Chapter 19 Organisms and their environment

Question 1

What is the principal source of energy to biological systems?

Answer 1

The Sun

Question 2

Describe the flow of energy through living organisms

Answer 2

Sunlight is harnessed by photosynthesizing plants and the energy is transferred between organisms in a food chain by ingestion
The energy released by animals comes ultimately from plants that they or their prey eat and since plants depend on sunlight to make their food, animals depend indirectly on sunlight
Eventually through one process or another, all the chemical energy in organisms is transferred to the environment

Question 3

Define a food chain

Answer 3

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

Question 4

How is energy transferred between organisms in a food chain?

Answer 4

Energy is transferred between organisms in a food chain by ingestion

Question 5

Define a food web

Answer 5

A network of interconnected food chains

Question 6

Define producer

Answer 6

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

Question 7

Define consumer

Answer 7

An organism that gets its energy by feeding on other organisms

Question 8

How may consumers be classified

Answer 8

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

Question 9

Define herbivore

Answer 9

An animal that gets its energy by eating plants

Question 10

Define carnivore

Answer 10

An animal that gets its energy by eating other animals

Question 11

Define decomposer

Answer 11

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

Question 12

Herbivore is a ______ consumer

Answer 12

Primary

Question 13

How do the arrows between each organism in a chain point?

Answer 13

The arrows between each organism in a food chain always points in the direction of energy flow from food to feeder

Question 14

Describe the effect of over-harvesting

Answer 14

1. Over harvesting causes the reduction in numbers of a species to the point where it is endangered or made extinct
2. As a result biodiversity is affected

Question 15

Describe the impact humans have through introducing foreign species to a habitat

Answer 15

An example of this process was the accidental introduction of rats to the Galápagos Islands.
The rats had no natural predators and food was plentiful; they fed on the eggs of bird, reptiles and tortoises along with young animals
The Galápagos Islands provide a habitat for many rare species, which became endangered as a result of the presence of the rats

Question 16

Describe how energy is transferred between trophic levels

Answer 16

Energy decreases as it moves up trophic levels because energy is lost as metabolic heat when the organisms from one trophic level are consumed by organisms from the next level

Question 17

Define trophic level

Answer 17

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

Question 18

Describe, draw and interpret the pyramid of numbers

Answer 18

• the pyramid of numbers shows the population at each stage in a food chain
• drawn as a bar chart with bars stacked on top of each other. The wider the bar the more organism it represents
• the producer is always at the bottom
• often it doesn’t look like a pyramid, possibly due to a large producer or a very small consumer

Question 19

Describe draw and interpret the pyramid of Biomass

Answer 19

• Biomass is the total dry mass of one animal or plant species in a food chain or food web
• a pyramid of biomass shows the biomass at each trophic level rather than the population
• nearly always correct pyramid shape
• more accurate indication of how much energy is passed on at each trophic level

Question 20

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

Answer 20

Because energy is lost while moving across trophic levels

This is because not the entire organisms consumed or digested

Question 21

Explain why food chains usually have fewer than five trophic levels

Answer 21

Because on average about 90% of the energy is lost at each level

Question 22

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

Answer 22

Pyramid of biomass is a more accurate indication of how much energy is passed on at each trophic level

Question 23

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

Answer 23

More efficient when crop plants are consumed by human directly as energy is passed directly to the human so less energy is lost.
Inefficient if fed to animals then human consumed the animals because as it passes through one more level of consumers, more energy is lost and less is being passed to human.

Question 24

Describe the carbon cycle

Answer 24

Removing carbon dioxide from the atmosphere:

• Plants use carbon dioxide from the atmosphere for photosynthesis
• the carbon becomes part of complex molecules in the plants, such as proteins, fats and carbohydrates

Passing carbon from one organism to the next:

• When an animal eats a plant, carbon from the plant becomes part of the fats and proteins in the animal
• When microorganisms and some animals feed on dead remains and waste material from animals, the carbon then becomes part of these organisms

Returning carbon dioxide to the atmosphere :

• Carbon dioxide is released to the atmosphere through respiration by animals, plants and microorganisms
• It is also released by the combustion of wood and fossil fuels (coal, oil, natural gas)
• Decomposition / decay also releases CO2. This process happens faster in warm, moist conditions with plenty of oxygen because it involves microorganisms

Question 25

Discuss the effects of the combustion of fossil fuels and deforestation on the carbon dioxide concentration

Answer 25

Burning fossil fuels such as coal and petroleum releases extra carbon dioxide into the atmosphere. This causes the concentration of carbon dioxide to increase.

Trees are responsible for removing gaseous carbon dioxide and trapping carbon in organic molecules
When they are cut down the amount of photosynthesis globally is reduced
Often deforestation is achieved by a process alert slash and burn, where the felled trees are burned to provide land for agriculture and this releases even more atmospheric carbon dioxide.

Question 26

Describe the water cycle

Answer 26

Evaporation: energy from the sun heats the earths surface and water evaporates from oceans, rivers and lakes. The warm air rises, carrying water vapor with it.
Transpiration: Transpiration from plants releases water vapor into the air.
Condensation: the moist air cools down as it rises. Water vapor condenses back into liquid water and this condensation process produces clouds
Precipitation: as the water droplets in the cloud get bigger and heavier they begin to fall as rain snow and sleet.

Question 27

Describe the nitrogen cycle in terms of decomposition of plant and animal protein

Answer 27

When a plant or animal dies, its tissues decompose, partly as a result of the action of saprotrophic bacteria. A product of the decay of animal and plant protein, ammonia is washed into the soil. It dissolves readily in water to form ammonium ions.

Question 28

Describe the nitrogen cycle in terms of nitrification

Answer 28

Nitrifying bacteria live in the soil, and they use ammonia from excretory products and decaying organisms as a source of energy.
In the process of getting energy from ammonia (nitrification), the bacteria produce nitrates
Nitrite bacteria oxidizes ammonium compounds to nitrites (NH4 - NO2)
Nitrate bacteria oxidizes nitrites to nitrates (NO2 -NO3)
Plant roots can take up ammonia in the form of its compounds, but they take up nitrates more readily so nitrifying bacteria increases the fertility of the soil by making nitrates available.

Question 29

Describe the nitrogen cycle in terms of nitrogen fixation by bacteria

Answer 29

Nitrogen fixing bacteria, a special group of nitrifying bacteria, can absorb nitrogen as a gas from air spaces in the soil and build it into ammonia compounds.
Nitrogen gas itself cannot be used by plants. When it has been made into a compound of ammonia, it can easily be changed to nitrates by other nitrifying bacteria.
The process of building nitrogen gas into ammonia compounds is called nitrogen fixation
Some of the nitrogen fixing bacteria live freely in the soil. Others live in the roots of leguminous plants, where they cause swellings called root nodules.
These leguminous plants can thrive in soils where nitrates are scarce because the nitrogen fixing bacteria in their nodules make compounds of nitrogen available for them
Leguminous plants are also included in crop rotations to increase nitrate content of the soil

Question 30

Describe the nitrogen cycle in terms of nitrogen fixation by lightning

Answer 30

The high temperature of lightning discharge causes some of the nitrogen and oxygen in the air to combine and form oxides of nitrogen
These dissolve in the rain and are washed into the soil as weak acids, where they form nitrates
Although several million tones of nitrate reaches the earths surface this way each year, only a small fraction is recycled

Question 31

Describe the nitrogen cycle in terms of absorption of nitrate ions by plants

Answer 31

Plant roots absorb nitrates from the soil and combines them with carbohydrates to make amino acids, which are built up into proteins
These proteins are then available to animals, which feed on the plants and digest the proteins in them

Question 32

Describe the nitrogen cycle in terms of denitrification

Answer 32

Denitrifying bacteria are bacteria that obtain their energy from breaking down nitrates to nitrogen gas, which then escapes from the soil into the atmosphere

Question 33

Define population

Answer 33

A group of organisms form species living in the same area at the same time

Question 34

Define community

Answer 34

All the populations of different species in an ecosystem

Question 35

Ecosystem

Answer 35

Unit containing the community of organisms in their environment interacting together

Question 36

Factors affecting the rate of population growth

Answer 36

Food supply
Predation
Disease

Question 37

Describe the sigmoid growth curve

Answer 37

Lag phase
The population is small. Although the numbers double at each generation, this does not result in a large increase. Low rates of reproduction.

Exponential(log)phase.
Continued doubling of the population at each generation produces a logarithmic growth rate. When a population of 4 doubles, it is not likely to strain the resources of the habitat, but when a population of 1021 doubles there is likely to be considerable competition for food and space and the growth rate starts to slow down. High rate of reproduction.

Stationary phase
The resources will no longer support an increasing population. At this stage, limiting factors come into play. The food supply may limit further expansion of the population, diseases may start to spread through the dense population and overcrowding may lead to a fall in reproduction rate. Now the mortality(death) rate equals the reproduction rate, so the population number stays the same.

Death phase
The mortality rate is now greater than the reproduction rate, so the population numbers begin to drop.
Fewer offspring will live long enough to reproduce. The decline in population numbers can happen because the food supply is insufficient, waste products contaminate the habitat or disease spreads through the population.