Topic 9: Ecosystems

Question 1

Describe the levels that ecosystems are organised in to

Answer 1

Individual - a single organism
Population - All the organisms of one species in a habitat
Community - All the organisms of different species living in a habitat
Ecosystem - A community of organisms along with all the abiotic conditions

Question 2

What is meant by interdependence?

Answer 2

• Organisms depend on each other for food/shelter to survive and reproduce
• It means that a change in the population of one species can have huge knock on effects for other species in the same community

Question 3

What’s mutualism? - add an example

Answer 3

• A relationship between two organisms from which they both benefit
• e.g. bees get food from plants and the plants get help reproducing

Question 4

Describe parasites

Answer 4

• Parasite lives very closely with a host species (in or on them) to take what they need to survive, but the host doesn’t benefit
• e.g. fleas feed on host’s blood without offering anything in return

Question 5

How do Abiotic environmental factors affect communities?

Answer 5

Temperature

Amount of water - daisies grow best in slightly damp soil, so when it is too dry or waterlogged, population of daisies will decrease

Light intensity - trees grow and provide more shade, so grasses may be replaced by fungi/mosses etc.. because they can better cope with lower light intensity

Levels of pollutants - Lichen are unable to survive if sulfur dioxide concentration in the air is too high

Question 6

How do Biotic environmental factors affect communities?

Answer 6

Competition - organisms compete with other species/members of their own species for the same resources e.g. red and grey squirrels live in the same habitat and eat the same food, leaving not enough food for the red squirrels so the population of red squirrels is decreasing

Predation - e.g. If number of a predator decreases, the number of their prey will increase

Question 7

Quadrats

Question 8

How do you estimate a population size from a sample area?

Answer 8

Find the mean number of organisms per Msquared, then multiply the mean by the total area of the habitat

Question 9

Belt transect core practical

Question 10

Explain the food chain, beginning with the sun

Answer 10

• Sun is a source of energy for nearly all life on earth, plants convert a small % of light energy that falls on them into glucose. Some of this glucose is used in respiration immediately and some of the rest is stored as biomass
• First animal eats the plant, uses some energy from the plant, some of the rest is stored in its body as biomass
• Second animal eats it and gets some of the energy stored in the animal’s biomass

Question 11

Explain how energy is used in the food chain

Answer 11

• Energy is used by organisms to stay alive at each stage like in respiration. This transfers energy for all life processes like movement. A lot of energy is transferred to the surroundings by heat
• The energy transferred to the surroundings isn’t stored as biomass, so isn’t transferred to the organisms in the next trophic level
• Not all energy stored as biomass gets transferred to the next trophic level as not all of the organism gets eaten (e.g. the bones). Also, not everything eaten can be digested, so undigested material is lost from the food chain in faeces

Question 12

Define Biomass

Answer 12

The mass of living material that makes up an organism

Question 13

What do pyramids of biomass show?

Answer 13

How much weight the creatures at each level of the food chain would weigh, and how much energy there is at each stage

Question 14

What are the levels in pyramids of biomass labelled as?

Answer 14

Producer –> primary consumer –> secondary consumer –> etc…

Question 15

How do you calculate the efficiency of energy transfers between trophic levels?

Answer 15

Energy at next level/Energy at previous level
x 100

Question 16

What’s biodiversity?

Answer 16

The variety of living organisms in an ecosystem

Question 17

Explain how fertilisers impact biodiversity

Answer 17

• Nitrates are put onto fields as fertilisers. If too much fertiliser is applied and it rains afterwards, the nitrates easily find their way into rivers and lakes.
• These excess nitrates cause the algae to rapidly grow which blocks out light.
• So, plants can’t photosynthesise due to this lack of light and begin to die.
• Now that more food is available, microorganisms that feed on decomposing plants increase in number so they use up oxygen in the water
• So, organisms that need oxygen for aerobic respiration like fish die

Question 18

Explain how Fish farming impacts biodiversity

Answer 18

• Reduce biodiversity
• Food is added to the nets to feed fish, fish produce huge amounts of waste which can leak into open water, causing the death of wild species
• Predators like sea lions are attracted to the nets and become trapped in them and die

Question 19

Explain how the introduction of non indigenous species impacts biodiversity

Answer 19

• Non-indigenous species compete with indigenous species for resources like food and shelter
• Sometimes, they out-compete the indigenous species so they decrease in numbers and die out eventually
• Non-indigenous species can also bring new diseases to a habitat which can infect and kill lots of the indigenous species which reduces the habitat’s biodiversity

Question 20

What’s a non-indigenous species?

Answer 20

A species that does not naturally occur in an area

Question 21

Explain how reforestation impacts biodiversity

Answer 21

• Reforestation helps to restore biodiversity
• Replanting to form a new forest where one previously stood
• Forests have high biodiversity as they contain a wide variety of trees and plants which provide food and shelter for lots o different animal species

Question 22

Explain how conservation schemes impact biodiversity

Answer 22

Conservation schemes protect biodiversity and the methods include:
- Protecting a species’ natural habitat so that individuals have a place to live
- Protecting species in safe areas outside of their natural habitat e.g. zoos, and introducing captive breeding programmes to increase numbers
- Seed banks to store and distribute seeds of rare and endangered plants

Question 23

Explain the benefits of maintaining biodiversity

Answer 23

Protecting human food supply - Conservation programmes to prevent over fishing so that future generations have fish to eat

Ensuring minimal damage to food chains - if one species becomes extinct, it will affect all the organisms in that food chain. So conserving one species helps others to survive

Ecotourism - People visit biodiverse areas with conservation programmes which helps bring money in so they can put even more money into conservation, this also provides NEW JOBS for locals

Question 24

What’s food security?

Answer 24

Ensuring that everyone has access to enough food that is nutritional and safe to eat

Question 25

Explain how an increase in population has affected food security

Answer 25

- more people need to eat food, so we have to produce more food so that everyone still has the same amount o food to eat

Question 26

Explain how an increase in meat and fish consumption has affected food security

Answer 26

- As people become wealthier, they buy more expensive food such as meat and fish - So there's a risk of overfishing wild fish so there won't be enough available to catch in the future

Question 27

Explain how new pests and pathogens have affected food security

Answer 27

- They cause damage to crops and livestock - If a new disease spreads to a crop, lots of the population may not be resistant to it, so a large number of crop plants will be damaged which reduces the amount that can be sold as food

Question 28

Explain how environmental changes caused by human activity have affected food security

Answer 28

- Greenhouse gases produced cause global warming (contributed to by humans) - Climate change affects the growth of crops and soil pollution which reduces our ability to grow crops

Question 29

Explain how sustainability issues have affected food security

Answer 29

Increase in crops to make biofuels in place of non renewable fossil fuels But, they take up land which could be used for food crops Higher prices for farmers (machinery, fertiliser etc...) means it is too expensive for some farmers to continue farming and maintain food production in the future

Question 29

Explain how materials are recycled in ecosystems

Answer 29

1) Living things are made of elements they take from the environment (plants take in carbon + oxygen from air and nitrogen from soil) 2) They turns these elements into complex compounds that make up living organisms. Elements are passed along food chains when animals eat the plants and each other 3) The elements are recycled - waste products and dead organisms are broken down my decomposers (usually microorganisms) and the elements are returned to the soil or air to be taken in by new plants and put back into the food chain

Question 30

Explain the carbon cycle

Answer 30

- Only a fixed amount of carbon in the world, so it is constantly recycled... 1) Plants take in CO2 in photosynthesis to make carbohydrates, fats and proteins 2) When animals eat these plants, carbon compounds are passed along to them in the food chain 3) Plant and animal respiration releases CO2 back into the air 4) When they die and decompose, they turn into useful products 5) When plants and animals decompose, they are broken down by microorganisms e.g. bacteria and fungi. These decomposers release CO2 back into the air by respiration as they break down the material 6) Wood and fuels are burned which releases CO2 back into the air 7) fill in if mark scheme requires it

Question 31

Explain the water cycle

Answer 31

1) Energy from the sun makes water evaporate from land and sea, turning it into water vapour. It also evaporates from plants in transpiration 2) Warm water vapour is carried upwards as warm air rises. When it gets higher up it cools and condenses to form clouds 3) Water falls from the clouds as precipitation onto land where it provides fresh water for plants and animals 4) It then drains into the sea and the process starts again

Question 32

Explain thermal desalination

Answer 32

- Removes salt from salt water to produce potable water - Thermal desalination: Water is boiled in a large enclosed vessel so that the water evaporates so that the steam rises and condenses in a pipe at the top and the salts stay at the bottom

Question 33

Explain reverse osmosis as a form of desalination

Answer 33

- Salt water is treated to remove solids and fed at high pressure into a vessel containing a partially permeable membrane - The pressure causes the water molecules to move from a higher salt concentration to a lower salt concentration - The water is forced through the membrane and the salts are left behind which removes them from the water

Question 34

Explain the nitrogen cycle

Answer 34

- 78% nitrogen gas in the air - Nitrogen needs to be turned into nitrate which plants can use - This is done by lightning and nitrogen fixing bacteria in roots and soil - Plants absorb these from the soil and use the nitrogen in them to make proteins - Nitrogen is passed along food chains - Decomposers (bacteria and fungi in soil) break down proteins in rotting plants and animals and urea in animal waste, which returns nitrogen to the soil

Question 35

Explain the role of different bacteria in the nitrogen cycle

Answer 35

DECOMPOSERS - decompose proteins and urea to turn them into ammonia which forms ammonium ions in solution that plants can use NITRIFYING BACTERIA - turn ammonia in decaying matter to nitrite, then to nitrates NITROGEN-FIXING BACTERIA - turn nitrogen into ammonia, forming ammonium ions DENITRIFYING BACTERIA - turn nitrates into nitrogen gas

Question 36

Why do farmers increase nitrates in the soil?

Answer 36

- Crops take up nitrates in the soil, but they are harvested instead of being left to decompose so the nitrates aren't returned back to the soil - So, the nitrogen content of the soil decreases, leading to poor crop growth

Question 37

Explain crop rotation

Answer 37

- Different crops are grown each year in a cycle, including peas or beans which put nitrates back into the soil

Question 38

Explain Fertilisers in increasing nitrates in soil

Answer 38

- Artificial fertilisers contain nitrates (but are expensive) - Animal manure or compost recycles nutrients left in plant and animal waste and returns them to the soil by decomposition

Question 39

How are indicator species used to monitor water pollution?

Answer 39

If nitrates are released into a river, microorganisms in the water increase in number and use up the oxygen so.... - Freshwater shrimps and stonefly larvae are very sensitive to concentration of dissolved oxygen, so the water is clean - Bloodworms and sludge worms indicate a very high level of water pollution as they are adapted to live in polluted conditions

Question 40

How are indicator species used to monitor air quality?

Answer 40

Lichen are sensitive to sulfur dioxide concentration (which is a pollutant). So, if there are lots of lichen, the air is clean

Question 41

How does Temperature affect the rate of decay?

Answer 41

Warm temperature speeds up rate of enzyme-controlled reactions in microbes, so decay happens faster. Enzymes denature if the temperature gets too high

Question 42

How does Water Content affect the rate of decay?

Answer 42

In moist environments, rate of decay increases as the organisms involved in decay need water to survive and carry out biological processes

Question 43

How does Oxygen Availability affect the rate of decay?

Answer 43

Rate of decay increases when there is plenty of oxygen available as many microorganisms need oxygen for aerobic respiration.

Question 44

How do you calculate the rate of decomposition?

Answer 44

Amount/time