Answer

The answers provided here reflect the style and content of a typical Examination Board Mark Scheme. Here is a key to expressions and symbols of a typical Mark Scheme:

Mark schemes usually start by showing the term "Expected Answers" this means the answers expected by the majority of candidates & agreed at a standardisation meeting of examiners.

/ this means that any one part of an answer will meet the criterion for a question

; a semicolon separates parts of an answer

AVP This standards for Alternative Valid Point which allows for an examiner to ask if the point can be awarded a mark

e.g. 2 of: 2 answers from choice of

alt.,: alternate valid wording

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Energy transferred through an ecosystem is measured in kJ m^-2 year^-1.

(a) What is an ecosystem?

Habitat/environment + community (/described system) / (all the) biotic and abiotic factors in an area/in an environment;

[ 1 ]

(b) Light trapped by producers is considerably less than light measurements over a given area. Give two reasons for the reduction in light trapped by the producers.

Reflected / absorbed by water;

Reflected from producers;

Transmitted / passes between chloroplasts/ between plants / too few chloroplasts;

(Reject .not absorbed. unqualified)

Wrong wavelength / some = heat / some = UV / used to evaporate water;

Used to drive reactions of photosynthesis / lost in photosynthesis;

Other limiting factor / named example . carbon dioxide / temperature; [ 2 max ]

[ 2 ]

(c) The biomass of producers is determined as being higher than that of consumers. Explain why.

Loss of energy/heat / use of energy / less energy to be passed on;

In respiration;

In excreta / excretion / urine / carbon dioxide;

Inedible parts / indigestible parts / egesta / egestion / to decomposers; [2 max]

[ 2 ]

(d) Oxygen is a by-product of photosynthesis. Where in the chloroplast does the light-dependent reactions occur?

Grana / granum / thylakoids / internal membranes / lamellae;

[ 1 ]

(e) An area of a field is to be sampled for the frequency of Ragwort. The area chosen measures 100m x 50m. Explain how the area should be sampled using a 0.5m quadrat.

Place (ignore if throwing / throw used) quadrats at random coordinates / described;

Find / score mean no. of ragwort per quadrat / total for all quadrats;

Mean x 5000 [area of field] / or mean x (ratio of area of field : area of quadrat) /

or/ total x (ratio of area of field : area of all quadrats);

[ 3 ]

(f) The field also has a thick hedgerow which is a habitat for the banded and white-lipped snail (Caepea spp). A group from a local wildlife trust used the Mark & Recapture method of sampling. 26 snails where captured and marked on day one. The next day, the group returned and captured 7 marked snails.

Suggest one criticism of the group's method. Identify how their method would reduce accuracy of an estimate of population number.

Initial sample / marked recapture sample too small;

Small change in data would give large change in population estimate /

leads to overestimate of population;

Or

Paint on shells > more visible to predators / paint toxic / paint comes off;

> overestimate of population size;

Or

One day too short;

thus

Too many marked snails recaptured > underestimate of population size /

too few marked snails recaptured > overestimate of population size; [ 2 max ]

[ 2 ]

[Total: 11]