Organisms and their environment

Question 1

What is the sun to biological systems?

Answer 1

The Sun is the principal source of energy input to biological systems

Question 2

Describe the flow of energy of living organisms

Answer 2

The light energy from the Sun is harnessed by producers (plants and some bacteria) which convert light energy into chemical energy. Some of this energy is used in carrying out life processes but the stored chemical energy is then passed on to the primary consumer through feeding. Some is used up in life processes but when it is consumed by secondary and then tertiary consumers the energy is passed further up the food chain. At every trophic level (producers, consumers, decomposers), energy is lost as heat to the surroundings during metabolic processes like respiration. The energy is returned to the environment through decomposition.

Question 3

Food chain definition

Answer 3

shows the transfer of energy from one organism to the next, beginning with a producer

Question 4

Food web definition

Answer 4

a network of interconnected food chains

Question 5

How to construct a food chain?

Answer 5

1. Identify the producer first (normally a plant)
2. Add the primary consumer next
3. Add secondary consumer and then tertiary consumer (add quaternary if there)

🌟 Arrows go from nutrient source to predator

Question 6

Producer definition

Answer 6

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

Question 7

consumer definition

Answer 7

an organism that gets its energy by feeding on other organisms
- Consumers may be classed as primary, secondary, tertiary and quaternary according to their position in a food chain

Question 8

Herbivore definition

Answer 8

an animal that gets its energy by eating plants

Question 9

Carnivore definition

Answer 9

an animal that gets its energy by eating other animals

Question 10

Decomposer definition

Answer 10

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

Question 11

Trophic level definition

Answer 11

the position of an organism in a food chain, food web or ecological pyramid
- Producer is trophic level one, quaternary consumer is trophic level five

Question 12

Why do most of the changes in populations of animals and plants happen?

Answer 12

Most of the changes in populations of animals and plants happen as a result ofhuman impact- either byoverharvesting of food speciesor by theintroduction of foreign species to a habitat

Question 13

How does overharvesting affect the food chains/web?

Answer 13

Overharvesting occurs when humans remove a large number of individuals from a species, such as fish or certain animals, at a rate faster than they can reproduce. If a species in a food chain is overharvested, it creates an issue as the predators that rely on them for food may struggle to find enough food, leading to a decline in their populations and it leads to an increase in their nutrient source as they have less predators

Question 14

How does the introduction of foreign species affect the food chains/web?

Answer 14

Introduction of foreign species into a habitat creates competition for resources which disrupts food chains and food webs. They may have no natural predators in the new environment, allowing them to reproduce rapidly and dominate the ecosystem leading to a decline in native species

Question 15

Pyramid of number

Answer 15

• Tells us the population numbers of organisms in different trophic levels
• Thewidth of the boxindicates thenumber of organismsat that trophic level
• A pyramid of number doesn’t always have to be pyramid shaped (This is because it doesn’t account for thesize of the organism, different sizes have different energy requirements)

🌟 General rule larger organisms tend to have smaller populations

When drawing remember that you can’t change the trophic levels. Trophic level 1 is always on the bottom

Question 16

Pyramid of biomass

Answer 16

• A pyramid of biomass shows the total dry mass of living organisms (biomass) at each trophic level in a food chain.
• Pyramids of biomass are always pyramid shaped because there must always be more biomass in the previous trophic level to support the next

Question 17

Why are pyramids of biomass more accurate than the pyramid of number?

Answer 17

Pyramids of biomass are more accurate than pyramids of number because they provide a much better idea of thequantityof the plant or animal material at each level of a food chain and therefore are a better way of representing interdependence within the food chain

Question 18

What does a pyramid of energy show?

Answer 18

• A pyramid of energy shows the total amount of energy that is transferred through each trophic level in an ecosystem over a certain period of time
• Not all of the energy grass plants receive goes into making new cellsthat can be eaten. Only the energy that is made into new cells remains with the organism to be passed on.

Question 19

How much energy gets passed on from one trophic level to the next?

Answer 19

Only 10% of energy gets passed on from one trophic level to the next

Question 20

Where is the majority of energy used up (90%) in organisms?

Answer 20

• making waste productsthat get removed from the organism
• as movement
• through respiration
• as heat(in mammals and birds that maintain a constant body temperature)
• as undigested waste(faeces) that is removed from the body and provides food for decomposers

Question 21

Why do food chains usually have fewer than five trophic levels

Answer 21

Food chains usually have fewer than five trophic levels because of the significant energy loss that occurs at each trophic level, making it difficult to sustain a large number of higher-level consumers. There is less and less energy available to support organisms as you move up the food chain, at higher trophic levels (e.g., tertiary and quaternary consumers), there is often insufficient energy to support large populations or additional predators.

In order to survive, it would have to:
- eat a huge number of prey every day to get the amount of energy it needed to survive
- not expend much energy itself hunting them

Question 22

Why is it more energy efficient for humans to eat crops?

Answer 22

• Given what we know aboutenergy transfer in food chains, it is clear that if humans eat the wheat there ismuch more energy availableto them than if they eat the cows that eat the wheat
• This is because90% of energy is lost each trophic level so the higher you go there is less available to pass on to humans. Therefore, it ismore energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores

Question 23

Explain the carbon cycle

Answer 23

• Carbonis taken out of the atmosphere in the form ofcarbon dioxideby plants to be used for photosynthesis
• It is passed on to animals (and microorganisms) byfeeding
• It is returned to the atmosphere in the form ofcarbon dioxideby plants and animals as a result ofrespiration
• When organisms die decomposers break down the organic molecules through the process of respiration to gain energy, releasing carbon dioxide back into the atmosphere
• If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies is trapped and can be converted, over millions of years and significant pressure, intofossil fuels
• When fossil fuels are burned in combustion, the carbon combines with oxygen andcarbon dioxide is releasedinto the atmosphere
• Increased use of fossil fuelsis contributing to an increase in the carbon dioxide content of the atmosphere.
  
  • In addition,mass deforestationisreducing the number of producersavailable to take carbon dioxide out of the atmosphere by photosynthesis. This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they areburnt down, releasing yet more carbon dioxide into the atmosphere

🌟 Carbon is stored in the atmosphere as CO2, in plants as sugars, in animals as sugars, in dead organisms and in fossil fuels

Question 24

Why is nitrogen needed and why can’t it be absorbed from the air?

Answer 24

Nitrogenis an element is required to make proteins. Neither plants nor animals canabsorb it from the airas N2gas is very stable and cannot be easily broken down

Question 25

Two ways that Nitrogen gas in the air can be converted into a usable form (called nitrogen fixation)

Answer 25

• Nitrogen fixing bacteriaconvert N2gas into ammonium compounds, which can then be converted to usablenitrates
  
  • Nitrogen fixing bacteria can be free-living in the soil or can live within the root nodules of some plants
• Lightningcan split the bond between the two N atoms combining it with water (H2O) to formammonia (NH3) and nitrates (NO3)

Question 26

Explain the nitrogen cycle without nitrogen fixation

Answer 26

• The plants can’t absorb ammonium compounds, sonitrifying bacteriaconvert the ammonium compounds to nitrites and then to nitrates, which can then be assimilated by plants
• Plants absorb nitrogen from the soil in the form ofnitratesand use it to build proteins
• Animalseatthe plants and get the nitrogen they need from the plant proteins
  
  • This nitrogen ispassed up the food chainthrough feeding
• Waste(urine and faeces) from animals sends nitrogen back into the soil in the form of ammonium compounds
  
  • Ex: Deamination is when excess amino acids are broken down in the liver. The nitrogen-containing part of the amino acid is removed and converted into ammonia (NH₃), which is then quickly converted into urea for safe excretion from the body
• The bodies of dead plants and animalsdecayand all the proteins inside them are broken down into ammonium compounds by decomposers
• Denitrifying bacteriatake nitratesout of the soiland convert them back into N2gas
  
  • This processreduces soil fertilityand is bad for plant growth
  • Denitrifying bacteria are anaerobic so aerating the soil, e.g. by reducing waterlogging and turning over the soil during ploughing, can reduce the rate of denitrification

Question 27

Population definition

Answer 27

a group of organisms of one species, living in the same area, at the same time

Question 28

Community definition

Answer 28

all of the populations of different species in an ecosystem

Question 29

Ecosystem definition

Answer 29

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

Question 30

Four main factors that affect population growth

Answer 30

• Food supply
• Competition
• Predation
• Disease

Question 31

What is the lag phase?

Answer 31

Lag phase- organisms areadapting to the environment before they are able to reproduce; food is abundant but population size is small limiting the maximum rate of population growth

Question 32

What is the log phase?

Answer 32

Log phase(exponential phase)-food supply is abundant,birth rate is rapidanddeath rate is low;growth is exponentialand only limited by the number of new individuals that can be produced

Question 33

What is the stationary phase?

Answer 33

Stationary phase- populationstays the same sizedue to afactor in the environment normally amount of resources; birth rate and death rate are equal and will remain so until the factor is resolved or becomes more limiting

Question 34

What is the death phase?

Answer 34

Death phase- populationdecreasesas death rate is now greater than birth rate; this is usually due to overpopulation, increased competition and limited resources