Energy Transfers in and between Organisms Flashcards
what is an ecosystem?
an ecosystem includes all the organisms living in a particular area and all the non-living conditions.
what is biomass?
biological molecules from glucose, as the product of photosynthesis, make up the plants biomass which is the mass of the living material
how can biomass be measured?
biomass can be measured in terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area.
what is dry mass?
dry mass is the mass of the organism with the water removed.
how is dry mass measured?
a sample of the organism is dried, often in an oven set to a low temperature.
the sample is then weighed at regular time intervals. once the mass becomes constant you know that all the water has been removed.
the mass of carbon present is generally taken to be 50% of the dry mass.
how can we calculate the amount of chemical energy stored in biomass?
using a calorimeter.
a sample of dry biomass is burnt and the energy released is used to heat a known volume of water.
the change in temperature of the water is used to calculate the chemical energy of the dry biomass.
what is gross primary production (GPP)?
the total amount of chemical energy converted from light energy by plants, in a given area.
what is respiratory loss (R)?
where approximately 50% of the gross primary production is lost to the environment as heat when the plants respire.
what is net primary production (NPP)?
the remaining chemical energy once respiratory loss has taken place.
this is the energy available to the plant for growth and reproduction, stored in the plant’s biomass, as well as the energy available to organisms at the next stage in the food chain.
what is the formula for NPP?
NPP = GPP - R
how do consumers get chemical energy to store in their biomass?
consumers get their energy by ingesting plant material, or animals that have eaten plant material.
why does biomass decrease along a food chain?
energy is lost in waste (urine) and faeces.
not all of the food is eaten.
energy is lost to surroundings as heat.
what is the consumers’ net production?
the energy that’s left, after around 90% of energy is lost, is stored in the consumers’ biomass and is available to the next trophic level.
how can the net production of consumers be calculated?
N = I - (F + R)
I : chemical energy from ingested food
F : chemical energy lost in faeces and urine
R : energy lost through respiration
how are food chains able to show how energy is transferred between organisms?
food chains show simple lines of energy transfer. each of the stages in a food chain are called trophic levels.
how are food webs able to show how energy is transferred between organisms?
food webs show lots of food chains in an ecosystem and how they overlap.
how do most farming practices aim to increase the amount of energy that is available for human consumption?
by reducing the energy lost to other organisms.
by reducing the energy lost through respiration.
explain how simplifying food webs reduces energy loss to other organisms. use ‘pests’ example.
pests are organisms that can reduce the amount of energy available for crop growth and therefore the NPP. this ultimately reduces the amount of energy available for humans.
by simplifying the food web, i.e getting rid of food chains that don’t involve humans, energy losses will be reduced and the NPP of the crop will increase.
how can farmers get rid of pests, in order to simplify the food web?
farmers can reduce pest numbers using chemical pesticides.
for example, insecticides kill insect pests that eat and damage crops. killing insect pests means less biomass is lost from crops, so they grow larger, which means NPP is greater.
herbicides kill weeds. killing weeds can remove direct competition with the crop for energy from the Sun. it can also remove the preferred habitat or food source of the insects pests, helping to remove further numbers and simplify the food web.
what else helps to reduce the number of pests?
biological agents.
e.g. parasites live in or lay their eggs on a pest insect. parasites either kill the insect or reduce its ability to function. .
explain how reducing respiratory losses means energy is transferred more efficiently. use an example which can help reduce respiratory losses.
farmers increase the net production of their livestock by controlling the conditions that they live in, so that more of their energy is used for growth and less is lost through respiration as well as activities that increase the rate of respiration. this means that more biomass is produced and more chemical energy can be stored, increasing net production and the efficiency of energy transfer to humans.
e.g movement increases the rate of respiration, so animals may be kept in pens where their movement is restricted. the pens are often indoors and kept warm, so less energy is wasted by generating body heat.
what is a natural ecosystem?
this is an ecosystem that hasn’t been changed by human activity. in natural ecosystems, nutrients are recycled through the food webs.
what important role do fungi have in nutrient recycling?
some fungi form symbiotic relationships with the roots of plants. these relationships are known as mycorrhizae.
how are some fungi able to form symbiotic relationships with the roots of plants?
the fungi are made up of long, thin strands called hyphae, which connect to the plant’s roots.
the hyphae greatly increase the surface area of the plant’s root system, helping the plant to absorb ions from the soil that are usually scarce. hyphae also increases the uptake of water by the plant.
in turn, the fungi obtain organic compounds, such as glucose, from the plant.
what are saprobionts?
they are a type of decomposer; they feed on the remains of dead plants and animals and on their waste products, breaking them down. this allows important chemical elements in the remains to be recycled.
what is extracellular digestion?
where saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need. during this process, organic molecules are broken down into inorganic ions.
what is saprobiotic nutrition?
obtaining nutrients from dead organic matter using extracellular digestion.
what does the nitrogen cycle show?
it shows how nitrogen is converted into a usable form and then passed on between different living organisms and the non-living environment.
why can’t organisms use nitrogen directly from the atmosphere?
nitrogen is very stable due to the strong covalent triple bond so it can’t be broken down as easily.
name the 4 main stages of the nitrogen cycle.
nitrogen fixation
ammonification
nitrification
denitrification
explain nitrogen fixation.
nitrogen fixation is when nitrogen gas in the atmosphere is turned into nitrogen-containing compounds. biological nitrogen fixation is carried out by bacteria such as Rhizobium. they turn nitrogen into ammonia, which goes on to form ammonium ions in solution that can then be used by plants.
Rhizobium are found inside root nodules of plants such as peas, beans and clovers. they form a mutualistic relationship with the plants; they provide the plant with nitrogen compounds and the plant provides them with carbohydrates.
explain ammonification.
ammonification is when nitrogen compounds from dead organisms are turned into ammonia by saprobionts, which goes on to form ammonium ions.
animal waste also contains nitrogen compounds. these are also turned into ammonia by saprobionts and go on to form ammonium ions.
explain nitrification.
nitrification is when ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants (nitrates).
the first nitrifying bacteria change ammonium ions into nitrites.
then other nitrifying bacteria change nitrites into nitrates.
explain denitrification.
denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria; they use nitrates in the soil to carry out respiration and produce nitrogen gas.
this happens under anaerobic conditions, e.g in waterlogged soils.
what are the other ways nitrogen is able to get into an ecosystem?
by lightning which fixes atmospheric nitrogen or by artificial fertilisers, produced from atmospheric nitrogen on an industrial scale in the Haber process.
why do plants and animals need phosphorus?
they need phosphorus to make biological molecules such as phospholipids, DNA and ATP.
where is phosphorus found?
phosphorus is found in rocks and dissolved in the oceans in the form of phosphate ions. phosphate ions dissolved in water in the soil can be assimilated by plants and other producers.
what does the phosphorus cycle show?
it shows how phosphorus is passed through an ecosystem.
explain the phosphorus cycle. (7 points)
-phosphate ions in rocks are released into the soil by weathering.
-phosphate ions are taken into the plants through the roots. mycorrhizae greatly increases the rate at which phosphorus can be assimilated.
-phosphate ions are transferred through the food chain as animals eat the plants and are in turn eaten by other animals.
-phosphate ions are lost from the animals in waste products.
-when plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. these microorganisms also release the phosphate ions form urine and faeces.
-the weathering of rocks also releases phosphate ions into seas, lakes and rivers. this is taken up by aquatic producers, such as algae, and passed along the food chain to birds.
-the waste produced by sea birds is known as guano and contains a high proportion of phosphate ions. guano returns a significant amount of phosphate ions to soils. it is often used as a natural fertiliser.
how are nutrients lost when crops are harvested?
crops take in minerals from the soil as they grow and use them to build their own tissues.
when crops are harvested, they’re removed from the field where they’ve grown rather than being allowed to die and decompose there. this means the mineral ions that they contain are not returned to the soil by decomposers in the nitrogen or phosphorus cycles.
how are phosphates and nitrates lost when animals or animal products are removed from the land?
animals eat grass and other plants, taking in their nutrients. when they are taken elsewhere for slaughter or transferred to a different field, the nutrients aren’t replaced through their remains or waste products.
why are fertilisers added to soils?
adding fertilisers replaces the lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer.
what are the 2 types of fertilisers?
artificial
natural
what are artificial fertilisers?
these are inorganic; they contain pure chemicals as powders or pellets.
what are natural fertilisers?
they are organic matter; they include manure, composted vegetables, crop residues and sewage sludge.
how does using fertilisers raise environmental issues?
-sometimes more fertiliser is applied than the plants need or are able to use at a particular time.
-this can lead to the fertilisers leaching into waterways.
-this can lead to eutrophication.
-inorganic ions in chemical fertilisers are relatively soluble. this means that excess minerals that are not used immediately are more likely to leach into waterways.
-in natural fertilisers, the nitrogen and phosphorus are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants. this means that their release into the soil for uptake by plants is more controlled, and leaching is less likely.
-the leaching of phosphates is less likely than the leaching of nitrates because phosphates are less soluble in water.
what is leaching?
leaching is when water-soluble compounds in the soil are washed away. they’re often washed into nearby ponds and rivers.
leaching is more likely to occur if the fertiliser is applied just before heavy rainfall.
what is eutrophication caused by?
excess nutrients
