ecosystems

Question 1

ecosystem

Answer 1

• a unit containing the community of organisms and their environment, interacting together
• consists of a living/biotic component (the communities) and a non-living/abiotic component (the environment in which the communities live)

Question 2

population

Answer 2

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

Question 3

community

Answer 3

all of the populations of different species interacting with each other in an ecosystem

Question 4

habitat

Answer 4

the place where organisms live

Question 5

examples of abiotic factors

Answer 5

• availability of oxygen
• availability of water
• light intensity
• pH (of water or soil)
• pollution
• temperature
• mineral ions

Question 6

effects of changing abiotic factors

Answer 6

• may affect the numbers of individuals in populations in the community which can affect the food web
• changes can also have positive effects e.g. an increase in temperature or light intensity can encourage plant growth which can provide more food for herbivores, or more camouflage, or sites for breeding

Question 7

examples of biotic factors

Answer 7

• competition
• disease
• food supply
• predation

Question 8

types of competition

Answer 8

• intraspecific: competition between organisms of the same species for resources (e.g. food, territory, mate)
• interspecific: competition between organisms of different species for resources
• intraspecific competition has a greater impact on the population size than interspecific

Question 9

Relationship between prey and predator numbers

Answer 9

• the breeding rate of the population may not be enough to replace those eaten by predators, so the number of individuals in the population will drop
• As the number of prey increases, the number of predators increases
• As the number of predators increase, the number of prey decreases so there is less food for the predators. The number of predators then decreases, and so on.
• There is always a time lag between changes in prey numbers and changes in predator numbers

Question 10

pollution

Answer 10

• the introduction of raw sewage into a water system which can reduce the oxygen available to fish
• acid rain, caused by combustion of fossil fuels such as coal, kills populations of trees and reduces populations of trout in lakes

Question 11

climate change

Answer 11

• Increases in water temp due to global warming have negative effects on coral. As corals bleach and die, food chains are destroyed so the whole community in that ecosystem is destabilised
• As water warms up, the solubility of oxygen in it decreases which is a problem as most species of aquatic animals rely on oxygen for aerobic respiration

Question 12

phases of growth for micro-organisms

Answer 12

• Lag phase: population is very small and takes time to acclimatise to a new environment, become mature and start reproducing
• Log/exponential phase: no limiting factors. rapid breeding in the population, resulting in significant increases in numbers, far more births than deaths
• Stationary phase: shortage of food and build-up of toxic materials in the environment start to have an effect, slowing down population growth, gets to the point where no. of deaths = no. of births, so line flattens
• Death phase: no. of deaths>no. of births so population numbers start to decrease, may be due to lack of food, accumulation of toxic materials, disease spreading through the population, or an influx of predators

Question 13

factors that cause a rise in population numbers for humans

Answer 13

• more births than deaths
• more efficient food production
• lower infant mortality rates
• better control of diseases

Question 14

mutualism

Answer 14

a close relationship between two organisms of different species where both organisms benefit

Question 15

parasitism

Answer 15

-a relationship in which the parasite benefits, whilst the host is harmed

Question 16

survival of the fittest + example

Answer 16

• Through intraspecific competition, stronger individuals in a population tend to survive and breed, passing their favourable genes to the next generation
• example: In Britain, the red squirrel is in decline because of interspecific competition with grey squirrels. Grey squirrels are more successful in forcing red squirrels out of their natural habitats because they are bigger, have a greater range of food sources and spread a disease which kills red squirrels but is not usually lethal to greys.

Question 17

fates of light

Answer 17

• 1% is absorbed by photosynthetic plants to make their food
• some light is reflected
• some light is used to evaporate water from leaves (transpiration)
• some light warms up the soil, plants and air

Question 18

photosynthesis

Answer 18

• carried out by green plants and some types of bacteria
• Photosynthesis is a process whereby plants absorb light energy, using pigments such as chlorophyll, and convert it into chemical energy – stored in molecules e.g. carbohydrates, fats and proteins
• The food produced and built up in a plant is known as its biomass
• carbon dioxide + water -> oxygen + glucose

Question 19

food chain parts

Answer 19

1. producers- photosynthetic plants
2. primary consumers - herbivores
3. secondary consumers - carnivores

Question 20

food chain definition

Answer 20

-A food chain shows the transfer of energy between one organism and the next, beginning with a producer

Question 21

food webs

Answer 21

• composed of many interlinked food chains

- they are more accurate because in reality each organism eats and is eaten by a variety of other organisms

Question 22

energy loss

Answer 22

-only 10% of energy is passed from one organism to another
Energy can:
-be lost due to heat (during respiration, movement, metabolism),
-remain in undigested food that passes through the organism and is removed in faeces
-stored in undigestible material (e.g. horns, fur) that is not eaten by the next organism

Question 23

uses for sugar produced by photosynthesis

Answer 23

• respiration (can be broken down again to provide energy)
• storage (can be converted to starch which is a storage sugar)
• structure (can be converted to cellulose, the main component of plant cell walls)
• metabolic pathways (sugars can enter other metabolic pathways that convert it to proteins/fats)

Question 24

decomposition

Answer 24

• When organisms die, they provide food for detritus feeders (e.g. worms, woodlice and microorganisms)
• Decomposition is the process by which bacteria and fungi break dead organisms into their simple compounds (CO2 and nitrate)
• Bacteria/fungi secrete digestive enzymes out of their cells into the soil or dead organism
• Some of the products are absorbed by the bacteria/fungi

Question 25

deforestation

Answer 25

Deforestation has a detrimental effect on the amount of carbon dioxide in the air because:

1. there are fewer trees photosynthesising, so less carbon dioxide is removed from the air
2. when the trees are cut down, the small branches and foliage are burned, adding more carbon dioxide back into the air through the process of combustion

Question 26

the water cycle

Answer 26

Transpiration – plants release water vapour into the atmosphere, mainly through stomata in the leaves. The water evaporates inside the leaf before it is released

Evaporation – occurs from the surface of bodies of water

Condensation – water vapour in the atmosphere condenses to form clouds

Precipitation – water in the clouds forms rain, snow, etc. which falls to the land and drains into water systems

Osmosis – the process used by plant roots, bacteria and other organisms to take up water

Excretion – water is lost from animals in the form of sweat, exhaled air, urine and faeces

Question 27

the carbon cycle

Answer 27

• Photosynthesis - plants absorb CO2 from the atmosphere
• Feeding - animals eat plants which contain carbon in many forms
• Decomposition - complex carbon compounds in dead organisms, urine and faeces are broken down into simpler carbon compounds by bacteria or fungi
• Respiration - living organisms (plants, animals and decomposers) respire, releasing CO2 into the atmosphere

Question 28

nitrification process

Answer 28

ammonium compounds -> nitrites -> nitrates