Chapter 13 - Energy And Ecosystems

Question 1

What is an ecosystem?

Answer 1

A transfer of energy between organisms

Question 2

What is the first group according to how organisms obtain their energy? Explain it + give other name

Answer 2

Producers

• photosynthetic organisms (plants) that make organic substances using light energy from sun
• called autotrophs

Question 3

What is the second group according to how organisms obtain their energy? Explain it + give other name

Answer 3

Consumers

• obtain energy by consuming other organisms
• called heterotrophs as cannot make own food

Question 4

What is the third group according to how organisms obtain their energy? Explain it

Answer 4

Saprobionts/ decomposers

• break down materials in dead organisms (by releasing enzymes) to obtain energy
• majority is fungi and bacteria

Question 5

What is biomass? What is it measured in?

Answer 5

Total dry mass of living material of an organism

• measured in specific area at a given time

Question 6

What is calorimetry?

Answer 6

Used to measure chemical energy stored in biomass of something

Question 7

Why is so little of suns energy converted to producers biomass?

Answer 7

1. Over 90% of suns light energy is reflected back / absorbed by atmosphere
2. Not all wavelengths of light can be absorbed by each plant for photosynthesis
3. Correct wavelengths wont all hit correct pigments that absorb them
4. Other limiting factors will limit rate of photosynthesis e.g. levels of CO2 in atmosphere

Question 8

What do gross primary products (GPP) and net primary productivity (NPP) measure?

What happens with remaining energy?

Answer 8

GPP - total amount of chemical energy stored in a plants biomass in given area/ volume

NPP - chemical energy store that is left when losses in energy to respiration is taken into account

• remaining energy is passed on to the next tropic level

Question 9

What is the equation for consumers net production?

Answer 9

N = I - (F+R)

N- net production for consumers
I - chemical energy of ingested food
F - energy lost in faces + urine (undigested)
R - energy lost in respiration

Question 10

What is the equation for % efficiency?

Answer 10

% efficiency = energy available after transfer/ energy available before transfer x 100

Question 11

How does intensive rearing of domestic livestock increase yields?

Answer 11

Increase yields by reducing energy loss to environment

• give livestock smallest quantity of food = reduced costs
• but get greatest quantity of biomass by minimising energy loss to environment

Question 12

What are the methods of minimising energy loss to the environment?

Answer 12

• keep animals in confined spaces (factory farming)
• movement is restricted = less energy for respiration + muscle contractions
• warm environment = less energy used to maintain body temp
• keep in dark = more sleep so less energy consuming food
• controlled feeding = receive optimum amount + type
• exclude predators = no loss of energy to other organisms in food web
• eliminate competitors = weeds/ pests that might damage

Question 13

What is used to describe flow of nutrients?

Answer 13

It is cyclic - nutrients are recycled as there is a limited availability of them

Question 14

Describe what occurs during the nitrogen cycle

Answer 14

1. Atmospheric nitrogen gas converted into ammonia via nitrogen fixation - carried out by nitrogen fixing bacteria
2. Ammonia dissolves in water in soil to form ammonium ions.
3. These undergo nitrification by nitrifying bacteria to form nitrate ions
4. Nitrate ions are assimilated by producers and converted into organic molecules. Consumers feed producers
5. Saprobionts feed on waste and convert organic molecules back into inorganic molecules. These undergo ammonification back into ammonia.
6. If soils become waterlogged, nitrate ions undergo denitrification by denitrifying bacteria into nitrogen gas

Question 15

Describe the phosphorus cycle

Answer 15

1. Rocks contain phosphate ions, which are weathered/ eroded to release these ions in the soil
2. Phosphate ions are assimilated by producer, converting them into organic molecules. Consumers feed producers.
3. Saprobionts break down organic molecules from dead matter into inorganic molecules to return phosphate ions to the soil.
4. Leaching may also occur whereby phosphate ions end up in bodies of water causing sedimentation
5. Overtime, geological uplifting occurs whereby sedimented rock is pushed up to top of water.

Question 16

What do leguminous plants have that other plants do not, and what does this allow them to do?

Answer 16

Contain nitrogen fixing bacteria on root nodules

• this means that they can collect nitrogen gas and release it as ammonia, therefore producing protein/ amino acids etc

Question 17

What are fertilisers used for?

Answer 17

Required to replace ions lost from soil, back into soil allowing for growth of similar crops in same fields over and over again

Question 18

What are the 2 types of fertilisers?

Answer 18

Natural: dead + decaying remains of plants + animals and animal waste

Artificial: contain mineral ions mined from rocks which are then converted to different forms and blended to give best balance of mineral ions for particular crops

Question 19

What 3 compounds are always present in artificial fertilisers?

Answer 19

Nitrogen, phosphorus and potassium

Question 20

Why can too much fertiliser be bad?

Answer 20

Lowers water potential of soil = movement of water from plant to soil so no movement of minerals dissolved in water into plants

Question 21

How do fertilisers increase productivity?

Answer 21

• plants require minerals for growth (nitrogen for amino acids, ATP and nucleotides)
• without these = no growth
• where these are more readily available, plants will grow more

Question 22

What are the 3 environmental effects of nitrogen containing fertilisers?

Answer 22

1. Reduces species diversity - nitrogen rich soils favour growth of rapidly growing species such as grasses which out compete other species = death
2. Leaching - into water bodies
3. Eutrophications - fertilisers in water feed algae, causing algal bloom. This leads to less sunlight into water so algae underneath dies and fish suffocate

Question 23

Describe what eutrophication is in detail

Answer 23

1. Nitrogen ions feed algae, causing algae bloom on surface of water
2. This dense layer absorbs sunlight and prevents it penetrating lower depths
3. Plants and algae at lower depths die due to no sunlight
4. More dead plants for Saprobionts so populations grow
5. Saprobiontic bacteria use oxygen for aerobic respirations so concentration of oxygen in water reduces + nitrates from decayed organisms are released
6. Oxygen becomes limiting factor for fish, so these die also.
7. Without aerobic organisms, there is less competition for anaerobic organisms so these increase in population

Question 24

How do mycorrhizae fungus increase growth of plants?

Answer 24

• attach to root network to increase the surface area of it
• acts as a sponge to absorb water containing minerals and nutrients in soil so more are absorbed (particularly during a drought)

Question 25

What type of relationship is there between mycorrhizae fungus and plants?

Answer 25

Mutualistic

• fungus get carbohydrates from plants formed during photosynthesis and plants get more nutrients