+ Photosynthesis Limiting Factors Noadswood Science, 2012

+ Photosynthesis Limiting Factors To know and understand the limiting factors of photosynthesis Thursday, August 13, 2015

+ Vocal Plants Is it the case that talking to your plants can help them grow?! Photosynthesis can be reduced by a variety of factors, including Temperature Carbon dioxide concentration Light intensity Plants also need water, however if a plant is so short of water that it becomes the limiting factor the plant will be in serious trouble If the environmental conditions are such that CO 2 is a limiting factor then talking to the plant may well help it grow (as you are supplying it with CO 2, a by-product of respiration)!

+ Experiment 1. Take 2 similar pieces of elodea 2. Place 1 piece of elodea in a test tube and submerge with hydrogen carbonate indicator 3. Place 1 piece of black paper around the test tube, ensuring the top is sealed (use the rubber band) 4. Repeat this experiment, this time placing 1 piece of tracing paper around the test tube 5. Finally set up a control – a test tube with only hydrogen carbonate indicator and no elodea in it or paper around it! Leave test tubes in a rack, by the window for >20 mins…

+ Test Hydrogen carbonate indicator reacts when carbon dioxide is present: - In normal atmospheric conditions, the indicator is orange/red When there is lots of carbon dioxide the indicator is yellow When there is not much carbon dioxide the indicator is purple So we can set up an experiment, changing the light intensity, and then measure the hydrogen carbonate indicator to see how the CO 2 levels vary…

+ Graph Using the secondary data, produce a graph for the time taken to fill the container, when the distance the light source was from the plant changed Distance apart between lamp & beaker (cm) Time taken for end of funnel to fill with oxygen (seconds)

+ Graph

+ Green Plants Green plants absorb light energy using chlorophyll in their leaves – they use it to react carbon dioxide with water to make glucose (used for respiration, or converted into starch and stored) Plants also need mineral ions, including nitrate and magnesium, for healthy growth – they suffer from poor growth in conditions where mineral ions are deficient

+ Photosynthesis Photosynthesis is the chemical change which happens in the leaves of green plants It is the first step towards making food - not just for plants but ultimately every animal on the planet Photosynthesis takes place in leaf cells – these contain chloroplasts, which are tiny organelles containing chlorophyll which absorbs light energy for the reaction to take place

+ Photosynthesis What is photosynthesis? Plants make their own food via photosynthesis (chlorophyll in the leaves) with the energy coming from the Sun carbon dioxide + water  glucose + oxygen 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 chlorophyll light energy

+ Limiting Factors What limiting factors affect photosynthesis? Photosynthesis can be reduced by a variety of factors, including Temperature Carbon dioxide concentration Light intensity

+ Limiting Factors Plants also need water, however if a plant is so short of water that it becomes the limiting factor the plant will be in serious trouble Environmental conditions influence which factor(s) limit the rate of photosynthesis (light limits it at night; temperature often limits it in winter; and when it is warm and bright CO 2 usually limits it)

+ Limiting Factors Light intensity – without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and CO 2 Increasing the light intensity will boost the speed of photosynthesis Draw a sketch graph of light intensity against photosynthesis rate…

+ Limiting Factors CO 2 – sometimes photosynthesis is limited by the concentration of CO 2 in the air Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient CO 2 Draw a sketch graph of CO 2 against photosynthesis rate…

+ Limiting Factors Temperature – if it gets too cold, the rate of photosynthesis will decrease Plants cannot photosynthesise if it gets too hot and enzymes within the chlorophyll begin to denature above 45 o C Draw a sketch graph of temperature against photosynthesis rate…

+ Greenhouse Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too

+ Limiting