C4.2 Transfers of energy and matter Flashcards
C4.2.1—Ecosystems as open systems in which both energy and matter can enter and exit
in closed systems only energy is able to pass in and out. eg . Earth is a closed
Ecosystems areopen systems, meaning thatboth energy and matter can enter and exit the system
C4.2.2—Sunlight as the principal source of energy that sustains most ecosystems
Sunlight as the principal source of energy that sustains most ecosystems
Exception: Food chains located indeep sea volcanic ventsandunderground caveswhere no light can penetrate; these rely on bacteria gainingenergy from chemical processes
C4.2.3—Flow of chemical energy through food chains
Students should appreciate that chemical energy passes to a consumer as it feeds on an organism that is
the previous stage in a food chain
energy from the sun is captured by plants/autotrophs;
light energy is converted to chemical energy by photosynthesis;
energy is passed to animals/consumers/along the food chain;
at each stage in the food chain energy is lost by respiration/as heat;
much less energy/only about 10
% is available at each stage/trophic level of the food chain;
some energy is made available to decomposers when organisms die/parts fall to the ground;
energy cannot be recycled; nutrients can as inorganic to organic.
energy is non-recyclable/lost from a community/ecosystem;
communities are made up of populations of different species;
C4.2.4—Construction of food chains and food webs to represent feeding relationships in a community
Represent relationships in a local community if possible. Arrows indicate the direction of transfer of energy
and biomass. arrow = transfer of energy
use:
Advantages:
a. food webs summarize all possible food chains «in the community» ✔ OWTTE
b. realistic representation ✔
Limitations:
c. some communities/ecosystems are too complex to represent ✔
d. only shows qualitative information/not quantitative data
C4.2.5—Supply of energy to decomposers as carbon compounds in organic matter coming from dead
organisms
Include faeces, dead parts of organisms and dead whole organism - all get eaten by decomposers
saprotrophs and detritivores
C4.2.6—Autotrophs as organisms that use external energy sources to synthesize carbon compounds from
simple inorganic substances
Students should understand that energy is required for carbon fixation and for the anabolic reactions that
build macromolecules.
understand photosynthesis
Describe how autotrophs absorb light energy
[3]
Markscheme
a. light absorbed by (photosynthetic) pigments;
b. chlorophyll absorbs blue and red / drawing of absorption spectrum for chlorophyll;
c. photosystems are groups of pigment molecules/are light harvesting complexes;
d. photosystems are located in thylakoid membranes;
e. electrons excited/raised to higher energy level;
C4.2.7—Use of light as the external energy source in photoautotrophs and oxidation reactions as the
energy source in chemoautotrophs
Students should understand that oxidation reactions release energy, so they are useful in living organisms.
Include iron-oxidizing bacteria as an example of a chemoautotroph.
- Chemoautotrophsoxidise inorganic chemicalsin the environment to provide electrons for ATP production
- E.g. some bacteria produce ATP byoxidising iron
- Iron(II), or Feis oxidised to iron(III), or Fe
- The donated electrons are used in the production of ATP
- These chemoautotrophs take the role ofproducersin habitats wherelight energy is not available, e.g. in deep sea vents or caves
C4.2.8—Heterotrophs as organisms that use carbon compounds obtained from other organisms to
synthesize the carbon compounds that they require
Students should appreciate that complex carbon compounds such as proteins and nucleic acids are
digested either externally or internally and are then assimilated by constructing the carbon compounds
that are required.
C4.2.9—Release of energy in both autotrophs and heterotrophs by oxidation of carbon compounds in cell
respiration
- Autotrophs produce their own carbon compounds, and heterotrophs gain carbon compounds from other organisms
- The chemical energy stored in these carbon compounds can bereleased by the process ofrespiration
- The carbon compoundglucoseis the fuel for respiration
- Other carbon compounds such as lipidscan be converted into glucosebefore being respired
- Respiration releases energy by theoxidation of carbon compounds
C4.2.10—Classification of organisms into trophic levels
Use the terms “producer”, “primary consumer”, “secondary consumer” and “tertiary consumer”. many organisms have a varied diet and occupy different trophic levels in different food chains.
could be different trophic levels depending on its food source;
to find tropic level for an organism you need to know - what its prey is and what its prey feeds on / what level prey tropic level is -
C4.2.11—Construction of energy pyramids
Application of skills: Students should use research data from specific ecosystems to represent energy
transfer and energy losses between trophic levels in food chains.
energy content in biomass/all organisms of each trophic level;
size of study area included;
over period of time / per year;
C4.2.12—Reductions in energy availability at each successive stage in food chains due to large energy
losses between trophic levels
Decomposers and detritus feeders are not usually considered to be part of food chains. However, students
should understand the role of these organisms in energy transformations in food chains. Consider the
causes of energy loss. respiration - Incomplete consumption
- Incomplete digestion Excretion of the waste products of metabolism e.g. carbon dioxide, water, and urea
C4.2.13—Heat loss to the environment in both autotrophs and heterotrophs due to conversion of
chemical energy to heat in cell respiration
Include the idea that energy transfers are not 100% efficient so heat is produced both when ATP is
produced in cell respiration and when it is used in cells.
C4.2.14—Restrictions on the number of trophic levels in ecosystems due to energy losses
At each successive stage in food chains there are fewer organisms or smaller organisms. There is therefore
less biomass, but the energy content per unit mass is not reduced.
- Loss of heat energy to the environment during respiration
- Excretion of the waste products of metabolism e.g. carbon dioxide, water, and urea and feces
C4.2.15—Primary production as accumulation of carbon compounds in biomass by autotrophs
The units should be mass (of carbon) per unit area per unit time and are usually g m−2 yr−1. Students should
understand that biomes vary in their capacity to accumulate biomass. Biomass accumulates when
autotrophs and heterotrophs grow or reproduce.
C4.2.16—Secondary production as accumulation of carbon compounds in biomass by heterotrophs
Students should understand that, due to loss of biomass when carbon compounds are converted to
carbon dioxide and water in cell respiration, secondary production is lower than primary production in an
ecosystem.
C4.2.17—Constructing carbon cycle diagrams
Students should illustrate with a diagram how carbon is recycled in ecosystems by photosynthesis,
feeding and respiration.
C4.2.18—Ecosystems as carbon sinks and carbon sources
If photosynthesis exceeds respiration there is a net uptake of carbon dioxide and if respiration exceeds
photosynthesis there is a net release of carbon dioxide.
C4.2.19—Release of carbon dioxide into the atmosphere during combustion of biomass, peat, coal, oil and
natural gas
Students should appreciate that these carbon sinks vary in date of formation and that combustion
following lightning strikes sometimes happens naturally but that human activities have greatly increased
combustion rates.
C4.2.20—Analysis of the Keeling Curve in terms of photosynthesis, respiration and combustion
Include analysis of both the annual fluctuations and the long-term trendgoes up fluctuates seasonally but overall trend goes up.
C4.2.21—Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis, and of
photosynthesis on atmospheric carbon dioxide produced by respiration
The fluxes involved per year are huge, so this is a major interaction between autotrophs and heterotrophs
fluxes are The process that transfer carbon are
C4.2.22—Recycling of all chemical elements required by living organisms in ecosystems
Students should appreciate that all elements used by living organisms, not just carbon, are recycled and
that decomposers play a key role. Students are not required to know details of the nitrogen cycle and
other nutrient cycles.
Decomposersbreak down the organic moleculesin dead tissues and waste matter,making them available againto producers
