Question
(a) Outline how carbon compounds are produced in cells using light energy. [5]
(b) Explain the transformations of carbon compounds in the carbon cycle. [7]
▶️Answer/Explanation
Ans
a.
a.occurs by the process of photosynthesis;
b.occurs in chloroplasts of plant cells/using chlorophyll;
c.chlorophyll absorbs red/blue light AND reflects green light;
d.raw materials/starting products are carbon dioxide and water/shown in an equation;
e.water is split by photolysis;
f.oxygen is produced as waste/by-product/lost;
g.glucose formed/shown in an equation;
h.glucose molecules combine to form starch for storage;
i. light energy transformed to chemical;
b.
a.occurs by the process of photosynthesis;
b.occurs in chloroplasts of plant cells/using chlorophyll;
c.chlorophyll absorbs red/blue light AND reflects green light;
d.raw materials/starting products are carbon dioxide and water/shown in an equation;
e.water is split by photolysis;
f.oxygen is produced as waste/by-product/lost;
g.glucose formed/shown in an equation;
h.glucose molecules combine to form starch for storage;
i. light energy transformed to chemical;
Question
Plants have widespread influences, from food chains to climate change.
Draw a diagram of a palisade mesophyll cell labelling only the structures that would not be present in a pancreatic cell.
Explain the process of photosynthesis.
Describe the process of peat formation.
▶️Answer/Explanation
Markscheme
a. cell wall
Must be shown as a double line
b. large vacuole
Labelled either inside or on the membrane
c. chloroplast/plastid
d. starch grain
e. tonoplast
Allow [2 max] if any features common to both plant cells and animal cells are labelled
[Max 3 Marks]
a. autotrophs perform photosynthesis
b. carbon dioxide and water are the reactants/raw materials required for «photosynthesis»
c. light splits water molecules/causes photolysis
d. «photolysis» releases oxygen as a «waste» product
e. light energy is converted into chemical energy
f. «photosynthesis» produces organic compounds/glucose/carbohydrates
g. photosynthesis occurs in chloroplasts
h. chlorophyll «photosynthetic pigment» absorbs light
i. different pigments absorb different wavelengths «of light»
j. chlorophyll absorbs red and blue light/ends of the spectrum
k. carbon dioxide concentration/temperature/light intensity are limiting factors
Award only [1] for correct display of equation unless further annotated or explained
Allow up to [2] for correct use of understandings specified as AHL topic 8
[Max 8 Marks]
a. formed from dead plant material/leaves/mosses/Sphagnum
b. formed in waterlogged sites/bogs/mires/swamps
c. where bacteria/fungi/saprotrophs are not active/are inhibited
d. organic matter not fully decomposed
e. «occurs» in acidic conditions
f. «occurs» in anaerobic conditions
Reject anaerobic respiration
g. «very» slow process/takes a long time
[Max 4 Marks]
Question
Outline the difference in absorption of red, blue and green light by chlorophyll.
Explain how the process of photosynthesis affects carbon dioxide concentrations in the atmosphere during a typical year and the likely consequences on Earth of the yearly rises in carbon dioxide concentrations.
▶️Answer/Explanation
Markscheme
a. blue and red light absorbed (the most);
b. greatest absorption in blue light;
c. red light absorbed in high amounts;
d. least/no absorption of green light / green light is reflected/transmitted;
Allow answers shown in an annotated diagram/graph.
Relationship between photosynthesis and carbon dioxide concentration: [4 max]
a. photosynthesis uses carbon dioxide;
b. CO2 fixed/made into organic molecules/compounds by photosynthesis;
c. lowering carbon dioxide level in atmosphere;
d. annual/seasonal fluctuations of carbon dioxide levels could be related to photosynthesis;
e. caused by increased photosynthesis during spring/summer;
Consequences: [5 max]
f. enhanced greenhouse effect caused by raised levels of carbon dioxide;
g. causing global warming;
h. rising of ocean levels / melting of polar ice caps/glaciers;
i. changes in weather (patterns);
j. ocean acidification;
k. alter food webs;
l. changes/loss of habitat;
m. changes in distribution of plants and animals;
n. may lead to extinction;
Question
All organisms take in and also release carbon compounds. Draw a labelled diagram of the carbon cycle.
Describe how the rate of photosynthesis can be measured.
Explain the mechanism of ventilation in humans.
▶️Answer/Explanation
Markscheme
CO2 in atmosphere/air;
plants/producers linked to carbon in air/CO2 with arrow labeled photosynthesis;
plants/consumers linked to animals/consumers with arrow labeled feeding;
plants/producers and animals/consumers linked to carbon in air/CO2 with arrow labeled (cell) respiration;
plants/producers and animals/consumers linked to decomposers/bacteria/fungi with arrow labeled death;
decomposers/bacteria/fungi linked to carbon in air/CO2 with arrow labeled (cell) respiration;
plants/producers connected to carbon in air/CO2 with arrow labeled combustion/forest fire;
decomposers/bacteria/fungi linked to fossil fuels/coal/oil/natural gas with arrow labeled (partial) decomposition;
fossil fuels/coal/oil/gas linked to carbon in air/CO2 with arrow labeled
combustion;
Award marking points only if arrows point in correct direction.
correct equation for photosynthesis in words or symbols;
measure production of oxygen;
example of method to measure oxygen production;
(eg count bubbles from water plant/collect oxygen data per unit of time using electronic sensors/probes)
measure uptake of CO2;
example of method; (eg method of measuring (aquatic) pH changes/shift per unit time)
measure increase in biomass;
example of method; (eg sample (dry) mass of crop before and after timed period)
not possible to measure water uptake since water is transpired/used in turgidity/many chemical processes;
another valid method if concept of rate (measurements per time) is included;
air enters/exits lungs through trachea, bronchi and bronchioles;
during inspiration/inhalation external intercostal muscles contract;
causing ribs to move upwards/outwards;
during inspiration diaphragm contracts/flattens;
causes increase in volume of thorax/lungs;
decrease in pressure allows air to enter (passively);
during expiration internal intercostal muscles contract/external intercostal muscles relax;
causing ribs to move down/in;
diaphragm relaxes/returns to original domed position;
abdominal muscles contract to push diaphragm up;
causes decrease in volume of thorax/lungs;
increase in pressure forces air out of lungs;
Award [5 max] for inhalation or exhalation only.
(Plus up to [2] for quality)
Question
Below is a graph of atmospheric CO2 levels measured at Mauna Loa Observatory, Hawai’i.
Explain the observed changes in atmospheric CO2 concentration from 1960 to 2005.
Outline the precautionary principle.
▶️Answer/Explanation
Markscheme
(from 1960–2005) atmospheric CO2 concentration increases/strong positive trend / increase between 1960–2005 of 65 ppm/figures to that effect;
CO2 released by human activities contributes to the increase;
examples of human activities e.g. combustion of fossil fuels / deforestation;
seasonal/annual fluctuations (do not prevent long-term increase);
some human-induced change can be very large/perhaps catastrophic;
those responsible for the change must prove it will cause no harm before proceeding;
appropriate (environmental/medical etc.) example e.g. companies must immediately reduce emission of greenhouse gases even though proof of human impact on global warming is still debated;
is reverse of historical practice / previously those concerned about change had to prove it will do harm to prevent such changes from going ahead / paradigm shift;
Question
The continued survival of all living organisms depends on sustainable communities in which plants play a vital role.
(a) Outline how energy flows in an ecosystem.[4]
(b) Describe how plants affect the amount of carbon dioxide in the atmosphere.[4]
(c) Explain how a newly discovered plant species would be classified and named.[7]
▶️Answer/Explanation
a. energy from the sun is captured by plants/autotrophs:
b. light energy is converted to chemical energy by photosynthesis;
c. energy is passed to animals/consumers/along the food chain;
d. at each stage in the food chain energy is lost by respiration/as heat;
e. much less energy/only about $10 \%$ is available at each stage/trophic level of the food chain;
f. some energy is made available to decomposers when organisms die/parts fall to the ground;
g. energy cannot be recycled
b
a. plants reduce the amount of carbon dioxide in the atmosphere by photosynthesis:
b. carbon dioxide is fixed/converted into organic substances/sugars/ OWTTE;
c. plants respire which releases carbon dioxide into the atmosphere;
d. plant decomposition may release $\mathrm{CO}_2$
e. carbon in dead plants is trapped/ stored in fossil fuels / peat
f. combustion of plants/wood/ fossil fuels adds to the amount of carbon dioxide in the atmosphere;
c
Naming:
a. binomial nomenclature / (plant is) given a binomial/double name;
b. first name is the genus and second name is the species / genus initial upper case and species lower case;
c. names (of plant species) are international/are universally understood/are published in journals;
Classification:
d. study the characteristics/structure/reproduction/chemical properties/DNA (of the plant);
e. put/classify (the plant) in a group/genus with other similar species;
f. natural classification corresponds with evolution / natural classification is based on many features
g. analogous features/features due to convergent evolution should not be used;
h. hierarchy of groups/taxa (in traditional classification / 3 or more taxa in correct sequence (kingdom-phylum-class);
i. two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named;
j. a clade is a group of organisms evolved from a common ancestor;
k. base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships;
I. cladograms show the relationships between clades/likely evolutionary divergence of clades;
$\mathrm{m}$. each branch point/node represents where species are formed via divergent evolution;
n. species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa);