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Date	May 2017	Marks available	2	Reference code	17M.2.SL.TZ1.2
Level	Standard level	Paper	Paper 2	Time zone	Time zone 1
Command term	Explain	Question number	2	Adapted from	N/A

Question

Pictured below are Louis Pasteur’s original drawings of swan-necked flasks.

Describe how Pasteur’s experiments provided convincing evidence to falsify the concept of spontaneous generation.

[3]

a.

State the function of life in Paramecium that is carried out by:

cilia.

[1]

b.i.

State the function of life in Paramecium that is carried out by:

the contractile vacuole.

[1]

b.ii.

Discuss the advantages and disadvantages of the use of adult stem cells.

[3]

c.

Explain the role of decomposers in an ecosystem.

[2]

d.

Markscheme

a. spontaneous generation is life appearing from nothing / from non-living / cells only come from pre-existing cells/life

b. broth/culture medium (for bacteria) (used/placed) in flasks

c. broth boiled/sterilized «in some flasks» to kill microbes

d. no clouding/signs of bacterial growth/reproduction / microbes did not appear «in flasks of boiled broth»

Allow bacteria or organisms instead of microbes.

e. after necks of flasks were snapped boiled broth became cloudy/growth of microbes

f. because microbes from the air contaminated the «boiled» broth

g. curved necks allowed indirect exposure to air but prevented entry of microbes

a.

movement/locomotion
OR
feeding/nutrition

b.i.

homeostasis
OR
maintain osmotic balance / expels «excess» water / maintains «cell» water content

b.ii.

Advantages:

a. «adult stem cells» can divide «endlessly» / can differentiate

b. «adult stem cells» can be used to repair/regenerate «tissues»

c. fewer ethical objections «than with embryonic stem cells»

d. adults can give «informed» consent for use of their stem cells

e. adult source is not killed / «source» would not have grown into new human / no death of embryos used to provide stem cells

f. no rejection problems / patient’s own cells used

g. less chance of cancer/«malignant» tumor development «than from embryonic stem cells»

h. most tissues in adults contain some stem cells

Disadvantages:

i. difficult to obtain/collect/find in adult body/very few available

j. some «adult» tissues contain few/no stem cells

k. «adult stem cells» differentiate into fewer cell types «than embryonic cells» /OWTTE

c.

a. saprotrophs/decomposers feed on/break down dead «organic» matter

b. saprotrophs/decomposers release energy «heat» accelerating decomposition/warming soil

c. saprotrophs/decomposers recycle nutrients / make nutrients available (to producers)
OR
improves soil fertility / returns nutrients (minerals/nitrates/phosphates/carbon)to soil/water/environment

d. saprotrophs/decomposers detoxify waste

d.

Examiners report

[N/A]

a.

[N/A]

b.i.

[N/A]

b.ii.

[N/A]

c.

[N/A]

d.

Syllabus sections

Core » Topic 4: Ecology » 4.2 Energy flow

Show 46 related questions

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19M.1.HL.TZ1.14:
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[Source: © International Baccalaureate Organization 2019]

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19M.1.SL.TZ1.18:
The diagram shows the food web for an aquatic ecosystem in which letters R–Z represent individual species.

[Source: © International Baccalaureate Organization 2019]

Which organism is a tertiary consumer?

A. Organism T

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The image shows an example of a soil food web.

[Source: Anon., n.d. The Soil Food Web. [image online] Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/
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Draw a labelled diagram of a pyramid of energy.
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Outline energy flow through a community in a natural ecosystem.
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21M.1.SL.TZ2.18:
The diagram shows the flow of energy through an ecosystem in ${kJ m}^{- 2} y^{- 1} .$

[Source: “Energy flow: Figure 3,” (https://cnx.org/contents/24nI-KJ8@24.18:fbNheNoN@8/Energy-Flow) by OpenStax College, Biology CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).]

What percentage of the energy passed from primary producers to primary consumers is lost to cellular respiration by tertiary consumers?

A. 0.001%

B. 0.08%

C. 0.2%

D. 0.4%
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Explain how energy enters, flows through and is lost from marine food chains.
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[Source: © International Baccalaureate Organization 2019]

What do level I and level III represent in the pyramid of energy?

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Core » Topic 4: Ecology