Unit 2.2 Communities and ecosystems

Question 1

Community

Answer 1

a group of populations living and interacting with eachother in one area.

Question 2

Photosynthesis

Answer 2

process by which green plants, algae, and certain bacteria convert carbon dioxide and water into glucose and oxygen, using sunlight as energy. This process is essential for producing the organic compounds and oxygen that sustain most life forms on Earth.

Chemical reactions:
6CO2 + 6H2O - (Sunlight) - C6H12O6 + 6O2

Question 2

Ecosystem

Answer 2

An ecosystem is a community and the physical environment it interacts with.

1. Terrestrial
2. Freshwater (rivers, lakes and wetlands)
3. Marine (sea, estuaries, salt marshes and mangroves)

Question 3

RespIration

Answer 3

process where cells convert glucose and oxygen into energy, carbon dioxide, and water. It’s crucial for energy production in living organisms
a series of inputs, energy transformations and outputs

Chemical reactions:
C6H12O6 + O2 – Energy 12 H20 + 6 CO2

Question 4

How can we model feeding relationships of a species in a system

Answer 4

food chains, food webs and ecological pyramids.

Question 5

Food chain

Answer 5

A food chain is the flow of energy from one organism to the next

Question 6

Producers

Answer 6

(autotrophs) make their own food from CO2 and water using energy from the Sun.

Question 7

Consumers

Answer 7

(heterotrophs) cannot make their own food so they feed on other organisms to obtain energy and matter

Question 8

Chemosynthetic organisms

Answer 8

producers that do not require sunlight to make their own food.

Question 9

Trophic levels

Answer 9

Trophic level 1 Producer Grass

Trophic level 2 Primary consumer Grasshopper

Trophic level 3 Secondary consumer Mouse

Trophic level 4 Tertiary consumer Owl

Question 10

Decomposers

Answer 10

(also heterotrophs) obtain their energy from dead organisms or feces or parts of an organism

provide a crucial
service for the ecosystem:

1. They break down dead organisms
2. They release nutrients back into the cycle
3. They control the spread of disease

Question 11

Food web

Answer 11

A complex network of interrelated food chains

Question 12

Ecological pyramid

Answer 12

model of the quantitative differences (differences in numbers) between amounts of living material stored at each trophic level of a food chain.

• Pyramids of numbers
• Pyramids of biomass
• Pyramids of productivity

Question 13

Pyramid of numbers

Answer 13

shows the number of individuals at each trophic level in a food
chain at one time.

The units are numbers per unit area.

Question 14

Pyramid of productivity

Answer 14

shows the flow of energy in an ecosystem over a period of time, usually a year.

It is measured in mass or energy per square metre per year (kg/m^2y or kJ/m2y)

Question 15

Pyramid of biomass

Answer 15

quantifies the amount of
biomass present at each
trophic level at a certain point in time.

They use units of mass per unit area (kg/m2 , g/m2)

Question 16

Pyramid of numbers

Advantages vs Disadvantages

Answer 16

Advantages:

• Gives us a quick overview
• Useful for comparing population numbers in different seasons

Disadvantages
- No account is taken of the size of organisms, so
pyramids that involve large producers such as
trees are inverted

• Numbers can be too great to represent accurately

Question 17

Pyramid of Biomass

Advantages vs Disadvantages

Answer 17

• Takes account of the size of organisms, so overcomes some of
  the problems of pyramids of numbers
• Only uses samples from populations, so difficult to measure biomass exactly
• Organisms must be killed to measure dry mass
• Seasonal variation leads to inverted pyramids
• Some animals have a lot of bone or shell, which
  can distort the results

Question 18

Pyramid of Energy

Advantages vs Disadvantages

Answer 18

• Shows energy transferred over a
  period of time, so allows for different rates of production
• Ecosystems can be compared easily
• Pyramids are never inverted
• Data is difficult to collect, as rate of biomass
  production over time must be measured
• Many species feed at more than one trophic level which can affect the results (this is true for all
  pyramids)

Question 19

Bioaccumulation

Answer 19

is the build-up of persistent pollutants within an organism or trophic level because it is not biodegradable

Question 20

Biomagnification

Answer 20

is the increase in concentration of persistent pollutants along a food chain

Question 22

DDT

Answer 22

1. DDT is a synthetic chemical compound used as an insecticide, known for its effectiveness in killing mosquitoes and other pests.
2. Introduced in the 1940s, DDT was widely used to combat diseases like malaria and typhus, and in agriculture to protect crops due to its effectiveness and low cost.
3. DDT enters food webs primarily through agricultural runoff and accumulation in soil and water, where it is absorbed by plants and consumed by animals, leading to bioaccumulation and biomagnification.
4. Still produced in a few countries
5. Stockholm Convention on POPs: international environmental treaty, signed in 2001, aims to eliminate the production and use of persistent organic pollutants (POPs), including DDT.
6. DDT can cause reproductive issues in birds (e.g., thinning eggshells) and fish, and can affect the nervous system of a wide range of wildlife.
7. highly persistent in the environment, with a half-life that can range from 2 to 15 years, leading to long-term contamination of soil and water bodies.