Chapter 17: Variation And Selection Flashcards
define Variation
differences between the individuals of the same species
What are the two types of variations
-discontinuous variation
-continuous variation
define discontinuous variation
variation in which there are distinct categories of phenotype,with no intermediates
Example of discontinuous variation
-blood groups
-seed colour in peas
-seed shape in peas
Define population
a group of organisms of one species,living in the same area at the same time
Define continuous variation
variation in which there is a continuous range of phenotypes between two extremes
Example of continuous variation
Height
Body mass
what are the causes of discontinuous variation
their genotypes are different
What are the causes for continuous variation
-their genotypes and the different environment they are in
Define mutation
a random change in a gene,which can produce new alleles;mutations involves a change in the base sequence in DNA
State two things which may increase the rate of mutation
-ionising radiation (they can damage the bases in DNA molecules)
-different chemicals : such as lead and mercury
How are new alleles formed
By mutation
define adaptive feature
an inherited feature that helps an organism to survive and reproduce in its environment
Define xerophyte
A plant that has adaptive features that help it to survive in an environment where water is scare
What are the common adaptations in a xerophyte
-closing stomata
-waxy cuticle
-hairy leaves
-sucked stomata on w underside of leaves
-Reducing the surface area of the leaves
-having deep or spreading roots
Why do xerophytes have a closing stomata
If the stomata is closed,transpiration slows down to an almost complete stop.
However photosynthesis cannot happen as carbon dioxide cannot diffuse into the leaf
Why does xerophytes have a waxy cuticle
It cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers the temperature
Why does xerophytes have hairy leaves
The hairs trap a layer of most air next to the leaf.the most air reduces the diffusion gradient for water vapour from the leaf into the air,so less water vapour diffuses out of the leaf
Why does xerophytes have a reducing surface area of the leaves
The smaller the surface area of the leaf,the less water vapour will diffuse out of it.
Why do xerophytes have deep or spreading roots
Desert plants may have to seek water very deep down in the soil or across a wide area
Define hydrophytes
Hydrophytes are a plant that has adaptive features that help to survive in water
State 3 advantages of hydrophytes
-wide and flat leaves
-large air spaces
-thin waxy cuticle
Define natural selection
a process in which individuals with advantageous features are more likely to survive,reproduce and pass on their alleles to the next generation
describe the process of natural selection
1: variation - the variation within a population of organisms,some of these variations are caused by having different alleles of genes while some affect the adaptive features of the organisms
2: over production - within a wild population,many more offspring are produced than will survive
3: Best adapted individuals more likely to survive and reproduce - the individuals have the best chance of surviving and reproducing
4: Alleles that confer useful adaptions more likely to be passed on - the alleles that confer the best chance of survival therefore increase in the population while alleles that are not advantageous become less common
Name two ways natural selection can cause change in a population
1.a new allele could arise by mutation so if the allele gives an organism a better adaptive feature than any of the individuals in the population,then this organism will be selected for- that is it will have a good chance of surviving and reproducing
2. the environment could change,so that features that once helped an organism to survive are are no longer as useful.
