Flashcards · 9201 · Topic 2

Bioenergetics flashcards

60 cards on Topic 2, subtopics 3.2.1 to 3.2.6. Pick a subtopic or study them all.

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3.2.1 Photosynthesis

Photosynthesis: word and balanced symbol equations: carbon dioxide + water → glucose + oxygen (light energy) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Where is light absorbed, and where do the raw materials come from?: Light is absorbed by chlorophyll in the chloroplasts (some plant cells and algae). Carbon dioxide comes from the air; water comes from the soil. Oxygen is the by-product.
Five ways a plant uses the glucose it makes: Respiration; insoluble starch for storage; fat or oil for storage (e.g. in seeds); cellulose to strengthen cell walls; protein for growth and repair (needs nitrate ions from the soil).
Limiting factor: The factor in shortest supply, which sets the maximum rate at that moment. The three are low temperature, shortage of carbon dioxide and shortage of light, and they interact.
How do you name the limiting factor from a graph?: Where the line is still rising, the x-axis factor is limiting. Where it is flat, another factor is limiting: compare a second line or name the factor held constant, and quote two numbers.
At light 4, the rate is 10 at 15 °C but 16 at 25 °C. What limits the rate at 15 °C?: Temperature. Warming raises the rate by (16 − 10) ÷ 10 × 100 = 60%, so light was not limiting at 15 °C.
When is it worth heating, lighting or adding CO₂ to a greenhouse?: Only when that factor is limiting and the value of the extra yield is greater than the cost. Net gain = extra yield × price − extra cost.
Required practical on the rate of photosynthesis: variables: Independent: one of lamp distance, CO₂ supply (hydrogencarbonate) or temperature. Dependent: bubbles or volume of oxygen per minute. Control: the other two factors, the same pondweed, the same time per setting.
Pondweed gives 60, 64 and 62 bubbles in 4 minutes. Mean rate?: Mean = (60 + 64 + 62) ÷ 3 = 62 bubbles. Rate = 62 ÷ 4 = 15.5 bubbles per minute.
Photosynthesis vs respiration: Photosynthesis: in cells with chloroplasts, only when there is light; takes in CO₂ and water; absorbs energy. Respiration: in all living cells, all the time; takes in glucose and oxygen; releases energy.

3.2.2 Exchange and transport in plants

Stomata and guard cells: A stoma is a pore in the leaf surface through which gases diffuse (CO₂ in, oxygen out). A pair of guard cells changes shape to open or close it, helping to control water loss.
Root hair: A tiny extension of a root cell that increases the surface area for absorbing water and mineral ions.
A leaf is 6 cm × 2 cm × 0.1 cm. Surface area to volume ratio?: SA = 2(12 + 0.6 + 0.2) = 25.6 cm². V = 1.2 cm³. Ratio = 21.3 : 1. Thin, flat shapes give high ratios.
How do internal air spaces help a leaf?: They let gases diffuse to the cells inside the leaf, giving a large internal surface area and a short diffusion path.
When is water lost fastest from leaves?: In hot, dry and windy conditions. Water vapour is lost mainly from the leaves, mostly through the stomata.
Wilting, and how stomata closing prevents it: Wilting is loss of firmness when water leaves cells faster than it is replaced. Water leaving the guard cells closes the stomata, which prevents wilting but reduces CO₂ uptake.
Transpiration stream vs translocation: Transpiration stream: movement of water from the roots, through the xylem, out of the leaves. Translocation: movement of dissolved sugars in the phloem from the leaves to the rest of the plant.
Xylem vs phloem: structure: Xylem: hollow dead tubes with strong walls containing lignin, so water flows and the walls resist collapse. Phloem: living sieve tubes with pores, and companion cells that supply energy.
Where do xylem and phloem carry substances?: Xylem: water and mineral ions from the roots to the stem and leaves. Phloem: dissolved sugars from the leaves to growing regions and storage organs.

3.2.3 Circulation in humans

The four chambers of the heart, and the order in which they contract: Right and left atria, right and left ventricles. Blood enters the atria; the atria contract and force blood into the ventricles; the ventricles contract and force blood out. Valves keep the flow one way.
Route of blood through the heart and lungs, from the vena cava: Vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body organs.
Double circulation, and why the left ventricle wall is thicker: Two circuits: heart to lungs and back, and heart to all other organs and back, so blood is pumped again after the lungs. The left ventricle pumps blood around the whole body; the right only to the nearby lungs.
Arteries, veins and capillaries: Artery: thick wall with muscle and elastic fibres, carries blood away from the heart. Vein: thinner wall, often has valves to prevent back-flow. Capillary: very thin wall, very narrow; substances pass in and out through the wall.
What does plasma carry?: Carbon dioxide (organs to lungs), soluble products of digestion (small intestine to organs) and urea (liver to kidneys).
How do red blood cells carry oxygen?: In the lungs: haemoglobin + oxygen → oxyhaemoglobin. In other organs: oxyhaemoglobin → haemoglobin + oxygen. Red cells have no nucleus.
How does blood clot?: At a wound, platelets help start a series of enzyme-controlled reactions. Soluble fibrinogen is changed to fibrin, which forms a network of fibres that traps blood cells, forming a clot.
Artificial pacemaker and stent: what each treats: Artificial pacemaker: an electrical device that corrects an irregular heart rate (the natural pacemaker cells are in the right atrium). Stent: holds open a coronary artery narrowed by fatty layers in coronary heart disease.
Biological vs mechanical replacement heart valves: Biological (from humans or other mammals): usually less need for lifelong anticoagulant drugs, but can wear out. Mechanical: can last a long time, but blood may clot on it, so anticoagulants are often needed.
Why can a transplanted organ be rejected, and how is rejection reduced?: The recipient's antibodies attack antigens on the donor organ that they do not recognise as their own. Reduce it by choosing a donor with a similar tissue type and giving immune-suppressing drugs.
ABO blood groups: antigens and plasma antibodies: A: antigen A, anti-B. B: antigen B, anti-A. AB: A and B, no antibodies. O: no antigens, anti-A and anti-B. Group O is the universal donor; AB can receive from all groups.
A pulse of 31 beats is counted in 20 s. Heart rate?: 31 ÷ 20 × 60 = 93 beats per minute.

3.2.4 Digestion

Why is food digested, and what are starch, protein and fat broken into?: They are insoluble, so they are broken into soluble substances that can be absorbed into the blood in the wall of the small intestine. Starch → sugars; protein → amino acids; fat → fatty acids and glycerol.
What happens in the large intestine?: Much of the water mixed with the food is absorbed into the blood. The indigestible food left makes up the bulk of the faeces, which leave through the anus.
Enzymes, and what high temperature does to them: Large proteins that act as biological catalysts, increasing the rate of reactions without being used up. High temperature denatures them: the active site changes shape, so the substrate cannot fit. Cooling does not reverse it.
Where are digestive enzymes made, and where do they act?: They are made in specialised cells in glands and the gut lining, then pass out of the cells into the gut to meet the food.
Amylase: where made, where it acts, and the reaction: Made in the salivary glands, pancreas and small intestine; acts in the mouth and small intestine; starch → sugars.
Protease and lipase: where made and the reactions: Protease: stomach, pancreas, small intestine; protein → amino acids. Lipase: pancreas, small intestine; lipid → fatty acids and glycerol.
Hydrochloric acid and bile: where made and their jobs: Hydrochloric acid (stomach): acid conditions in which stomach enzymes work best. Bile (made in the liver, stored in the gall bladder): neutralises the acid, giving alkaline conditions for small intestine enzymes. Neither is an enzyme.
Emulsification: Bile breaks large fat drops into small droplets. The volume is unchanged but the surface area increases, so lipase has more surface to act on.
Required practical: starch is digested in a mean of 60 s. Rate, and how it compares with 30 s?: Rate = 1000 ÷ 60 = 16.7 (arbitrary units). At 30 s, 1000 ÷ 30 = 33.3, twice as fast. Use a water bath for temperature and buffer solutions for pH.
Uses of enzymes from microorganisms: Protease and lipase: biological washing powders. Lactase: lactose-free milk. Pectinase: fruit juice extraction. Amylase: breaking starch into sugars in food manufacture.
Denatured vs slowed enzyme: Denatured: the shape of the active site is lost, permanently (high temperature, extreme pH). Slowed: at low temperature there are fewer successful collisions, and it is reversible.

3.2.5 Breathing

Function and position of the breathing system: It moves air in and out, so oxygen passes into the blood and carbon dioxide passes out by diffusion. The lungs are in the thorax, protected by the ribcage and separated from the abdomen by the diaphragm.
Path of air into the lungs: Trachea → bronchi → bronchioles → alveoli.
Inhaling: what happens: Intercostal muscles contract and pull the ribcage up; the diaphragm contracts and flattens; thorax volume increases; pressure falls below that of the outside air; air enters.
Exhaling: what happens: Intercostal muscles relax and the ribcage moves down; the diaphragm relaxes and becomes domed; thorax volume decreases; pressure rises above that of the outside air; air leaves.
How are the alveoli adapted for gas exchange?: They provide a very large surface area, richly supplied with blood capillaries, with thin walls, so gases diffuse readily into and out of the blood.
Negative pressure vs positive pressure ventilators: Negative pressure: pressure is lowered around the chest in a sealed chamber, so air is drawn into the lungs. Positive pressure: air is pushed into the airway above outside pressure, so it is forced into the lungs.
Why can a ventilator save a life?: When spontaneous breathing stops through disease or injury, oxygen cannot reach the blood. A ventilator moves air into the lungs, so oxygen can still diffuse into the blood and carbon dioxide out.
Breathing vs respiration: Breathing is moving air into and out of the lungs. Respiration is the chemical reactions in cells that transfer energy from glucose.

3.2.6 Respiration

Aerobic respiration: word and balanced symbol equations: glucose + oxygen → carbon dioxide + water C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O It happens continuously in plants and animals; most of the reactions occur inside mitochondria.
What is the energy from respiration used for?: Building larger molecules from smaller ones; muscle contraction (animals); keeping a steady body temperature in cold surroundings (mammals and birds); building sugars, nitrates and other nutrients into amino acids and proteins (plants).
How does the body respond to exercise?: Heart rate rises, so more blood flows to the muscles; breathing rate and depth rise; muscle glycogen is converted back to glucose. More glucose and oxygen are supplied and carbon dioxide is removed faster.
Anaerobic respiration in muscle: word and symbol equations: glucose → lactic acid C₆H₁₂O₆ → 2C₃H₆O₃ Much less energy is transferred than in aerobic respiration.
Anaerobic respiration in plants and yeast: word and symbol equations: glucose → ethanol + carbon dioxide C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Oxygen debt: The oxygen needed after exercise to oxidise the lactic acid that built up to carbon dioxide and water. It is repaid after exercise, which is why you keep breathing hard; it is not a store of oxygen.
Why do muscles become fatigued?: During long vigorous activity lactic acid builds up in the muscles and they stop contracting efficiently. Blood flowing through the muscles eventually removes the lactic acid.
Why is less energy transferred in anaerobic respiration?: Glucose is only partly broken down, to lactic acid. The lactic acid still holds energy, which is only released when it is later oxidised using oxygen.
Resting pulse is 72 bpm and 126 bpm after exercise. Percentage increase?: (126 − 72) ÷ 72 × 100 = 54 ÷ 72 × 100 = 75%.
Required practical on exercise: method and controls: Record resting pulse and breathing rate; exercise for a set time at a set intensity; measure straight afterwards and at regular intervals until back to resting. Same person, same step, same timing; count for 15 s and multiply by 4.