Ecology (CQC&SCR&JBW)

Question 1

What is a habitat

Answer 1

A habitat is the place where an organism lives. It is a description of the geographical location, the type of ecosystem, the physical location within the ecosystem and both the physical and chemical conditions. It usually refers to one species but the habitat of one organism, a whole population or a whole community.

Question 2

Biotic and abiotic factors

Answer 2

The environment of an organism is everything that is around it. This includes other living organisms and non-living materials such as air, water and rock. Living things are referred to as biotic factors and non-living things are referred to as abiotic factors. Biotic factors dominate in ecosystems where there are dense communities of organisms. All organisms are adapted to their abiotic environment

Question 3

what are the challenges facing plants in sand dunes

Answer 3

Sand dunes are accumulations of wind-blown sand at the top of beaches. Sand on beach dunes may contain high salt concentrations, hindering water uptake by osmosis. These are the challenges for plants on beach dunes:

• tolerance of sand accumulation
• tolerance of high salt concentrations
• water conservation

Question 4

Adaptations of grasses in sand dunes (Lyme grass)

Answer 4

Special adaptations are required to meet these challenges. Grasses are the dominant plant in this habitat in many parts of the world. Lyme grass occurs where sand is accumulating at the seaward edge of the dunes in North America. It has rhizomes (underground stems) that grow upwards as sand accumulates and extend deep into the dune to obtain water, and provide extra stability. They also have:

• A thick waxy cuticle to reduce transpiration
• Fructans (a carbohydrate) which accumulates in leaf root cells, which increases osmotic potential and thus water uptake
• Stomata at the base of hairy furrows humid air is trapped, even in windy conditions (reduces water loss by transpiration)
• During droughts tough sclerenchyma tissue near one leaf surface prevents wilting and causes the leaf to roll up, creating a humid chamber which is less exposed to wind (also reduces transpiration)

Question 5

Challenges of mangrove trees

Answer 5

Mangrove swamps develop on the coast in the tropics and subtropics where there are sheltered conditions and mud accumulates. These swamps are flooded with seawater at high tide. The dominant species are trees.

These are the environmental challenges of mangrove swamps:

• Waterlogged anaerobic soils which make it difficult for tree roots to obtain the oxygen they need for cell respiration
• High salt concentrations which tend to draw water out of cells by osmosis to prevent water uptake. The salt concentration of the mud can be twice as high as that of seawater. This is due to the daily flooding with seawater and evaporation concentrating the salt in the mud.

Question 6

Adaptations of mangrove trees

Answer 6

The main adaptations are:

• Large buoyant seeds produced by trees which drop into the water and are dispersed by ocean currents
• Salt glands on the leaves which secrete excess salt
• Stilt roots which grow out in a downward arch from the central trunk to buttress the tree in the soft mud
• Cable roots which grow close to the soil surface where there is most oxygen
• Pneumatophores, vertical root branches that grow up into the air and can absorb oxygen for roots to use in the anaerobic soil.
• Root epidermis which is coated in suberin (cork) which reduces permeability to salt so prevents excessive uptake
• Root and leaf cells which contain mineral ions and carbon compounds such as mannitol, which increase osmotic potential, enabling water absorption from the very saline environment.

Question 7

what is species distribution?

Answer 7

The distribution of a species is where it lives in the world. Distribution is limited by abiotic factors. The adaptations of plants and animals suit them for living in some physical environments but not others.

Question 8

what are the abiotic factors affecting plant and animal distribution?

Answer 8

Plant distribution:

• temperature
• water availability
• light intensity
• soil pH
• soil salinity
• availability of mineral nutrients

Animal distribution:

• water availability
• temperature

The adaptations of species give it ranges of tolerance

Question 9

Formation of coral reef

Answer 9

Coral reefs are biodiverse ecosystems that can only develop where conditions are suitable for hard corals, as their skeletons form the rocky structure of the reef. Hard corals contain mutualistic zooxanthellae which need light for photosynthesis.

Question 10

coral reef ecosystem

Answer 10

• Depth- water less than 50m, so enough light penetrates
• pH- above 7.8 so CaCO3 can be deposited in the skeleton
• Salinity- between 32 and 42 parts per thousand of dissolved ions to avoid osmotic problems
• Clarity- turbidity would prevent penetration of light so the water must be clear
• Temperature- 23-29 degrees Celsius so both the coral and zooxanthellae remain healthy

Question 11

Terrestrial biome distribution

Answer 11

• With any combination of abiotic factors, one particular type of ecosystem is likely to develop
• For example, taiga (boreal forest) develops in subarctic regions, with spruces and other conifers as the dominant trees
• Species composition will vary depending on the geographical location, but the adaptations of the species are likely to be similar
• All ecosystems of a specific type are a biome
• Temperature and rainfall are the principal determinants of biome distribution on earth
• The most likely ecosystem with any particular combination of these factors can be shown using a graph

Question 12

what are biomes?

Answer 12

Biomes are groups of ecosystems that resemble each other, even though they may be widely separated worldwide. The resemblance is due to similar abiotic conditions, with organisms evolving similar adaptations.

Question 13

Climatic conditions in major biomes (temperate forest, grassland, taiga, tundra):

Answer 13

Temperate forest: temperatures moderate with summers warm and winters cold, rainfall medium to high, moderate light intensity

Grassland: temperatures medium to high in summer but may be cold in winter, rainfall moderate with a dry season, light intensity medium/high

Taiga (boreal forest): temperatures low with short summers, precipitation medium to high, light intensity low to medium

Tundra: temperatures very low with very short summer, precipitation low to medium (mostly as snow), low light intensity

Question 14

Climatic conditions of hot deserts

Answer 14

Very high daytime temperatures and much colder nights. There is little rainfall and long droughts. Soil development is minimal, with little soil organic matter. The saguaro cactus and fennec fox are adapted to these conditions.

Question 15

Adaptations of saguaro cactus (inhabitant of hot desert environment)

Answer 15

• wide-spreading roots to collect water from a wide range
• tap roots to collect water from deep in the subsoil
• wide stems with water storage tissue
• pleated stems that shrink in droughts and swell after rain
• vertical stems to avoid overheating by hot midday sun
• thick waxy cuticle on stem epidermis- less transpiration
• leaves. reduced to spines- less surface area so less transpiration
• CAM metabolism so stomata open only at night and close during the heat of the day, reducing transpiration

Question 16

Adaptations of Fennec fox (inhabitant of hot desert environment)

Answer 16

• nocturnal so it avoids daytime temperatures
• builds underground den where it stays cool in the day
• long thick hair, heat insulation in cold nights and hot days
• hair covers the pads of the feet to provide insulation when walking on very hot sand
• pale-coloured coat reflects sunlight (a darker coat would absorb it)
• large ears radiate heat- keeps body temperature down
• ventilation rate rises very high (panting) to cause heat loss by evaporation

Question 17

Conditions of tropical rainforest envronment

Answer 17

High light intensity, high temperatures, no cold season and much rainfall. Soils tend to be thin and nutrient-poor due to leaching. Yellow meranti and the spider monkey are adapted to these

Question 18

Yellow meranti adaptations (TRF inhabitant)

Answer 18

• grows over 100m tall to avoid competition for light
• trunk of hard dense wood to provide support against wind stress
• trunk buttressed at base to provide support in shallow soil
• smooth trunk to shed rainwater rapidly
• oval leaves with pointed tips to shed rainwater rapidly
• evergreen leaves to carry out photosynthesis all year
• leaf enzymes work in temperatures as high as 35 degrees celsius
• flowers and seeds produced in large quantities only about one year in five, to deter animals that eat the seeds.

Question 19

Spider monkey adaptations (TRF inhabitant)

Answer 19

• long arms and legs for climbing and reaching for fruit
• flexible shoulders allowing swinging from tree to tree
• large hook-like thumbless hands to grasp branches and lianas (woody vines) and pick fruit
• feet can grasp branches so arms can be used for feeding
• long tail to grip branches
• highly developed larynx for communication in the dense rainforest canopy
• only awake in the daytime- vision is better so movement between branches is safer
• breeding in any season, as food always available

Question 20

What are ecological niches?

Answer 20

The position of a species within an ecosystem
A key concept in ecology is that each species in an ecosystem fulfils a unique roll, called its ecological niche. Niches have both biotic and abiotic elements.

• Zones of tolerance for abiotic variables determine the habitat of a species- where it lives in the ecosystem
• Food supply is a biotic element and an be autotropic (synthesis using an energy source, water and carbon dioxide), or heterotrophic (taking food from other organisms). To minimise competition, species become specialists in sourcing food. To compete effectively with any specialised mode of nutrition, adaptations are required.
• Other biotic elements of ecological niches are utilization of other species to provide a diverse range of services, such as pollination of flowers or nesting sites in tree holes.

The ecological niche of a species is made up of many factors- it is multidimensional. Unless all the dimensions of the niche are satisfied in an ecosystem, a species will not be able to survive, grow or reproduce.

Question 21

what are requirements for obligate aerobes?

Answer 21

Oxygen must be continually available for aerobic respiration

Question 22

what are requirements for obligate anaerobes?

Answer 22

Conditions must be anoxic as oxygen kills or inhibits the organism

Question 23

what are requirements for facultative anaerobes

Answer 23

Oxygen is used if available but anoxic conditions are tolerated

Question 24

what are examples of obligate aerobes?

Answer 24

• all plants and animals
• micrococcus luteus

Question 25

what are examples of obligate anaerobes?

Answer 25

• clostridium tetani
• methanogenic archaea

Question 26

what are examples of facultative anaerobes?

Answer 26

• E-coli
• Saccharomyces

Question 27

what is photosynthesis?

Answer 27

In photosynthesis energy from sunlight is used for fixing carbon dioxide and making the carbon compounds such as sugars and amino acids on which life is based.

Question 28

which organisms photosynthesise?

Answer 28

• plants- mosses, ferns, conifers and flowering plants
• eukaryotic algae- including seaweeds that grow on rocky shores and unicellular algae such as chlorella
• cyanobacteria- (blue-green bacteria) and several other groups of bacteria, but many aren’t photosynthetic

Question 29

which domains of life does photosynthesis occur in?

Answer 29

Photosynthesis occurs in two of three domains of life (eukaryotes and bacteria). It does not occur in the other domain (archaea)

Question 30

what is Holozoic nutrition?

Answer 30

Animals obtain supplies of carbohydrates, amino acids and other carbon compounds by consuming food. They are heterotrophic because the carbon compounds come from other organisms. Molecules such as polysaccharides and proteins must be digested before they can be absorbed. Digestion in most animals happens internally , after the food has been ingested. This is holozoic nutrition- whole pieces of food are swallowed and then fully digested.

Question 31

what are the stages of holozoic nutrition?

Answer 31

• ingestion- taking the 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; this makes them part of the body’s tissues
• egestion- voiding undigested material from the end of the gut

Question 32

why arent spiders holozoic?

Answer 32

Some animals digest their food externally and so aren’t holozoic. Spiders for example inject digestive enzymes into their prey and suck out the liquids produced. They absorb the products of digestion in their gut and assimilate them

Question 33

what is mixtrophic nutrition?

Answer 33

Some protists (unicellular eukaryotes) can obtain carbon compounds from other organisms or can make them themselves. Organisms that aren’t exclusively autotrophic or heterotrophic are mixotrophic.

Question 34

what are facultative mixotrophs?

Answer 34

Facultative mixotrophs can be entirely autotrophic, or use both modes. Euglena gracilis, for example has chloroplasts and carries out photosynthesis when there is sufficient light, but it can also feed on detritus or smaller organisms by endocytosis.

Question 35

what are obligate mixotrophs?

Answer 35

Obligate mixotrophs cannot grow unless they utilise both autotrophic and heterotrophic modes of nutrition. This may be because the food that they consume supplies them with a carbon compound that they cannot synthesise. In other cases, a protist that does not have its own chloroplasts obtains them by consuming algae. It uses the “klepto-chloroplasts” obtained this way for photosynthesis until they degrade and have to be replaced.

Question 36

what is saprotrophic nutrition?

Answer 36

Saprotrophs feed on dead organic matter, but have cell walls so cannot take it in by endocytosis. Instead, they secrete organic matter around them and digest it externally. They secrete proteases to digest proteins into amino acids and other enzymes depending on the composition of the dead organic matter , for example cellulase to digest cellulose into glucose.

If the small soluble products of digestion diffuse into the saprotrophs plasma membrane, they are absorbed and used. Many types of bacteria and fungi are saprotrophic.

Question 37

what are Archaea?

Answer 37

There are three domains of life: archaea, bacteria and eukaryotes. The archaea are unicellular and have no nucleus, which is a similarity with bacteria. In other respects, archaea are closer to eukaryotes. Some types of archaea are adapted to extreme environments such as hot springs, salt lakes and soda lakes. Many are are difficult to culture in the laboratory, so they are less well researched than the other domains of life. Archaea are extremely diverse in their sources of energy for ATP production and carbon.
3 main types of archaea; photoheterotrophs, chemoheterotrophs and chemoautotrophs

Question 38

how do Chemoheterotrophs gain energy for ATP production?

Answer 38

Oxidation of carbon compounds obtained from other organisms

Question 39

how do Chemoheterotrophs gain carbon compounds?

Answer 39

Obtained from other organisms- not photosynthesis

Question 40

how do photoheterotrophs gain energy for ATP production?

Answer 40

Absorption of light using pigments (not chlorophyll in archaea)

Question 41

how do photoheterotrophs gain carbon compounds?

Answer 41

Obtained from using sunlight in photosynthetic reactions

Question 42

how do chemoautotrophs gain energy for ATP production?

Answer 42

Oxidation of inorganic chemicals e.g. Fe2+ ions oxidised to Fe3+ ions

Question 43

how do chemoautotrophs gain carbon compounds?

Answer 43

Synthesised from carbon dioxide by anabolic reactions

Question 44

Dentition and diet in the family Hominidae

Answer 44

The family Hominidae includes the genera that contain humans (Homo), orang-utans (Pongo), gorillas (Gorrila), and chimpanzees (Pan). Some members of the Hominidae have an exclusively herbivorous diet and others are omnivores as animal prey are sometimes eaten to supplement their plant-based diet.

Living members of the Hominidae show a relationship between diet and dentition. The teeth of herbivores tend to be large and flat to grind down fibrous plant tissues. Omnivores tend to have a mix of different types of teeth to break down both meat and plants in their diet. Humans have flat molars in the back of their mouth to crush and grind food, and sharper canines and incisors than herbivores to tear tougher food, like meat.

Question 45

what are herbivores?

Answer 45

Animals that feed only on plants are herbivores. They have structural features that adapt them to their diet. Insect mouthparts show great diversity but are all homologous-they have been derived by evolution from the same ancestral mouthparts.

Question 46

what are examples of herbivores?

Answer 46

• beetles and other insects that feed on leaves have jaw-like mouthparts with tough mandibles for biting off, chewing, and ingesting leaves
• aphids and other insects that feed on phloem sap have sharp, tubular mouthparts for piercing leaves or stems to reach phloem sieve tubes
• butterflies and other insects that feed on nectar have tubular mouthparts long enough to reach the nectary in flowers

Question 47

what are adaptations of plants for deterring herbivore attacks

Answer 47

• sharp spines
• stings to cause pains
• synthesis and storage of secondary metabolites that are toxic to herbivores. They may be stored in any part of a plant, particularly seeds, which are attractive to herbivores because of their high concentrations of protein and starch or oil. Primarily metabolites are substances that are part of the basic metabolic pathways of a cell.

(In some cases, herbivores have responded to toxic compounds in plants by developing metabolic adaptations for detoxifying them. This has resulted in plant-herbivore specificity, with only a few species of herbivore adapted to feed on a particular plant.)

Question 48

Structural adaptations of predators (vampire bats)

Answer 48

large pointed upper front teeth in vampire bats for piercing prey to suck blood

Question 49

Structural adaptations of Prey
(molluscs)

Answer 49

shells of limpets on rocky shores to protect soft parts of the molluscs body

Question 50

Chemical adaptations of predators
(black mambas)

Answer 50

Venom containing toxins produced by black mambas to paralyse and kill prey

Question 51

Chemical adaptations of prey
(moth larvae)

Answer 51

In cinnabar moth larvae toxins are accumulated from ragwart plants eaten

Question 52

Behavioural adaptations of predators
(anglerfish)

Answer 52

Waving of a modified luminescent fin ray in anglerfish to lure prey

Question 53

Behavioural adaptations of prey
(blue striped snappers (fish))

Answer 53

Swimming in tight groups (schooling) in blue-striped snappers and other fish

Question 54

adaptations of plants for harvesting light

Answer 54

In ecosystems where light intensity is the limiting factor for photosynthesis, especially forests, plants compete for light. Plants use a variety of strategies in forests for obtaining light, so they show great diversity of form.

• Trees have dominant leading shoot, allowing rapid growth in height up to the forest canopy so other trees do not cast shade
• Lianas climb other trees using them for support, so they need less xylem tissue (wood) than free-standing trees
• Epiphytes grow on the trunks and branches of trees so they receive higher light intensity than if they grew on the forest floor, but there is minimal soil for their roots
• Strangler epiphytes climb up the trunks of trees, encircle them and outgrow the trees branches shading out its leaves. Eventually the tree dies leaving only the epiphyte.
• Shade-tolerant shrubs and herbs absorb the small amounts of light that reach the forest floor

Question 55

what are fundamental realised niches

Answer 55

The range of conditions that an organism can survive and reproduce itself (range of tolerance)
Each species tolerates a range of abiotic conditions and their adaptations do not allow them to survive outside this range. There are also biotic factors that a species needs. The fundamental niche of a species is the range of abiotic conditions tolerated together with the requirements for biotic factors. If a species was living without any competitors, it would occupy the entire fundamental niche.

In natural ecosystems, there is competition and typically a species is excluded from parts of its fundamental niche by competitors. The actual extent of the potential range that a species occupies its realised niche.

Question 56

what is competitive exclusion?

Answer 56

Where the fundamental niches of two species overlap, one species is expected to exclude the other from that part of its range by competition. This was demonstrated experimentally with the flour beetles Tribolium castaneum and Tribolium confusum. These species both thrived when put individually into flour at varying combinations of temperature and humidity. However, when they were both introduced to the flour, T. castaneum was excluded by T. confusum in some combinations of temperature and humidity, but T. confusum was excluded by T. castaneum in other combinations. So they had different realised niches.

If two species in an ecosystem have overlapping fundamental niches and one species outcompetes the other in all parts of the fundamental niche, the outcompeted species does not have a realised niche and will be competitively excluded from the whole ecosystem. According to ecological theory, every species must have a realised niche that differs from the realised niches of all other species if it is to survive in an ecosystem.

Question 57

what are open systems?

Answer 57

open systems where resources can enter or exit, including both chemical substances and energy

Question 58

what are closed systems?

Answer 58

closed systems where energy can enter or exit, but chemical resources cannot be removed or replaced.

Question 59

how does sunlight sustain most ecosystems?

Answer 59

Organisms that use an external source of energy to make carbon compounds are producers. Energy fixed by producers in carbon compounds is available to other organisms, so sustains the whole ecosystem.

The principle source of energy in most ecosystems is sunlight and the process used by producers to make carbon compounds is photosynthesis.

There are ecosystems where little or no light penetrates, e.g. caves and oceans at depths greater than 200m. Some energy may pass to these ecosystems in dead organic matter transferred from other ecosystems, which can be digested by sapotrophs. Another source of energy is inorganic chemical reactions, which chemoautotrophs us. In sealed caves, this is the only energy source for an ecosystem.

Question 60

how does chemical energy flow through food chains?

Answer 60

A food chain is a sequence of organisms, each of which feeds on the previous organism. Producers are the first organisms in a typical food chain because they do not feed on another organism. Producers are the first organisms in a typical food chain because they do not need to feed on another organism; they use an external energy source instead to make all the carbon compounds they require from simple inorganic substances such as CO₂. The other organisms in a food chain are consumers. They obtain chemical energy from carbon compounds in the organisms on which they feed. Primary consumers feed on producers; secondary consumers feed on primary consumers; tertiary consumers feed on secondary consumers, and so on. The last organism in a food chain is not fed on. Chemical energy thus flows along a food chain from organism to organism.

In any ecosystem, there are many specific food chains that provide organisms with a supply of energy. For example, in the Monte Desert (in South America), leaves of a shrub with the local name of tara (Senna arnottiana) are eaten by guanaco (Lama guanicoe). Pumas (Puma concolor) are predators of the guanaco. They are regarded as apex predators because nothing kills or eats them, though fleas and other parasites can obtain energy from them by feeding on their blood.

Question 61

what are food chains and webs?

Answer 61

Feeding relationships within ecological communities tend to be complex and web-like. This is because many consumers feed on more than one species and are fed upon by more than one species. A food web is a model that summarizes all of the possible food chains in a energy and biomass.
community. Arrows indicate the direction of transfer of When a food web is constructed, organisms at the same trophic level are often shown at the same level in the web. However, this is not always possible because some organisms feed at more than one trophic level.

Question 62

what are decomposers?

Answer 62

Dead organic matter is generated by these processes

• death of whole organisms
• defecation (removal of faeces from the gut)
• shedding of (leaves, skin cells, hairs, arthropod exoskeletons and other unwanted body parts)

Dead organic matter contains chemical energy in carbon compounds.

Some dead organic matter is eaten by animals such as earthworms and vultures, but large amounts are digested by saprotrophs. Dead organic matter supplies sapotrophs with amino acids, glucose and other carbon compounds, which are used for growth and also as a source of energy, which is released by cell respiration.

Saprotrophic bacteria and fungi are decomposers because they break down insoluble macromolecules in dead organic matter into small, soluble molecules and ions. By doing this, they cause the gradual breakdown of solid structures. For example, a tree trunk on the forest floor will gradually soften and crumble away and fallen leaves dissapear.

Without extracellular digestion carried out by decomposers, dead organic matter would build up year by year. Also ions such as ammonium would not be released into the abiotic environment, so other organisms that absorb them would lose their supply. Decomposers are the waste disposers and recyclers of ecosystems.

Question 63

what are autotrophs?

Answer 63

All organisms need a variety of carbon compounds
Some organisms make all of these carbon compounds themselves, using carbon dioxide (CO₂) or hydrogen carbonate (HCO₃-) as a carbon source. Organisms that do this are called autotrophs, meaning self-feeding.
A reduction reaction inside autotrophic cells converts the simple inorganic carbon sources into an initial carbon compound. This process is carbon fixation. The initial carbon compound produced by carbon fixation is then built up into a wide variety of other carbon compounds by anabolic reactions

Carbon fixation and anabolic reactions in autotrophs require an external energy source. The two possible sources of external energy are inorganic chemical reactions and light.

Question 64

what are photoautotrophs and chemoautotrophs?

Answer 64

Photoautotrophs use sunlight to make carbon compounds by photosynthesis. Chemoautotrophs use exothermic inorganic chemical reactions. A substrate in a reduced state, such as sulfur, hydrogen sulfide, iron, hydrogen or ammonia, is absorbed and then oxidised. Oxidation reactions release energy. Chemoautotrophs use energy from the oxidation reaction to synthesize carbon compounds such as sugars and amino acids. Two of the three domains of life contain chemoautotrophs: bacteria and archea. Iron oxidising bacteria are an example, such as Acidithiobacillus ferroxodians.

Iron oxidising bacteria absorb Fe2+ ions from the environment and remove an electron from them. Because this is an oxidation reaction, the energy is excited.

Fe2+ → Fe3+ + extra electron (excited)

The excited electrons are accepted by chains of electron carriers in the plasma membrane of the iron-oxidising bacterium. Energy is released as the electrons flow along these chains. Some electrons flow to proton pumps and their energy is used to build a proton gradient that is then used for ATP production by chemiosmosis. Other excited electrons are passed to NAD, converting it to reduced NAD (NADH).

NADH and ATP can be used to fix carbon dioxide and produce carbon compounds by reactions similar to those of photosynthesis.

Question 65

what are heterotrophs?

Answer 65

Many organisms obtain carbon compounds from other organisms. These organisms are heterotrophic, which means they feed on others. They digest carbon compounds that were part of another organism and then use the products of digestion to build the large complex carbon compound they need. For example, guanacos digest proteins in the leaves of tara bushes, breaking them down into amino acids. Then they use these amino acids to synthesise the proteins they need. The process of absorbing carbon compounds and making them part of the body is called assimilation. Assimilation requires absorption of carbon compounds into cells, so the molecules must be small and soluble enough to pass across cell membranes. Proteins, polysaccharides, nucleic acids and other large compounds must be digested before they can be absorbed.

Heterotrophs are sub-divided according to whether they digest food internally or externally.
- Saprotrophs grow into or across the surface of food and secrete hydrolytic enzymes to digest the food externally.
- Consumers ingest their food.
- Multicellular consumers take food into their gut by swallowing it. Then they mix the food with enzymes from digestive glands. This is regarded as internal digestion although the food has not yet entered any cells.
- Unicellular consumers such as Paramecium take the food into their cells by endocytosis, then digest it inside phagocytic vacuoles into their cytoplasm

Question 66

Release of energy by cell respiration

Answer 66

All organisms require supplies of energy in the form of ATP in their cells. They use the energy for the following four processes.

• anabolic reactions to synthesise molecules such as proteins, polysaccharides, triglycerides, and nucleic acids
• active transport to generate concentration gradients
• movement of vesicles and other structures inside cells; movement of whole organisms and of blood and other fluids in organisms due to muscle contraction
• maintaining constant body temperature (birds and mammals)

In both autotrophs and heterotrophs, ATP is produced by cell respiration. Carbon compounds such as carbohydrates and lipids are oxidised to release energy and this energy is used to phosphorylate ADP, producing ATP.

Question 67

what is the energy transfer between trophic levels

Answer 67

In any ecosystem, there are large energy losses between trophic levels. These losses vary and are not always 90%. There are three main forms of energy loss from food chains.

Question 68

incomplete consumption as a reason for inefficient trophic level transfer

Answer 68

Some organisms are never consumed and instead they eventually die. Energy in dead organisms, or dead parts of organisms, passes to saprotrophs or detritus feeders, which aren’t part of food chains.

Question 69

incomplete digestion as a reason for inefficient trophic level transfer

Answer 69

Not all substances in food are digested. For example, some animals cannot digest cellulose. Indigestible material is egested in faeces and the energy passes to saprotrophs.

Question 70

cell respiration as a reason for inefficient trophic level transfer

Answer 70

Substrates are oxidised to carbon dioxide and water to release energy from them, which is used by the respiring organism. Carbon compounds that have been oxidised in respiration cannot pass to the next trophic level and the energy that they contained is lost from the food chain.

Biomass is also lost between trophic levels so organisms in higher trophic levels do not need to eat a greater mass of food to gain enough energy

Question 71

heat lost to the environment as a reason for inefficient trophic level transfer

Answer 71

Energy transfers are never 100% efficient, so when energy is released by oxidising substrates in cell respiration, some of the energy is converted to heat. When the ATP is used within cells, more energy is converted to heat. Both autotrophs and heterotrophs generate heat this way. Ultimately all of the energy that enters food chains is transformed into heat and lost to the abiotic environment. For this reason, energy flows through food chains and cannot be recycled (unlike chemical elements).

Question 72

why are food chains limited in length

Answer 72

Food chains are limited in length because so much energy is lost between each trophic level and the next. After only a few stages, not enough energy remains to support another trophic level. For this reason the number of trophic levels in an ecosystem is restricted to a maximum of four or five.

Animals in higher trophic levels do not have to eat more food to gain enough energy. Their prey contains large amounts of energy per unit mass- there just is not much prey available. A condor for example is mainly a tertiary consumer and may need a territory of more than 10000km^2 to find enough to eat.

Question 73

Primary production

Answer 73

Production in ecosystems is the accumulation of carbon compounds in biomass. Both autotrophs and heterotrophs produce biomass by growth and reproduction.

• primary production is mass of carbon compounds synthesized by CO2 and other simple substances by autotrophs (producers). The units of measurement are usually grams of carbon accumulated per square metre of ecosystem per year.
• Gross primary production is the total biomass of carbon compounds made by plants
• Net primary production is GPP minus the biomass lost due to respiration of the plant. It is the amount of biomass available to consumers

Question 74

Secondary production

Answer 74

Animals and other heterotrophs obtain carbon compounds such as sugars and amino acids from organisms in a lower trophic level and use them in growth and reproduction. This results in an increase in biomass.

Secondary production is accumulation of carbon compounds in biomass by consumers

Carbon compounds are used as respiratory substrates by all organisms. Cell respiration results in a loss of carbon compounds and therefore biomass in every trophic level.

These are the consequences for ecosystems:

• secondary production is lower than primary production
• net secondary production is lower than gross secondary production in every trophic level of consumers
• secondary production declines with each successive trophic level from primary consumers onwards

Question 75

The carbon cycle

Answer 75

• Photosynthesis- absorption of CO2 from air or water and its conversion to carbon compounds
• Feeding- gaining carbon compounds from other organisms
• Respiration- release to the atmosphere of CO2 produced by respiring cells

In marine and aquatic ecosystems, the inorganic pool of carbon is dissolved CO2, and also hydrogen carbonate ions (HCO-) both of which can be absorbed by producers and used in photosynthesis.

Question 75

Carbon sinks and carbon sources

Answer 75

Ecosystems are open systems because both matter and energy can enter and exit.

Carbon enters and exits in the form of carbon dioxide, through photosynthesis and respiration.

The rates of these processes for an ecosystem as a whole are not always equal.

If photosynthesis exceeds respiration, there is net uptake of carbon. The ecosystem is acting as a carbon sink. This happens in growing forests and also in waterlogged habitats (bogs or swamps) where anaerobic respiration and acidic conditions prevent decomposition of dead organic matter by saprotrophs, so peat containing carbon accumulates

If respiration exceeds photosynthesis, there is a net release. The ecosystem is acting as a carbon source. This happens if peatlands are drained and the peat decomposes. Fires in forests and other ecosystems cause release of CO2 by combustion of carbon compounds in living organisms and dead organic matter. The ecosystem therefore becomes a carbon source

Question 76

Release of carbon dioxide from comubstion

Answer 76

Ecosystems can act as carbon sinks by accumulating biomass. Forests can store over 5,000 tonnes of biomass per hectare. Carbon atoms may remain sequestered in the wood of trees. Peat formed in wetland ecosystems can store carbon for thousands of years. Dead organic matter has been converted to coal, oil and natural gas at different times in the Earth’s history and the carbon in these sinks can remain sequestered for many millions of years.

When carbon compounds burn in air, carbon dioxide is produced and released into the atmosphere. Fires are natural and frequent in some ecosystems, ignited by lightning strikes.

In recent years, there have been increasingly frequent fires in areas of tundra located inside the arctic circle, combustion of peat, accumulated over thousands of years, has released large quantities of carbon dioxide. Most coal, oil and natural gas is deeply buried and so cannot burn due to a lack of oxygen. Humans have developed methods of extracting these materials and burning them as an energy source. Since the start of the Industrial revolution, the rate of extraction and combustion of fossil fuels has risen rapidly and huge quantities of carbon dioxide have been released into the atmosphere.

Question 77

The keeling curve

Answer 77

Since 1959, atmospheric carbon dioxide concentrations have been measured at Mauna Loa Observatory in Hawaii. Graphs of the results (Keeling Curve) show two trends:

1. Annual fluctuations

Carbon dioxide concentration increases between October and May and then falls from May to October, due to global imbalances in rates of carbon dioxide fixation by photosynthesis and release due to respiration. There is relatively more photosynthesis during summer in the northern hemisphere, when plants over most of the Earth’s land surface are in their growth season, and relatively more respiration during the northern hemisphere winter.

2. Long-term trend

The graph of carbon dioxide concentrations for one year shows that the increase is not completely reversed by the decrease, so the concentration at the end of the year is higher than it was at the start. This is also shown by the full Keeling curve, from 1959 onwards. This trend is largely due to burning of fossil fuels by humans, together with other anthropogenic factors such as deforestation.

Question 78

what is the greenhouse effect?

Answer 78

The “greenhouse effect” keeps the earth much warmer than it would otherwise be. Greenhouse gases absorb long-wave thermal radiation. Without any greenhouse gases in the atmosphere, the average temperature on Earth would be below zero degrees celsius. The higher the concentrations of greenhouse gases, the warmer the Earth becomes.

Question 79

Recycling in ecosystems

Answer 79

Living organisms contain large amounts of C, H, O, N and P in their molecules. About 15 other elements have roles in living organisms. The quantities of each element are finite on Earth, but despite living organisms using them for three billion years, no element has run out. This is because all elements can be endlessly recycled. They are absorbed from the abiotic environment as inorganic ions or molecules, used within living organisms and then returned to the abiotic environment with the atomic structure unchanged. Autotrophs obtain all elements they need as inorganic nutrients from the abiotic environment, including C and N. Heterotrophs obtain these two elements and several others as part of the carbon compounds in their food. They obtain some other elements as inorganic nutrients from the abiotic environment, including Na+, K+ and Ca2+. Decomposers play a key role in recycling because as a consequence of their saprotrophic nutrition they digest carbon compounds and return elements from them to the abiotic environment. All elements needed by plants are in the first four periods of the periodic table.

Question 80

How does global warming occur?

Answer 80

1. short-wave radiation is emitted by the Sun
2. short-wave radiation can pass through the atmosphere
3. the earths surface is warmed by absorbing sunlight
4. long-wave radiation is emitted by the warmed earth
5. greenhouse gases absorb long-wave radiation emitted by the Earth, making the atmosphere warmer

Question 81

what are the two most significant greenhouse gases?

Answer 81

Methane and carbon dioxide are the most significant greenhouse gases. Humans are increasing the amounts of both that are released into the atmosphere, resulting in anthropogenic climate change.

Carbon dioxide is released by respiration and removed by photosynthesis. These natural processes would normally be in balance, but humans area causing the carbon dioxide concentration to increase

Methane is naturally emitted by methanogenic organisms in marshes and other waterlogged habitats. It is gradually oxidised in the atmosphere so the atmospheric concentration would naturally remain stable.

Question 82

what are the anthropogenic emissions of carbon dioxide?

Answer 82

• combustion of fossil fuels
• burning or decomposition of biomass during deforestation
• increases in frequency and severity of forest fires
• drainage and decomposition or burning of peat

Question 83

what are the anthropogenic sources of methane?

Answer 83

• anaerobic decomposition of organic matter in landfill sites
• leaks during fossil fuel extraction and processing
• digestive systems of ruminants (cattle and sheep)
• bubbles of methane released from melting permafrost

Question 84

how does climate change occur as a result of global warming?

Answer 84

• changes in prevailing wind direction
• increased cloud cover
• increased rainfall overall, but some areas are drier with longer and more severe droughts
• increased average wind speeds with more frequent and intense cyclones, hurricanes and typhoons

Question 85

what are the cycles of positive feedback in global warming?

Answer 85

Positive feedback is the amplification of a process by its end product. Global warming is amplified by positive feedback cycles, because an increase in the earths temperature causes increases in factors that cause warming.

Proportion of sunlight that is reflected (albedo)

• snow and ice are white so they reflect solar radiation back out into space. With global warming, snow and ice are melting and are being replaced by open ocean, rock, or vegetation, all of which are darker in colour so they tend to absorb solar radiation rather than reflect it, causing further warming.

Atmospheric CO2 concentration

• Decomposition of peat and other dead organic matter by saprotrophs speeds up as temperature rises. Cell respiration in saprotrophs releases carbon dioxide
• Global warming causes the temperature of the oceans to rise, which reduces the solubility of carbon dioxide in the water. Carbon dioxide is therefore released from deep in the oceans into the atmosphere. This carbon dioxide then contributes to the greenhouse effect, whereas dissolved carbon dioxide in the oceans does not.
• Increased temperatures lead to drier, more fire prone conditions, so forest fires are more frequent and severe. Carbon dioxide emissions from combustion are increased. Also there is less absorption of carbon dioxide by photosynthesis in the ecosystems that replace forest

Atmospheric methane concentration

• Permafrost is soil that remains frozen throughout the year. Any dead organic matter in permafrost (such as peat) remains undecomposed because saprotrophic bacteria and fungi are inactive. When global warming causes melting, frozen soils become waterlogged and anaerobic. This encourages methanogenic microbes to break down dead organic matter and release methane into the atmosphere.

Question 86

what are the effects of climate change on boreal forests?

Answer 86

Boreal forest (also known as taiga) covers huge areas of the northern hemisphere, with tundra further north and temperate forests to the south.

Ecosystems can be carbon sources or sinks. Boreal forests are typically sinks because carbon is stored in the biomass of conifer trees and because dead wood, leaf litter and peat accumulate. It is in the cold conditions that it is digested by saprotrophs more slowly than it is produced. With climate change, summers in the boreal forest have become warmer and drier, resulting in widespread fires and huge carbon emissions of CO2 from combustion of the legacy carbon.

As global temperatures continue to rise, a tipping point could be reached beyond which boreal forests as a whole change from being carbon sinks to carbon sources. Instead of helping to keep the earth cooler by removing carbon dioxide from the atmosphere, they would contribute to warming by releasing it instead and further hastening the loss of this biome.

Question 87

what are the effects of the changes in ocean currents?

Answer 87

The ocean is stratified. Warmer, less salty water is less dense and floats on top of denser, colder, saltier water. There is some mixing of the upper and lower layers, but transfers of heat and chemicals are restricted by the stratification.

Atmospheric warming increases ocean stratification. This happens because the upper warmer water becomes less dense as it is heated and less saline as freshwater from melting ice flows into the ocean. As a result, there is less mixing.

Rotation of the earth and prevailing winds cause currents that bring the colder, deeper water towards the coast in some parts of the oceans. This water is forced up to the surface, displacing warmer water. It causes an upwelling of mineral nutrients, increasing the growth of producers and therefore availability of food for consumers. Areas where upwelling occurs have very productive biological communities. If surface water becomes warmer, there tends to be less upwelling, reducing availability of mineral nutrients and therefore productivity. Areas of upwelling cover about 1% of the ocean surface but provide about 50% of the fish harvested for human consumption.

Question 88

what are the effects of global warming on polar ecosystems?

Answer 88

Ice floats on the surface of seawater, so it forms a solid surface. Sea ice moves, due to the wind and ocean currents, whereas landfast ice remains attached to a shore. The extent of landfast and sea ice is reducing due to global warming, with consequences for animals that use it as a habitat in both the Arctic and and Antarctic.

Walruses use sea ice to rest between feeding sessions, shelter from rough seas and evade predators. They also use sea ice for breeding, giving birth and nursing their young. They can also use areas of coastal land for these purposes but they are limited in area and females prefer sea ice, so as to avoid the risk of their pups being trampled by the larger males. Sea ice also expands access to a broader range of feeding sites. Global warming is reducing sea ice so land-based walruses are having to make more feeding trips from coastal haul-outs to areas of high prey abundance that are far from shore. Walruses lose more heat in the water than when out of the water, so they expend more energy on these trips on thermoregulation.

Emperor penguins breed on landfast ice in the Antarctic. It provides a relatively flat surface and the penguins are too large and unagile to climb over rocks or broken sea ice. To avoid predation, communal breeding sites are chosen at least 5km from the landfast ice edge; however, breeding success drops as distance from the ice edge increases beyond this, due to the difficulty of returning to the open ocean to feed. Climate change is making the extent of landfast ice very variable and unpredictable, making it difficult for emperor penguins to choose where they can successfully breed.

Question 89

how is global warming shifting climate zones?

Answer 89

Continental climates are not influenced much by the oceans and tend to be hot in summer and very cold in winter. Temperate climates have intermediate temperatures throughout the year with nearby oceans making the summers cooler and the winters warmer.

Plants and animal species that are adapted to temperate zones are therefore having to move their ranges towards the poles. Animal species may be able to achieve this by migration. Plant species are sessile, so range changes are due to deaths at the hotter end of the range nearer the equator and colonisation of cooler areas nearer the poles.

On mountains, the climate becomes colder as altitude increases. There is therefore a series of altitudinal climate zones. Species adapted to the temperate zone on a mountain are having to move upslope as global warming shifts the zones upwards.

Question 90

what is an example of poleward range shift?

Answer 90

There is evidence that the ranges of temperate tree species in North america are shifting northwards. A large study of seed productionand seedling survival rates in tree species showed that many species are indeed shifting northwards, with the shift happening faster in western species. Another study suggested that conifers are moving north but trees that are flowering plants are tending to shift westwards.

Question 91

what is an example of upslope range shift

Answer 91

There is evidence that temperate-zone montane bird species in New Guinea are shifting their range upslope. The upper altitude limit of the ranges of 20 species were measured in 1969 and again in 2013. The limit in all but four of the species had shifted upslope by up to 650 metres. In the other four species, the upper limit had not changed or had reduced a little

Question 92

what are the threats to coral reefs?

Answer 92

In addition to its contribution to global warming, emissions of carbon dioxide are affecting the oceans. Over 500 billion tonnes of carbon dioxide released by humans since the start of the industrial revolution have dissolved, reducing the pH of the Earths oceans. In the late 18th century, when there had been a little industrialisation, the average surface pH was 8.18, the average pH is now below 8.06 (this is 30% acidification).

Marine animals that deposit calcium carbonate in their skeletons need to absorb carbonate ions from seawater. The concentration of these ions in seawater is low, because they aren’t very soluble. Dissolved carbon dioxide makes the carbonate concentration even lower as a result of two chemical reactions. Carbon dioxide reacts with water to form carbonic acid, which dissociates into hydrogen and hydrogencarbonate ions. Hydrogen ions react with dissolved carbonate ions, reducing their concentration.

Reduced carbonate ion concentrations make it more difficult for reef-building corals to absorb carbonate and use it to calcify their skeletons. Also, if seawater ceases to be saturated with carbonate ions, calcium carbonate tends to dissolve, so existing skeletons of reef building corals are eroded.

Hard corals live in a mutualistic in a mutualistic association with photosynthetic algae called zooxanthellae. The algae benefit by being kept safe from organisms that would feed on them and close to the ocean surface where they can access the sunlight penetrating the water. The corals get the benefit of carbohydrates and oxygen produced by the algae. When the ocean water surrounding corals becomes too warm, the zooxanthellae are ejected leading to a loss of colour, hence the term “coral bleaching”, which is happening more frequently leading to global warming.

Coral species with calcium carbonate skeletons are collectively the keystones of the reef. Many other species depend on them and their loss due to ocean acidification, and warming would cause the collapse of reef ecosystems globally.

Question 93

what is carbon sequesteration?

Answer 93

Carbon sequestration is capture and storage of carbon dioxide from the atmosphere. Two biological processes sequester carbon

• accumulation of biomass, produced in ecosystems by photosynthesis, especially the long lasting wood of trees
• accumulation of undecomposed or partially decomposed organic matter, especially peat in wetlands

Question 93

how is afforestation a good approach to carbon sequestration?

Answer 93

Afforestation is planting trees in areas where they currently do not exist. This should only be done where forests are the natural ecosystems. There is ample opportunity for afforestation. For example, it is estimated that in the 8,000 years since the end of the last glaciation, the forests that grew in the upper Midwest of the US stored nearly a billion tonnes of carbon. This carbon was released into the atmosphere as forests were cleared, to extract timber and convert land to agriculture, over about 150 years. If such areas were reforested, large amounts of carbon could be sequestered.
There is active scientific debate over whether non-native or native species offer the best approach to carbon sequestration. Native species have evolved to be adapted to the conditions in an area so they should grow rapidly, but climate change may result in non-native species being better adapted than the native species.

Question 94

how is restoration of wetlands a good approach to carbon sequestration?

Answer 94

Restoration of wetlands: Peat is partially decayed organic matter that forms in waterlogged ecosystems in both temperate and boreal zones and also very rapidly in some tropical ecosystems. Peatlands are a huge carbon sink, but in many areas they have been drained to convert the land to plantation, forestry or agriculture. After the soils have dried out, saprotrophs can decompose the peat and may also be lost through the fire. It can be difficult to rewet former peatlands so that carbon sequestration restarts, but it can be done by blocking drains, restoring high water levels and re-establishing native species such as sphagnum moss

Question 95

what is phenology?

Answer 95

Living organisms are adapted to carry out stages of their life cycles at the most appropriate time of year. Photoperiod and temperature are used as cues by living organisms to determine when the appropriate time of year has arrived. There is much variation between species in how these cues are used.

Photoperiod is the length of daylight during a 24-hour period. Each year it follows the same cycle of change with minimum and maximum daylength in the winter and summer solstices. Towards the poles there is greater variation in daylength through the year. Plants can measure the length of the night to an accuracy of five minutes and many species use it to time flowering. In most birds, the timing of migration and egg-laying are determined mainly by daylength.

Temperature follows an annual cycle of warming and cooling in many parts of the world, though there is variation from year to year in how quickly temperatures rise in spring and drop in the autumn. Warm temperatures in spring advance the dates of egg laying in some bird species and bud-burst in many deciduous trees. Warm temperatures in the autumn delay leaf abscission (leaf-drop) in many trees.

Phenology is studying the timing of seasonal events. Data obtained each year for as many years as possible can provide evidence of global warming and other climate changes. For example, the date of opening the first bud on a tree in Geneva has been recorded each year since 1810. It varies considerably from year to year, but there is a clear trend in the date becoming earlier.

Question 96

how does climate change effect the phenology of reindeer?

Answer 96

Rangifer tarandus is native to tundra ecosystems in the Arctic. They are known as caribou in North America and reindeer in Europe. Their spring migration coincides with the emergence and growth of food plants such as the Arctic mouse-ear (Cerastium arcticum). This allows females secreting milk for their calves to obtain enough food. Evidence suggests that climate change has led to a mismatch between plant growth and caribou migration patterns so caribou and reindeer are less able to meet their nutritional needs.

Question 97

how does climate change effect the phenology of parus major?

Answer 97

Parus major (great tit) feeds its young on caterpillars. The dates of egg-laying and peak caterpillar biomass have been studied for over 50 years in a population of Parus major in the Netherlands. Caterpillar biomass now peaks much earlier in spring. The mean date of egg-laying has also become earlier, but not by as much.

Question 98

how is climate change increasing the number of insect life cycles?

Answer 98

Insects vary in how long their life cycle takes. Some species complete several cycles per year. Others take one or more years for a single cycle. In some species the time taken per cycle has become shorter due to global warming. An example is the spruce bark beetle, Dendroctonus rufipennis, which is native to forests in North America. Its larvae feed on the inner bark of older and weaker spruce trees and also deadwood and stumps. It takes between one and three years to complete a life cycle, but warmer temperatures have reduced the average time, increasing the potential population growth rate. The health of older spruce trees has declined due to reduced rainfall and droughts, together with warmer temperatures, so more trees are succumbing to beetle attacks. As a result, there have been major outbreaks in Alaska and other areas of boreal forest with hundreds of millions of spruce trees killed.

Question 99

how is climate change leading to evolution?

Answer 99

Global warming and other climate changes on earth are changing the adaptations that living organisms need to thrive. Many traits are now subject to directional selection. For example Strix aluco (tawny owl) varies in colour, with its feathers ranging from brown to pale grey. This is a heritable trait. A single gene has a dominant allele for brown and a recessive allele for pale grey feathers. The pale grey variant is better-camouflaged against snow. Winters have become milder in Finland, reducing snow cover. Between 1985 and 2010, the percentage of brown owls in the Finnish population of tawny owls more than doubled.

Question 100

What is ecosystem diversity

Answer 100

variety in the combinations of species living together in communities. This diversity is partly due to the very varied environments on Earth and the geographical ranges of organisms

Question 101

What is species diversity

Answer 101

The many different species on the evolutionary tree of life. These species have varied body plans, internal structure, life cycles and modes of nutrition

Question 102

what is genetic diversity

Answer 102

within species- variety in the gene pool of each species. There is variation between geographically separated populations and within populations

Question 103

Overharvesting as a main cause of extinction

Answer 103

Animals/ plants are overharvested to the point it is very unsustainable, and they die off

Question 104

Habitat destruction as a main cause of extinction

Answer 104

• • Natural habitats have been destroyed leading to species extinctions. Agriculture is the main cause, with over 13 billion hectares of land now cultivated or used for rearing livestock. Natural habitats have also been destroyed to build towns and cities

Question 105

invasive (ALIEN) species as a main cause of extinction

Answer 105

when alien species are introduced to ecosystems, they can drive native species to extinction by predation, spreading of pests and diseases or competition for resources. Endemic species become extinct if they hybridise with alien species

Question 106

Pollution as a main cause of extinction

Answer 106

chemical industries produce a vast range of substances that are used and then discarded in the environment. Burning of fossil fuels, agriculture, mining, oil extraction and pharmaceuticals are all major sources of pollutants

Question 107

global climate change as a main cause of extinction

Answer 107

human activities are currently causing very rapid changes in temperature rainfall and other climatic variables. Species that fail to adapt quickly enough or cannot migrate face extinction.

Question 108

what are categories of direct and indirect species loss?

Answer 108

1. Agriculture- the main cause of ecosystem loss. Most temperate forests and grasslands were cleared before the 1970s. Since then, much tropical forest has been lost
2. Urbanisation- building of homes, offices and factories, together with associated infrastructure of roads and railways. This has been inevitable given the rapid and continued rise in the human population;
3. Overexploitation of natural resources- such as gathering of fuel wood, hunting of animals for bushmeat and fishing. Loss of a single keystone species can threaten whole ecosystems
4. Mining and smelting- opencast mines destroy areas of natural ecosystem entirely. Smelting and disposal of waste from mining can cause pollution and more widespread damage. Much tropical rainforest has been lost due to mining
5. Water management- reservoirs created by building dams can flood natural ecosystems. Extraction of water for irrigation and for industrial or domestic use can greatly reduce river flows
6. Drying of wetlands- swamps and other wetlands are drained for conversion to agriculture. Wetlands are also destroyed by diverting the water that flowed into them for human use.
7. Leaching- washing of fertilisers into rivers and lakes causes eutrophication and algal blooms. Oligotrophic ecosystems in which organisms are adapted to low nutrient concentrations have been lost
8. Climate change- anthropogenic climate change is the most common cause of loss.

Question 109

The EDGE of existence programme

Answer 109

The EDGE of existence programme uses two criteria to identify animal species that are most deserving of conservation

• Evolutionary Distinct: does the species have few or no close relatives, so it is a member of a very small clade?
• Globally Endangered: Is the species likely to become extinct because all remaining populations are threatened

Species that fit both criteria (EDGE species) are listed and targeted for intense conservation efforts. Some species are the last members of a clade that has existed for tens or hundreds of millions of years and it would be tragic for them to become extinct as a result of human activities

Question 110

what is a population

Answer 110

A population is a group of individual organisms of the same species living in an area. Members of a population interact in various ways. They normally interbreed with each other and interbreeed less often or not at all with individuals in other populations. There are usually many non-breeding interactions between individuals in a population, such as competition for food or cooperation to avoid predation. The number of individuals in a population can be anything from a few up to billions. There may be one population of a species or many. Populations of a species are often separated by a geographical barrier, for example the sea that separates two islands.

Question 111

How to use mark-release-recapture to estimate populations size of motile organisms

Answer 111

1. capture as many individuals as possible in the area occupied by the animal population, using netting, trapping or careful searching
2. mark each captured individual, without making them more visible to predators
3. release all the marked individuals and allow them to settle back into their habitat
4. after a time period, recapture as many individuals as possible and count how many are marked and how many unmarked
5. calculate the population size using the lincoln index

population size= ((number of individuals initially caught)(number of individuals recaptured))/ number of individuals recaptured that are marked

Question 112

What is species richness

Answer 112

The number of different species in the area. If there are loads of different species, there is a high species richness

Question 113

What is species evenness

Answer 113

The relative abundance of different species in a given area. If the number of individuals of each species are similar, the evenness is high.

Question 114

What is species diversity

Answer 114

species richness+species evenness

Question 115

Carrying capacity

Answer 115

Resources needed by populations, such as water and food, vary in abundance but are all limited. Resource limitation determines maximum population size.

Carrying capacity is the maximum population size that an environment can support.

If a resource becomes scarce, the members of a population will compete for it. If a population grows too large, some individuals will be unable to obtain enough of the resource. These individuals are likely to die, reducing the population size to the carrying capacity of the environment.

Question 116

What resources can affect carrying capacity in animals

Answer 116

water
space for breeding
food or territory for obtaining food
dissolved oxygen in water

Question 117

what resources can affect carrying capacity in plants?

Answer 117

water
light
soil nitrogen/phosphorus

Question 118

density independent factors

Answer 118

Density-independent factors have the same effect whatever the population size. For example, in a population of plants that are not adapted to low temperatures, a frost kills all the plants, whether the population is large or small. Forest fires kill plants and animals. Density-independent factors cause populations to fluctuate.

Question 119

density dependent factors

Answer 119

Density-dependent factors have an increasing effect as a population becomes larger. They are the basis for negative feedback mechanisms because they reduce larger populations and allow smaller populations to increase. Density dependent factors tend to bring population size back to carrying capacity.
- competition for limited resources such as water and food in animals and light in plants
- predation- this becomes more intense if a population of prey becomes denser and therefore easier to find, and less intense if the prey becomes scarcer. There are similar interactions between plants and herbivores
- Infectious disease, parasitism and pest infestation- these increase with population density because the transfer of pathogens, parasites and pests from host to host is easier if the hosts are closer together

Question 120

what factors can contribute to change in the number of individuals in a population

Answer 120

natality- offspring produced and added to the population

mortality- individuals die and are lost from the population

immigration- individuals move into the area from elsewhere

emigration- individuals move from the area to live elsewhere

The overall change in the size of a population can be calculated using this equation:

population change= (natality + immigration) - (mortality + emigration)

Question 121

How do sigmoid graphs show population curves?

Answer 121

1. Exponential phase- if a population is established in an ideal unlimited environment, it follows an exponential growth pattern, with the population increasing more and more rapidly. This is because the natality rate is higher than the mortality rate. The resources needed by the population are abundant, and diseases and predators are rare. With abundant resources, immigration to the area is more likely than emigration
2. Transitional phase- population growth slows as the carrying capacity of the environment is reached- the maximum population size that can be supported by the environment. The natality rate starts to fall and/ or the mortality rate starts to rise. Natality is still higher than mortality, but by a decreasing amount
3. Plateau phase- Something has limited the population such as (shortage of food or other resources, more predators, more diseases or parasites) All of these factors limit population increase because they became more intense as the population rises and becomes more crowded. They either reduce the natality rate or increase the mortality rate. Emigration is now more likely than immigration. If the population is limited by a shortage of resources, it has reached the carrying capacity of the environment

Question 122

How to test sigmoid population growth curves?

Answer 122

• this is tested using any organism that proliferates under experimental conditions, provided there are no ethical concerns
• a small number of organisms is given abundant resources and the numbers in the population are counted at regular intervals. There should be repeats so that reliability can be tested

Question 123

Communities

Answer 123

All species depend on relationships with other species for their long term survival. A population of one species can never live in isolation. Instead, groups of populations live together. In ecology, a group of populations living together in an area and interacting with each other is known as a community. A typical consists of hundreds or even thousands of species, including all the plants, animals, fungi and bacteria, that live together in an ecosystem.

Question 124

Intraspecific competition vs cooperation

Answer 124

An intraspecific relationship is one that exists between individuals of the same species and usually also within the same population. Competition and cooperation are categories of intraspecific relationship.

1. Competition

Members of a population have the same ecological niche so require the same resources. Unless a resource is abundant, there will be competition for it. Some individuals will be more successful and gain more of the resource, helping them to survive and reproduce. As a result, there is natural selection over the generations for traits that allow individuals to compete more effectively

2. Cooperation

Individuals in a population may cooperate in a variety of ways. The extent of cooperation varies, with most in social animals.

Cooperation relationships have strong advantages because all individuals benefit, whereas in competitive relationships all individuals tend to be harmed to some degree

Question 125

Types of interspecific relationship within communities. (relationships between species not living in close association)

Answer 125

Herbivory
Primary consumers feed on producers. The producer may or may not be killed

Predation
One consumer species (the predator) kills and eats another consumer species (the prey)

Interspecific competition
Two or more species use the same resource, with the amount taken by one species reducing the amount available to the other species

Question 126

Types of interspecific relationships within communities. (relationships between species living in close association)

Answer 126

Mutualism
Two species live in close association, with both species benefiting from the association

Pathogenicity
One species (the pathogen) lives inside another species (the host) and causes a disease in the host

Parasitism
One species (the parasite) lives in or on another species (the host) and obtains food from them. The host is harmed and the parasite benefits

Question 127

What is mutualism?

Answer 127

Mutualisms are close associations between species, where both species benefit. In many cases, the two species are from different taxonomic kingdoms so they have different capabilities and supply different services.

Question 128

What are invasive (alien) species

Answer 128

Species that occur naturally in an area are endemic. Species that were introduced by humans, deliberately or accidentally are alien. Density-dependent factors usually regulate the population size of endemic species. However, many alien species aren’t effectively regulated, because the pests or predators that would control them in their native habitat are absent in their new habitat. If an alien species increases in number and spreads rapidly, it is invasive.

Question 129

what are the effects of invasive species?

Answer 129

Invasive species can have devastating impacts on communities. The competitive exclusion principle predicts that two species cannot occupy the same ecological niche indefinitely. Alien species compete for the resources with endemic species that have the same or overlapping ecological niches. To become invasive, an alien species must be successful in competition for resources with endemic species. As a result, the endemic species may occupy a smaller realised niche, causing a decline in population, or lose its niche entirely and become extinct in an area. This is currently a widespread phenomenon because humans transport high numbers of a species to new areas, where there are no limiting factors (or not enough) to control the populations of alien species

Question 130

How can you investigate interspecific competition?

Answer 130

A range of approaches can be used to test for interspecific competition between species in a community that require the same resource

1. field manipulation can be used. e.g. one of two species can be removed from quadrats in grassland. There is evidence of interspecific competition if the other then increases in number/ biomass
2. laboratory experiments can be performed, under controlled conditions. Species can be grown together and apart to investigate whether they compete for resources
3. Tests for association between species can be carried out by random sampling

Question 131

Density-dependent control of animal populations by predator-prey relationships

Answer 131

Predators kill and consume prey, but in many communities, the population of prey does not change much overall, because new prey individuals are born at about the same rate as they are lost due to predation. Similarly, the birth and death rates of the predator are approximately equal, so the predator population remains stable. Some communities do not show this dynamic equilibrium and instead there are cyclical oscillations in numbers of prey and predators, due to four types of density-dependent interaction:
- A rise in prey numbers increases prey availability, so predator numbers rise
- A rise in predator numbers increases predation, so prey numbers fall
- a fall in prey decreases prey availability, so predator numbers fall
- a fall in predator numbers decreases predation so prey numbers fall

Question 132

Top down control of populations in communities

Answer 132

• Top down control acts from a higher trophic level to a lower one. For example an increase in predator numbers will decrease the numbers of prey in lower trophic levels

Question 133

Bottom up control of populations in communities

Answer 133

• Bottom up control acts from a lower trophic level to a higher one. For example, a population of producers may be limited by the availability of mineral nutrients in the soil or water

Question 134

What are antibiotics and allelopathic agents?

Answer 134

Antibiotics and allelopathic agents are secondary metabolites. A secondary metabolite is a substance produced by a pathway that only exists in some taxonomic groups. Such substances are not essential for cell growth and instead have a wide range of other functions. Antibiotics and allelopathic agents are two functional groups of secondary metabolites. Both antibiotics and allelopathic agents are released into the environment, where they are toxic to other organisms and deter potential competitors.

Antibiotics are secreted by microorganisms to kill, inhibit or prevent the growth of other species of microorganism.

Allelopathic agents are secreted into the soil by plants to kill or deter the growth of neighbouring plants. This can result in bare areas of soil near the secreting plant, reducing competition for water or mineral ions.

Question 135

Sustainable ecosystems

Answer 135

Systems are sustainable if they can continue for an unlimited period of time. Ecosystems have the potential to be sustainable. This is demonstrated by examples that have existed for very long periods of time.

The mechanisms that sustain ecosystems are fragile and easily disrupted , so ecosystems are not always stable. Even minor perturbations can cause change

Question 136

how is sustainability in ecosystems maintained?

Answer 136

• there must be a steady supply of energy, as it cannot be recycled. Sunlight is the energy source in most ecosystems. Very rarely this has been blocked by dust from volcanic activity, causing ecosystem collapse and mass extinctions
• nutrient cycles should replenish abiotic reserves of all chemical elements needed by organisms. Any losses from the ecosystem should be balanced by gains
• climatic variables, especially temperature and rainfall must remain within changes of tolerance of organisms in the ecosystem
• individual species, especially keystone species, must have high genetic diversity, so there is variation for natural selection to work on. This allows adaptations in response to environmental change, so new conditions can be endured.

Question 137

Tipping points in ecosystem sustainability

Answer 137

The amazon rainforest is so vast that it has major effects on climate. Evaporation of water from leaves (transpiration) has a cooling effect. Water vapour that has transpired from leaves condenses in the atmosphere above the forest, lowering air pressure and causing air flow (wind). The condensed water falls as rainfall, so it can be absorbed by trees and transpired again.

Ecosystems show resilience, but this is not unlimited. Above a certain level of disturbance, a tipping point may be reached, beyond which positive feedback mechanisms cause rapid changes that are difficult or impossible to reverse. In the amazon rainforest there is disturbance due to deforestation. If a tipping point is reached, a positive feedback cycle will cause unstoppable changes. Even without further deforestation, all remaining parts of the amazon rainforest would then change to another ecosystem type, probably grassland. It is uncertain what area of the Amazon rainforest is needed to prevent tipping point being reached

Question 138

percentage change formula

Answer 138

(final amount-initial amount)/initial amount *100%

Question 139

How is ecosystem sustainability monitored?

Answer 139

Ecosystems have the potential to be sustainable over long periods of time. As long as nutrients are recycled and there is a supply of energy, usually in the form of light, ecosystems have the potential to persist endlessly. This can be investigated using mesocosms.

A mesocosm is a small experimental enclosure, set up for ecological research. Fenced-off enclosures in grassland or a forest model terrestrial mesocosms. Open tanks or sealed glass vessels model aquatic ecosystems. Sealed vessels allow entry and exit of matter to be controlled, with energy transfer happening freely.

For sustainability, autotrophs and saprotrophs are essential components, but consumers and detritivores may not be essential. It is unethical to include large animals in mesocosms that cannot obtain enough food or oxygen.

Question 140

What is a keystone species?

Answer 140

A keystone species has a disproportionate effect on the structure of an ecological community. Species diversity decreases if a keystone species is lost and there may be a collapse of the entire ecosystem.

Question 141

How is balance maintained in sustainability?

Answer 141

Before agriculture was developed, all foods and other resources needed by humans were harvested from natural ecosystems. This is sustainable if the rate of harvesting is lower than the rate of replacement . There is a long history of unsustainable harvesting and it has resulted in many species extinctions.

Question 142

Sustainability of agriculture

Answer 142

• Tillage is preparing soil for a crop. Soils are loosened by plowing, harrowing and other cultivations. Soil structure can become degraded and both wind and water can cause soil erosion at much faster rate than new soil is being generated. Tropical forests that are cleared for agriculture often have soils which quickly degrade and cannot sustain high yield agriculture for long
• Nutrient depletion of soils is caused by removal of harvested crops and by leaching. Repeated applications of chemical fertiliser are required because of depletion. Phosphate and most other minerals are mined from non-renewable rock deposits. The manufacture of nitrogen fertiliser from fossil fuels requires energy
• Cultivating large areas of single variety of crop plant (monoculture) and growing the same crop year after year encourages pests and weeds to become increasingly problematic. Intensive agriculture responds to this with applications of pesticide and herbicide. This can cause pollution problems. Resistance to an agrochemical tends to evolve in pests or weed if the chemical is repeatedly used. Manufacture of agrochemicals requires an energy source, which currently is supplied by fossil fuels
• Mechanical tillage requires power, most of which comes from diesel oil used in tractors. Energy is also required for heating glasshouses and animal housing. The carbon footprint of agriculture is high. It makes a significant contribution to climate change.

Question 143

How does human activity lead to water pollution

Answer 143

When rainwater falls on terrestrial ecosystems, soluble nutrients such as phosphates and nitrates dissolve and are washed out of the soil as water drains through it (leaching). The nutrients enter river catchments and are eventually carried out to sea. Intensive crop production increases leaching, because of the use of artificial fertilisers. Intensive livestock production also increases the transfer of nutrients into river systems, especially if manure and urine aren’t stored correctly or are spread on land before rainfall. Intensive agriculture therefore tends to cause nutrient enrichment of ponds and lakes also flowing water in streams and rivers and in estuaries and shallow seas. Nutrient enrichment of aquatic and marine ecosystems is eutrophication.

The water in some ecosystems is naturally eutrophic but agriculture has caused eutrophication of many lakes and rivers.

1. eutrophication due to leaching of mineral nutrients
2. excessive growth of algae and cyanobacteria due to to eutrophication
3. algae and cyanobacteria rise to seek light (algal bloom) but some are shaded out and die
4. decomposition of dead organisms causes a high biochemical and oxygen demand
5. water becomes anoxic due to high biochemical and oxygen demand resulting from decomposer respiration, so fish die

Question 144

Effects of plastics on the oceans

Answer 144

Plastic is accumulating because it is either non-degradable, or degrades very slowly

Macroplastics are large visible items, such as fishing nets, ropes, drinks bottles and grocery bags. Marine wildlife such as seabirds and turtles can become entangled in nets and ropes and ingest plastic bags and other debris because they are mistaken for prey. Albatrosses confuse floating plastic bags with jellyfish or squid and give them to their chicks resulting in gut blockages and high mortality

Microplastics are tiny granules of plastic, which are present in many products. They have been found in every marine ecosystem investigated

Nanoplastics are less than 1 micrometer in diameter and can pass through cell plasma membranes and can accumulate in organs. They almost certainly have harmful effects, but they aren’t researched as of yet.

Question 145

What is bioaccumulation?

Answer 145

Bioaccumulation is an increase in concentration of a toxin in body tissues during an animals life. It is a particular problem with toxins that are fat soluble and therefore not easily excreted.

Question 146

what is biomagnification?

Answer 146

Biomagnification is an increase in concentration of a chemical substance at each successive trophic level in a food chain. Predators tend to accumulate higher concentrations of toxin than their prey. This is because the predator consumes large quantities of prey during its lifetime and biomass accumulates the toxins that they contain.

Question 147

What is rewilding and why is it important?

Answer 147

Natural ecosystems have been degraded by human actions and relatively little of the Earths surface remains as pristine natural habitat. Among the consequences are:

• loss of biodiversity
• rapid rates of species extinction
• loss of ecosystem services e.g. carbon sequestration and climate regulation, flood protection, prevention of soil erosion and purification of air and water

In many parts of the world, efforts are being made to encourage natural ecosystems to return. One approach to this is rewilding. The essential principle of rewilding is that there should be as little intervention by humans as possible because natural processes restore habitats more effectively than humans. A first step is to stop or reduce human activities such as agriculture, logging and other forms of resource harvesting. That may be all that is required for forests to recolonise abandoned farmland or for marine ecosystems to re-establish fishing exclusion zones. More commonly there is need for specific interventions to undo human actions:

• spreading of seeds of plants that should be part of the ecosystem but no natural seed source is present
• reintroduction of apex predators and other keystone species
• re-establishment of connectivity where natural ecosystems have become fragmented
• control of alien invasive species

Question 148

Triggers of ecological succession

Answer 148

Ecological successions are sequences of changes that progressively transform ecosystems. Species composition of the community and abiotic factors both change over time

Consider an area of grassland that is being colonised by shrubs or trees. As the trees grow, light intensity at ground level diminishes and lower temperatures and higher humidity result. Leaf litter from the trees increases nutrient concentration, water infiltration and capacity for water retention of the soil. This means that plant species adapted to conditions in grassland will be lost from the community and others adapted to conditions in the forest will join it. There will also be changes in the animal species because of interdependency between specific species of animal and plants.

Changes in an ecosystem often trigger other changes, so one ecosystem replaces another in a series. This is an ecological succession. A stable and persistent ecosystem then may develop that does not undergo further significant change. This is the climax community

Question 149

Principles of primary succession

Answer 149

Succession is either primary or secondary. Primary succession begins in environments where living organisms are largely or completely absent. On land, this could be bare rock or deposits of silt, sand or larger rock fragments, but not soil. Only organisms such as bacteria, lichens and mosses can colonise these inorganic substrata. Early colonisers generate small amounts of soil, allowing herbs with roots to start to colonise. As deeper soul develops, successively larger plants colonise. Animal populations change with plant populations, as do populations of decomposers.

These are the general principles of primary succession:

• species diversity increases as more species join the community than are eliminated
• primary production increases as larger plants colonise and there is more photosynthesis per unit area
• food webs become more complex
• nutrient cycling increases as animals and plants generate more dead organic matter

Question 150

what is cyclical succession?

Answer 150

Some ecosystems are characterised by cycles of change rather than stable climax. In cyclical succession, species replace each other over time repeatedly, even without the stimulus of large-scale disturbance.

Cyclical succession also occurs when a community is changed by recurring events. E.g. repeated fire cycles leading to disturbance to an ecosystem

Question 151

how can human activities block climax communities from developing?

Answer 151

As succession proceeds, a stable climax community may develop that is not superseded. The type of climax community that develops depends on climate and other environmental conditions. Human influence can cause a deflected arrested succession, so a plagioclimax develops (an alternative stable community). Grazing by farm livestock and drainage of wetlands both result in a plagioclimax, instead of the climatic community.

• grazing is the method of feeding farm livestock such as cattle and sheep. The livestock are kept at high stocking densities so grazing is more intense than in natural ecosystems. Grasses and many herbs can tolerate grazing, but tree and shrub seedlings are killed, so grassland persists as a plagioclimax where it would naturally be replaced by shrub and then forest
• drainage of wetlands removes water from swamps and other waterlogged sites and increases soil aeration. Plants and animals adapted to wetlands migrate or die and saprotrophic fungi, which were inhibited by the lack if oxygen, can decompose any peat that had developed in the swamp. If the land is not cultivated, shrubs and trees may be able to colonise areas that were previously waterlogged.

Question 152

r-strategists vs k-strategists

Answer 152

r- strategists
e.g. fish
small body size
large number of offspring
no parental care
very short gestation period
large population
shorter lifespan

k-strategists
e.g. humans
large body size
few offspring
long term care to children
large gestation period
small population size
longer lifespan.

Question 153

what are limiting factors

Answer 153

resources in the environment that limit the growth, abundance and distribution of organisms/ populations in ecosystems