Topic 10 Sunshine and fresh air to cheese Flashcards
Energy enters the dairy production system as sunlight, how does it leave?
Energy from sunlight is 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, which will ultimately be lost as heat via human respiration, having been eaten.
Nitrogen enters the dairy production system via a number of routes, which routes are these?
- Atmospheric deposition
- Nitrogen fixing bacteria
- Fertiliser
In what form does nitrogen leave the dairy production system?
A proportion ends up in the end product, cheese, in which is is a component of protein. Some nitrogen is lost at each stage of the process: litter from plants, urine and faeces from cows and whey from cheese making.
In what form does nitrogen leave the dairy production system?
A proportion ends up in the end product, cheese, in which is is a component of protein. Some nitrogen is lost at each stage of the process: litter from plants, urine and faeces from cows and whey from cheese making.
Recall the names of the three photosynthetic pathways that capture and store the energy from sunlight by converting carbon dioxide into organic compounds?
- C3 - relies on Rubisco to fix CO2 directly
- C4 - Initially fixes CO2 using a more efficient enzyme, PEP carboxylase; but to complete the transformation of energy from sunlight to chemical energy, it still requires the C3 cycle, so it re-releases CO2 to produce a high concentration within specialised cells where Rubisco can work efficiently.
- CAM - many similarities to C4 in terms of process, but has become specialised to maximise the efficiency of water use by opening stomata only at night.
What photosynthetic pathway is most common in grass species?
C3 pathway, whilst a few use C4 (mainly in the tropics)
What does the term ‘grass’ refer to?
Members of the Poaceae family, but is sometimes used to describe any plant that has a similar structure to the Poaceae
What is the key attribute of a graminoid?
It’s growing point is kept level with the ground for most of its life and is therefore out of reach to most herbivores, and safe from fires that pass across quickly above.
Describe the structure of a grass plant.
The individual flowers are known as florets, several of which are clustered into a typically small, green spikelet which rely on wind pollination. Spikelets are grouped together into a larger inflorescence - either a spike (no branching), or a feathery panicle with many branches.
What is ‘net primary production’ (NPP)?
The total amount of carbon fixed by a strand of vegetation (known as gross primary production, GPP) minus the fraction used by plants for their own respiration (R). Can be expressed mathematically as: NPP=GPP-R
What is the total amount of carbon fixed by a stand of vegitation known as?
Gross primary production (GPP)
What is the quantity of light energy arriving at the Earth’s suface a function of?
- The position of the sun in the sky (Depends on time of day and season of the year)
- Weather conditions, particularly the amount of water vapour (cloud, mist, fog) in the atmosphere
What is light energy / irradiance measured in terms of?
Watts per metre-square, where a watt is defined as a joule per second.
What is photosynthetically active respiration (PSR)?
The portion of the electromagnetic spectrum in which the wavelength is appropriate to excite chlorophyll and therefore drive photosyntheses. Corresponds closely to the visible spectrum for humans and therefore the terms ‘PAR’ and ‘light’ can often be used interchangeably.
What is the amount of energy captured by plants measured by?
The amount of carbon they fix (GPP) which can be expressed in a variety of units:
* 1 g carbon is equivalent to 39 kJ stored chemical energy
* 1 g dry plant tissue contains 0.46 g carbon
* 1 g dry plant tissue is equivalent to 18 kJ stored chemical energy
At their most efficient, what percentage of PAR can plants convert into chemical energy?
25%
What percentage of the total energy in sunlight is photosynthetically active (Can be absorbed and used by chlorophyll to drive chemical reactions)?
45%
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 do plants need to achieve maximum efficiency of energy conversion?
- Optimal temperatures (15C - 30C)
- Unlimited water supply
- Unlimited access to nutrients (primarly nitrogen) and CO2
- Freedom from competition
What are the three life startegies seen in plants (CSR classification)?
- Competitor
- Stress-tolerator
*Ruderal
Describe competitors in terms of life strategy in plants
Survive in environmental with relatively opimal growth conditions. The main threat to survival is competition with neighbouring plants. They have rapid growth rates, large canopies, and extensive root systems. They are effective at gathering resources from the environment before their neighbours can capture them. The traits that are well developed are height and delayed reproduction.
Why is a there n advantage for using the competitor life strategy?
Tall plants are able to capture more sunlight and to shade their neighbours.
Why do competitor species of plant 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.
Give one example of a competitor plant.
Stinging nettle (Urtica dioica) - can grow over a meter high in just a few weeks
Describe the Stress-tolerator life stategy in plants.
Slow growth rates. Strategy is to cope with stresses, such as low nutrient availability by using resources efficiently and avoiding waste. Slow tissue turn over and tend to live for a long time.
Give an example of a stress-tolerator plant.
Bilbery (Vaccinium myrtillus) - long lived low growing shrub of heaths and woodlands
Describe the ruderal life strategy in plants.
Short life-span, all plant’s resources devoted to producing seeds quickly. Inhabit habitats that experience regular disturbance and/or periods that are very hostile to survival.
Give an example of a ruderal plant
Groundsel (Senecio vulgaris) - a garden weed
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.
In a plant community ,what do the proprtion of plant species assigned to each three life strategies giev indication of?
The resource availability and the frequency of disturbance.
What type of life strategy plants do low input dairy systems usually have and why?
Low input systems have limited nutrients and negular low-level disturbance (Cutting and grazing), allowing species with all three strategies to coexist.
What type of life strategy plants do high input dairy systems usually have and why?
High input systems have nutrients in excess and therefore they favour competitors even though the low level disturbance is maintained.
