B3- Humans and their environment

Question 1

Why did the human population increase?

Answer 1

Before the beginning of agriculture - around 10,000 years ago - small groups of humans wandered across large areas, hunting and gathering just enough food to stay alive. Population numbers were kept low because of the difficulty of finding food.
Over time, the development of agriculture led to increases in population around the world. But it was not until the 20th century that population numbers began to explode, and this steep rise was accelerated by huge improvements in hygiene and healthcare.

Question 2

What else has there been a rise in?

Answer 2

People in the developed world now enjoy a high standard of living - with abundant food, cars and comfortable housing. People in the developing world have a lower standard of living, but many countries are catching up quickly.

Question 3

How does the large human population and an increase in the standard of living affect the world?

Answer 3

Non-renewable energy resources (such as coal, oil and natural gas) are being used up rapidly.
Raw materials are being used up rapidly.
More land is being used for buildings and transport networks, quarrying, farming and dumping waste - reducing the amount of land available to other animals and plants.
More waste is being produced - causing more pollution.

Question 4

What is pollution?

Answer 4

the addition of substances to the environment that may be harmful to living organisms .

Question 5

What are herbicides and pesticides used for?

Answer 5

Herbicides increase crop yield by killing or inhibiting the growth of weeds, reducing the competition for resources such as minerals, space and sunlight. Pesticides increase yield by killing off pests, such as small insects or plant pathogens, which would otherwise feed on or damage the crops.

Question 6

What is the problem with herbicides and pesticides?

Answer 6

some of these chemicals can remain in the soil for long periods, polluting the land, and they may also be washed into rivers, lakes and seas. There can also be consequences further up food chains within an eco-system- with pollution disrupting food chains or accumulating to toxic levels.

Question 7

What is the problem with waste?

Answer 7

Most rubbish is buried in landfill sites and some of it may be unsafe. Even common household items can contain toxic chemicals such as poisonous metals. Industrial waste is also discharged onto the land.

Question 8

What causes water pollution?

Answer 8

Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas.

Question 9

What is the problem with fertilizers?

Answer 9

Fertilisers are used by farmers to increase their crop yield, supplying extra minerals to their plants so they grow better. However, these minerals can run off into waterways and lead to a process called eutrophication. This involves the over-growth of algae and ultimately leads to oxygen depletion from the water and the death of invertebrates and fish. This causes food chains within the eco-system to collapse.

Question 10

What does eutrophication mean?

Answer 10

excessive nutrients in a lake or other body of water, usually caused by runoff of nutrients (animal waste, fertilizers, sewage) from the land, which causes a dense growth of plant life; the decomposition of the plants depletes the supply of oxygen, leading to the death of animal life

Question 11

What is the problem with sewage?

Answer 11

Sewage contains high mineral levels and can promote the process of eutrophication. It may also contain harmful pathogens.

Question 12

What is the problem with toxic chemicals?

Answer 12

Toxic chemicals from industries and mining can also pollute waterways. These chemicals might be highly toxic, or might accumulate in food chains to toxic levels.

Question 13

What is the source of smoke and what is its effect?

Answer 13

Caused by the Incomplete combustion of fossil fuels, especially coal. It Deposits soot on buildings and trees, causing them damage. Permeates the air - which can cause breathing problems in living creatures.

Question 14

What is the source of sulfur dioxide and what is its effect?

Answer 14

Caused by Combustion of fossil fuels with sulfur impurities in them, eg coal and Contributes to acid rain. This can cause weathering of buildings, the release of toxic metals from the soil, damage to aquatic ecosystems and to forests.

Question 15

What is the source of carbon dioxide and what is its effect?

Answer 15

Caused by Combustion of hydrocarbon fuels.It is a Greenhouse gas that contributes to global warming .

Question 16

What is the source of methane and what is its effect?

Answer 16

Caused by Rice fields, cows, anaerobic decomposition of landfill waste. It is a Greenhouse gas that contributes to global warming.

Question 17

What are forests- particularly rainforests important?

Answer 17

hey provide unique habitats for many unique species. They also act as a ‘carbon sink’, trapping away lots of carbon in their biomass that was previously absorbed for photosynthesis.

Question 18

What is deforestation?

Answer 18

The cutting down of trees on a large scale and at an accelerated pace.

Question 19

Reasons for deforestation?

Answer 19

To provide timber as a fuel or a building material.
To provide extra land for agriculture. This agricultural land is often used to grow rice in paddy fields or to rear cattle in order to satisfy the increasing demand for food. However, increasingly this land is being used to grow crops for biofuel production (based around bioethanol ) in order to satisfy the increasing demand for energy.

Question 20

Consequences of deforestation?

Answer 20

It reduces the rate at which carbon dioxide is absorbed and ‘locked away’ in the plant biomass by photosynthesis, as there are fewer trees.
As timber is burnt to clear space, it increases the release of carbon dioxide into the atmosphere. The remaining parts of the tree (eg the roots) are then decomposed by microorganisms. This adds further carbon dioxide to the atmosphere and so contributes to global warming.
Forest habitats are destroyed and biodiversity is reduced - meaning we lose species that could have been useful in the future- moral obligation
Cattle are often reared on the land, producing methane. Methane, a greenhouse gas, contributes more to global warming than carbon dioxide
Rice fields - created to satisfy the need for food production due to the growing population - are grown on previously deforested land and also produce methane when the crop rots.

Question 21

What is peat?

Answer 21

Peat is formed in waterlogged, acidic fens and bogs over thousands of years by the growth of mosses and other plants, which absorb and ‘lock away’ carbon dioxide during photosynthesis. When the moss dies, the waterlogged bog provides anaerobic conditions which, together with the acidity of the bog, prevent the total decomposition of the moss. It accumulates in the bogs in a partially-decomposed state, forming peat.

Question 22

Why is peat important?

Answer 22

Peat bogs cover nearly 2-3% of the Earth’s surface and are an important carbon sink,containing more ‘locked-away’ carbon than the Earth’s forests. However, the amount of biomass it contains means it can be dried and burnt as a fuel, which makes it an important energy source in some countries. Peat also has valuable properties when mixed in with soil - including improved soil structure, mineral retention, water retention and acidity - making it valuable in agriculture and gardening.

Question 23

Problems of peat?

Answer 23

Burning the peat releases its stored carbon back into the atmosphere as carbon dioxide. Similarly, as peat is mixed in with soil it is exposed to aerobic conditions and begins to decompose - which again causes the release of its trapped carbon as carbon dioxide. This is in addition to the carbon dioxide released in extracting the peat.

Question 24

What is the greenhouse effect?

Answer 24

The presence of certain greenhouse gases in our atmosphere naturally results in the Earth being warmer than it should be, as the gases trap some of the Sun’s heat and prevent it escaping from our atmosphere.

Question 25

What is global warming?

Answer 25

the term which is used to describe the increase in the Earth’s temperature above the natural greenhouse effect. This increase is caused by additional greenhouse gases being released.

Question 26

What are the two main greenhouse gases that are increasing in the earth’s atmosphere?

Answer 26

Carbon Dioxide and methane.

Question 27

Why are carbon dioxide levels increasing?

Answer 27

Humans are burning more fossil fuels to provide energy.
Humans are cutting down forests - reducing the number of trees that can absorb carbon dioxide.
Humans are destroying peat bogs – and the process of destroying them releases carbon dioxide.

Question 28

Why are methane levels increasing?

Answer 28

Humans are rearing more cattle to supply food. During their digestive process, cows produce a lot of methane.
Humans are planting more rice paddy fields to supply food. These grow in water, creating anaerobic conditions - and therefore as plants rot, methane is produced.
Humans are producing more waste - which produces methane as it decays anaerobically.

Question 29

Why do greenhouse gases cause global warming?

Answer 29

Heat from the Sun enters the Earth’s atmosphere and warms the Earth’s surface.
The Earth’s surface becomes hotter and radiates heat back out.
Some of this heat is absorbed by greenhouse gases. These gases then radiate the heat back towards Earth.
The Earth becomes warmer as a result.

Question 30

What may happen if the atmosphere raises by a few degrees?

Answer 30

cause big changes in the Earth’s climate and weather patterns
cause ice caps on land to melt causing a rise in sea level - resulting in flooding and low lying areas being submerged
reduce biodiversity as habitats are lost and organisms fail to adapt to the changed environment
cause changes in the migration patterns of birds and other organisms
result in changes to the distribution of species (ie where they are found) as some species move to cooler areas to cope with the increase in global temperatures

Question 31

What is sequestration?

Answer 31

The oceans, lakes and ponds of planet Earth are important as they absorb and ‘lock away’ over a quarter of the carbon dioxide that humans emit into the atmosphere. The process by which they absorb and lock away the carbon dioxide is known as sequestration.

Question 32

Why does sequestration occur?

Answer 32

Carbon dioxide being soluble and dissolving directly in the water.
Phytoplankton performing photosynthesis which absorbs carbon dioxide, trapping the carbon within their biomass.

Question 33

How can sequestration help global warming?

Answer 33

As carbon dioxide levels in the atmosphere rise, it is likely that more would be sequestered in the oceans, rivers and ponds.Many organisations and companies are also looking at how more carbon dioxide can be sequestered by enhancing natural sequestration (eg getting the phytoplankton to do more photosynthesis) or by using artificial sequestration.

Question 34

What are biofuels?

Answer 34

Biofuels are produced from natural products, often plant biomass containing carbohydrate. As biofuels are produced from plants, they are renewable and theoretically carbon neutral.

Question 35

How are some biofuels made?

Answer 35

Some biofuels are produced by using microorganismsto anaerobically ferment carbohydrate in the plant material, as is the case with bioethanol and biogas production (each process uses different microorganisms).

Question 36

How is bioethanol made?

Answer 36

Ethanol can be made by a process called fermentation. This converts sugar into ethanol and carbon dioxide if conditions are anaerobic. Single-celled fungi, called yeast, contain enzymes that are natural catalysts for making this process happen:
In some countries, eg Brazil, the source of sugar is sugar cane - which yeast can directly ferment into ethanol. In other countries, plants such as maize are used. Because maize contains starch rather than sugar, the enzyme amylase must first break down the starch into sugar before the yeast can ferment it into ethanol.
The ethanol produced by yeast only reaches a concentration of around 15 per cent before the ethanol becomes toxic to the yeast. In order to make it sufficiently concentrated to be burnt as a fuel, the ethanol must be distilled.

Question 37

What are the disadvantages of bioethanol?

Answer 37

The demand for biofuel crops means greater demand on rainforest land.
Crops grow slowly in parts of the world that have lower light levels and temperatures, so growing biofuel crops in these countries would not satisfy the demand for fuel.
For bioethanol to be burnt in a car engine, some engine modification is needed.
Although biofuels are in theory carbon neutral, this does not take into account the carbon dioxide emissions associated with growing, harvesting and transporting the crops, or producing the ethanol from them. Therefore, overall, more carbon dioxide is emitted than is absorbed - which means that it contributes to global warming.
Some people morally object to using food crops to produce fuels. For example, it could cause food shortages or increases in food prices.

Question 38

What is biogas?

Answer 38

Biogas is a biofuel produced from the anaerobic fermentation of carbohydrates in plant material or waste (eg food peelings or manure) by bacteria.

Question 39

What is biogas made off?

Answer 39

It is mainly composed of methane, with some carbon dioxide and other trace gases. However, the proportion of methane within the biogas can vary between 50% and 80%, depending on whether some oxygen is able to enter at the beginning or during the process. If some oxygen is present, the bacteria will respire aerobically and will produce a gas with a higher proportion of carbon dioxide and a lower proportion of methane.

Question 40

How does a biogas generator/digester work?

Answer 40

The carbohydrate-containing materials are fed in, and a range of bacteria anaerobically ferment the carbohydrate into biogas. The remaining solids settle to the base of the digester and can be run off to be used as fertiliser for the land. These types of biogas generator are most commonly used in the developing world to satisfy the needs of a small family.

Question 41

What is the optimum temperature for biogas production?

Answer 41

32-35 Degrees Celsius

Question 42

What is the problem and the solutions to using biogas generators/disgesters in colder countries?

Answer 42

Temperatures below optimum slow the respiration rate of bacteria resulting in slower biogas production. The solution is to bury the biogas generator or build the biogas generator with thick walls to insulate the generator and keep the inside warmer than the external temperature.

Question 43

What is the problem and the solutions to using biogas generators/digesters in hotter countries?

Answer 43

Temperatures above optimum begin to denature bacterial enzymes, resulting in slower biogas production. The solution is to bury the biogas generator in the ground. The ground helps to insulate the biogas generator to keep it cool during the day and warm at night.

Question 44

How can biogas be produced from landfill sites?

Answer 44

Biogas is naturally produced in landfill sites as bacteria anaerobically break down our rubbish, but normally the methane escapes into the atmosphere where it contributes to global warming. If a pipe network with holes in it can be built into the landfill site - and the methane is prevented from escaping into the atmosphere by covering the site - then the methane can be collected via the pipe network.

Question 45

How can the efficiency of food production be improved?

Answer 45

by reducing the number of levels in the food chain. This is because fewer energy losses occur along a shorter food chain, meaning a greater proportion of the energy that entered the food chain is available to humans and more people can be fed.

Question 46

The efficiency of food production from animals can be improved by reducing the amount of energy lost to the surroundings. How can this be done?

Answer 46

Preventing animals moving around too much - this conserves energy which can be used to increase biomass.
Keeping their surroundings warm - this preserves the energy which would have been used to maintain their body temperature, so that it can be used to increase biomass.
Such practices are known as factory farming.

Question 47

What are the advantages and disadvantages of factory farming?

Answer 47

The main advantages for keeping animals in warm sheds with little space to move are that it results in more efficient food production - and therefore cheaper food. However, there are disadvantages in terms of reduced animal welfare, increased risk of injury, and increased risk of diseases (eg salmonella amongst chickens).

Question 48

How do you work out the efficiency of an energy transfer?

Answer 48

By working out the percentage of the energy transfer.

Question 49

What is Mycoprotein?

Answer 49

Mycoprotein is a high-protein food produced from the fungal biomass of a soil fungus called Fusarium . It also has a high fibre content, and is low in fat with no cholesterol. This makes it a healthy, vegetarian alternative to meat.

Question 50

What is mycoprotein grown in?

Answer 50

Mycoprotein is grown in a fermenter - an apparatus for growing cultures on a large scale.

Question 51

How is the fermenter set up to grown mycoprotein?

Answer 51

The fermenter is aseptically filled with a sterile broth containing glucose syrup, obtained from the breakdown of plant starch by amylase enzymes. To this is added a small starter culture of the Fusarium fungus.
Sterile glucose syrup, ammonia and air (containing oxygen) are then added continuously for a period of six weeks, so that the fungus has the correct nutrients and conditions to grow.
The role of the ammonia is to provide a nitrogen source for the fungus to produce amino acids - the building blocks of protein - while the air ensures that the conditions in the fermenter are aerobic as well as mixing the broth to ensure it is uniform throughout.

Question 52

What happens during the six-week period in the fermenter and afterwards?

Answer 52

During the six-week period, the fungus and grows, doubling its biomass every five hours. The cooling coils remove the excess heat generated by the fungus during respiration, keeping the temperature inside the fermenter constant at its optimum level.
At the end of the six-week period, the fungal biomass is harvested and purified by heating it to 65oC to remove harmful substances, and spinning it dry using a centrifuge. The yellow solid substance which is obtained can then be flavoured and shaped into different products.

Question 53

What is the definition of unsustainability?

Answer 53

An activity which uses up resources or damages the environment so that it cannot be continued in the future.

Question 54

What happened to the North sea cod?

Answer 54

North Sea cod have been overfished since the 1960s. Increasing numbers of boats - using increasingly sophisticated technology - were able to catch more and more cod. At first, catches continued to rise each year. However, the size of catches then started to decline as cod populations fell, leaving fewer and fewer breeding fish to maintain cod numbers.

Question 55

Why is it important to conserve fish stocks?

Answer 55

In order to prevent the disappearance of certain fish species in some areas, it is important to maintain fish stocks at a level that allows breeding to occur and ensures that fish populations remain at a sustainable level.

Question 56

What regulations did the European union introduce to converse fish stocks?

Answer 56

Setting fishing quotas for EU countries and for individual fishing vessels, which limited the amount of each species of fish which could be caught. By catching fewer fish, more are left to breed, so in time the population should recover.
Limiting mesh size of the nets. By increasing the size of the holes in nets, only mature, full-sized fish can be caught and immature fish can escape and eventually breed, allowing the population to recover.

Question 57

What are food miles?

Answer 57

The distance that food travels from the farm where it is produced to the consumer is referred to as ‘food miles’. Locally grown produce has far fewer food miles than produce grown in other countries.

Question 58

What is the advantage of having a lot of food miles?

Answer 58

In order to supply cheap produce all year round, many supermarkets import food from other countries around the world - where it is cheaper to produce or grows more plentifully. Some developing countries rely on food exports to the UK to generate income.

Question 59

What are the disadvantages of having a lot of food miles?

Answer 59

The greater the distance the food has travelled, the greater the impact on the environment. This is due to the pollution from carbon dioxide emissions, generated by the transporting vehicles.
A compromise must be found between the monetary cost to the consumer, the impact on developing economies and the environmental cost of the pollution associated with transporting food over such long distances.