[13.1] food chains and energy transfer

Question 1

definition of an ecosystem

Answer 1

interaction of biotic and abiotic factors within an area

Question 2

definition of species

Answer 2

a group of organisms capable of naturally reproducing to produce viable offspring

Question 3

definition of habitat

Answer 3

• the place where an organism normally lives
• it has biotic and abiotic features which separate it from other habitats

Question 4

definition of community

Answer 4

the different populations of species that live in a habitat

Question 5

definition of decomposers

Answer 5

microbes, bacteria, and fungi that obtain nutrients by breaking down dead organisms and faeces

Question 6

definition of detritus feeders

Answer 6

organisms such as earthworms which feed on small fragments of organic debris, called detritus

Question 7

what non-living material is detritus made up of?

Answer 7

• faeces
• fallen leaves
• remains of dead organisms

Question 8

definition of niche

Answer 8

• the interrelationship of a species with all the biotic and abiotic factors affecting it
• the role of an organism within an ecosystem / community

Question 9

definition of trophic level

Answer 9

the position an organism occupies within a food web

Question 10

definition of autotroph / producer

Answer 10

• able to produce organic molecules from inorganic molecules
• the first trophic level in the food chain

Question 11

definition of heterotroph

Answer 11

• an organism unable to synthesise its own organic molecules
• must feed on organic matter

Question 12

definition of primary consumer / detritivore

Answer 12

an organism which consumes producers / dead matter

Question 13

definition of secondary consumer

Answer 13

an organism which feeds on primary consumers

Question 14

definition of saprotroph / saprobiont

Answer 14

• an organism which digests its food externally then absorbs the contents
• feeds on dead or decaying matter

Question 15

what is saprotrophic nutrition?

Answer 15

extracellular digestion via secretion of digestive enzymes which releases inorganic ions into the soil, most of which are absorbed by saprobionts

Question 16

how are producers always photoautotrophic and what is the importance of this?

Answer 16

they make their own food using light energy

Question 17

what is the importance of producers always being photoautotrophic?

Answer 17

all photoautrophs use the same photosynthesis reaction, suggesting they evolved from the same ancestor

Question 18

what is the role of a producer?

Answer 18

to absorb light energy and use it to convert atmospheric CO₂ (land plants) or aquatic CO₂ (underwater plants) to glucose and other sugars for chemical energy

Question 19

what is biomass?

Answer 19

the mass of carbon in an organism OR the dry mass of tissue

Question 20

where does biomass come from?

Answer 20

• light energy absorbed by producers is used to convert CO₂ to organic, C-based molecules eg. glucose
• this is either used as a respiratory substrate or to build large molecules in producers, (proteins, cellulose etc.) forming biomass

Question 21

how is biomass transferred from a producer to a consumer?

Answer 21

• the molecules that make up biomass (proteins etc.) contain chemical energy
• when a consumer eats a plant, it takes in the plant’s biomass, digests it and builds its own molecules and therefore biomass
• chemical energy from plant’s biomass is now in animal’s biomass

Question 22

what are the 2 ways of measuring biomass?

Answer 22

1. dry pass per area per time or carbon per area per time
2. calorimetry

Question 23

how do you work out the dry mass of tissues?

Answer 23

• every organism has variable amounts of water, so you don’t want to include this in the biomass
• place your sample in the oven at a low temperature so it doesn’t burn
• weigh it at regular intervals and reheat until the weight remains constant
• units = mass / area / time

Question 24

describe the process of finding the dry mass of a plant sample

Answer 24

1. weigh crucible without sample
2. place sample in crucible
3. place crucible in oven
4. set oven to low temp
5. remove and weigh crucible, with sample, at regular intervals during the drying process
6. once mass of crucible and sample stops decreasing and becomes constant, sample is fully dehydrated
7. to find dry mass of sample, subtract original mass of crucible, without sample, from final constant mass

Question 25

what are the limitations of meauring dry biomass? [3]

Answer 25

• difficulty in sampling
• variability in biomass
• destruction of samples

Question 26

describe the process of calorimetry

Answer 26

• burning a sample releases energy, which is used to heat a known mass of water with a known shc
• use the temperature change of the water to work out the energy released from the sample
• E = m × c × θ

Question 27

what are the limitations of calorimetry? [7]

Answer 27

• long time to fully dehydrate to find dry mass
• precise equipment is needed, which may not be available
• all of sample may not be burnt
• water may not be pure, so shc may not be 100% accurate
• more simple basic calorimetrry = less accurate estimate
• some energy released is used to heat beaker with water
• some heat released is lost to surroundings