Energy Transfers

What is an ecosystem?

All the living organisms in a particular area and all the abiotic conditions

What are producers?

An organism that photosynthesises to make it’s own sugars

What is a consumer and what types are there?

• A consumer is any organism that eats another

• This includes primary consumers which will eat plants and secondary consumers which eat the primary consumer

What is a decomposer?

An organism that hydrolyses dead organic material and recycles nutrients back into the ecosystem.

What does an arrow in a food chain mean?

It shows the energy transfer between organisms

What is a trophic level?

A stage of the food chain

How can biomass be measured?

It can be measured in terms of the mass of carbon that an organism contains or the dry mass of it’s tissue per unit area per unit time

What is dry mass and why do we use it to measure biomass?

• The mass of an organism with all the water removed

• The water content of living organisms varies so dry mass is used to measure biomass rather than wet mass

• The mass of carbon is generally taken as 50% of the dry mass

How can we get a measure of dry mass and how do we use this to calculate biomass?

• We can take a sample and dry it in an oven

• To remove all the water, we need to dry the sample until it’s mass is constant

• We can then scale up the dry mass to the total population of the area being investigated

• Biomass changes over time so it is often quoted over a time period too

What are the units for biomass?

Kg m^-2 yr^-1

How can we measure energy using calorimetry?

• We can estimate the amount of chemical energy stored in biomass using a calorimeter

• The sample of organic material is burned

• The heat energy released is used to heat a known volume of water

• The change in the water temperature is used to calculate the chemical energy in the dry biomass

What problems are there with simple calorimetry equipment and what equipment can be used to improve this?

• Heat loss and incomplete combustion

• We can use a bomb calorimeter to minimise these problems

How is a bomb calorimeter more suited for calorimetry?

• It is insulated to prevent heat loss to the surroundings so all heat energy is transferred to water

• Provides an excess supply of oxygen to prevent incomplete combustion

• There is a motorised stirrer to distribute heat energy throughout the water

What is biomass?

The mass of living material/biological molecules within an organism

How is energy stored in organisms?

Stored in biological molecules that when hydrolysed release energy

What is gross primary production (GPP)?

The store of light energy converted into chemical energy in plant biomass in a given area at a given time

What is net primary production (NPP)?

The store of chemical energy after respiratory losses that is available to the next trophic level in a given area at a given time

How can GPP be calculated?

GPP= NPP + R

R= respiratory loss

What is net production?

The amount of chemical energy stored in the consumers available to the next trophic level

What does assimilation mean?

The production and storage of biological molecules from digested food molecules absorbed from the blood into body cells

What percentage of energy is absorbed from the sun to be used in photosynthesis by producers?

1%

What is the original source of energy for nearly all organisms and what is an exception?

• The sun

• Some bacteria can used hydrogen sulphide gas from hydrothermal vents to produce sugars

Why isn’t more light energy absorbed by producers?

• Some light is reflected

• Some is the wrong wavelength (green light)

• Some light doesn’t hit the chlorophyll or passes through the leaf

• Other limiting factors such as temperature and carbon dioxide concentration

How do energy losses occur between organisms?

• Respiration- energy lost as heat

• Production of faeces and urine- herbivores lose a lot more energy from this because cellulose in plant cell walls is indigestible

• Not all of an organism may be eaten such as bones which are indigestible

  • The energy of the dead matter goes to decomposers

• Predators use a lot of energy from respiration in order to hunt

• Very little light energy is absorbed by plants for photosynthesis

How is net production in consumers calculated?

N= I-(F+R)

N- Net production

I- Chemical energy ingested from food

F- Chemical energy lost in faeces and urine

R- Energy lost to the environment by respiration

How is energy transfer efficiency calculated?

Net production of trophic level/net production of previous level x 100

Why do energy transfers actually become more efficient between organisms as we move up trophic levels?

• Animals at the top of a food web aren’t eating indigestible cellulose because they are likely carnivores or if they are omnivores, they eat meat whereas herbivores eat only plants

• This means that more biological molecules can be digested and assimilated as biomass within animals further up in a food web

What is meant by productivity in farming?

The rate at which energy is stored in crops and livestock/ The rate at which biomass is added

How can energy losses be reduced and productivity increased?

• Eliminate weeds

• Introduce predators of pests

• Reduce energy losses to non-humans by simplifying food webs

• Shorten food chains

What are the two different types of pesticide?

• Biological control- introducing a predator of a pest in order to prevent damage to crops

• Pesticides- Using chemicals in order to kill pests and protect crops

These will both increase the yield of crops

What are the pros and cons of using biological control to increase crop yield?

• No bioaccumulation in food chain

• Long term effects on a food chain

But

• Pest numbers wont reach zero

• Slower acting

What are the pros and cons of using pesticides to increase crop yield?

• Pest number brought to zero 

• Fast acting 

But

• Can lead to bioaccumulation within organisms

• Biomagnification

• Needs to be reapplied

• A pest with a resistant allele may survive and reproduce

What is bioaccumulation?

The build up of toxins within an individual organism

What is bioamplification/biomagnification?

The build-up of toxins as you move up the food chain

What farming practices can increase crop productivity?

• Control the pH of soil

• Pest or biological control

• Adding fertilisers

• GM crops and selective breeding

• Increase the rate of photosynthesis: optimum temperature, high light intensity and CO₂ concentration

• Herbicides added

• Rearing livestock on the same field

• Ploughing

• Draining waterlogged soil

• Ploughing leguminous plant roots into soil

• Crop rotation

• Removing hedgerows 

Why may farmers not want to increase temperature too much for livestock and crops?

• It increases the rate of respiration

• This means that more glucose stored as glycogen or starch will be used up in respiration

• This decreases biomass and therefore yield

Why is removing hedgerows good for farmers?

• It gives them more space to grow their crops

• It also removes a habitat for pests that may be destroying their crops and decreasing crop yield

Why may farmers rear livestock on the same field they are growing crops?

• They will excrete waste

• This provides natural fertiliser

Why may farmers use herbicides on their fields?

To kill weeds that are competing for light, nutrients and space against their crops

What is crop rotation and why is it done?

• This involves changing which crop is growing in your field every year or so

• This improves soil fertility as different crops having different nutrient requirements

  • For example, leguminous plants can fix nitrogen from the air into nitrite and nitrate ions through nitrogen fixing bacteria in their root nodules

  • The crop that you plant next will then have a plentiful supply of nitrate ions in the soil to improve grow

• It also disrupts pest and disease cycles

How can the productivity of livestock be increased?

• Restricting movement

• Giving them highly digestible foods with little fibre

• Controlling temperature of sheds/barns

• Prophylactic use of antibiotics

• Selective breeding

How does restricting movement increase the productivity of livestock?

• More movement means more activity (more muscle contraction)

• This means that more respiration must occur which releases heat energy and uses up glucose to produce more ATP

• Therefore by restricting movement we decrease respiratory losses and increase the net production of animals

How does controlling the temperature of barns/sheds increase productivity of livestock?

• We want temperature to be optimal as we want decrease respiratory losses as much as possible while also preventing energy being used for homeostasis/thermoregulation (shivering for example)

• This decreases respiratory losses

Why do we want to feed animals highly digestible food and how do we do this?

• This reduces the production of faeces so less energy is wasted, more material is incorporated into an animal’s biomass as biological molecules

• We do this by feeding them foods high in fibre

What is prophylactic use of antibiotics and how does it increase the productivity of livestock?

• This is where medication is taken to prevent an infection from ever occurring rather than using it to treat an existing infection

• This leads to less infections so less energy from respiration wasted in fighting disease

• This decreases respiratory losses

How does selective breeding increase livestock productivity?

• Picking the heaviest/largest livestock to breed means that we can breed even larger livestock

• It also allows us to pass on beneficial alleles which may help livestock in fighting off disease or for survival in general