Topic 9: Ecosystems

Question 1

Describe the levels that ecosystems are organised in to

Answer 1

Individual - a single organism
Population - All the organisms of one species in a habitat
Community - All the organisms of different species living in a habitat
Ecosystem - A community of organisms along with all the abiotic conditions

Question 2

What is meant by interdependance?

Answer 2

• Organisms depend on each other for food/shelter to survive and reproduce
• It means that a change in the population of one species can have huge knock on effects for other species in the same community

Question 3

What’s mutualism? - add an example

Answer 3

• A relationship between two organisms from which they both benefit
• e.g. bees get food from plants and the plants get help reproducing

Question 4

Describe parasites

Answer 4

• Parasite lives very closely with a host species (in or on them) to take what they need to survive, but the host doesn’t benefit
• e.g. fleas feed on host’s blood without offering anything in return

Question 5

How do Abiotic environmental factors affect communities?

Answer 5

Temperature

Amount of water - daisies grow best in slightly damp soil, so when it is too dry or waterlogged, population of daisies will decrease

Light intensity - trees grow and provide more shade, so grasses may be replaced by fungi/mosses etc.. because they can better cope with lower light intensity

Levels of pollutants - Lichen are unable to survive if sulfur dioxide concentration in the air is too high

Question 6

How do Biotic environmental factors affect communities?

Answer 6

Competition - organisms compete with other species/members of their own species for the same resources e.g. red and grey squirrels live in the same habitat and eat the same food, leaving not enough food for the red squirrels so the population of red squirrels is decreasing

Predation - e.g. If number of a predator decreases, the number of their prey will increase

Question 7

Quadrats

Question 8

How do you estimate a population size from a sample area?

Answer 8

Find the mean number of organisms per Msquared, then multiply the mean by the total area of the habitat

Question 9

Belt transect core practical

Question 10

Explain why food chains can only have a limited number of trophic levels

Question 11

Explain the food chain, beginning with the sun

Answer 11

• Sun is a source of energy for nearly all life on earth, plants convert a small % of light energy that falls on them into glucose. Some of this glucose is used in respiration immediately and some of the rest is stored as biomass
• First animal eats the plant, uses some energy from the plant, some of the rest is stored in its body as biomass
• Second animal eats it and gets some of the energy stored in the animal’s biomass

Question 12

Explain how energy is used in the food chain

Answer 12

• Energy is used by organisms to stay alive at each stage like in respiration. This transfers energy for all life processes like movement. A lot of energy is transferred to the surroundings by heat
• The energy transferred to the surroundings isn’t stored as biomass, so isn’t transferred to the organisms in the next trophic level
• Not all energy stored as biomass gets transferred to the next trophic level as not all of the organism gets eaten (e.g. the bones). Also, not everything eaten can be digested, so undigested material is lost from the food chain in faeces

Question 13

Define Biomass

Answer 13

The mass of living material that makes up an organism

Question 14

What do pyramids of biomass show?

Answer 14

How much weight the creatures at each level of the food chain would weigh, and how much energy there is at each stage

Question 15

What are the levels in pyramids of biomass labelled as?

Answer 15

Producer –> primary consumer –> secondary consumer –> etc…

Question 16

How do you calculate the efficiency of energy transfers between trophic levels?

Answer 16

Energy at next level/Energy at previous level
x 100