Topic 2: Classification, Communities & Species

Question 1

SPECIES

• A species is defined as a group of organisms that have similar structural characteristics, can interbreed under natural conditions and produce fertile offsprings.
• They are reproductively isolated.

Answer 1

REPRODUCTIVE ISOLATION

• Caused by reproductive barriers.
• Prevents gene flow between species (breeding to produce fertile offsprings)
• Barriers can be pre-zygotic or post-zygotic

Question 2

PRE-ZYGOTIC

• Time; Some closely related plant species release pollen at different times of the year.
• Chemical; Some closely related frogs give off pheromones which only attract their own species.
• Behavioural; Some closely related birds perform dances which only attract the females of their species.
• Physical; incompatible genitals

Answer 2

POST-ZYGOTIC

- Production of infertile offsprings

Question 3

POPULATIONS

• A group of individuals from one species that interbreeds with another in a particular place.
• Organisms in one population share a common gene pool (the sum of all the genes in the population).

Answer 3

COMMUNITIES

• A community is the populations of living organisms found in a particular area at the same time. The area in which the community exists is named after the dominant species in that area.
• The populations make up the community and give it its unique properties. these unique population interactions are organised into tropic structures.

Question 4

TROPIC STRUCTURE

• Producers; autotrophs which produce food for the ecosystem
• Consumers; Organisms that feed on the producers (herbivores) and organisms that feed on other animals (carnivores).
• Decomposers; Organisms that breakdown dead material.

Answer 4

SPECIES INTERACTION

• Species living within an area will need to interact with each other to survive. These interactions may be positive or negative and may occur within populations or between populations.
• The three main areas are;
• Competition
• Predation
• Symbiosis

Question 5

COMPETITION

• Organisms that compete for the same resources.
• Most intense among organisms of the same species.
• Also exists between organisms of different species.
• Less intense because no two species will have the exact same requirements.

Answer 5

PREDATION

• Where an organism feeds on another.
• Can be animals feeding on plats or other animals.
• Predation has profound effects on the overall number of organisms, biodiversity of a community and on the evolution of species.

PREDATION STRATEGIES

• Strategies displayed by predators are usually obvious.
• Predator avoidance strategies are harder to spot

Question 6

PLANT DEFENCE

• Chemical
• Many plants contain a vast array of chemical to deter herbivores.
• Some simply taste bad and are very toxic.
• Physically
• Many plants contain thorns to protect themselves from large predators and waxy layers to protect them from insects.

Answer 6

ANIMAL DEFENCE

• Colouration
• Colour is used very effectively by animals.
• Bright colours suggest toxic and should be left alone
• Camouflage is used to conceal from potential predators
• Mimicry is used to mimic the colouration of toxic species
• Chemical
• Many animals have chemical defences to either deter or kill predators

Question 7

SYMBIOSIS

• A distinct relationship between 2 different species.
• There are three different types;
• Mutalism
• Commensalism
• Parasitism

Answer 7

MUTUALISM
- Relationship where both species benefit from their interaction

COMMENSALISM
- One species benefits and the other is unharmed but does not benefit

PARASITISM
- One species is benefitted and the other is harmed but not usually killed