Energy and ecosystems
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Practical skills
Control systems
Origins of genetic variation
Modern genetics
Microbiology and pathogens
Energy for biological processes
Exchange and transport
Surface area to volume ratio and gas exchange
Cell membrane structure and permeability
Simple and facilitated diffusion
Osmosis and investigating water potential
Active transport and co-transport
Gas exchange in fish, insects, plants and humans
Mammalian circulatory system and blood vessels
Haemoglobin and the Bohr effect
Heart structure and the cardiac cycle
Heart rate regulation and electrocardiograms
Transport in plants - xylem
Transport in plants - phloem
Classification and biodiversity
Cells, viruses and reproduction of living things
Biological molecules
Carbohydrates: types, structure and function
The structure and function of lipids
The structure and function of proteins
Nucleic acids: DNA and RNA
DNA replication
DNA, genes and chromosomes
RNA, protein synthesis and the genetic code
Enzymes: activation energy, properties and structure
Factors affecting enzyme activity
Inorganic ions: iron, hydrogen, sodium and phosphate
The properties and functions of water
Explainer Video
Summary
Energy and ecosystems
In a nutshell
Producers are the starting point in an ecosystem as they use energy from the sun to produce the biomass that will then be passed down the food chain. However, not all of the energy will be transferred to the next trophic level. This summary explains the reasons for this and how productivity can be calculated.
Ecosystems
Definition
An ecosystem is all living organisms and the abiotic factors in an area.
Producers use light energy and carbon dioxide to produce organic molecules, such as glucose, in a process known as photosynthesis. This glucose can then be used to produce biological molecules, such as starch and cellulose. These biological molecules make up the plant's biomass.
Energy is passed through an ecosystem when organisms eat one another. Primary consumers are herbivores that eat the producers. Then, secondary consumers eat the primary consumers. The tertiary consumers will eat the secondary consumers and so on.
Biomass
Definition
Biomass is the total mass of living material in a specific area at any specific time. When biomass is being measured in an area like a grassland, the unit of measurement is grams per square metre (). When biomass is being measured in an area like a pond, the unit of measurement is grams per cubic metre ().
How to measure biomass
Biomass can be measured in two ways. These are explained below.
Dry mass | A sample of an organism is taken and heated in an oven. The mass is measured every day and the dry mass is reached when the mass becomes constant. This is because all of the water has evaporated. |
Calorimetry | The chemical energy stored in the biomass can be estimated using a bomb calorimeter. A sample of dry material is burnt and the energy that is released will heat a known volume of water. It is known how much thermal energy is required to raise the temperature of of water by . Therefore, the energy released from the biomass can be calculated. The units for this method would be . |
Efficiency of photosynthesis
Photosynthesis is not a efficient process as not all of the light energy that hits the leaf is used. This is shown below.
Primary production
Gross primary production
Gross primary production (GPP) is the amount of chemical energy stored in plant biomass in a given area (or volume) and in a given time.
Net primary primary production
Plants will use between and of their total energy on respiration. Therefore, net primary production (NPP) is the amount of energy left for growth and reproduction. This energy is also what is available for organisms in the next trophic level.
Calculating primary production
Note: Primary production is often measured in (which means kilojoules per hectare per year) or
Example
What is the net primary productivity of trees in an ecosystem when their gross primary productivity is and is lost as heat through respiration?
Secondary production
Secondary production is the net production of consumers. Consumers gain energy through eating plant matter or other matter that has consumed plant matter. However, around of the consumed energy is not transferred to the next trophic level. There are many reasons for this and some are explained below.
Reason | Explanation |
| Not all of the plant gets eaten | Some parts of the plant like the roots and twigs may not be eaten by the animals. |
| Some of the energy is egested | Animals may be unable to digest molecules like cellulose as they don't have the correct enzymes to do so. Therefore, they will be egested in faeces. |
| Respiration | A lot of the energy intake of a primary consumer will be lost during respiration. |
| Chemical reactions | Primary consumers may need to regulate their body temperature. This process requires energy and this will mean there is less energy to pass to the next trophic level. |
Calculating secondary production
| | Net production. |
| | Chemical energy from ingested food. |
| | Chemical energy lost in faeces and urine. |
| | Energy lost through respiration. |
Example
What is the net productivity of squirrels in a woodland ecosystem if they ingest of energy but lose through faeces and urine and lose a further through respiration?
Calculating the efficiency of energy transfers
The efficiency of energy transfers between trophic levels can be calculated.
Example
The NPP of grass was . The net productivity of the grasshoppers that eat the grass is . What is the efficiency of this energy transfer?
Farming practices impacting production
In order to maximise the amount of energy their crops are able to transfer to humans, farmers can reduce the number of pests and the losses from respiration.
Reducing pests
Pests will reduce the biomass of the crops so farmers can target these to increase the energy available for the plant to grow.
Control method | Explanation |
| Insecticides | Insecticides are chemicals that kill the pests, which means they won't be able to feed on the crops. As a result, there will be more energy available for the plant to use to grow. This will result in a higher NPP. |
| Herbicides | Herbicides are chemicals that kill weeds, which will reduce competition for light. As a result, the crops can photosynthesise more as there is more light available. This will increase the amount of glucose produced and also the biological molecules that plants use glucose to produce. As a result, the NPP will increase. |
| Parasites | Parasites can infect pests or they can lay their eggs on the pests. This will reduce the number of pests. ExampleSome wasps can lay their eggs inside caterpillars. When the eggs hatch, the caterpillar is killed. |
| Pathogenic bacteria and viruses | Bacteria and viruses can infect the pests and reduce their population size. ExampleBacillus thuringiensis produces a toxin called Bt. This toxin kills caterpillars. |
Reducing loss from respiration
to of the total energy of an organism can be lost through respiration. Farmers can reduce the amount of energy lost through respiration and therefore increase the amount of energy transferred to humans through consumption. They achieve this through limiting activities that may increase the rate of respiration.
Examples
- Animals respire more when they move around, so farmers may limit the movement of their animals.
- Maintaining body temperature requires energy and this energy is transferred through respiration. Farmers can therefore keep their animals inside in warmer conditions to reduce this respiration loss.
However, the examples described above have ethical issues surrounding them as some may argue that keeping the animals in an environment that is unlike their natural environment is inhumane. The animals may also be distressed.
FAQs - Frequently Asked Questions
What is net primary production?
Net primary production (NPP) is the amount of energy left for growth and reproduction. This energy is also what is available for organisms in the next trophic level.
How do herbicides increase the NPP?
Herbicides are chemicals that kill weeds, which will reduce competition for light. As a result, the crops can photosynthesise more as there is more light available. This will increase the amount of glucose produced and also the biological molecules that plants use glucose to produce. As a result, the NPP will increase.
What is an ecosystem?
An ecosystem is all living organisms and the abiotic factors in an area.