UNIT 5

Question 1

Define species, population, community, habitat, ecosystem and biome.

Answer 1

Species: a group of organisms that can interbreed to produce fertile offspring;
Population: a group of organisms of the same species living in the same place at the same time;
Community: populations living and interacting with each other in an area;
Habitat: the abiotic environment in which an organism lives;
Ecosystem: a community and its abiotic environment;
Biome: a group of ecosystems with the same climate and similar dominant communities;

Question 2

Outline the challenges of sand dunes and adaptations of one species to this environment.

Answer 2

Challenges
Low water availability and precipitation;
High salinity and temperature;
Low nutrient levels and biodiversity;
Adaptations
E.g. marram grass or sea oat;
Rolled up leaves to reduce exposure to wind and trap water vapour;
Sunken stomata to trap water vapour;
Inner surface of leaves covered in tiny hairs to trap water vapour;
Thick waxy cuticle to reduce evaporation;
Large, widespread root system;
Dense, interwoven roots to maximise water uptake after rain;

Question 3

Outline the challenges of mangroves and adaptations of one species to this environment.

Answer 3

Challenges
High salinity;
Low fresh water availability;
Low oxygen availability (due to being underwater);
Adaptations
E.g. red mangrove
Spider-like root system/prop roots above water line which can absorb oxygen so roots in the mud can be oxygenated, can also provide stability in unstable soil;
Roots can filter out salt so freshwater can be obtained, allows for tolerance of high salinity shorelines;
Targeted root growth under trees provide protective habitats for various marine species;
Fruit contains germinating seed that grows before falling off the parent plant, seed can also float and orientate itself (shoots upwards roots downwards);

Question 4

Define abiotic factor.

Answer 4

Abiotic factors are non-living factors that effects organisms within their habitat;

Question 5

Outline an example of an abiotic factor and its relationship with living organisms.

Answer 5

Light intensity
Light is required by plants for photosynthesis;

Temperature
Temperature affects the rate of enzyme-controlled reactions;

Water availability
Water is required by all living organisms for survival;

Soil pH mineral content
Different plant species require different pH levels and nutrient concentrations;

Wind speed
High wind speeds can increase water loss by evaporation from the leaves of plants;

CO2 concentration
CO2 is required by plants for photosynthesis;

O2 concentration
O2 is required by all organisms that carry out aerobic respiration;

Question 6

Describe the relationship between abiotic factors and species distribution.

Answer 6

Abiotic factors can act as limiting factors for species distribution;
Species exist within a range of tolerance (where certain conditions are ideal/optimum but some amount of variation from these levels can be tolerated);
Species will not be found in areas with abiotic conditions that are outside their range of tolerance;
Species adapted to extreme conditions may have an especially wide range of tolerance;

Question 7

Describe the conditions required for the formation of coral reefs.

Answer 7

Water depth of less than 50m to allow light penetration;
pH > 7.8 so CaCO3 can be deposited in the skeleton;
32-42% salinity;
Water clarity to allow light penetration;
23-29C water due to range of tolerance, high temperatures can lead to coral bleaching;

Question 8

Outline terrestrial biome distribution using a diagram and describe features of each.

Answer 8

Tropical rainforest: high temperature and precipitation, high biodiversity and supports many trophic levels, fierce competition between species;
Temperate forest: average temperature and precipitation, four seasons and no temperature/precipitation extremes, rich biodiversity;
Grassland: range of temperatures depending on latitudes, low precipitation, dominated by grass plants due to lack of water, majority of species present are grazers and herbivores with few predators, have wet and dry seasons;
Desert: high temperatures, low precipitation, low biodiversity, animals and plants adapted to extremely hot environments;
Tundra: low temperature and precipitation, animals adapted to hibernate for long periods of time or migrate when conditions become too difficult, dark for long periods of time;
Taiga (cold forest): medium to low temperatures, high precipitation (in the form of snow), largest terrestrial biome by landmass, animals adapted to extremely cold environments;

Question 9

Describe the adaptations of one animal and one plant species to hot deserts.

Answer 9

E.g. Marram grass
Thick waxy cuticle on epidermis to prevent evaporation;
Rolled-up leaves, sunken stomata and tiny hairs to trap water vapour and reduce transpiration;
Deep widespread root system to increase water uptake;
Tap roots to collect water from deep in the subsoil;
CAM metabolism so stomata only open at night, reduces transpiration;

E.g. Fennec fox
Large ears that radiate heat and keep body temperature low;
Nocturnal to avoid exposure to sun/heat;
Long Loop of Henle to increase water retention;
Long thick hair for insulation during cold nights and hot days;
Hairs covering pads of feet to provide insulation from hot sand;
Pale coloured coat to reflect sunlight;
Ventilation rate rises very high to cause heat loss by evaporation;

Question 10

Describe the adaptations of one animal and one plant species to rainforests.

Answer 10

E.g. Kapok tree
Tall trunk to increase competitiveness for sunlight;
Strong buttress roots for support against wind stress;
Smooth trunk to shed rainwater rapidly;
Extensive root system provides stability in shallow soil;

E.g. Spider monkey
Long arms and legs for climbing and reaching fruit;
Flexible shoulders allowing swinging from tree to tree;
Long tail to grip branches;
Highly developed larynx for communication in dense forest canopy;
Only awake during daytime when vision is better so movement is faster;

Question 11

Suggest two abiotic factors other than temperature and nutrient supply that may affect the production of biomass of a grassland.

Answer 11

Water availability/rainfall/humidity;
Light/sunlight (intensity) / daylength;
Soil salinity/pH;
Chemical pollution / herbicides / allelopathy / parasitic weeds;

Question 12

Compare and contrast the exchange of energy with nutrient cycling in ecosystems.

Answer 12

BOTH
Both flow through the ecosystem;
Both used for metabolism/growth;

ENERGY
Lost as heat between each trophic level
Source of energy is the sun
Is not recycled

NUTRIENT
Escape food chain/web as litter/faeces/detritus etc;
Source of nutrients is soil/rock;
Are recycled;

Question 13

Suggest why some deciduous plants shed leaves once a year.

Answer 13

During dry season;
To prevent water loss/transpiration due to no rainfall;

Question 14

Distinguish between obligate aerobes, obligate anaerobes and facultative anaerobes.

Answer 14

Obligate aerobes
Oxygen must be continuously available for aerobic respiration;
Must live in an oxic environment;
E.g. all plants and animals
Obligate anaerobes
Must live in an anoxic environment;
Oxygen kills or inhibits the organism;
E.g. methanogenic archaea
Facultative anaerobes
Oxygen is used if available but anoxic conditions are tolerated;
Can live in an oxic or anoxic environment;
E.g. E. coli

Question 15

Describe holozoic nutrition by heterotrophs.

Answer 15

Method of internal digestion;
Ingestion: taking of food into the gut;
Digestion: breaking large food molecules into smaller molecules;
Absorption: transport of digested food across the plasma membrane of epidermis cells and thus into the blood and tissues of the body;
Assimilation: using digested foods to synthesise proteins and other macromolecules;
Egestion: removal of undigested material from the end of the gut;

Question 16

Distinguish between autotrophs, heterotrophs and mixotrophs.

Answer 16

Autotrophs are organisms that synthesise their own organic matter from inorganic matter;
Heterotrophs are organisms that obtain organic matter by feeding on other organisms;
Mixotrophs can be autotrophic or heterotrophic;

Question 17

Distinguish between facultative mixotrophs and obligate mixotrophs.

Answer 17

Facultative mixotrophs can be entirely autotrophic, heterotrophic or both;
Obligate mixotrophs must utilise both autotrophic and heterotrophic modes of nutrition;

Question 18

Describe an example of a mixotroph and state whether it is an obligate or facultative mixotroph.

Answer 18

Euglena - single-celled protists;
Can ingest food from the water around it;
Have photosynthetic pigments for photosynthesis;
Is a facultative mixotroph;

Question 19

Describe the diversity of nutrition in archaea.

Answer 19

Huge diversity of nutrition: phototrophic, heterotrophic or chemotrophic;
Chemoheterotrophs: oxidation of carbon compounds obtained from other organisms;
Photoheterotrophs: absorption of light using pigments (not chlorophyll in archaea);
Chemoautotrophs: oxidation of inorganic chemicals e.g. Fe2+ to Fe3+;
Many archaea are called extremophiles as they live in extreme conditions;
Methanogens live in anaerobic acidic conditions, produce methane;
Halophiles live in high salinity conditions;
Thermophiles live in high temperatures, e.g. Taq polymerase;

Question 20

Explain the adaptations of dentition for diet in the family Hominidae.

Answer 20

Incisors for cutting and biting, located at the front of the mouth;
Canines for ripping and tearing up food, located next to incisors;
Premolars for crushing up food, next to canines;
Molars for grinding and reducing the food to a pulp before swallowing, located furthest back;
Narrower and serrated molars are better adapted for eating meat;
Rounded and blunt molars are better adapted for plant material;
E.g. great apes have more developed molars and premolars as well as larger incisors for biting and grinding plant fibres;

Question 21

Describe the adaptations of herbivores for feeding plants.

Answer 21

Stylets to pierce plant and suck out sap;
Mandibles to cut into grass blades;
Flat and broad back teeth for chewing plant fibres;
Adaptive digestive systems with bacteria and archaea that help break down cellulose;
Tubular mouthparts to reach into nectary in flowers;

Question 22

Describe the adaptations of plants for resisting herbivory.

Answer 22

Strong and thick bark/stems that are difficult to penetrate;
Thorns/spikes/spines to deter herbivores;
Nettle (tiny silica hairs) that generate a stinging/burning sensation when rubbed against;
Phytotoxins can cause nausea/hallucinations when ingested;
Synthesis and storage of secondary metabolites that are toxic to herbivores;

Question 23

Describe the adaptations of some animals for the detoxification of phytotoxins.

Answer 23

Ruminants and insects have microbes in the gut;
In mammals they are passed along the blood into the liver for neutralisation;
Browsing herbivores have proteins in saliva that can neutralise tannins;

Question 24

Describe the chemical, physical and behavioural adaptations of predators and prey.

Answer 24

CHEMICAL
Predators
Toxins for paralysis in bite;
Mimickery of sex pheromones to lure in prey;
Prey
Produce chemicals that taste bad or toxins/poison;

PHYSICAL
PREDATORS
Electrolocation (bats and dolphins);
Excellent eyesight / adaptations for night-hunting (owls);
Sharp claws and teeth to kill/extract nutrients;
Run/swim/fly fast;
Acute sense of smell;
Special sensing organs to detect electromagnetic field (sharks);
Quick assessment of rapid changing circumstances;
PREY
Camouflage (fixed or adaptive);
Aposematism (venomous animals using bright colours to warn predators) / mimickery by non-venemous animals;
Warning calls to warn others;
Hard shells for protection;

BEHAVIOURAL
PREDATORS
Ambush predators (hide and pounce);
Pack hunting increases chances of bringing down large animals;
Pursuit predators (persistence hunting) can wear out prey;
PREY
Instinct (run/hide in danger);
Strength in numbers (large groups reduces kills and protects young);

Question 25

Describe the adaptations of plants for harvesting light.

Answer 25

Trees have strong and tall trunks as well as many branches to reach the canopy; Lianas are unable to grow strong stems/trunks so they use trees as a scaffold to reach the canopy, they also need less xylem tissue than free-standing trees; Epiphyte seeds grow on trunks and branches on trees and take advantage of this to reach the canopy or understorey, they also derive moisture and nutrients from the air and rain; Strangler epiphytes are hemiepiphytes that can push their stems upwards/climb up the trunks of trees, encircle them and outgrow the tree’s branches (may kill them) to reduce competition; Shade-tolerant shrubs have different photosynthetic pigments that absorb different wavelengths of light that ramin after filtered through tall plants (e.g. blue, purple, red);

Question 26

Outline what is meant by the niche concept.

Answer 26

The role of an organism in its environment; Includes spacial habitat, feeding activities and interactions with other species in the community; Principle of competitive exclusion: no two species can occupy the same niche / limits niche; Can be fundamental or realised;

Question 27

Distinguish between fundamental and realised niche.

Answer 27

Fundamental niche is all the potential range of conditions a species could live in; Realised niche is the actual range of conditions under which a species lives in;

Question 28

Explain the principle of competitive exclusion.

Answer 28

States that no two species can occupy the same niche; The numbers of both populations will decrease if they coexist for a certain period of time; One species may replace the other in the long run;

Question 29

Define population.

Answer 29

A group of organisms of the same species living in the same area at the same time;

Question 30

Describe how members of a population and separate populations interact.

Answer 30

Members of a population normally interbreed with each other; Rarely interbreed with individuals in other populations (reproductive isolation); Non-breeding interactions between individuals in a population e.g. competition for food, cooperation to avoid predation etc; Populations of a species are often separated by a geographical barrier;

Question 31

Describe how population size can be estimated using quadrat sampling.

Answer 31

Separate study area into coordinates and generate random coordinates; Quadrats are placed at generated coordinate; Count the number of organisms / percentage coverage in the quadrat; Repeat as many times as possible and take the mean count per quadrat; Population estimate = (mean count per quadrat * area of whole site) / area of one quadrat;

Question 32

Discuss the advantages and disadvantages of quadrat sampling.

Answer 32

Advantages No bias, random sampling; No need to count every individual; Disadvantages Can only be used for sampling sessile organisms; Organisms may be unevenly distributed, hence results may not show distribution pattern; Cannot be used for large organisms / organisms under the soil;

Question 33

Outline what the standard deviation indicates.

Answer 33

A measure of the variability of data; Low standard deviation = little variation between values in a sample /OE; Low standard deviation = population is evenly distributed /OE;

Question 34

Explain how capture-mark-release-recapture can be used to estimate the population size of a motile organism, including assumptions made for this method.

Answer 34

Random sample is captured and marked (n1); Mark must not harm or affect the survival of the organism; Captured sample is released and allowed to mix with general population / allow time to become randomly dispersed; Capture a second sample and count the total number of organisms (n2) and marked individuals within those recaptured (n3); Population size (N)=n1n2/n3; Only estimates could be obtained; Assumes sample size is large enough to be significant; Assumes there is no emigration/immigration of individuals; Assumes no misidentification of species; Assumes marked organisms do not lose their mark;

Question 35

Define carrying capacity.

Answer 35

The maximum number of individuals an environment can support; Varies with abundance of limiting resources; Population growth slows/fluctuates as the carrying capacity of environment reached;

Question 36

Distinguish between density-independent and density-dependent factors.

Answer 36

Density-independent factors have the same effect no matter the population size (e.g. natural disasters etc.); Density-dependent factors act as negative feedback, reducing larger populations and allowing smaller populations to increase; Density-dependent factors tend to being population size back to carrying capacity / control population size so it does not exceed carrying capacity; Three groups of density-dependent factors: competition (for limited resources), predation and parasitism/infectious disease/pest infestation;

Question 37

Define natality, mortality, immigration and emigration in terms of individuals in a population.

Answer 37

Natality is the production of offspring and added to the population; Mortality is the death of individuals and are lost from the population; Immigration is individuals moving into the area from elsewhere; Emigration is individuals moving elsewhere from the area;

Question 38

Discuss the factors affecting population growth that result in a sigmoid population curve.

Answer 38

Population growth determined by natality, mortality, immigration and emigration; population change = (natality+immigration)-(mortality+emigration); Exponential growth occurs in ideal/unlimited environment; Natality and immigration increases population; Natality > mortality will cause exponential growth; Absence of limiting factors will cause exponential growth; Transitional phase is slowed but still increasing population growth; Presence of limiting factors in the transitional phase: increased competition for resources, predation and disease; Curve will plateau when the carrying capacity is reached (limited resources, predation, disease); When natality and immigration is equal to or lower than mortality and emigration, population growth will slow or population will decrease;

Question 39

Explain intraspecific relationships, including competition and cooperation

Answer 39

Exists between individuals of the same species and usually also within the same population; Competition due to members of a population having the same ecological niche hence requiring the same limited resources, individuals tend to be harmed to some degree; E.g. over food, sunlight, mates, territory etc; Usually density-dependent; Cooperation is beneficial to all individuals/the group as a whole; E.g. pack hunting, huddling to conserve body heat, warning calls etc;

Question 40

Define interspecific relationships and outline six examples.

Answer 40

Exists between individuals of different species; Herbivory: primary consumers feeding on producers, where the producer may or may not die; Predation: one consumer species (predator) killing and feeding on another (prey); Interspecific competition two species competing for the same resource, with the amount taken by one species reducing the amount available to the other species; Mutualism: two species living in close association and both benefit; Pathogenicity: one species (pathogen) living in another (host) and causes disease in host; Parasitism: one species (parasite) lives in/on another (host) and obtains/depends on host for food for at least part of its life cycle, host is harmed and parasite benefits;

Question 41

Describe three examples of mutualism.

Answer 41

Mycorrhizae in orchids: mycorrhizae acts as extension to the root system and passes water/nutrients to orchids as they do not have enough nutrients on their own, orchids provide protection and sugars/other carbon compounds made by photosynthesis; Root nodules in legumes: root nodule provides protection for Rhizobium bacteria as well as sugars and a low oxygen environment, Rhizobium provides nitrates and ammonium ions through nitrogen fixation; Zooxanthellae in hard corals: zooxanthellae provide oxygen and carbon compounds from photosynthesis, corals provide protection and carbon dioxide from aerobic respiration;

Question 42

Describe the relationship between invasive and endemic species and provide an example.

Answer 42

Alien species are not native, artificially introduced by humans deliberately or accidentally; If alien species increases in number and spreads rapidly it is invasive; Endemic species occur naturally / native to a geographical area; Principle of competitive exclusion means alien species and endemic species compete for resources if they have overlapping niches, if alien species is successful it becomes invasive; May result in endemic species occupying a smaller realised niche, decline in population or become extinct; E.g. Galapagos tortoises (endemic, native to Galapagos islands) and feral goats (invasive) compete for forests that provide them with shade and moisture / red lionfish compete for prey with native Atlantic fish in coral reefs;

Question 43

Describe tests to investigate interspecific competition.

Answer 43

Field study/manipulation: removing one species and observing the change in population; Laboratory experiments: under controlled conditions, species grown together and apart; Test for association by random sampling: chi-squared;

Question 44

Outline how chi-squared can be used to test for association between two species.

Answer 44

In each quadrat, determine the presence or absence of each species; Set a null hypothesis: no significant difference/association between the two species / alternative hypothesis: significant difference/association between the two species; x2=sum of [(O-E)^2/E]; Degreed of freedom = number of categories - 1; At p<0.05, if the calculated x^2 value is higher than the critical value, accept the alternative hypothesis and reject the null hypothesis / if the calculated x^2 value is lower than the critical value, accept the null hypothesis and reject the alternative hypothesis;

Question 45

Explain how animal populations are controlled by density-dependent factors using an example of a predator-prey relationship.

Answer 45

E.g. lynx and snowshoe hare; Rise in predator numbers increases predation so prey numbers fall; Fall in prey numbers decreases prey availability, causing predator numbers to fall; Fall in predator numbers decreases predation, causing prey numbers to rise; Rise in prey numbers increases prey availability so predator numbers rise;

Question 46

Explain top-down and bottom-up control of populations in communities.

Answer 46

Top-down control acts from a higher trophic level to a lower one; E.g. predation, herbivory etc; Bottom-up control acts from a lower trophic level to a higher one; E.g. resource availability, disease in low trophic levels = less prey etc;

Question 47

State two bottom-up factors affecting algal bloom.

Answer 47

Minerals; Nutrients; Phosphorus; Nitrogen;

Question 48

Explain how top-down factors control algal bloom

Answer 48

Herbivores/primary consumers regulate algal bloom; Predators prey on herbivores to reduce herbivory/regulat algal bloom; Overfishing/death of predators/decreased reproduction of predators decreases algal bloom as herbivory/herbivoer population increases; Habitat degradation can decrease algal bloom; Pathogens of algae will decrease algal bloom / alien/invasive species may compete for habitat and affect algal bloom;

Question 49

Explain how an excessive growth of algae on coral reefs can be controlled by top-down factors

Answer 49

Top-down factors acts from a higher trophic level to a lower one / refer to herbivory/predation; Limit/control population growth; E.g. parrotfish;

Question 50

Explain how potential competitors are deterred using antibiotics and allelopathic agents as examples.

Answer 50

Antibiotics are secreted by microorganisms to kill/inhibit/prevent the growth of other species of microorganism; Penicillium secrete the antibiotic penicillin which inhibits bacterial growth by interfering with cross-linking of peptidoglycan molecules in the cell wall, causing bacteria to burst and die; Allelopathic agents are secreted into the soil by plants to kill/deter the growth of neighbouring plants; Black walnut tree secretes juglone which inhibits the germination/growth/survival of other plants in the vicinity;

Question 51

Distinguish between open and closed systems in terms of energy and matter recycling.

Answer 51

In an open system, energy and matter can enter or exit; In a closed system, only energy can enter or exit, matter is recycled;

Question 52

Describe two exceptions to sunlight as the principal energy source sustaining ecosystems.

Answer 52

In coastal waters, sunlight cannot penetrate deeper than 50m; In ocean waters, sunlight cannot penetrate deeper than 200m; Ecosystems with no light are sustained my chemoautotrophs which use inorganic chemical reactions to synthesise organic compounds; E.g. Movile caves, Romania;

Question 53

Describe how energy flows through and is used by organisms in ecosystems.

Answer 53

Producers/autotrophs/plants obtain energy from light/inorganic sources; Energy is passed along food chains/between trophic levels in the form of carbon compounds; Consumers obtain energy by feeding on other organisms/previous trophic levels; Energy is released in organisms through cell respiration; ATP produced; ATP/energy is used for biosynthesis/movement/active transport etc; Energy is lost between each trophic level as heat and in faeces;

Question 54

Compare and contrast between detritivores and saprotrophs.

Answer 54

Saprotrophs digest food externally by secreting digestive enzymes and absorbing the products; Detritivores ingest food and digest food internally; Both are decomposers / obtain nutrients from dead organic matter; Dead organic matter includes faeces, dead parts of organisms or dead whole organisms;

Question 55

Define what is meant by autotrophs and outline how they synthesise carbon compounds.

Answer 55

Organisms that synthesise their own organic matter/carbon compounds from simple inorganic substances using external energy sources; Photoautotrophs use light as their energy source for carbon fixation by photosynthesis; Chemoautotrophs use inorganic chemical/oxidation reactions to synthesise carbon compounds, such as iron-oxidising bacteria (iron(II) → iron(III), electrons used to make ATP to fix CO2);

Question 56

Define what is meant by heterotrophs.

Answer 56

Obtain organic matter/carbon compounds from feeding on other organisms; Complex carbon compounds are digested internally/externally and assimilated by constructing carbon compounds required;

Question 57

Outline how energy is released in autotrophs and heterotrophs.

Answer 57

ATP produced by cell respiration; Oxidation of carbon compounds to release energy used to phosphorylate ADP; ATP used for metabolic processes e.g. growth, movement, homeostasis, active transport, anabolism etc;

Question 58

Describe what a pyramid of energy illustrates and outline the reasons for its shape.

Answer 58

Shows the flow of energy between trophic levels; Measured in kJm-2year-1; Producers at the base and highest trophic level/apex predators at the top; Only a small proportion/10% of energy can pass from one trophic level to the next / large proportion/90% lost between trophic levels; Energy released by respiration and lost as heat; Energy loss due to uneaten parts/undigested parts/faeces/egestion of food; Not enough energy to sustain 4th/5th/later stages of a food chain;

Question 59

Explain the reasons for the reduction in energy availability at each successive stage in food chains.

Answer 59

Incomplete digestion/undigested parts of food is passed out bygestion/as faeces e.g. some animals cannot digest cellulose due to lack of cellulase; Incomplete consumption/uneaten parts e.g. bones; Energy is required for cell respiration to make ATP and lost as heat;

Question 60

Define biomass and outline the changes between trophic levels.

Answer 60

Dry mass of an organism; Less biomass at each successive trophic level but energy per unit mass remains constant; Fewer organisms with each successive trophic level; Not all biomass consumed (e.g. bones) from one trophic level to the next;

Question 61

Explain primary and secondary production.

Answer 61

Primary production is the mass of carbon compounds synthesised by autotrophs; Usually measured in gm-2year-1; Net primary production (NPP) = gross primary production (GPP) - respiration (R);

Question 62

Explain secondary production and contrast it with primary production.

Answer 62

Accumulation of carbon compounds in biomass by heterotrophs; Lower than primary production since energy is lost from one trophic level to the next; Declines with each successive trophic level from primary consumers onwards;

Question 63

Describe and explain what the Keeling curve illustrates.

Answer 63

Graphs atmospheric CO2 concentration against time in years; Annual fluctuations due to summer and winter months, relatively more photosynthesis during summer and relatively more respiration during winter; Long-term increasing trend due to combustion of fossil fuels by humans and anthropogenic factors such as deforestation;

Question 64

Outline recycling in ecosystems.

Answer 64

Elements such as C, H, O, N are endlessly recycled; Saprotrophic nutrition by decomposers digest carbon compounds and return elements from them to the abiotic environment;

Question 65

Outline two general characteristics of all ecosystems.

Answer 65

Interactions between organisms/community plus the environment / biotic and abiotic components; Ecosystems show sustainability; Nutrients are recycled; Energy flows through ecosystems but are not recycled; Producers are part of all ecosystems; Decomposers/saprotrophs are part of all ecosystems;

Question 66

Describe the process of peat formation.

Answer 66

Formed from dead plant material; Formed in waterlogged soil/bogs/mires/swamps; Where bacteria/fungi/saprotrophs are not active/are inhibited; Organic matter not fully decomposed; Occurs in acidic conditions; Occurs in anaerobic conditions; Very slow process/takes a long time;

Question 67

Outline the roles bacteria play in the carbon cycle

Answer 67

Decomposition of dead organic material by saprotrophic bacteria; Leads to CO2 formation/regeration due to respiration; Saprotrophic bacteria partially decompose dead organic matter in acidic/anaerobic conditions in waterlogged soil; Results in peat formation in bogs/swamps; Photosynthetic bacteria/cyanobacteria fix CO2 in photosynthesis;

Question 68

State two causes of the decrease of biomass along food chains in terrestrial ecosystems.

Answer 68

Cell respiration/loss of CO2/biomass consumed to provide/as a source of energy; Loss of energy as heat between trophic levels means less energy available for building biomass; Waste products/loss of urea/faeces/egestion; Material used/CO2 released by saprotrophs; undigested/uneaten material/detritus buried/not consumed / formation of peat/fossils/limestone;

Question 69

Outline energy flow through a food chain.

Answer 69

Energy from the sun/light energy is converted to chemical energy by photosynthesis; Chemical energy flows through food chains by feeding; Energy is released by respiration as heat; Heat is not recyclable / is lost from food chains; Energy is lost in excretion/uneaten material/egestion/faeces; Energy losses between trophic levels limits the length of food chains / energy transfer is only 10% between trophic levels;

Question 70

Explain the movement of energy and inorganic nutrients in an ecosystem.

Answer 70

autotrophs/producers obtain inorganic nutrients from the abiotic environment; Energy is provided mainly by sunlight; Light energy is converted to chemical energy through photosynthesis; Photosynthesis converts inorganic carbon and water into organic compounds; Carbon compounds are a source of energy; Carbon compounds/energy is transferred along food chains when eaten by consumers/heterotrophs; Respiration returns carbon dioxide to the environment; Respiration releases stored/chemical energy as heat/ATP; Energy/ATP is used to carry out the functions of life/synthesis/growth/movement; Energy is lost/not recycled; Nutrients are recycled; Decomposers recycle minerals/inorganic nutrients;

Question 71

Distinguish between the transfers of energy and inorganic nutrients in ecosystems.

Answer 71

Energy is lost between trophic levels / not all passed on / not reused / must be supplied; Nutrients are recycled/reused;

Question 72

Outline the role of methanogenic archaeans in the movement of carbon in ecosystems.

Answer 72

Methane produced from organic matter by methanogenesis; In anaerobic conditions; Methane diffuses into atmosphere/accumulates in ground/soil; Oxidised/converted to carbon dioxide (in atmosphere);

Question 73

Describe processes in the carbon cycle that produce or use carbon dioxide.

Answer 73

Photosynthesis uses carbon dioxide; Autotrophs/plants/cyanobacteria convert/fix carbon dioxide into carbon/organic compounds; Cell respiration produces/releases carbon dioxide; Glucose/carbon/organic compounds oxidised/broken down to produce/release carbon dioxide; Carbon dioxide released from aerobic cell respiration and anaerobic respiration in yeast/fungi; Carbon dioxide released from saprotrophs/detritivores/decomposers from deda organic matter / during decomposition/respiration/decay; (partially) decomposed dead otganic matter can lead to the formation of peat / fossilised organic matter (coal/oil/natural gas); Carbon dioxide released when carbon compounds burn / during combustion of fossil fuels / forest fires; Carbon dioxide dissolves in aquatic ecosystems / can form carbonic acid/HCO3- ions; Reef-building corals/molluscs use calcium carbonate to make/build shells/exoskeletons or other body parts; Hard parts/shells/exoskeletons / precipitation of calcium carbonate to form limestone;

Question 74

Compare and contrast food chains and food webs.

Answer 74

BOTH In both organisms are arranged by trophic levels/feeding positions; Both represent the transfer of food/energy in an ecosystem; Both include producers and consumers; Food chains One species can only occupy one trophic level; Represents one possible feeding option for each organism; Food webs One species can occupy multiple trophic levels; Represents more possible feeding relationships/trophic levels;

Question 75

Evaluate the use of food webs to represent ecological communities.

Answer 75

Summarise all possible food chains; Realistic representation; Some communities/ecosystems are too complex to represent; Only shows qualitative information/not quantitative data / saprotrophs/abiotic factors not taken into account;