Biology A2 Chapter 13 - Energy and Ecosystems

Question 1

Define the term producers

Answer 1

Photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide, and mineral ions

Question 2

Define the term consumers

Answer 2

Organisms that obtain their energy by feeding on other organisms rather than using the energy from the sunlight directly

Question 3

Define the term primary consumers

Answer 3

Animals that directly eat producers (green plants)

Question 4

Define the term secondary consumers

Answer 4

Animals that eat primary consumers

Question 5

Define the term tertiary consumers

Answer 5

Animals that eat secondary consumers

Question 6

Define the term saprobionts (decomposers)

Answer 6

A group of organisms that break down the complex materials in dead organisms into simple ones

Question 7

What is the importance of saprobionts

Answer 7

When the break down the complex materials, they release valuable minerals and elements in a form that can be absorbed by plants and so contribute to recycling

Question 8

What is a trophic level?

Answer 8

A stage in a food chain

Question 9

Define the term biomass

Answer 9

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

Question 10

How is biomass measured?

Answer 10

Using dry mass per given area, in a given time. More specifically, in grams per square metre if land, if a volume then grams per cubic metre

Question 11

What is calorimetry used for?

Answer 11

Estimating the chemical energy store in dry mass

Question 12

Describe the process of bomb calorimetry

Answer 12

• A sample of dry material is weighed and then burnt in pure oxygen within a sealed chamber called a bomb
• This bomb is surrounded by a water bath and the heat of combustion causes a small temperature rise in this water
• We know how much heat (energy) is required to raise the temperature of 1g of water by 1 degree, if we know the volume of water and the temperature rise, we can calculate the energy released from the mass of burnt biomass in kJ/kg

Question 13

Define the term gross primary production

Answer 13

The total quantity of the chemical energy store in a plant biomass, in a given area or volume, in a given time

Question 14

Define the term net primary productivity

Answer 14

The chemical store left when when energy losses for respiration have been taken into account

Question 15

What is the formula for net primary production?

Answer 15

Gross primary production - respiratory losses

Question 16

What is the formula for the net production of consumers?

Answer 16

N = I - (F+R)
Where:
N is the net production
I is the chemical energy store of ingested food
F is the energy lost in faeces or urine
R is the energy lost in respiration

Question 17

What is the simple sequence of a nutrient cycle?

Answer 17

1. The nutrient is taken up by producers as simple, inorganic molecules
2. The producer incorporates the nutrient into complex organic molecules
3. When the producer is eaten, the nutrient passes into consumers
4. It then passes along the food chain when these animals are eaten by other consumers
5. When they die, their complex molecules are broken down by saprobiontic microorganisms that release the nutrient in its original, simple form for the cycle to begin again

Question 18

How do plants take up the nitrogen they require?

Answer 18

In the form of nitrate ions (NO3-) from the soil which are absorbed using active transport through the roots

Question 19

What are the four main stages of the nitrogen cycle?

Answer 19

Ammonification, nitrification, nitrogen fixation, and denitrification

Question 20

What happens in ammonification?

Answer 20

It is the production of ammonia from organic nitrogen-containing compounds, such as urea and nucleic acids. Saprobiontic microorganisms feed on faeces and dead material, releasing ammonia which then forms ammonium ions in the soil

Question 21

What happens in nitrification?

Answer 21

When bacteria obtain their energy from chemical reactions involving inorganic ions, such as the conversion of ammonium ions to nitrate ions, an oxidation reaction which releases energy. It is carried out by nitrifying bacteria and is carried out in two stages:
- Oxidation of ammonia to nitrite ions (NO2-)
- Oxidation of nitrite ions to nitrate ions (NO3-)

Question 22

What happens in nitrogen fixation?

Answer 22

The process by which nitrogen gas is converted into nitrogen containing compounds

Question 23

What are the two types of microorganisms which carry out nitrogen fixation?

Answer 23

• Free living nitrogen fixing bacteria: reduce gaseous nitrogen to ammonia which they then use to manufacture amino acids. Nitrogen rich compounds are then released from then when they die and decay
• Mutualistic nitrogen fixing bacteria: live in nodules on the roots of plants and obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria

Question 24

What happens in denitrification?

Answer 24

When denitrifying bacteria convert soil nitrates into gaseous nitrogen, reducing the availability of nitrogen containing compounds for plants

Question 25

When are denitrifying bacteria found?

Answer 25

When soils become water logged and have low oxygen concentration, fewer aerobic nitrifying and nitrogen fixing bacteria are found and there is an increase in anaerobic denitrifying bacteria

Question 26

What is the definition and role of mycorrhizae in nutrient cycles?

Answer 26

• Mycorrhizae are associations between certain types of fungi and the roots of the vast majority of plants
• They increase the surface area for the absorption of water and minerals and act like a sponge to hold the water and minerals. This enables the plant to better resist drought and to take up inorganic ions more readily

Question 27

Why is the mycorrhizal relationship between plants and fungi and mutualistic one?

Answer 27

The plants benefit from improved water and inorganic ion uptake while the fungus receives organic compound such as sugars and amino acids from the plant

Question 28

Why are fertilisers added to soil?

Answer 28

To offset a loss of mineral ions

Question 29

What are the two types of fertilisers?

Answer 29

• Natural (organic) fertilisers: consist of the dead and decaying remains of plants and animals as well as animal waste
• Artificial (inorganic) fertilisers: mined from rocks and deposits and then converted into different forms and blended together to give the appropriate balance of minerals for a particular crop

Question 30

What are the positives of nitrogen containing fertilisers?

Answer 30

They increase the rate of photosynthesis and improves crop productivity, they provide us with cheaper food

Question 31

What are the negatives of nitrogen containing fertilisers?

Answer 31

• Reduced species diversity
• Leaching
• Eutrophication

Question 32

How does the use of nitrogen containing fertilisers lead to reduced species diversity?

Answer 32

Due to nitrogen rich soils favouring the growth of grasses, nettles and other rapidly growing species. These outcompete many other species, which die as a result, reducing species diversity

Question 33

What is leaching?

Answer 33

The process by which nutrients are removed from the soil by rainwater which dissolves any soluble nutrients and carrying them deep into the soil, eventually beyond the reach of plant roots. These leached nitrate ions find their way into water sources where they may have a harmful effect on humans and fish

Question 34

What does a high nitrate ion concentration in drinking water lead to?

Answer 34

• Prevent efficient oxygen transport in babies
• Has a link to stomach cancer in humans

Question 35

What is eutrophication?

Answer 35

The process by which nutrient concentrations increase in a body of water

Question 36

What are the sequence of events by which eutrophication occurs?

Answer 36

1. In most lakes and rivers there is naturally a very low concentration of nitrate and so nitrate ions are a limiting factor for plant and algal growth
2. As the nitrate ion concentration increases as a result of leaching, it ceases to be a limiting factor and so the populations grow
3. As algae mostly grow on the surface, the upper layers of water become densely populated (algal bloom)
4. This absorbs light and prevents it from penetrating to lower depths
5. Light then becomes the limiting factor for plants at lower depths so they die
6. The increase in dead plants becomes beneficial for saprobiontic bacteria so their populations grow
7. The saprobiontic bacteria require oxygen for respiration, creating an increased demand for oxygen
8. The concentration of oxygen in the water is reduced and nitrates are released from the decaying organisms
9. Oxygen becomes the limiting factor for the population of aerobic organisms, such as fish, who then die
10. There is less competition for anaerobic organisms, whose populations now rise
11. The anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes, such as hydrogen sulphide, which make the water putrid