Sunshine And Fresh Air To Cheese Flashcards
Nitrogen, enters the dairy system via a number of routes (e.g. atmospheric deposition, nitrogen-fixing bacteria or fertiliser.) In what form does it leave the system?
A proportion of the nitrogen makes it through to the end product, cheese, in which it is a component of a major constituent, protein. However, some nitrogen is lost at each stage of the process: litter from plants, urine and faeces from cows and whey from cheese making; so all these aspects can affect the efficiency of the process.
Energy enters the dairy system as sunlight. How does it leave?
Energy from sunlight captured by photosynthesis and stored as chemical energy is then used by all the organisms in the system (plants, animals, fungi and microbes) to fuel their life processes and leaves the system via respiration as heat. A small amount is retained in the end product, cheese, most of which will ultimately be lost as heat via human respiration, having been eaten.
Why are grasses so tolerant to fire and grazing?
The key attribute of a graminoid (meaning ‘grass-like’) plant is that its growing point is kept level with the ground for most of its life and as such is out of reach to most herbivores, and safe from fires that pass across quickly above.
Why do grasses dominate areas regularly disturbed by grazing or fire?
When the shoots have been grazed or burned, the growing tips of graminoids (grasses) can produce a new canopy faster than most dicotyledons (broad-leaved herbs and shrubs), which compete with them for light. Grasses therefore tend to dominate in habitats that are regularly disturbed either by grazing or fire.
What is net primary production and how can the relationship between primary producer respiration be expressed?
This is the total amount of carbon fixed by a stand of vegetation (known as gross primary production, GPP) minus the fraction used by the plants for their own respiration (R). The relationship between these three quantities can be expressed mathematically as: NPP = GPP − R
What is photosynthetically active radiation (PAR)?
The portion of the electromagnetic spectrum in which the wavelength is appropriate to excite chlorophyll and therefore drive photosynthesis. PAR corresponds closely to the visible spectrum for humans and therefore the terms ‘PAR’ and ‘light‘ can often be used interchangeably.
Why do many plants become less efficient at converting energy in strong sunshine?
Because when light energy begins to saturate the cell’s photosynthetic apparatus, the C2 cycle (photorespiration) starts to release some of the fixed carbon back to CO2 in order to protect it.
What are the three main strategies employed by plants for evolutionary survival?
Competitors, stress-tolerators and ruderals.
Outline the methods employed by competitors as a plant survival strategy.
Competitors have evolved to survive in environments with relatively optimal conditions for growth, in which a large number of species have the potential to grow well. The main threat to survival, therefore, is the presence of a neighbouring plant which may use some of the available resources. Plants with a competitive strategy have developed rapid growth rates, large canopies and extensive root systems. They are effective at gathering resources from the environment (e.g. light, water, nutrients) before their neighbours are able to capture them. The traits that are well developed in this type of plant are height and delayed reproduction.
Why is there an advantage to being tall in the competitor plant strategy?
Tall plants are able to capture more sunlight and to shade their neighbours.
Why do competitor plant species tend to delay their reproduction?
Because they initially devote all their energy and materials to rapid growth of leaves and roots in order to maximise resource capture.
Outline the methods employed by stress-tolerators as a plant survival strategy.
These species are characterised by slow growth rates. Their strategy is to cope with stresses, such as low nutrient availability, by using resources very efficiently and avoiding waste. Their tissues turn over very slowly and they tend to live to a great age.
Outline the methods employed by ruderals as a plant survival strategy.
This strategy is primarily characterised by a short lifespan, in which all the plant’s resources are devoted to producing seeds quickly. Ruderals tend to inhabit habitats that experience regular disturbance and/or periods that are very hostile to survival.
Why might natural selection have favoured plants that produce seed rapidly in environments that experience regular disturbance?
Seeds are able to survive periods of disturbance, so being able to produce seeds before the next disturbance event increases fitness.
What is the main difference between low-input and high-input agricultural systems?
It refers to the methods of rearing grazing livestock. Low-input systems have natural mixed meadows (multiple species of grass) without artificial fertilisers. High-input systems put artificial nitrogen onto pasture with just one-five species of grass to maximise yield. Low-input present hay in winter and high-input more frequently use silage.
