase surface area. - Tracheoles have moist ends to maintain concentration gradient. |
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Why do larger insects move/fly more slowly than smaller insects? |
Size of animal limited by relatively slow diffusion. |
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How is oxygen delivered to insects? |
Delivered directly to respiring cells - insects do not have a circulatory system. |
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What feature causes spiracles to open? |
High CO2 concentration stimulates spiracles to open. |
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What feature causes spiracles to close?
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High O2 concentration stimulates spiracles to close.
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Where is chlorophyll contained and does it do? |
Chlorophyll is contained in the chloroplasts for light absorption in photosynthesis. |
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What is the formula for respiration? |
Oxygen + Glucose = Carbon dioxide + Water (+energy) |
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What is the formula for photosynthesis? |
Carbon Dioxide + Water = Glucose + Oxygen |
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Use Fick's law to explain how the plant gas exchange system is adapted to make diffusion of gases more efficient. |
- Numerous stomata increase surface area. - Long, thin, flat shape of leaf decreases length of diffusion pathway. - Concentration gradient is maintained by photosynthesis/respiration. |
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How else do plants increase rate of gas diffusion? |
They have numerous air spaces (spongy mesophyll) which increases rate of gas diffusion as it is easier for oxygen and carbon dioxide to diffuse through this medium compared to diffusing through cell membrane and cytoplasm. |
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What are Xerophytes? |
Plants adapted to live in dry conditions/on very little water. |
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Give 4 examples of xerophytes. |
Aloe Vera Pines Holly Cacti |
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Give 4 examples of how xerophytes slow down the rate of water loss. |
- Thick waxy cuticle (forms waterproof barrier and increases length of diffusion pathway) - Rolled up leaves/leaves reduced to spines (protects the lower epidermis and therefore stomata from exposure to dry air which reduces water potential gradient between the inside and the outside) - Hairy leaves (traps moist air next to the leaf and so reduces water potential gradient) - Small surface area to volume ratio (small and roughly circular in cross sections as opposed to broad and flat so less water loss from the surface by diffusion). |
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Why does it not matter if water is a gas exchange medium in fish? |
There is no problem in keeping the cell membranes of the gas exchange surface moist. |
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How do fish use operculum to ventilate gills? |
- Water flows into mouth; mouth closes and tongue moves up (this increases pressure in cavity) - Water is forced over the gills and out under operculum. - Water low in oxygen then leaves the mouth cavity via the operculum. |
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Use Fick's law to explain how the fish's gas exchange system is adapted to make diffusion of gases more efficient.
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- Gills have a large surface area (four arches with flat filaments with lamelae fields). - Gills are thin walled and in close contact with water so short distance for diffusion. - Gills have a very high blood supply to bring CO2 and carry away O2 (hence dark red colour). - Counter current flow. |
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What is counter current flow? |
Water and blood in the gills flow in opposite directions which maintains a favourable concentration of gradient for diffusion of both gases. |
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Why is the counter current flow more efficient than a parallel flow? |
Parallel flow is where equilibrium is reached so does not maintain a gradient over the whole length of the gill filament. - Concentration gradient for oxygen diffusion is not maintained so the system is inefficient as oxygen stops diffusion from water into the blood. |
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Describe how the trachea is adapted to support the gas exchange system. |
The trachea is a flexible airway supported by C-shaped rings of chitin and D-shaped rings of cartilage. The walls are made up of muscle lined with ciliated epithelium and goblet cells, which produce mucus and trap dirt and bacteria. |
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How is the trachea split up? |
The trachea divides into two bronchi (they have a similar structure to the trachea) which further branch out into bronchioles. The bronchioles connect to groups of air-filled sacs called alveoli. |
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Describe the alveoli. |
Alveoli contain collagen and elastic fibres which allows them to stretch when they fill with air. They recoil during the process of breathing out, which allows carbon dioxide to be expelled. The alveoli are the site of gas exchange - where oxygen and carbon dioxide diffuse to and from the blood. |
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Use Fick's law to explain how the human gas exchange system is adapted to make diffusion of gases more efficient.
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- Numerous alveoli with numerous air sacs inside increase surface area. - Constant diffusion of oxygen as it is immediately taken away by the circulatory system (pumping of the heart and ventilation). - Squamous epithelial cells means there is a shorter diffusion pathway. |
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Describe the pathway of oxygen from an alveolus to the blood. |
Diffuses through the alveolar epithelium into the blood via the capillary endothelium. |
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Explain how ventilation maintains a concentration gradient. |
Air high in oxygen is continuously entering alveoli. Air low in oxygen is continuously being removed from the alveoli, blood high in oxygen is removed. |
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Describe the process of inspiration (breathing in). |
External intercostal muscles contract. Internal intercostal muscles relax. Ribs move up and down. Diaphragm muscles contract causing it to flatten and move downwards. Volume of chest cavity increases whilst pressure of chest cavity decreases. Atmospheric pressure outside the body is higher than inside the lungs so air moves in. Stretch receptors send impulses to brain to stop further expansion. |
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What is the formula for pulmonary ventilation? |
Pulmonary Ventilation (dm3min-1) = Tidal Volume (dm3) x Breathing Rate (min) |
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What is tidal volume? |
Volume of air in each breath whilst in rest. |
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What is breathing rate? |
Number of breaths per minute. |
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Explain how paralysis of diaphragm leads to breathing difficulties. |
- Diaphragm will not flatten. - So lung volume will not increase. - Therefore a pressure gradient cannot be established so air cannot move in. |
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What symptoms would a lack of oxygen lead to? |
Fatigue, tiredness, cramps (due to lactic acid build up), blue tinge to the skin. |
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What breaks down and how is sucrose broken down? |
Broken down by Sucrase (membrane bound, small intestine epithelium). Breaks down into alpha glucose and fructose. |
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What breaks down and how is lactose broken down? |
Broken down by Lactase (membrane bound, small intestine epithelium). Breaks down into alpha glucose and galactose. |
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How is starch broken down? |
- Salivary amylase (and pancreatic amylase) breaks down starch to maltose. - Maltase (membrane bound enzyme, small intestine epithelium) breaks down maltose into glucose by hydrolysis (breaking glycosidic bonds) |
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How is fat broken down? |
Lipidsare emulsified into micelles by bile salts (produced by the liver and secretedby the gall bladder into the lumen of the small intestine) thisincreases the surface area.
Lipases(secreted by pancreas) hydrolysetriglycerides into fatty acids and monoglycerides by breakingester bonds in a hydrolysisreaction. |
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How do endopetidases break down proteins? |
(Produced by the stomach) Hydrolyse peptide bonds between amino acids in central regions of proteins; creates smaller peptides. |
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How do exopeptidases break down proteins? |
(Produced by the pancreas) Hydrolyse peptide bonds on terminal amino acids; progressively release dipeptide and single amino acids. |
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How do dipeptidases break down proteins? |
(Membrane bound and produced in the small intestine epithelium) Hydrolyse peptide bonds between two amino acids. |
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Name the adaptions the small intestine epithelium has developed for more efficient diffusion. |
- Cells have microvilli to increase surface area. - Thin walled therefore reduce length of the diffusion pathway. - Villi contain muscles and are able to move and so maintain a concentration gradient (as products of digestion are continually moved). - Well supplied with blood vessels to maintain a concentration gradient (circulation of blood). - Squamous epithelium and endothelium so short diffusion pathway. - Numerous and specific carrier, channel and symport proteins. - Cells have numerous mitochondria to supply ATP for active transport by respiration. |
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Describe the co-transport of glucose/amino acids. |
- Na+ ions actively pumped out of epithelial cells into blood by sodium -potassium pump using ATP. - This maintains low concentration of sodium in the cell. - Sodium diffuses into cell from lumen of small intestine. - Glucose/amino acids move into cell with sodium via symport proteins (co-transport). - Glucose/amino acids diffuse from cell into blood by facilitated diffusion. |
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Why does inhibiting respiration prevent co-transport? |
- Less ATP/no ATP for active transport. - So sodium cannot be pumped into blood. - Sodium concentration in cell becomes too high. - Can't maintain a concentration gradient for sodium cannot diffuse into cells. |
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How are monoglycerides and fatty acids transport around the body? |
- Micelles are broken down by lipases, releasing monoglycerides and fatty acids which are absorbed into epithelial cells. - They are then transported into the ER (golgi may be involved) where they combine with cholesterol and lipoproteins to form chylomicrons. - Chylomicrons move out of cells by exocytosis and then enter lacteals (lymphatic capillaries), from where they enter the blood stream. |
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How does haemoglobin transport oxygen around the body? |
Readily associates (loads) with oxygen at surfaces where gas exchange takes place, as it has a high affinity here. Readily dissociates (unloads) from oxygen at respiring tissues, as it has a low affinity here. |
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Why does bonding the first oxygen molecule to Hb make it easier to bond the second and third molecule? |
The first oxygen changes to shape of the Hb and increases its affinity. |
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Why is it more difficult to bond the fourth oxygen molecule to Hb? |
The oxygen binding sites are becoming more full. |
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On an oxygen dissociation curve what does a curve further to the left represent? |
Greater affinity for oxygen (takes it up readily). |
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On an oxygen dissociation curve what does a curve further to the right represent?
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Lower affinity for oxygen (releases it easily). |
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Describe the loading, transport and unloading of oxygen by Hb. |
1) CO2 is constantly being removed at the gas exchange surface. 2) pH is higher due to low levels of CO2. 3) Hb loads oxygen more readily. 4) Hb has a high affinity in this state so does not release oxygen during transport. 5) CO2 is produced in respiring cells. 6) CO2 is acidic in solution so pH is lower. 7) Shape of Hb changes into one with a lower affinity for oxygen. 8) Hb releases its oxygen into respiring tissues. |
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Explain why haemoglobin unloads oxygen. |
- Respiration levels at tissues are high so more carbon dioxide is produced. - pH of the blood becomes lower (more acidic). - Hb changes shape (ionic bonds in tertiary structure are affected which changes shape of oxygen binding site. - More oxygen is released more quickly for more respiration. |
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Explain the advantage of the curve being to the left i n an organism in a high oxygen environment. |
High % staturation og Hb with oxygen at low ppO2. |
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Explain the advantage of the curve being to the rightin an organism with a high level of activity/high metabolic rate/highexercise.
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Hb has a lower affinity for oxygen so releases more oxygen more readily to respiring tissues so more respiration can take place. |
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Describe the cardiac cycle. |
- Atria contract (atrial systole). - Increased pressure in atria. - AV valves open (when pressure in atria is higher than in ventricles). - Blood flows into ventricles. - AV valves shut (when pressure in ventricles is higher than pressure in atria). - Ventricles contract (ventricular systole). - Increased pressure in the ventricles (biggest difference). - Semi-lunar valves open (when pressure in ventricles is higher than pressure in arteries). - Blood moves into arteries fast at first (rapid ejection) and then more slowly. - Semi-lunar valves close (when pressure in ventricles low and in arteries high). - Diastole (heart relaxes and atria accept more blood from the veins). |
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What is the role of valves in control of blood flow? |
- AV valves prevent backflow when ventricular pressure exceeds atrial pressure. - Semi-lunar valves prevent backflow when recoil of arteries creates greater pressure then in the ventricles. - Pocket valves in veins ensure blood flows back to the heart when veins are squeezed (eg, during muscle contraction). |
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How can you calculate heart rate? |
- Work out how long it takes to complete 1 cardiac cycle (approx 0.8 secs). - Divide this by 60 to get beats per minute. - REMEMBER heart rate increases during exercise so answers for humans would be in a range of 50-200. - Smaller animals like mice have a higher heart rate so you can expect answers <200. |
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Describe the structure and function of arteries. |
Structure: Thick elastic layer which stretches when pressure is high and recoils when pressure is low. Function: Evens out blood pressure/flow. Structure: Thick walls (muscle). Function: Prevents damage caused by high pressure - stops bursting. |
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Describe the structure and function of arterioles. |
Structure: Thick muscle layer which contracts to constrict (narrow) the lumen (vasoconstriction) then relaxes. Function: Reduces blood pressure and flow into the capillaries. |
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Describe the structure and function of veins. |
- Muscle layer is thin as their construction and dilation cannot allow control over blood flow. - Elastic layer is thin as pressure is low. - Wall thickness is small as pressure is low (this allows the veins to collapse in order to squeeze blood back to the heart). - Valves present to prevent backflow. |
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Describe the structure and function capillaries. |
Ficks Law: - Increased rate of diffusion as numerous and branched so surface area is large. - Diffusion pathway is short as thin endothelium. - Maintains steep concentration gradient as constant circulation of blood. - More time for diffusion to occur as red blood cell is approx. same size as capillary lumen so passage of blood is slow. |
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Why do arteries, arterioles and veins have endothelium (lining tissue)? |
To create a smooth, inner, surface to reduce resistance to blood flow.
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How is tissue fluid formed? |
- Water forced out of capillary into tissues down pressure gradient (which is greater than the effect of osmosis). - Pressure high in capillary due to heart contraction (ventricular systole). |
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How is tissue fluid reabsorbed? |
- Water is forced into capillary due to higher hydrostatic pressure in the tissues compared to that in the capillary. - Also water re-enters the capillary by osmosis because the plasma proteins are too big to leave the capillary. - As their concentration in the capillary increases so does the water potential (becomes more negative) than that in the surrounding fluid. |
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Why might a person experiencing high blood pressure get swelling? |
- Hydrostatic pressure of blood is high so more water is forced out the arteriole end of the capillary. - Some tissue fluid accumulates as not all of it can be reabsorbed. |
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Why might a starving person get swelling? |
- Fewer plasma proteins in the blood so concentration gradient is not as steep and inside of capillary is less negative. - Therefore less water can be reabsorbed into the capillary by osmosis. |
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Why does tissue fluid result in 'cankles'? |
- Gravity pulls tissue fluid down so it tends to accumulate in ankles and feet. - Feet have very few lymph vessels. - Blockages of lymph vessels can result from some bacterial infections and this would also lead to excess tissue fluid and swelling. |
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Other than someone who was starving, what other diseases can result in low levels of plasma proteins leading to swelling? |
Metabolic diseases (eg, hypoketonuria). |
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How do lymph vessels reduce tissue fluid? |
- Contraction of body muscles surrounding the lymph vessels squeeze the lymph back to the chest where is can be drained and eventually excreted. |
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Define risk (in terms of health). |
A measure of the probability that damage to health will occur as a result of a given hazard. |
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Define risk factor. |
Anything that increases the likelihood of a person getting a disease after being exposed to that factor. |
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What is the purpose of a control experiment? |
- To ensure that any change in the result is due to the independent variable. - For the comparison of other results. |
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How do you set up a control experiment? |
- Remove the factor that is being changed (eg, a placebo drug, or for an enzyme reaction either a denatured enzyme or distilled water). - KEEP EVERYTHING ELSE THE SAME. |
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What is the advantage of expressing results as a ratio? |
- Allows comparison as they have different values (eg, initial masses, starting lengths). |
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How can you improve the reliability of results? |
- Allows anomalies to be identified and removed. - Allows calculation of a more reliable mean. |
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How does taking additional readings improve a graph?? |
- Line of best fit may be more reliable. - Point where the line crosses may be more reliable. - Error bars could be plotted. - To show variability about the mean. |
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How does water enter a plant root hair cell? |
- RHC absorbs ions by active transport (needs ATP). - Water potential of RHC becomes more negative/lower. - Water enters RHC from soil by osmosis. - This entry of water into the RHC creates root pressure. |
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How does water travel across the root cortex? |
- Via cohesion into the apoplastic (cell wall pathway) - drawn through by transpiration pull. - Or by osmosis in the symplastic (cytoplasm pathway): water in the cell wall meets Casparian strip of endodermal cells, water is forced into symplastic pathway. |
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How does water enter the xylem? |
- Cells surround xylem pumps ions into the xylem by active transport. - Water potential of xylem becomes more negative/lower. - Water enters xylem from cells by osmosis. |
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How does water move up the xylem (cohesion-tension theory)? |
- Cohesion of water molecules by hydrogen bonding into continuous columns of water. - Drawn by transpiration pull. - Adhesion (minor forces of attraction) to xylem walls creates tension) xylem becomes longer and thinner. |
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What evidence for transpiration pull is there? |
Break continuous column eg, by injecting an air bubble. Xylem draws in air. |
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What evidence is there for root pressure? |
- Root pressure increases with temperature (particles have more kinetic energy). - If you block respiration (By removing oxygen or giving a metabolic inhibitor like cyanide), root pressure stops because: 1) No ATP 2) No active transport of ions into RHC 3) Water potential gradient between RHC and soil is reduced (WP of cells is higher) so water cannot enter RHC by osmosis. |
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Why does a tree trunk diameter decrease at midday? |
- Light intensity is high, more photosynthesis so more gases need to be exchanged therefore more open stomata. - More water is lost from stomata by transpiration so greater transpiration pull created. -Water is in continuous columns joined together by hydrogen bonds so xylem is under more tension (thinner). |
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Describe how light affects transpiration. |
Stomata open in the light for photosynthesis therefore an increase in light intensity increases transpiration rate. |
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Describe how temperature affects transpiration. |
Increase in temperature increases kinetic energy and decreases the water potential of the air around it therefore increases transpiration rate. |
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Describe how humidity affects transpiration. |
Increase of water molecules in the air decreases the water potential gradient therefore less water is being moved by transpiration which decreases transpiration rate. |
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Describe how air movement affects transpiration. |
An increase in air movement increases the rate of diffusion of water molecules out of the stomata and therefore increases transpiration rate. |
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How can a potometer be used to calculate the rate of transpiration? |
By measuring the uptake of water on a mm or cm scale over a set amount of time. |
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Why cut the shoot and connect to the potometer under the water? |
To prevent air entering/being drawn in; to maintain a continuous column. |
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What measurements would have to be taken in order to calculate rate of water uptake in mm^3min-1? |
- Time - Distance moved by bubble in mm - Radius/diameter of capillary tube to enable calculation of volume. |
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Why might the rate of water uptake not be equivalent to the rate of transpiration? |
- Water used in photosynthesis. - Water produced by respiration. - Water may be used in tissues to support the stem. About 95% of water absorbed is evaporated. |
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How do xerophytes limit water loss? |
- Thick waxy cuticle to increase diffusion pathway. - Rolled up leaves to decrease surface area for diffusion. - Hairy leaves to trap a layer of moisture and decrease water potential gradient. - Sunken stomata to trap moist air and reduce water potential gradient. - Reduced surface area to volume ratio. ALL THESE ADAPTIONS REDUCE WATER LOSS BY TRANSPIRATION. |
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Describe ringing experiments.
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-Rings cut around tree trunks/branches to remove bark and phloem vessels. - Area above the cut swells and is full of sugar. - Are below dies due to a lack of sugar (inhibits respiration). |
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Describe tracer experiments. |
- Radioactive carbon dioxide supplied to plants. - Plants photosynthesis and incorporate radioactive carbon into glucose and sucrose. - X-ray film used to identify locations of radioactive compounds as they move around the plant. |
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Where is sucrose made? |
By sources (cells that photosynthesise). eg, palisade layer in leaves. |
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How is sucrose transported from sources to phloem? |
Flows downwards (mass flow hypothesis). |
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Where is sucrose transported from phloem? |
Sinks (cells that use sucrose for respiration or store it). |
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Describe Mass flow hypothesis. |
- Sucrose is transported (facilitated diffusion) from source cells to phloem sieve tube elements. - Lowers the water potential in the phloem so water enters the phloem from the xylem by osmosis (down water potential gradient). - This increases the hydrostatic pressure at the top of the tubes. - Sucrose is transported out the phloem into sink cells which increases the water potential of the phloem so water moves back into the xylem by osmosis. - This decreases the hydrostatic pressure at the bottom of the phloem; a pressure gradient is created so water flows in one direction carrying sucrose from sources to sinks. |
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Define gene. |
Short section of DNA coding for one polypeptide. |
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Define allele. |
An alternative form of gene (usually dominant or recessive). |
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Define locus. |
The position of a particular gene on a chromosome. |
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Define chromosome. |
Supercoiled DNA wrapped around histone proteins. |
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Define intron. |
Non-coding sequence within a gene. |
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Define exon. |
Coding sequence within a gene. |
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What are multiple repeats of DNA? |
Sections of DNA found within introns where the same base or series of bases are repeated many times. |
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Define phenotype. |
An individual's physical characteristics or behaviour. |
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Define genome. |
An organism's entire set of genes. |
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Define proteome. |
The entire set of proteins an organism makes encoded by its genes. |
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Define the genetic code.
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- Every 3 bases (triplet/codon) codes for 1 amino acid. - Degenerate. - Read in a particular direction along only one strand. - Start and stop codons mark the beginning and ending of the chain. - Non-overlapping (each base is read only once). - Universal (same in all organisms). |
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How would you work out the number of amino acids from DNA bases? |
Divide by 3. |
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How would you work out the number of bases from an amino acid? |
Multiple by 3. |
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What are the similarities and differences between DNA and RNA? |
- DNA contains deoxyribose sugar; RNA contains ribose. - DNA has thymine; RNA has uracil. - DNA is double stranded with complementary bases pairs and hydrogen bonding. - DNA has a double helix shape. - DNA is much larger and only found in nuclei. - mRNA is a single linear helix with no base pairs. - tRNA is a cloverleaf shape (some pairs/hydrogen bonding). - tRNA is much smaller. - RNA is found throughout the cytoplasm, RER, ribosomes; mitochondria and chloroplasts have their own RNA. |
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Describe transcription. |
- DNA double helix unzips. hydrogen bonds are broken. - RNA polymerase binds. - Free mRNA nucleotides complementary base pair with exposed DNA nucleotides (only on the template strand). - RNA polymerase seals the new backbone of mRNA (catalyses the formation of new phosphodiester bonds between adjacent nucleotides). - When RNA polymerase reaches a stop-codon it detaches and pre-mRNA is formed. - DNA strands rejoin. |
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Describe post-transcriptional modification of pre-mRNA (splicing). |
- Pre-mRNA copies whole section of a gene including non-coding regions. - Introns are removed (spliced) from the mRNA by enzymes. - Functional exons are joined together. - Mature mRNA molecules leave nucleus via a nuclear pore. |
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Where does splicing not occur? |
During prokaryotic protein synthesis as prokaryotic genes do not contain introns. |
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Describe translation. |
- Ribosome attaches to mRNA at start codon (AUG). - tRNA is activated in the cytoplasm by binding to a specific amino acid (requires ATP). - tRNA brings specific amino acids to the ribosome. - tRNA with complementary anticodon, sequence base pair with mRNA codons. - Ribosome moves along the mRNA bringing together two tRNAs at any one time. - Two amino acids on the tRNA are joined by a peptide bond (requires ATP). - tRNA is released from the amino acid and is recycled. - Synthesis continues until the ribosome reaches a stop codon, polypeptide chain then detaches and is folded into a functional protein. |
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Define gene mutation. |
A chemical change to one or more DNA bases in a coding sequence within a gene. |
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Define chromosomal mutation. |
A change to the DNA within a chromosome (eg, a missing chromosome, an extra chromosome). |
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Define mutagenic agents (mutagens). |
Substances capable of chemically altering the DNA base sequence. |
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Give examples of mutagens. |
- UV light - Ionising radiation (eg, X-rays, CT scans) - Benzene - Bromine - Sodium azide - Nitrosamines |
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How many different types of amino acids are there? |
20 |
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How many different types of codons are there? |
64 |
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Define degenerate. |
Same amino acid is coded by several different codons. |
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What is a nonsense mutation? |
Occurs if the base change results in the formation of 1 of 3 stop codons that mark the end of the polypeptide chain. |
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What would be the effect of a nonsense mutation? |
Polypeptide sequence would be terminated and protein would be shorter - it may lose essential function (eg, if a specific binding site or active site is affected). |
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What is a mis-sense mutation? |
Occurs when the base change results in a different amino acid in a sequence is being coded for. |
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What would be the effect of a mis-sense mutation? |
Changes to the primary sequence of amino acids changes the tertiary structure of the protein which could affect the function of the protein (eg, active site may affect the ability of a substrate to bind - fewer E-S complexes form). |
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What is a silent mutation? |
Occurs when the substituted base, although different, still codes for the same amino acid. |
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What would be the effect of a silent mutation? |
Same amino-acid coded for - no effect on the protein. |
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What is a frame-shift mutation? |
When a nucleotide is lost/added from/to the normal DNA sequence. The reading frame of three letters of a code has been shifted by one letter). |
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What is the effect of a frameshift mutation? |
May result on a different amino acid sequence in a polypeptide. This has more of an impact if the mutation occurs near to the start of the transcribed sequence. |
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What is produced through meiosis? |
Gametes: - genetically different, - half the number of chromosomes. |
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How does meiosis produce genetic variation? |
- Recombination of sister chromatids after crossing over during prophase of meiosis 1. - Produces new combinations of alleles. - Independent segregation of homologous chromosomes during anaphase of meiosis 1. - Produces gametes with randomly assorted chromosome combination. |
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Define a diploid number of chromosomes. |
Full set of chromosomes. |
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Define haploid number of chromosomes. |
Half set of chromosomes. |
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What are the differences between mitosis and meiosis? |
- Meiosis produces gametes; mitosis produces other body cells. - Meiosis produces cells with haploid (n) chromosomes; mitosis produces cells with diploid (2n) chromosomes. - Meiosis produces cells that are genetically different; mitosis produces cells that are genetically identical. - Meiosis involves the separation of homologous pairs; mitosis doesn't have homologous pairs of chromosomes. |
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What are the similarities between meiosis and mitosis? |
- Both go through prophase, anaphase, metaphase and telophase. - Both involve the attachment of spindle fibres to the centromere. - Meiosis is the same as mitosis (both involve the separation of sister chromatids). |
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Describe the chromosome movement during meiosis. |
- In first division, chromosomes pair up. - Equivalent portions of chromatids may cross over. - Homologous pairs separate during meiosis 1, with 1 chromosome from each pair going into the daughter cells. - This happens randomly (independent segregation). - Chromatids move apart during anaphase of the second meiotic division. - After second division, four haploid daughter cells (n) are formed with half the amount of DNA/chromosomes as the parent cell. |
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Other than meiosis, how else is variation caused? |
- Random mutations in DNA due to a chance event producing a useful protein. - Fusion of gametes during sexual reproduction. |
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Define genetic diversity. |
Number of different alleles of genes in a population or gene pool. |
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Define gene pool. |
The sum of all the alleles of all the genes of all the organisms of one species in one place at a particular time. |
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Describe natural selection. |
- Variation exists in the original population caused by random mutation. - This confers a selective (survival) advantage on some individuals who are better adapted to their environment. - These are more likely to survive and breed to pass on the alleles to their offspring (differential reproductive success). - The frequency of this allele in the gene pool increases over time. |
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Define speciation. |
When selection is taken to an extreme level where changes become so apparent that a new species forms. The organisms are no longer able to interbreed to produce fertile offspring. |
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Describe directional selection. |
- Occurs when environmental conditions change. - The mean characteristic or feature of a species changes as one extreme is selected against the other extreme. - The standard deviation (variation) of the population remains the same. (Eg antibiotic resistant in bacteria). |
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Describe stabilising selection. |
- Occurs when environmental conditions do NOT change over time (instead they remain stable). - More individuals survive that have the mean characteristics or feature. - Standard deviation decreases as there is less variation decreases as there is less variation within the population. - Both extremes are selected against (mean individuals are selected for). (Eg human birth weights). |
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Define species. |
Group of similar organisms that can breed to produce fertile offspring. |
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Define taxonomy. |
The study of these groups and their positions in a hierarchical order. |
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Define hierarchy. |
Groups contained within large groups which do not OVERLAP. |
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Describe the hierarchy of classification (taxonomy). |
Kingdom - Phylum - Class - Order - Family - Genus - Species. |
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Define phylogeny. |
The study of evolutionary relationships. |
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Why is courtship behaviour necessary? |
- Allows animals to recognise a member of their own species (to allow production of fertile offspring). - Allows animals to create a pair bond to raise offspring successfully. - Allows animals to recognise the opposite gender. - Stimulates release of gametes. - To synchronise mating (maximise gametes fusing). |
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How can we compare genetic diversity to classify relationships between organisms? |
- Comparing DNA sequences in specific genes. - Comparing mRNA sequences. - Comparing the amino acid sequences of specific proteins (eg haemoglobin or immunoglobulins). The more similar the sequences, the more closely related the species are. |
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Define biodiversity. |
The number and variety of living organisms in a particular area. |
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Define species biodiversity. |
Number of species in a given area. |
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Define genetic biodiversity. |
Variety of genes or alleles of individuals in one species. |
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Define ecosystem biodiversity. |
Range of habitats in one area. |
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Define species richness. |
This is a measure of the number of different species in a community (all the organisms living and interacting in a particular place or habitat). |
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What does index of diversity measure? |
- Number of different species in a given area. - Proportion of the community that is made up of an individual species. |
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Explain why it may be more useful to calculate the index of diversity than to record only the number of species present. |
Measure the number of individuals pf each species and the number of species; some species may be present by only in small numbers. |
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Describe the impact of agriculture. |
- Farmers may select species for particular characteristics that make them more productive. - Pesticides may be used to exclude species that compete with farmed species. - Monoculture (large areas of land are given over to a single type of crop/animal). |
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Describe the impact of deforestation. |
- Loss of habitats - Extinction of species - Potential loss of medicinal plants - Lower biodiversity - Lower biomass and productivity - Desertification |
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What is the impact of agriculture on species diversity? |
Decreases species diversity. So the number of species and their genetic variety of their alleles is limited. |
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How can conservation reverse the effects of agriculture? |
Increases species diversity by protecting a particular habitat to encourage more species to grow and live there. |
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How can you remove chance from sampling procedures? |
- Use a large sample size as it is more representative. - Statistically analyse the data collected. |
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How can remove bias from a sample? |
Random sample. |
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How would you conduct a random sample with quadrats? |
1. Set up a grid with co-ordinates, 2. Select co-ordinates using a random number generator, 3. Take several samples to calculate a mean. |
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What shape graph does a normal distribution curve create? |
Bell shape |
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What does it mean if there is overlap in the ranges of the means of two or more samples? |
The results are NOT significantly different (results are probably due to chance). |
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What does it mean if there is no overlap in the ranges of the means of two or more samples? |
The results are significantly different and therefore the results are not due to chance. |
