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Flashcards in Sunshine And Fresh Air To Cheese Deck (29):

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.


What is limiting the annual grass yield in the low-input system?

A lack of available nitrogen. Supplying additional nitrogen boosts yields by 64%.


Why is a single strategy dominant in the vegetation of the high-input system in agriculture?

The high resource (nitrogen) availability in that system favours the competitive strategy at the expense of the other two.


Why is the plant species diversity so much lower in the high-input agricultural system than the low input system?

The fastest-growing, most competitive grass species, perennial ryegrass (Lolium perenne) is released from the restriction caused by lack of nitrogen that it experiences in the low-input system, allowing it to out-compete other species by growing taller than them and taking the majority of the light.


If a plant is stressed through lack of water, which hormone (growth regulator) is likely to be produced in its tissues?

Abscisic acid (ABA) is the plant growth regulator that is released by cells whose turgor is falling.


How might the production of such a stress hormone affect the root : shoot ratio of a grass plant?

Logic would suggest that a plant under water stress might direct resource to roots, which absorb moisture, and away from shoots, which lose moisture; thereby increasing its root : shoot ratio. Root : shoot ratios do indeed increase in response to drought. Elevated ABA concentration in the tissues of plants growing in dry soil act to depress the leaf expansion rate whilst stimulating root extension rate by increasing the elasticity of the cell walls in the roots whilst decreasing it in the shoots.


What is the consumption efficiency?

The proportion of the food produced at the lower trophic level that is ingested by the organism at the higher trophic level, expressed as a percentage.


What is the assimilation efficiency?

The proportion of consumed food that has been digested and absorbed, expressed as a percentage.


Explain production efficiency.

The proportion of energy assimilated by an organism that is then used in the creation of new body tissue, e.g. muscles, or products, e.g. a fetus or milk, expressed as a percentage.


How do you calculate the conversion efficiency of a species or trophic level?

Conversion efficiency = consumption efficiency × assimilation efficiency × production efficiency.


Outline the details of the cow ovarian and breeding cycle.

They first breed at around two years of age. Cattle have a 21 day ovarian cycle and calf once a year. They are re-inseminated at around 100 days post partum.


Outline the way the ruminant digestive system works.

Ruminants have four distinct compartments to their stomachs. Chewed food entering the first two compartments (or forestomachs) is mixed with saliva and clumps (or cuds) are formed that are regurgitated back up into the mouth where they are chewed again and thoroughly mixed with saliva, before being swallowed for the final time. Microbes in the forestomachs ferment the otherwise indigestible fibres and other nutrients into short-chain volatile fatty acids before they move into the later stomachs and ultimately to the intestines where absorption takes place.


List some examples of ruminant animals

herbivores such as giraffes, antelopes, cows, sheep and deer.


What happens to heifer calves born into dairy herd?

Heifer calves are kept and raised to become part of dairy herd.


When and why do heifers and cows need to build up adipose reserves?

Heifers and cows need to build up their adipose reserves during pregnancy and following birth to maintain milk production and build up reserves for resumption of ovarian function, conception, development of fetus and ready for their following lactation.