B12 : Organisms and their environment

Question 1

Ecosystem

Answer 1

1. Ecosystem is a unit containing all of the organisms and their environment, interacting together, in a given area,
2. e.g. a lake
3. Ecosystem is composed of both biotic and abiotic things

Question 2

biotic

Answer 2

living things

Question 3

abiotic

Answer 3

non-living things

Question 4

Organism

Answer 4

individual species that can reproduce fertile offspring

Question 5

Community

Answer 5

populations living together

Question 6

Producers

Answer 6

1. organisms that produce their own organic nutrients usually using energy from sunlight
2. plants are producers as they carry out photosynthesis to make glucose
3. also known as Autotroph

Question 7

Herbivore

Answer 7

an animal that gets its energy by eating plants

Question 8

Carnivore

Answer 8

an animal that gets its energy by eating other animals

Question 9

Primary consumers

Answer 9

1. feed on producers (plants)

2. herbivores

Question 10

Secondary consumers

Answer 10

predators that feed on primary consumers

Question 11

Tertiary consumers

Answer 11

predators that feed on secondary consumers

Question 12

Decomposers

Answer 12

bacteria and fungi that get their energy from feeding off dead and decaying organisms and undigested waste (e.g. faeces) by secreting enzymes to break them down

Question 13

Trophic level

Answer 13

the position of an organism in a food chain or food web

Question 14

Trophic level (in order)

Answer 14

1. Producer
2. Primary Consumer (first ones to eat)
3. Secondary Consumer
4. Tertiary Consumer
5. Quaternary Consumer

Question 15

Consumer

Answer 15

1. an organism that gets its energy by feeding on other organisms
2. also known as Heterotrophs

Question 16

Explain why food chains usually have fewer than five trophic levels?

Answer 16

1. Living organisms cannot convert heat to other forms of energy
2. Cannot convert heat energy into any other form of energy. Energy pyramids illustrate the quantity of energy within the biomass of each trophic level. Only a portion of energy in any level is transferred to the next, commonly being 10-20% of the plant biomass consumer by a typical herbivore
3. 50% is not assimilated: lost as feces (indigestible cellulose)
4. 35% is assimilated but lost as heat during cellular respiration
5. 15% is consumed and assimilated and incorporated into biomass
6. There is not enough energy to sustain more than 5 trophic levels

Question 17

Food chains

Answer 17

1. A food chain shows the transfer of energy from one organism to the next, starting with a producer (not the sun even though the sun is the principal source of energy input to biological systems)
2. The source of all energy in a food chain is light energy from the Sun
3. The arrows in a food chain show the transfer of energy from one trophic level to the next
4. Energy is transferred from one organism to another by ingestion (eating)
5. • e.g. Dessert Biome: Grass -> Rabbit -> Rattlesnake -> Bacteria

Question 18

Food webs

Answer 18

1. A food web is a network of interconnected food chains
2. Food webs are more realistic ways of showing connections between organisms within an ecosystem as animals rarely exist on just one type of food source
3. Food webs give us a lot more information about the transfer of energy in an ecosystem
4. Most of the changes in populations of animals and plants happen as a result of human impact – either by over harvesting of food species or by the introduction of foreign species to a habitat
5. Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web

Question 19

Interdependence

Answer 19

how the change in one population can affect others within the food web

Question 20

Energy Transfer in Human Food Chains

Answer 20

1. Humans are omnivores, obtaining energy from both plants and animals, and this gives us a choice of what we eat
2. These choices, however, have an impact on what we grow and how we use ecosystems
3. As energy is lost per trophic level, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores

Question 21

Population

Answer 21

1. A population is defined as a group of organisms of one species, living in the same area at the same time
2. All living organisms compete with each other for food, water and living space
3. Those which are the best adapted to their environments generally increase their populations at the expense of those less well adapted

Question 22

Factors Affecting Population Growth

Answer 22

1. Food supply
2. Predation
3. Disease