Topic 5: On the Wild Side Flashcards
(37 cards)
5.1 Explain the term ‘ecosystem’.
A biological community of interacting organisms and their physical environment. It includes both abiotic and biotic factors.
5.1 Explain the term ‘habitat’.
Habitat is the place, with a distinct set of conditions, where an organisms lives.
5.1 Explain the term ‘population’.
A population consists of all the organisms of the same species living in a particular area (habitat), with the capability of interbreeding.
5.1 Explain the term ‘community’.
A community consists of all of the organisms of different species (various populations) that live in the same habitat and interact with each other.
5.2 How is the abundance of organisms in a habitat controlled by abiotic factors?
The abundance of any species varies because of abiotic factors:
- the amount of light (which is in turn affected by latitude, season, cloud cover and changes in the Earth’s orbit)
- climate i.e. the rainfall, wind exposure and temperature
- topograpy, which includes altitude (and this affects the climate), slope, aspect (which direction the land is facing) and drainage
- oxygen concentration
- the soil pH, texture and mineral ion concentration
- pollution of the air, water or land
When abiotic conditions are ideal for a species, organism can grow fast and reproduce successfully, increasing their population size (and vice versa).
5.2 How is the abundance of organisms in a habitat controlled by biotic factors?
- Interspecific competition is when organisms of different species compete with each other for the same resources. This can mean that the resources available to both populations are reduced. The populations might be limited by lack of a particular resource, and have less energy for growth and reproduction: so the population size will decrease.
- Intraspecific competition is when organisms of the same species compete with each other for the same resources. The population of a species increases when resources are plentiful. Eventually resources will become limiting, and the population will begin to decline. A smaller population results in less competition for resources, which is better for growth and reproduction: so the population starts to grow again.
- Predation is where an organism (the predator) kills and eats another organism (the prey). The population sizes or predators and prey are interlinked. As the prey increases, the predator population increases (because more food is available). As the predator population increases, the prey are eaten and their population begins to decrease. This means there’s less food for the predators, so their population decreases.
- Grazing is a method of feeding in which a herbivore feeds on plants such as grasses, or other multicellular organisms such as algae.
- Parasitism is a non-mutual relationship between species, where one species, the parasite, benefits at the expense of the other, the host
5.2 How is the distribution of organisms in a habitat controlled by abiotic and biotic factors?
Organisms only exist where the abiotic factors they can survive in exist. Interspecific competition (a biotic factor) can also affect the distribution of species: if two species are in competition, but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.
5.3 Explain how the concept of niche accounts for distribution and abundance of organisms.
A niche can be defined as the way an organism exploits its environment. The niche a species occupies within an habitat includes its interactions with other living organisms, and its interactions with non-living organisms. Every species occupies its own unique niche.
The abundance of a different species can be explained by the niche concept: two species occupying similar niches will compete, so fewer individuals of both species will be able to survive in the area.
The distribution of different species can also be explained by the niche concept: organisms can only exist in habitats where all the conditions that make up their role exist.
5.4 Outline the stages of primary succession.
Primary succession begins in newly formed or exposed land, where there has never been a community before. 1. Seeds and spores are blown by the wind and begin to grow - the first species to colonise the area are called pioneer species. The pioneer species are specially adapted to cope with the hostile abiotic conditions (e.g. there’s no soil to retain water or nutrients, as well as a high salt concentration).
2. The pioneer species change the abiotic conditions as they die: microorganisms decompose the dead organic matter, forming a basic soil.
3. As the conditions become less hostile, the seeds of new organisms with different adaptions move in and grow. As these organisms die and decompose, the accumulation of organic matter in the soil increases the mineral ion content and water-holding capacity.
4. Larger and more complex organisms begin to move in. New species can change the environment so that it becomes less suitable for previous species.
At each stage, different organisms that are better adapted for the improved conditions move in, and out-compete the species already there.
Succession proceeds until a stable climax community is established. The nature of the climax community depends on the environmental conditions, such as climate, soil and species availability. While the number of niches increases as succession progresses, often the climax community will have lower biodiversity than preceding stages in the succession (as dominant species outcompete others).
5.4 Explain what the difference between primary succession and secondary succession is.
Succession is the process by which an ecosystem changes over time. The biotic conditions change as the abiotic conditions change.
Primary succession begins in newly formed or exposed land, where there has never been a community before.
Secondary succession takes place on bare soil, where a previously existing community has been cleared. The pioneer species tend to be larger organisms than in primary succession (as the initial abiotic conditions are less hostile).
5.5 Explain the overall reaction of photosynthesis.
Photosynthesis:
6CO2 + 6H2O (+ energy) → C6H12O6 + 6O2
The overall reaction of photosynthesis requires energy from light to split apart the strong bonds in water molecules (photolysis). Hydrogen (from the breakdown of water) is then combined with carbon dioxide, reducing it, to form a carbohydrate fuel, glucose. Hydrogen is therefore effectively stored in the fuel glucose, with oxygen being released into the atmosphere as a waste product. Glucose can later be oxidised during respiration to release energy.
5.6 Outline the phosphorylation of ADP and the hydrolysis of ATP.
During respiration, glucose is oxidised to release energy. This energy is then used to make ATP in a phosphorylation reaction:
ADP(aq) + Pi(aq) (+energy) → ATP(aq)
In solution, the inorganic phosphate ions are hydrated (i.e. they are bonded to water). In the formation of ATP, the inorganic phosphate ions are separated from water: a large amount of energy is required to break these bonds.
ATP synthase then catalyses the phosphorylation of ADP into ATP. ATP(aq) is higher in energy than ADP(aq) and Pi(aq). So ATP in water stores energy in the form of chemical potential energy.
When energy is required (e.g. for metabolic reactions), ATP is hydrolysed:
ATP(aq) → ADP(aq) + Pi(aq) (+energy)
While a small amount of energy is initially required to remove the phosphate group from ATP, once removed the phosphate group hydrated: a large amount of energy is released as bonds form between the inorganic phosphate ion and water. ADP is now formed.
Phosphorylation is the addition of phosphate to a molecule.
Hydrolysis is the splitting of a molecule using water.
5.7 Outline the light-dependent reaction in photosynthesis.
In the thylakoid membranes, photosynthetic pigments are arranged in photosystems (PSI and PSII).
When light is absorbed by PSII, the energy raises the electrons in the chlorophyll to a higher energy level. They are now in an ‘excited’ state. These electrons move down the electron transport chain (to PSI).
The electrons in PSII now need replacing. Light energy splits water molecules into protons, electrons and oxygen: H2O → 2H+ + 2e- + 1/2O2
The electrons produced replace those in PSII.
The protons are used in chemiosmosis: as the excited electrons from PSII move down the electron transport chain, going from one electron carrier to another in a series of redox reactions, energy is released. This energy is used by the electron carriers to pump protons from the stroma into the thylakoid space. This creates a steep electrochemical gradient across the thylakoid membrane. Protons move down the electrochemical gradient, back into the stroma, via the enzyme ATP synthase: this synthesises ATP from ADP and Pi in non-cyclic photophosphorylation.
Light energy is absorbed PSI, raising the electrons to an even higher energy level. These electrons, along with the protons from the stroma, combine with NADP to form reduced NADP.
5.7 Outline cyclic photophosphorylation.
Cyclic photophosphorylation only uses PSI. In cyclic electron flow, the electron begins PSI, passing from one electron carrier to another, down an electron transport chain, and then returning to the chlorophyll. This energy is used by the electron carriers to pump protons from the stroma into the thylakoid space. This creates a steep electrochemical gradient across the thylakoid membrane. Protons move down the electrochemical gradient, back into the stroma, via the enzyme ATP synthase: this synthesises ATP from ADP and Pi in non-cyclic photophosphorylation. Cyclic photophosphorylation produces neither O2 nor NADPH (unlike non-cyclic photophosphorylation, NADP+ does not accept the electrons).
5.8 i) Outline the light-independent reaction in photosynthesis.
Carbon dioxide is reduced using the products of the light-dependent reaction. The CO2 enters the leaf through the stomata and diffused into the stroma of the chloroplast.
1) In a reaction catalysed by RuBISCO, CO2 [1C] combines with ribulose bisphosphate (RuBP), a [5C] compound, to form an unstable 6C compound.
2) This rapidly breaks down into two molecules of the 3C compound, glycerate-3-phosphate (GP).
3) The hydrolysis of 2ATP (from the light-dependent reaction) provides energy to turn 2GP into 2 molecules of a different 3C compound, glyceraldehyde 3-phosphate (GALP). This is a reduction reaction, requiring 2H+ ions, provided by 2 reduced NADP molecules (from the light-dependent reaction). 2ADP, 2Pi and 2NADP are also produced.
4) Two molecules of GALP can be used to make a hexose sugar (e.g. glucose).
5) Five out of every six molecules of GALP produced in the cycle are used to regenerate RuBP. This requires ATP.
Overall:
6CO2 [1C] + 6RuBP [5C] (+ RuBISCO) = 12GP [3C] (+ 12NADP + 12ATP) = 12GALP [3C]:
2GALP [3C] = Glucose [6C]
10GALP [3C] (+ 6ATP) = 6RuBP [5C]
5.8 ii) Discuss how the products of respiration are used in biological synthesis.
The Calvin cycle involves carbon fixation: where the carbon dioxide is incorporated into organic molecules. The products are simple sugars used by plants, animals and other organisms in respiration and the synthesis of biological molecules (polysaccharides, amino acids, lipids and nucleic acids).
- Carbohydrates: simple sugars (e.g glucose) are made from 2 GALP molecules, and polysaccharides are made by joining hexose sugars together.
- Lipids are made using glycerol (which is synthesised from GALP) and fatty acids (which is synthesised from GP).
- Amino acids can be made from GP.
- Nucleic acids: the sugar in RNA (which is ribose) is made using GALP.
5.9 Outline the structure of chloroplasts in relation to their role in photosynthesis.
The site of photosynthesis is in the chloroplast. Chloroplasts are flattened organelles found in plant cells.
1) They have a double membrane called the chloroplast membrane - this keeps the reactants for photosynthesis close to their reaction sites. While the outer membrane is freely permeable to molecules such as CO2 and H2O, the inner membrane contains transporter molecules (membrane proteins) which regulate the passage of substances in and out of the chloroplast.
2) Thylakoids (fluid-filled sacs) have a large surface area to allow as much light energy to be absorbed as possible. The thylakoid space contains enzymes for the photolysis of water. Photosystems, electron carriers and ATP synthase are all embedded in the thylakoid membrane (to produce reduced NADP and ATP in the light-dependent reaction). Thylakoids are stacked up into structures called grana (singular: granum), linked together by bits of thylakoid membrane called lamellae (singular: lamella).
3) The stroma is the fluid surrounding the thylakoid membranes. It contains all the enzymes required for the light-independent reaction to take place. The compartmentalisation of these reactions within the stroma means that enzymes and substrates can be at concentrations that allow the reactions to be catalysed quickly.
4) Chloroplasts contain genes for some of their proteins (i.e. a DNA loop/plasmid).
[Photosynthetic pigments, including chlorophyll, combine with proteins to form a photosystem]
- 10 i) How is net primary productivity calculated?
ii) Outline the relationship between gross primary productivity, net primary productivity, and plant respiration.
NPP = GPP - R
The rate at which energy is incorporated into organic molecules by an ecosystem is the gross primary productivity (GPP) i.e. the total energy absorbed by the autotroph (producer).
Some of this energy is released in respiration (where respiratory substrates, such as the carbohydrate fuel glucose, are broken down). The rest of the energy becomes new plant biomass.
The rate at which energy is transferred into the organic molecules that make up the new plant biomass is called net primary productivity (NPP) i.e. this is the amount of energy available (at one trophic level) for the next trophic level.
5.11 Outline how energy is transferred through ecosystems, explaining the role of each group in a food chain.
Producers are autotrophic organisms, capable of producing complex organic compounds from simple inorganic molecules through the process of photosynthesis. When carbon dioxide is fixed (or incorporated) into organic molecules that make up biomass, the energy fixed within these molecules can be transferred to other organisms in the ecosystem - this happens when organisms eat other organisms.
- Primary consumers (which tend to be herbivores), secondary consumers, and tertiary consumers (both of which tend to be carnivores) are all heterotrophs.
- Detritivores are primary consumers that feed on dead organic matter called detritus (e.g. woodlice and earthworms).
- Decomposers are species of bacteria and fungi that feed on the dead remains of organisms and animal faeces.
- The position a species occupies in a food chain is called its trophic level.
5.11 Explain why only 10% of the energy available at a previous trophic level is transferred to the next trophic level.
The position a species occupies in a food chain is called its trophic level. The energy available in one trophic level is called the net productivity (or biomass). However not all energy gets transferred to the next trophic level:
- 60% of the available energy at each trophic level is not taken in by the next trophic level:
1. Autotrophs don’t use all the light energy available e.g. some is the wrong wavelength, some is reflected off the leave or passes through the leaf, and some misses the leaf.
2. Some parts of feed (e.g. roots or bones), aren’t eaten by organisms so the energy isn’t taken in, and decomposers break down the dead or undigested material.
3. Some food indigestible and comes out as waste (e.g. faeces).
About 40% of the energy from a previous trophic level is taken in to the next trophic level, as gross productivity. However:
1. 30% of this energy is then lost to the environment when organisms use energy produced from respiration for movement or body heat (respiratory loss).
2. 10% of the energy taken becomes biomass (e.g. it’s stored or used for growth). This is called net productivity.
5.11 Outline how to calculate the efficiency of biomass and energy transfer.
Net productivity (the biomass/energy available in one trophic level) = gross productivity (the energy taken in from the previous trophic level) - respiratory loss
To calculate how efficient energy transfer from one trophic level to another is:
(Net productivity or biomass / gross productivity or energy received ) x 100
To calculate the energy transfer between two trophic levels you need to calculate the difference between the amount of energy in each trophic level (the net productivity of each level): first calculate the amount of biomass in a sample of the organisms. Then multiply this by the size of the total population. The difference in energy between the trophic levels is the amount of energy being transferred. However, there are problems: consumers might have taken in energy from sources other than the producer measured.
5.12 Outline how records of both carbon dioxide levels and temperature form evidence for climate change.
Temperature records show a general trend of increasing global temperature over the last century. The temperature around the globe is measured using thermometers, giving it a reliable, if short-term record of global temperature change.
The carbon dioxide levels are similarly measured around the world, and show a correlating increase. It is generally assumed that an increase in CO2 results in an increase in global temperature. However, the difference between correlations (a common relationship between two variables) and causation (when a change in one variable caused a change in another variable) should be evaluated when given such data.
5.12 Outline how dendrochronolgy can form evidence for climate change.
2) Dendrochronolgy determines how old a tree is using tree rings. Most trees produce one ring within their trunks every year. The thickness of the ring depends on the climate when the ring was formed (i.e. in a warmer climate, the conditions for growth are better and so the ring is thicker). Scientists can take cores through tree trunks, and date each ring. The thickness of the rings reveals what the climate was like each year i.e. the most recent rings are usually the thickest.
5.12 Outline how pollen from peat bogs can form evidence for climate change.
3) Pollen is often preserved in peat bogs (due to the anaerobic and often acidic conditions of peat bogs slowing down the rate of decay). Peat bogs accumulate in layers so the age of the preserved pollen increases with depth. Scientists can take cores from peat bogs and extract pollen grains from the different aged layers. They then identify the plant species the pollen came from. Only fully grown (mature) plants produce pollen, so the samples only show the species that were successful at the time. Because plant species vary with climate, the preserved pollen will vary as climate changes over time e.g. a gradual increase in pollen from a plant species that’s more successful in warmer climates, or a decrease in pollen from a plant that needs cold climates, would show a rise in temperature.
