5.3 Energy & Ecosystems

Question 1

What are most of the sugars synthesised by plants used as in plants?

Answer 1

Respiratory substrates (e.g. glucose)

Question 2

What are remaining sugars not used in respiration/as respiratory substrates used for?

Answer 2

Making other groups of biological molecules (e.g. starch)

Question 3

What is biomass made of?

Answer 3

The different groups of biological molecules formed from sugars synthesised by plants during photosynthesis

Question 4

What is biomass? (there are two definitions)

Answer 4

1. Mass of living/biological material excluding water of an organism or tissue
2. Chemical energy stored within the organism or tissue

Question 5

Biomass can be measured in terms of:

Answer 5

1. dry mass of an organism or tissue IN A GIVEN AREA
2. mass of CARBON an organism or tissue contains

Question 6

What can the chemical energy store in dry biomass be estimated by?

Answer 6

Calorimetry!

Question 7

What is dry mass?

Answer 7

Mass of organism or tissue after all water has been removed

Question 8

Why is biomass sometimes given with units of time?

Answer 8

Biomass can change over time (e.g. biomass of deciduous trees decreases during autumn & winter as leaves are lost)

Question 9

Typical units of biomass

Answer 9

kgm^-2 or kgm^-3

Question 10

How does calorimetry work (general overview)?

Answer 10

1. Burn a sample of dry biomass in a calorimeter
2. The burning sample heats a known volume of water
3. The change in temperature of water provides an estimate of the chemical energy of the sample

Question 11

What is the name of the more precise/accurate calorimeter, and how is it more precise/accurate than a classroom calorimeter?

Answer 11

Bomb calorimeter
1. Stirrer - ensures heat is evenly distributed throughout the water
2. Oxygen - ensures complete combustion of the sample

Question 12

Formula to calculate chemical energy stored in dry mass via calorimetry

Answer 12

temp increase x mass of water x 4.2 (J per °C) / mass of food

Question 13

Organisms can be divided into 3 groups, according to how they obtain energy - what are they?

Answer 13

1. Producers/Autotrophs
2. Consumers/Heterotrophs
3. Saprobionts

Question 14

What are producers/autotrophs?

Answer 14

Organisms that use light energy & inorganic molecules (CO2 & H2O) to make organic molecules (glucose)

Question 15

What are consumers/heterotrophs?

Answer 15

Organisms that get energy by consuming other organisms

Question 16

What are saprobionts?

Answer 16

Organisms that feed on other organisms but not exactly a predator (eg. parasites)

Question 17

What do saprobionts do?

Answer 17

Break down complex organic molecules into simple inorganic molecules.
This releases the inorganic substances back into the ecosystem - material is always recycled!

Question 18

Why is so little of the energy available from the Sun captured by plants/producers in photosynthesis?

Answer 18

1. some is the wrong wavelength (eg. plants can’t use green light to photosynthesise)
2. other factors limit rate of photosynthesis (eg. CO2 concentration)
3. light may hit a non-photosynthetic part of the plant

Question 19

Why is only around 10% of chemical food energy passed on between organisms in a food chain?

Answer 19

1. some parts are left uneaten (eg. bones)
2. decay of dead material (eg. bacteria may decay some material)
3. excretion (eg. energy lost in faeces)
4. exothermic reactions (eg. heat lost in respiration)

Question 20

Define gross primary productivity (GPP)

Answer 20

The chemical energy store in plant biomass, in a given area or volume

Question 21

Define net primary productivity (NPP)

Answer 21

The chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

Question 22

What is the formula linking GPP and NPP?

Answer 22

NPP = GPP - R
R: respiratory losses to the environment

Question 23

What is NPP available for?

Answer 23

Plant growth and reproduction, and other trophic levels in the ecosystem (eg. herbivores & decomposers)

Question 24

What are the units of GPP?

Answer 24

kJ m^-2 yr^-1
J m^-3 hr^-1

Question 25

Why do warm-blooded (endothermic) animals have greater respiratory losses than cold-blooded (exothermic) animals?

Answer 25

They need to constantly respire to maintain a constant body temperature (they have a higher respiration rate)

Question 26

What parts of all plants cannot be digested by most animals?

Answer 26

Cellulose cell walls

Question 27

Formula for net production of consumers (N)

Answer 27

N = I - (F + R)
I: chemical energy store in ingested food
F: chemical energy lost to environment in faeces & urine
R: respiratory losses to environment

Question 28

Methods of increasing production of crop plants

Answer 28

1. Use biological control/pesticides: pests decrease biomass of crops
2. Fertilisers/crop rotation: increases mineral ions in soil
3. Greenhouses/artificial light: maximises rate of photosynthesis

Question 29

Methods of increasing production of animals raised for meat

Answer 29

1. Keep animals in confined spaces (although ethically questionable) - reduces energy loss via respiration
2. Keep warm (although $$ to install heaters) - reduces energy loss via respiration
3. Easily digested food (preferably high protein) - reduces energy loss via undigested food