Topic 5B - Energy Transfer And Nutrient Cycle Flashcards
What is biomass?
An ecosystem includes all the organisms living in a particular area and all the abiotic conditions. In all ecosystems, there are produces - organisms that make their own food such as plants and algae. During photosynthesis plants use energy and carbon dioxide to make glucose and other sugars. Some of the sugars are used in respiration, to release energy for growth. The rest of the glucose is used to make other biological molecules, such as cellulose. These biological molecules make up the plants biomass - the mass of living material. Biomass can also be thought of as the chemical energy stored in the plant. Energy is transferred through the living organisms of an ecosystem when organisms eat other organisms e.g producers are eaten by primary consumers, which are eaten by secondary consumers, which are eaten by tertiary consumers. Food chain.
How can you measure biomass?
Made of carbon that an organism has or the dry mass of its tissue per unit area. The water content of living tissue varies which is why wet mass is not used. A sample of the organism is dried, often in an oven set to a low temperature. The sample is then weighed at regular intervals. Once the mass becomes constant you know all the water has been removed. If needed, the result from the sample can be scaled up to give the biomass of the total population or the area being investigated. E.g kg m^-2
The mass of carbon is generally taken to be 50% of the dry mass.
You can estimate the amount of chemical energy stored in biomass by burning the biomass in a colorimeter. The amount of heat given off tells you how much energy is in it. 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 GPP and NPP?
Gross primary production is the total amount of chemical energy converted from light energy by plants, in a given area. Approximately 50% of the gross primary production is lost to the environment as heat when the plants respire. This is called respiratory loss (R). The remaining chemical energy is called the net primary production, which is GPP-R.
The NPP is the energy available to the plant for growth and reproduction - the energy is stored in the plants biomass. It’s also the energy available to organisms at the next trophic level. This includes herbivores and decomposed. Often primary production is expressed as a rate of biomass in a given area in a given time. Typical units might be Kj per hectare per year. When primary production is expressed as a rate, it is called primary productivity. Net primary production = gross primary production- respiratory loss.
How do you calculate net production for consumers?
Consumers also store chemical energy in their biomass. They get energy by ingesting plant material, or animals that have eaten plant materials. However not all the chemical energy stored is transferred - around 90% of the total available energy is lost in various ways. Some of the food is not eaten. For what’s ingested, some are heated as faecesZ the chemical energy is lost to the environment. Some energy is also lost through respiration or excretion of urine. The energy that’s left is stored in the consumers’ biomass and is available to the next trophic level. This energy is the consumers’ net production.
Net production = chemical energy in ingested food - (chemical energy lost in faeces and urine + energy lost through respiration)
The net production of consumers can also be called secondary production (or secondary productivity when it’s expressed as a rate).
How can farming practices increase the efficiency of energy transfer?
1) The energy lost to other organisms can be reduced. 2) The energy lost though respiration can be reduced.
1) the weed, the mouse and aphid are pests - organisms that reduce the amount of energy available for crop growth and therefore the net primary production. Therefore simplify the food web by using insecticides that kill insect pests that eat and damage crops. Killing insect pests means less biomass is lost from crops, so they grow to be larger, which means NPP is greater. Herbicides kill weeds which remove direct competition with the crop for energy for the sun. It can also remove the preferred habitat or food source of the insect pests, helping to further reduce their numbers and simplify the food web.
2) Biological agents also reduce the numbers of pests, so crops lose less energy and biomass, increasing the efficiency of energy transfer to humans. Parasites live or lay their eggs on a pest insect. Parasites either kill the insect or reduce its ability to function. Pathogenic bacteria and viruses can kill pests. Integrated systems can combine both and increase NPP even more.
2) animals may be kept in pens where movement is restricted, and the pens are often indoors and kept warm so less body heat is generated. Therefore more biomass is produced and more chemical energy can be stored, increasing net production and the efficiency of energy transfer to humans. The benefits are that more food can be produced, but ethical issues
How are fungi and bacteria important in nutrient recycling?
A natural ecosystem is one that hasn’t been changed by human activity. Microorganisms such as bacteria and fungi, are an important part of food webs. Many are saprobionts (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. Saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need. This is known as extracellular digestion. During this process, organic molecules are broken down into inorganic ions. Obtaining nutrients from dead organic matter using extracellular digestion is known as saprobiotic nutrition. Some fungi form symbiotic relationships with the roots of plants. These relationships are known as mycorrhizae. 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 (e.g phosphorus). Hyphae also increase the uptake of water by the plant. In turn, the fungi obtain organic compounds, such as glucose from the plant.
What is the nitrogen cycle?
Nitrogen is needed to make proteins and nucleic acids.
1) Nitrogen fixation - Nitrogen gas in the atmosphere is turned into nitrogen-containing compounds. It’s 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 (growths on the roots) of leguminous plants. They form a mutualistic relationship with the plants - they provide the plant with nitrogen compounds and the plant provides them with carbohydrates.
2) Ammonification - nitrogen compounds from dead organisms are turned into ammonia by saprobionts, which goes on to form ammonium ions. Animal waste also contains nitrogen compounds which are turned into ammonia.
3) nitrification - ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants. First nitrifying bacteria called nitrosomonas change ammonium ions into nitrites. Then other nitrifying bacteria called nitrobacter change nitrites into nitrates.
4) denitrification - 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 happens in the phosphorus cycle?
Plants and animals need phosphorus to make phospholipids, DNA and ATP. 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 (absorbed and then used to make more complex molecules) by plants and other producers.
Phosphate ions in rocks are released into the soil by weathering. Phosphate ions are taken into the plants through the roots. Mycorrhizae greatly increase 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 from urine and faeces. 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 (particularly in coastal areas). It is often used as a natural fertiliser.
How are nutrients lost?
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’re grown rather than being allowed to die and decompose there. This means the mineral ions that they contain (e.g phosphate and nitrates) are not returned to the soil by decomposers in the nitrogen or phosphorus cycles. Phosphates and nitrates are also lost from the system 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? What are some issue
Replaces lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer. Fertilisers can be artificial or natural.
Artificial fertilisers are inorganic - they contain pure chemicals as powders or pellets. Natural fertilisers are organic matter - they include manure, composted vegetables, crop residues and sewage sludge.
Sometimes more fertiliser is applied than the plants need or are able to use. This can lead to the fertilisers leaching into waterways. Leaching is when water-soluble compounds in the soil are washed away. They’re often washed into nearby ponds and rivers. This can lead to eutrophication. Leading is more likely to occur if the fertiliser is applied just before heavy rainfall. 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 decomposed by microorganisms before they can be absorbed by plants. This means they their release into the soil for uptake by plants is more controlled, and leaching is less likely. The leaching of phosphate is less likely than the leaching of nitrates because phosphates are less soluble in water. Too much of a particular nutrient can cause crops and other plants to die.
What is eutrophication?
Mineral oils leached from fertilised fields stimulate the rapid growth of algae in ponds and rivers. Large amounts of algae block light from reaching the plants below. Eventually the plants die because they’re unable to photosynthesis enough. Bacteria feed on the dead plants matter. The increased numbers of bacteria reduce the oxygen concentration in the water by carrying out aerobic respiration. Fish and other aquatic organisms die because there isn’t enough dissolved oxygen.
