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Date May 2017 Marks available 3 Reference code 17M.2.SL.TZ1.2
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term Discuss 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 1: Cell biology » 1.1 Introduction to cells
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