key area 3.2 - photosynthesis

Question 1

light

Answer 1

• form of electromagnetic radiation which travels in waves
• distance between 2 crests on a wave is called wavelength and is measured in nanometers
• absorbed by photosynthetic pigments for photolysis and to generate ATP

Question 2

three fates of light striking a leaf

Answer 2

• absorption
• reflection
• transmission

Question 3

pigments in the leaf

Answer 3

• chlorophyll a
• chlorophyll b
• carotenoids
• all absorb different wavelengths of light
• chlorophyll is the most important

Question 4

caretonoids

Answer 4

• accessory pigments in the leaf which allow plants to carry out photosynthesis in a wider range of wavelengths
• they pass energy they capture onto chlorophyll

Question 5

photosynthesis definition

Answer 5

• process by which green plants absorb and convert light energy into chemical energy in carbohydrates

Question 6

aborbption spectrum

Answer 6

• shows the wavelengths of light absorbed by each pigment

Question 7

action spectrum

Answer 7

• graph which shows the rate of photosynthesis at different wavelengths of light

Question 8

light dependant stage of photosynthesis

Answer 8

• photosynthetic pigments absorb light energy, exciting electrons in the pigment molecules
• each pigment has a different structure so therefore requires different wavelengths for the electrons to become excited
• high energy electrons move through a series of electron carrier molecules attached to membranes of chloroplasts, releasing their energy, which is then used by ATP synthase to generate ATP
• some energy is also used in photolysis to split water into oxygen, which is released (evolved), and hydrogen which becomes bound to coenzyme NADP to form NADPH
• NADPH and ATP are passed to next stage, the carbon fixation (calvin) cycle

Question 9

process of carbon fixation stage (calvin cycle)

Answer 9

• carbon dioxide enters the cycle and becomes attached to RuBP, this reaction is controlled by the enzyme RuBisCo and forms 3PG
• the 3PG accepts hydrogen from NADPH and is phosphorylated by ATP to form G3P
• some G3P is then used to regenerate RuBP to continue this process and the remainder is used to synthesise glucose

Question 10

uses of glucose

Answer 10

• respiration
• starch (storage carbohydrate)
• cellulose (structural carbohydrate)
• biosynthesis of metabolites such as DNA, proteins and fats

Question 11

photolysis

Answer 11

• water is split into hydrogen and oxygen (by energy from high energy electrons passing down an ETC)