B8 Photosynthesis Flashcards
Basics of Photosynthesis
-plants are autotrophs-this means that they can make their own food using light, water and carbon dioxide.
-this is why they are called producers in food chains
- photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplast by light. The leaves are plant are where most photosynthesis takes place,in specialised mesophyll cells which are packed with chloroplasts containing chlorophyll to absorb as much light energy as possible.
-the sugars are produced by photosynthesis are used to make all the substance a plants needs, as wellnas being used in respiration to release energy.
Formula for photosynthesis
Carbon dioxide + water —–> (light)—-> glucose + oxygen
6CO2 + 6H2O —–> (light) —–> C6H12O6 + 6O2
Light energy is harnessed by the chloroplasts. The light energy is used to convert carbon dioxide and water into glucose. This essentially converts light energy into chemical energy in the form of glucose. Oxygen is released as a by-product. Because this requires an input of energy,it is classed as an endothermic reaction.
Leaf adaptations
-most leaves are broad, giving them a large surface area for light to fall on.
-most leaves are thin so diffusion distances for gases are short.
-they contain chlorophyll in the chloroplasts to absorb light.
-they have veins, which bring plenty of water in the xylem to cells of the leaves and remove the products of photosynthesis in the phloem.
-they have air spaces that allow CO2 to get to cells and O2 to leave by diffusion.
-They have guard cells that open and close the stomata to regulate gas exchange
The rate of photosynthesis-light
Between points a and b as light intensity increases so does the rate of photosynthesis. The rate constantly increases at a high speed before slowing. This can be seen in points b to c as the rate of photosynthesis remains constant even though light intensity is continouing to increase.
This happens as the rate of photosynthesis increases at first due to light energy is needed for photosynthesis to occur. Light energy is a limiting factor between points a and b. From points b to c light energy is no longer a limiting factor. The rate of photosynthesis is being limited by temperature and carbon dioxide concentration
The rate of photosynthesis- Temperature
-the temperature of the environment affects how much kinetic energy all particles have-so temperature affects the speed at which carbon dioxide and water move through plants.
-the lower the temperature, the less kinetic energy particles have, resulting in fewer successful collisions occurring over a period of time.
-increasing temperature increases the kinetic energy of particles,increasing the likelihood of collisions between reactants and enzymes which results in formations of products
-at higher temperatures, however, enzymes that control the process of photosynthesis can be denatured which reduces the overall rate
The rate of photosynthesis-carbin dioxide concentration
-Carbon dioxide is one of the raw materials required for photosynthesis
- this means that the more carbon dioxide that is present, the faster the reaction can occur.
- This trend will continue until some other factor for photosynthesis (light intensity and temperature) prevents the rate from increasing further because it is now short of supply.
The rate of photosynthesis-chlorophyll
-the number of chloroplasts will affect the rate of photosynthesis
- the more chloroplasts a plant has, the faster the rate of photosynthesis.
-amount of chlorophyll can be affected by: diseases, lack of nutrients,loss of leaves
How does carbon dioxide and water reach the the cells they are photosynthesizing
Carbon dioixde- The CO2 diffuses down a concentration gradient into the stomata which will open to allow the CO2 into the spongy mesophyll layer which then diffuse into the air spaces which then diffuse the CO2 into the pallisade cells which contain lots of chloroplasts which are needed for photosynthesis and its the main site if photosynthesis. The paliside cells use the CO2 for photosynthesis.
Water-The water enters through the root hair cells from the soil which have a large surface area to allow osmosis into the roots of the plant. The water is then taken by osmosis in the xylem cell through the transpiration stream into the vascular bundle which is then used in the palisde cell for photosynthesis
Interactions of limitng factors
-Rate of photosynthesis is affected by the intensity of light, the volume of carbon dioxide and temperature. They all need to be at right level to allow plant to photosynthesise as quickly as possible.
-If any of these factors are too high or low, it will become the limitng factor
For example:
-The rate of photosynthesis increases with the light intensity, temperature and carbon dioxide.
All three experiments level off when light intensity is no longer the limiting factor.
1) Top line, has the highest temperature and concentration of carbon dioxide so the rate of photosynthesis is much higher
2) the concentration of carbon dioxide is limiting factor and light intensity is non longer the limiting factor
Examples of limitng factors
-At night there’s much less light than there is during the day, so light intensity is the limiting factor at night
-In winter its usually cold, so low temperature is often the limiting factor
-if It’s warm and bright enough, the amount of CO2 is usually limiting
Cellulose for strength,starch for storage
-energy transferred in respiration may be used to build smaller molecules into bigger molecules. E.g they use glucose build up to become complex carbohydrates such as cellulose in order to strengthen their walls.
-plants convert some of the glucose into starch to be stored. Glucose is soluble in water. If stored in plant cells, it could affect the way water moves into and out of the cells by osmosis. Lots of glucose can cause affect on water balance of whole plant
Starch is insoluble in water. Has no effect on water balance of the plants so plants can store large amounts of starch in their cells. It is the main energy store in plants:
-starch is stored in the cells of leaves. It provides energy store when it is dark or when light levels are low
-Starch is kept in special storage areas of plant. E.g to help them survive through winter they produce tubers and bulbs to store it in.
Use of glucose for making nitrates, proteins and carniverous plants
In plants, glucose combines with nitrate ions (which are absorbed in soil) to make amino acids. These amino acids are built up into proteins to be used in plant cells e.g including in enzymes. Uses energy for respiration.
Very few plants can survive well if soil they are growing in is low in minerals. E.g bogs are wet and their peaty soul has very few nutrients in it so hard for plants to live.
Using glucose to make lipids
Plants and algae use some of of the glucose from photosynthesis and energy transferred from respiration to build up fats and oils. These may be used in the cells as energy stores.
Storage of glucose
-plants can convert some of the glucose they produce in lipids (fats and oils). They use fats and oils as energy store in seeds and seeds provide food for new plant to respire as it germinates
- Plants can convert glucose into starch. Glucose is stored as starch so it’s ready for use when photosynthesis isn’t happening as much, like in winter. In plants, starch is stored in roots,stems,seeds and leaves.
-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
Photosynthesis practical
Aim: investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed
You will:
-measure the volume lf oxygen produced by the pondweed as the light intensity changes as the light source is moved.
-measure and calculate rates of photosynthesis
-extract and interpret graphs of photosynthesis rate involving one limiting factor
Appartus:
- lamp
-glass tanked filled with water
-thermometer to monitor temperature
-inverted boiling tube
-oxygen bubbles produced as photosynthesisnoccurs
-water with sodium hydrogen carbonate
- imverted funnel
-photosynthesising pondweed
-ruler
Method:
-pondweed is placed in a test tube full water with sodium hydrogen carbonate. The tope is sealed with a bung.
-A source of white light is placed at a specific distance from the pondweed
- you should then leave the pondweed for a couple minutes to adjust to the new light intensity before starting experiment
- when ready, the pondweed is left to photosynthesise for a set amount of time
-Record the number of bubbles observed in three minutes
-The experiment is repeated twice with the light source at same distance and mean bubbles produced is calculated. Then whole experiment is repeated with the light source at different distances from pondweed
Variables we control:
–temeprature
-sodium hydroxide concentration
-natural light
-the amount of water
Independent variable- light intensity
Dependent variable- the amount of bubbles produced
Improvements to exeperiment
-use a gas syringe to collect the volume of gas produced
-repeated the experiment at least twice for each distance and calculate the mean number of bubbles
-use a glass tank between lamp and plant to prevent heating of plant or use LED bulb that releases very little heat energy
Conclusion
At beginning of investigation, the rate of photosynthesis in water plant increases as the light is moved closer to plant, which increases light intensity.
-this tells us that light is acting as the limiting factor. When moved further away from plant, rate of photosynthesis falls, shown by a slowing down in stream of bubbles produced.
-If light intensity is moved closer again the stream of bubbles become faster, showing an increased rate of photosynthesis
-eventually, no matter how close light is, the rate of photosynthesis stays the same. At this point, no longer light is limiting the rate of photosynthesis
The inverse square law
-in experiment when lamp is moved away from the pondweed, the amount of light that reaches the pondweed decreases. You can say that as the distance increases, the light intensity decreases.
-Distance and light are inversely proportional to each other.
-However, it turns out that light intensity decreases in proportion to the square of distance-inverse square law
Light intensity proportional 1/d*2
This means that if you have the distance, the light intensity will be four times greater and if you have a third the distance, the light intensity will be 9 times greater.
Growing in greenhouse
-commercial horticulturists will grow their plants in a greenhouse
-this means they are able to control as many of the limiting factors of photosynthesis as possible
- limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis whilst still maintaining profit.
-keeping plants in greenhouse has associated costs, but the increased yield of crop and fact that crop can be harvested more frequently, means farmer will make more money
-the levels of heat,light,water, carbon dioxide and nutrients are carefully controlled so only the smallest amounts needed are used so that farmers are not wasting money
-e.g spending money on increasing the concentration of CO2 beyond a point when some other factors limit the rate of photosynthesis is a waste
Greenhouses use:
-artificial light for winter/darker hours
-shades removed from ceiling to allow maximum light
-ventilation prevents plants getting too hot
-heater burns paraffin and produces CO2
-watering system to make sure plants stay well watered
-keeping plants in greenhouse makes it easier to keep pests and diseases and add fertiliser
-greenhouse traps the sun heat so temperature doesn’t li it photosynthesis
