B2.3 Photosynthesis

How does the temperature impact the rate of photosynthesis?

Usually is the temperature is the limiting factor it's because it's too low - the enzymes needed for photosynthesis work more slowly at low temperatures. 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°C. Experimentally, the best way to control the temperature of the flask is to put it in a water bath.

What's the equation for photosynthesis?

carbon dioxide + water → glucose + oxygen CO₂ + H₂O → C₆H₁₂O₆ + O₂

How do plants use glucose?

1) For respiration. Plants manufacture glucose in their leaves. They then use some of the glucose for respiration. This releases energy which enables them to convert the rest of the glucose into various other useful substances, which they can use to build new cells and grow. To produce some of these substances they also need to gather a few minerals from the soil. 2) Making cell walls. Glucose is converted into cellulose for making strong cell walls especially in a rapidly growing plant. 3) Making proteins. Glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into proteins. 4) Stored in seeds. Glucose is turned into lipids (fats and oils) for storing in seeds. Sunflower seeds, for example, contain a lot of oil - we get cooking oil and margarine from them. Seeds also store starch. 5) Stored as starch. Glucose is turned into starch 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. Potato and parsnip plants store a lot of starch underground over the winter so a new plant can grow from it the following spring. We eat swollen storage organs.

How do artificially create the ideal conditions for farming?

1) The most common way to artificially create the ideal environment for plants is to grow them in a greenhouse. 2) Greenhouses trap the Sun's heat, and make sure that the temperature doesn't become limiting. In winter a farmer or gardener might use a heater as well to keep the temperature at the ideal level. In summer it could get too hot, so they might use shades and ventilation to cool things down. 3) Light is always needed for photosynthesis, so commercial farmers often supply artificial light after the Sun goes down to give their plants more quality photosynthesis time. 4) Farmers and gardeners can also increase the level of carbon dioxide in the greenhouse. A fairly common way is to use a paraffin heater to heat the greenhouse. As the paraffin burns, it makes carbon dioxide as a by-product. 5) 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 healthy growth. 6) Sorting all this out costs money - but if the farmer can help the conditions just right for photosynthesis, the plants will grow much faster and a decent crop can be harvested much more often, which can then be sold. It's important that a farmer supplies just the right amount of heat, light, etc. - enough to make the plants grow well, but not more than the plants need, as this would just be wasting money.

What are the limiting factors of photosynthesis?

Any these factors can become the limiting factor. This just means that it's stopping photosynthesis from happening any faster. Which factor is limiting at a particular time depends on the environment conditions: -at night it's pretty obvious that light is the limiting factor -in winter it's often the temperature -if it's warm enough and bright enough, the amount of CO₂ is usually limiting.

How does too little carbon dioxide slow the rate of photosynthesis 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 the graph flattens out showing that CO₂ is no longer the limiting factor. As long as light ans CO₂ are in plentiful supply then the factor limiting photosynthesis must be temperature. There are loads of different ways to control the amount of CO₂. One way is to dissolve different amounts of sodium hydrogencarbonate in the water, which gives off CO₂.

How does not enough light slow down the rate of photosynthesis?

Light provides the energy needed for photosynthesis. As the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain point. Beyond that, it won't make any difference because then it'll be either by the temperature or the CO₂ level which is the limiting factor. In the lab you can change the light intensity by moving a lamp closer to or further away from your plant.

How does photosynthesis produce glucose?

Photosynthesis is the process that produces 'food' in plants and algae. The 'food' it produces is glucose. Photosynthesis happens inside the chloroplasts. Chloroplasts contain a green substance called chlorophyll, which absorbs sunlight and uses its energy to convert carbon dioxide (from the air) and water (from the soil) into glucose. Oxygen is also produced as a by-product. Photosynthesis happens in the leaves of all green plants - this is largely what the leaves are for.