10.2Air and the Environment
Photosynthesis and the carbon dioxide balance in air — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 9 parts Lesson 5 of 7 Unit quiz
Lesson summary
10.2 Photosynthesis and the carbon dioxide balance in air — COMBINED SCIENCE (CHEMISTRY) notes: State the word and balanced equations for photosynthesis, explain why it is endothermic and describe how it removes carbon dioxide from the air.Photosynthesis — green plants use light …
- Conditions
- Word equation
- Balanced symbol equation (extended tier)
- Photosynthesis is endothermic
- Respiration
- Removal of carbon dioxide
Section 1 of 9Photosynthesis: reactants, products and conditions
Photosynthesis
- Photosynthesis green plants use light energy to convert carbon dioxide and water into glucose and oxygen
Reactants
- Reactants carbon dioxide enters the leaves from the air and water is taken up through the roots
Conditions
- Conditions light energy and chlorophyll in chloroplasts are required
- Light and chlorophyll are not reactants, so they are written over the arrow.
Section 2 of 9Equations for photosynthesis
Word equation
Word equation carbon dioxide + water → glucose + oxygen (light, chlorophyll)
Balanced symbol equation (extended tier)
6CO2 + 6H2O → C6H12O6 + 6O2
- Six CO2 molecules supply the six carbon atoms of glucose.
- Each side has 6 C, 12 H and 18 O atoms.
Section 3 of 9Energy change in photosynthesis
1Photosynthesis is endothermic
- Photosynthesis is endothermic energy is taken in from the surroundings
- Chlorophyll in the chloroplasts absorbs energy from sunlight.
2Glucose
- Glucose stores some of this energy in its chemical bonds
Section 4 of 9Fate of glucose in the plant
Respiration
- Respiration glucose is used to release energy
Storage
- Storage glucose is converted to starch
Growth
- Growth glucose is used to make other substances
Section 5 of 9Photosynthesis and carbon dioxide in the air
1Removal of carbon dioxide
- Removal of carbon dioxide photosynthesis takes CO2 from the air and fixes its carbon in plant material
2Return of carbon dioxide
- Return of carbon dioxide respiration and combustion add CO2 to the air
- Photosynthesis is therefore one part of the carbon cycle.
| Process | Effect on atmospheric CO2 |
|---|---|
| Photosynthesis | Removes |
| Respiration | Adds |
| Combustion of fuels | Adds |
Section 6 of 9Reducing atmospheric carbon dioxide with plants
Reducing atmospheric carbon dioxide with plants
Planting trees and reducing deforestation
- Planting trees and reducing deforestation more photosynthesis removes more CO2
Rate of removal
- CO2 is removed faster only if light, water and a suitable temperature are available
Limit
- Limit plant uptake alone does not cancel all emissions from burning fossil fuels
Section 7 of 9More from the specification
More from the specification
Greenhouse Gases and Climate Change
- Greenhouse gases such as carbon dioxide and methane in the Earth's atmosphere absorb infrared radiation re-emitted from the Earth's surface, trapping thermal energy and contributing to global climate change.
Atmospheric Pollutants from Fossil Fuels
- Combustion of fossil fuels releases acidic gases including sulfur dioxide and oxides of nitrogen,
- which dissolve in rainwater to form acid rain that harms aquatic ecosystems and damages forests and limestone structures.
Strategies to Reduce Atmospheric Emissions
- Catalytic converters reduce harmful nitrogen oxides and carbon monoxide emissions in vehicle exhaust,
- while switching from fossil fuels to renewable sources helps mitigate greenhouse gas buildup.
Photosynthesis and Carbon Dioxide Balance
- Photosynthesis by terrestrial plants and phytoplankton removes carbon dioxide from the atmosphere and releases oxygen, balancing the carbon cycle against respiration and combustion.
Greenhouse Gases and Climate Change
- Greenhouse gases such as carbon dioxide and methane in the Earth's atmosphere absorb infrared radiation re-emitted from the Earth's surface, trapping thermal energy and contributing to global climate change.
Atmospheric Pollutants from Fossil Fuels
- Combustion of fossil fuels releases acidic gases including sulfur dioxide and oxides of nitrogen,
- which dissolve in rainwater to form acid rain that harms aquatic ecosystems and damages forests and limestone structures.
Strategies to Reduce Atmospheric Emissions
- Catalytic converters reduce harmful nitrogen oxides and carbon monoxide emissions in vehicle exhaust,
- while switching from fossil fuels to renewable sources helps mitigate greenhouse gas buildup.
Photosynthesis and Carbon Dioxide Balance
- Photosynthesis by terrestrial plants and phytoplankton removes carbon dioxide from the atmosphere and releases oxygen, balancing the carbon cycle against respiration and combustion.
Climate change
- A long-term shift in worldwide weather patterns and conditions
Sulfur dioxide
- An acidic gas made when sulfur-containing fuels burn.
Incomplete combustion
- Burning in limited oxygen to give CO, soot and water.
Global warming
- Rise in the Earth's average temperature caused by extra greenhouse gases.
Carbon monoxide
- A toxic gas that binds to haemoglobin.
Complete combustion
- Burning in plenty of oxygen to give carbon dioxide and water.
Greenhouse effect
- Absorption and re-emission of thermal energy by atmospheric gases, which reduces energy lost to space.
Catalytic converter
- A device that converts toxic exhaust gases into less harmful gases.
Oxide
- A compound of oxygen with one other element.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Photosynthesis | Process in green plants that uses light energy to make glucose and oxygen from carbon dioxide and water. |
| Chlorophyll | Green pigment in chloroplasts that absorbs light for photosynthesis. |
| Endothermic | A reaction that takes in energy from the surroundings. |
| Carbon cycle | Movement of carbon between the air, living things and fuels. |
| Reforestation | Planting trees to replace those removed, increasing CO₂ uptake. |
Section 9 of 9Exam technique
1
Writing light or chlorophyll as reactants — they are conditions shown over the arrow
2
Calling photosynthesis exothermic — it takes in energy from sunlight
3
Saying plants take in oxygen for photosynthesis — they take in CO₂ and release O₂
4
Assuming planting trees fully cancels fossil-fuel emissions — the net effect depends on the balance of all processes
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