C1.3 - photosynthesis

Question 1

limiting factor

Answer 1

factor that limits the rate of reaction and it nearest to its minimum

Question 2

photosynthesis?

Answer 2

production of carbon compounds in chloroplasts within cells using light energy

Question 3

photolysis

Answer 3

breakdown of a molecule in the presence of light and use of water in the conversion of light energy to chemical energy during photosynthesis

Question 4

what energy transformation occurs during photosynthesis?

Answer 4

light energy –> chemical energy when carbon compounds are produced in photosynthesis

Question 5

why is light important in photosynthesis?

Answer 5

without light energy, plants cannot convert CO2 into glucose
- absorbed by chlorophyll which is a green pigment found in chloroplasts

Question 6

why is energy transformation needed?

Answer 6

supplies most of the chemical energy needed for life processes in ecosystems - e.g) glucose is respired to release ATP to support metabolic reactions in living organisms
- stored in covalent bonds

Question 7

what organisms carry out photosynthesis?

Answer 7

plants, algae and cyanobacteria

Question 8

where do plants obtain CO2?

Answer 8

absorbed through the air in stomata or from water

Question 9

how is glucose used by plants?

Answer 9

• forms carbohydrates or other carbon compounds
• nitrates are used to produce nitrogen-containing compounds such as amino acids, nucleotides and ATP
• phosphates are used to produce phosphate-containing compounds such as phospholipids, nucleotides and ATP

Question 10

what is the by product of photosynthesis?

Answer 10

oxygen - used in aerobic respiration and is released as a waste gas

Question 11

what is the process of photosynthesis?

Answer 11

1. photolysis occurs - splitting of water to produce oxygen using light (light dependent reaction)
2. hydrogen ions are released, which reduce carbon dioxide which is fixed when it is converted into glucose (light independent reaction)
3. glucose is converted to a wide range of organic compounds

Question 12

what happens when a photosynthetic pigment absorbs light?

Answer 12

when a pigment molecule absorbs light, some if its electrons become excited and can be used to make chemical bonds to transfer light energy to chemical energy

Question 13

what does exciting an electron require?

Answer 13

requires a specific amount of energy to raise it to a higher energy level and the amount of energy depends on the pigment molecule so different wavelengths of light are required

Question 14

what wavelengths of light are absorbed the most and least by chlorophyll?

Answer 14

most - red and blue
least - green (it is reflected)

Question 15

what is an absorption spectrum?

Answer 15

a spectrum that indicates the different wavelengths of light absorbed by each pigment , causing them to have different peaks and a wider action spectrum

Question 16

what is an action spectrum?

Answer 16

a spectrum that shows the relative amount of photosynthesis occurring at each wavelength of light

Question 17

what are the similarities and differences between an absorption and action spectrum?

Answer 17

similarity - both have a horizontal axis of wavelength or colour and have similar shapes
difference - action shows the relative rate of photosynthesis and absorption shows which wavelengths of light are absorbed by each pigment

Question 18

how can we determine rates of photosynthesis for varying wavelengths?

Answer 18

recording the rate of oxygen production or carbon dioxide intake allows direct measurement of photosynthesis rate, but must have corrected rates of cell respiration (consistent)
- if the independent variable is wavelength of light, the rate of photosynthesis can be plotted using an action spectrum

Question 19

what happens during TLC if pigments are not soluble?

Answer 19

pigments that are not soluble in the extraction solvent are not added to the dots at the origin and do not move, so they are absent from the chromatogram

Question 20

what are characteristics of pigments with a higher Rf value?

Answer 20

• more soluble in the solvent
• often smaller
• have a lower affinity with the solid phase material on the TLC plate.

Question 21

what is the process of separating photosynthetic pigments by chromatography?

Answer 21

1. extract photosynthetic pigments by crushing leaves in a suitable solvent
2. small concentrated dots of extract are made towards the bottom of the TLC plate
3. the solvent moves up the TLC carrying the pigments
   - pigments move at different rates depending on their solubility and separate
4. measure the distances travelled by the solvent font and each pigment
5. calculate the Rf value: distance moved by pigment / distance moved by solvent front
6. identify the pigments by comparing Rf values and using pigments colours

Question 22

what are the 3 limiting factors of photosynthesis?

Answer 22

• temperature
• carbon dioxide concentration
• light intensity

Question 23

how is carbon dioxide concentration a limiting factor for photosynthesis?

Answer 23

• higher carbon dioxide concentration increases the rate of photosynthesis
• this is because carbon dioxide is a reactant and is fixed to form glucose and other organic molecules
• at high concentrations of carbon dioxide, the rate of photosynthesis plateaus and another factor has become limiting

Question 24

how is light intensity a limiting factor for photoysnthesis?

Answer 24

• higher light intensity increases the rate of photosynthesis.
• this is because light is the source of energy for photosynthesis, with light energy being converted to chemical energy.
• at high intensities of light the rate of photosynthesis plateaus, because another factor has become limiting.

Question 25

how is temperature a limiting factor of photosynthesis?

Answer 25

• Photosynthesis is a metabolic reaction and therefore controlled by enzymes.
• Higher temperatures increase enzyme activity, because there is more molecular kinetic energy, so faster molecular motion, leading to more frequent enzyme-substrate collisions.
• However, if the temperature exceeds the optimum for the essential enzymes of photosynthesis, they denature and the rate of photosynthesis falls.

Question 26

what are hypotheses?

Answer 26

provisional explanations that require repeated testing
- during scientific research, hypotheses can be either bases on theories and then tested in an experiment or be based on evidence from an experiment that has already been carried out

Question 27

what are possible methods to investigate the effects of limiting factors on photosynthesis?

Answer 27

• counting bubbles or measuring the volume of oxygen releases by aquatic plants per unit time
• using pH indicators or sensors, with aquatic plants or algae, to measure the decrease in acidity over time, as plants consume carbon dioxide from the water
• using electronic sensors to measure the concentration of carbon dioxide or oxygen, in aquatic settings and closely-controlled terrestrial settings

Question 28

what are possible control variables used to investigate the effects of limiting factors on photosynthesis?

Answer 28

• factor that is not the independent variable
• plant sample (species and mass)
• water availability

Question 29

what are possible independent variables used to investigate the effects of limiting factors on photosynthesis?

Answer 29

• carbon dioxide concentration
• temperature
• light intensity

Question 30

what are enclosed greenhouse experiments?

Answer 30

growing plants within a greenhouse whose atmosphere has added carbon dioxide to increase photosynthesis rate and plant growth

Question 31

what are free-air carbon dioxide enrichment experiments?

Answer 31

studies in natural settings, where the conditions cannot be controlled as they can in laboratories or greenhouses