6. Plant Nutrition Flashcards
Define Photosynthesis
Photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
Word Equation for Photosynthesis
Symbol for Photosynthesis Equation
How plants get the materials they need
Refer Image
The Products of Photosynthesis
Refer Image
2 Uses of carbohydrates
- Used in respiration to produce energy
- Used in structural component like cellulose for cell walls
Starch Test for Leaves
A leaf is dropped in boiling water to kill and break down the cell walls
The leaf is left for 5-10 minutes in hot ethanol in a boiling tube. This removes the chlorophyll so colour changes from iodine can be seen more clearly
The leaf is dipped in boiling water to soften it
The leaf is spread out on a white tile and covered with iodine solution
In a green leaf, the entire leaf will turn blue-black as photosynthesis is occuring in all areas of the leaf
This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white)
The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black
The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored
The Need for Light in Photosynthesis
The same procedure as above can be used to investigate if light is needed for photosynthesis
Before starting the experiment the plant needs to be destarched by placing in a dark cupboard for 24 hours
This ensures that any starch already present in the leaves will be used up and will not affect the results of the experiment
Following destarching, a leave of the plant can be partially covered with aluminium foil and the plant placed in sunlight for a day
The leaf can then be removed and tested for starch using iodine
The area of the leaf that was covered with aluminium foil will remain orange-brown as it did not receive any sunlight and could not photosynthesise, while the area exposed to sunlight will turn blue-black
This proves that light is necessary for photosynthesis and the production of starch
The Need for Carbon Dioxide in Photosynthesis
Destarch a plant
Tie a clear bag containing sodium hydroxide, which will absorb carbon dioxide from the surrounding air, around one leaf
Tie a clear bag containing water (control experiment), which will not absorb carbon dioxide from the surrounding air, around another leaf
Place the plant in bright light for several hours.
Test both leaves for starch using iodine
The leaf from the bag containing sodium hydroxide will remain orange-brown as it could not photosynthesise due to lack of carbon dioxide
The leaf from the control bag containing water should turn blue-black as it had all necessary requirements for photosynthesis
Investigating the Rate of Photosynthesis
- The plants usually used are Elodea or Camboba – types of pondweed
- As photosynthesis occurs, oxygen gas produced is released
- As the plant is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed
- The number of bubbles produced over a minute can be counted to record the rate
- The more bubbles produced per minute, the faster the rate of photosynthesis
- A more accurate version of this experiment is to collect the oxygen released in a test tube inverted over the top of the pondweed over a longer period of time and then measure the volume of oxygen collected
Investigating the effect of changing temperature
Change in carbon dioxide concentration
What is a Limiting Factor?
If a plant is given unlimited sunlight, carbon dioxide, and water and is at a warm temperature, the limit on the rate (speed) at which it can photosynthesise is its own ability to absorb these materials and make them react
However, most often plants do not have unlimited supplies of their raw materials so their rate of photosynthesis is limited by whatever factor is the lowest at that time
Limiting factors can be defined as something present in the environment in such short supply that it restricts life processes.
3 main factors which limit the rate of photosynthesis
CLT
Temperature
Light intensity
Carbon dioxide concentration
Although water is necessary for photosynthesis, it is not considered a limiting factor as the amount needed is relatively small compared to the amount of water transpired from a plant so there is hardly ever a situation where there is not enough water for photosynthesis
Temperature as Limiting Factor
As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes
However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases
Light intensity as Limiting Factor
The more light a plant receives, the faster the rate of photosynthesis
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Carbon Dioxide Concentration as Limiting Factor
- Carbon dioxide is one of the raw materials required for photosynthesis
- This means the more carbon dioxide that is present, the faster the reaction can occur
- This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Effect of Light on Net Gas Exchange
- Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration
- Plants also photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis
- At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide
During the day, especially when the sun is bright, plants are photosynthesising at a faster rate than they are respiring, so there is a net intake of carbon dioxide and a net output of oxygen
Colour indicators for carbon dioxide concentration
Refer image
Effect of Light on Leaves - using hydrogencarbonate indicator
Cross-section of a leaf
Leaf Structure and Description
Adaptation of Leaf for Photosynthesis
Effects of Mineral Ion Deficiencies (picture)
