B1.2 Photosynthesis and Plants - Investigating Photosynthesis

Question 1

Photosynthesis

Answer 1

A process where plants and algae synthesise glucose from carbon dioxide and water, using light energy from the sun

Question 2

Glucose (C6H12O6)

Answer 2

The main chemical product of photosynthesis that has many different uses in a plant, including respiration

Question 3

Insoluble starch

Answer 3

A complex carbohydrate made from the products of photosynthesis and used for storage, will not be present if photosynthesis has not occurred

Question 4

Chloroplast

Answer 4

An organelle found in plant and algae cells where photosynthesis occurs

Question 5

Chlorphyll

Answer 5

A green pigment in plants that absorbs light energy used to carry out photosynthesis

Question 6

Light intensity effect

Answer 6

Photosynthesis rate increases as more energy is available, up to a certain point

Question 7

Carbon dioxide concentration effect

Answer 7

Photosynthesis rate increases as more carbon is available to synthesise glucose, up to a certain point

Question 8

Photosynthetic rate

Answer 8

The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose

Question 9

Testing leaves for starch

Answer 9

Plant leaves can be tested for the presence of starch using iodine solution, after the leaf has been intensely heated and submerged in ethanol

Question 10

Adding a leaf to boiling water during a starch test

Answer 10

Kills the leaf to prevent any further reactions that might break down starch or affect its presence

Question 11

Adding hot ethanol during a starch test

Answer 11

Causes the leaf to become decoloured, so iodine results can be easily visualised

Question 12

Washing the leaf before examination during a starch test

Answer 12

Softens the leaf

Question 13

Risk of starch tests

Answer 13

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

Question 14

Iodine test for starch

Answer 14

Iodine solution will change colour from orange to blue-black in the presence of starch

Question 15

Starch results for plants kept in light conditions

Answer 15

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

Question 16

Starch results for plants kept in the dark

Answer 16

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

Question 17

Starch results for variegated leaves

Answer 17

Leaves that are variegated have patches absent of chlorophyll, these regions will not cause iodine to change colour as photosynthesis cannot occur here

Question 18

Dependent variable

Answer 18

The variable that is measured, in this case the presence of starch or colour of iodine test

Question 19

Independent variable

Answer 19

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

Question 20

Control variables

Answer 20

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

Question 21

Subjectivity

Answer 21

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