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A2 Biology > Topic 5B - Energy Transfer and Nutrient Cycles > Flashcards

Topic 5B - Energy Transfer and Nutrient Cycles Flashcards

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1
Q

What is an ecosystem?

A

All of the organisms living in a particular area and all the abiotic conditions

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2
Q

What is found in all ecosystems?

A

Producers - organisms that make their own food

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3
Q

What 2 things is the glucose, made in photosynthesis, used for?

A
  1. Some is used in respiration, to release energy for growth
  2. Some is used to make other biological molecules like cellulose. These biological molecules makesup a plant’s biomass - the mass of living material
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4
Q

What is dry mass?

A

The mass of organism with water removed = measured in kg m^-2)

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5
Q

How can you use dry mass to measure the biomass of an organism

A

A sample of the organism is dried in an oven at a low temp. The sample is then weighed at regular intervals and once the reading becomes constant, all the water has been removed
- If needed, result from sample can be scaled up to give the dry mass/biomass of the total population of the area being investigated.

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6
Q

What proportion of the dry mass is carbon?

A

The amount of carbon the organism contains is taken to be 50% of the dry mass

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7
Q

Why is dry mass a measure of biomass rather than wet mass?

A

It can’t be a measure of wet mass as the water content of living tissue varies

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8
Q

How can you use calorimetry to estimate the amount of chemical energy stored in biomass?

A

By burning the biomass in a calorimeter

  1. A sample of dry biomass is burnt and the energy released is used to heat a known volume of water
  2. The change in water temp is usedto calculate the chemical energy of the dry biomass
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9
Q

Define these key words:

  1. Gross Primary production (GPP)?
  2. Respiratory loss (R)?
  3. Net Primary production?
A
  1. GPP = The total amount of chemical energy converted from light energy by plants, in a given area.
  2. R = The 50% of the GPP that is lost to the environment as heat when the plants respire.
  3. NPP = The remaining chemical energy (NPP=GPP-R). - - It is the energy available to the plant for growth and reproduction.
    - It is also the energy available to organisms at the next stage of the food chain. These include herbivores and decomposers.
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10
Q

What is primary productivity?

A

When primary production is expressed as rate (i.e the total amount of chemical energy (or biomass) in a given area, in a given time.
- typical units are kJ ha^-1 year ^-1 (kj per hectare per yr) OR kJ m^-2 yr^-1

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11
Q

Do only plants store chemical energy in their biomass?

A

No, consumers also store chemical energy in their biomass, which they get and transfer by eating plants and other animals.

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12
Q

How much of the total energy, available to a consumer , is lost and not transferred to the next trophic level?

A

90%

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13
Q

Give 3 of the ways that energy is lost from the food chain?

A
  1. Not all the food is eaten (e.g. bones, plant roots) so the energy it contains is not taken in.
  2. Some parts are indigestible, so are egested as faeces (or urine when kidney filters out substances substances such as ions). The chemical energy stored in these parts is therefore lost to the environment.
  3. Some energy is lost to the environment through respiration or excretion.
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14
Q

Define ‘consumers net production’ and how can you calculate it?

A

Consumers net production (AKA secondary production) = The energy that’s left and available to other trophic levels after some of it is lost in the various ways mentioned.

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15
Q

What is the calculation to work out ‘consumers net production’?

A

N = I - (F + R)

N = net production
I = Chemical energy ingested in food 
F = Chemical energy lost in faeces or urine
R = Energy lost by respiration
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16
Q

What does a food chain show?

A

simple lines of energy transfer

- each stage of the food chains is callled a trophic level

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17
Q

What does a food web show?

A

They show lots of food chains in an ecosystem and how they overlap

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18
Q

What are decomposers and give an example of one?

A

They are part of the food webs that break down or undigested materials, allowing nutrients to be recycled.

EXAMPLE: fungi

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19
Q

What are the 2 main methods that farmers use to increase the efficiency of energy transfer ?

A
  1. They reduce the energy lost to other organisms by simplifying the food web
  2. They reduce the energy lost through respiration
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20
Q

What substances do farmers to reduce pest numbers/ reduce energy lost to other organisms?

A
  1. They use chemical pesticides
  2. Thy use biological agents
  3. They can use both chemical and biological methods (which is the most efficient and increases NPP the most)
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21
Q

Give examples of chemical pesticides.

A
  • Insecticides: they kill insects that eat and damage crops, which means les biomass is lost from crops so they grow larger, increasing NPP
  • Herbicides: They kill weeds. This can remove direct competition with crop for energy from sun. ** It can also remove the preferred habitat or food source of the insect pests, helping to further reduce their numbers and simplify the food web.
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22
Q

Give examples of biological agents.

A
  • Parasites: Parasites live in/lay their eggs on a pest insect. This either kills the insect or reduces its ability to function
  • Pathogenic bacteria and viruses: These give pests diseases to kill them.

(natural predators can be used to kill pests, but this wouldnt really simplify the food web)

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23
Q

How do farmers reduce respiratory losses?

GIVE EXAMPLE

A

By controling the conditions that animals live in, so that more biomass is available and more energy can be stored and used for growth, increasing NPP.

E.G. movement increases the rate of respiration, so animals are kept in pens to restrict movement. .
- The pens are often indoors and warm, so less energy is wasted through respiration

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24
Q

However, what are the downsides of farmers techniques to reducing respiratory losses?

A

It raises ethical issues

25
Q

What is a natural ecosystem?

A

A natural ecosystem is one that hasn’t been changed by human activity.
- ** In natural ecosystems, nutrients are recycled through the food webs, but human activity often disrupts the cycling of nutrients

26
Q

What are saprobionts?

Give examples of some saprobionts

A

They are a type of decomposer that feed on the remains of dead plants and animals and on their waste products (faeces, urine), breaking them down. This allows important chemical elements in the remains to be recycled.
- many micro-organisms, such as bacteria and fungi, are saprobionts and are an important part of food webs

27
Q

How do saprobionts digest their food?

A

Via extracellular digestion: they secrete enzymes and digest their food externally, then absorb the nutrients they need
- during the process, organic molecules are broken down into inorganic ions

28
Q

Define saprobiotic nutrition

A

Saprobiotic nutrition is obtaining nutrients from dead organic matter using extracellular digestion

29
Q

What does fungi form a symbiotic relationship with?

A

The roots of plants

30
Q

Describe 3 ways that depict fungis symbiotic relationship (aka mycorrhizae) with the roots of plants

A
  1. Fungi are made up of long, thin strands called hyphae, which connect to plant roots.
  2. The hyphae greatly increase the SA of the plants roots system, helping it to absorb more water/ ions from the soil that is usually scarce (E.h phosphorus).
  3. In turn, the fungi obtain organic compounds, such as glucose, from the plant.
31
Q

There’s about 78% if nitrogen in the air, why don’t plants and animals just use that nitrogen DIRECTLY to make proteins and nucleic acids???

A

Because plants and animals can’t use it in that form - they need bacteria to convert it into nitrogen-containing compounds first.

32
Q

State the 4 steps of the nitrogen cycle

DIAGRAM

A
  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
33
Q

Describe stage 1 of the nitrogen cycle

A

NITROGEN FIXATION (when N2 in the atmosphere is turned into nitrogen-containing compounds)

  • carried out by bacteria like Rhizobium which turn N2 into ammonia, which goes on to form ammonium ions in solution that can then by used by plants
  • Rhizobium are found inside root modules (growths in the roots) of leguminous plants (peas, beans)
  • they form a mutualistic relationship with plants: they provide plants with nitrogen compounds and plants provides them with carbohydrates
34
Q

Describe stage 2 of the nitrogen cycle

A

2- AMMONIFICATION (N2 compounds from dead organisms are turned into ammonia by saprobionts, which goes on to form ammonium ions)
- animal waste also contains N2 compound. These are also turned into ammonia by saprobionts and go on to form ammonium ions

35
Q

Describe stage 3 of the nitrogen cycle

A

3- NITRIFICATION: ammonium ions in the soil are changed into nitrogen compounds (nitrates) that can then be used by plants

  • first nitrifying bacteria called Nitrosomonas change ammonium ions into nitrites
  • then other nitrifying bacteria called nitrobacter change nitrites into nitrates
36
Q

Describe stage 4 of the nitrogen cycle

A

4 - DENITRIFICATION (nitrates in soil converted back into N2 gas by denitrifying bacteria)

  • the bacteria use nitrates in the soil to carry out respiration and produce N2 gas
  • this happens under anaerobic conditions e.g. in waterlogged soils
37
Q

Name 2 other ways that Nitrogen enters an ecosystem.

A
  1. Lightning (which fixes atmospheric N2)

2. Artifical fertilisers (produced from atmospheric N2 on an industrial scale in the Haber Process)

38
Q

How do animals receive nitrogen compounds from plants?

A

By eating the plants and each other. (passing along food chains)

39
Q

Why do plants and animals need phosphorus?

A

To make biological molecules such as phospholids, DNA, and ATP

40
Q

Where is phosphorus found and in what form?

A

Phosphorus is found in rocks and dissolved in the oceans in the form of phosphate ions

41
Q

Define assimilated

(Give example of how a molecule may be assimilated)

A

Phosphate ions dissolves in water in the soil may be assimilated (absorbed and then used to make more complex molecules) by plants and other producers

42
Q

Define ‘phosphorus cycle’

A

A cycle that shows how phosphorus is passed through an ecosystem, by passing through a food web

43
Q

Name step 1-3 of the phosphorus cycle

DIAGRAM

A
  1. Phosphate ions in rocks are released into soil by weathering
  2. These ions are taken into plants through roots. Mycorrhizae greatly increases the rate at which phosphorus can be assimilated
  3. Ions are transferred through food chain as animals eat plants and each other
44
Q

Name steps 4-7 of the phosphorus cycle

DIAGRAM

A
  1. The P ions are lost from animals in waste products
  2. When plants/animals die, saprobionts will break down organic compounds and urine/faeces, releasing the P ions into the soil for assimilation by plants.
  3. Weathering of rocks also releases P ions into seas, lakes and rivers. This is taken up by by aquatic producers like algae, and passed along the food chain to birds.
  4. Waste produced by sea birds is known as guano and contains a high proportion of P ions. Guano returns a significant amount of P ions to soils (particularly in coastal areas). It is often used as a natural fertiliser.
45
Q

Where do crops get their minerals from and what do they use them for?

A

They take in minerals from the soil as they use them to grow and build their own tissues

46
Q

How are nutrients lost when crops are harvested?

A

As harvesting would mean that crops are removed from the field where they’re grown (rather than being allowed to die and decompose there), mineral ions wouldn’t be returned to the soil by decomposers in the nitrogen/phosphorus cycle.

47
Q

How are nutrients lost when animals are removed from the land?

A

Animals take in nutrients by eating plants, but if they’re taken elsewhere to be slaughtered/transferred to a different field, the nutrients aren’t returned to the soil through their remains/waste products

48
Q

What is the main purpose of fertilisers?

A

They replace lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer.

49
Q

Outline the 2 types of fertilisers

A
  1. Natural fertilisers: organic matter E.g. Manure, composted vegetables, crop residues (parts left after harvest), sewage sludge
  2. Artifical fertilisers: inorganic matter (E.g. Pure chemicals like ammonium nitrate in the form of powders or pellets)
50
Q

What are the disadvantages of using fertilisers?

A
  1. They can cause leaching (which can lead to eutrophication)
  2. They can change the balance of nutrients in the soil - too much of a particular nutrient can cause crops and other plants to die
51
Q

What is leaching and what can cause it?

A

Leaching: when water-soluble compounds in the soil are washed away e.g. by rain or irrigation systems, into places like ponds and rivers

It can be caused when more fertiliser is applied than the plants need/are able to use at a particular time

52
Q

Which type of fertilisers are more likely/less likely to leach into waterways?

A

MORE LIKELY: chemical fertilisers as excess inorganic ions in them are relatively soluble.

LESS LIKELY: natural fertilisers as the N2 and P ions are contained in organic molecules that need to be decomposed by micro-organisms before they can be absorbed by plants. This means that their release into soil for uptake by plants is more controlled, and leaching is less likely.

53
Q

Which type of ion is more likely/less likely to leach into waterways?

A

Leaching of phosphates is less likely than the leaching of nitrates because phosphates are less soluble in water

54
Q

Describe the process of eutrophication (5 points)

DIAGRAM

A
  1. Mineral ions leached from fertilised fields stimulate the rapid growth of algae in ponds/rivers
  2. Large amounts of algae block light from reaching plants below.
  3. Eventually plants die because they can’t photosynthesise enough
  4. Bacteria feed on dead plant matter. Increase numbers of bacteria reduce O2 conc in water by carrying out aerobic respiration
  5. Aquatic organisms since not enough O2
55
Q

Why is the biomass of primary consumers less than the biomass of consumers in most communities?

A

Energy may be lost during respiration so there would be less energy to pass on to the primary consumers.

56
Q

Why may the biomass of producers be less than that of primary consumers?

A

The producers rate of reproduction may be equal to or less than their rate of consumption.

57
Q

Give 2 advantages of an organic fertiliser?

A
  1. Reduces eutrophication/leaching

2. Improves soil quality

58
Q

Give 2 advantages of inorganic fertiliser?

A
  1. Nutrients available immediately

2. They don’t contain pests

A2 Biology (11 decks)

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