SNAB Model exam answers

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Topic 5: On the Wild Side
Suggest reasons why 95% of the light hitting the surface of a leaf is not used by the chloroplasts.
(2)*Reflection; *incorrect wavelength/colour/ frequency; *light doesn't hit the chloroplast/
chlorophyll, it is transmitted; *light being in excess e.g. at max. photosynthesis so no more light
can be used.
The light dependent reactions The
products of the light-dependent reactions that are used in the light-independent reactions are
reduced NADP and.... ATP
Oxygen is produced when water molecules are split in the process of......photolysis
When light is absorbed by chlorophyll, it excites.......electrons
Describe the structures in a chloroplast that are involved in the LD reactions (3)
The LD reactions involve the *thylakoids that are arranged into stacks of granum. *The grana are
connected by lamellae. The *thylakoid membrane contains electron carriers, proteins and
*photosynthetic pigments such as chlorophyll which are *arranged into
photosystems/quantasomes; the membrane also has *ATPase/ ATPase channels.
Explain how the energy from light is made available in ATP molecules for the synthesis of
organic materials. (6)
*The light dependent reactions occur in the thylakoids *in the granum in *accessory pigments
such as chlorophyll. The process begins when *light energy raises the energy level of two electrons
so that they are excited, the electrons are then *released from the chlorophyll/ photosystem.
They then travel down the *electron carrier chain, travelling to each carrier molecule through a
series of *oxidation and reduction (redox) reactions, releasing energy/ *the electrons' energy level
falls. The energy released is used to *synthesise ATP from ADP and an organic phosphate ion
*(phosphorylation); the *enzyme synthase/ synthetase is needed to make the ATP. *Photolysis of
water produces 2 electrons which are used to replace those lost from the chlorophyll.
Explain how oxygen is produced during the light-dependent reactions of photosynthesis. (2)
Using *energy from light the *photolysis *of water occurs that produces/releases oxygen
The light independent reactions/ The Calvin Cycle
RuBP combines with carbon dioxide in...... The light-independent reactions of the Calvin cycle.
RUBISCO the enzyme that catalyses carbon fixation.
Carbon fixation takes place in..... the stroma of a chloroplast.
Explain why the light-independent stage cannot take place without the light-dependent stage.
(3) Because the *products of the light-dependent stage are needed for/used in the
light-independent stage/Calvin cycle. *Thee products of the light-dependent stage are reduced
NADP and ATP, *rNADP is used in the reduction GP/carbon dioxide whilst *ATP is used as a source
of energy.

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Topic 5: On the Wild Side
Suggest why the development of plants depends on the rate of carbon fixation. (3)
*Carbon fixation produces {GP / eq}, this *product is converted to glucose/ starch/ eq. *The faster
the C- Fixation the faster the glucose/ starch production, as the *rate of growth of a plant is
dependent on the rate of C-Fixation, if this increases so will the *GPP of the crop/plant.
Suggest how GALP may be used to synthesise cellulose.…read more

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Topic 5: On the Wild Side
Because *there is not enough data to *confirm its reliability (*may be place specific). The fact that
there are *great fluctuations in most climate change data suggest that there is no real trend (as
scattered) and thus *poor representation of raw data. *A scatter of results may show poor
In addition the method of* estimating temperature from growth rings of trees is questionable as
*other environmental changes affecting the trees are not taken into account.…read more

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Topic 5: On the Wild Side
Suggest how global warming may affect the distribution of species (3)
*Global warming will increase the temperature (especially at the latitudes) *so that the
temperature may become too high for any of the current species. *This new temperature may be
above the maximum to be able to complete development/ above the lethal temperature limit.
*Species may also move north/ to cooler regions or they may have a *change to their food
source/predators/ competition.…read more

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Topic 5: On the Wild Side
increase *because there is less competition for food (from lizards), however the *lizards' predator
may decrease/eat other prey/migrate.
Suggest why an increase in temperature may cause an increase in NPP. (2)
*The rate of (bio)chemical/metabolic/photosynthetic reactions increases due to an *increase in
movement/kinetic energy of enzyme/substrate/molecules; *thus increasing the reaction rate
because of more enzyme substrate interaction/ collisions.
What is the unit J m­2 year­1? Joules/ energy per metre squared per year/ unit time.…read more

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Topic 5: On the Wild Side
shrubs to grow, *these may also out-compete the other species by interspecific competition for
(a)biotic resources. *As the plants continue to lose leaves and die/decay they will *increase the
amount of organic matter/humus.
Why is a climax community stable? (4)
*A climax community is where (both) animals and plants are present/has many species/has high
biodiversity; *there will be interaction between these species but they *will have reached a
balanced equilibrium of species.…read more

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Topic 5: On the Wild Side
*restriction of gene flow *between extremes of the population. Each habitat would have different
environmental factors and so different selection pressures. *Mutations may then have arisen
(*causing a change in the allele frequency) and *other plant features so that the *plants adapted
to a specific region, advantageous features/mutations would allow the plants to *survive and
reproduce, passing on new genes and creating *differences between gene pools.
Suggest how ecological isolation contributes to speciation.…read more

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Topic 5: On the Wild Side
What tissue would form the vessels in a root, following differentiation? Xylem
hydrogen and glycosidic bonds are what would need to be broken to digest cellulose.
Describe the chemical nature of cellulose. (3)
Cellulose is a *polysaccharide with an *unbranched/ straight chain. The cellulose is made up of *B
glucose joined by *1-4 glycosidic bonds between the glucose molecules. Between each chain there
are *intermolecular hydrogen bonds to hold the structure together.…read more

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Topic 5: On the Wild Side
cytoplasm, where *translation occurs (expand with ribosomes, codon-anticodon interaction).
*tRNA will carry an amino acid and *peptide bonds form between the amino acids on different
tRNA molecules; this I is the *sequence/ order of amino acids is the primary structure of a protein.
How does mRNA form during transcription in the nucleus? (3)
First the *DNA strands unzip, *one side of the DNA strand is the template strand that is used to
from a mRNA strand *from free nucleotides.…read more

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Topic 5: On the Wild Side
*Fibrous­ long/linear/straight chains and *Globular­ compact/spherical; *Globular are folded and
fibrous are not; *Globular are soluble and fibrous are not; Fibrous are involved in structural
functions (keratine) and globular are not; *Globular are involved in catalysis/metabolism
(enzymes) and fibrous are not.
Explain how the work of zoos could be important to the survival of endangered species.…read more


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