Bioenergetics
- Created by: Natasha02
- Created on: 24-04-18 17:17
Photosynthesis and limiting factors
- Photosynthesis uses energy to change carbon dioxide and water into glucose and oxygen
- It takes place in chloroplasts in green plant cells - they contain pigments like chlorophyll that absorb light
- Energy is transferred to the chloroplasts from the environment by light
- Photosynthesis is endothermic - this means energy is transferred from the environment in the process
- Word equation is carbon dioxide + water ---- glucose + oxygen
- Symbol equation is 6CO2 + 6H20 ---- C6H12O6 + 6O2
Plants using glucose
- For respiration - This transfers energy from glucose which enables plant to convert the rest of the glucose into various other useful substances
- Making cellulose - Glucose is converted into cellulose for making strong plant cell walls
- Making amino acids - Glucose is combined with nitrate ions to make amino acids, which sre then made into proteins
- Stored as oils or fats - Glucose is turned into lipids for storing and seeds
- Stored as startch - Glucose is turned into startch and stored in roots, stems and leaves, ready for use when photosynthesis isn't happening, like in the winter. Starch is insoluble which makes it much better for storing than glucose - a cell with lots of glucose in would draw in loads of water and swell up
Limiting factors
- Rate of photosynthesis is affected by intensity of light, conc of co2 and temp
- Any of these three factors can become the limiting factor - this just means stopping it from happeing any factor
- These factors have a combined effect on the rate of photosynthesis but which factor is limiting at a particular time depends on the environmental conditions:
- at night light is limiting factor
- in winter it's often temp
- if it is warm and bright enough, the amount of co2, is usually limiting
- chlorophyll can also be a limiting factor of photosynthesis
The amount of chlorophyll in a plant can be effected by disease or environmental stress, such as a lack of nutrients. These factors can cause chloroplasts to become damaged or to not make enough chlorophyll. This means the rate of photosynthesis is reduced bc they can't absorb as much light
Graphs for photosynthesis
Not enough light slows down rate of photosynthesis:
- Light provides the energy needed for photosynthesis
- As the light level is raised, the rate of photosynthesis increases steadily but only til certain point
- Beyond that, it won't make any difference - as light intensity the rate will no longer increase. This is bc it'll be either temp of co2 level which is now limiting factor, not light
- In the lab you can change the light intensity by moving a lamp closer to or further away from your plant
- But if you just plot the rate of photosynthesis against "distance of lamp from the plant" you get a weird shaped graph. To get a graph like the one above you either need to measure the light intensity at the plant using a light meter or maths
Graphs for photosynthesis II
Too little carbon dioxide slows it down:
- CO2 is one of the raw materials needed for photosynthesis
- As with light intensity, the amount of CO2 will only increase the rate of photosynthesis up to a point. After this graph flattens out - as the amount of CO2 increases, the rate no longer increases. This shows that CO2 is no longer the limiting factor
- As long as light and CO2 are in plentiful supply then the factor limiting photosynthesis must be temp
Graphs for photosynthesis III
Temp has to be just right:
- Usually, if the temperature is the limiting factor it's because it's too low - the enzymes needed for photosynthesis work more slowly at low temp
- But if the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be damaged
- This happens at about 45 degrees (which is pretty hot for outdoors, although greenhouses can get that hot if not careful)
Rate of photosynthesis
- In the experiment, when the lamp is moved away from the pondweed the amount of lightb that reaches the pondweed decreases
- You can say that as the distance increases, the light intensity decreases. Distance and light intensity are inversely proportional to each other
Equation = light intensity (proportion to symbol) 1 divided by distance squared
- The inverse square law means that if you halve the distance, the light intensity will be 4 times greater and if you third the distance the light intensity will be 9 times greater. Likewise if you double the distance, the light intensity will be four times smaller.
Artificial conditons
- The most common way to create the ideal environment for plants is to grow them in a greenhouse
- Greenhouses help to trap the suns heat, and make sure that the temp doesn't become limiting. In winter a farmer or gardener might use a heater as well to keep the temp at the ideal level. In summer it could get too hot, so they might use shades and ventilation to cool things down
- Light is always needed for photosynthesis, so commercial farmers often suppy artifical light after the sun goes down to give plants more photosynthesis time
- Farmers and gardeners can also increase the level of carbon dioxide in the greenhouse. E.g. by using a paraffin heater to heat the greenhouse. As the paraffin burns, it makes carbon dioxide as a by-product
- Keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases. The farmer can add fertilisers to the soil as well, to provide all the minerals needed for healthly growth
- Costs money but increases photosynthesis. Plants grow much faster and a decent crop can be harvested more often and sell to get money.
Respiration and metabolism
Respiration involves many reactions. All respiraration transfers the energy that the cell needs to do most things - this energy is used for all living processes
- Respiration is the process of transferring energy from the breakdown of glucose - and it goes on in every cell in body continuously
- It happens in plants too, all living things respire. It's how they transfer energy from their food to their cells
- Respiration is exothermic - and it transfers energy to the environment
Here are 3 examples of how organisms use the energy transferred by respiration:
- To build up larger molecules from smaller ones like proteins to amino acids
- In animals it's used to allow the muscle to contract (so they can move about)
- In mammals and birds the energy is used to keep their body temp steady in colder surroundings.
Metabolism
Metabolism is all the chem reactions in an organisms:
- In a cell there are lots of chem reactions hapepening all the time, which are controlled by enzymes
- Many of these reactions are linked together to form bigger reactions
reactant --- product --- product --- product
In some reactions, larger molecules are made from smaller ones
- Lots of small glucose molecules are joined together in reactions to form starch (storage molecule in a plant cell) glycogen (storage molecule in animal cells) and cellulose
- Lipid molecules are each made from one molecule of glycerol and three fatty acids
- Glucose is combined with nitrate ions to make amino acids which are then made into proteins
Metabolism II
In other reactions, larger molecules are broken down into smaller ones e.g.
- Glucose is broken down into respiration. Respiration trasnfers energy to power all the reactions in the body that make molecules
- Excess protein is broken down in a reaction to produce urea, which is then secreted though urine
- The sum total of all reactions that happen in a cell or the body is called metabolism
Aerobic respiration
- Aerboic respiration is respiration using oxygen- it's the most efficent way to transfer enery from glucose
- Aerobic respiration goes on all the time in plants and animals
- Most of the reactions in aerboic respiration happen inside the mitochondria
- Word equation - glucose + oxygen ---- carbon dioxide + water
- Symbol equation - C6H12O6 + 6O2 --- 6CO2 + 6H2O
Anaerobic respiration
- When vigorous excercise and your body can't supply enough oxygen to your muscles, they start doing anaerobic respiration
- Anaerobic just means without oxygen. It's the incomplete breakdown of glucose, making lactic acid
- Word equation - glucose ---- lactic acid
- Anaerobic respiration does not transfer nearly as much energy as aerboic respiration. This is because glucose isn't fully oxidised
- So, anaerobic respiration is only useful in emergancies e.g. during excercise when it allows you to keep on using your muscles for a while longer
Anaerobic respiration in yeast
- Plants and yeast cells can respire w/o oxygen too, but they produce ethanol and carbon dioxide instead of lactic acid
- Word equation - glucose --- ethanol + carbon dioxide
- Anaerobic respiration in yeast cells is called fermentation
- In the food and drink industry, fermentation by yeast is of great value bc it's used to make bread and alchoholic drinks e.g. beer and wine
- In bread-making, it's the carbon dioxide for fermentation that makes bread rise
- In beer and wine-making, it's fermentation process that produces alcohol
Exercise effect on respiration
- Muscles need energy from respiration to contract. When you excersise, some of your muscles contract more frequently than normal so you need more energy which comes from increased respiration
- The increase on respiration in your cells means you need to get them more oxygen
- Your breathing rate and breath volume increase to get more oxygen into the blood, and your heart rate increases to get this oxygenated blood around the body faster. This removes CO2 more quickly at the same time
- When really vigorous excercise is done your body can't supply oxygen to your muscles quickly enough, so they start respiring anaaerobically
- This is not the best way to transfer energy from glucose because lactic acid builds up in muscles which gets painful
- Long periods of excercise also cause muscle fatigue - the muscles get tired and then stop contracting efficently
Oxygen debt
- After resorting to anaerobic respiration, when you stop exercising you'll have an oxygen debt
- An oxygen debt is the amount of extra oxygen your body needs to react with the build up of lactic acid and remove it from cells. Oxygen reacts with lactic acid to form harmless co2 and water
- You have to 'repay' the oxygen that you didn't get from your muscles in time, because your lungs, heart and blood couldn't keep up with demand earlier
- This means you have to keep breathing hard for a while after you stop, to get more oxygen into your blood, which is transported to the muscle cells
- Your body also has another way of coping with the high level of lactic acid, - the blood that enters your muscles transports the lactic acid to the liver. In the liver the lactic acid is converted back to glucose
Investigate effect of exercise on body
- You can measure breathing rate by counting breaths and the heart rate by taking the pulse
E.g. you could take your pulse after:
- sitting down for 5 mins
- then after 5 mins of gentle walking
- then after 5 mins of slow jogging
- then after 5 mins of running
Your pulse rate will increase the more intense the exercise is, as your body needs to get more oxygen to the muscles and take more carbon dioxide away from the muscles
- To reduce the effect of any random errors on your results, do it as a group and plot the average pulse rate for each exercise
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