PHOTOSYNTHESIS

Question 1

Define photosynthesis

Answer 1

|using light energy to synthesis large organic molecules from smaller inorganic ones
Light energy –> chemical energy

Question 2

Autotroph

Answer 2

Able to form organic substances from inorganic substances

Self feeding

Question 3

Chemoautotrophs

Answer 3

Synthesise complex organic molecules using energy from exogenic chemical reactions
E.g. nitrifying bacteria

Question 4

Photoautotrophs

Answer 4

Organisms that photosynthesise

Use energy from sunlight to produce complex organic molecules from water + carbon dioxide

Question 5

Heterotrophs

Answer 5

Other feeding
Digest complex organic molecules into simple soluble ones
Cannot make their own food

Question 6

Word equation

Answer 6

Carbon dioxide + water –> glucose + oxygen

Question 7

Symbol equation

Answer 7

6CO2 + 6H20 –> C6h2O6 + 6O2

Question 8

Light dependent stage

Answer 8

Light energy converted to chemical energy
Photolysis of water occurs splitting it into H+ ions and oxygen
Produces reduced NADP + ATP

Question 9

Light independent stage

Answer 9

Products of light reactions are used to reduce CO2 to sugars + organic molecules

Question 10

Importance of photosynthesis

Answer 10

Plants, animals and microorganisms rely on it to produce carbohydrates and oxygen

• oxygen required for aerobic respiration
• carbohydrates produce energy stores
• control green house effect

Question 11

How photosynthesis and respiration interrelate

Answer 11

Plants respire all the time, only photosynthesise in the light
In photosynthesis, ATP is synthesised using light energy- ATP then used to build organic compounds such as glucose
In respiration, organic molecules (e.g. glucose) are broken down to release energy

Question 12

What is the compensation point

Answer 12

During photosynthesis and respiration there is no net gain or loss of oxygen or carbohydrates

Question 13

How is a leaf adapted for photosynthesis

Answer 13

Large SA- absorb maximum sunlight
More chlorophyll on top of the leaf
Waxy cuticle reduces water loss
Guard cells close stomata pores (reduces water loss)

Question 14

Structure and function of chloroplast envelope

Answer 14

Double membrane
Selectively permeable

Outer membrane is permeable to small ions, inner membrane is less permeable
Contains transporter proteins

Question 15

Structure and function granac(chloroplast)

Answer 15

Stack of thylakoids

Provide SA for chlorophyll + other pigments to attach to (photosystem II)
Enzyme ATP synthase

Question 16

Structure and function of inter-granal lamellae (chloroplast)

Answer 16

Thylakoids between grana

Contains photosystem I pigments

Question 17

Structure and function of stroma (chloroplast)

Answer 17

Fluid filled matrix

Contains enzymes for light independent reactions for photosynthesis

Question 18

Structure and function of DNA (chloroplast)

Answer 18

No histones, circular

Codes proteins (e.g. enzymes for photosynthesis)

Question 19

Structure and function of ribosomes (chloroplast)

Answer 19

18nm

Protein synthesis

Question 20

Function of starch grains

Answer 20

insoluble storage molecule

Question 21

Function of lipid droplets

Answer 21

Maintain membranes (phospholipid bilayer)

Question 22

What is a photosynthetic pigment

Answer 22

absorbs certain wavelengths of light

Question 23

What is the colour of the pigment due to

Answer 23

The wavelength of light which is reflected

Question 24

Chlorophyll

Answer 24

Collection of green pigments
Porphyrin like ring structure head (contains magnesium)
Hydrocarbon tail- embeds itself in membrane of thylakoids
Head remains on surface

Question 25

Two forms of chlorophyll a

Answer 25

P680 + P700

Question 26

Carotenoids

Answer 26

Includes carotene and xanthophyll Ranges in colour (red, orange, yellow) Absorb wavelengths of light not efficiently absorbed by chlorophyll a Protect chlorophyll from high light intensities

Question 27

Phycobillins

Answer 27

Red seaweed contains additional pigments | Allows them to absorb blue/green light (shorter wavelength of light penetrates water)

Question 28

Explain the distribution of bacteria in response to the absorption spectrum

Answer 28

Congregation of oxygen seeking bacteria surrounding blue and red area of spectra Suggesting algae is absorbing the light and photosynthesising to produce oxygen Little to no bacteria absorbing green light, no photosynthesis, no oxygen

Question 29

Describe and explain the relationship between the absorption and action spectra

Answer 29

Both peak at the blue and red light (increased photosynthesis)- most light absorbed Action spectra shows some photosynthesis occurs at green and yellow regions- shows carotenoids and other pigments are involved in photosynthesis

Question 30

What is a photosystem

Answer 30

Pigment molecules arranged in clusters in the thylakoid membrane Contain hundreds of chlorophyll a + b and carotenoids

Question 31

Explain a photosystem

Answer 31

One chlorophyll a molecule (primary pigment) acts as a reaction centre for each photosystem Remaining pigments, (accessory pigments) absorbs light and funnel the energy to the reaction centre Act as light harvesting systems (aka antennae complex)

Question 32

Photosystem I

Answer 32

Contains chlorophyll with an absorption peak at 700nm at its reaction centre (P700) Mainly found in inter-granal lamellae

Question 33

Photosystem II

Answer 33

Contains chlorophyll a with an absorption peak at 680nm (P680) Mainly found on granal lamellae

Question 34

Light dependent reactions

Answer 34

Take place in thylakoid | Photolysis- PSII contains enzymes to split water, hydrogen to NADP + ATP

Question 35

Light independent reactions

Answer 35

Takes place in stroma | Uses ATP + reduced NADP from light dependent

Question 36

Stages of Calvin cycle

Answer 36

1. CO2 diffuses into stroma 2. CO2 combines with ribulose bisphosphate (RuBP) 3. rubisco= catalyst 4. this product 6C compound which is unstable + immediately splits into 3C compounds 5. two 3C compounds= gylcerate phosphate (GP) 6. each GP reduced + phosphorylated to triode phosphate 7. ATP + reduced NADP (from light dependent) provides phosphate, energy + hydrogen 8. 5/6th of TP regenerated to RuBP 9. requires ATP from light dependent

Question 37

Uses of products from Calvin cycle

Answer 37

Pairs of TP combine to form hexose (6C) sugars (e.g. glucose + fructose) Join to form disaccharides (e.g. sucrose) Polymers may also form (e.g. starch= storage)

Question 38

Factors affecting rate of photosynthesis | CO2 concentration

Answer 38

CO2 air conc= 0.04% Concs lower in dense vegetation Often limiting factor as essential factor for Calvin cycle Concs in stroma lower than air

Question 39

Factors affecting rate of photosynthesis | Temperature

Answer 39

Temp may affect light independent Increased temp= increased KE (hence enzyme controlled Rea actions in Calvin cycle) Increased temp= enzymes denature Above 25 degrees rubric changes to catalysing RuBP with O2 instead of CO2= photorespiration

Question 40

Factors affecting rate of photosynthesis | Water stress

Answer 40

1. plant roots produce absicic acid- translocated to leaves 2. causes stomata to close, reduces availability of CO2 3. rate of photosynthesis reduces IF roots cant take up water fast enough to replace water lost from transpiration= cells plasmoylsed

Question 41

Limiting factors + Calvin cycle | Light intensity

Answer 41

Low= products of light dependent (ATP + reduced NADP) will be in short supply Limits conversion of GP to TP + regeneration of RuBP GP still made

Question 42

Limiting factors + Calvin cycle | CO2 concentration

Answer 42

Low= conversion of RuBP to GP will be slow as less CO2 | Less CO2 to combine with RuBP

Question 43

Limiting factors + Calvin cycle | Temperature

Answer 43

All stages of Calvin cycle catalysed by enzymes (rubisco) Low temps= cycle= slower High temp= enzymes denature + photorespiration may occur