6 - MZH - Ecosystems

Question 1

8 abiotic factors

Answer 1

• Temperature - rate of reaction of endothermis / ectotherms
• Light intensity - Rate og photosynthesis + behaviour in animals
• O₂ conc - Water affects aerobic respiration
• Water supply - Affects all organisms
• Wind speed - Affects rate of transpiration + lowerd temp
• Atmospheric hymidity - Affects rate of water loss by sweating or transpiration
• Ion availability - e.g. nitrates affect plant growth
• Soil type

Question 2

4 biotic factors

Answer 2

• Feeding - herbivores on plants
• Predation - of animals on prey animals
• Competition for shared resources - food, light… these resources are often in short supply leading to intense competition between organisms
• Human activities

Question 3

Define

Gross primary productivity

Net primary productivity

Equation for NPP = ?

Answer 3

Gross primary productivity = total production of organic substances in a given area in a given time. It depends on the types of plants, their density and the climate

Net primary productivity = Rate of production of organic substances after allowing for the loss via respiration in the plants

NNP = GPP - Respiration

NNP / KJm^-2Year^-1

Question 4

What do the arrows represent?

Answer 4

Direction of energy flow

Question 5

Question:

Answer 5

1. Trout no’ will fall because 1 of their main prey specied is in short supply
2. Troup will start to eat more water boatmen which are an alternative prey species
3. Tubifex worm / midge larvae / caddis fly population will increase between fewer will be eaten by minnows

Question 6

Another word for trophic = ?

Answer 6

Feeding

Question 7

What are:

• Herbivores
• Carnivores
• Tertiary concumers / top carnivores
• Quaternary consumers + example
• Omnivores

Answer 7

Herbivores = consumers that feed firectly on plants

Carnivores / secondary consumers = consumers that feed on herbivores

Tertiary concumers / top carnivores = consumers that feed on secondary consumers

Quaternary consumers = Consumers that feed on tertiary consumers, usually parasites

Omnivores = consumers that feed on both herbivores and carnivores

Question 8

What are the 2 different types of plankton you can get?

Answer 8

Phytoplankton

Zooplankton

Question 9

How is energy lost at trophic level 1? (4)

Answer 9

Trophic level 1 = plants

• > 90% os solar energy is reflected back into space by clouds and dust or absorbed by the atmosphere and re-radiated
• Not all wavelengths of light can be absorbed and used for photosynthesis
• Light may enter a leaf but not strike a chloroplast
• Low CO₂ levels may lmit the rate of photosynthesis

Plants also lose 20-50% of GGP via respiration

Question 10

Why does only approx 10% of the APP of plants is used by herbivored for growth? (4)

Answer 10

• Some plant not eaten
• Some parts are eaten but can’t be digested
• Lost in excretory materials
• Some energy losses occur in respiration and head loss to the environment

Question 11

Are carnivores more or less efficient than plants at transferring energy available into biomass?

Answer 11

Slightly more efficient at approx 20%

Question 12

What 3 things can be explained due to the inefficiency of energy transfer between trophic levels?

Answer 12

• Most food chains have only 4 or 5 tropic levels because insufficient energy available to support organisms in trophic levels higher than this
• Biomass of organisms is less at higher trophic levels
• Total amount of energy stored at each trophic level decreases as one moves up the food chain

Question 13

Equation: % energy transfer = ?

Units = ?

Answer 13

% energy transfer = (energy available after transfer / energy available before transfer) x 100

Units = KJm^-2year^-1

Think of it as a basic percentage calculation

Question 14

Name the 3 different types of ecological pyramids that are used + what does each one show?

Answer 14

Pyramid of numbers = Numbers of each organism at each trophic level

Pyramid of biomass = Amount of living tissue (wet mass) at each trophic level

Pyramid of energy = Energy transferred between each trophic level - using dry mass

Question 15

What is the drawback of using pyramid of numbers?

Answer 15

No allowance is made for differences in the size between individual organisms, this results in inverte pyramids and other variations

If asked to draw one, make the sizes obvious!

Question 16

What do ecological pyramids show?

Answer 16

Shows the structure of an ecosystem in terms of numbers, biomass or energy equivalents of organisms existing at a given time at each trophic level

Question 17

Shape of pyramids of biomass and pyramids of energy?

Answer 17

Pyramids of energy

• Always pyramid shape. Arises due to generally approx 10% of energy is transferred between each trophic level

Pyramids of biomass

• Always pyramid shape with the exception in a marine ecosystem

Question 18

How is energy lost in food chains? (5)

Answer 18

Animals:

• Never eat all the available food
• Can’t digest all the food they eat - passed onto decomposers
• Use energy in their respiration so they can move, hunt etc…
• Lose heat energy to their environment
• Lose energy in urine and faeces: this energy may be passed onto decomposers

Question 19

How do you calculate energy loss in a food chain? (4)

Answer 19

Bomb calorimeter:

1. Dry sample in a oven to remove water - dry mass
2. Burn dried sample in oxygen in a bomb calorimeter
3. Heat energy produced by the complete oxidation of the dried sample passes to a known mass of water. Measure the temp rise of the water
4. Given that 4.12J of energy raises temp of 1g of water by 1ºC (specific heat capacity of water) you can calculate the energy content of each sample

Question 20

Advantages of using biomas rather than dry mass (2)

Answer 20

Easy to do

Non lethal

Question 21

How do human activities change the energy flow through an ecosystem? Give 5 examples of how this is done

Answer 21

In farming, forestry and fishing changing the productivity of ≥ 1 trophic level will manipulate the energy flow through an ecosystem e.g.

• Replacing natural vegetation and fauna w/ crops + lifestock
• Deflecting natural succession to maintain natural grassland
• Increasing the productivity of producers theough soil improvement, irrigation, fertilisers and the removal of damaging pathogens + pests
• Increasing productivity of producers + consumers theough selective breeding or genetic engineering
• Shelting organisms from damaging environmental factors

Question 22

Why do crops are often able to convert a higher % of light energy into energy into biomass than plants growing in the wild? (3)

Answer 22

• Often irrigated + supplied w/ fertiliser
  
  • Shortage of water + mineral ions don’t limit growth
• Crop plants have been bred for high productivity
  
  • ​∴ have alleles which ensure they are efficient at converting light energy → energy in plant tissue
• Treated w/ pesticides
  
  • ​Little damage to their leaves ∴ can photosynthesis more efficiently

Question 23

How do human activities increase the primary productivity of an ecosystem? (6)

Answer 23

Through manupulation of the environment:

• Light availability
  
  • Can be increased by planting crops earlier in the year or growing them in a greenhouse
• Water
  
  • Increased by irrigation, or frought-resistant crops can be grown
• Temperature
  
  • High in greenhouses
• Ion availability
  
  • e.g Nitrates is increased by crop rotation, using nitrogen fisxing plants or fertilisers
• Pests
  
  • Insecsticides and fungicides to control insects and fungi. Can also use pest resistant varieties
• Competition
  
  • ​Competition from weeds is reduced by using herbicides or appropriate cultivation methods

Question 24

How do human activities increase the secondary productivity of an ecosystem? (4)

Answer 24

Humans can manipulate energy transfers from producers → consumers to increase secondary productivity:

• Selective breeding
  
  • Produce breeds w/ faster growth rates, increased egg proction, higher milk yields
• Housing
  
  • Animals kept indoors to minimise heat loss ∴ restricting energy loss due to movement
• Food availability
  
  • e.g. high protein supplements to increase muscle growth
• Antibiotics
  
  • Prevent energy losses to combat diseases

Question 25

Units for biomass for:

Terrestial and aquatic organisms

Answer 25

Terrestial = gm^-2

Aquatic = gm^-3