5.2.1 Photosynthesis COMPLETE

Question 1

DEFINITION- Photosynthesis

Answer 1

The use of light energy to synthesise large organic molecules from smaller inorganic ones.

Question 2

Autotrophs

Answer 2

Can synthesise their own organic nutrients using inorganic carbon source (self feeding)

Question 3

Chemoautotrophs

Answer 3

Synthesise complex organic molecules using energy from exergonic chemical reactions

Question 4

Photoautotrophs

Answer 4

Photosynthesising organisms, e.g. plants, some bacteria and phytoplankton

Question 5

Heterotrophs

Answer 5

Eat and Digest

digest complex organic molecules into simple soluble ones.

Question 6

Photosynthesis word equation

Answer 6

water + CO2 —> O2 + glucose

Question 7

Glucose Symbol

Answer 7

C6H12O6

Question 8

Light-Dependant Stage

Answer 8

Photolysis of water, produces ATP and NADP

Question 9

Light-Independant Stage

Answer 9

Products from light reactions were used to reduce CO2 into sugars and organic molecules.

Question 10

Importance of photosynthesis

Answer 10

• Oxygen required for aerobic respiration
• CO2 removed from the air
• Production of fossil fuels
• Controls greenhouse effect

Question 11

Grana function

Answer 11

Chlorophyll are embedded, so provides a large SA for pigments

Question 12

Inter-granal Lamella function

Answer 12

Where PS1 is found

Question 13

Stroma function

Answer 13

Contains the enzymes for light independant reactions

Question 14

Features of a Leaf for photosynthesis

Answer 14

• Large SA
• Transparent waxy cuticle
• Thin
• Lots of air space
• Stomata on the bottom to reduce water loss

Question 15

Definition- Photosynthetic Pigments

Answer 15

A substance that absorbs certain wavelengths of light, photosynthetic ones capture light specifically for photosynthesis.

Question 16

Chlorophyll Pigments

Answer 16

• Green pigments with a hydrocarbon tail that embeds itself into the thylakoid membrane
• The Porphyrin Head contains Mg and remains on the surface
• Chlorophyll a and Chlorophyll b exists

Question 17

Carotenoid Pigments

Answer 17

• Includes both carotenes and xanthophylls
• Range of colours from red to orange to yellow
• They absorb the wavelengths not efficiently absorbed by chlorophyll
• Pass energy onto the chlorophyll
• May also help to protect the chlorophyll

Question 18

Phycobilin Pigments

Answer 18

Red seaweeds contain additional pigments allowing blue/ green wavelengths to be absorbed

Question 19

Chromatography

Answer 19

Thin layer chromatography can be used to operate leaf extracts to identify the pigments inside

Question 20

Absorption and Action Spectrum

Answer 20

Rate of absorption and rate of action corresponds and when more light is absorbed photosynthesis increases.
Plants with more pigments can absorb more light

Question 21

Photosystems

Answer 21

• Pigment molecules are arranged in clusters in the thylakoid membrane, these are photosynthetic units
• Chlorophyll a is the primary pigment and acts like the reaction centre for each photosystem

Question 22

Two types of Photosystem

Answer 22

PS1- Contains chlorophyll a with an absorption peak at 700nm at its reaction centre
PS2- Contains chlorophyll a with an absorption peak at 680nm at its reaction centre

Question 23

Photolysis

Answer 23

2H2O –> 4H+ + 4e- + O2
An enzyme in photosystem 2 splits water when activated by light.
The Hydrogen ions are used to reduce NaDP
Electrons replace those lost to PS1
Oxygen diffuses out and is used for respiration

Question 24

Photophosphorylation

Answer 24

ADP + Pi –> ATP
Process of adding a phosphate to a molecule using light energy
When light hits chlorophyll a or energy is funnelled in, 2 electrons gain energy and become excited

Question 25

Light dependant Stage Summary

Answer 25

Takes place in the thylakoid membrane
Light is absorbed by photosystems 
Water is split to produce e- and H+
ATP and Reduced NADP produced 
Oxygen released as waste

Question 26

Cyclic Photophosphorylation

Answer 26

Only involves PS1
Electrons get excited and move up
Electron carrier chains then move them down again to the same chlorophyll
Energy from electrons is used to make ATP

Question 27

Non Cyclic Photophosphorylation

Answer 27

Electrons get excited in both PS1 and PS2
ATP generated as the electron carrier chains move the electrons down
However elections from PS2 replace those lost by PS1
Electrons lost by PS1 are used with H+ to produce reduced NaDP

Question 28

Light independent Stage Summary

Answer 28

Takes place in the stroma of the chloroplast
Uses the ATP and reduced NaDP produced from the light stage
Sugar is being produced from the reduction of CO2
Reactions are called the Calvin cycle

Question 29

Compounds involved in the Calvin cycle

Answer 29

1. CO2 first combines with RIBULOSE BISPHOSPHATE
2. The enzyme RUBISCO catalyses the reaction
3. This forms an unstable intermediate that splits into two GLYCERATE 3 PHOSPHATE
4. GP is then reduced in TRIOSE PHOSPHATE
5. 5/6 of TP is used to regenerate RuBP
6. 1/6 is converted into glucose

Question 30

Uses of the products of the Calvin Cycle

Answer 30

• TP pairs can be used to form hexose sugars such as glucose or glycerol
• These can join to form saccharides such as sucrose
• GP can produce amino acids and fatty acids, nitrates and mineral ions will also be needed
• Fatty Acids + Glycerol can form lipids

Question 31

Light intensity on Photosynthesis rate

Answer 31

Light provides energy for photosynthesis
So higher intensity means faster rate
Light is required for photolysis and photophosphorylation

Question 32

Carbon Dioxide conc. on Photosynthesis rate

Answer 32

Its essential for the Calvin cycle so can be limiting

Concentration of CO2 will be lower in the chloroplast and stroma than the air

Question 33

Temperature on Photosynthesis rate

Answer 33

Temp. mainly effects the light independent reactions
Increase temp increases the kinetics
All reactions in the Calvin cycle are enzyme controlled
Plants evolved lower optimum temps
If too high then enzymes denature
Or rubisco reacts with oxygen instead (competitive inhibition)
High temp also means more water loss

Question 34

Photorespiration

Answer 34

Rubisco begins to catalyse the reaction of RuBP with O2 instead when temp is above 25 degrees

Question 35

Water Stress on Photosynthesis rate

Answer 35

If roots can’t take up water fast enough to replace the loss from transpiration the stomata close so there’s less CO2 for the Calvin cycle
Plant roots produce Abscisic Acid which is translocated to the leaves

Question 36

Limiting Factors of the Calvin cycle

Answer 36

Light intensity- ATP and NaDP produced which limits the conversion of GP to TP and the regeneration of RuBP, GP conc will increase if its limited
CO2- Less production of GP when limited so RuBP conc. will increase
Temp- All stages catalysed by enzymes so increased temp just increases rate