Download Chemosynthesis – a new source of life

Chemosynthesis – a new source of life
Teaching notes
Introduce the activity by showing a clip about photosynthesis. The site below is useful.
http://www.bbc.co.uk/learningzone/clips/plants-and-photosynthesis/6021.html
Continue by showing images/video of life around hydrothermal vents. The site below
has some examples.
http://www.bbc.co.uk/nature/habitats/Hydrothermal_vent
Pairs of students choose information sheet 1 or sheet 2.
They try to identify similarities and differences between the two processes. Once they
have found an example they write it on a slip of paper and go to stick it on a group Venn
diagram.
3 – 4 pairs can share a large Venn diagram with two circles.
With the class, discuss the information included on all the Venn diagrams.
Working in their pairs students come up with a statement which summarises what they
have learnt about chemosynthesis in the smallest number of words.
Small prizes, credits, merits, praise, applause go to the pair who can say the most in the
shortest statement.
Sources:
http://www.bigelow.org/foodweb/chain4.html
http://unvrso.hubpages.com/hub/What-are-Chemosynthetic-Bacteria
(Links all available at time of publishing.)
Suggested answers
Information sheet 1
Similarities

both processes produce sugars

the sugars produced are used to give the organism energy

the organisms which use chemosynthesis or photosynthesis are both primary
producers/ are the first step in food chains
© www.teachitscience.co.uk 2014
22247
Page 1 of 4
Chemosynthesis – a new source of life
Differences
Chemosynthesis

occurs in total darkness/ does not require light

carried out by bacteria (and archaea)

uses chemicals to power the process
Photosynthesis

requires light (and chlorophyll)

carried out by green plants and algae

uses light energy to power the process
Information sheet 2
Similarities

both are chemical reactions

both have reactants and products

use carbon dioxide

use elements H, C and O

require a source of energy to activate the reaction
Differences
Chemosynthesis

requires hydrogen sulphide

produces water and sulphur

there are several forms of chemosynthesis

energy for the reaction comes from breakdown of hydrogen sulphide molecules
Photosynthesis

requires water

produces oxygen

there is only one form of photosynthesis

requires light energy
© www.teachitscience.co.uk 2014
22247
Page 2 of 4
Chemosynthesis – a new source of life
Information sheet 1
In 1977 marine scientists were astounded to discover communities of creatures many
miles below the ocean’s surface, thriving in total darkness. The organisms were
clustered around cracks in the ocean floor where super-heated lava released clouds of
dissolved chemicals into the surrounding water.
Special bacteria around the hydrothermal vents use these dissolved chemicals to obtain
energy to manufacture sugars in a process known as chemosynthesis.
Like plants, these bacteria use the sugars they produce to give them energy to grow and
reproduce. These bacteria are eaten by organisms such as shrimps and form the first
step in a series of deep ocean food chains. Until this tremendous discovery, scientists
thought that the primary producers in all food chains were green plants and algae which
use light energy to make sugars in a process called photosynthesis.
Chemosynthetic bacteria have now been found in a wide variety of environments such as
cave water, sunken ships, ice caps, coastal mud, the decaying bodies of whales and
hydrothermal vents. Incredibly, in 2013 researchers reported finding bacteria living
within igneous rocks in the ocean’s crust.
© www.teachitscience.co.uk 2014
22247
Page 3 of 4
Chemosynthesis – a new source of life
Information sheet 2
Photosynthesis
carbon
dioxide
+
water
→
carbohydrate(sugars)
+
oxygen
Chemosynthesis
carbon
dioxide
+
hydrogen
sulphide
→
carbohydrates
(sugars)
+
water
+
sulphur
Photosynthesis
6CO2
+
6H2O
→
C6H12O6
+
6O2
Chemosynthesis
6CO2
+
12H2S
→
C6H12O6
+
6H2O
+
12S
There are many different forms of the chemosynthetic process but just one form of
photosynthesis. Both methods of making carbohydrates require an energy source. Plants
use light energy from the sun whilst chemosynthetic bacteria use energy produced from
the breakdown of hydrogen sulphide molecules.
© www.teachitscience.co.uk 2014
22247
Page 4 of 4