chapter 19 - organisms and their environment

Question 1

*what is the main source of energy input to biological systems?

Answer 1

the sun.
photosynthesizing plants use sunlight as energy, and the energy is then passes through food chains.
with the exception of atomic energy and tidal power, all energy released on Earth is derived from sunlight.

Question 2

*describe the flow of energy through living organisms and its eventual transfer to the environment

Answer 2

Energy enters ecosystems in the form of sunlight or chemical compounds. Some organisms use this energy to make food. Other organisms get energy by eating the food.

Question 3

*define

food web

Answer 3

a network of interconnected food chains.

Question 4

*define

producer

Answer 4

an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis.

Question 5

*define

consumer

Answer 5

an organism that gets its energy by feeding on other organisms.

Question 6

*define

trophic level

Answer 6

the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass.

Question 7

*how is energy transferred between organisms in a food chain?

Answer 7

by ingestion.

Question 8

what is interdependence?

Answer 8

the way in which living organisms depend on each other in order to remain alive, grow and reproduce.

Question 9

*explain why the transfer of energy from one trophic level to another is inefficient

Answer 9

• primary consumers eat only a small proportion of of the available vegetation (producers).
• consumers may not digest all the food they ingest.
• energy is wasted on movement, respiration and other life processes of consumers.
• only about 10% energy is transferred and used from one trophic level to another.

Question 10

*explain why food chains usually have fewer than 5 trophic levels

Answer 10

• about 90% of the energy is lost at each trophic level.

- very little of the energy entering the chain through the producer is available to the top consumer.

Question 11

what is a pyramid of numbers?

Answer 11

the width of the bands are meant to represent the relative number of organisms at each trophic level.

Question 12

*explain why there is greater efficiency in supplying plants as human food.

Answer 12

• there is a relative inefficiency in feeding crop plants to livestock that will be used as food.

Question 13

*explain why there is greater efficiency in supplying plants as human food.

Answer 13

• there is a relative inefficiency in feeding crop plants to livestock that will be used as food, because only 10% of the plant material is converted to animal products.
• it is more efficient to eat bread made from wheat, than to wheat to chickens and the eat their eggs and meat —> no energy is wasted on keeping the animal alive.

Question 14

*describe how energy is transferred between trophic levels

Answer 14

a herbivorous animal eats a plant, so the chemical energy in the plant is transferred to the herbivore.
when a carnivore eats the herbivore, energy is transferred in the same way.
the carnivore may be eaten by another carnivore.

Question 15

what is a pyramid of biomass?

Answer 15

biomass is the word used when the mass of living organisms is being considered, and pyramids of biomass can be constructed.

Question 16

*what are the trophic levels represented by food webs, food chains, pyramids of numbers and biomass?

Answer 16

producers
primary consumers
secondary consumers
tertiary consumers
quaternary consumers

Question 17

*what trophic levels can consumers be classified into?

Answer 17

primary consumers
secondary consumers
tertiary consumers
quaternary consumers

Question 18

*define

herbivore

Answer 18

an animal that gets its energy by eating plants.

Question 19

*define

carnivore

Answer 19

an animal that gets its energy by eating other animals.

Question 20

*define

decomposer

Answer 20

an organism that gets its energy from dead or waste organic material.

Question 21

why do humans harvest animals?

Answer 21

species may be harvested for food, body parts, or for selling as pets.

Question 22

what is overfishing?

Answer 22

commercial fishing (large nets + small holes) ---> catching methods have become more sophisticated + more small non-mature fish are caught ---> decline in number of fish.
in some cases, stocks are so depleted that it is no longer economical to exploit them.
whaling ---> extinction of whales.
the use of heavy nets dragged along the sea floor to catch fish can wreck coral reefs ---> destroys habitats of many other animal species.

Question 23

*use food chains and food webs to describe the impacts humans have through overharvesting of food species

Answer 23

• it causes the reduction in numbers of a species to the point where it is endangered or made extinct.
• hunting animals or fishing is not always regulated or controlled and rare species can be threatened as a result of indiscriminate killing.
• biodiversity is affected —> if some events interfere with a food web, all the organisms are affected in some way.
• fishing for the top predators has a direct effect on the food chain: fish lower down the chain increase in numbers and overgraze on the reef.

Question 24

*use food chains and food webs to describe the impacts humans have through introducing foreign species to a habitat

Answer 24

• the accidental introduction of foreign species can disrupt food chains.
• the foreign animals feed on other other animals and have no natural predators —> other species are brought to extinction while the foreign species thrive.
• the foreign species need to be exterminated.

Question 25

*how would you draw and interpret a pyramid of biomass

Answer 25

pyramids of biomass must be drawn with the:
1- bars equally spaced around the midpoint
bars touching
2- bar for the producer at the bottom
3- length of each bar is proportional to the amount of biomass available at each trophic level

Question 26

*how would you draw and interpret a pyramid of numbers

Answer 26

A pyramid of numbers shows the total number of individual organisms at each level in the food chain of an ecosystem.

Question 27

*discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a food chain

Answer 27

• displaying food chains using pyramids of number can produce inverted pyramids, because the top consumer may be represented by large numbers of very small organisms.
• so instead of considering the number of a trophic level, it is better to look at the biomass of the total organisms in a trophic level.
• a pyramid of biomass is nearly always the correct pyramid shape.

Question 28

decomposers do not belong to any food chains, so how do they survive?

Answer 28

fungi and bacteria in the soil.

• they don’t obtain their food by photosynthesis, nor do they kill and eat living animals or plants. instead, they feed on decaying matter.
• they produce extracellular enzymes that digest the decaying matter and then absorb the soluble products back into their cells.
• they also break down remains into substances that can be used by other organisms.
  ex) bacteria break down proteins into ammonium to release nitrates.

Question 29

*describe the carbon cycle

Answer 29

photosynthesis, respiration, feeding, decomposition, fossilization and combustion.

Question 30

*describe the water cycle

Answer 30

evaporation, transpiration, condensation and precipitation.

Question 31

*Describe the nitrogen cycle

Answer 31

– decomposition of plant and animal protein to 
ammonium ions
– nitrification 
– nitrogen fixation by lightning and bacteria
– absorption of nitrate ions by plants 
– production of amino acids and proteins
– feeding and digestion of proteins
– deamination
– denitrification

Question 32

*State the roles of microorganisms in the nitrogen

cycle

Answer 32

decomposition, nitrification,
nitrogen fixation and denitrification (generic
names of individual bacteria, e.g. Rhizobium, are
not required)

Question 33

• discuss the effects of the combustion of fossil fuels and the cutting down of trees on the carbon dioxide concentrations in the atmosphere.

Answer 33

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Question 34

*define

population

Answer 34

a group of organisms of one

species, living in the same area, at the same time

Question 35

*define

community

Answer 35

all of the populations of

different species in an ecosystem

Question 36

*define

ecosystem

Answer 36

a unit containing the
community of organisms and their environment,
interacting together,

Question 37

*Identify and state the factors affecting the rate
of population growth for a population of an
organism

Answer 37

• food supply —> enables organisms to breed more successfully to produce more offspring.
  shortage of food leads to starvation —> death and emigration.
• predation
• disease

Question 38

*explain the factors that lead to each phase in the sigmoid curve of population growth, making reference, where appropriate, to the role of limiting factors.

Answer 38

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