4.3 Cycles within ecosystems

Question 1

carbon cycle

Answer 1

the cycle where carbon moves between organisms and the environment, namely in the form of carbon dioxide and involving:
respiration
photosynthesis
fossilisation
combustion

Question 2

decomposers in the nitrogen cycle

Answer 2

organisms that release enzymes that catalyse the breakdown of dead plant and animal material
releasing nitrogen containing compounds such as ammonia into the soil

Question 3

Combustion

Answer 3

when fossil fuels are burnt
- releases carbon dioxide into the atmosphere

Question 4

nitrogen fixation

Answer 4

the process by which atmospheric nitrogen in the air is converted to nitrates and ammonia in the soil.
Nitrogen fixation happens in two ways:
Via lightning - lightning converts atmospheric nitrogen directly into nitrates

Via nitrogen-fixing bacteria - these convert atmospheric nitrogen into ammonia

Question 5

Nitrification

Answer 5

Nitrification is carried out by nitrifying bacteria in the soil, and consists of two steps:
Ammonia in the soil is first converted to nitrites.
Those nitrites are then converted to nitrates.

Question 6

What happens to nitrates after being absorbed by plant roots?

Answer 6

they are combined with carbohydrates (from photosynthesis)
to form amino acids which are then made into proteins, and nucleotides which are joined to make DNA and RNA

Question 7

What happens when animals eat plants?

Answer 7

they digest the proteins and DNA, absorbing the small soluble molecules (amino acids ad nucleotides)
these are then used by the animal to synthesise new proteins and DNA (assimilation)

Question 8

What happens when a plant or animal dies?

Answer 8

its tissues are decomposed by bacteria and fungi (saprotrophic nutrition)

Question 9

What happens to the molecules containing nitrogen such as proteins?

Answer 9

broken down by the bacteria and fungi and ammonia is released into the soil

Question 10

deritrification

Answer 10

In denitrification, denitrifying bacteria in the soil convert nitrates back into atmospheric nitrogen.

Question 11

denitrifying bacteria

Answer 11

bacteria that convert nitrates in the soil into nitrogen gas
occurs when conditions are anaerobic and can be prevented by ploughing the soil –> ensures there is enough oxygen to prevent the growth of these organisms

Question 12

nitrifying bacteria

Answer 12

aerobic organisms that convert ammonia to nitrites and then nitrates which can be absorbed by plants using active transport

Question 13

nitrogen cycle

Answer 13

the cycle through which nitrogen moves between living organisms and the environment

Question 14

nitrogen fixing bacteria

Answer 14

bacteria that convert nitrogen gas into nitrogen containing compounds that plants can use
- can be free living in the soil or found in root nodules of leguminous plants

Question 15

What is the name of the process that converts nitrates to atmospheric nitrogen?

Answer 15

Denitrification

Question 16

Which process describes how plants use nitrogen to build biological molecules?

Answer 16

Assimilation

Question 17

Where is nitrogen-fixing bacteria found?

Answer 17

soil
roots of some plants

Question 18

Assimilation

Answer 18

Assimilation is the process by which plants absorb nitrates and ammonium ions, and use them to create biological molecules such as proteins. These biological molecules form part of the plant’s tissues.

When animals eat plants they assimilate these nitrogen containing compounds (e.g. proteins) into their own bodies

Question 19

Decomposition

Answer 19

Decomposition occurs when decomposers feed on the waste excretions of animals, and the rotting corpses of dead plants and animals. During this process they convert urea and proteins into ammonia.

The ammonia in the soil forms ammonium ions, which is one of few the nitrogen-containing compounds plants can absorb and assimilate

Question 20

Why is denitrification bad for plants?

Answer 20

Denitrification is bad for plants because it means there are fewer nitrates in the soil, reducing the amount available for the plants to absorb and assimilate.

Question 21

Human activity which acts as a source for: carbon dioxide

Answer 21

burning fossil fuels
slash and burn forest clearance

Question 22

Human activity which acts as a source for: methane

Answer 22

Generated by bacteria in anaerobic conditions, for example:
cattle produce large volumes of methane
from the anaerobic activity of bacteria in their gut
Bacteria in waterlogged paddy fields for rice cultivation give off methane

Question 23

Human activity which acts as a source for: nitrous oxides

Answer 23

burning fossil fuels

Question 24

Human activity which acts as a source for: CFCs

Answer 24

Until the 1990’s CFCs were used as a solvent for aerosols such as deodorants
They were also used in fridges and freezers

Question 25

The potential effects of climate change: melting of polar ice caps

Answer 25

If ice shelves over land melt, such as over Greenland and Antarctica, this will lead to sea level rises, causing flooding in coastal regions worldwide

Question 26

The potential effects of climate change: destruction of habitats

Answer 26

For example, grassland may turn to desert (desertification), leading to the loss of habitat for resident species. This could lead to the extinction of species.

Question 27

The potential effects of climate change: drought and desertification

Answer 27

can lead to crop failure and therefore to food shortages and famines

Question 28

The potential effects of climate change: increased extreme weather events

Answer 28

Extreme weather event such as hurricanes could become more frequent as there is more energy present in weather systems due to global warming

Question 29

The potential effects of climate change: spread of diseases

Answer 29

As the planet warms it will be possible for disease carrying organisms, such as mosquitos, to survive in a wider range of countries. This means diseases such as malaria and dengue fever are likely to become more common

Question 30

The potential effects of climate change: change in crops

Answer 30

As areas warm it will become possible to grow different crops (e.g. olives and grapes in Southern England). This will be beneficial to some countries.

Question 31

The potential effects of climate change: increase in heat related illness and deaths

Answer 31

In recent years there have been increases in death rates in the elderly associated with heat waves

Question 32

Define the term decomposer

Answer 32

organisms that break down the dead plant and animal matter

Question 33

Define the term 'locked in' in relation to the carbon cycle

Answer 33

formation of fossil fuels over millions of years

Question 34

What is the enhanced greenhouse effect?

Answer 34

increased intensity of the natural greenhouse effect due to human activities

Question 35

Explain how increasing carbon dioxide can cause climate change

Answer 35

greenhouse gas traps air causes global warming