Energy transfer and nutrient cycles Flashcards
what are autotrophs?
the producers (plants)
organisms that make their own food
What are the synthesised sugars used for in plants?
- make up other biological molecules (cellulose in cell walls) → makes up the plants biomass
- respiration
photosynthesis equation
carbon dioxide + water → glucose + oxygen
what are heterotrophs?
(e.g animals) cannot synthesise their own energy so must obtain it from autotrophs or other heterotrophs, they act as consumers in the food web
how does biomass and its stored energy get transferred?
through trophic levels in a food web (inefficently)
How to measure biomass?
- sample of dry biomass in an oven set to a low temperature
- sample reweighed at regular intervals
- all water is removed when mass remains constant
- mass of carbon generally taken to be 50% of dry mass
How to estimate the chemical energy stored in dry biomass?
using a calorimeter
1. sample of dry biomass is burnt
2. energy released to heat a known volume of water
3. change in temp of water is used to calculate the chemical energy
Gross primary production (GPP)
chemical energy store in plant biomass in a given area/volume in given time
e.g. total energy resulting from photosynthesis
Net primary production (NPP)
chemical energy in plant biomass AFTER respiratory losses to the environment have been taken into account
NPP is available to trophic levels such as herbivores
Net primary production (NPP) formula
NPP = I - (F + R)
I - ingested
F - faeces
R - respiration
How can energy transfer between trophic levels become inefficient?
Sun → producer
- wrong wavelength of light
- light strikes non-photosynthetic regions (e.g. bark)
- light reflected
- lost as heat
Producer → primary consumer → secondary consumer etc.
- Respiratory losses (e.g. energy used for active transport)
- Lost as heat
- Not all plant/animal is eaten e.g. bones
- Not all food is digested e.g. faeces
How do farmers simplify food webs to reduce energy loss to non-human food chains in CROPS?
Herbicides → kill weeds → less competition from the sun → more energy to create biomass
Fungicides → reduce fungal infections → more energy to create biomass
Pesticides → reduces loss of biomass from crops
Fertilisers → e.g. nitrates to prevent poor growth due to lack to nutrients
How do farmers simplify food webs to reduce energy loss to create more biomass in LIVESTOCK?
- Restrict movement (rate of respiration decreases)
- Keep warm (especially in winter) less energy wasted in generating body heat
- slaughter the animal while young/still growing (when most of their energy is used for growth)
- selective breeding → produce breeds with higher growing rates
- treated with antibiotics to prevent energy loss due to pathogens
What are the advantages of removing pests?
energy losses are reduced and NPP increase
