chapter 21: ecology

Question 1

what does an abiotic environment consist of?

Answer 1

• it consists of physical, non-living factors such as light, water and pH of the soil and water

Question 2

what does a biotic environment consist of?

Answer 2

• it consists of all the living things that an organism interacts with

Question 3

what is habitat?

Answer 3

a place where an organism lives

Question 4

what is population?

Answer 4

it is a group of organisms of the same species that live together in a habitat

Question 5

what is a community?

Answer 5

it is made up of all the populations living and interacting with one another in a habitat

Question 6

what is ecosystem?

Answer 6

ecosystem is a community of organisms interacting with one another and with its abiotic environment

Question 7

how does light intensity affect organisms?
( the abiotic environment)

Answer 7

• light intensity affects the rate of photosynthesis and growth in plants
  > affects the rate of growth of animals
  > animals depend directly or indirectly on plants for food

Question 8

how does temperature affect organisms?
( the abiotic environment)

Answer 8

• temperature affects the rate of enzyme reactions
  > affect the metabolic rate and the rate of growth of organisms

Question 9

how does water availability affect organism?
( the abiotic environment)

Answer 9

• water is important for survival of all living things
  > the main component of protoplasm
• some animals adapted to live in arid regions
• desert rats have comparatively long loops of Henle (where water is reabsorbed) in their kidneys
  > most of the water filtered is reabsorbed by the kidneys
  > the urine of desert rats is relatively concentrated

Question 10

how does oxygen content affect organisms?
( the abiotic environment)

Answer 10

• oxygen is needed for aerobic respiration
  > aerobic respiration releases energy for cell activities such as active transport of mineral salts
• plants living in oxygen-poor soil usually have special adaptations to obtain the amount of oxygen needed
• eg. mangroves plants (avicennia) have their roots buried in oxygen-poor mud
  > have special breathing roots called pneumatophores
  > that project above the mud surface
  > the roots have openings for gas exchange
  > oxygen diffuses into these root openings to the whole root system of the plant

Question 11

how does the salinity of soil and water affect organisms?
( the abiotic environment)

Answer 11

• it affects the water potential of a solution
  > organisms living in freshwater constantly remove excess water that enter their bodies via osmosis
  > those living in sea water have to conserve water

Question 12

how does the pH of soil and water affect organisms?
( the abiotic environment)

Answer 12

• organisms are sensitive to the pH of soil or water in which they live in
  > pH of surroundings affect rate of enzyme reactions within bodies
  > extreme changes in the pH will result in denaturation of these enzymes

Question 13

what is an ecological community?

Answer 13

• when different populations of plants and animals live together and interact within the same environment
  > AN ECOLOGICAL COMMUNITY
• the various populations in any community live interdependently
  > a change in one population, affects the other populations of the community

Question 14

what are producers?

Answer 14

• producers can make their own food by photosynthesis
  > like plants, algae and photosynthetic bacteria and organisms
• the contain chlorophyll which traps and converts light energy into chemical energy
• they synthesise glucose from carbon dioxide and water and they produce oxygen as a by-product during photosynthesis
• producers affect the lives of other organisms
  > they provide them with energy and oxygen

Question 15

what are consumers?

Answer 15

• consumers are organisms that are not able to make their own food
  > they obtain energy and nutrients by feeding on other organisms

primary consumers: herbivores (plant eaters)
>they feed directly on plants

secondary consumers: carnivores (meat eaters)
>they feed on primary consumers

tertiary consumers: carnivores
> they feed on secondary consumers

Question 16

what are decomposers?

Answer 16

• decomposers feed on decaying organic matter
  > bacteria and fungi
• they break down dead bodies of organisms, faeces and excretory products
• their activities return nutrients to the environment

Question 17

explain the non-cyclic energy flow in an ecosystem

Answer 17

1. the ultimate source of energy is the sun
   > sun provides light energy
2. light energy absorbed by chlorophyll in producers is converted into chemical energy during photosynthesis
3. energy in producers is passed from one trophic level to another by feeding
4. the flow of energy through the ecosystem is non-cyclic
   > energy lost as heat to the environment through respiration
   > since heat energy does not return to the same system or the organisms that produce it
   > it cannot be recycled in the ecosystem
5. egested and excreted materials and dead organisms contain trapped chemical energy
   > the energy is released through the activity of decomposers
   > decomposers use some of this trapped energy for their needs
   > the rest of the energy is lost as heat

• living organisms cannot use heat energy to do work
  > can only use light and chemical
  > thus, light energy has to be constantly supplied to the ecosystem

Question 18

what is the pyramid of numbers used for?

Answer 18

• it allows us to compare the number of organisms present in each trophic level at a particular time

Question 19

what is the pyramid of biomass used for?

Answer 19

• it allows us to compare the mass of organisms
  > the dry mass of organisms in each trophic level at any one time
  > the dry mass of an organism is the mass of the organism when all its water has been removed

Question 20

why are short food chains more efficient in energy transfer?

Answer 20

• since large amount of energy is lost at each trophic level (arnd 90%)
  > less and less energy is available for the organisms at the next trophic level as we move along the food chain
• the shorter the food chain, the greater amount the energy available to the final consumer because less energy is lost to the environment

Question 21

describe the carbon cycle.

Answer 21

• carbon is constantly being removed from and released into the environment as carbon dioxide
  > the carbon dioxide concentration remains relatively constant

1. PHOTOSYNTHESIS (removing CO2)
   - plants absorb carbon dioxide and use it to synthesise carbohydrates
   > some of the carbohydrates are converted into fats and proteins
2. FEEDING (removing CO2)
   - animals obtain carbon compounds by feeding on plants or other animals
3. RESPIRATION (returning CO2)
   - plants and animals respire, releasing carbon dioxide into the environment
4. DECOMPOSITION (returning CO2)
   - decomposers: bacteria, microbes and fungi
   > break down organic matter and release carbon dioxide
5. COMBUSTION (returning CO2)
   - dead bodies of organisms buried in the earth for millions of years produce fossil fuels
   > coal, natural gas and oil
   > combustion of these fossil fuels releases carbon dioxide into the environment

Question 22

what is the importance of the carbon cycle?

Answer 22

• ensures that there is a continuous supply of carbon dioxide for plants to carry out photosynthesis
  > photosynthesis converts light energy from the sun into chemical energy in food
  > which non-photosynthetic organisms can use to stay alive
• enables energy to flow through the ecosystem
  > carbon compounds carry the stored energy from organism to organism in the food chains of an ecosystem
• it maintains the correct concentration of carbon dioxide in the atmosphere

Question 23

what is a carbon sink?

Answer 23

• a carbon sink is an area that stores carbon compounds for an indefinite period
  > stores more carbon than it releases

Question 24

why is the ocean a carbon sink?

Answer 24

• about one third of the carbon dioxide released by human activities is absorbed by the oceans
• the role of oceans as carbon sinks is driven by SOLUBILITY and PHOTOSYTHESIS
  > the carbon dioxide that dissolves in the ocean’s water is absorbed and used by phytoplankton and algae in photosynthesis
• a portion of the carbon compounds found in the oceans in buried in the seabed
  > and is in the form of fossil fuels such as natural gas and oil
• to increase the photosynthetic activity of phytoplankton
  > add iron compounds such as iron oxide and iron sulfate into the ocean
  > stimulates the growth of phytoplankton and increases the phytoplankton’s photosynthetic rate

Question 25

why are forests carbon sinks?

Answer 25

• atmospheric carbon dioxide is absorbed by the plants and used in photosynthesis
  > large amount of carbon compounds is stored in trees
  > when they die, their remains may be buried deep in the ground
  > after millions of years, the remains form coal- a fossil fuel
• the study of the asian , african and south american tropical forests show that forests absorb about 20% of all the carbon dioxide released by the burning of fossil fuels

indiscriminate deforestation has damaging effects
> effective forest management is important
- canada has about 10% of the world’s forest and it claims that less than 0.5% of its forests are harvested in a year
> harvested areas are allowed to regenerate again

Question 26

what is the kyoto protocol?

Answer 26

• it requires participating industrialised countries to reduce their carbon dioxide emission
  eg. USA should reduce their carbon dioxide emission by 7%
  > they would need to plant millions of fast-growing trees per year to reforest lands over a period of 40 years
• in 2001, the US pulled out of the Kyoto protocol
  > but most of the other industrialised nations still collectively agreed to reduce their greenhouse gases emissions by 5.2% for the period of 2008-2012
• singapore joined the kyoto protocol in 2006
  > in SG, the primary greenhouse gas is carbon dioxide generated for energy consumption
  >in trying to reduce energy consumption, singapore has made it compulsory for all air conditioners and refrigerators to be energy efficient