3.5 alevel biology flashcards

What is ecology ?

The study of how living organisms interact with their surroundings and eachother

What are abiotic factors?

Physical factors such as light intensity , soil , ph and temperature

what are biotic factors ?

biological factors such as pathogens and bacteria

What is an ecosystem ?

Made up of the community , biotic component , habitat and abiotic component 

What is a community ?

It is made up of the different populations of species in a habitat 

What is a population ? 

Interbreeding group of organisms of the same species occupying a particular habitat

What is a habitat ?

the place where an organism lives

What determines the size of the population ?

• Birth rate

• Death rate

• Immigration

• Emigration 

Factors affecting population growth

• biotic potential 

• Environmental resistance 

• Carrying capacity 

What is biotic potential ?

the maximum rate at which it can reproduce when given all the resources it needs 

What is environmental resistance ?

all factors that could limit the growth of a population

What is carrying capacity ?

The maximum number around which a population fluctuates  in a given environment 

Population growth curve

• for equilibrium species

• Sigmoid shape

• Has 4 phases

Phases of population growth curve 

1. Lag phase

2. Log phase 

3. Stationary phase 

4. Death phase 

What is the lag phase ?

• preparation and adaptation for growth 

• Intense metabolic activity 

• little or no increase in population

What is the log phase ?

• population growth increases rapidly 

• Rapid rate isn’t maintained as long as the effcets of environmental resistance kick in 

What is stationary phase ?

• Birth rate = death rate

• Population number fluctuates around carrying capacity 

What is death phase ?

-factors limiting growth becoming significant -death rate exceeds birth rate 

What are environmental factors ?

all factors that could limit the growth of a population

What are the types of environmental factors ?

• Density dependent 

• Density independent 

What are density dependent factors ?

• factors tha vary in effect based on population size 

• always biotic 

What are density independent factors ?

• affect all plants and animals regradless of population size 

• Tend to be abiotic 

What is a niche ?

The role an organism plays in its environment

What is succession ?

Transition between one stage and the next 

What is primary succession ?

• starting from bare rock , sand or water 

• Takes place in stages - called “sere”

First stage of primary succession

• pioneer species 

• first species to colonise an area 

• Able to withstand desiccation, extreme temperatures, and low nutrient levels 

Second stage of primary succession

1. Pioneer species penetrate and break up the rock.  Freeze-thaw erosion occurs here 

2. Pioneer species die and decompose, and humus builds up

3. Simple plants, such as ferns and mosses, can now grow 

Third stage in primary succession

• Mosses and ferns cast a shadow to prevent lichens from further growth 

• roots are longer and further break up the rock 

• Organic material increases as these palnts die.More water is retained by this so grasses , small flowering plants and shrubs can now grow.

Fourth stage of primary succession

• Growth of larger plants and animals would make further changes in soil and light conditions 

• The shading effect by plants causes soem smaller plants to die 

last stage of Primary succession

• Climax community 

• when the area is colonised by a dominant species 

What is secondary succession ?

• Occurs when a current seral stage is removed abruptly

What happens in secondary succession ?

• Succession occurs quickly, as there is soil and probably seeds present 

What is delfected succession/disclimax ?

• when a climax community is not reached 

• This can be due to human activity of limiting factors in teh surrounding environment 

Types of organisms involved in the decay of dead organisms

• detritivores

• Saprophytes 

What are detritivores ?

• animals with a tube gut that feed on dead organic materials

• They help to speed up decomposition by increasing the surface area of the dead organic material for the action of saprophytes 

What are saprophytes ?

• Fungi and bacteria that carry out extracellular digestion of the organic material to obtain nutrients

• Decompose dead material

Three key processes in carbon cycle

• Photosynthesis 

• Respiration 

• Combustion

How does photosynthesis impact carbon cycle ?

Photoautotrophs remove carbon dioxide from the atmosphere and “fix” it into organic molecules 

How does respiration impact carbon cycle ?

Returns carbon dioxide from the atmosphere

How does combustion impact carbon cycle ?

plant material and fossil fuels releasse carbon dioxide into the atmosphere 

Global impacts of carbon cycle impacted by human actions 

• Melting polar ice caps and rising sea levels

• Increased frequency of extreme weather

• Increased desertification and soil erosion

• Increased extinction rate

• Changes in the distribution of disease vectors, such as mosquitos

How does farming have a high carbon footprint ?

• The production of farm tools

• The production of insecticides, fungicides, and fertilisers

• Farm machinery, powered by fossil fuel

• Transport of the produce

Key processes of Nitrogen cycle

1. Putrefaction

2. Nitrification

3. Nitrogen fixation

4. Denitrification

What is putrefaction done by ?

• Decomposers 

• organisms that feed on dead organic matter and faeces saprophytically

Process of Putrefication

1. Proteins and nitrogen containing compounds are broken down into smaller soluble compounds 

2. These are absorbed by organisms 

3. Any excess nitrogenous compounds are converted into ammonium and excreted by the micro-organism

4. nitrogenous compounds are converted into ammonium in the soil 

What is nitrification ?

The process by which ammonium is oxidised into nitrite and then nitrate by bacteria 

What happens in nitrification ?

1. The nitrogenous compounds ammonium and nitrite are being used as a source of energy by bacteria 

2. These are nitrifying bacteria 

What is nitrobactor ?

converts nitrite to nitrate

What is nitrosomonas ?

Converts ammonium into nitrite

What is nitrogen fixation ?

The conversion of nitrogen gas into ammonium which is carried out by nitrogen fixing bacteria .

Types of bacteria involved in nitrogen fixation

1. Azotobacter 

2. Rhizobium

What is Azotobacter ?

Nitrogen fixing bacteria that is free living in the soil 

What is Rhizobium ?

• Nitrogen fixation occurs in the roots of legumes 

• Live in a mutually beneficial relationship 

How does Rhizobium function ?

• bacteria invade in the roots of plants and the plant repsonds by forming a nodule where the bacteria can live 

• NItrogen gas diffuses into the nodule from the soil 

• The nitrogen gas is then utilised by bacteria to make ammonium and amino acids 

• Excess ammonium and amino acids are exported to the plant for protein synthesis

• Rhizobium gains sugars for respiration from the plant

Conditions of nitrogen fixation

• anaerobic environement 

• Plant produces leghaemoglobin 

• This takes up oxygen in the nodule and removes it from bacterial environment 

Farming activities that aim to improve soil fertility

• Adding chemical fertilisers (ammonium nitrate)

• Adding manure (animal waste)

• Adding treated sewage (human waste)

• Planting legumes such as clover

• Ploughing or draining to improve aeration

Human activity causing nitrogen pollution

• Excess nitrates on grassland leads to increased growth of weeds, such as nettles, this

• decreases biodiversity due to competition for resources

• Draining wetlands destroys unique habitats

• Nitrate pollution (excess fertilisers, manure, etc) in waterways causes eutrophication

– ultimately causing a decrease in dissolved oxygen and a decrease in biodiversity

What is denitrification ?

• Pseudomonas 

• Use nitrate to provide oxygen for respiration 

• The nitrogen atoms remaining are converted to nitrogen gas 

Conditions of denitrification

• anaerobic 

• Usually due to water logging - air spaces in soil filled with water 

• Water logged soils - defecient in nitrates and soil fertility decreases 

How do farmers try to avoid water logging ?

• Ploughing 

• Mixes soil with air 

• Oxygen from the air inhibits the denitrifying bacteria (Pseudomonas) 

• Encourages the growth of Nitrosomonas, Nitrobacter, and Rhizobium Nitrosomonas

What plant lives in water logged conditions ?

• Carnivorous plants

• gain carbohydrates from photosynthesis 

• Gain nitrogenous compounds from digestion of invertebrates