6.3.1 Ecosystems

Question 1

what’s an ecosystem?

Answer 1

all living organisms and nonliving components and their interactions

Question 2

what’s a population?

Answer 2

all the organisms of one species living in the same place at the same time

Question 3

what’s a community?

Answer 3

all the organisms of all different species living in a habitat

Question 4

what’s a niche?

Answer 4

role of an organisms within an ecosystem

Question 5

what is a biotic factor and some examples of how it can affect ecosystems?

Answer 5

living features of an ecosystem

• parasites
• disease
• food
• predation

Question 6

what’s an abiotic factor and some examples of how it can affect ecosystems?

Answer 6

non living features of an ecosystem

• temperature
• pH
• soil type

Question 7

what factors increase net primary production?

Answer 7

• high temperature
• increase in sunlight
• more photosynthesis occurs = more storage of biomass

Question 8

what’s a trophic level?

Answer 8

place in the food chain

Question 9

what’s a producer?

Answer 9

fixes carbon using sunlight

Question 10

why do producers only convert 1-3% of sunlight into chemical energy in the first place (in an ecosystem)?

Answer 10

• transmitted through leaf of wrong wavelength
• some is reflected
• some light hits part of plant that can’t photosynthesise. it does NOT HIT THE CHLOROPLASTS

Question 11

why is the biomass in each tropic level lower than the one before?

Answer 11

• not all biomass is eaten
• some of transferred to environment as heat
• some is excreted
• some is indigestible

Question 12

describe (NOT DEFINE) pioneer communities.

Answer 12

• arrive before climax
• subject to greater change
• low biodiversity
• less stable

Question 13

why are pioneer communities important?

Answer 13

• fix nitrogen
• photosynthesis
• weather rocks to create layer of humus

Question 14

outline primary succession

Answer 14

1. pioneer community
   - begins with bare rock
   - arrived as seeds
   - have adaptations like nitrogen fixation
2. intermediate community
   - herb species
   - followed by shrubs and trees
3. climax community
   - dominance by a few tree species
   - little change over time

Question 15

what factors can have an impact on ecosystems?

Answer 15

• biotic
• abiotic

Question 16

what are some biotic and abiotic factors affecting rock pools ecosystems?

Answer 16

biotic —
• seaweed as a food source
• competition for food

abiotic —
• high tides
• pH, temp of ocean

Question 17

what are some biotic and abiotic factors affecting playing field ecosystems?

Answer 17

biotic —
• producers like grass act as a food source
• competition for food

abiotic —
• rainfall and sunlight affect growth of producers (grass)

Question 18

what are some biotic and abiotic factors affecting large tree ecosystems?

Answer 18

biotic —
• leaves of tree as source of food

abiotic —
• droughts can negatively impact trees

Question 19

what’s a primary consumer?

Answer 19

something that eats/feeds on the producer

Question 20

what’s a secondary consumer?

Answer 20

something that eats/feeds on the primary consumer

Question 21

what’s biomass transfer the annoying exam phrase for? and what’s the units for it?

Answer 21

• energy transfer
• kg

Question 22

by what factor does the biomass decrease between each trophic level?

Answer 22

10

Question 23

what is the gross productivity in terms of like trophic levels and stuff?

Answer 23

the energy that’s actually taken in

Question 24

what is the respiratory loss in terms of like trophic levels and stuff?

Answer 24

energy used for respiration for movement, NOT TOTAL ENERGY THATS NOT ABSORBED

Question 25

how do you calculate efficiency in terms of energy transfer in trophic levels and what not?

Answer 25

(energy actually transferred ➗ energy available for transfer) * 100

Question 26

what are some ways humans can intervene (ofc they do) to increase transfer of energy in trophic levels?

Answer 26

by **adding**: - **herbicides** - **fungicides** - **insecticides**

Question 27

how can introducing herbicides increase energy transfer?

Answer 27

- **they kill weeds that compete w crops** for **energy** - **reducing competition** = **crops** receive **more energy** - **grow faster** and **increases productivity**

Question 28

how can introducing fungicides increase energy transfer?

Answer 28

- **they kill fungal infections** that **damage crops** - **crops will now use more energy to grow** rather than **wasting it fighting infections** - **grow faster** and **increases productivity**

Question 29

how can introducing insecticides increase energy transfer?

Answer 29

- **they kill insect pests that eat and damage crops** - this will mean **less biomass lost from crops** - crops **grow larger** and **productivity is greater**

Question 30

what happens in the nitrogen cycle?

Answer 30

- there’s a **plant which needs nitrogen** to make **proteins and amino acids** - **NITROGEN FIXATION:** • **N2 gas in the air is converted into NH3 then NH4+** by **rhizobium and azotobacter** • **rhizobium forms a mutualistic rs w the plant** as it **provides plant w N** and **plant provides it w carbohydrates (awww)** • **azotobacter does NOT form a mutualistic rs** w plant **(bruh)** - **NITRIFICATION:** • **NH4+** from before is **changed into nitrates** by **nitrosomonas** • **nitrates then converted to nitRITES** by **nitrobacter** - **plants can finally take NITRITES** as its **source of N** - **plants die** and are also **eaten by animals who later die** - **AMMONIFICATION:** • **amino acids** from **dead plants/animal waste** (bc they ate the plants) **converted into NH3 then NH4+** by **decomposers** - **DENITRIFICATION:** • **nitrates in soil converted** into **N2 gas by denitrifying bacteria** • **ANAEROBIC CONDITIONS** for this, eg in waterlogged soils

Question 31

what’s our little story for what happens in the nitrogen cycle?

Answer 31

there’s an annoying brat (plant) who wants a toy (nitrogen) from her parents (azotobacter and rhizobium), but the toy store doesn’t have that specific toy it has a diff toy instead (N2 gas) so it has to convert that toy (N2) into the one she wants (NH3), but the toy rusts as soon as they buy it (NH3 —> NH4+), they give ts anyways and the dad (rhizobium) loves her too much so has fun while giving the present (mutualistic rs), but the mum (azotobacter) doesn’t care for this at all (no mutualistic rs). the cool aunts then want to make the rusted toy better and work together in a diff room (soil). one of them (nitrosomonas) does one step (NH4+ —> nitrATES) then the other (nitrobacter) finishes it (nitrATES —> nitrITES). the brat (plant) then loves the gift (nitrITES) and has fun w it by changing it (makes amino acids). when the brat (plant) and her friend who she played with (animal) dies LOOOL, her changed toy (amino acids) converted back into the toy the parents initially gave but it rusts straight away again (NH3 —> NH4+). this is done by the funeral ppl. the extra bits and pieces the aunts used in the other room (soil) to make the toy better then gets converted back into the OG OG toy that she didn’t want (N2 gas) to not waste it

Question 32

where is rhizobium and azotobacter made/found?

Answer 32

- **rhizobium** —> inside **ROOT NODULES of LEGUMINOUS PLANTS** - **azotobacter** —> in **soil**

Question 33

what happens in the carbon cycle?

Answer 33

1. **carbon in the form of CO2** is **absorbed by plants** when they **photosynthesise** 2. **becomes carbon compounds** in **plant tissues** 3. **carbon passed onto primary consumer** when they **eat the plant** and **secondary consumer** when they **eat the primary consumer** etc 4. the **living organisms die** and **carbon compounds in the dead bodies are digested** by **decomposers** 5. **carbon is delivered back to environment** due to **respiration**

Question 34

what is succession? how are biotic and abiotic conditions related to ts

Answer 34

- **process** by which an **ecosystem changes over time** - **biotic conditions change as abiotic conditions change**

Question 35

what’s primary succession?

Answer 35

**succession** that **happens on land** that’s been **newly formed or exposed**, eg **volcano erupting** to **form a new rock surface**

Question 36

what’s secondary succession?

Answer 36

**succession** that happens on **land that’s been cleared of all the plants** but **soil remains**, eg land that’s **been deforested**

Question 37

what’s the chronological order of these in succession? also what are they? climax community, pioneer species, intermediate species.

Answer 37

1. **pioneer species** —> **first species to colonise** the **area** (primary OR secondary succession) 2. **intermediate species** —> **species that OUTCOMPETE primary** once they **die** and add to the **soil’s pH** 3. **climax community** —> ecosystems supporting the **largest community of plants that it can** and it’s **NOT SUBJECT TO MORE SUCCESSION AND IS STABLE**

Question 38

what’s deflected succession?

Answer 38

when a **plagioclimax formed instead of climax community** when **succession is PREVENTED**, and **stopped artificially by humans**

Question 39

what are some examples of processes and activities which can increase the availability of nitrogen and its compounds in the soil?

Answer 39

- **fixing of nitrogen** by **nitrogen fixing bacteria** - **application** of artificial **fertilisers** - **defamation of animals** onto soil - **decay of organic matter** by **bacteria**

Question 40

what are plants like in the pioneer community vs the climax community?

Answer 40

pioneer: - **fast** growing - **asexual** reproduction - **able** to **tolerate extreme environments** climax: - **more species** than **pioneer community** - **unable** to **tolerate extreme environments** - **slow*$ growing

Question 41

what are animals like in the pioneer community vs the climax community?

Answer 41

pioneer: - **few** species - **mostly small** species climax: - **larger** species - **more herbivore** species - **longer food chains**