Energy and ecosystems

Question 1

What is the main way energy enters an ecosystem?

Answer 1

Photosynthesis

Question 2

Define autotrophic

Answer 2

Organisms able to build up organic compounds from simple molecules.

Question 3

Define producer.

Answer 3

Photosynthetic organisms that build up complex organic compounds in the process of photosynthesis, from light, water CO2 and minerals.

Question 4

Define heterotrophic.

Answer 4

Organisms that rely on an external source of organic compounds i.e. they have to take in organic compounds.

Question 5

Define consumers.

Answer 5

Organisms that eat other organisms.

Question 6

What are saprobionts?

Answer 6

Also known as decomposers, they break down complex organic compounds in dead organisms. Bacteria and fungi are decomposers.

Question 7

Define biomass.

Answer 7

The total quantity or weight of organisms in a given area or volume. Units gm-2.

Question 8

What are food chains?

Answer 8

They display the feeding relationship between organisms. Each level in a food chain is known as a tropic level, the arrows between tropic levels display the energy transfer within the food chain.

Question 9

What are food webs?

Answer 9

Food chains do not occur in isolation and in a particular habitat many food chains can be linked together to form a food web.

The higher the diversity the more the complex the food web and this means that any one change in the food web will have less of an effect.

Question 10

How is some energy from the sun lost?

Answer 10

Only about 1-3% of available sunlight energy is trapped in photosynthesis and converted to organic molecules. This is due to:
-Some of the light is reflected by the atmosphere
-Some of the light is the wrong wavelength
-Some light does not fall on chloroplasts and misses the chlorophyll

Question 11

How is energy lost when consumers eat producers?

Answer 11

Only about 5-10% of energy in the organic molecules (biomass) of the producer is passed to the primary consumer. Due to:
- Some parts of plant being indigestible
- Not all the plant is eaten

Question 12

How is energy lost when consumers eat consumers?

Answer 12

Only about 15-20% of energy in the organic molecules (biomass) of the primary consumer is passed to the secondary consumer. This is due to:
-Large amounts of the animal may be indigestible
-Not all of the animal may be eaten
-Some energy is lost in excretion such as energy lost in urine
-Energy lost in respiration and as heat to the environment.

Question 13

Is energy transfer efficient?

Answer 13

Energy transfer is inefficient and results in large losses at each trophic level
Food chains are therefore usually no more than 4-5 trophic levels as there is not enough energy to support a breeding population at a higher trophic level.

Question 14

What is the equation for net primary production?

Answer 14

NPP = GPP - R
Net primary production = gross primary production - respiration

Remaining glucose available as biomass = glucose produced during photosynthesis - glucose used in respiration

Question 15

What is the equation for net production?

Answer 15

N = I - (F+R)
Net production = chemical energy stored in ingested food - (energy lost is faeces and urine + energy lot due to respiration)

Question 16

How do you calculate percentage efficiency?

Answer 16

percentage efficiency = (energy available after transfer/energy available before transfer) x 100

Question 17

Why does fresh mass vary?

Answer 17

It is dependent on the varying water content of organisms.

Question 18

What is a limitation of using mass of carbon or dry mass?

Answer 18

The organism must be killed

Question 19

How is dry biomass obtained?

Answer 19

Via drying out the same in an oven at 100C in order for the all the water to evaporate. The dry mass is determined when the mass is constant.

As dry biomass is measure per given area, in a given time a common unit would be per gram per square meter (gm-2).

Question 20

What is calorimetry?

Answer 20

It is used to measure the energy stored in the dry biomass of an organism. The dry mass is burnt, within the bomb. The energy released is used to heat the surrounding water which can be measure in kJkg-1.

Question 21

Explain why only a small proportion of the light reaching the leaves of the oak trees is used to produce new biomass. (3)

Answer 21

Wrong wavelength;
Does not hit chlorophyll/chloroplast;
Reflected;
Used for evaporation of water;

Question 22

Explain why an increase in biomass can be taken as a measurement of net primary productivity. (2)

Answer 22

1. Represents dry mass / mass of carbon;

2.      Represents gross production minus respiratory losses;

    Accept: NPP = GPP −R.

   Accept: Chemical energy minus respiratory losses.

1 and 2. Chemical energy store minus respiratory losses = 2 marks.

Question 23

What ways do farmers increase productivity/yield?

Answer 23

An increase in productivity is usually brought about by increasing the efficiency of energy conversion. Ways of doing this include:
· Using fertilisers
· Using chemical pesticides, biological agents or integrated systems to control pests
· Intensive rearing of domestic livestock.

Question 24

Why are fertilisers needed?

Answer 24

As the levels of inorganic ions in the soil is reduced the productivity is reduced, this is because nitrogen is required to produce proteins and DNA, both of which are needed for growth. Soil which is not deficient in nitrates will produce plants that have a higher growth rate and as plants have a greater leaf area the rate of photosynthesis will increase increasing productivity. It is therefore important to replace the lost ions. This can be done by the use of fertilisers.

Question 25

What are the two types of fertiliser?

Answer 25

· Organic/natural: These are waste materials such as manure

· Inorganic/artificial: These are manufactured powders or pellets produced in factories containing Nitrogen, Phosphorous and Potassium.

Question 26

What are the advantages vs disadvantages of organic fertiliser?

Answer 26

Advantages:
- Contain a mixture of inorganic ions released slowly giving steady supply to plants over longer period.
- Ions released slowly less problems less likely to leach
- Adds organic matter, improves soil structure and therefore water holding capacity
- Cheap

Disadvantages:
- Bulky and hard to transport large amounts
- Difficult to spread

Question 27

What are the advantages vs disadvantages of inorganic fertiliser?

Answer 27

Advantages:
- Exact composition of certain ions which are released quickly, good for periods of max growth
- Concentrated and can be applied in smaller amounts ( less transport costs)
- Easy to apply
- Clean

Disadvantages:
- Soluble so that ions are immediately available, but problems with leaching
- Does not improve soil structure
- Costly to produce

Question 28

What is the law of diminishing returns?

Answer 28

As the amount of fertiliser is increased the yield increases, the ion concentration is a limiting factor.
At a certain point any increase in fertiliser does not give an increase in yield, the yield remains constant, the ion concentration is no longer a limiting factor.
After a certain point the increase in amount of fertiliser results in a decrease in yield, the ions in such high concentration could lower the water potential of the soil resulting in loss of water from roots by osmosis, or the level of ions is now toxic.

Question 29

What are environmental impacts of using fertilisers?

Answer 29

· Reduced species diversity - plants which are adapted to soils high in Nitrates out compete other species.

· Leaching - Inorganic fertilisers result in more ions applied to the soil than are actually taken up by the plants. This leads to leaching, the ions dissolve in soil water and are washed from the soil into streams, rivers and lakes.

Question 30

What is eutrophication?

Answer 30

· Ions which washed away into water courses build up.
· High concentration of ions causes rapid growth of algae (surface photosynthesisers)
· Algae block light and less light penetrates the water
· Algae start to die off
· Plants that can’t photosynthesise under the surface also die off
· Large increase in population of bacteria decomposing dead plants and algae
· Bacteria respire and reduce Oxygen concentration of the water
· Oxygen levels depleted resulting in death of other aerobic organisms

Question 31

How is energy conserved when rearing domestic livestock?

Answer 31

· Restricting movement- so less respiratory loss due to muscle contraction.
· Keeping animals indoors and controlling temperature- in order to reduce heat loss from body.
· Feeding – feed is used which is of the optimum type (and amount) for growth i.e. containing macro-nutrients and minerals and vitamins in known amounts. Usually food source is easier to absorb reducing loses in faeces.
· Predators excluded so energy does not pass to other organisms.
· Selective breeding- some varieties or breeds are more efficient at converting energy into new tissue/mass, these are genetically selected for their high productivity.
· Use of hormones to increase growth rate.
· Slaughtered when still growing so more energy transferred to biomass.

Question 32

Define monoculture.

Answer 32

The process of increasing the productivity of a specific area, via growing the same crop over a large area.

Question 33

What are advantages and disadvantages of monocultures?

Answer 33

Advantages:
· More space for crops.
· Easier access for machinery.
· Removes habitats pest.
· Less weeds to compete for resources.

Disadvantages:
· Monoculture makes it very easy for disease to spread and also for insects to travel from plant to plant.
(A very large area can be affected in a very short space of time.)
· Removal of hedgerows removes habitats leads to reduced biodiversity and food sources which may be natural predators of pests and could cause soil erosion.
· Removes the same nutrient from soil, therefore more fertiliser needed.

Question 34

“Write an essay on how energy is transferred within and between organisms”
What topics link?

Answer 34

Photosynthesis
Energy transfer through ecosystems
Food production
Digestion (as in fuel)
Absorption (by cells)
Mass transport
Respiration
ATP
Stimuli and responses
Muscle contraction
Nerve impulses