topic 4.1- species, communities and ecosystems

Question 1

define a species

Answer 1

a group of organisms that can potentially interbreed to produce fertile offspring

Question 2

define a population

Answer 2

a population is a group of organisms of the same species who live in the same area at the same time

Question 3

what happens if two populations live in different areas? what are the consequences of this?

Answer 3

• the members of the populations are reproductively isolated in separate populations and unlikely to breed with each other
• they may therefore develop recognisable differences

Question 4

define and describe the two methods of obtaining organic carbon compounds (eg glucose, amino acids) needed for growth and reproduction.

Answer 4

• autotrophic (self-feeding): make their own carbon compounds from CO2 and other simple substances
• heterotrophic (feed on others): obtain carbon compounds from other organisms

Question 5

what is a mixotrophic organism?

Answer 5

organisms that are not solely autotrophic or heterotrophic, but can use both methods of nutrition

Question 6

define a consumer

Answer 6

heterotrophs that feed on living organisms by ingestion

Question 7

define a detritivore

Answer 7

heterotrophs that obtain organic nutrients from detritus by internal digestion

Question 8

define a saprotroph

Answer 8

heterotrophs that obtain organic nutrients from dead organisms by external digestion

Question 9

describe the method by which saprotrophs digest food externally

Answer 9

secretion of digestive enzymes onto the extracellular material and absorption of the organic products

Question 10

how is a community formed?

Answer 10

by populations of different species living together in the same area and interacting with each other.

Question 11

why can a population of one species never live in isolation?

Answer 11

all species are dependent on relationships with other species for their long-term survival

Question 12

how is an ecosystem formed?

Answer 12

by the interactions of a community with the abiotic environment

Question 13

describe the interaction of autotrophs with their abiotic environment

Answer 13

they obtain all of the elements that they need as inorganic nutrients from the abiotic environment

Question 14

describe the interaction of heterotrophs with their abiotic environment

Answer 14

obtain the elements that they need as part of the carbon compounds in their food; obtain other elements as inorganic nutrients from the abiotic environment (eg sodium, potassium, calcium)

Question 15

how is the supply of inorganic nutrients maintained?

Answer 15

by nutrient cycling

Question 16

describe nutrient cycling with a flow diagram

Answer 16

reserves of an element in the abiotic environment <–> element forming part of a living organism

Question 17

describe the process of nutrient cycling

Answer 17

organisms absorb the elements that they require as inorganic nutrients from the abiotic environment, use them and then return them to the environment with the atoms unchanged

Question 18

describe the sustainability of ecosystems.

Answer 18

ecosystems have the potential to be sustainable over long periods of tine

Question 19

give 3 requirements for sustainability in ecosystems

Answer 19

• nutrient availability
• detoxification of waste products
• energy availability

Question 20

what do mesocosms do?

Answer 20

mesocosms are small experimental areas that can be set up to try and establish sustainability

Question 21

when is something sustainable?

Answer 21

when is can continue indefinitely

Question 22

nutrients —- —- recycled indefinitely, so

Answer 22

can be; there should not be a lack of the chemical elements on which life is based

Question 23

energy —- —- recycled, so

Answer 23

cannot be; sustainability depends on continued energy supply to ecosystems (mostly supplied from the sun)

Question 24

what does the chi-squared test do?

Answer 24

it tests for the hypotheses:
- two species are distributed independently
- two species are associated (either positively so they tend to occur together or negatively so they tend to occur apart)

Question 25

describe how you could conduct a chi-squared test

Answer 25

1. construct a table of frequencies (both observed and expected)
   EXPECTED FREQUENCY = (Row total × Column total) ÷ Grand total
2. Apply the chi-squared formula to each part of the table
3. Add each value to give the chi squared result
4. Determine the degree of freedom (df) (always 1 when there are 2 species)
5. identify the p-value, which is considered significant if there is less than a 5% probability (p < 0.05) the results are attributable to chance