B1.2 Photosynthesis and Plants - Investigating Photosynthesis Flashcards
Photosynthesis
A process where plants and algae synthesise glucose from carbon dioxide and water, using light energy from the sun
Glucose (C6H12O6)
The main chemical product of photosynthesis that has many different uses in a plant, including respiration
Insoluble starch
A complex carbohydrate made from the products of photosynthesis and used for storage, will not be present if photosynthesis has not occurred
Chloroplast
An organelle found in plant and algae cells where photosynthesis occurs
Chlorphyll
A green pigment in plants that absorbs light energy used to carry out photosynthesis
Light intensity effect
Photosynthesis rate increases as more energy is available, up to a certain point
Carbon dioxide concentration effect
Photosynthesis rate increases as more carbon is available to synthesise glucose, up to a certain point
Photosynthetic rate
The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose
Testing leaves for starch
Plant leaves can be tested for the presence of starch using iodine solution, after the leaf has been intensely heated and submerged in ethanol
Adding a leaf to boiling water during a starch test
Kills the leaf to prevent any further reactions that might break down starch or affect its presence
Adding hot ethanol during a starch test
Causes the leaf to become decoloured, so iodine results can be easily visualised
Washing the leaf before examination during a starch test
Softens the leaf
Risk of starch tests
Water baths can be made using Bunsen burners, however ethanol is also used to remove pigments from the plant, ethanol is very flammable and should be kept away from flames
Iodine test for starch
Iodine solution will change colour from orange to blue-black in the presence of starch
Starch results for plants kept in light conditions
Plants store glucose as starch in the leaves, plants that are kept in the light will photosynthesise and store starch so their leaves will change colour to blue-black
Starch results for plants kept in the dark
Plants in the dark will be unable to photosynthesise meaning glucose will not be made and stored as starch, so iodine will not change colour
Starch results for variegated leaves
Leaves that are variegated have patches absent of chlorophyll, these regions will not cause iodine to change colour as photosynthesis cannot occur here
Dependent variable
The variable that is measured, in this case the presence of starch or colour of iodine test
Independent variable
The variable that is changed such as the type or source of leaf, leaves could be tested that have been kept in the light or in the dark, leaves could also be tested that are either variegated or not variegated
Control variables
The variables that are kept the same, such as the species of plant, the availability of water, temperature, soil mineral or pH content, the amount of time that leaves have been submerged in ethanol or hot water
Subjectivity
A person may have bias presumptions about the results and therefore record false positives or the iodine colour of the leaf may be difficult to visualise, results should be compared and collated to reduce the effect of bias
