Topic 5: Photosynthesis Flashcards
Definition of an ecosystem
All the organisms living in a particular area + Abiotic (non-living) factors
Definition of a niche
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
Definition of a community
All of the organisms OF A PARTICULAR SPECIES living in a particular habitat at a time
Definition of a habitat
The place where an organism lives
Definition of a population
All of the organisms of one species in a habitat
Examples of Abiotic factors
Light
Oxygen
Moisture levels
Temperature
Examples of biotic factors
Predators
Food availability
Parasitism
Disease
Definition of distribution
Definition of Abundance
Distribution = How spread out everything is
Abundance = Number of something
Difference between primary and secondary succession
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
Explain the process of succession
- 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.
Outline cyclic phosphorylation
- Photon hits chlorophyll in photosystem I (PSI).
- Electrons are excited.
- Electrons taken up by an electron acceptor.
- Electrons pass along an electron transport chain. Energy is released, and ATP is synthesised.
- Returns to chlorophyll in PSI.
Outline non-cyclic phosphorylation
- Photon hits chlorophyll in photosystem II (PSII).
- Electrons are excited.
- An electron acceptor takes up electrons and passes along an electron transport chain to PSI. Energy is released, ATP is synthesised.
- 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.
- Photon hits chlorophyll in Photosystem I.
- Electrons are excited.
- Electrons are taken up by an electron acceptor and passed along an electron transport chain to NADP.
- NADP takes up an H+ ion from dissociated water and forms reduced NADP.
Definition of evolution
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.
Outline the process of evolution via natural selection
- 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.
Where do the light-independent reactions take place?
Where do the light-dependent reactions take place?
Light-independent = Stroma
Light-dependent = Thylakoid membrane
Explain the light-dependent reaction of photosynthesis
-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.
Define net primary productivity
Define gross primary productivity
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
Reasons why energy is lost at different trophic levels
- Undigested matter
- Respiration (exothermic, transfers thermal energy to surroundings)
- Metabolic waste products like urea
What is GP used to produce?
-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
What is GALP used to produce?
-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
Explain the Calvin cycle
-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 (glycerate 3-phosphate)
-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
Carbon dioxide and RuBP are combined
Describe the role of the products of the light-dependent reactions in the Calvin cycle (3)
-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
Explain the importance of RUBISCO to the productivity of an ecosystem (2)
- 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
Describe how GP is produced by carbon fixation (2)
-Rubisco combines carbon dioxide with RuBP
-Unstable 6C molecule breaks down into 2xGP
Describe the role of RUBISCO in the production of GALP in the light-independent reaction (4)
-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
Explain why the light-independent stage cannot take place without the light-dependent stage (3)
-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
Describe how starch is formed from the products of the light-independent reactions of photosynthesis (4)
- 2xGALP is used to produce a glucose molecule
- Glycosidic bonds join Glucose molecules together to form starch
- Via condensation reactions
- Producing amylose and amylopectin
Describe how the structure of granum is related to its function (3)
-Large surface area
-To absorb as much light as possible
-Containing chlorophyll
Describe how the membranes inside the chloroplast are involved in photosynthesis (3)
- 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
Describe the light-dependent reactions of photosynthesis (5)
- 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
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)
-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
State the location of the Calvin cycle
Stroma of the chloroplast
Describe the roles of the products of the light-dependent reactions in the Calvin cycle (3)
-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
Describe how carbon dioxide is used in photosynthesis (4)
-CO2 is needed for carbon fixation
-It combines with RuBP
-Reaction is catalysed by RUBISCO
-To produce GP , GALP, glucose
Explain why and increase in carbon dioxide concentration above 1000 ppm may not increase the rate of photosynthesis (3)
-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
Describe how DCPIP can be used to measure the effect of temperature on the rate of the light-dependent reactions in isolated chloroplasts (4)
-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
Explain how chloroplasts are adapted for their role in photosynthesis (4)
-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
Explain how ‘tiny changes’ in chlorophyll molecules could result in a change in the wavelength of light absorbed (3)
-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)
Explain what the solution should contain for the optimum growth of
duckweed (3)
-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
