Topic 2 notes – Organisms and energy • • • •
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AEROBIC RESPIRATION All cells in the body need energy - this energy is released in a process known as ‘respiration’ Cells that are more active need more energy - e.g during exercise, muscles contract to cause movement – this requires a lot of energy from respiration Aerobic respiration – respiration in the presence of oxygen: o Equation: glucose + oxygen à carbon dioxide + water (+ energy released) o The energy released during aerobic respiration can then be used by cells o Aerobic respiration takes place inside organelles called mitochondria Delivering glucose and oxygen to respiring cells: In humans, glucose and oxygen needed for aerobic respiration are carried around the body by the blood The blood also carries waste carbon dioxide (product of aerobic respiration) Glucose, oxygen and carbon dioxide move between respiring cells and tiny (one cell thick) blood vessels called capillaries by a process called ‘diffusion’… o Diffusion is the movement of particles from an area of high concentration to an area of lower concentration § i.e particles diffuse down a concentration gradient o Respiring cells produce carbon dioxideàcarbon dioxide concentration is higher in respiring cells than in the bloodàcarbon dioxide diffuses down its concentration gradient into the blood o Respiring cells use up oxygen and glucoseàconcentrations of glucose and oxygen are higher in the blood than in the respiring cellsàglucose and oxygen diffuse down their concentration gradients into the respiring cells Gas exchange: Tiny air sacs called ‘alveoli’ in the lungs are surrounded by capillaries Alveoli are the sites of ‘gas exchange’:
o As we discussed above, in the body… § oxygen diffuses from the blood into cells for use in respiration § waste carbon dioxide produced during respiration diffuses out of respiring cells and into the blood o àblood arriving at the alveoli has a high concentration of carbon dioxide and a low concentration of oxygen…à:
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The concentration of carbon dioxide is higher in the blood than the alveoliàcarbon dioxide moves into the alveoli by diffusion v Carbon dioxide is then removed from the body when we breathe out (‘exhale’) § As we breathe in through the lungs, oxygen enters alveoli… concentration of oxygen in the alveoli is higher than in the blood àoxygen moves into the blood by diffusion o àblood leaving the alveoli has a high concentration of oxygen and a low concentration of carbon dioxide… § The oxygen is then transported in the bloodstream (in ‘red blood cells’) to cells for use in respiration...and process repeats… EXERCISE AND ANAEROBIC RESPIRATION The amount of blood pumped out by the heart in one minute is called the ‘cardiac output’ The cardiac output depends on the…: o Heart rate – beats per minute o Stroke volume – volume of blood pumped out of the heart each beat o The higher the stroke volume and the heart rate, the higher the cardiac output § àequation: cardiac output = stroke volume x heart rate During exercise… o Muscles need more energyàthey need more oxygen from respiration o à1. the heart rate and stroke volume increase § àcardiac output is increased – i.e more blood reaches respiring tissues faster o However, this wouldn’t be much use if the blood reaching the respiring tissues didn’t contain enough oxygen o à2. breathing rate also increases… § àmore oxygen enters alveoliàmore oxygen diffuses into the blood o So more oxygen reaches muscle cells fasteràfaster rate of aerobic respiration in muscle cellsàmore energy released During intense exercise: o even increasing the heart rate and the breathing rate isn’t enough to supply oxygen to muscle cells quickly enough o àanaerobic respiration starts to happen (alongside aerobic respiration) inside muscle cells Anaerobic respiration breaks down glucose without using oxygen…the waste product lactic acid is produced: o Equation: glucose à lactic acid (+ energy released) o The energy released by anaerobic respiration is less than the energy released by aerobic respiration Breaking down the lactic acid: The waste lactic acid produced during anaerobic respiration is toxicàmust be broken down as soon as possible Lactic acid can be broken down by oxygen into carbon dioxide and water… o àafter exercise has finished, increased oxygen is needed so that the lactic acid can be broken down (the lactic acid can’t be broken down during exercise because there isn’t enough oxygen available - it is being used in aerobic respiration)
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o This requirement for additional oxygen after exercise is called ‘excess post-exercise oxygen consumption’ (EPOC) o Note: the increased oxygen available after exercise can also be used for other processes in cells (e.g cell repair) The extra oxygen needed after exercise is obtained by keeping the breathing rate and the heart rate high for a few minutes after exercise (i.e until the oxygen has broken down all the lactic acid produced into carbon dioxide and water) The time taken for the heart rate to return to normal (resting) after exercise is the ‘recovery time’ - the faster the recovery time, the fitter the person PHOTOSYNTHESIS Plants (like animals) have mitochondria in their cellsàthey respireàthey need a supply of glucose In animals/humans, glucose needed for respiration is obtained from the breakdown of starch Unlike animals/humans, plants can make their own glucose by a process called photosynthesis Equation for photosynthesis:
Photosynthesis takes place inside plant cell organelles called chloroplasts: o Chloroplasts contain a green substance called ‘chlorophyll’ o Chlorophyll absorbs sunlight, transferring the light energy into stored chemical energy in glucose o àchloroplasts and chlorophyll are essential for photosynthesis – without them, photosynthesis cannot occur Leaf adaptations: The leaf is the main plant organ in which photosynthesis occurs Leaves are adapted for photosynthesis: o They have chloroplasts containing a substance called chlorophyll that absorbs light energy from the sun o They are broad and flatàhave a large surface area – this helps the leaves absorb as much light energy as possible o On the underside of leaves are microscopic pores called stomata – these are the sites of gas exchange § Air spaces inside the leaf give cells a large surface area to volume ratio – this makes gas exchange through the stomata more efficient Gas exchange in the stomata: Carbon dioxide from the atmosphere diffuses into the leaf through the stomata o The carbon dioxide is then taken up by cells in the leaf for use in photosynthesis Oxygen produced in photosynthesis diffuses from the inside of the leaf into the atmosphere through the stomata Water produced during respiration can evaporate from cells inside a leaf – the water vapour can then diffuse out of the leaf through the stomata Stomata open when it’s light and close when it’s dark:
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o When it’s light, stomata openàallow gas exchangeàphotosynthesis can take place (if stomata were closed, carbon dioxide could not enter the leaf àphotosynthesis would not take place) o When it’s dark, stomata close for two reasons: § 1. Photosynthesis can’t take placeàgas exchange is not necessary § 2. Plants still respire in the dark, producing water vapour… v Water vapour diffuses out of the leaf through the stomata v àstomata close at night to prevent loss of water vapour Note: o Water needed for photosynthesis does NOT enter through stomata in the leaf - it is taken up in the roots and then transported to the leaf in xylem vessels (see ‘water transport’ section below) LIMITING FACTORS The higher the rate of photosynthesis, the more glucose that is produced - glucose is needed by plants for growth and for respiration Factors affecting the rate of photosynthesis: o Concentration of carbon dioxide o Water o Light intensity o Temperature (reactions in photosynthesis are catalysed by enzymes àtemperature can also affect the rate of photosynthesis) In any process that is affected by several factors, the maximum rate at which the process can occur is controlled by the factor that is in the shortest supply – the factor in the shortest supply is the ‘limiting factor’ o I.e the limiting factor is the factor that is responsible for slowing down the rate of photosynthesis E.g: o If a plant has lots of carbon dioxide, lots of water, is grown at the right temperature but in dim light, it will photosynthesise slowly o Increasing the concentration of carbon dioxide, or giving the plant more water or increasing the temperature will not increase the rate of photosynthesis o Only increasing the amount of light will increase the rate of photosynthesis…àin this example, the limiting factor is light (intensity) Interpreting graphs:
o At point x: § Increasing light intensity increases the rate of photosynthesis… § àinitially light intensity is the limiting factor o At point y:
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Increasing light intensity doesn’t increase the rate of photosynthesis any further… àanother factor (i.e temperature, CO2 concentration or water) must be limiting the rate of photosynthesis at this point
o At point A – increasing the temperature increases the rate of photosynthesis (the high temperature trace at the same light intensity has a much higher rate of photosynthesis) § àthe limiting factor at this point is temperature o At point B – increasing the light intensity increases the rate of photosynthesis § àthe limiting factor at this point is light intensity o At point C – increasing temperature or light intensity doesn’t increase the rate of photosynthesis any further § àthe limiting factor at this point could either be the amount of carbon dioxide or water available to the plant WATER TRANSPORT Roots don’t just anchor plants to the ground – they also take up water and mineral salts from the soil ‘Root hair cells’ are present in roots – they have two main adaptations that help them take up water and minerals from the soil: o 1. They have long, thin extensions that reach into the surrounding soil o 2. They have a large surface area Water is taken up by osmosis: Water enters the root hair cells by osmosis Osmosis is the movement of water molecules from an area where there is a higher concentration of water molecules to an area where there is a lower concentration of water molecules, through a partially permeable membrane o A partially permeable membrane is a membrane that only lets certain substances pass through it E.g:
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o Water moves from a region of higher water concentration to a region of lower water concentration until ‘equilibrium’ is reached (i.e until the water concentration is the same on both sides of the partially permeable membrane) o Sucrose molecules can’t move because they are too big to fit through the gaps in the partially permeable membrane Dissolved minerals can be taken up by active transport: The concentration of minerals dissolved in soil water is very low compared to the concentration of minerals in the plant àIn order for minerals dissolved in soil water to be taken up into the roots, they must be absorbed against their concentration gradient – i.e from an area of lower concentration to an area of higher concentration Absorbing particles against a concentration gradient is called ‘active transport’ Active transport requires energy – the energy comes from respiration Transporting substances round the plant – xylem and phloem: Once water and minerals have entered the root cells, they need to get to all the plant’s tissues… o Minerals help plants grow o Water needs to be transported to the leaves for use in photosynthesis Xylem vessels: o transport water and dissolved mineral salts o also give support to the plant The glucose made in the leaves during photosynthesis is converted to sucrose and then transported to other parts of the plant by phloem vessels Note: glucose can also be stored in the form of starch How do water and minerals travel up xylem vessels against gravity? As discussed above, water produced during respiration can evaporate from cells inside a leaf and then diffuse out of the leaf through the stomata… o The loss of water from the leaf pulls water and dissolved minerals up through xylem vessels (against the force of gravity) § This movement of water and dissolved minerals up through xylem vessels from the roots is called ‘transpiration’ o Increased rate of evaporationàfaster loss of water through stomata àincreased rate of transpiration § I.e the rate of evaporation determines the rate of transpiration § àfactors that increase the rate of evaporation will also increase the rate of transpiration - e.g on a warm and windy day, the rate of transpiration will be greater Note: transpiration can be monitored experimentally using a ‘potometer’ ORGANISMS AND THEIR ENVIRONMENT When ecologists study the biodiversity (i.e the different species of animals and plants) of living organisms in a habitat (the place where an organism lives), they want to know: o Where particular organisms are found (their ‘distribution’) in the habitat o How many individuals of each species (the ‘population size’) there are in a habitat It takes too long to study the whole habitatàecologists usually look at just a small portion of an area – this is called ‘sampling’
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Random sampling - every point within an area has an equal chance of being selectedàthe sample is likely to be representative of the whole area Sampling techniques: Pooter - used to catch small invertebrates: o It has two tubes which are connected to a container o You suck on one of the tubes and any small invertebrates are sucked up into the container through the other tube (called the ‘inlet tube’) Sweep net – this is used in areas of long grass to catch some of the organisms present Pond net – can be used to sample aquatic (i.e water) habitats Pitfall traps: o Useful for trapping small animals such as spiders, beetles and woodlice o They can be set up and left overnightàpossible to catch nocturnal animals (i.e animals that are only active at night) Quadrats - these are square frames, typically used to sample the number (population) of different plant species in a habitat: o The quadrat is placed at random locations (e.g by throwing) – at each location, the number of plants of each type within the quadrat are counted o For spreading plants (e.g clover), the % of the quadrat area covered by the plant is estimated o The mean number of a particular type of plant found in each quadrat can be used to estimate the population size of that plant in the area Environmental factors: Different conditions can sometimes be found within a habitat (e.g at different points in a field) – this can affect the distribution of organisms: o E.g understanding how light intensity varies in a habitat might help to explain the distribution of different species of plants… § Some species of plant may need lots of lightàyou will only find them in the part of the field that receives the most sunlight § Other species of plants may be able to survive with less lightàyou might find some in darker, more sheltered parts of the field Other factors such as temperature or soil/water pH may also have an effect on the distribution of organisms in a habitat When investigating changes in a habitat caused by one environmental factor, it’s sometimes useful to carry out ‘systematic sampling’ along a line: o Using systematic sampling makes it easier to spot patterns…àmakes it easier to see the effect that the environmental factor is having on the distribution of organisms in a habitat o Systematic sampling can be done by placing quadrats at regular intervals along a straight line