4.2 Energy flow Flashcards
Diagram showing energy flow
Where do all ecosystems on Earth get energy from?
-Sunlight
-But, the energy that arrives here from our star is useless as energy for consumers, unless it is converted into forms that can be used by living organisms.
Which organisms have evolved to carry out photosynthesis?
Producers such as bacteria, protists, plants and algae have evolved to be able to make pigments, such as chlorophyll, which captures light during the light-dependent reactions of photosynthesis.
How can some organisms carry out photosynthesis?
-Producers such as bacteria, protists, plants and algae have evolved to be able to make pigments, such as chlorophyll, which captures light during the light-dependent reactions of photosynthesis.
-This light breaks water, H2O, into protons and electrons, which, via electron transport pathways, ATP synthase and the Calvin cycle, transform carbon dioxide and water into glucose and many other carbon-based compounds.
-This process converts light energy into chemical energy in the form of carbon compounds.
How can organisms use chemicals to generate energy and why would they need to do this?
-There are a few ecosystems that do not directly depend on sunlight as a source of energy because it may not be available.
-If light is not available, photosynthesisers cannot be the starting point of chemical energy. Instead certain organisms use chemicals in their surrounding environments to generate energy in a process called chemosynthesis, where ‘chemo’ has to do with chemicals and ‘synthesis’ means ‘to make’.
-This occurs in ecosystems starting with chemoautotrophs, which include species of bacteria and archaea, some of which are extremophiles living in extreme environmental conditions such as deep-sea hydrothermal vents.
Diagram showing photosynthesis: conversion of light energy into chemical energy in the form of structural plant material and glucose
What is the carbon from photosynthesis used for?
-Some of the carbon compounds are used by the producers in cellular respiration to generate energy in the form of ATP for their own use; heat loss occurs during this process.
-Most of the carbon compounds made by producers end up as cell walls and other structural components.
-The energy contained in these structural components is available to heterotrophs.
-For instance, when deer eat leaves, they consume converted solar energy.
-In this way, the energy from the sun that had entered the ecosystem via the producers, is passed through feeding relationships among organisms.
What is the energy that is contained in the carbon compounds consumers ingest used for?
Cellular activities e.g.:
-Nucleic acid and protein synthesis
-Ion exchange across membranes
-Cell division for reproduction, growth and repair
-Movement of components within cells.
What form is energy needed in for cellular activities e.g. protein synthesis?
ATP
How is ATP produced?
By oxidising, or breaking down, glucose and other carbon compounds through the process of respiration.
Describe the use of ATP in cellular activities
-For all of these cellular activities, energy is needed, usually in the form of ATP.
-This ATP is immediately available to organisms as energy for cellular processes.
Explain how heat is lost in the production of ATP (check)
-None of the oxidative steps are 100% efficient, so heat is lost at each of the many steps.
-It should be noted that living organisms cannot convert heat to other forms of energy, thus they release it in their immediate surroundings.
-You may notice how a room becomes warmer when there are more people in it, especially if more work, for example, exercise, is being done by those people.
-Exercise creates a need for more energy, therefore more respiration is required to create ATP, which means more oxidative steps where heat can be lost.
How is heat lost through respiration in ecosystems?
-All organisms in an ecosystem respire, during which energy is lost to their immediate surroundings as heat.
-Therefore, heat is lost from ecosystems.
-An ecosystem is the abiotic, or non-living, environmental factors plus the biotic, or living, environmental factors, which is the community of living organisms.
-When heat is lost from the living organisms, it is released to their surrounding environment.
Explain how energy is lost between trophic levels
-Chemical energy is made, then used by producers as energy for their own cellular processes, structural components and growth, while some is lost to the environment as heat.
-Therefore, the energy available to the primary consumer is much less than the total energy fixed by the producer through photosynthesis.
-When a primary consumer is eaten by a secondary consumer, or dies and is consumed by detritivores and saprotrophs, again, not all energy can be used.
-The sequence of energy flow from producers through consumers is called a food chain.
What is a food chain?
-A model that shows how nutrients and energy are passed from producer to primary consumer, then secondary consumer, and so on.
-It clearly shows how each organism in the chain gets its food as well as the direction the energy flows through the chain.
-Food chains generally begin with plants and end with animals.
What is the role of producers (autotrophs) in food chains?
-Producers, or autotrophs, are always the first organism in a food chain because they do not feed on anything, they produce their own food as carbon compounds using energy from the sun.
-The successive consumers, or heterotrophs, obtain energy from these carbon compounds in the organisms on which they feed.
Flow of energy in a food chain
Producer ⇒ primary consumer ⇒ secondary consumer ⇒ tertiary consumer
The arrows always point in the direction of nutrient and energy flow.
Each of these steps represents a trophic level.
Which trophic level is usually the top predator?
-The last organism in the food chain, for example, the tertiary consumer, is usually the top predator.
-However, detritivores and saprotrophs could break down the organisms at any trophic level in the food chain if that organism were to die.
Define a trophic level
A word coming from the Greek word trophikós which means to nourish and refers to the position of an organism in a food chain (where the producer belongs to trophic level 1).
Diagram of a simple food chain
In the food chain depicted below, the grizzly bear is the tertiary consumer, however, it is in the fourth trophic level of the food chain.
In this example, the grizzly bear is at the top of the food chain.
Food webs
-These are models of ecosystems that represent many different food chain possibilities and, therefore, show how they are interconnected.
-Most organisms have more than one food source and may have more than one predator.
-This is shown more clearly by using a food web.
-Also, you can see how some organisms may fit into more than one trophic level depending on their food source.
-Like the food chain, the arrows point in the direction of energy flow.
Define a food web
-A food web shows the interconnections that exist among food chains.
-In a food web, each organism may have several sources of nutrition or may be a source of nutrition for several other organisms.
Diagram of a food web including the trophic level numbers
Food webs for exam
-You should be able to create and label your own food chain and food web using specific organism names and make sure it is realistic with at least four trophic levels.
-Don’t forget to add arrows that point in the direction of energy flow.
Diagram of a simplified energy flow
Which organism(s) in the food web below is (are) both secondary consumer(s) and tertiary consumer(s)?
Eagle and fox
To what other energy transfer is the energy transfer level from the woodlice to the moles the same as?
The same as the energy transfer from the slugs to the skunks.
Woodlice and slugs are in the same trophic level and are both primary consumers. Moles and skunks are also in the same trophic level and are both secondary consumers in the food web.
Diagram of an energy pyramid showing the percentage of energy that is present at each level
Diagram of a pyramid of energy for a typical grassland ecosystem.
The units here are megajoules, MJ, rather than kilojoules, where 1kJ=0.001MJ, because these ecosystems contain a greater amount of energy.
Exceptions to the tiered step model that an ecological pyramid of numbers typically represents
-In the temperate forest below, the producers, although low in numbers are large in comparison to the primary consumers. Imagine that these are caterpillars living on a large oak tree.
-The tree is able to support many caterpillars because of its sheer size.
-However, if the producer was feeding a much larger primary consumer, this could be a problem.
-For example, if there were only a few patches of grass on an African grassland, zebras may have a hard time finding food and could face starvation.
Diagram showing examples of biomass pyramids for different ecosystems
Diagram showing how both energy and nutrients flow through an ecosystem
Identify level B of the numbers pyramid below:
Secondary consumer
