2.2 Communities and Ecosystems

Question 1

Define ecosystem

Answer 1

An ecosystem is a community of living and non-living things that work together.

Question 2

Define community

Answer 2

Community refers to all the populations in a specific area or region at a certain time.

Question 3

Community description

Answer 3

a community that has a high diversity is more complex and stable than a community that has a low diversity

Question 4

Describe photosynthesis in terms of inputs, outputs and energy transformations

Answer 4

Photosynthesis should be understood as requiring carbon dioxide, water, chlorophyll and certain visible wavelengths of light to produce organic matter and oxygen. The transformation of light energy into the chemical energy of organic matter should be appreciated.

• inputs:
  sunlight as energy resource, carbon dioxide and water
• processes:
  chlorophyll traps sunlight; energy is used to split water molecules; hydrogen from water is combined with carbon dioxide to produce glucose.
• outputs:
  glucose used as an energy source for the plant and as a building block for other organic molecules; oxygen is released to the atmosphere through stomata.
• transformations:
  light energy is transformed to store chemical energy.

Question 5

Describe respiration in terms of inputs, outputs and energy transformations

Answer 5

Respiration should be recognized as requiring organic matter and oxygen to produce carbon dioxide and water. Without oxygen, carbon dioxide and other waste products are formed. Energy is released in a form available for use by living organisms, but is ultimately lost as heat.

• inputs:
  glucose and oxygen
• processes:
  oxidation processes inside cells
• outputs:
  release of energy for work and heat
• transformations:
  stored chemical energy to kinetic energy and heat

Question 6

Summarise equation for respiration

Answer 6

glucose + oxygen → carbon dioxide + water (+ energy)

Energy is shown in brackets because it is not a substance. Notice that:
Glucose and oxygen are used up
Carbon dioxide and water are produced as waste products

Question 7

Define entropy

Answer 7

a measure of the amount of disorder in a system

Question 8

State how energy in an organism can be lost

Answer 8

Energy is lost in organisms mainly as heat during respiration, a process that converts food and oxygen into usable energy and heat as a byproduct.

Question 9

define primary producer/autotroph

Answer 9

organisms that can produce their own food.

Question 10

Describe how plants use some of the end products of photosynthesis

Answer 10

primary producers are self-sufficient when it comes to meals: they produce their own food using light, carbon dioxide, water and sometimes other chemicals too.
Typiclly plants or algae

Question 11

Summarise the equation for photosynthesis

Answer 11

6CO2 + 6H2O + light energy → C6H12O6 + 6O2

Plants need only light energy, CO2, and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.

Question 12

Define biomass

Answer 12

The mass of organic material in organisms or ecosystems, usually per unit area

Question 13

Connection between photosynthesis and the production of biomass?

Answer 13

Photosynthesis produces the raw material for producing biomass.

Biomass contains energy first derived from the sun: Plants absorb the sun’s energy through photosynthesis, and convert carbon dioxide and water into nutrients (carbohydrates).

Question 14

Define trophic level

Answer 14

the trophic level is the position that an organism occupies in a food chain, or a group of organisms in a community that occupy the same position in food chains - what it eats, and what eats it.

Question 15

Identify and explain trophic levels in food chains and food webs selected from the local environment.

Answer 15

1. Primary Producers (Trophic Level 1): In a local environment, this could include grass, trees, or aquatic algae. They convert solar energy into chemical energy stored in carbohydrates.
2. Primary Consumers (Trophic Level 2): These are herbivores that eat primary producers. In a local setting, this could be insects like grasshoppers, small mammals like rabbits, or herbivorous fish, depending on the ecosystem. They obtain energy by consuming plant material.
3. Secondary Consumers (Trophic Level 3): These organisms are carnivores or omnivores that eat primary consumers. Examples might include birds like hawks or small carnivores like foxes. They gain energy by consuming herbivores.
4. Tertiary Consumers (Trophic Level 4): These are higher-level carnivores that feed on secondary consumers and, occasionally, primary consumers. In a local ecosystem, this could include larger predators such as wolves or large fish like pike.
5. apex predators, which are at the top of the food chain and have no natural predators. Examples might be eagles, large cats, or large sharks in various ecosystems.

Question 16

Distinguish between autotroph and chemosynthetic organisms.

Answer 16

Autotrophs produce their own food using light or chemicals. Photoautotrophs use sunlight (e.g., plants), while chemoautotrophs derive energy from chemical reactions (e.g., bacteria at hydrothermal vents).

Question 17

Define consumer with reference to a named example

Answer 17

feed on other organisms, they do not contain photosynthesis pigments so they cannot make their own food.

e.g. rabbits

Question 18

Define decomposer with reference to a named example

Answer 18

get their food from the breakdown of a dead organism matter. e.g. fungi

Question 19

Define an Apex predator with reference to a named example

Answer 19

an organism at the top of the food chain that preys on other animals and has no natural predators. e.g. lion

Question 20

Explain ecological pyramid

Answer 20

An ecological pyramid is an illustration of the reduction in energy as you move through each feeding (trophic) level in an ecosystem. The base of the pyramid is large, since the ecosystem’s energy factories (the producers) are converting solar energy into chemical energy via photosynthesis. A food chain can also depict a reduction in energy at each feeding level if the arrows, drawn between the different levels, continue to be reduced in size.

Question 20

Discuss how entropy affects the structure of an ecological pyramid

Answer 20

second law of thermodynamics!
When energy transfers between organisms in an ecosystem, most of it is lost as heat, according to the second law of thermodynamics. For example, when a plant is eaten by a herbivore, the herbivore can only use about 10% of the plant’s stored energy. The rest is lost mainly through metabolic processes as heat. This results in an increase in disorder, or entropy, in the ecosystem.

Question 21

Define bioaccumulation

Answer 21

Bioaccumulation refers to how pollutants enter a food chain. It is an increase in concentration of a pollutant from the environment to the first organism in a food chain.

Question 22

Bioaccumulation with reference to a named example

Answer 22

Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy

Question 23

Define biomagnification

Answer 23

Biomagnification refers to the tendency of pollutants to concentrate (builds up) as they move from one trophic level to the next. It is an increase in concentration of a pollutant from one link in a food chain to another.
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Question 24

Explain how DDT and mercury accumulate in a food chain

Answer 24

Birds consume insects exposed to DDT, a pesticide that is slowly degraded in the environment and the body. As birds eat multiple insects, the DDT accumulates and concentrates in their fat tissues, leading to higher levels of DDT in birds than in the original insect population.

Question 25

What is a pyramid of numbers used for?

Answer 25

shows the number of organisms at each trophic level in a food chain. Pyramids of numbers can sometimes display different patterns; for example, when individuals at lower trophic levels are relatively large (inverted pyramids).

Question 26

Advantage pyramid of numbers

Answer 26

• easy method of giving an overview
• good for comparing changes in population numbers over different times

Question 27

disadvantage pyramid of numbers

Answer 27

• all organisms included regardless of their size
• numbers can be too great to represent accurately

Question 28

What is a pyramid of biomass used for?

Answer 28

This pyramid shows the biomass, or total mass of organisms, at each trophic level, measured in grams per square meter. It represents the biomass available at a specific time and can sometimes show larger amounts at higher levels due to seasonal changes.

Question 29

Advantages pyramid of biomass

Answer 29

• overcomes the problems of pyramids of numbers

Question 30

disadvantage pyramid of biomass

Answer 30

• only uses samples from populations, so it’s impossible to measure biomass exactly
• organisms must be killed to measure dry mass

Question 31

What is a pyramid of productivity used for?

Answer 31

This represents the flow of energy through each trophic level, showing the rate at which energy or biomass is produced over a certain period, typically measured in grams per square meter per year (g m-2 yr-1) or Joules per square meter per year (J m-2 yr-1). It illustrates the energy available as food to the next level within a fixed time frame.

Question 32

Advantages pyramid of productivity

Answer 32

• shows the actual energy transferred and allows for rate of production

Question 33

Disadvantages pyramid of productvity

Answer 33

• very difficult and complex to collect energy data as the rate of biomass production over time is required

Question 34

Explain the transfer and transformation of energy as it flows through an ecosystem.

Answer 34

*loss of radiation through reflection and absorption
*conversion of light to chemical energy
*loss of chemical energy from one trophic level to another
*efficiencies of transfer
*overall conversion of light to heat energy by an ecosystem
*re-radiation of heat energy to the atmosphere.

Question 35

Difference in bioaccumulation verses biomagnification?

Answer 35

Bioaccumulation is the buildup of absorbed chemicals in an organism over time. Biomagnification is the increase in concentration of these chemicals in each organism up the food chain.