L6 bio mock Paper 2

what is decompisiton?

the breakdown of dead organic matter and waste products by microorganisms, releasing nutrients back into the ecosystem

how are bacteria and fungi involved in decomposition?

they feed saprotrophically

what is extracellular digestion?

Digestion outside the organism where enzymes are secreted onto food and the soluble products are absorbed.

why are decomposers important in ecosystems?

They recycle nutrients and release mineral ions back into the soil for plant uptake.

what is ammonification?

The conversion of organic nitrogen compounds from dead organisms and waste into ammonium ions by decomposers

which molecules are broken down during ammonification?

Proteins, nucleic acids and urea

what mineral ion is released during ammonification?

Ammonium ions (NH₄⁺)

what are mycorrhizae?

Mutualistic associations between fungi and plant roots

how do fungi benefit from mycorrhizae?

receive organic compounds such as glucose from the plant

why is Nitrogen important in living organisms?

needed to make:

• amino acids

• proteins

• nucleic acids

• ATP

why can’t plants use atmospheric nitrogen directly?

Nitrogen gas (N2) is very stable and inert

what is nitrogen fixation

The conversion of atmospheric nitrogen gas into ammonia or ammonium compounds

which bacteria carry out nitrogen fixation?

• rhizobium

• azotobacter

where are rhizobium bacteria found?

in root nodules of legume plants

where are azotobacter bacteria found

free living in the soil

what enzyme is used in nitrogen fixation?

Nitrogenase

why does nitrogen fixation require a lot of ATP?

Breaking the triple bond in nitrogen gas requires large amounts of energy

What is the role of leghaemoglobin in root nodules

It maintains a low oxygen concentration to protect nitrogenase while still supplying oxygen for respiration

why must oxygen conc be low in root nodules

oxygen inhibits or denatures nitrogenase

what is nitrification

the conversion of ammonium ions into nitrites and then nitrates by nitrifying bacteria

what are the 2 stages of nitrification?

• Ammonium ions → nitrite ions

• Nitrite ions → nitrate ions

which bacteria convert ammonium ions into nitrates?

Nitrosomonas

which bacteria converts nitrites into nitrates?

Nitrobacter

what conditions are needed for nitrification?

Aerobic conditions with oxygen present

why does waterlogging reduce nitrification?

waterlogged soils contain less oxygen

why are nitrates important to plants?

nitrates are absorbed by roots and used to make amino acids, proteins and nucleic acids

why are nitrifying bacteria described as chemoautotrophs?

They obtain energy from chemical reactions and use it to synthesise organic molecules

what is denitrification?

The conversion of nitrates into nitrogen gas by denitrifying bacteria.

what conditions favour denitrification?

anaerobic conditions such as waterlogged soil

why does denitrification increase in waterlogged soils?

Oxygen levels are low, favouring anaerobic bacteria.

what is a consequence of denitrification for plants?

soil nitrate levels decrease, reducing plant growth

why is denitrification important in the nitrogen cycle?

it returns nitrogen gas to atmosphere

how does nitrogen enter food chains?

Plants absorb nitrate ions and use them to make organic molecules which are then eaten by animals.

how is nitrogen returned to the soil from animals?

Through waste products, death and decomposition

why can nitrate ions be easily lost from soil?

they are soluble and can be leached away by water

what are the 4 main processes in the nitrogen cycle?

• nitrogen fixation

• ammonification

• nitrification

• denitrification

why is nutrient recycling important in ecosystems?

ensures essential elements are continuously available for living organisms

why are legumes important in agriculture?

They contain nitrogen-fixing bacteria which increase soil nitrogen levels

how do human activities affect the nutrient cycle?

Fertiliser use and farming can increase nitrate levels and alter nutrient cycling

why can excessive nitrate fertiliser use be harmful?

can lead to eutrophication in aquatic ecosystems

what happens to light energy that fall on a plant leaf?

• only convert 1-3% of light energy into chemical energy

how is energy lost between the sun and producers?

• reflection of light

• transmission of light

• light of incorrect wavelength for absorption of chlorophyll

• evaporation of water from leaf

• heat loss as biproduct of respiration

how much energy is lost between trophic levels?

around 90%

where is energy lost between trophic levels going?

• not ingested all of it

• not digested or assimilated

• excreted

• lost as heat from respiration

how is energy lost between producers and consumers?

• lots can’t be eaten by primary consumer e.g. roots

• producers have cellulose walls which can’t be digested as consumers don’t have the enzyme cellulase

• much material is egested

• energy used by gut bacteria in consumer

• energy lost as heat as biproduct of respiration

how is energy lost between consumers?

• excretion - urine

• egestion - faeces

• respiration - heat loss

• not all the animal/plant is eaten (e.g. bones)

why does biomass decrease between trophic levels?

because chemical energy stored in biomass is lost between trophic levels

why is biomass often used to measure energy transfer?

Because energy is stored in the chemical bonds of biomass.

why are food chains limited in length?

Too much energy is lost at each trophic level

what eventually makes very high trophic levels unviable?

The energy required for foraging exceeds the energy gained from food

why do primary consumers often lose more energy in their faeces than secondary consumers?

The primary consumers can't digest the cellulose in the plants so it stays in their fasces and so more energy is lost

why do secondary consumers often lose more energy in respiration than primary consumers?

• Movement - they have to do lots of exercise to catch their pray

• Thermoregulation - to maintain our temperature (bigger animals)

what does calculating energy efficiency allow you to do?

• allows you to see the productivity of a food chain

• e.g. the rate of biomass production/the amount of biomass produced per unit time through a food chain

what is the productivity of a producer called?

primary productivity

what is gross primary production (GPP)?

Total amount of energy converted into chemical energy by producers as a result of photosynthesis

what is net primary production (NPP)?

• the actual rate of production of new biomass by the producers

• represents the biomass available for consumers to eat

what is the equation for Net Primary Production (NPP)?

net primary production (NPP) = gross primary production (GPP) - respiratory energy loss (R)

what is the ecological efficiency equation?

ecological efficiency = energy (or biomass) available after transfer/ energy (or biomass) available before the transfer x100

what is a decomposer?

organisms that consume any waste material

what can GPP/NPP vary because of? why?

• environmental temp

• day length

• light intensity

• availability of soil mineral

All of above affect species of plant that grow and their density and so affect GPP/NPP

how can we increase NPP by increasing the productivity of producers?

• greenhouses - control temp, CO2 conc (photosynthesis)

• Irrigation - ensures enough water (photosynthesis)

• Selective breeding/genetic modification - e.g. decreased stem length to prevent wind damage; make plants produce insecticides to kill pests

• Pesticides (maintain healthy plants and so maximise productivity)

• Fungicides (maintain healthy plants and so maximise productivity)

• Herbicides (maintain healthy plants and so maximise productivity)

• Crop rotation - maintains optimum mineral content of soil

• Monoculture - prevents competition for things like soil minerals or space with unwanted species

how can we increase secondary productivity (consumer to consumer)?

• Harvesting animals at an earlier age

• Steroids to increase growth rates

• Selective breeding to produce fast growing organisms, higher egg production, increased milk yield

• Antibiotic treatments to prevent energy loss to pathogens

• Temperature control (in barns)

• Restriction of movement (in barns)

what do arrows in a food chain show?

show the flow of energy

what 3 ecological pyramids are there?

• pyramids of number

• pyramids of biomass

• pyramids of energy

what do pyramids of numbers show?

they represent numbers of organisms in each trophic level in a food chain

are pyramids of numbers always pyramid shaped?

no

why are pyramids of numbers not always pyramid shaped?

they only show the number of organisms in each trophic level, and don’t take into account the size of organisms

what are some advantages of pyramids of numbers?

• Simple method of giving an overview

• Good at comparing changed in population numbers with time or season

what are some disadvantages of pyramids of numbers?

• The size of the organism isn't taken into account i.e. an oak tree producer would lead to an inverted pyramid

• Do not allow for juveniles or immature forms

• Numbers can be too large to represent accurately

what do pyramids of biomass show?

the total mass of organisms in each trophic level of a food chain

are they usually pyramid shaped?

• yes

• as energy and material are lost at each stage of the chain

why do we measure organisms dried for pyramids of biomass?

measuring them dry makes sure water mass isn’t taken into account as water in organisms vary

what units is the biomass at each trophic level measured in?

• grams per square meter for land  (gm-²)

• grams per cubic meter for water (gm-³)

why is this marine pyramid of biomass an inverted shape?

• mass of phytoplankton at any given time is often quite small but they reproduce quickly so over a period of time

• there is always more phytoplankton than zooplankton, but sampling is carried out at one moment of time

• therefore pyramids of biomass measures the standing crop rather than productivity over time

what is an advantage of pyramids of biomass?

• Overcomes the problems of pyramids of number to give a more representative picture of the feeding relationships in an ecosystem

what are some disadvantage of pyramids of biomass?

• Only uses samples from populations - impossible to measure biomass exactly

• Time of year biomass is measured can affect the result - standing crop does not take into account changes over time

• To obtain dry mass calculations, organisms must be killed so samples are small

what is biomass?

total dry mass of organic matter in organisms or ecosystems which can be equated to energy content

what is the method for measuring biomass? (5 steps)

1. representative samples are collected

2. organisms are sorted into trophic levels

3. organisms are dried (due to varying amounts of water) in an oven at 80°C until all water has evaporated

4. mass is measured with an electronic balance

5. drying and measuring may be repeated

what is a disadvantage of the method of measuring biomass?

• samples must be killed to be dried

• can only used small samples (and so may not be represented)

what do pyramids of energy show?

these show the energy contained in the organisms in each trophic level of a food chain

are pyramids of energy always pyramid shaped?

• yes

• they are always pyramid shaped as energy and material are lost at each stage of the chain

• also takes into account time of year

what are pyramids of energy measured in?

Kilojoules per meter squared per year (kJm-²yr-1)

or

Kilojoules per meter cubed per year (kJm-³yr-1)

what are some advantages of pyramids of energy?

• Most accurate representation of the feeding relationships between the organisms at different trophic levels

• It takes into account the energy gains and losses over a period of time

what is a disadvantage of pyramids of energy?

Very difficult and complex to collect energy data

how do you use a bomb calorimeter to construct a pyramid of energy?

• the energy content of samples of organisms from each trophic level is measured

• each sample is dried in an oven

• the samples are weighed

• samples are burned in a bomb calorimeter in oxygen

• energy produced passes to a known mass of water and the temp rise of the water is measured

• how much energy is released per gram is calculated and converted to kJ

what is an ecosystem?

made up of all the living organisms that interact with one another in a defined area, and also the physical factors present in that region

what size are ecosystems?

they vary dramatically in size from a tiny bacterial colony to the entire biosphere of earth

how are boundaries of an ecosystem defined?

they are defined by the persons/people carrying out the study

are ecosystems dynamic or not?

ecosystems are dynamic

what does dynamic mean in terms of an ecosystem?

dynamic = a process or system characterised by constant change, activity, or progress

what do different species have to have to be able to live in the same habitat?

2 species can only occupy the same habitat if they occupy different niches

what happens if 2 species have the same niche within a habitat?

• they will compete with each other

• the better adapted species will out-compete the other and exclude it from the habitat

what is an example of a structural niche?

broad cliff ledges and the sea

what is an example of a feeding niche?

dives into the water for fish

what determines which species occur in a habitat?

• the conditions in which species compete for survival are defined by the ecological factors in there habitat

what can ecological factors be divided into?

• abiotic

• biotic

what are some examples of abiotic factors?

• Climatic Factors –temperature, wind, rainfall.

• Soil (edaphic) Factors –soil pH, mineral salt

• availability, soil texture (clay or sand based).

• Topographic Factors –altitude, aspect, inclination, drainage.

• Water availability

• Light availability –affected by latitude, season, cloud cover.

• Oxygen Availability (particularly in aquatic systems).

• Pollution

• Catastrophes e.g.. floods, earthquakes, volcanic eruptions, fires.

what are some biotic factors?

• competition for resources

• grazing

• predation

• parasitism

• mutualism

• effects related to size of population (density)

what do food chains show?

transfer of energy

what is a trophic level?

stage of a food chain at which organisms feed