P2 Ecosystems

Question 1

What is an ecosystem?

Answer 1

All of the interacting living organisms and non-living conditions in an area.

Question 2

What are the factors affecting ecosystems?

Answer 2

1. Biotic factors:
   - predation
   - competition
   - hunting
2. Abiotic factors:
   - light
   - temperature
   - pH

Question 3

What is biomass?

Answer 3

The mass of all the living material present in an ecosystem - travels through ecosystem by feeding.

Question 4

Why is not all of the light that hits a plant converted into biomass?

Answer 4

• Some of the light may not hit a chloroplast.
• Some of the light may have the wrong wavelength, and be reflected.
• Another factor, eg. concentration of carbon dioxide, limits the rate of photosynthesis.
• The total amount of light energy the light uses to form biomass is called gross production.
• Some light energy in plants is used for respiration, the resulting biomass after respiration is the net production.

Question 5

Why is energy lost to the ecosystem at trophic levels?

Answer 5

• Not all of the organism is eaten.
• Some of the organism won’t be digested, meaning energy is lost in faeces.
• Some energy will be lost by respiration and by other waste products.

Question 6

How do farmers increase percentage efficiency of biomass?

Answer 6

1. Simplify food webs to remove competing organisms.
2. Reduce respiratory losses, eg. by reducing reliance on respiration to keep organisms warm (heat lamps etc.)

Question 7

What is succession?

Answer 7

When an ecosystem changes from simple to complex over time.

Question 8

What are the seral stages of succession?

Answer 8

1. Pioneer species
2. Intermediate community
3. Climax community

Question 9

What is the first stage of succession?

Answer 9

• Uninhabited land is colonised by a pioneer species (such as moss or lichen), usually in the form of small seeds or spores.
• Pioneer species are often adapted for colonisation, eg. tolerant to extreme conditions and able to reproduce asexually.
• Pioneer species change the environment, making it less hostile and enabling other species to survive.

Question 10

What is the second stage of succession (intermediate community)?

Answer 10

• Over time herb species, such as grass begin to grow, followed by shrubs and trees.
• When these species decompose, they release their nutrients into the soil.

Question 11

What is the third stage of succession (climax community)?

Answer 11

• Over time, the intermediate community allows a stable community to form, that no longer experiences succession.

Question 12

What is deflected succession?

Answer 12

• When human activity halts succession, and prevents climax communities from forming.
• This can occur due to agriculture.