Unit 3: Ecosystems

Question 1

Define ecosystem

Answer 1

Physical environment and its interacting organisms through food web

Question 2

Difference between food web and food chain.

Answer 2

Web: everything interconnected
Chain: only 1 path of energy

Question 3

How are the food webs regulated?

Answer 3

Vertically by predation

Horizontally by competition

Question 4

What are the characteristics/general features of a food web?

Answer 4

• no more than 4-5 trophic levels
• generally full, no empty space
• complex is more stable

Question 5

Define biomagnification.

Answer 5

The process by which a compound (such as a pollutant or pesticide) increases its concentration in the tissues of organisms as it travels up the food chain

ex: molecule DDT is magnified as it goes from algae to birds in the sky, concentration increases.

Question 6

For biomagnification to happen, what type of molecule is required?

Answer 6

Fat-soluble

it can accumulate in body tissues of organisms.

Question 7

Give an example of biomagnification.

Answer 7

Algae accumulate selenium in tissues, Se is magnified and has a positive effect. Fish accumulate the poison methyl mercury that is magnified

Eat fish: eat a lot of mercury

Eat algae: eat a lot of selenium

Question 8

Define primary productivity.

Answer 8

• Measure of useful energy entering an ecosystem
• at the bottom of the food chain.
• Rate of conversion of sun’s energy into organic molecule
• estimate photosynthesis

Question 9

What is the % of the sun’s energy that is harnessed by plants?

Answer 9

1.2%

Question 10

Define the 2 possible models of pyramids of numbers.

Answer 10

1. Up triangle: many more producers, which are small, for less consumers, which need to eat many producers to have enough energy.
2. Diamond: few, large producers for more consumers, who need to eat less producers to have enough energy.

Question 11

Define the 2 possible models of pyramids of biomass.

Answer 11

1. Up triangle: Large biomass, small and numerous producers, big and less numerous consumers
2. Down triangle: Small biomass, very small consumer, very lightweight, but extremely numerous (algae can be very numerous but not heavy, with very fast reproduction rate

Question 12

Define the model of pyramids of energy.

Answer 12

Up triangle: always need more energy at the bottom for sustainability, energy is transferred up.

Question 13

What are the 4 possibilities of the biogeochemical cycles?

Answer 13

• available organic
• available inorganic: soil, water, atmosphere
• unavailable organic: coil, oil
• unavailable inorganic: rocks, minerals

Question 14

Decribe the water cycle.

Answer 14

Largest reservoir: oceans, precipitations not distributed evenly, most fall over oceans
1. cycle of evaporation and precipitation

2. transiting water can release/absorb energy by changing state or T
3. causes transport of energy, nutrients, chemicals in and out of ecosystems

Question 15

Decribe the carbon cycle.

Answer 15

Largest reservoir: sediments, rocks

Most common form: CO2

Question 16

Decribe the nitrogen cycle.

Answer 16

Largest reservoir: atmosphere
Most common form: N2 cannot use it so
N-fixing bacterias N2 → NH3/NH4+
Other bacterias: NH3 → NO2 → NO3 (nitrate for plants

Question 17

Decribe the phosphorous cycle.

Answer 17

Largest reservoir: rocks (lithosphere)

Most common form: PO4 3-

Question 18

Example of nitrogen cycle.

Answer 18

Cyanobacteria can fix N2 into available N, so can survive even when NO3 supply is exhausted.