COMMUNITIES AND ECOSYSTEMS
- An ECOSYSTEM is a community of organisms and their surroundings, the environment in which they live and with which they interact.
- A HABITAT is the locality in which an organism occurs, it is where the organism is normally found.
- The POPULATION is the living species of the same species in a habitat at any one time.
- A COMMUNITY is all the living things in a habitat or an ecosystem - total of all populations.
- A SPECIE is the group of individuals of common ancestry that closely resemble each other and that are normally capable of interbreeding to produce fertile offspring.
- ENVIRONMENT is the term we commonly use for the 'surroundings'.
- An AUTOTROPH is an organism that synthesises its organic molecules from simple inorganic substances. (Green Plants are known as autotrophic)
- A HETEROTROPH is an organism that obtains organic molecules from other organisms.
- CONSUMERS depend on plant nutrition or primary consumers/secondary consumers for nutrition.
- A DETRITIVORE is an organism which ingests non-living inorganic matter (e.g. dead plants/animals/animal waste)
- A SAPROTROPH is an organism which lives on or in living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.
- A FOOD CHAIN is a feeding relationship in which a carnivore eats a herbivore which itself has eaten plant matter.
- A FOOD WEB is more complex than a food chain and it includes a larger variety of organisms.
- Each of which feed on a variety of other organisms and they are in turn fed on by more organisms.
- Therefore, if one species becomes extinct the ecosystem will still be able to exist.
- TROPHIC LEVEL: Position in the food chain, determined by the number of energy-transfer steps to that level;
- A functional classification of taxa within a community that is based on feeding relationships (eg, plants make up the first trophic level, herbivores make up the second).
Light is the initial source of energy in a food chain. Between each trophic level in a food chain, energy bis transferred.
When the herbivore consumes the tissues of a green plant, the energy is locked up in the organic matter of the plant. The energy is then transferred when a carnivore consumes a herbivore.
However not all energy is transferred as energy is lost through movement, excretion, growth and respiration. So energy transformations are NEVER 100% efficeint.
- A pyramid of energy shows the flow of energy from one trophic level to the next in a community. The units of pyramids of energy are therefore energy per unit area per unit time.
- Energy can enter and leave an ecosystem but nutrients must be recycled. Sun light is the main source of energy on this planet. It is absorbed by photosynthesizing organisms, which convert light to chemical energy. Nutrients must be recycled by obtaining them from other organisms or products of organisms.
There are 5 major processes involved:
- Cellular Respiration
The role of saprotrophic bacteria and fungi (decomposers) in recycling nutrients:
- These organisms feed on dead organisms and products of living organisms.
- They secrete enzymes on these materials that cause decomposition, and then they absorb decomposed and digested foods.
- They absorb only what they need to survive, the remainder of the nutrients are reabsorbed into the ecosystem.
- They are essential as they unlock these nutrients, readying them for reabsorbtion.
- Examples include many species of bacteria and fungi.
- These are essential organisms to an ecosystem, since they cause recycling of materials between biotic and abiotic parts of the ecosystem.
THE GREENHOUSE EFFECT
- Radiation from the Sun includes short and long wave radiation (e.g. ifnra red)
- Earth reradiates some of this back as IR
- Clouds reflects some back, some is absorbed by the gases in the atmosphere which warm up, some escapes into space.
Changes in concentration of atmospheric carbon dioxide using historical records:
- Increased melting of sea ice as temperature increase is felt most at poles
- Rise in sea levels (flooding)
- More extreme weather patterns e.g. hurricanes, droughts
- Extinction of species
- Changes in the ocean currents
THE PRECAUTIONARY PRINCIPLE:
- This states that if the effects of a human - induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will NOT DO HARM before proceeding.
- E.g. action should be taken to reduce CO2 emissions before proved it is the cause.
- 'As levels of carbon dioxide, methane, and nitrous oxides increase more radiation is reflected back to Earth instead of being lost to space.
Consequences of a global temperature rise on arctic ecosystem:
Effects include increased rates of decomposition of detritus previously trapped in permafrost, expansion of the range of habitats available to temperate species, loss of ice habitat, changes in distribution of prey species affecting higher trophic levels, and increased success of pest species, including pathogens.
· If (natality + immigration) > (mortality + emigration) then a population is increasing. These factors determine whether a population is increasing or decreasing.
Reasons For The Exponential Growth Phase, The Plateau Phase, And The Transitional Phase Between These Two Phases:
· During the Exponential phase the population increases exponentially because the natality rate is higher than the mortality rate. The resources needed by the population such as food and space are abundant, and diseases and predators are rare.
· During the Transitional Phase, the birth rate begins to decrease. Natality is still larger than mortality, but the difference between them is slowly decreasing.
· During the Plateau phase, available resources become so low that no further reproduction can take place. Mortality starts to become larger than natality. A species may have reached its Carrying Capacity.
CARRYING CAPACITY: The maximum number of organisms of a species, or the maximum population size which an environment is able to support.
There are three factors which limits population increase:
- Available resources.
- Space available
RANDOM SAMPLE: is a sample where every individual in a population has an equal chance of being chosen and there is no bias.
One Technique Used To Estimate The Population Size Of An Animal Species Based On A Capture-Mark-Release-Method:
- One method of estimating the population size of an animal species is the capture-mark-release method.
1. As many individuals of a population are caught.
2. These individuals are marked. The individuals are released back into their environment.
3. After a while, as many individuals of a population are caught in the same area again.
4. The total number is taken note of and the number of those caught which are marked
The total number is taken note of and the number of those caught which are marked
This is known as the "Lincoln Index"
- The formula (n1 × n2) / n3 is then used where:
- n1 = the number of individuals caught in the first trial.
- n2 = the number of individuals caught in the second trial.
- n3 = The number of individuals in the second trial which were marked.
- There are 2 methods used for random sampling: LINE QUADRAT and FRAME QUADRAT.
- To calculate the mean of a set of values:
Mean= Total sum of values / number of values
EVOLUTION is the culmulative change in the heritable characteristics of population.
Evidence For Evolution:
- Fossil Records
- Similar genes to other animals
- Domestication of animal breeds
- Comparitive anatomy - homologous structures
Populations tend to produce more offspring than the environment can support.
Populations of living organisms tend to increase exponentially.
1. More offspring are produced than the environment can support. There is a struggle for important resources such as food and space. Intraspecific competition. Some individuals survive and others die.
2. Characteristics in organisms differ from one another. Some have characteristics which make them better suited to survive in their environment. These are the most likely to survive.
Note:- Members of a species show variation
Sexual Reproduction promotes variation in a species:
Variation is essential for natural selection and therefore for evolution.
Although mutation is the original source of new genes or alleles, sexual reproduction promotes variation by allowing the formation of new combinations of alleles.
Two stages in sexual reproduction promote variation.
1. Meiosis allows a huge variety of genetically different gametes to be produced by each individual
2. Fertilization allows alleles from two different individuals to be brought together in one new individual.
Natural Selection leads to evolution:
Two examples of reveolution in response to environmental change:
- Before Penicillin was invented, bacteria was the leading cause of death.
- However, once it began to be used, since it's an antibiotic, some individuals of bacteria may carry the gene Penicillinase, which codes for an enzyme that deactivates Penicillin, making them resistant to an antibiotic such as Penicillin.
- Thus, when it is indeed used, they will be the only ones left to reproduce and new bacteria will also be resistant to the antibiotic.
- The Peppered Moth is another example of evolution in response to environmental change.
- When Britain began industrialising, soot would come from factories and land on trees.
- A species of peppered moth with a lighter colour vanished and those with a darker colour flourished because they could hide themselves easily.
The binomial systems of nomenclature:
Called binomial because two names are used.
1. First name is genus, with first name being a capital.
2. Second name is species, with no capital.
3. Italics are used when the name is printed.
4. The name is underlined if it is handwritten.
Organisms are classified into the kingdoms:
- Prokaryotae - bacteria
- Protoctista - Including unicellar organisms like Amoeba and Algae
- Fungi - Including moulds and yeasts
- Plantae - Including conifer, ferns, mosses and flowering plants
- Animilia - Multicellular and locomotive, including sponges, corals, birds and mammals
HIERACHY OF TAXA:-
This is the process of classification which involves giving an organism an agreed name, and then arranging them into groups of apparently related organisms.
There are seven levels in the hierarchy of taxa:
A way of remembering it is: King Phillip Carried Our Family's Golf Sticks
Example 1: [ A Whale ]
KINGDOM .... Animalia
PHYLUM ... Chordata (backbone)
CLASS ... Mammalia
ORDER ... Cetacea (teeth)
FAMILY ... Delphinidae (same family as dolphins)
GENUS ... Orcinus
SPECIES ... Orcha
Example 2: [ A Common Oak Tree ]
KINGDOM .... Plantae
PHYLUM ... Angiospermaphyta
CLASS ... Dicotyledonae
ORDER ... Fagales
FAMILY ... Fagacaea
GENUS ... Quercus
SPECIES ... Robur
Distinguishing Phyla of Plants:
There are 4 main phyla in the kingdom of plantae.
- land plants (but poorly adapted to terrestial conditions)
- tiny stem
- no roots, instead thizards
- leaves not covered in waxy cuticle (not protected from water loss)
- no water conducting cells in stem
- spore containing capsule
- Some, exist as flat leaf-like structures on the soil surface (liver warts)
- green plants with stem, leaves and roots
- adapted to terrestial conditions
- Vascular tissue for conducting water and nutrients around the plant
- leaves are covered by a waxy cuticle that protects against water lossand evaporation
- reproduce asexually
- cone-bearing trees, larger, strong stem (trunks)
- leaves are waxy and needle shaped
- almost always evergreen
- leaves able to resist damage e.g. low temp and snow
- reproduces asexually - seed bearing plant
- row fast and straight (used for soft wood)
- non-woody plants/hard woods/shrubs
- has vascular tissues
- waxy leaves
- flowers are unique - seeds are formed from flowers
- reproduces sexual
- divided into two sub groups: MONOCOTYLEDONS and DICOTYLEDONS.
- MONOCOTYLEDONS (grasses) have parallel veins in their leaves, single seed leaf in the embryo of the seed
- DICOTYLEDONS (broad - leaved plants) have no veins in their leaves and 2 seed leaves in the embryo
Distinguishing between the following phyla of animals, using simple external recognition features:
- Porifera: sponges
- Cnidaria: jelly fish, sea anemones, corals
- Platyhelminthes: flatworms
- Annelida: round, segmented worms
- Mollusca: snails, slugs, and octopus
- Arthropoda: insects, crustaceans, spiders, scorpions, millipedes