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Define variation.

Variation is defined as differences between individuals of the same species


What is phenotypic variation.

Phenotypic variation is the difference in features between individuals of the same species


Define Continuous variation.

Continuous Variation is when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
Examples include height, mass, finger length


Define Discontinuous variation.

is when there are distinct differences for a characteristic
For example, people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not – there are no ‘inbetweens’


How can phenotypic variation be caused?

-It can be genetic – controlled entirely by genes
-Or it can be environmental – caused entirely by the environment in which the organism lives


Define Mutation.

Mutations are random genetic changes
eg- sickle cell anaemia


Define gene mutation.

gene mutation is a change in the base sequence of DNA


Define Adaptive features.

An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment


What are Hydrophytes ?

Plants adapted to live in extremely wet conditions


Write adaptations of hydrophytes.

Large air spaces in their leaves to keep them close to the surface of the water where there is more light for photosynthesis
Small roots as they can also extract nutrients from the surrounding water through their tissues
Stomata usually open all the time and mainly found on the upper epidermis of the leaf where they can exchange gases much more easily with the air


What are Xerophytes?

Plant adapted to live in extremely dry conditions


Write adaptations of Xerophytes.

Thick waxy cuticle – the cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers temperature
Sunken stomata: stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces evaporation rate
Leaf rolled with stomata inside and an inner surface covered in hairs – traps moist air and prevents air movement across stomata which reduces transpiration
Small leaves: many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface
Extensive shallow roots allowing for the quick absorption of large quantities of water when it rains
Thickened leaves or stems which contain cells that store water


What is natural selection?

In any environment, the individuals that have the best adaptive features are the ones most likely to survive and reproduce
This results in natural selection


Define antibiotic

An antibiotic is a chemical that can kill or inhibit the growth and reproduction of bacteria


Define selective breeding.

Selective breeding means to select individuals with desirable characteristics and breed them together


For what characteristics do humans bred plants.

disease resistance in food crops
increased crop yield
hardiness to weather conditions (e.g. drought tolerance)
better tasting fruits
large or unusual flowers


Exposure to what substances will increase the rate of mutation.

Gamma rays, x – rays and ultraviolet rays
Certain types of chemicals – for example chemicals such as tar in tobacco


Brief, Sickle cell anemia.

1.mutation changes the molecule haemoglobin, causing the red blood cells (RBC’s) to become stiff and sometimes sickle-shaped when they release oxygen to the body
2.The sickled cells tend to get stuck in narrow blood vessels, blocking the flow of blood
3.They may suffer strokes, blindness, or damage to the lungs, kidneys, or heart. They must often be hospitalized for blood transfusions and are at risk for a life-threatening complication called acute chest syndrome


Relation between sickle cell anaemia and malaria

African children who are heterozygous for the sickle cell allele have a ten-fold reduction in their risk of getting malaria.


Brief adaptive features and fitness

Adaptive features are the inherited functional features of an organism that increase its fitness
Fitness is the probability of an organism surviving and reproducing in the environment in which it is found


Describe the process of natural selection.

-variation within populations
- production of many offspring
-competition for resources
-struggle for survival
-reproduction by individuals
-that are better adapted to the environment than others
-passing on of their alleles to the next generation

eg- antibiotic resistance


Define evolution

the change in adaptive features of a population overtime as the result of natural selection


Define the process of adaptation

process of adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations


Define selective breeding

Selective breeding means to select individuals with desirable characteristics and breed them together


State the differences between natural and artificial selection.

-natural selection- -Artificial selection-
1.happens naturally 1.only occurs with when
2.usually take long time humans intervene
3.results in development of 2.Takes less time- as
features better adapted to the individuals with desired
environment features are bred
3. results in features
useful to humans