Topic 19

Question 1

Energy flow

Answer 1

1. The sun is the principal source of energy input to biological systems -> light energy
2. Plants make biomass (store of chemical energy) from some of the glucose made by photosynthesis -> this chemical energy gets transferred to other organisms in the food chain when animals eat the plants and eachother
3. Biomass and energy are lost at each trophic level in the food chain

Question 2

Biomass and energy are lost at each trophic level in the food chain

Answer 2

. Small amount of the total energy available to trophic level becomes biomass (eg energy is stored or used for growth
. Large amount of total eneegy available to trophic level is lost -> energy transfer between trophic levels is very inefficient
- Lost in parts of food which aren’t eaten by organisms
- Lost in some parts of food that are indigestible -> pass throughthe body and come out as waste
- Most of this energy is eventually transferred to the environment as heat
-> This explains why there’s nearly no food chains with more than 5 trophic levels so much energy lost at each stage doesn’t mean that there’s not enough left to support more organisms after 4 or 5 stages -> tend to get fewer organisms at each trophic level

Question 3

Food chain

Answer 3

Shows transfer of energy from one organism to the next -> start always with a producer

Question 4

Food chains and food webs: producers

Answer 4

Organismas that make their own organic nutrients -> usually using energy from the sun during photosynthesis

Question 5

Food chains and food webs: consumers

Answer 5

Organisms that get energy by feeding on other organisms -> can be classified as primary, secondary, tertiary and quaternary according to their position in the food chain

Question 6

Food chains and food webs: decomposers

Answer 6

Organsims that get their energy from dead or waste organic material

Question 7

Food web

Answer 7

Network of interconnected food chains

Question 8

Trophic level

Answer 8

Position of an organism on a food chain, food web or ecological pyramid

Question 9

Ecological pyramids: pyramids of numbers

Answer 9

The bars show the number of organisms at a particular trophic level in the food chain
. Lowest bar: shows the producer -> trophic level 1
. Shape: upright pyramid

Question 10

Ecological pyramids: pyramids of biomass

Answer 10

The bars show the relative mass of living material at a particular trophic level -> bars don’t always get progressively smaller from the bottom to the top
. Biomass: mass of living material in food chain -> store of energy
. Lowets bar: shows the producer -> trophic level 1
. Shape: upright pyramid, inverted pyramid or not quite a pyramid

Question 11

Ecological pyramids: pyramids of energy

Answer 11

Show the rate of energy transfer between trophic levels -> the majority of energy present at one trophic level will not be available to the next
. Lowest bar: shows the producer -> trophic level 1
. Shape: upright pyramid

Question 12

Ecological pyramids: Pyramids of numbers VS pyramids of biomass

Answer 12

Pyramids of biomass are more accurate and used more often -> pyramids of numbers don’t always show what’s happening in a food chain very well

Question 13

Ecological pyramids: pyramids of energy VS pyramids of biomass/numbers

Answer 13

Pyramids of energy are more useful when showing the efficiency with which different food chains transfer energy and allow it to be directly compared -> pyramids of biomass/numbers might be misleading when doing this

Question 14

Ecological pyramids: drawing ecological pyramids

Answer 14

1. Use numbers, or figures for biomass or energy transfer given to draw bars of correct scale
2. The pyramid must follow the order of the food chain -> starting with the producer
3. Each bar must be labelled -> if you’re given units for biomass or the rate of energy transfer include them

Question 15

Humans and food webs: factors affecting species in food web

Answer 15

. Overharvesting: people take so much or an organism that its population is unable to reproduce quickly enough to keep up, and the population size falls -> this can lead to an extinction and the other species connected to it in the food web are all affected
. Foreign species: doesn’t naturally occur in the area -> can be introduced intentionally or unitentionally

Question 16

Humans and food webs: efficiency of plants and animals

Answer 16

As energy is lost at each trophic level in a food chain it is more efficient for humans to eat plants them to eat animals -> when eating animals you would be higher up the food chain as the animal has preciously eaten another animal or plant BUT plants can be producers (be on first trophic level)
. Farming crops to directly feed humans is more efficient than farming crops to feed livestock (farm animals) that are then used to feed humans

Question 17

Population sizes: population

Answer 17

A group of organisms of one species living in the same place at the same time

Question 18

Population sizes: comunity

Answer 18

Alk the populations of different species living in an ecosystem

Question 19

Population sizes: ecosystem

Answer 19

A unit containing a community and its environment, interacting together

Question 20

Population growth rate: food supply

Answer 20

More food available = population will likely grow

Question 21

Population growth rate: disease

Answer 21

Presence of pathogens = affects a population’s growth rate -> most likely will decrease

Question 22

Population growth rate: predation

Answer 22

• Predators: consumers that hunt and kill other animals -> prey are what they eat
  . Population of predator increases = population of prey will probably decrease
  . Population of prey increases = population of preadtors will probably grow
  . Population of prey decreases = population of oredators will probably decrease
  . Predator population removed = populations size of prey would increase until number of prey reached maximum envrionment could support -> prey population would then level off or start to decrease
  -> It takes time for one population to respond to changes in other population SO predator-prey cycles are always out of phase with eachother

Question 23

Population growth rate: competition

Answer 23

Presence of competitors affects population size -> most likey will decrease
. Plants: compete for light, space, water and mineral ions
. Animals: compete for space, food, water and mates

Question 24

The nitrogen cycle

Answer 24

1. Nitrogen in air has to be turned into mineral ions (eg nitrate ions) in soil before plants can use it -> this happens through nitrogen fixation
2. Plants absorb these ions from the soil and use the nitrogen in them to produce amino acids which join to make proteins
3. Nitrogen passes through food chains in form of proteins as animals eat plants and eachother -> when proteins digested they are converted back to amino acids
4. Deamination: in animals excess amino acids are broken down in the liver and ammonia is a waste product from this process -> gets converted into urea and excreted and nitrigen ions eventually return to soil
5. Denitrifying: bacteria in soil turn nitrates back to nitrogen gas

Question 25

The nitrogen cycle: lightning

Answer 25

Energy in bolt of lightning makes nitrogen react with oxygen in air to give nitrates

Question 26

The nitrogen cycle: nitrogen-fixing bacteria

Answer 26

Found in soil and the roots of some plants turn atmospheric nitrogen into nitrogen compounds that plants can use (eg ammonia which dissolved in water forms ammonium ions)

Question 27

Roles of microorganisms in the nitrogen cycles: Decomposition (decomposers)

Answer 27

Break down proteins (in rotting plants and animals) and urea (in animal waste) and turn them into ammonia -> forms ammonium in soil

Question 28

Roles of microorganisms in the nitrogen cycles: Nitrification (nitrifying bacteria)

Answer 28

Turn ammonium ions in decaying matter into nitrate ions and then nitrates

Question 29

Roles of microorganisms in the nitrogen cycles: Denitrification (denitrifying bacteria)

Answer 29

Turns nitrate back into nitrigen gas -> no benefit for living organisms

Question 30

The carbon cycle

Answer 30

Constant cycling of carbon -> from air through food chains (via plants, algae and animals, and decomposers) and eventually back out into air again

Question 31

The carbon cycle: photosynthesis

Answer 31

CO2 is removed from the atmoshpere by green plants and algae during photosynthesis where it’s used to make glucose -> can be turned into carbohydrates, fats and proteins that make up the bodies of plants and algaes

Question 32

The carbon cycle: respiration

Answer 32

plants and algae respire and some carbon is returned to atmosphere as CO2

Question 33

The carbon cycle: feeding

Answer 33

Plants and algae are eaten by animals and some carbon becomes part of the fats and proteins in their bodies -> carbon moves through the food chain and when animals respire some carbon is returned to the atmosphere as CO2

Question 34

The carbon cycle: decomposition

Answer 34

Decomposeres feed on the remains of plants, algae and animals when they die and break down waste produced by animals -> these can be types of animals (detritus feeders) or microorganisms and when these organisms respire CO2 is returned to the atmosphere

Question 35

The carbon cycle: formation of fossil fuels

Answer 35

Some dead organisms have been compresses over millions of years forming fossil fuels -> coals, oil and natural gas

Question 36

The carbon cycle: combustion

Answer 36

Combustion (burning) of wood and fossil fuels releases CO2 back into the air