Organisms and Their Environment.

Question 1

What is ecology?

Answer 1

The study of organisms in their environment.

Question 2

What is a habitat?

Answer 2

The place where an organism lives.

Question 3

What is the source of all energy in an ecosystem?

Answer 3

The Sun is the source of all energy in an ecosystem.

Question 4

Describe the flow of energy through living organisms.

Answer 4

Plants absorb light energy and convert it into chemical energy during photosynthesis → Plants produce food and the energy is trapped in the bonds of biological molecules such as carbohydrates, proteins, and fats → The energy is transferred from a plant to an animal and then to other animals on a food chain.

Question 5

What do food chains and food webs show?

Answer 5

Food chains and food webs show what living organisms feed on in a community.

Question 6

What is a food web?

Answer 6

A food web is a network of interconnected food chains.

Question 7

What does a food chain show?

Answer 7

A food chain shows the transfer of energy from one organism to the next, beginning with a producer.

Question 8

What is a producer?

Answer 8

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

Question 9

What is a consumer?

Answer 9

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

Question 10

What is a herbivore?

Answer 10

A herbivore is an animal that gets its energy by eating plants.

Question 11

What is a carnivore?

Answer 11

A carnivore is an animal that gets its energy by eating other animals.

Question 12

What is a decomposer?

Answer 12

A decomposer is an organism that gets its energy from dead or waste organic matter.

Question 13

Give 8 causes of food chain and food web impacting and unbalancing;

Answer 13

• Humans over-harvesting food species.
• Humans introducing foreign species to a habitat.
• Over-predation or hunting.
• Disease.
• Pollution.
• Use of pesticides.
• Lack of food.
• Emigrations.

Question 14

What is a trophic level?

Answer 14

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

Question 15

What is a pyramid of numbers?

Answer 15

A diagrammatic representation of the numbers of different organisms at each trophic level in an ecosystem at any one time.

Question 16

What are the disadvantages of pyramids of numbers?

Answer 16

• The range of numbers may be enormous so drawing the pyramid to scale may be very difficult.
• Pyramids may be inverted, particularly if the producer is very large or parasites feed on the consumers.

Question 17

What is a pyramid of biomass?

Answer 17

Represents the biomass at each trophic level at any one time.

Question 18

What do pyramids of energy show?

Answer 18

They show energy transfer in an ecosystem.

Question 19

Why are the processes of collecting data for pyramids of energy destructive?

Answer 19

The process of collecting data for pyramids of energy is destructive because the organisms have to be killed and burned to measure their energy content so this is not done very often.

UNITS USED ARE kJ per m² per year.

Question 20

What type of pyramids are produced by pyramids of energy?

Answer 20

A normal-shaped pyramid is always produced because there is a reduced amount of energy at each successive level.

Question 21

What is an energy loss?

Answer 21

Energy is not recycled. The transfer of energy from one tropic level to another is inefficient as energy is lost to the environment at each level of the food chain.

Question 22

Name five ways energy can be lost at each level of the food chain;.

Answer 22

• Through respiration, energy is used for active transport and protein synthesis.
• Used up in movement.
• To maintain a constant temperature for warm-blooded animals.
• As heat energy in faeces and urine from warmed-blooded animals.
• Some material is not used - it is indigestible.

Question 23

If we cut down on the number of links in the food chain more individuals at the end of the food chain can be fed. Why?

Answer 23

This is because we are cutting down the loss of energy at each trophic level.

Question 24

Why do food chains usually have less than five trophic levels?

Answer 24

Food chains usually have less than five trophic levels because there is not enough energy left to supply the next link. In shorter food chains, less energy is lost.

Question 25

Give an example of an inefficient energy transfer.

Answer 25

maize → cow → human.
100 → 10 → 1.

Question 26

Give an example of a conservation of energy food chain.

Answer 26

maize → human.
100 → 10.

Question 27

Explain why it is more energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants.

Answer 27

If humans eat the plants there is much more energy available to them than if they eat the livestock that eat the plants. This is because energy is lost from the livestock, so there is less energy available to pass on to humans.

Therefore, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores

Question 28

What is the nutrient cycle?

Answer 28

Plants absorb elements (C, H, O, N, P, S) from the air and soil and pass them on to animals. When the plants and animals die, they are decomposed and the nutrients are recycled into the air and soil.

Question 29

Explain the process of decomposition.

Answer 29

Some fungi and bacteria feed on waste materials. They secrete enzymes onto the food to break down carbohydrates, fats, and proteins into small molecules that they absorb.
During aerobic respiration, they produce carbon from carbohydrates as carbon dioxide and nitrogen from amino acids as ammonia. These simple compounds are recycled and used by plants to make organic compounds.

Question 30

Describe the carbon cycle: Use single terms.

Answer 30

Photosynthesis → Respiration → Feeding → Decomposition → Formation of fossil fuels → Combustion.

Question 31

Describe the carbon cycle: Use complex terms.

Answer 31

• Carbon dioxide in the air diffuses through the stomata in a leaf for photosynthesis.
• Animals and plants release carbon dioxide back into the air through respiration.
• Feeding.
• Decomposers (bacteria and fungi) break down the organic molecules through the process of respiration, to release energy. This also releases CO₂ back into the air.
• Over a long period of time, this can form fossil fuels such as coal, oil, and gas.
• Combustion of fossil fuels releases carbon dioxide back into the air.

Question 32

What is nitrogen required for?

Answer 32

Nitrogen is required to make amino acids, proteins, DNA and chlorophyll.

Question 33

How do nitrogen compounds become available for plants in the soil?

Answer 33

• 78% of air is nitrogen gas, the energy from lightning causes nitrogen to react with oxygen (nitrogen fixing).
• Some microorganisms can “fix” nitrogen to provide usable nitrogen-containing substances.
• Dead organisms are decomposed by bacteria and fungi releasing ammonium salts into the soil.
• Nitrification: nitrifying bacteria in the soil change ammonium ions into nitrate ions.
• The addition of artificial fertilizers, compost, and manure.
• Dentrification and the return of nitrogen to the soil or the atmosphere.

Question 34

Some microorganisms can “fix” nitrogen to provide usable nitrogen-containing substances. Give examples of microorganisms that do this.

Answer 34

• Some nitrogen-fixing bacteria are found in the soil - these convert nitrogen gas from the air into nitrates for their own use.
• Some nitrogen-fixing bacteria live in root nodules of legumes (please, beans, clover) they change nitrogen gas into ammonia that the legume plant uses to make amino acids.

Question 35

Nitrification: nitrifying bacteria in the soil change ammonium ions into nitrate ions. Explain how these nitrate ions are made useful to the plant.

Answer 35

Plants absorb nitrate ions into their roots by active transport. The nitrates are combined with glucose (from photosynthesis) to form amino acids, which combine to form proteins in plants. Animals eat the plant and digest the proteins. The amino acids produced can be reorganized to form different proteins.

Question 36

Denitrification and the return of nitrogen to the soil or the atmosphere. Explain this further.

Answer 36

Denitrifying bacteria break down nitrates into nitrogen gas in water-logged soil.

Question 37

Nitrates and other ammonium compounds are very soluble, so they are easily leached out of the soil and can cause pollution. Famers can increase the fertility of their soil:

Answer 37

• Adding artificial fertilizer e.g. ammonium nitrate, to replace harvested plant material.
• Adding manure of compost for decomposers to act upon.
• Growing leguminous plants, then ploughing the roots with the nodules into the soil.

Question 38

What is a population?

Answer 38

A group of organisms of the same species, living in the same are, at the same time.

Question 39

What is a community?

Answer 39

All of the populations of different species in an ecosystem.

Question 40

What is an ecosystem?

Answer 40

A unit where a community of organisms and their environment interact.

Question 41

The rate of growth of a population depends on environmental resistance (limiting factors): Give 4 examples.

Answer 41

• Food supply: Shortage of food can result in death or forced emigration, reducing the population.
• Predation.
• Disease: Disease can cause population crashes if the species has no resistance or immunity.
• Competition.

Question 42

When a limiting factor influences population growth, a sigmoid curve is created. What are the four phases of a sigmoid curve?

Answer 42

• LAGphase.
• LOG or exponential phase.
• Stationary phase.
• Death.

Question 43

What leads to the LAG phase?

Answer 43

The number of mature reproducing individuals is low and they may be widely dispersed. When reproduction begins, a doubling of small numbers does not have a big impact on the total population size, so the line of the graph rises only slowly.

Question 44

What leads to the LOG phase?

Answer 44

There are no limiting factors such as food or water. The population is increasing rapidly. A steady doubling in numbers per unit of time produces a straight line.

Question 45

What leads to the Stationary phase?

Answer 45

Limiting factors such as shortages of food and build-up of waste products take effect. The rate of reproduction slows down and there are more deaths in the population. The population growth rate reduces.
When the birth rate and death rate balance, equilibrium is reached. There is no increase in numbers and the graph forms a plateau.

Question 46

What leads to the Death phase?

Answer 46

As food runs out, toxic materials build up and oxygen becomes short, more organisms die than are being produced. The population declines.

Question 47

Explain population growth in the absence of limiting factors.

Answer 47

If there are no limiting factors there will be no stationary or death phase and the log phase continues upwards, instead of leveling off.