AQA GCSE Biology paper 2

State the levels of organisation in an ecosystem.

Individual, population, community, ecosystem

What is an ecosystem?

The interaction between the living components and the non-living components

State the factors that plants may compete for

• light

• space

• water

• mineral ions from the soil

State the factors that animals might compete for

• food

• mates

• territory

What is intraspecific competition?

competition within a species

What is interspecific competition?

Competition between different species

What is interdependence?

Different species in an ecosystem depend on each other for various resources, if one species is removed, the whole community may be affected

What is a stable community?

A community in which all the biotic and abiotic factors are balanced so that population sizes remain relatively constant

What are abiotic factors?

non-living factors

State the abiotic factors that may affect an ecosystem?

• light intensity

• temperature

• moisture

• soil pH and mineral content

• wind intensity and direction

• carbon dioxide level

• oxygen level

Why might light intensity affect an ecosystem?

Different species of plants may have different optimum light intensities for growth.

Why does temperature affect an ecosystem

Different species of plants and animals may have different optimum temperatures for growth and survival.

How does soil pH affect an ecosystem?

Certain plants may grow better in either alkaline or acidic soil. Soil pH may affect the appearance of the plant eg. colour of hydrangea

How does moisture level affect an ecosystem?

Many plants cannot survive in waterlogged soil as their roots cannot respire Certain plants are adapted to high moisture levels

How does wind intensity affect an ecosystem?

Plant seeds are more likely to germinate in locations with lower wind intensity, which may also attract animals that depend on the plant to live nearby.

How does soil mineral content affection an ecosystem?

Most plants require a high level of soil minerals to grow well

Give an example of a type of plants that have adapted to low soil mineral content

Carniverous plants catch insects to compensate for the low level of soil mineral content

How does carbon dioxide concentration affect an ecosystem

Higher carbon dioxide concentration leads to more plant growth

How does oxygen concentration affect an ecosystem?

Aquatic animals cannot survive in areas with low oxygen concentration.

State the biotic factors that may affect an ecosystem.

• food

• new predators

• new pathogens

• competition

What are adaptations?

Features that enable organisms to survive in their living environment

What are organisms living in extreme environments called?

Extremophiles

Give three examples of extreme living environments

• high temperature

• high pressure

• high salt concentration

State an example of where extremophile bacteria can be found.

In deep sea vents

Define population

A species that occupy the same habitat

Define habitat

the place in which an organism lives

Define community

populations of different species interacting

Define ecosystem

The interactions between the biotic and abiotic factors in an area

What do food chains show?

Food chains show the feeding relationships of different organisms and the flow of energy between the organisms.

Define biomass

The total mass of living material

What are trophic levels?

The stages in a food chain

What do the arrows in a food chain represent?

The direction of biomass transfer

Describe a simple food chain

producer --> primary consumer --> secondary consumer --> tertiary consumer

What is a producer?

An organism that makes its own food

What types of organisms are primary producers?

Photosynthetic organisms like green plants and algae that trap energy from the sun

What is a primary consumer?

An organism that feeds on producers.

What is a secondary consumer?

an organism that feeds on primary consumers.

What is a tertiary consumer?

An organism that feeds on secondary consumers

what is a predator?

A consumer that kills and eats other animals

What is prey?

an animal that is killed and eaten by another animal

Describe the pattern of predators and prey in a stable community

The numbers of predators and prey rise and fall in cycles

Why are producers the first trophic level?

• Producers provide all biomass for the food chain (via photosynthesis)

• The rest of the food chain involves the transfer of this biomass

What piece of apparatus is used to measure the abundance and distribution of organisms in an area?

Quadrat

What piece of apparatus is used to study the distribution of organisms across a gradient

Belt transect

When considering the abundance of organisms, what is meant by the term "mean"?

The average number of organisms

Describe how materials cycle through the living and non-living components of an ecosystem?

• organisms take in elements form their surroundings

• elements converted to complex molecules which become biomass

• elements transferred along food chains

• elements returned to environment during excretion and decomposition

give three molecules which are cycled through ecosystems

• Oxygen

• Carbon dioxide

• water

Describe the carbon cycle

• plants fix carbon dioxide into organic molecules during photosynthesis

• the organic carbon-containing molecules are passed onto organisms that eat the plant

• carbon dioxide is released back into the atmosphere by respiration from plants and animals

• burning fossil fuels also releases carbon dioxide into the atmosphere

Why is the carbon cycle important?

Carbon-containing molecules such as glucose are important for living organisms to grow and provide energy for vital functions within cells.

Describe the water cycle

• Water from lakes and oceans evaporates.

• The evaporated water condenses into clouds and returns to earth as precipitation.

• The water from precipitation is useful for life on land.

• The water then returns to rivers and oceans through surface runoff.

Why is the water cycle important?

Living organisms require water and the water cycle provides organisms on land with a continuous supply of water.

Why are microorganisms important for the cycling of materials through an ecosystem?

Microorganisms return carbon to the environment by releasing carbon dioxide through respiration while they decompose dead matter. The decomposition of dead matter in soil returns mineral ions to the environment for other organisms to use

How can different temperatures be bad for certain communities?

• if the temperature is too low, growth will be sower as organisms will use more energy to stay warm

• If the tempreature is too high, organisms can die and water will become limited as evaporation increases

How can changes in water levels affect ecosystems?

• Animals may have to migrate to find water.

• Melting ice caps may destroy the habitats of some animals (either animals living in icy regions or by sea level rise).

How can atmospheric gases affect ecosystems?

• Some organisms cannot survive when certain gases are present

• Polluted water can cause illness to animals that drink it

What detrimental impacts can sulfur dioxide have on the environment?

• formed when fossil fuels containing impurities are burnt

• sulfur dioxide can dissolve in water to form acid rain which can erode buildings and pollute water sources

What detrimental impacts can carbon monoxide have on the environment?

• carbon monoxide is formed from the incomplete combustion of fossil fuels

• carbon monoxide binds irreversibly to haemoglobin which prevents it from carrying oxygen

• too much exposure can cause unconsciousness and death

Name 4 green house gases

• water vapour

• carbon monoxide

• nitrus oxide

• methane

Give 3 human activities that contribute to greenhouse gases

• burning fossil fuels

• deforestation

• large scale livestock farming

How do greenhouse gases lead to global warming?

• Greenhouse gases allow heat from the sun to enter the atmosphere.

• The gases act as a 'blanket' and trap the heat in the atmosphere.

State 3 negative consequences of global warming

• Sea level rise caused by melting icebergs.

• Disrupted farming and agriculture.

• Increased spread of diseases in warmer climates.

What is biodiversity?

The variety of different species of organisms on Earth or within an ecosystem

What is the importance of biodiveristy?

To maintain the stability of an ecosystem

How does biodiveristy ensure the stablity of an ecosystem

It reduces the dependence on particular species for resources, so that even if one species is removed another can still survive

Why have humans' consumption of resources and waste production increased?

• rapid increase in human population

• increase in standard of living

Where does pollution occur?

• air

• land

• water

State an example of water pollutants

• sewage

• fertiliser -chemicals

How does eutrophication occur?

Fertiliser from farms pollute the water, causing excessive algae growth, depleting the oxygen in the water, causing other plants and animals to die. Dead plants are decomposed by bacteria and the oxygen level decreases further.

State an example of air pollutants

• smoke

• acidic gases

State an example of land pollutants

• Landfill waste

• Chemicals

Which human activities reduce the land available for animals and plants?

• building

• farming

• quarrying

• disposing of waste

Why have peat bogs been destroyed?

To produce compost to increase food production.

Why does the destruction of peat bogs greatly contribute to the greenhouse effect?

Peat bogs are stores of carbon and burning them releases a large volume of carbon dioxide into the atmosphere

Why have large-scale deforestation activities occurred?

• To provide land for cattle or rice fields

• to grow crops to produce biofuels

What is the greenhouse effect?

Greenhouse gases trap energy from the Sun as heat in the atmosphere, keeping the temperature on earth suitable for life.

What causes global warming?

The increase in levels of greenhouse gases causing the temperature on earth to increase

What are the harmful effects of deforestation?

• Destruction of many animals' habitats

• Releases large amounts of greenhouse gases

State the consequences of global warming

• Rising sea levels

• Melting polar ice caps

• Changing weather patterns

• Migration of animals to find suitable habitats

• Tropical diseases becoming more common

• Extinction of species

Describe the steps taken to maintain biodiversity?

• Breeding programmes for endangered species.

• Protection and rebuilding habitats.

• Replanting field margins and hedgerows.

• Reduce deforestation.

• Reduce carbon dioxide emissions.

• Recycling rather than disposing in landfills.

What is the purpose of replanting hedgerows and field margins?

There is higher biodiversity in the margins than the field that they surround

What is homeostasis?

Homeostasis is the maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular function

Give examples of conditions maintained by homeostasis in the body?

• blood glucose concentration

• body temperatures

• water levels

What two types of responses are used in body control systems?

Nervous and chemical

What three components do all control systems have?

• receptors

• coordination centres

• effectors

What is the function of a receptor?

Receptors detenct a change in the environment (stimuli)

What is the function of coordination centres?

Coordination centres obtain and process information from receptors

What is the function of an effector?

Effectors (muscles or glands) bring about responses to stimuli

What is the function of the nervous system?

The nervous system allows the body to react to its surroundings and coordinate an appropriate response

How does a stimulus lead to a response being carried out by the body?

• Stimulus is converted into an electrical impulse by the receptors

• The electrical impulse passes along sensory neurones to the central nervous system

• the CNS coordinates an appropriate responses and an electrical impulse is sent along motor neurones to the effector, which carries out the response

What sequence of events describes how the nervous system works?

Stimulus --> receptor --> coordinator --> effector --> response

What is a reflex action?

A reflex action is an automatic and rapid response which does not involve any conscious input from the brain

Describe how a reflex action occurs via a reflex arc

• the stimuli is detected by a receptor

• an electrical impulse passes along a sensory neurone to the spinal cord (CNS)

• at a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap and stimulates a new impulse which passes along the relay neurone

• the same process occurs at a synapse between a relay neurone and a motor neurone

• at the effector and appropriate response is carries out

What is the difference between a reflex pathway and a conscious pathway?

Within a reflex pathway, the coordination centre is a relay neurone found in the spinal cord/ unconscious parts of the brain. In a conscious pathway, the coordination centre is in the conscious part of the brain

Give the name of the body's coordination system which involves hormones

The endocrine system

What is a hormone?

A hormone is a chemical messenger secreted by a gland. It travels in the blood to a target organ, where it causes a response

What type of organ secretes horomones?

Glands

Which gland controls many other glands in the body?

The pituitary gland

Why is the pituitary gland called the master gland?

It secretes a wide range of hormones, some of which may stimulate other endocrine glands

What is the role of the pituitary gland in the endocrine system?

• secretes human growth hormone - controls human growth

• stimulates the thyroid gland

• stimulates ovulation and the production of eostrogen in the ovaries

• stimulates the production of sperm and testosterone in the testes

What is the role of the thyroid gland in the endocrine system?

Secretes the hormone thyroxine - controls metabolism, heart rate and body temperature