The Carbon Cycle

Question 1

Which (debatably) are the most important elements for life

Answer 1

‘CHOP’
Carbon, hydrogen, oxygen and phosphorus

Question 2

How could you say CO₂ and O₂ is cycled between aerobically respiring organisms and primary producers

Answer 2

Plants produce O₂ in photosynethesis
Animals and plants utilsise O₂ in respiration and produce CO₂ as a byproduct

Question 3

How does photosynthesis work

Answer 3

Light will promote electrons with chlorophyll and CO₂ reacts with RuBP, and through a series of reaction large complex organic sugars are formed
Water is then used to remove any electrons
These sugars are then stored and used by the plant

Question 4

How does aerobic respiration work?

Answer 4

breaks down large organic sugars using oxygen forming ATP
ATP is then hydrolysed to release energy

Question 5

What is the difference between organic and inorganic carbon

Answer 5

Organic carbon has been reduced (gain of electrons) e.g. organic sugars
Inorganic carbon has been oxidised (loss of electrons) e.g. CO₂, H₂CO₃
HCO₃
Photosythesis is considered the reduction of carbon (CO₂ to complex sugars)
Aerobic respiration is considered oxidation of carbon (complex sugars to CO₂)

Question 6

How would the presence of lots of reduced carbon in the world, related to its oxidation state

Answer 6

Low levels of oxygen, as the large organic carbon molecules have not been oxidised, and hence remain in the reduced form

Question 7

What is Oxidation

Answer 7

The loss of electron OR and increase in oxidation number

Question 8

What is Reduction

Answer 8

Is the gain of electrons OR a decrease in the oxidation number

Question 9

What is a redox reaction

Answer 9

A reaction where one species is oxidised and one species is reduced

Question 10

If a substance has a highly positive redox potential

Answer 10

It is likely to gain electron (be reduced)

Question 11

If a substance has a highly negative redix potential

Answer 11

it is likely to losses electron (oxidised)

Question 12

Name a way dead organic matter can be broken down

Answer 12

Fungi and microbes will consume organic matter in the form of decay

Question 13

What is the shortest Organic Carbon cycles

Answer 13

• On land, production of reduced organic carbon by photosynthesis is balanced by the production of oxidised carbon by respiration and decay
  (plants however need to be consumed for this repsiration to occur
  It is a never ending cycle)
• Photosynthesis is also balance by decay as the of the tree will return any carbon back to the atmosphere in the form of photosynthesis

Question 14

The short-term carbon cycles occurs around every 1000yrs
What does it involve

Answer 14

Microscopic microplankton will photosynthesis (short life span where they will quickly die) and life the ocean floor, where it decays back to CO₂
The deep oceans becomes enriched in CO₂
But carbon is recyled to the surface every 1000yrs, when water is slowly moved from the N.Atlantic to the Pacific ocean and brought up to the surface

Question 15

dead microscopic microplankton line the ocean floor when they have died and broken down into CO₂ during decay
Why would this not happen

Answer 15

Small amounrs of organic carbon will become buried in ocean sediments which will become rock, becoming part of the fossil record
Hence they don’t move to the Pacific as they become part of ocean sediment like rock

Question 16

Describe the long-term carbon cycle (across around 300 million years)

Answer 16

This reduced carbon does not decay and instead returns its carbon and oxygen to the atmosphere quickly
Over millions of years, it has accumulated into a vast reservoir of reduced carbon (including coal, oil and gas)
However, the reduced carbon in rocks is turned back to CO₂ by exposure to atmospheric oxygen

Question 17

In the long term carbon cycle there are 4 ways CO₂ can be returned to the atmosphere, name them:

Answer 17

• Subducted Calcium carbonate and Organic carbon forms mantle and the is put back into the atmosphere by volcanoes
• Coal, oil and gas is converted back to CO₂ when it comes into contact with oxygen at the surface
• Release of CO₂ from sedimentary organic C weathering
• Release of CO₂ and CH₄ from metamorphism and deep diagenesis

Question 18

In the long term carbon cycle there are 4 ways carbon can enter this system, name them:

Answer 18

• Subduction of calcium carbonate and organic carbon
• conversion of CO₂ to dissolved HCO₃⁻ by Ca-Mg silicate weathering
• Burial of calcium carbonate into oceans
• Burial of Organic carbon into oceans

Question 19

What is metamorphism

Answer 19

is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. It takes place at high temperatures temperatures (excess of 150 to 200°C) and pressures

Question 20

What is silicate weathering

Answer 20

CaSiO₃ + CO₂ → CaCO₃ + SiO₂
Silicate weathering of rocks uses gaseous CO₂
The byproducts are the transported into rivers and oceans where they are stored
The calcium carbonate is used by organisms to build shells etc

Question 21

In the Long-term carbon cycle, describe to feedback loop between weathering and volcanism

Answer 21

Weathering - removes CO₂ from the atmosphere
Volcanoes - returns CO₂ to the atmosphere

Question 22

How can the weathering and volcano feedback loop also affect the stability of our climate

Answer 22

• If CO₂ levels are higher - temperature will increase - leading to faster silicate weathering - leading to more CO₂ to be removed from the atmosphere
• If CO₂ levels are lower - temperature will decrease - leading to slower silicate weathering - leading to less CO₂ to be removed from the atmosphere

Question 23

The Earth’s temperature is stabilised by opposing CO₂ inputs from volcanic activity and CO₂ removal by silicate weathering
Why does this guarantee absolute stability

Answer 23

• Volcanic acitivity varies
• Greenhouse gases can be added in other ways (anthropogenic impacts)
• Silicate weathering rate varies
• Carbon bural rate varies

Question 24

For most of the time the Earth has been warmer than it is today (there has been temperature decline for the past 60MYA)
Has this been caused by less CO₂ in or out

Answer 24

The level of volcanic eruption has not changed
Therefore it must be to do with more silicate weathering - hence more CO₂ being removed from the atmosphere
It is suspected due to the increase in mountainous terrian which will experience high levels of weathering (in particular the Andes and Himalayans)
There have also been increase Monsoons, leading to higher rainfall and weathering

Question 25

Why are the Himalayans and Andes said to be responsible for this increases weathering

Answer 25

Around 50MYA there was a super continent which included the US, New Zealand, India and Australia
India started rapidly moving North, where it eventually collided with Asia
This contiental collision created mountain belts and the Himalayans being pushed up - this is thought to have affected weathering and hence the current climate

Question 26

Why are volcanoes so important

Answer 26

if all the volanoes ceased to be active you would not have any replenishment of CO₂
All atmospheric and oceanic CO₂ would be removed in 1MY