Transcript File

Use of other
resources in
agriculture
Producing enough
for human survival
Where was
agriculture first
developed?
The impact on the
biosphere
Why study
agriculture?
Key facts to
find out
When was
agriculture first
developed?
pollution
The impact on a
country’s
development
What % of the
earth’s surface is
used for agriculture?
Autotrophic &
Heterotrophic
Nutrition
Autotrophic Nutrition
Heterotrophic Nutrition
Autotrophic Nutrition is…
…when organisms can produce their own food or energy.
It is the basis of all agriculture as all food production
relies directly or in directly on photosynthesis.
For example:
Crops
Livestock
Dairy products
Farmed Fish
Most use light energy during photosynthesis and are called
photoautotrophs. E.g. plants, algae and some bacteria.
Some are chemoautotrophs e.g. bacteria that harness
energy by oxidising inorganic substances (e.g. hydrogen
sulphide.
Photosynthesis equation quiz
Word equation to symbol equation
Heterotrophic Nutrition
Heterotroph means…
… ‘different-feeders’. Organisms that cannot
produce their own high energy molecules and
gain their energy from other living organisms.
E.g. animals, fungi and many bacteria
Title Page
Heterotrophic Nutrition
Herbivores: eat plant foods eg, cattle, sheep, poultry, carp.
Omnivores: eat both plants & animal foods eg. Pigs. Can be
fed on wastes.
Carnivores: eat animal foods, eg many farmed fish such as
salmon and trout are fed on fish waste and low value fish.
All of the food production systems which humans use are inefficient;
whether we consume plants or animals we are only able to obtain a
fraction of the original energy supplied in solar radiation
Farming
System
Cereals
% of solar radiation
available as human
food
Energy lost
0.2
Sugar
beet/potatoes
0.25
Intensive beef
0.005 - 0.025
Intensive milk
0.03 - 0.080
Cattle ranching
0.002 - 0.004
Mixed farming
0.03 - 0.150
R
Grass
R
Cow does not
eat all of the
grass plant
Man does not
eat all of the
cow
Cow
Faeces
R = Respiration (energy is lost as heat)
R
Man
Faeces
Energy transfer in the food chain
Energy loss in food chains
NB much of the food that is eaten is not digested
and therefore is not assimilated.
Feeding relationships
A luxury item?
How can the costs of these food items be compared fairly?
A 400 g steak costs
An 800 g loaf of bread costs
£4.00.
£0.80.
This equals £1.00 per 100 g. This equals £0.10 per 100 g.
Why is meat more expensive than bread?
How energy efficient is it to eat meat?
Food chains can be used to understand why some foods cost
more than others. Which of these chains is the most efficient?
The first food chain is the most efficient because it
contains fewest trophic levels, so less energy will be lost.
Is eating meat less energy efficient?
Cattle and other livestock are fed grain and cereals.
Would it be more energy efficient if humans ate the plant
crops instead?
If a one-acre field of corn is
used to feed cows, it can
support one person.
If the same area is used
to feed humans directly, it
can support 10 people.
Why is so much energy lost?
Assimilation Efficiency
Food chain efficiencies are well below
100%, so the amount of energy
available drops rapidly as it passes
along successive trophic levels
A = C - (F + U) and:
AE = A
C
x 100
A:
C:
F:
U:
AE:
Assimilation
Consumption
Faeces
Urine
Assimilation Efficiency
The closer the similarity between the tissues of the consumer and the
tissues of the food it eats, the higher the assimilation efficiency
Feeding type
Typical assimilation efficiency / %
Herbivore
30-60
Ruminant
50
Carnivore
70-90
Homeotherms (animals which regulate their internal temperature) use
e.g. 95% of the assimilated material just keeping warm
This means that their growth or production efficiency (P/A) is very low
- usually just 1 - 3%
An animals digestive system may be adapted to
enable it to live in a habitat that cannot be
exploited by other species?
Can you think of examples of this?
Cattle and sheep symbiotic gut bacteria that can
digest cellulose. Therefore they can eat foods
unavailable to other livestock and can graze poor
pasture land which may have no other agricultural
uses.
What trophic level does this food
come from?
Why do some animals need more
energy?
Mammals and birds are
able to regulate their body
temperature. This has many
advantages but it uses lots
of energy.
Other animals, such as
snakes, lizards and fish, are
unable to regulate their body
temperature, so need less
energy.
Would it be more energy
efficient to farm snakes
for food than chickens?
How do you calculate efficiency?
Energy efficiency can be calculated using the following
equation:
energy used for growth (input)
efficiency =
energy supplied (output)
For example, if grass receives 1,000,000 kJ of energy from
the Sun and uses 20,000 kJ of energy for growth, then:
20,000 kJ
efficiency
=
1,000,000 kJ
= 0.02 = 2%
Assimilation Efficiency
However, homeothermy allows them to exploit cold environments which
poikilotherms cannot
PE of animals vary with:
1. food quality
2. the length of the life cycle
Farmers try to maximise PE by:
1. using high quality foodstuffs (increasing AE)
2. reducing metabolic energy loss (by keeping the animals
warm and by restricting their movement)
Most humans are omnivores - they eat both meat and vegetables.
In terms of our AE, our digestive systems are better suited to cope with meat
than vegetables because:
•
•
we lack cellulose-digesting bacteria in the equivalent of a rumen
we don’t eat our soft faeces e.g. as rabbits do.
However, in terms of energy efficiency and land use, humans would be much
better off trying to satisfy their energy requirements by eating vegetables and
crops, rather than feeding them to cattle and eating the meat
By introducing another stage into the food chain (crop  cattle  humans
rather than crop  humans) a huge amount of energy is lost
Energy efficiency calculations