Topic 5: Photosynthesis

Question 1

Definition of an ecosystem

Answer 1

All the organisms living in a particular area + Abiotic (non-living) factors

Question 2

Definition of a niche

Answer 2

The role and organism plays in an environment at a certain point in time. No two species can occupy the same niche but they cant compete for it

Question 3

Definition of a community

Answer 3

All of the organisms OF A PARTICULAR SPECIES living in a particular habitat at a time

Question 4

Definition of a habitat

Answer 4

The place where an organism lives

Question 5

Definition of a population

Answer 5

All of the organisms of one species in a habitat

Question 6

Examples of Abiotic factors

Answer 6

Light
Oxygen
Moisture levels
Temperature

Question 7

Examples of biotic factors

Answer 7

Predators
Food availability
Parasitism
Disease

Question 8

Definition of distribution

Definition of Abundance

Answer 8

Distribution = How spread out everything is

Abundance = Number of something

Question 9

Difference between primary and secondary succession

Answer 9

In primary succession, the pioneer species is less complex and starts with nothing where as in secondary succession the pioneer species is more complex and already has nutrients in the soil

Question 10

Explain the process of succession

Answer 10

• The area is first colonised by the pioneer species e.g. lichens which are adapted to survive in harsh conditions
• As organisms die, they are decomposed by microorganisms, thus adding humus (the organic component of soil). This leads to the formation of soil, which makes the environment more suitable for more complex organisms
• As more organisms are decomposed overtime, the soil becomes richer in minerals, thus enabling larger, more varied and more productive plants such as shrubs to survive.
• -Eventually, a climax community is established - the most productive, self-sustaining and stable community of organisms the environment can support, usually with only one or two species.

Question 11

Outline cyclic phosphorylation

Answer 11

1. Photon hits chlorophyll in photosystem I (PSI).
2. Electrons are excited.
3. Electrons taken up by an electron acceptor.
4. Electrons pass along an electron transport chain. Energy is released, and ATP is synthesised.
5. Returns to chlorophyll in PSI.

Question 12

Outline non-cyclic phosphorylation

Answer 12

1. Photon hits chlorophyll in photosystem II (PSII).
2. Electrons are excited.
3. An electron acceptor takes up electrons and passes along an electron transport chain to PSI. Energy is released, ATP is synthesised.
4. Photolysis: light energy breaks apart the strong bonds in water molecules - forming hydrogen and hydroxide ions. Electrons released replace lost electrons in the chlorophyll of PSII. Hydroxide ions react together to form water and oxygen.
5. Photon hits chlorophyll in Photosystem I.
6. Electrons are excited.
7. Electrons are taken up by an electron acceptor and passed along an electron transport chain to NADP.
8. NADP takes up an H+ ion from dissociated water and forms reduced NADP.

Question 13

Definition of evolution

Answer 13

Evolution is a change in the heritable traits of biological populations over successive generations. It occurs as a result of a change in allele frequency which in turn is affected by changing selection pressures.

Question 14

Outline the process of evolution via natural selection

Answer 14

• A variety of phenotypes exist within a population due to random mutation.
• An environmental change occurs and as a result of the selection pressure changes
• Some individuals possess advantageous alleles which give them a selective advantage and allow them to survive and reproduce.
• The advantageous alleles are passed on to their offspring.
• Overtime, the frequency of alleles in a population changes.

Question 15

Where do the light-independent reactions take place?

Where do the light-dependent reactions take place?

Answer 15

Light-independent = Stroma

Light-dependent = Thylakoid membrane

Question 16

Explain the light-dependent reaction of photosynthesis

Answer 16

-Light energy excites chlorophyll in PS2 causing it to release electrons

-Electrons are then passed down the electron transport chain from one electron carrier to the next and this process generates ATP in a process called photophosphorylation.

-Phosphorylation can be cyclic or non-cyclic. The final electron acceptor is NADP. When it accepts an electron it forms reduced NADP. Both ATP and reduced NADP from the light-dependent reactions are used in the light-independent stages of photosynthesis.

Question 17

Define net primary productivity

Define gross primary productivity

Answer 17

NPP - The rate at which energy from the sun is converted into the organic molecules that make up new plant biomass.

GPP - Energy transferred to primary consumers

Therefore NPP = GPP - R

Question 18

Reasons why energy is lost at different trophic levels

Answer 18

• Undigested matter
• Respiration (exothermic, transfers thermal energy to surroundings)
• Metabolic waste products like urea

Question 19

What is GP used to produce?

Answer 19

-Amino acids which can be used in protein synthesis for building polypeptides
-Fatty acids which form the tails of lipid molecules such as triglycerides and phospholipids

Question 20

What is GALP used to produce?

Answer 20

-Hexose sugars e.g. glucose
-Hexose sugars can be joined to make polysaccharides such as starch and cellulose
-Glycerol can be used for building lipid molecules such as triglycerides and phospholipids
-Nucleic acids form the basis of DNA and RNA

Question 21

Explain the Calvin cycle

Answer 21

-RUBISCO catalyses the reaction between Rubulose bi-phosphate (5-carbon compound) and a single Carbon dioxide atom to form an unstable 6-carbon compound which is unstable and splits immediately, to form 2xGP

-GP is reduced to GALP in a reaction involving reduced NADP and ATP. Energy from ATP and hydrogen from reduced NADP, both produced during the light-dependent reactions, are used to reduce the two molecules of GP to two 3C molecules of GALP. Some of the carbons in GALP go towards the production of useful organic molecules such as glucose, while the rest allow the regeneration of RuBP

-RuBP is regenerated from GALP in reactions that use ATP

Question 22

Describe the role of the products of the light-dependent reactions in the Calvin cycle (3)

Answer 22

-Products are ATP and reduced NADP
-ATP is used to convert GP to GALP and GALP to RuBP
-Reduced NADP used to convert GP to GALP

Question 23

Explain the importance of RUBISCO to the productivity of an ecosystem (2)

Answer 23

• Carbon fixation
• Allowing the formation of organic molecules by the Calvin cycle
  -These organic molecules allow the transfer of energy to the next trophic level

Question 24

Describe how GP is produced by carbon fixation (2)

Answer 24

-Rubisco combines carbon dioxide with RuBP
-Unstable 6C molecule breaks down into 2xGP

Question 25

Describe the role of RUBISCO in the production of GALP in the light-independent reaction (4)

Answer 25

-RUBISCO catalyses the reaction of a carbon dioxide molecule and RuBP (carbon fixation) in the calvin cycle to form GP which is converted to GALP using reduced NADP and ATP

Question 26

Explain why the light-independent stage cannot take place without the light-dependent stage (3)

Answer 26

-Products of the light-dependent stage are needed for/used in the light-independent stage (calvin cycle) - Reduced NADP and ATP are needed for converting GP to GALP -ATP is a source of energy

Question 27

Describe how starch is formed from the products of the light-independent reactions of photosynthesis (4)

Answer 27

- 2xGALP is used to produce a glucose molecule - Glycosidic bonds join Glucose molecules together to form starch - Via condensation reactions - Producing amylose and amylopectin

Question 28

Describe how the structure of granum is related to its function (3)

Answer 28

-Large surface area -To absorb as much light as possible -Containing chlorophyll

Question 29

Describe how the membranes inside the chloroplast are involved in photosynthesis (3)

Answer 29

- They are the site of the light-dependent reaction - Contain chlorophyll, photosystems and electron carrier proteins - ATP synthase in the thylakoid membrane - Thylakoid membranes provide a space for the accumulation of H+ ions

Question 30

Describe the light-dependent reactions of photosynthesis (5)

Answer 30

- Light energy excites electrons in chlorophyll - Photolysis produces oxygen, electrons and hydrogen ions - Electrons used in the electron transport chain to replace those lost by chlorophyll - Generation of ATP via photophosphorylation - Reduction of ATP

Question 31

With reference to the structures in a chloroplast, explain how the energy from light is made available in ATP molecules for the synthesis of organic materials (6)

Answer 31

-Chloroplast has thylakoid membranes which are stacked to form grana -Light energy excites electrons in chlorophyll which releases electrons from PS2 -Electrons sent down electron carrier -ATP is synthesised -Electrons from photolysis are used to replace lost electrons from chlorophyll

Question 32

State the location of the Calvin cycle

Answer 32

Stroma of the chloroplast

Question 33

Describe the roles of the products of the light-dependent reactions in the Calvin cycle (3)

Answer 33

-ATP and reduced NADP are the products -ATP is used by the enzyme converting GP to GALP / GALP to RuBP -Reduced NADP used to convert GP to GALP

Question 34

Describe how carbon dioxide is used in photosynthesis (4)

Answer 34

-CO2 is needed for carbon fixation -It combines with RuBP -Reaction is catalysed by RUBISCO -To produce GP , GALP, glucose

Question 35

Explain why and increase in carbon dioxide concentration above 1000 ppm may not increase the rate of photosynthesis (3)

Answer 35

-All the active sites of the enzymes are occupied -No more enzyme-substrate complexes can be formed -RUBISCO cannot fix carbon dioxide any faster -Therefore limiting the rate of photosynthesis

Question 36

Describe how DCPIP can be used to measure the effect of temperature on the rate of the light-dependent reactions in isolated chloroplasts (4)

Answer 36

-Use plants which are the same species -Keep light intensity constant for duration of investigation -Control the concentration of DCPIP and PH of soil -Grow plants in a range of temperatures between 0C and 50C -Measure time taken for DCPIP to decolourise / change colour at each temperature

Question 37

Explain how chloroplasts are adapted for their role in photosynthesis (4)

Answer 37

-Large surface area of thylakoid membrane -Thylakoid membrane contain photosynthetic pigments to absorb light -Thylakoid (membrane) enables photophosphorylation -Stroma contains enzymes for light independent reaction -Stroma contains {DNA / ribosomes} to produce {enzymes / proteins} involved in photosynthesis

Question 38

Explain how ‘tiny changes’ in chlorophyll molecules could result in a change in the wavelength of light absorbed (3)

Answer 38

-Change in the {3D structure / tertiary structure / bonds formed} -Changes shape of (chlorophyll) light absorbing region -Changing the quantity of energy needed to {release / excite} an electron (1)

Question 39

Explain what the solution should contain for the optimum growth of duckweed (3)

Answer 39

-Solution should contain all the mineral / ions that duckweed needs -In excess -Nitrate ions for amino acids / protein / nucleic acid -Magnesium ions for chlorophyll -Calcium ions for cell wall / pectate / middle lamella -Phosphate ions for nucleic acid /ADP

Question 40

State the location of chlorophyll in a chloroplast (1)

Answer 40

Thylakoid membrane / grana / granum

Question 41

Describe how plant photosynthesis converts carbon dioxide from the air into simple organic molecules (4)

Answer 41

-CO2 combined with RuBP -By RUBISCO -Forming molecules of GP -Each GP is converted to GALP using ATP and reduced NADP -GALP used to form glucose / hexose sugars

Question 42

Explain how chloroplasts are adapted for their role in photosynthesis (4)

Answer 42

-Large surface area of thylakoid (membrane) -Thylakoid (membrane) contain photosynthetic pigments to absorb light -Thylakoid (membrane) enables photophosphorylation -Stroma contains enzymes for light independent reaction -Stroma contains DNA / ribosomes to produce enzymes / proteins involved in photosynthesis

Question 43

Explain how energy of the electrons passed along an electron transport chain ‘is used to power the synthesis of ATP (3)

Answer 43

-By photophosphorylation -Transfer of electrons releases energy -That is used to pump hydrogen ions into the thylakoid space -Hydrogen ions move back down concentration gradient through ATP synthase -Which forms ATP from ADP and inorganic phosphate

Question 44

Describe the role of chlorophyll in the light-dependent reactions of photosynthesis (2)

Answer 44

-Absorb light -Transfer (light) energy to electrons -Provides (high energy) electrons to the electron transport chain

Question 45

Describe the role of RUBISCO in the light-independent reactions of photosynthesis (3)

Answer 45

-RUBISCO is an enzyme -RUBISCO combines carbon dioxide with RuBP -To form {GP / glycerate 3-phosphate}