5.3 Energy and Ecosystems

Question 1

What are producers?

Answer 1

Photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide and mineral ions

Question 2

What are consumers?

Answer 2

organisms that obtain their energy by feeding on other organisms rather than using the energy of sunlight directly

Question 3

What are primary consumers?

Answer 3

Those that directly eat producers (green plants) because they are the first in the chain of consumers

Question 4

What are secondary consumers?

Answer 4

those animals eating primary consumers, usually predators but may also be scavengers or parasites

Question 5

What are tertiary consumers?

Answer 5

those eating secondary consumers, usually predators but may also be scavengers or parasites

Question 6

What are saprobiants?

Answer 6

• decomposers
• group of organisms that break down the complex materials in dead organisms into simple ones
• in doing so they release valuable minerals and elements in a form that can be absorbed by plants and so contribute to recycling
• majority of this is carried out by fungi and bacteria

Question 7

What is a food chain?

Answer 7

• a feeding relationship in which the producers are eaten by primary consumers etc.
• each stage is referred to as a tropical level

Question 8

What is a food web?

Answer 8

Most animals do not rely on a single food source and within a single habitat many food chains will be linked together to form a food web

Question 9

What is biomass?

Answer 9

• a biological material derived from living or recently living organisms.
• In the context of biomass for energy this is often used to mean plant based material,
• but biomass can equally apply to animal derived material

Question 10

What happens within an ecosystem?

Answer 10

within any ecosystem, plants synthesise organic compounds (those obtaining carbon) from carbon dioxide obtained from the atmosphere or in the case of aquatic plants the water. These organic compounds include glucose, lipids, cellulose and proteins

Question 11

How do you measure biomass?

Answer 11

• Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area per given time
• Grams per metre squared per year
• Kilograms per hectare per decade

Question 12

What is biomass composed of?

Answer 12

• biomass is carbon based and is composed of a mixture of organic molecules containing hydrogen, usually including atoms of oxygen, often nitrogen and also small quantities of other atoms

Question 13

What is the equation for biomass?

Answer 13

Net Primary productivity = Gross Primary productivity - respiratory loss
NPP=GPP-R

Question 14

What is the GPP?

Answer 14

a measure of the total energy or mass in a plant

Question 15

What is the NPP?

Answer 15

what becomes available to organisms in the next trophic (feeding) level

Question 16

Why is most of the suns energy not converted to organic matter by photosynthesis?

Answer 16

• over 90% of the suns energy is reflected back into space by clouds and dust or absorbed by the atmosphere
• not all wavelengths of light can be absorbed and used for photosynthesis
• light may not fall on a chlorophyll molecule
• a factor, such as low carbon dioxide levels, may limit the rate of photosynthesis

Question 17

Why is there a low percentage of energy transferred at each stage of the food chain?

Answer 17

• some of the organism is not consumed
• some parts are consumed but cannot be digested and are therefore lost in the faeces
• some of the energy is lost in excretory materials
• some energy losses occur as heat from respiration and lost to the environment

Question 18

What is the net production of consumers?

Answer 18

N = I - (F+R)
N = net production
I = ingestion
F = Faeces
R = respiration

Question 19

How do you reduce energy transfer in modern farming?

Answer 19

• animals kept inside in warm conditions -> reduces energy loss by ‘heating’ their bodies
  >restricting movement -> kept in cramped conditions

Question 20

What do fertilisers do in modern farming?

Answer 20

encourage plant growth - more yield
> eutrophication - rivers, lakes encourage plant growth

Question 21

What do pesticides do in modern farming?

Answer 21

Kill organisms that damage crops
> Chemical pesticides might kill other species
> biological control - use the predator of the pest - invasive species

Question 22

What do greenhouses do in modern farming?

Answer 22

Control temperature, confined space no in or out for pests, water levels, carbon dioxide

Question 23

What does diet do in modern farming?

Answer 23

high protein and low fibre diets this could reduce the amount of faeces

Question 24

What does selective breeding do in modern farming?

Answer 24

breeding for fast growth and high yields

Question 25

What does growth hormones and antibiotics do in modern farming?

Answer 25

accelerating growth and prevention of bacterial disease
ethical issues

Question 26

What are the organic compounds?

Answer 26

Glucose, Lipids, Cellulose and proteins

Question 27

Why is the length of food chains limited?

Answer 27

• energy is lost at each trophic level
• so there is insufficient energy to support a higher trophic level

Question 28

What is the general equation for % efficiency

Answer 28

energy converted to a useful from x 100 / total energy supplied

Question 29

Outline some common farming practises used to increase the efficiency of energy transfer

Answer 29

• exclusion of predators: no energy lost to other organisms in food web
• artificial heating: reduce energy lost to maintain constant body temperature
• restriction of movement
• feeding is controlled at the optimum

Question 30

Define primary and secondary productivity.

Answer 30

• rate of primary or secondary production
• biomass in a specific area over a given time period

Question 31

Why does biomass decrease along a food chain?

Answer 31

-Energy lost in nitrogenous waste and faeces
- some of the organism is not consumed
- energy lost to surroundings as heat

Question 32

How could a student ensure that all water had been removed from a sample before weighing?

Answer 32

heat the sample and reweigh it until the mass reading is constant

Question 33

How can chemical energy store in dry biomass be estimated?

Answer 33

using calorimetry