Ecosystems

Question 1

What is a producer?

Answer 1

Plants which photosynthesise to produce food.

Question 2

What is a consumer?

Answer 2

An animal that eats plants or other animals.

Question 3

What is a decomposer?

Answer 3

Decay dead material and help to recycle nutrients.

Question 4

What is a physical environment?

Answer 4

Is the sum total of all the non-biological components of the ecosystem e.g. The water and soil in a pond or the air and soil in a forest.

Question 5

What is a habitat?

Answer 5

Are places where specific organisms live and within each ecosystem there is a range of habitats, e.g. rock shore or a field

Question 6

What is a population?

Answer 6

Is all the organisms of a particular species found in an ecosystem at any one time.

Question 7

What is a community?

Answer 7

Is all organisms of all species found in a particular ecosystem at any one time.

Question 8

What is an ecosystem?

Answer 8

Is a distinct, self supporting system of organisms interacting with each other and the physical environment.

Question 9

What are the different interactions in ecosystems?

Answer 9

Feeding among the organisms, competition, interaction between organisms and the environment.

Question 10

Describe a pyramid of numbers

Answer 10

• Represents the number of organisms at each trophic level in a food chain, irrespective of their mass
• They have limitations because, for example, one tree can be home to many different plant-eating animals
• Dandelions go on the bottom because they are at the bottom of the food chain
• Sometimes the number pyramid is not pyramid shape at all, as 1 fox may feed 500 fleas

Question 11

Describe a pyramid of biomass

Answer 11

• Shows the total mass of the organisms in each trophic level, irrespective of their numbers
• Represent the total biomass of organisms at each trophic level in a food chain

Question 12

What does biomass mean?

Answer 12

• Is the total amount of living material in an organism

- Is the mass of biological material that makes up an organism

Question 13

Why are pyramids of biomass always pyramid shape?

Answer 13

1. Some parts of the producer are not eaten (e.g. Roots), 2. Some parts are not digested, but egested and so are not absorbed,
2. Some of the materials absorbed form excretory products
3. Many of the materials are respired to release energy, with the loss of carbon dioxide and water.

Question 14

Why is only 10% of energy transferred from one trophic level to the next?

Answer 14

1. Respiration
2. Biological processes
3. Some parts are not eaten by the next trophic level (e.g. Roots/bones)
4. Some parts are indigestible (e.g. Fibre) so are not absorbed instead egested (so the energy is NOT taken in)!
5. Most of energy is eventually lost to the surroundings as heat
   - Only 10% of the total energy available becomes biomass, i.e it is stored or used for growth

Question 15

How do you use a quadrat?

Answer 15

1. A pair of random numbers is generated (to avoid bias) which are used as coordinates to positioning the quadrat (using the two tape measures as the coordinate) - random number generator
2. The number of each plant species present in the quadrat are counted
3. A bar graph is created

Question 16

How do you estimate population sizes using a quadrat?

Answer 16

1. A quadrat is a square frame enclosing a known area, e.g. 1m squared
2. Place a 1m squared quadrat n the ground at a random point within the area you are investigating
3. Count all the organisms within the quadrat
4. Multiply the number of organisms by the total area (in m squared) of the habitat
5. You can do this again in a another area and compare the population sizes
6. Samples should be random to avoid bias (random number generator)

Question 17

What are two important points about using a quadrat?

Answer 17

1. The sample may not be representative of the population i.e. what you find in your particular sample might be different from what you would have found if you had looked at other bits of the habitat
2. The sample size affects the accuracy of the estimate, the bigger your sample the more accurate your estimate of the total population is likely to be, so it is better to use the quadrat at several points, get an average value for the number of organisms in a 1m squared quadrat, then multiply that by the total area

Question 18

How can you use quadrats to investigate the distribution of organisms?

Answer 18

1. You can use quadrats to help find out how organisms (like plants) are distributed across their habitat e.g. how species change from a hedge towards the middle of a field
2. The quadrats are laid out along a lien called a transect
3. Mark out a line in the area you want to study e.g. from the hedge to the middle of the field
4. Then collect data along the line using quadrats placed next to each other

Question 19

What does a food chain show? How is it organised?

Answer 19

1. Food chains show what is eaten by what in an ecosystem
2. Food chains always start with a producer e.g. a plant
3. Producers make (produce) their own food using energy from the Sun
4. Producers are eaten by primary consumers, primary consumers are then eaten by secondary consumers and secondary consumers are then eaten by tertiary consumers
5. All these organisms eventually die and get eaten by decomposers e.g. bacteria
6. Decomposers break down (decompose) dead material and waste
7. Each stage is called a trophic level

Question 20

What do food webs show?

Answer 20

1. Food webs show how food chains are linked
2. There are many different species within an environment, which means lots of different possible food chains
3. All the species in a food web are interdependent, which means if one species changes it affects all the others

Question 21

Describe the water cycle

Answer 21

1. Heat from the Sun makes the water evaporate from the land and sea, turning it into water vapour
2. Water also evaporates from plants (transpiration)
3. The water vapour is carried upwards, as warm air rises
4. When it gets higher up it cools and condenses to from clouds
5. Water falls from these clouds as precipitation, usually rain but sometimes snow and hail and is returned to the land and sea

Question 22

Describe the carbon cycle

Answer 22

1. (Only one arrow going down) The whole thing is ‘powered’ by photosynthesis as green plants use the carbon from carbon dioxide in the air to make carbohydrates, fats and proteins. Photosynthesis fixes carbon atoms from atmospheric carbon dioxide into organic molecules
2. Feeding and assimilation pass carbon atoms already in organic compounds along food chains
3. Respiration produces inorganic carbon dioxide from organic compounds (mainly carbohydrates) as they are broken down to release energy
4. Fossilisation is when sometimes living things do not decay fully when they die due to the conditions in the soil, as decay is prevented if it is too acidic and fossil fuels are formed e.g. coal, oil, natural gas, peat
   - When plants and animals decompose they are broken down by bacteria and fungi, and these decomposers release CO2 back into the air by respiration, as they break down the material
5. Combustion releases carbon dioxide into the atmosphere when fossil fuels are burned

Question 23

Describe the nitrogen cycle

Answer 23

1. Feeding and assimilation pass nitrogen atoms already in organic compounds along food chains
2. Decomposition by decomposers produces ammonia from the nitrogen in compounds like proteins, DNA and vitamins
3. The ammonia is oxidised first to nitrite and then to nitrate by nitrifying bacteria. The overall process is called nitrification
4. Plant roots can absorb the nitrates. They are combined with carbohydrates (from photosynthesis) to from amino acids and then proteins, as wells as other nitrogen-containing compounds
5. Also denitrifying bacteria use nitrates as an energy source and convert them into nitrogen gas. Denitrification reduces the amount of nitrate in the soil
6. Free-living nitrogen-fixing bacteria in soil convert nitrogen gas into ammonia, This is used by the bacteria to make amino acids and proteins, When the bacteria diem these proteins decompose, releasing ammonia back to the soil
7. Nitrogen fixing bacteria in root nodules also make ammonia but this is converted by the plant into amino acids and other organic nitrogen compounds. Death and decomposition of the plant returns the nitrogen to the soil as ammonia
   - Lightening converts nitrogen gas in the air into various oxides of nitrogen. These dissolve in rainwater and enter the soil to be converted into nitrates by nitrifying bacteria

Question 24

Where does nitrogen come from and why is it important?

Answer 24

1. The atmosphere contains about 78% nitrogen gas, this is very unreactive and so it cannot be used directly by plants or animals
2. Nitrogen is needed for making proteins for growth, so living organisms have to get it somehow

Question 25

What is nitrogen fixation?

Answer 25

• The process of turning N2 from the air into nitrogen compounds in the soil which plants can use:
  1. Lightning: there is so much energy in a bolt of lighting that it is enough to make nitrogen react with oxygen in the air to give nitrates
  2. Nitrogen fixing bacteria in roots and soil

Question 26

Why does the biomass of organisms get less at each level?

Answer 26

1. Some parts of the organism are not eaten e.g. plant roots, animal bones
2. The food cannot all be digested and absorbed, some is passed out as faeces
3. Some of the food eaten is broken down and excreted as waste e.g. urea
4. Some of the food is respired and used to release energy for the cells of the body
5. Only a small part of the food is used to produce growth and new body mass

Question 27

Describe pyramids of energy transfer

Answer 27

Pyramids of energy transfer are always pyramid shape and they show the energy transferred to each trophic level in a food chain

Question 28

Why are pyramids of energy transfer always pyramid shape?

Answer 28

1. The interactions between organisms in an ecosystem can be shown as a transfer of energy along a food chain
2. Light energy is fixed into food molecules by plants during photosynthesis
3. Energy is released during respiration and used for movement, growth, reproduction etc.
4. Energy that is used for growth can be passed on to the next trophic level or the decomposers
5. Energy used for any other process will eventually be transferred to the environment as heat
6. Only about 10% of the energy is passed on at each level of a food chain
7. This limits the number of trophic levels in a food chain, because eventually there is not enough energy left

Question 29

What are the 5 key stages of the nitrogen cycle?

Answer 29

1. Nitrogen fixing
2. Nitrification
3. Assimilation
4. Decomposition / Ammonification
5. Denitrifying

Question 30

Describe nitrogen fixing and where this happens

Answer 30

1. Turns nitrogen in the atmosphere (N2), into nitrogen containing compounds e.g. NH4+
   - This can happen by lightning, but not a massive amount
   - Nitrogen fixing bacteria do this in the soil or in the roots of certain plants such as legumes
   - This is because the roots have a symbiotic relationship with the Rhizobium in root nodules, (Nitrogen Fixing Bacteria), as the plants get nitrates and the bacteria get glucose from the plant
   - The plants can use the NH4+ (ammonia) to make amino acids etc.

Question 31

Why can plants and animals not use atmospheric nitrogen as their source of nitrogen?

Answer 31

It is a triple bonded molecule, which requires too much energy to break a part

Question 32

Why do living organisms require nitrogen?

Answer 32

1. To make proteins (amino acids)

2. DNA (+RNA), parts of DNA have nitrogen inside

Question 33

Describe nitrification and where this happens

Answer 33

1. It turns toxic NH4+ into useful, nitrogen oxide and then nitrates
   - Nitrifying bacteria oxidise the ammonia to nitrites and hen to nitrates
2. NH4+ is poisonous so nitrifying bacteria turn
   - NH4+–>NO2–>NO3- (done by different nitrifying bacteria)

Question 34

Describe assimilation and where this happens

Answer 34

1. The tree will absorb the NO3- and turn it into DNA and amino acids
2. NO3- is not triple bonded and not particularly toxic

Question 35

Describe decomposition and ammonification and where this happens

Answer 35

1. Living matter is broke down
2. Denitrifying bacteria turn NO3- into N2 (and they make a living out of this, as they use nitrates as an energy source and break them down into nitrogen gas)
3. The giraffe will eat the leaves (containing proteins) and excrete nitrogenous waste
4. When the plants and animals die they will be broken down by decomposers by ammonification and release ammonia into the soil

Question 36

How do farmers cope with the nitrogen cycle?

Answer 36

1. They use fertiliser, however sometime eutrophication which is bad
2. Farmers grow bean every 3 years (crop rotation) to return some nitrogen to soil and plowing in

Question 37

Why do Venus fly traps eat bugs?

Answer 37

1. They live in peat bogs
2. There are no air pockets so no nitrogen
3. But the flies are their source of nitrogen as the flies contain nitrogen