Food Chains and Ecosystems

Food chains, Productivity and Pyramids

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Food Chains

Sunlight Energy ----->Producer (Photoautotroph) ---->Primary Consumer (Herbivore)---->Secondary Consumer(Carnivore)

Energy is only passed on through growth by mitosis so 2% of energy is passed from sun to producer and then 10% passed up at each of the next stages

Energy losses at Photoautotroph (1st trophic level):

  • Not all light while hit the photosynthesising leaves
  • Due to the green pigment chlorophyll, all green light is reflected

Energy Losses from 2nd trophic level up:

  • Not all of the plant/prey is eaten by the predator
  • Not all of the material consumed is digestive ie Cellulose - we lack the enzyme needed to digest it
  • Muscular contraction and Maintaining body temperature in endotherms
  • Reprodcution
  • Excretion and Egestion
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Multiple prey means that all essential vitamins and amino acids are consumed and means that if one food source becomes extinct, the predator does not also die out

Pyramid of Numbers - count all of the organisms in the area

Pyramid of Energy - Burn all the organisms in a bomb calorimeter to heat water and work out the energy released per gram

Pryamid of Biomass - collect the organisms and heat 80dc so that all the water evaporates, weigh the dry mass on a calibrated balance

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Primary Productivity (rate of photosynthesis)

Gross Primary Productivity:- the rate at which plants convert light energy into chemical energy

To improve productivty:

  • limit the damage to plants - protectives covering, insecticides, fungicides all stop pests harming the plants. You could also genetically modifiy the crop
  • Reduce the effect of limiting factors:- greenhouses to keep warmth, pump in CO2, fertilisers for the minerals, light banks and irrigate the plants regularly
  • Increase growth factors:- Add plant growth hormones, crop rotation and fertilisers put nutrients back into the soil
  • Prevent Interspecific competition:- use herbicides or cut down trees and hedges
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Secondary Productivity

Net Primary Productivity:- the rate at which new boimass becomes avaliable for consumption by heterotrophs

To Improve Productivity:-

  • Manipulate the energy transfer - harvest just before adulthood after growth has finished
  • Antibiotics - animals do not waste energy fighting infection
  • Constnant supply of food and maintian warm temperatures
  • limit movement


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