Chapter 11 - Photosynthesis

Question 1

What does organic mean in biochemistry?

Answer 1

Contains carbon

Question 2

What does inorganic mean in biochemistry?

Answer 2

Does not contain carbon

Question 3

Define coenzyme

Answer 3

Molecule that helps enzyme to work by transferring other molecules. (NAD, NADP and FAD in respiration and photosynthesis)

Question 4

Define phosphorylation

Answer 4

Adding a phosphate

Question 5

Define photophosphorylation

Answer 5

Using light energy to add a phosphate

Question 6

Define photolysis

Answer 6

Using light energy to split a molecule

Question 7

Define ETC

Answer 7

When electrons flow through proteins in a series of redox reactions to transfer energy in a cell membrane

Question 8

What occurs in photosynthesis and where?

Answer 8

Light dependant = Thylakoid membrane

Light independant = Stroma

Question 9

Summarise structure of chloroplast

Answer 9

Double membrane with grana (discs of thylakoid) joined by lamellae surrounded by stroma

Question 10

What adaptations do thylakoids have for photosynthesis?

Answer 10

• High SA for photosynthesis

- Contain chlorophyll for light absorbance

Question 11

Summarise the light dependant reaction

Answer 11

• Light strikes PSII and excites e- to a higher energy level
• e- released down ETC, PSII becomes ionised, and e- releases energy to proton pumps and then reaches PSI
• H+ builds up in thylakoid and diffuses down gradient through ATP synthase causing photophosphorylation
• Light strikes PSI causing e- to leave membrane into stroma and bond with H+ and NADP to produce NADPH to maintain gradient
• Light strikes water and splits water into 2H+, 2e- and 0.5O2

Question 12

Summarise the light independent reaction

Answer 12

• Uses products of light dependant to form organic compounds
• RuBP carboxylated by rubisco to form 2 GP
• GP reduced into TP by one NADPH and one ATP
• TP the converted into useful organic substances such as glucose or reformed into RuBP by ATP

Question 13

What occurs if no light is present in photosynthesis?

Answer 13

• RuBP decreases as converted into GP but not reformed from TP as no ATP
• GP increases

Question 14

What occurs if no CO2 is present in photosynthesis?

Answer 14

• RuBP increases as reformed from TP but not converted into GP as no CO2
• GP decreases

Question 15

Summarise the effect of light intensity on photosynthesis and suggest how to combat it as a limiting factor

Answer 15

• Higher light provides higher rate of LDR as more energy
• Light must be right wavelength for chlorophyll pigments
• Use lighting at night and greenhouse to allow light to pass

Question 16

Summarise the effect of CO2 concentration on photosynthesis and suggest how to combat it as a limiting factor

Answer 16

• CO2 limiting during the day
• Optimum at 0.4%
• Greater than optimum has negative effect as
• Burn fossil fuel in greenhouse to increase CO2

Question 17

Summarise the effect of temperature on photosynthesis and suggest how to combat it as a limiting factor

Answer 17

• Photosynthesis controlled by enzymes
• Increase temp increase reaction until after optimum
• Higher temperature causes more transpiration so less water and closed stomata so less CO2
• Burn fuel to increase temperature
• Greenhouse traps warm air
• Thermostat to control temperature

Question 18

What are the two purposes of the light-dependant reaction?

Answer 18

• To add inorganic phosphate to ADP creating ATP

- TO split water into H+ ions (protons) and OH- ions

Question 19

How are chloroplasts adapted for the light-dependant reaction?

Answer 19

• Membranes provide large SA for attachment of chlorphyll, electron carriers and enzymes
• Proteins hold grana to maximise light absorption
• Grana membranes have ATP synthase and are selectively permeable to maintain proton gradient
• Chloroplasts contain DNA and ribosomes to manufacture own products

Question 20

How is the chloroplast adapted for the light-independent reaction?

Answer 20

• Fluid of stroma contains enzymes and membrane bound so high concentration of required substances
• Stroma surrounds grana so products of light dependant reaction diffuse readily
• Contains DNA and ribosomes to manufacture proteins

Question 21

How are leaves adapted for photosynthesis

Answer 21

• Large SA for sunlight
• Leaves that minimise overlapping
• Thin so diffusion distance short
• Transparent cuticle and epidermis to let light through to mesophyll
• Long mesophyll with chloroplasts to collect sunlight
• Stomatas for gas exchange near mesophyll for short diffusion pathway
• Stomata open and close according to LI
• Air spaces for diffusion
• Xylem for water and phloem for sugars