5.2.1 - photosynthesis

Question 1

photosynthesis definition

Answer 1

the process by which energy, in the form of light from the Sun us used to build complex orgnaic molecules, like glucose

Question 2

autotrophic

Answer 2

plants and algae that can photosynthesise

Question 3

heterotrophic organisms

Answer 3

animals, obtain complex organic molecules by eating ither organisms

Question 4

photosynthesis equation

Answer 4

carbon dioxide + water —> glucose + oxygen

Question 5

where does photosynthesis take place?

Answer 5

chloroplast

Question 6

structure of chloroplast

Answer 6

membranes of flattened sacs called thykaloids, which are stacked to form grana
the grana are joined by lamellae
fluid enclosed is called the stroma

Question 7

role of pigment molecules in chloroplast

Answer 7

to absorb specific wavelenhths of light and reflect others

Question 8

primary pigment in photosynthesis and what does it absorb?

Answer 8

chlorophyll - mainly red and blue light, reflecting green light

Question 9

affect of the different pigment on leaf colour

Answer 9

lots of different shades and colours of leaves

Question 10

light harvesting system

Answer 10

proteins and pigments that absorb and harvest light energt of different wavelengths and transfer this energy quickly and efficiently to the reaction centre

Question 11

where is chlorophyll a located

Answer 11

in the reaction centre

Question 11

photosystem

Answer 11

complex structures within chloroplasts of plants that capture light energy and use utr to generate ATP and NADPH

Question 12

structure of a photosystem

Answer 12

funnel shaped structure with chlorophyll a at its reaction centre, and accessory pigments funnel thr light onto the reaction centre

Question 13

Photosystem I

Answer 13

P700 form of chloophull a - where peak absorption of light is at 700nm

Question 14

Photosystem II

Answer 14

P680 form of chlorophyll a - peak absorption of light is at 680nm

Question 15

why is it useful that plants have a range of different pigments?

Answer 15

leaf can absorb a greater range of different light wavelengths - increasing energy absorbed, higher rate of PHS, increasing carbs produced

Question 16

absorption spectrum

Answer 16

data is collected by shining different wavlenths onto chloroplast and using a colourimiter to measure absobance of each, then plotting on a graph

Question 17

photosystems in non cyclic photophosphorylation

Answer 17

PSII and PSI

Question 18

steps of non cyclic photophosphorlyation

Answer 18

1. chlorophyll a in PSII abosrbs light
2. electrons become excited to a higher energy level and passed along a electron transport chain
3. the electron carriers are oxidised when they pass the electrons on
4. H+ ions are pumped out
5. This causes energy to be released, causing ATP to be synthesised at ATP synthase
6. Photolysis
7. PSI is also absorbing this light, and receving the electrons
8. ferredoxin passes the electron along with a H+ proton to NADP
9. this forms reduced NADP

Question 19

what are the products of the light dependent reactoon

Answer 19

ATP, and NADPH (used for light independent reaction) and oxygen

Question 20

photolysis

Answer 20

water molecules being split, forming oxygen, electrons and hydrogen atoms (protons)

Question 21

reason for photolysis

Answer 21

electrons released are used to replace the electrojs lost from PSII when light is absorbed

Question 22

cyclic photophosphorylation

Answer 22

electrons that leave the electron transport chain after PSI can be returned to PSI instead of being used to form reduced NADP.

NADPH is not produced when this happens

Question 23

chemiosmosis

Answer 23

the process of ATP production

Question 24

where does the light independent reaction take place

Answer 24

stroma

Question 25

steps of the calvin cycle

Answer 25

1.CO2 diffuses into the leaf via stomata
2. picked up by RuBP, catalysed by the enzyme rubisco
3. unstable 6 carbon molecule formed
4. this splits into 2 GP
5. the NADPH and ATP are used to convert the 2 GP into 2 TP
6. 5/6 of the TP is used to regenerate the RuBP
7. 1/6 of the TP can be used to make other carbs and crucial substances

Question 26

calvin cycle summarised into three steps

Answer 26

• fixation - co2 is fixed in the first step
• reduction - GP is reduced to TP using LDR producs
• regeneration - RuBP is regenerated from TP

Question 27

how are the LDR products used in the LIR?

Answer 27

• the NADPH donates hydrogen atoms
• ATP acts as an energy source

Question 28

why is rubsico not an efficient enzyme? how is this dealt with?

Answer 28

competitively inhibited by oxygen

rubisco has a higher affinity for co2 than for o2 - the higher the co2 concentration, the less likely the enzyme is to react with o2

Question 29

limiting factor

Answer 29

reducing the rate

Question 30

how does light intensity affect the rate of photosynthesis

Answer 30

light is needed as an energy source, as light intensity increases ATP and NADPH are produced at a higher rate

Question 31

how does co2 concentration affect the rate of photosynthesis

Answer 31

increasing the co2 conc increases the rate of carbon fixation in the calvin cycle and therefore the rate of TP production

Question 32

how does temperature affect the rate of photosynthesis

Answer 32

affects the rate of enzyme control reactions, however may increase the rate of photorespiration

Question 33

photorespiration

Answer 33

when rubisco reacts with oxygen, reducing the rate of photosytnethsis

Question 34

effect of reducing light intensity on calvin cycle

Answer 34

whilst it doesnt necessarily use light energy, it will mean there are less products being available to use in the Calvin cycle.