Chapter 23 - Ecosystems

Question 1

Community

Answer 1

multiple populations of diff species living + interacting in the same area

Question 2

ecosystems

Answer 2

communities interact with each other = environment they live in

Question 3

biotic factors

Answer 3

living components
- anything that influences the populations within a community due to another organism’s activity
eg. predation, competition and disease

Question 4

abiotic factors

Answer 4

non-living components
- physical or chemical factor that influences the populations within a community
eg. light, water availability, temp, humidity

Question 5

Biomass

Answer 5

• mass of living material of the organism/tissue
• chemical energy stored within the organism/ tissue

Question 6

Biomass measurements

Answer 6

• dry mass of an organism/tissue
• mass of carbon that an organism/tissue contains
• mass of carbon that a sample contains is approx. 50% of the dry mass of the sample
• chemical energy content of the organism when burned in pure oxygen

Question 7

Dry mass

Answer 7

mass of the organism/ tissue after all the water has been removed

Question 8

Calorimetry

Answer 8

• used to estimate chem energy stored in dry biomass
• inv. burning the sample of dry biomass in a calorimeter
• burning sample heats a known volume of water
• change in temp of the water provides an estimate of the chem energy the sample contains

Question 9

Feeding relationships

Answer 9

• energy transfer = main goal

Question 10

Efficiency of transfer

Answer 10

Efficiency of transfer = (biomass transferred/ biomass intake) x100

WHERE:
Biomass transferred = biomass that has passed to the higher trophic level
Biomass intake = biomass of the lower trophic level that has been consumed

Question 11

Small % of plant biomass becomes biomass in the primary consumer (why)

Answer 11

• not all the plant’s biomass is eaten by the primary consumer
• not all the consumer’s biomass intake is digested
• primary consumer converts chem energy -> movement + heat, + only a small amount to new biomass
• efficiency of biomass transfer from one trophic level to the next is low, around 10%

Question 12

efficiency of energy transfer between trophic levels

Answer 12

efficiency of energy transfer= net productivity of primary consumers/ net productivity of producers x100

efficiency of energy transfer= net productivity of secondary consumers/ net productivity of primary consumers x100

Question 13

Net productivity of producers

Answer 13

NPP = GPP - R

GPP = gross primary productivity
R = respiratory losses

Question 14

Net productivity of consumers

Answer 14

N = I - (F + R)

I = the chemical energy store in ingested food
F = the chemical energy lost to the environment in faeces and urine
R = the respiratory losses to the environment

Question 15

How human activities can manipulate the transfer of biomass through ecosystems

Answer 15

• maximising agricultural productivity

producers:
use of fertilisers
selective breeding for fast growth
use of fungicides/pesticides
fencing to exclude grazers
ploughing + herbicides to kill weeds

livestock farmers can adopt these methods for primary consumers:
use of food supplements
use antibiotics + vaccines to reduce disease
control predation with fencing
reduce competition for grazing e.g. rabbits, deer

Question 16

succession

Answer 16

• ecosystems are dynamic (constantly changing)
• change from being simple -> complex
• biotic + abiotic conditions change over time

Question 17

Primary succession

Answer 17

• process that occurs when newly formed/ newly exposed land with no species present is gradually inhabited by an increasing number of species

Question 18

Primary succession process

Answer 18

• seeds + spores carried by wind land on exposed rock + begin to grow
  = pioneer species die + decompose, the dead organic matter forms a basic soil
• seeds of plants + grasses land on soil + begin to grow
  = small plants + shrubs die and decompose, the new soil becomes more nutrient-rich
  roots form a network that helps hold soil in place and prevents it from being washed away
• larger plants + shrubs that require more nutrient-rich soil can now grow
  = require more water asw
• soil is sufficiently deep + contains enough nutrients and can hold enough water to support the growth of large trees
  = final species to colonise = dominant species

Question 19

Climax community

Answer 19

• final community formed, cont. all the diff plant + animal species that have now colonised the new land

Question 20

pioneer species

Answer 20

• first species to colonise the new land

Question 21

Saprobionts

also known as saprotrophs

Answer 21

➜ mainly fungi or bacteria
➜ basically they eat dead stuff
➜ they eat dead stuff by secreting enzymes which break down (digest) dead stuff - extracellular digestion
➜ products formed by digestion of dead stuff is eaten
➜ this process = saprobiotic nutrition
➜ not all products formed is eaten, some remain in environment like soil
➜ so plants love saprobionts cuz plants eat the product they make
➜ without dead stuff eaters (saprobionts) dead stuff wouldn’t be broken down to more useful products so they are very important for food web
➜ some saprobionts even excrete important nutrient mineral ions as waste products from their own metabolism

Question 22

Mycorrhizae

Answer 22

➜ it is the relationship between plant roots and fungi
➜ basically plants have evolved to have symbiotic relationships with fungi
➜ this way they both benefit from each other
➜ e.g
∘ fungi have thin filaments (hyphae) that ineract with roots of plant
∘ hyphae increase SA of root system so more water/ions can be absorbed
∘ in return fungi recieve organic compounds like glucose from plant

Question 23

why is nitrogen required by all living organisms?

Answer 23

➜ amino acids
➜ proteins
➜ enzymes
➜ hormones
➜ antibodies (animals)
➜ receptors
➜ organelles
➜ DNA
➜ RNA

Question 24

Summary of Nitrogen cycle

Answer 24

1. Nitrogen fixation
   ∘ Fixing is a way to turn the unreactive N in the air into a more useful form of N
   ∘ Lightning strikes forms nitrogen oxides
   ∘ Fertiliser made from haber process
   ∘ bacteria (nitrogen fixing bacteria)
2. Nitrification
   ∘ First arrow = Nitrosomonas
   ∘ Second arrow = Nitrobacter
   ∘ NH₄⁺ 🠮 NO₂⁻ 🠮 NO₃⁻
3. Denitrification
   ∘ Need to have a way of putting N back ito atmosphere
   ∘ NO₃⁻ 🠮 N₂

look at the cycle cuz memorising isnt enough u need to be able to visualise it

Question 25

bacteria involved in N cycle

Rhizobium

Nitrogen-fixing bacteria

Answer 25

➜ found in root nodules of legume plants
➜ Reactants: N2 and H⁺
➜ Product: NH₃ becomes NH₄⁺ so u can say either
➜ Reduction

anaerobic conditions

Question 26

bacteria involved in N cycle

Azotobacter

Nitrogen-fixing bacteria

Answer 26

➜ found in the soil
➜ Reactants: N2
➜ Product: NH₄⁺
➜ Reduction

anaerobic conditions

Question 27

bacteria involved in N cycle

Nitrosomonas

nitrification done by chemoautotrophic bacteria

Answer 27

➜ found in the soil
➜ Reactants: NH₃ or NH₄⁺
➜ Product: NO₂⁻ (nitrite)
➜ Oxidation

arobic conditions

Question 28

bacteria involved in N cycle

Nitrobacter

nitrification done by chemoautotrophic bacteria

Answer 28

➜ Found in the soil
➜ Reactant: NO₂⁻ (nitrite)
➜ Product: NO₃⁻ (nitrate)
➜ Oxidation

aerobic conditions

Question 29

bacteria involved in N cycle

Denitrifying bacteria

Denitrification to put N2 back into air

Answer 29

found in the soil
➜ Reactants: NO₃⁻
➜ Product: N₂ gas
➜ Reduction

anaerobic conditions

Question 30

e.g of how C is stored

Answer 30

➜ atomsphere as CO₂
➜ in sedimentary rocks
➜ in fossil duels
➜ in soil and other organic matter
➜ in vegetation
➜ dissolved in oceans

Question 31

Carbon cycle

Photosynthesis

Answer 31

➜ autotrophs use sunlight to fix CO2 (e.g calvin cycle)
➜ this removes CO2 from atmosphere
➜ terrestrial plants use gaseous CO2 directly from the air
➜ aquatic organisms use CO2 dissolved in water

Question 32

Carbon cycle

Respiration

Answer 32

➜ all life respire which puts CO2 in air
➜ Heterotrophs rely on respiration for all their energy needs
➜ CO2 released in link reaction and krebs cycle
➜ anaerobic resp also releases CO2 via fermetation of yeast, mould and bacteria

Question 33

Carbon cycle

Combustion

Answer 33

➜ the burning of fossil fuels release CO2 in air
➜ warmer temps mean less CO2 is dissolved in oceans and so its released into air
➜ causes climate change

Question 34

Carbon cycle

Sedimentation

Answer 34

➜ plants die and not fully decomposed by saprobionts (rememeber they eat dead stuff)
➜ instead their bodies form layers of sediment that accumulate over millions of years, locking carbon into the ground
➜ sediment is a store of energy and can form peat and coal
➜ Aquatic organisms that die also form sediments on the sea bed (can form oil and gas)
➜ Shells and other calcium-containing body parts can form sedimentary rocks such as limestone

Question 35

Carbon cycle

Feeding

Answer 35

➜ Carbon is passed from autotroph to heterotroph during feeding
➜ also passed from primary consumer to secondary
➜ biomass transfer always includes transfer of carbon

Question 36

Carbon cycle

Decay & Decomposition

Answer 36

➜ Dead plants and animals are fed upon by detritivores and decayed by saprophytes which releases C into atmosphere
➜ Waste matter such as faeces and urine is used by decaying saprobionts