Chapter 19

Question 1

the principal source of energy input to biological systems

Answer 1

The sun

Question 2

food chain

Answer 2

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

Question 3

How is energy transferred between organisms in a food chain?

Answer 3

Via ingestion

Question 4

trophic level

Answer 4

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

Question 5

Explain why there is a greater efficiency in supplying plants as human food, and that there is a relative inefficiency in feeding crop plants to livestock that will be used as food

Answer 5

When energy is being transferred from one organism to another, only 10% of that energy is actually passed down. Therefore, if we were to eat the livestock that eats plants, we are not getting as much energy as if we were to just eat plants.

Question 6

food web

Answer 6

a network of interconnected food chains

Question 7

producer

Answer 7

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

Question 8

consumer

Answer 8

an organism that gets its energy by feeding on other organisms

Question 9

How are consumers classed?

Answer 9

they can be classed as primary, secondary and tertiary according to their position in a food chain

Question 10

herbivore

Answer 10

an animal that gets its energy by eating plants

Question 11

carnivore

Answer 11

an animal that gets its energy by eating other animals

Question 12

decomposer

Answer 12

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

Question 13

What are the effects of the combustion of fossil fuels and the cutting down of forests on the carbon dioxide concentrations in the atmosphere

Answer 13

The combustion of fossil fuels creates carbon dioxide as a product and cutting down forests will decrease the number of organisms going through photosynthesis which used carbon dioxide as one of its reactants. Therefore these 2 processes cause an increase in carbon dioxide in the atmosphere.

Question 14

Describe the nitrogen cycle

Answer 14

Nitrogen is fixed by lightning and bacteria (converts atmospheric nitrogen into nitrogen plants can absorb), decomposers break down plant and animal protein into ammonium ions, nitrifying bacteria convert ammonia into nitrites and nitrates, plants absorb the nitrate ions, denitrifying bacteria release nitrogen back into the atmosphere. Nitrogen is also a part of the production of amino acids and proteins in plants (via deamination) and when they are consumed, they are passed off to the consumers.
(Deamination is a process in the nitrogen cycle where nitrogen atoms are changed around to become other useful elements for plant growth.)

Question 15

State the roles of microorganisms in the nitrogen cycle

Answer 15

They cause the decomposition of plant and animal protein into ammonium ions, convert ammonia into nitrogen, make atmospheric nitrogen into nitrogen oxides and such that can be absorbed by plants and releasing nitrogen back into the atmosphere (decomposition, nitrification, nitrogen fixation and denitrification)

Question 16

population

Answer 16

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

Question 17

community

Answer 17

all of the populations of different species in an ecosystem

Question 18

ecosystem

Answer 18

a unit containing the community of organisms and their environment, interacting together, e.g. a decomposing log, or a lake

Question 19

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

Answer 19

These factors include food supply, predation and disease

Question 20

Describe the flow of energy through living organisms including light energy from the Sun and chemical energy in organisms and its eventual transfer to the environment

Answer 20

Light energy from the sun is converted into chemical energy (carbohydrates) via green plants. Chemical energy is then transferred to the animals that eat the plant, and then given to the animals who ate those animals. When those animals die, their body decomposes and their energy is given into the environment.

Question 21

Describe how energy is transferred between trophic levels

Answer 21

Energy is transferred between trophic levels vis consumption

Question 22

Explain why food chains usually have fewer than five trophic levels

Answer 22

Less energy is transferred at each level of the food chain so the biomass gets smaller. Meaning that there is less food to be consumed. As a result, there are usually fewer than five trophic levels in food chains.

Question 23

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

Answer 23

Only 10% of the energy is actually transferred between trophic levels. This is due to egestion, excretion, respiration and the production of bones and shells.

Question 24

Use food chains and food webs to describe the impacts humans have through over-harvesting of food species and through introducing foreign species to a habitat

Answer 24

In food chains and food webs, they show how each animal is connected to each other through their consumption. So if there is a lack of one animal, or overpopulation of one animal, it affects other animals too. When humans over-harvest food species, more of the animals that consume those species either die out from hunger or rely on another food species, decreasing their population as well. Also, when we introduce another foreign species, they end up unbalancing the food web and can cause some species to decrease in population.

Question 25

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

Answer 25

Pyramid of biomass give a better idea of energy loss as you progress down the food chain than pyramid of numbers. They are also more accurate in terms of showing the sizes of organisms (e.g one tree but millions of insects)

Question 26

Describe the carbon cycle

Answer 26

Respiration causes CO2 to be released into the atmosphere, photosynthesis absorbs the CO2 from the atmosphere. Plants form carbon compounds in their body. When a herbivore eats a plant, it absorbs those carbon compounds. When a carnivore eats the animal, it absorbs those compounds and so on. Decomposers can also feed on their dead matter and waste material, also transferring the carbon compounds into the environment. There is also fossilisation where those animal and plants form carbon stores and they can go through combustion in factories into the atmosphere.

Question 27

Describe the water cycle

Answer 27

Heat from the sun leads to the evaporation of water from transpiration in plants and water substances into the atmosphere, they can then go through condensation and form clouds and when they become saturated with water, rain occurs as precipitation. It can then land back into water sources and in the soil of plants.

Question 28

What is the lag, exponential (log), stationary and death phases in the sigmoid population growth curve for a population growing in an environment with limited resources

Answer 28

The lag is the flat beginning, the log is rising, the stationary is the one high up that is flat and the death phase is the decreasing one.

Question 29

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 29

the lag phase is organisms adjusting to their environment, the log is the growth of the population increasing at a fast, exponential rate, the stationary is when the amount of births and deaths are equal and death is when the resources are starting to get used up (due to the large population and limited resources) and more of the species compete and die from starvation.

Question 30

Explain the increase in human population size over the past 250 years and its social and environmental implications

Answer 30

The human population has not followed the sigmoid curve (yet) and has only risen exponentially. This means that food and limited resources have been “claimed” by humans and less for animals, we produce a lot of waste that pollute rivers and also affect an increase in CO2 in the air (global warming), and depending on the population pyramid, medical resources, poorness and employment are affected.