Igcse biology edexcel 4.1 4.17

Ecology & Environment

Definitions 4.1 understand the terms population, community, habitat and ecosystem

• Population: all the individuals of a particular species within a defined area

• Community: a group of different populations living in the same area

• Habitat: the physical, chemical and biological environment in which an organism lives

• Ecosystem: a community of living things and the environment in which they live

How to Use a Quadrat (1) 4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas

4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.

• A quadrat can be used to calculate the total population of a species (e.g. snails).

• Simply count the number of individuals in the quadrat.

• This technique only works for large organisms which can be distinguished as individuals and do not move fast (not always easy for plants, e.g. grass and tigers)

How to Use a Quadrat (2)4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas


• A quadrat can be used to calculate the percentage cover of a species (e.g. moss).

• The quadrat is divided into 100 smaller squares.

• The percentage cover of the quadrat is simply the number of squares filled with the species.

How to Use a Quadrat (3)4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas


• A quadrat can be used to calculate the percentage frequency of a species (e.g. daisies in a field).

• The quadrat is divided into 100 smaller squares. You simply count a 1 for each square the species is in and a 0 for those where it is absent.

• This gives you an indication of the frequency of the species, it does not tell you the total population.

USE of A Sample Quadrat4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas


The best use of a quadrat is in obtaining a sample (it is not practical to count all of the species)

e.g. one cannot count all of the grass plants in a field!

Ecologists use quadrats to sample from a habitat.

You can use the data to:4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas


Compare different species in ONE area

Compare the same species in TWO or MORE areas

Using a Quadrat4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas


Sampling: 1) Sample has to be random (so no bias is

introduced).2) Samples have to be representative, so we have to

take a large enough sample. At least 5% of habitat.

How to make a quadrat sample?• Find the boarders of your habitat (measure)• Divide your habitat into a grid with X and Y coordinates.• Randomly place your quadrat (use a random numbers for X & Y

coordinates)• Count number or organism/organisms, percentage cover or frequency of

organisms.• Record all data in a table.• Repeat until a large enough sample size is completed• Average all data• Scale up average (multiply average per quadrat by number of quadrats in

habitat)• Compare:

1. Different species in same habitat2. Same species from a different habitat

Using a Quadrat4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas


Review from the past4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers

Food chains are used to show the relationships between species in a habitat. E.g.

The secondary Consumer (eats the Primary Consumer) The Primary Consumer (eats the producer)

The Primary Producer (all food chains start with this)

RABBIT

FOX

GRASS

Each level in a food chain is called a Trophic Level

Feeding Relationships4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers

Definitions of Different Trophic levels 4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and

decomposers

• Producers: Plants (use sunlight to obtain nutrients)• Primary Consumer: Herbivores (plant eaters)• Secondary Consumer: Carnivore (animal / herbivore eaters)• Tertiary Consumer: Carnivore (animal / carnivore eaters)• Decomposers: Usually a bacterium or fungi, that breaks down the cells of dead plants and animals into simpler substances.

FOOD WEBS 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

Food chains can be built up into complex food webs. The difference between food chains and

food webs is that food webs have branches, chains never do.

A Pyramid of Numbers 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

In a pyramid of numbers, the length of each bar represents the number of organisms at each trophic level in a specified area.

Pyramid of numbers (complex) 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

Pyramid of Biomass 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

In a pyramid of biomass, the length of each bar represents the amount of organic matter – biomass – at each trophic level in a specified area.

At each trophic level, the amount of biomass and energy available is reduced, giving a pyramid shape.

Pyramid of Biomass 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

Compare Numbers to Biomass 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy

transfer

Pyramid of Energy 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

• It is a graphical representation of the trophic levels, by which the incoming solar energy is transferred to the ecosystem.

• It shows the total energy flow in the ecosystem.• There does not exist an inverted energy pyramid.

Energy is never ‘lost’, it is transferred. Not all the energy is transferred to the next

stage is converted into growth.

Pyramid of Energy 4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

4.6 understand the transfer of substances and of energy along a food chain 4.7 explain why only about 10% of energy is transferred from one trophic level to the next.

Pyramid of Numbers, Biomass & Energy4.5 understand the concepts of food chains, food webs, pyramids of numbers, pyramids of biomass and pyramids of energy transfer

Cycles within Ecosystems4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation (TA)

transpiration

Some quick definitions4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation (TA)

Evaporation: To change from a liquid or solid state into vapour.Condensation: To become liquid or solid, as a gas or vapour. Precipitation: Rain, snow, sleet, dew, etc, formed by condensation of water vapour in the atmosphere.Transpiration: The passage of watery vapour through the skin or through any membrane or pore in plants.

CARBON CYCLE 4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

Some quick definitions4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

• Respiration : The process in living organisms of taking in oxygen from the surroundings and giving out carbon dioxide (external respiration).

• Photosynthesis : The synthesis of organic compounds from carbon dioxide and water (with the release of oxygen) using light energy absorbed by chlorophyll.

• Decomposition : To break down (organic matter) physically and chemically by bacterial or fungal action.

• Combustion : The process of burning

NITROGEN CYCLE 4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying

bacteria and denitrifying bacteria (specific names of bacteria are not required). (TA)



Wait!! What other forms of

denitrification can there be?

Nitrogen Cycle4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of

bacteria are not required). (TA)

This is not particularly easy to understand. You need to know the roles of all the different bacteria. There are 4;

• Decomposers – turn nitrogen in protein into ammonium (NH4+)

• Denitrifying Bacteria – turn Nitrates (NO3

-) into Nitrites (NO2-)

into ammonium (NH4+ ) into Nitrogen gas (N2)

• Nitrifying bacteria – turn ammonium (NH4

+) into nitrites (NO2-)

and then nitrates (NO3-)

• Nitrogen-fixing bacteria – turn N2 into ammonium (NH4

+)

There is more that you are not expected to know from your syllabus, but may be included as additional information in

your exam on the Nitrogen Cycle

• Extension - leguminous plants • All of the above bacteria are naturally present in the soil.

The only exception to this is that some Nitrogen-fixing bacteria (e.g. Rhizobium) live in the roots of some plants. These plants are called legumes (e.g. peas, clover etc). They have a symbiotic relationship with the bacteria i.e. both the bacteria and the plant benefit from working together.

WAIT!!!4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of

bacteria are not required). (TA)

Human influences on the environment4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

Acid rain:SO2, CO2 and NOx (oxides of nitrogen) dissolve in rain to form Sulphuric Acid, Carbonic Acid and Nitric Acid.

This falls as acid rain, which destroys soil, pollutes waterways and causes erosion.

BIOLOGICAL CONSEQUENCES4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

1) Acid rain can 'burn' trees. This stops photosynthesis.

2) Sulphuric acid causes Calcium and Magnesium to be leached out of the soil. Without Calcium and Magnesium ions in the soil plant’s leaves turn yellow/wither and the plant can't grow.

3) Reduce the pH of the streams & lakes. The affect is that it releases aluminum ions (Al3+) which causes the thickening of mucus in the fishes gills. Fish have difficulty in obtaining oxygen. The fish numbers decrease.

CO4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

Carbon Monoxide (CO) is a gas added to the atmosphere by the combustion of fossil fuels (particularly coal) burned with

insufficient oxygen. • Carbon monoxide combines with our hemoglobin inside our

blood and blocks hemoglobin from carrying oxygen which reduces oxygen circulation.

• This is toxic, too much carbon monoxide can be fatal.

Greenhouse Gasses 4.12 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases

4.13 understand how human activities contribute to greenhouse gases

Global Warming4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may

lead to global warming and its consequences

Greenhouse gases trap heat around the surface of the Earth and are needed to keep the planet warm

enough for life.

1) Incoming shortwave radiation passes through the atmosphere and hits the Earth, where it is absorbed. (LIGHT)

2) The Earth re-emits the radiation as longer-wavelength Infra-Red radiation. (HEAT)

This is the problem.

3) Too much IR radiation is absorbed by greenhouse gases on its way out of the atmosphere. This traps the too much heat in the atmosphere.

GREENHOUSE EFFECTGOOD

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences

GREENHOUSE EFFECTBAD

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences

The theory goes that the greenhouse effect is causing global warming, which is bad. Global warming might

cause:

a) Polar ice cap melting (Sea levels rising) b) Extinction of species living in cold climates

c) Changes in rainfall (both droughts and flooding) d) Changes in species distribution (i.e. tropical species spreading, like mosquitoes)

GREENHOUSE EFFECT4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and

its consequences

Eutrophication 4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing depletion of oxygen (TA)

4.16 understand that eutrophication can result from leached minerals from fertiliser

Eutrophication is what happens when too much chemical fertiliser is used on crops and it washes/leaches into rivers and streams.

(also nitrates can come from sewage)

1) The nitrates in the fertilisers are essential to get crops to grow well and increase yields.

NITRATES ADDED2) However, if too much is used, or it rains soon after it is added to fields, the fertiliser gets washed away.

RUN OFF 3) The nitrates then help plants in the rivers and streams to grow very quickly, especially algae.

ALGAL BLOOM

4) But after the initial massive growth in algae there isn't enough light and water plants die

MASSIVE PLANT DEATH5) Without sunlight and when the nitrates run out MOST of the algae die

MASSIVE ALGAL DECAY6) All those dead plant start to decay. Respiring bacteria remove oxygen from the water.

ANOXIC CONDITIONS7) No Oxygen kills fish and other animals.

ANIMAL DEATH AND DECAY

8) Then even more algae and animals die.MORE DEATH & DECAY

9) pH levels fall as decomposition produces acidspH DROPS

10) Everything dies and waterway can no longer support life

TOTAL DEATH

So farmers have to be very careful using fertilisers so as not to wipe out all river and lake life.

Simply but Clearly4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing

depletion of oxygen (TA)

Nitrates > Algae Grow > Algae Die >

Algae Decay > No Oxygen >

Fish & Animals Die

Deforestation 4.17 understand the effects of deforestation, including leaching, soil erosion, disturbance of the water cycle

and of the balance in atmospheric oxygen and carbon dioxide

Cutting down trees and not replacing causes:• Leaching of soil minerals • Soil erosion / washed and blown away (no roots

holding soil together) • Desertion (new deserts forming) • Disturbance of the water cycle (less transpiration

can lead to flooding and / or drought) • Increase in CO2 levels

• Decrease in O2 production Less photosynthesis

Burning trees

Igcse biology edexcel 4.1 4.17

Science

Transcript of Igcse biology edexcel 4.1 4.17