The Earth’s Atmosphere (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards

1. Photosynthesis

2. Respiration

3. Combustion

4. Decay

5. Industrial uses of limestone (e.g. making cement)

False.

Plants both absorb CO₂ during photosynthesis and release CO₂ during respiration. The net effect depends on the balance between these two processes.

During decay, microorganisms break down dead organisms and release carbon dioxide back into the atmosphere as they respire.

Limestone (calcium carbonate, CaCO₃) is heated during cement and concrete production. This causes thermal decomposition, releasing CO₂:

CaCO₃ → CaO + CO₂

1. As carbon dioxide in the atmosphere

2. Dissolved in ocean water

3. As calcium carbonate (CaCO₃) in shells and limestone

4. In fossil fuels (coal, oil, natural gas)

5. As carbohydrates in living organisms

True.

Decomposers break down dead material and release carbon dioxide as they respire, returning carbon to the atmosphere as part of the carbon cycle.

Carbon passes along food chains when animals feed on plants, transferring carbon compounds to animal tissues.

Combustion of fossil fuels releases carbon dioxide that has been locked underground for millions of years back into the atmosphere, rapidly increasing atmospheric CO₂ concentration beyond natural cycling rates.

The greenhouse effect is the process by which greenhouse gases in the atmosphere absorb outgoing long-wavelength (infrared) radiation from Earth's surface, reducing heat lost to space and keeping Earth warm enough to support life.

1. Carbon dioxide (CO₂)

2. Methane (CH₄)

3. Water vapour

Short-wavelength radiation from the Sun passes (is transmitted) through the atmosphere and is absorbed by Earth's surface, which then re-emits it as long-wavelength (infrared) radiation.

True.

Greenhouse gases absorb the long-wavelength infrared radiation re-emitted by Earth's surface. This reduces the amount of radiation that escapes to space, raising the surface temperature.

Different substances absorb, transmit or reflect electromagnetic radiation differently depending on wavelength. The atmosphere transmits the short-wavelength radiation from the Sun, but greenhouse gases absorb the longer-wavelength infrared radiation re-emitted by Earth's surface.

False.

Without greenhouse gases, more heat would escape to space and Earth's surface would be much colder — too cold to support life as we know it. Greenhouse gases are essential for maintaining habitable temperatures.

1. Short-wavelength radiation from the Sun is transmitted through the atmosphere

2. Earth's surface absorbs this radiation

3. The surface re-emits it as long-wavelength (infrared) radiation

4. Greenhouse gases absorb this outgoing radiation

5. This reduces heat lost to space, raising Earth's surface temperature

Increasing levels of carbon dioxide and methane are significantly upsetting Earth's natural conditions by trapping extra heat energy.

1. Burning fossil fuels (coal, oil, gas) for electricity, transport and industry

2. Deforestation — fewer trees means less CO₂ removed from the atmosphere by photosynthesis

True.

Farming (especially livestock) and landfill sites (where organic waste decomposes) are major sources of increased methane emissions.

Climate change is a long-term shift in worldwide weather patterns and conditions, linked to rising levels of greenhouse gases in the atmosphere causing global temperatures to increase.

The scientific consensus that human activities are causing climate change is based on systematic reviews of thousands of peer-reviewed publications, where results are checked by other scientists.

Future methane levels depend on unpredictable human behaviour, for example:

• Whether livestock farming will increase or decrease

• Whether people will eat less meat

• Whether landfill production will change

• Whether greater climate awareness will drive down emissions

True.

Historical data lacks the precision of modern instruments and covered fewer locations (no satellites or global networks). Methods such as ice cores, fossil records and tree rings are used to estimate past conditions but are less precise.

Climate models must account for many complex changes on Earth, and detailed data is not available from all parts of the world. Scientists also have to make assumptions about future greenhouse gas emissions, introducing uncertainty into predictions.

Methods used to estimate past climate conditions include analysis of the fossil record, tree rings and gas bubbles trapped in ice.

Scientists conclude this is more than a correlation — the rise in greenhouse gas concentrations has caused the rise in temperature. This conclusion is supported by systematic reviews of thousands of peer-reviewed publications.

Mitigation means taking steps to slow climate change by reducing the rate at which greenhouse gases enter the atmosphere. It does not reverse changes already caused.

1. Rising sea levels — melting ice caps cause coastal flooding and habitat loss

2. Loss of habitats and biodiversity — flooding and temperature changes destroy ecosystems

3. Changes in species distribution — species forced to move to cooler regions or higher altitudes

False.

Rising sea levels also cause increased soil salinity, damaging agricultural land, as well as destroying habitats for birds, fish and plants, and permanently reducing usable land.

Protecting forests helps mitigate climate change because trees absorb CO₂ during photosynthesis, and stopping deforestation preserves these carbon stores.

Recycling reduces energy needed to manufacture new products, reducing fossil fuel combustion and CO₂ emissions. It also reduces the volume of waste in landfill, which decreases methane emissions from decomposing organic material.

True.

Renewable energy sources (solar, wind, tidal, hydroelectric) do not release greenhouse gases during electricity generation, making them a key mitigation strategy to replace fossil fuels.

Peat bogs store large amounts of carbon in organic matter. If they are drained, burned or disturbed, the stored carbon is released as CO₂. Protecting them prevents this release and keeps the carbon locked away.

Carbon capture and storage technology captures CO₂ produced at power stations before it reaches the atmosphere and stores it underground.

As global temperatures rise, some previously cool regions may experience conditions warm enough for agriculture that were not viable before. However, this benefit is outweighed globally by the reduced yields in regions suffering drought and heat stress.

Carbon monoxide (CO) is a colourless, odourless toxic gas produced by incomplete combustion of fuels. It binds to haemoglobin in red blood cells, preventing them from carrying oxygen.

Carbon monoxide forms during incomplete combustion, when there is a limited supply of oxygen. The carbon in the fuel is only partially oxidised to CO rather than fully oxidised to CO₂.

True.

Some fossil fuels contain sulfur as an impurity. During combustion, sulfur reacts with oxygen to form sulfur dioxide: S + O₂ → SO₂

Oxides of nitrogen form when nitrogen and oxygen from the air react at the extreme temperatures reached in car engines and power stations.

CO binds to haemoglobin, so red blood cells carry less oxygen. The heart beats faster to compensate and try to deliver enough oxygen to cells.

Acid rain is caused by sulfur dioxide (SO₂) and oxides of nitrogen (NO_x) dissolving in water in clouds to form acids.

Effects include:

1. Corrosion of metal structures and limestone buildings

2. Damage to aquatic organisms in rivers and lakes

False.

Greenhouse gases cause global warming by trapping heat in the atmosphere. Pollutants (like SO₂ and CO) cause harm closer to the ground, such as acid rain, smog, and respiratory damage.

Particulates are tiny solid particles released into the atmosphere by human activity, including soot from diesel engines and dust from roads. Smaller particulates penetrate deep into the lungs and can cause heart disease and lung cancer.

Larger particulates clump together as soot and blacken buildings, while smaller ones are inhaled and penetrate deep into the lungs, potentially causing heart disease and lung cancer.

False.

Soot (carbon particles) forms during incomplete combustion when there is very little oxygen. Hydrocarbons break down without fully combusting, releasing solid carbon particles.

Evaporation is the process by which liquid water gains energy from the Sun and turns into water vapour, rising into the atmosphere.

True.

Water exists as a solid (glaciers and ice), a liquid (oceans, rivers and lakes) and a gas (water vapour in the atmosphere).

As water vapour rises, the air cools and the vapour condenses into tiny liquid droplets, forming clouds.

When water droplets in clouds become heavy enough, they fall back to Earth as precipitation, which can be rain, sleet, snow or hail.

Water acts as the solvent for chemical reactions in cells, allowing many substances to dissolve so that biochemical reactions can take place.

False.

Water is a product of respiration, not a reactant. In photosynthesis, water acts as the reactant.

Two biochemical reactions involving water as a reactant or product are:

1. Photosynthesis: carbon dioxide + water → glucose + oxygen

2. Respiration: glucose + oxygen → carbon dioxide + water

Solid water in glaciers can melt to form liquid water, which may then evaporate and enter the atmosphere as water vapour.

Potable water is water that has been processed and is safe for human consumption. It may contain small amounts of dissolved minerals but must be free from bacteria and harmful microbes.

False.

Pure water contains only H₂O molecules. Potable water may also contain small amounts of dissolved minerals and salts but is safe to drink.

The two main stages are:

1. Filtration: passing water through sand and gravel filter beds to remove particles

2. Sterilisation: using chlorine, ozone or ultraviolet light to kill bacteria and harmful microbes

In water treatment, chlorine is added to water (or ozone or UV light used) to kill any remaining bacteria and make the water safe to drink.

Desalination is the process of producing potable water from seawater or salty water where fresh water supplies are limited. It can be done by distillation or reverse osmosis, both of which require significant energy.

In reverse osmosis, salt water is forced under pressure through a semi-permeable membrane that allows water molecules to pass through but blocks dissolved salts and ions.

True.

In anaerobic digestion, sealed tanks allow anaerobic bacteria to break down sewage sludge, releasing methane that can be used as an energy source. The remaining waste can be used as fertiliser.

In sedimentation, water stands still in a settlement tank so that heavier solids sink to form sewage sludge, while lighter matter (effluent) floats to the top for further treatment.

During sewage treatment, aerobic digestion involves pumping air into the effluent so that aerobic bacteria can break down organic matter.

The purpose of the dissolved solids practical is to determine the amount of dissolved solid in water samples, using evaporation from a weighed evaporating basin.

The sample is filtered first to remove any suspended solid particles, so that only the truly dissolved solids remain in the water that is then evaporated.

True.

A pH meter gives decimal values, while universal indicator paper only gives whole number values. The two methods have different resolution and cannot be averaged together.

In the distillation practical, the thermometer must be positioned to measure the temperature of the vapour, not the boiling liquid, so that an accurate boiling point is recorded.

Two ways to confirm the distillate is pure water:

1. Test its pH — should be 7

2. Measure its boiling point — should be 100°C

False.

The delivery tube must sit above the liquid in the collecting tube. If submerged, cold water can be sucked back into the hot flask when heating stops, causing the glass to crack.

Placing an ice bath around the collecting tube or using a Liebig condenser increases the rate of condensation and so improves the volume of pure water collected.

In simple distillation, the water sample is heated until it evaporates, the vapour rises and is then condensed, so that pure liquid water is collected.