4. ecology and the environment

Question 1

4.1 what does the term population mean?

Answer 1

the total number of individuals of one species in a particular habitat at a particular time

Question 2

4.1 what does the term community mean?

Answer 2

it’s formed of the populations of all the species present in an ecosystem at a particular time

Question 3

4.1 what does the term habitat mean

Answer 3

the places where specific organisms live

Question 4

4.1 what does the term ecosystem mean?

Answer 4

an easily described system or area where organisms interact with their physical environment

Question 5

4.2 practical: investigate the population size of an organism in two different areas using quadrats

Answer 5

• calculate the area of the habitat
• measure number of individuals in 1 quadrat & repeat many times to check result is reliable (at least 10 quadrats needed) - random sampling to make sure data is valid
• calculate avg no. of individuals in a quadrat
• calculate how many quadrats fit into total area
• how many quadrats fit into total area x avg number of individuals in a quadrat
• repeat this in another area

Question 6

4.2 practical: what do you do if an individual is on the edge of a quadrat?

Answer 6

so either count them as half or count those on top & left edges only to make data consistent

Question 7

4.2 practical: if it’s difficult to count individuals for chosen species (e.g. grass) what do you do?

Answer 7

estimate the % of the quadrat area covered by the species, some quadrats divided into grids to help with this

Question 8

4.2 practical: why do we do random sampling & how?

Answer 8

to make sure our data is valid, so avoiding choosing areas which may be interesting as it would bias our result

• lay out 2 tape measures at right angles to make 10m by 10m set of axes. generate pairs of random numbers between 0-10 (coordinates)
• use coordinates to place quadrat

Question 9

4.4B practical - what are the 2 ways you could do the practical (investigate the distribution of organisms in their habitat and measure biodiversity using quadrats)?

Answer 9

1. pick 2 contrasting areas & set up a grid in each. use random sampling to take repeated measurements w a quadrat & compare avg results
   or
2. use a transect - a line across a habitat, which is place to pass through a range of abiotic conditions (e.g. from light to shade, or across a path). a quadrat is placed at regular intervals along transect & used to measure the no. or % cover of species

Question 10

4.4B practical: investigate the distribution of organisms in their habitat and measure biodiversity using quadrats

Answer 10

• place quadrat randomly within sampling area
• count no. of members of same species within quadrat
• repeat this numerous times within sampling area using same size quadrat
• repeat process in another area to compare results
• also, results can be shown on map of sampled area, displaying which areas are densely populated by certain species & vice verse

Question 11

4.4B practical: investigate the distribution of organisms in their habitat and measure biodiversity using quadrats - how could you increase the reliability?

Answer 11

• randomly place quadrat
• use quadrat of same size w each repeat
• take more samples to collect larger data size

Question 12

4.5 what are some abiotic factors that affect the population size and distribution of organisms?

Answer 12

• light intensity
• one area may be trampled
• temperature
• CO2 and O2 concentrations
• minerals in soil

Question 13

4.5 what are some biotic factors that affect the population size and distribution of organisms?

Answer 13

idk fill this in later

Question 14

4.6 what does producer mean?

Answer 14

organisms which make their own food (e.g. photosynthesising plants)

Question 15

4.6 what are consumers?

Answer 15

organisms which eat other living things (e.g. animals)

Question 16

4.6 what are decomposers?

Answer 16

organisms which secrete digestive enzymes to decay (breakdown) dead organic matter to obtain their food; they help to recycle nutrients

Question 17

4.6 what are primary, secondary and tertiary consumers?

Answer 17

the first animal in a food chain/web is the primary consumer, it usually eats the producer; the secondary is the second; tertiary is the third

Question 18

what are the trophic levels?

Answer 18

the stages in a food chain/web

Question 19

4.7 what are pyramids of number?

Answer 19

these are drawn to show the number of each organism counted in the ecosystem. they can be odd shapes due to the different masses of organisms

Question 20

4.7 what are pyramids of biomass?

Answer 20

• these are drawn to show total mass of organisms in each trophic level (i.e. mass of an individual x number of individuals)
• they’re a more accurate way of looking at the relative amounts of organisms.

Question 21

4.7 what are pyramids of energy transfer?

Answer 21

• these are drawn to show total energy available in each trophic level per square metre per year
• there should be a decrease in energy between each trophic level

Question 22

4.9 why is only about 10% of energy transferred from one trophic level to the next?

Answer 22

• some parts of organisms not eaten (so the biological molecules not available for respiration)
• some parts not digested & absorbed, they’re egested as faeces (so biological molecules not available for respiration)
• some materials are respired to release energy - the energy is used for: muscle contraction (movement & breathing), maintaining constant body temp (mammals/birds), synthesising biological molecules (including excretory products), movement of molecules (active transport), cell division

Question 23

what is the least efficient energy transfer from?

Answer 23

light energy to the producer, because:
- some light will miss plant/plants chloroplasts
- some light will be reflected by cuticle
- some light has wrong wavelength to be absorbed by chlorophyll

Question 24

4.10 describe the stages in the carbon cycle

Answer 24

when plants photosynthesise, C atoms from CO2 become part of glucose molecules (which stored as starch) in plant - what happens to C in this glucose?
- some of the glucose broken down by plant in respiration: C in glucose becomes part of CO2 molecule again, & is released back into air
- some of C compounds in plant eaten by animals; animals respire, releasing some of it back into air as CO2
- when plant/animal dies, decomposers (bacteria & fungi) will feed on them. the C becomes part of decomposers’ bodies. when they respire they release CO2 into air again
- fossilisation occurs when living things don’t decay fully when they die due to conditions in the soil. fossil fuels then formed over millions of yrs by process called locking in. these include coal, oil, natural gas & peat
- when fossil fuels are burnt (combustion), CO2 released into atmosphere

Question 25

4.11B describe the stages in the nitrogen cycle

Answer 25

- nitrogen fixing bacteria in soil & roots of legume plants absorb nitrogen and reduce it to make ammonia, this process called nitrogen fixation - ammonia converted to nitrates & nitrites by **nitrifying bacteria**, process called **nitrification** - plant roots can **only** absorb the **nitrates**. they’re combined with carbs (from photosynthesis) to form amino acids which then made into proteins, and nucleotides which are joined to make DNA and RNA - animals **eat** plants. they **digest** the proteins & DNA, absorbing the small soluble molecules (amino acids & nucleotides). these are used by the animal to synthesise (make) new proteins and DNA (**assimilation**) - when a plant/animal dies its tissues **decomposed** by bacteria & fungi (**saprotrophic feeding**) - molecules containing nitrogen such as proteins are broken down by bacteria & fungi and **ammonia** released into soil - some nitrates converted into N2 by denitrifying bacteria. this process is **denitrification**

Question 26

4.11B what is decomposition in the nitrogen cycle, and what bacteria is involved?

Answer 26

- protein in dead plants & animals broken down - ammonia released into soil - decomposing bacteria

Question 27

4.11B what is nitrification and what bacteria is involved?

Answer 27

- ammonia converted to **nitrites**, and nitrites converted into **nitrates** - nitrifying bacteria

Question 28

4.11B what is denitrification and what bacteria is involved?

Answer 28

- nitrates are converted to nitrogen gas (**denitrification** reduces amount of nitrate in soil & therefore makes soil **less fertile**) - denitrifying bacteria

Question 29

4.11B what is nitrogen fixation and what bacteria are involved?

Answer 29

- nitrogen gas converted to ammonia in bacteria which is used to make proteins, when bacteria die their proteins decompose, releasing ammonia back into soil - nitrogen fixing bacteria found in **soil** and in **root nodules** of plants

Question 30

4.11B what is the mutualistic relationship between some nitrogen fixing bacteria and the legume plants?

Answer 30

- the bacteria receive glucose from plant - plant absorbs ammonia from bacteria in nodule

Question 31

4.11B why do farmers rotate the crops they grow in each field?

Answer 31

when the nitrogen fixing bacteria in the nodules of the roots of legume plants decompose they make soil much more fertile by releasing ammonia which can be converted into nitrates

Question 32

4.1B what does the term biodiversity mean?

Answer 32

the variety of living organisms in an ecosystem

Question 33

4.12 what are the biological consequences of pollution of air by sulphur dioxide & carbon monoxide?

Answer 33

sulphur dioxide: - combines with water vapour to form acid rain, damaging plants, aquatic life, and soil - causes respiratory problems in humans carbon monoxide: - binds to haemoglobin irreversibly, reducing oxygen transport in blood - can lead to suffocation & death in high concentrations

Question 34

4.13 what are examples of greenhouse gases?

Answer 34

water vapour, carbon dioxide, nitrous oxides, methane, and CFCs

Question 35

4.14 how do human activities contribute to greenhouse gases?

Answer 35

CO2: burning fossil fuels, slash & burn forest clearance methane: generated by bacteria in anaerobic condition, for example: - ruminants such as cattle produce large volumes of methane from anaerobic activity of bacteria in their gut, this largely comes out of their mouths - bacteria in waterlogged paddy fields for rice cultivation give off methane nitrous oxides: burning fossil fuels CFCs: until 1990s CFCs used as solvent for aerosols such as deodorants; they were also used in fridges & freezers. CFCs were blamed for the hole in the ozone layer (don’t confuse this w greenhouse effect)

Question 36

4.15 how does an increase in greenhouse gases result in an enhanced greenhouse effect

Answer 36

- sun emits radiation, which travels through space. some reflected by earths atmosphere, but some passes through & absorbed by earth’s surface. this warms earth, which then emits IR radiation - some IR radiation passes through atmosphere into space, but some gases in atmosphere absorb it, preventing it from escaping back into space - this leads to more energy being held by atmosphere, heating it - gases which cause this effect are water vapour, CO2, methane, nitrous oxides and CFCs

Question 37

4.16 understand the biological consequences of pollution of water by sewage

Answer 37

- water pollution can occur when **sewage** washed into waterways, e.g. when sewers overflow or agricultural waste is washed off fields due to heavy rain - this can have harmful effects on aquatic ecosystems: 1. sewage can cause inc in **growth of aerobic bacteria**, which feed on biological waste 2. these bacteria **reduce availability of dissolved O** in water 3. **aquatic organisms that are sensitive to O levels die,** leaving only organisms that can survive at low conc.s of O 4. the aquatic ecosystem **dec in biodiversity** - sewage in waterways can also result in an inc in no. of **pathogenic bacteria** present

Question 38

4.17 understand the biological consequences of eutrophication caused by leached minerals from fertiliser

Answer 38

- fertilisers **high in N**, an essential mineral for plant growth, so this can result in the **overgrowth of aquatic plants & algae** at the water surface - aquatic plants below surface die due to reduced light levels, & are **broken down by decomposers** - decomposers inc in no., & inc, respiration of these organisms uses up O in water, **reducing dissolved O levels** - water no longer contains enough O to support organisms, so **many aquatic organisms die**

Question 39

4.18B understand the effects of deforestation - leaching

Answer 39

- while trees usually absorb minerals & nutrients from soil through roots, loss of trees will lead to **unused nutrients & minerals** remaining in soil - as result, these unused nutrients & minerals may be washed into rivers and lakes by rain - leaching, hence causing **eutrophication**

Question 40

4.18B what's the definition for deforestation?

Answer 40

permanent destruction of a forest via the removal or clearance of trees

Question 41

4.18B understand the effects of deforestation - soil erosion

Answer 41

- while tree roots help in **stabilising the soil** to prevent erosion by rain, the loss of trees will cause soil to be **loose** and **unstable** - as result, the soil may be washed away by rain, inhibiting vegetative growth

Question 42

4.18B understand the effects of deforestation - disturbance in water cycle

Answer 42

- as transpiration in trees release water vapours into atmosphere to condense into clouds & returned to land via precipitation, the loss of trees will result in **less transpiration** - as a result, this will have knock-on effect on water cycle, causing **droughts due to lack of precipitation**