Chapter 13 - Energy and ecosystems

Question 1

What is the initial source of energy for most organisms?

Answer 1

Sunlight

Question 2

How is energy passed between organisms?

Answer 2

Biomass

Question 3

What are producers?

Answer 3

Photosynthetic organisms that manufacture organic substances using light, water, CO2 and minerals

Question 4

What are consumers?

Answer 4

Organisms that get their energy from feeding on other organisms

Question 5

What are primary consumers?

Answer 5

Consumers that eat producers

Question 6

What are secondary consumers?

Answer 6

Those that consume primary consumers

Question 7

What are saprobionts?

Answer 7

Organisms that break complex material in dead organisms down into simple molecules

Question 8

What is a food chain?

Answer 8

A feeding relationship in which producers are eaten by primary consumers, they are eaten by secondary consumers, who are eaten by tertiary consumers

Question 9

What is each stage in a food chain called?

Answer 9

A trophic level

Question 10

What is a food web?

Answer 10

Many overlapping food chains

Question 11

What is biomass?

Answer 11

The total mass of living material in a specific area at a given time

Question 12

Why is it better to measure the dry mass?

Answer 12

The presence of water in an organism varies dependent on conditions

Question 13

Describe the process of calorimetry

Answer 13

A sample of dry material is weighed and burned in pure oxygen. The ‘bomb’ is surrounded by a water bath and we measure the change in temperature of this water

Question 14

Why is such a small percentage of the suns energy used in photosynthesis?

Answer 14

Reflected by clouds
Not all wavelengths of light can be used in photosynthesis
Light may not fall on chlorophyll
Limiting factors may reduce photosynthesis

Question 15

What is gross primary production?

Answer 15

The total quantity of chemical energy stored in plant biomass at a given time

Question 16

What is net primary production?

Answer 16

The chemical energy that remains when the loss of energy used in respiration has been accounted for

Question 17

What is the equation for net primary production?

Answer 17

Net primary production = gross primary production - respiratory losses

Question 18

Why is such a low percentage of energy transferred between trophic levels?

Answer 18

Not all of the organism is consumed
Some parts are consumed but can’t be digested so are lost in faeces
Urine
Heat is lost through respiration

Question 19

Why are fertilisers needed especially in agricultural settings?

Answer 19

Normally, plants would die and decompose, returning their nutrients to the soil. In agriculture, the plants are removed before they can decompose so the nutrients must be returned in another way

Question 20

What are natural fertilisers?

Answer 20

Consists of the dead and decaying parts of plants and animals

Question 21

What are artificial fertilisers?

Answer 21

NPK fertilisers!

Mined from rocks and deposits and combined to produce the right ratio for the crop

Question 22

How do fertilisers increase productivity?

Answer 22

Plants grow healthier and photosynthesise more

Question 23

What is nitrogen used for?

Answer 23

DNA, amino acids, ATP

Question 24

What are some of the detrimental effects of nitrogen fertilisers?

Answer 24

Leaching, eutrophication, reduced species diversity (nitrogen favoring species out-compete others so diversity decreases)

Question 25

What is leaching?

Answer 25

The process by which nutrients are removed from the soil

Question 26

Describe the process of leaching

Answer 26

Rainwater dissolved minerals and leaches it into water courses and drain into fresh water lakes. This can cause eutrophication and illness in humans if water is contaminated

Question 27

Describe the process of eutrophication

Answer 27

In most lakes, nitrate ions act as a limiting factor for algal growth
Leaching increases the concentration of nitrate ions so they are no longer limiting
An algal bloom develops
This prevents light from reaching lower depths
Plants and algae at these depths die
Saprobionts break down dead plant matter
Saprobionts use up oxygen and release co2
Oxygen becomes limiting for aerobic respiration and so fish and plants die
There is less competition for anaerobic organisms who decay the material, turning the water putrid

Question 28

Describe the phosphorus cycle

Answer 28

Phosphate ions in rocks are released by weathering
Plants absorb phosphorus through their roots
Mycorrhizae increase the rate of absorption
Phosphate ions are transferred through the food chain as organisms consume one another
Phosphate ions are lost from animals in waste products
When these animals and plants die, saprobionts break down complex material into the soil to be absorbed by plants
Weathering rocks releases phosphate into the water sources, which is taken up by aquatic producers

Question 29

What is the role of mycorrhizae in the phosphorus cycle?

Answer 29

It forms a mutualistic relationship with plants - plants benefit from the increased uptake of phosphorus and the mycorrhizae benefit from organic materials from the plant

Question 30

What is denitrification?

Answer 30

Nitrates in the soil are converted into nitrogen gas by denitrifying bacteria under anaerobic conditions

Question 31

What is nitrogen fixation?

Answer 31

Nitrogen gas in the atmosphere is converted into nitrogen-containing compounds by bacteria

Question 32

What are the two microorganisms involved in nitrogen fixation?

Answer 32

Free-living bacteria (Reduce nitrogen gas into ammonia, which they use to produce amino acids)
Mutualistic bacteria (

Question 33

What is nitrification?

Answer 33

Ammonia is oxidised to nitrite ions which are oxidised to nitrate ions

Question 34

What is ammonification?

Answer 34

Saprobionts turn nitrogen compounds in dead organisms into ammonia

Question 35

Why do nitrogen compounds easily leach through the soil?

Answer 35

They are very soluble