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How does energy from the sun enter the ecosystem?
- Plants photosynthesise, converting light energy into glucose
- The glucose is then converted to organic matter
What is a producer?
Any organism capable of photosynthesis
What happens to the primary consumers?
- They are consumed by secondary consumers
- Secondary consumer are consumed by tertiary consumers etc
What is the simplest way of representing feeding relationships?
Using a food chain
Give an example of a food chain
Grass > Caterpillar > Robin > House-cat
What do the arrows in a food chain represent?
The direction the energy flows
What are ecological pyramids?
Quantitive diagrams where the width of the bars represents the amount of energy in each trophic level
What do pyramids of number display?
The number of organisms in a particular area
Why are pyramids of number not always pyramid shaped
Large producers can support many consumers in some cases
What does a pyramid of Biomass display?
The dry mass of organisms in a particular area in kg/m2
Why are pyramids of biomass always pyramidal?
Energy is always lost between trophic levels
Why is biomass lost between trophic levels?
- Respiration oxidising glucose to carbon dioxide and water
- Inedible parts of animals not being eater (lignin, bones)
- Indigestible matter that is eaten but not absorbed then excreted as faeces
What do pyramids of energy display?
The energy contained in the biomass in a particular area during a particular time (kJ/m2/year)
Why are pyramids of energy always pyramidal?
Energy is always lost between trophic levels
How is energy lost by plants?
- Sunlight may not be used by the leaf in photosynthesis (only 2% of light that hits the leaf is converted into sugar)
- Light passes through the leaf without being absorbed by chlorophyll
- Some wavelengths of light cannot be used for photosynthesis (green light)
- Light is reflected by the leaf
- Limiting factors e.g. carbon dioxide
What is the glucose not converted into starch used for by plants?
Used for the glycolysis and respiration
What percentage of plant energy is typically incorporated into herbivore biomass?
Why is such a small percentage of plant energy converted into herbivore biomass?
- Some energy is lost as heat during respiration
- Not all of the plant material will be eaten
- Not all of the plant can be digested (cellulose) so energy is lost in faeces
What percentage of herbivore energy is converted into carnivore biomass?
Why is a small percentage of herbivore energy converted to carnivore biomass?
- Some energy is lost as heat during respiration
- Not all material is eaten (bones)
- Some energy is lost in faeces although protein is very digestible
What should one never say in relation to energy and photosynthesis?
- Energy is used for photosynthesis
- Say energy is lost as heat during respiration instead
What is primary productivity?
- The amount of energy converted from light energy into chemical energy in 1 m2 over a year in kJ/m2/year
What is an alternate measurement for primary production?
Amount of new plant biomass in 1m2 in one day measured in g/m2/day
What is the GPP?
The gross primary productivity: the rate at which the products of photosynthesis accumulate
What is the NPP
- The net primary productivity: the amount of biomass available as food
- Plants use some of the products of their photosynthesis for respiration
Write a word equation for Net primary productivity
NPP = GPP - respiratory loss
Name 5 biotic and abiotic factors that affect productivity
- Light intensity
- Availability of minerals
- Competition from other species
- Damage by pests
- Water availability
What is the energy input for a natural ecosystem?
What is the energy input for a farm ecosystem?
- Solar energy
- Chemical energy as food for workers
- Fossil fuels for machinery
Describe the productivity of a natural ecosystem
- Low due to:
- Higher rates of competition
- Increased damage by pests
- Reduced availability of minerals
Describe the productivity of a farm ecosystem
- High due to:
- Pesticides removing competition and pests
- Fertilisers increasing the availability of minerals
Describe the diversity of a natural ecosystem
High due to a variety of niches
Describe the diversity of a farm ecosystem
Low due to monoculture
What do fertilisers provide for plants?
- Nitrates for amino acid synthesis
- Phosphates for synthesising DNA, RNA and ATP
- Potassium for maintaining the balance of positive and negative ions in and out of the cells
What will happen to productivity of plants if mineral ions are in short supply?
- They will become a limiting factor
- Productivity will decrease
How may fertilisers have negative effects on plants?
If too much is added the water potential in the soil may be affected
Why is less fertiliser than the amount needed for maximum productivity added?
- Fertiliser is expensive
- The slight increase in yield is not worth the increase in costs
Give 3 examples of natural fertiliser
- Animal manure
- Sewage sludge
What are the advantages of natural fertiliser?
- Feeds soil microbes important in the nitrogen cycle
- Improves humus content of the soil allowing it to hold more water and reduce leeching of minerals during rainfall
- Releases minerals over a long period
- Less soluble than inorganic- not leeched as easily
What are the disadvantages of natural manure?
- Bulky to store
- Difficult to apply to the land
- Farmer cannot know the ratio of Nitrogen Potassium and Phosphor
- Takes time for microbes to convert it into nitrates
What are the advantages of artificial (inorganic fertiliser?
- High nutrient content
- Precise ratios of Potassium, Phosphor and Nitrogen
- Soluble and releases minerals quickly
- Easy to store
What are the disadvantages of inorganic fertiliser?
- Does not improve humus levels of soil
- Easily leeched from the soil after rainfall
What are pesticides?
Chemicals which kill insects
What are the advantages of pesticides?
- Can potentially kill all pests on a crop
- Starts working immediately
What are the disadvantages of pesticides?
- Leaves residue on crops which can be poisonous to humans
- Will kill all insect species including helpful ones that eat other insects or pollinators, this also reduces food supplies for consumers such as birds
- Insects can evolve resistance to the pesticide
- Vary in how long they take to be broken down by bacterial enzymes and biodegrade
How could the use of a pesticide lead to bioaccumulation?
- If used in low concentrations some pests are not killed but contain low concentrations of the chemical
- Predators such as birds eat many of these insects and the pesticide accumulates in their fat stores
- Large predators eat many of the birds and levels of the pesticide in fat stores becomes fatally high
What is a biological control?
The introduction of a natural predator or parasite of the insect pest that will kill it
What are the advantages of biological control?
- It is specific to the pest species
- Cheaper as it only needs to be applied once and it can then reproduce rather than regular applications of chemicals
- Reduces the use of insecticides so pests are less likely to develop resistance
- No toxic residue left on plants
What are the disadvantages of biological controls?
- Takes time for the biological control organisms to reach numbers that reduce pest numbers
- Pest numbers will never reach 0 due to predator-prey relationships
- Control organism may become a pest due to the absence of a natural predator (cane toad)
What does integrated pest management combine?
- Chemical pesticides (starts work immediately whilst control organisms are reproducing)
- Biological control
- Selecting crops for pest resistance
- Providing habitats for natural predators (hedgerows)
What is intensive rearing of livestock?
Farming practices which increase the efficiency of energy transfer through a food chain by reducing energy losses between trophic levels
When are intensively reared livestock slaughtered?
When they are young and growth rates are highest
What are intensively reared livestock fed on?
Concentrates which are very digestible, reducing energy lost in faeces
How is movement of intensively reared livestock controlled?
- Movement is restricted with animals kept in pens
- Reduces energy lost as heat through muscle contractions
How is the environment controlled for intensively reared livestock?
- Environment is kept warm
- Reduces energy lost as heat
How are growth rates affected for intensively reared livestock?
Growth hormones are used to increase growth rates
How is breeding controlled for intensively reared livestock?
- Selective breeding is implemented
- Varieties are produced that convert more food to biomass
What are the advantages of intensive rearing?
- Less energy is lost so more is passes to humans in the food chain
- Food is cheeper due to reduced energy losses
- Less land is taken up for pasture meaning there is less deforestation and more biodiversity
What are the disadvantages of intensive rearing?
- Animals are raised in unnatural conditions which can cause stress, discomfort and aggressive behaviour
- Close proximity of animals means faster spread of pathogens
- More energy from fossil fuels is required in order for pens to be heated, increasing global warming
- Selective breeding leads to a lack of genetic variation
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