15. Relationships of Organisms with one another and the Environment

Question 1

Energy Flow in an ecosystem

• what is an ecosystem?
• describe the non-cyclical nature of energy flow

Answer 1

• A community of living organisms and the habitat in which they live.
  Sunlight > Plant producers (-heat energy) > consumers (-heat energy) > decomposers (-heat energy) > nutrients
• energy given out by organisms is lost to the environment

Question 2

• The Basic Carbon Cycle

- Additional processes

Answer 2

1 - Plants uptake carbon-dioxide from the atmosphere during photosynthesis
- Carbon is used to make carbohydrates: cellulose, proteins, pigments etc.
2 - Animals eat them: plant material is digested and built up into animal tissues
3 - Dead animal matter is used by saprotrophs: decompose carbon compounds into carbon-dioxide
Additionally:
- Respiration: plants and animals obtain energy by oxidizing carbohydrates in their cells to carbon-dioxide and water. CO2 returns to the atmosphere
- Combustion: Burning carbon-containing fuels oxidises carbon and CO2 released to atmosphere

Question 3

• The Basic Nitrogen cycle
• Additional processes
• What is nitrifying bacteria, what is its role in the cycle?
• What is nitrogen-fixing bacteria, what is its role in the cycle?

Answer 3

• most of it happens as exchange of nitrates
  1 - Plants take up nitrates from the soil and build them into compounds
  2 - Animals eat them, break down, then use in making own tissue
  3 - Organisms die: ammonia (NH3) is produced during tissue decomposition and washed into the soil
  4 - Nitrifying bacteria break down ammonia compounds into nitrates
  Additionally:
  1 - Animals’ excretory products contain nitrogen compounds, which are also broken down by bacteria
  2 - Nitrogen-fixing bacteria take up nitrogen and convert it to ammonia compounds
  3 - Lightning oxidises nitrogen to form nitrogen oxides: they are dissolved in the rain, washed into soil as weak acids, form nitrates.
  4 - nitrates are very soluble, removed from the soil during leaching by water
  5 - Denitrifying bacteria obtain energy from breaking down nitrates to nitrogen gas, which escapes to the atmosphere.

Nitrifying bacteria:
- bacteria living in the soil that use ammonia and decaying organisms as sources if energy: produce nitrates in the process
- nitrite bacteria: oxidize ammonium (NH4-) compounds to nitrites (NO2-)
- Nitrate bacteria oxidize nitrites to nitrates (NO3-)
-Plants take up nitrates very readily. So basically: nitrifying bacteria increase fertility of the soil
Nitrogen-fixing bacteria:
- A special group of nitrifying bacteria that can absorb nitrogen as a gas from the air spaces in soil. and build it into compounds of ammonia
- Nitrogen gas cannot be used by plants, but ammonia compounds get converted to nitrates (by nitrifying bacteria) and can be used.
- The process of building nitrogen gas into ammonia compounds is called nitrogen fixation
- Some live freely in soil, some live in roots of leguminous plants

Question 4

Parasitism 
- What is a parasite?
- What is a vector?
- What causes malaria, how is it spread?
- describe the transmission and control of
the malarial pathogen
- Symptoms of malaria

Answer 4

• An organism that lives on or in a host organism and gets its food from or at the expense of its host.
• Something that carries and transmits an infectious pathogen.
• Malaria is caused by a protozoan (single-celled) parasite called Plasmodium.
• Spread from person to person by the bite of infected mosquitoes of the genus anopheles. Infected mosquitoes insert their sharp pointed mouth parts into human capillaries and inject saliva + malarial parasites.
• Parasites reach liver via circulation and reproduce in liver cells.
• Their daughter cells escape and enter red blood cells. Symptoms increase every time they leave and enter new RBCs.
  Control:
  1- Drugs: protective. Don’t kill the parasites in the liver but reach bloodstream. Thus effective on healthy person
  2- Killing mosquitoes by spraying oil and insecticides, draining stagnant water, repellents etc.
• Though many have become resistant, so preventing reproduction by destroying habitat becomes best way.
  Symptoms:
  1- chills and violent shivering
  2- fever and profuse sweating

Question 5

Pollution
evaluate the effects of water pollution by
1 - sewage
2 - inorganic waste
3 - nitrogen-containing fertilisers
evaluate the effects of Air pollution by
1 - greenhouse gases
2 - acidic gases
evaluate the effects of pollution due to insecticides

Answer 5

Water pollution by
1 - Sewage: untreated: diseases like cholera and typhoid
- treated: nitrates and phosphates: eutrophication
2 - inorganic waste: industrial: poisonous
3 - fertilisers: eutrophication
Air pollution by
1 - greenhouse gases: CO2 and methane: global warming, climate change
2 - Acidic: acid rain: kill plants, irritants, monuments
Insecticides: kill useful insects, poisonous

Question 6

Conservation

• reasons for conservation of species
• reasons for recycling materials, with reference to named examples

Answer 6

Conservation:
- maintenance of biodiversity
- management of fisheries
- management of timber production
Recycling:
- Cost efficient use of materials
- Reduces amount f energy used in manufacturing
- Conservation of fuel
- Reduce pollution
- eg 1: Producing aluminium alloys from scraps uses 5% of the energy it takes to produce them from aluminium ores
- eg 2: manufacturing glass bottles takes 3 times more energy than collecting, sorting, cleaning and reusing
- eg 3: reusing paper to make more reduces import bill for timber