12. Biodiversity Flashcards
What is biodiversity
a general term used to describe the variety of living organisms in a community/habitat.
It includes species diversity and genetic diversity.
What is a habitat
the place where an organism lives
What is a community
all the organisms (of different species) in a habitat
What is species richness
Counting the number of different species in a habitat
What is the species diersity index
A single number that describes species diversity. it relects:
-The number of different species present
-The number of individuals in each species
Enables us to make an objective assessment of diversity in any community
How is the species diversity index calculated
D = N(N-1) / E n(n-1)
N = total number of organisms of all species
n = total number of organisms of a particular species
why is it more useful to calculate diversity index rather than just record the number of species present.
measures number of individuals in each species as well as the number of species
takes into account the fact that some species may be present in very low or high numbers
When is the diversity index used
to compare the diversity of different habitats, or of the same habitat over time
What does the diveristy index indicate
A High value of D indicates a stable and ancient site with a diverse community.
A low value of D suggest agricultural management, a recently deforested site or a polluted area. These are only generalisations.
What does a low D valuve explain about the environment
Harsh environment
-Few species present and ofter populations are small
-Generally abiotic factors determine which species are present
-Ecosystmes are usually unstab;e
Only few species are adapted to survive the harsh conditions
What does a high species index value explain about the environment
Favourable environment
-Many species present and populations are large
-Biotic factors determine which species are present
-Ecosystmes are stable
-Complex food webs so a change in population of one species is less likley to affect other populations
How may organimsms be distributed in an area
Ranodm
Regular
Clumped
What is the only method of gaining an unbiased measure of the species present
Sample the area randomly to avoid bias
e.g chosing a palce that is easy to get to or are more obvious is biased
How do you radom sample
· Quadrat laid out across the sample area using tape measures.
·random numbers are generated to provide coordinates on the grid. These are the sample points where a quadrat is placed.
· Within each quadrat the community is sampled, in this case each organism in the quadrat is identified and the number of each species is counted.
· As any one sample point is unlikely to be representative of the area, a large number of randomly placed quadrats are used.
How many quadrats are needed to give a representative sample
a rule of thumb you need to take at least 20 quadrats to be able to do any statistical analysis of the results.
What is intensive farming
intensive farming usually involves the removal of existing vegetation and the growth of one crop species, a system called monoculture
aim is to provide ideal conditions for the crop to grow and supply a high yield.
How does agriculture provide ideal conditions for crop photosynthesis and growth
· Fertilisers added to provide minerals for growth.
· Fields irrigated so there is enough water.
· The crop species are specially selected to grow well in the conditions provided and to provide high yields of useful product.
How are weeds and pest species removed
Weeds can be physically picked out or chemical herbicides used which kill the weeds but not crop plants.
Animal pesticides are toxic chemicals which kill a wide range of similar species.
Removing hedgerows and field boundaries, unprofitable pockets of woodland and draining marshy areas make maximum use of land for crops, and remove sources of pests and disease
Why will so few species exist, and therefore species diversity be so low in the fields
· A lower variety of habitats/ niches
· Fewer plant species because just one crop species grown and most weeds removed or killed by herbicides.
· Few species of herbivores as so little variety of plant food types.
· Fewer types of carnivore species because so few herbivore species to feed on.
· Use of pesticides will reduce diversity of insect species
What conservation techniques are used to increase species and habitat diversity, without raising food costs or lowering yields.
· Maintain existing hedgerows at the most beneficial height and shape.
· Plant hedges rather than erect fences as field boundaries.
· Maintain ponds and where possible create new ones
· Leave wet corner of fields rather than drain them.
· Plant native tree species on land with a low species diversity rather than in species-rich areas.
· Reduce the use of pesticides – use biological control or genetically modified organisms that are resistant to pests.
· Use organic fertilisers.
· Use crop rotation that includes a nitrogen-fixing crop, rather than fertilisers, to improve soil fertility.
· Create natural meadows and use hay rather than grasses for silage.
· Leave the cutting of verges and field edges until after flowering and when seeds have dispersed.
· Introduce conservation headlands – areas at the edge of fields where pesticides are used restrictively so wild flowers and insects can breed.
How do hedgerows increase biodiversity
contain several plant species which will provide a greater variety of habitats and food for animals.
may be habitats for predators of pests. An increase in the number of these should increase the yield and reduce the need for using pesticides.
habitats for pollinating species. An increase in these would also improve the crop yield
What are disadvantages to hedgerows
take up a lot of room, reducing the land area available for growing crops
Habitats for pests, so may lead to an increase in pest populations and reduce crop yields.
Crops will face increased competition for resources,
What is genetic diversity
the number of different alleles of genes in a population.
Why does genetic diveristy matter
If a population has many different alleles for a particular gene, then the population is said to be genetically diverse.
The bigger the gene pool, the greater the variation within that species and the greater the genetic diversity.
The greater the genetic diversity the better the survival chances as they are more likely to be able to adapt to a change in the environment.
Creates variation within a population.
Which specific alleles will increase over time and which decrease is dependent on if they cause differential changes in survival and reproduction.
What is a gene
a section of DNA that codes for a polypeptide / protein
What is an allele
a different version of a particular gene
What causes genetic diversity
Mutations (Only way for asexual redproduction)
Meiosis
Random funsion of gametes
How does mutations lead to genetic diversity
Causes a change in amount or sequence of bases in the DNA of an organism. Can cause a change in the characteristics
Can arise during DNA replication and include base deletion and base substitution.
Mutagenic agents can increase the rate of gene mutation.
How can Gene mutations can lead to production of non-functioning proteins
· A gene is the sequence of bases in DNA that codes for the production of a protein.
· If sequence of DNA bases is altered in a gene then this will change the sequence of bases in the mRNA that is transcribed.
· May change the sequence of amino acids in the protein.
·Change in the primary structure of the protein causes a change in the tertiary structure, as hydrogen, ionic and disulphide bonds form in different places
·Can lead to a loss or reduction in function of the protein.
Where does meiosis occur
occurs in the formation of gametes
Cells of this type are genetically different from each other so meiosis is a major cause of variation within a species
What are the key features of meiosis
- DNA replicates itself once but there are two nuclear divisions so 4 daughter cells are formed from each cell
- Daughter cells have half the number of chromosomes found in a normal body cell. the haploid number
-When male and female gametes join together at fertilisation, diploid number is restored. meiosis ensures that the chromosome number is kept constant from one generation to the next.
What is meiosis 1 and 2
M1 - Homologous pairs separate and the cells become haploid
M2 -Centromere breaks and chromatids separate
What is Chromosome non-disjunction
Sometimes homologous chromosomes don’t separate properly during meiosis and both chromosomes of a pair go into same cell.
So after fertilisation zygotes can end up with an extra copy of a particular chromosome.
How does meiosis leads to variation and what are the two ways it can occur
Meiosis provides opportunities for new combinations of alleles to occur in the gametes.
Leads to intraspecific variation in offspring produced by fertilisation of the gametes.
1. Independent segregation (or random assortment) of homologous chromosomes
2.Crossing over
How does independent segregration lead to variation
When pairs of homologous chromosomes line up along the equator of the spindle, their orientation is completely random.
Subsequent separation of these pairs of chromosomes results in different combinations of maternal and paternal chromosomes in the gametes formed.
A cell that has ‘n’ pairs of chromosomes has 2n different numbers of combinations.
How does crossing over lead to variation
· When homologous pairs of chromosomes associate, at the start of meiosis they form a bivalent and one of the chromatids of each homologous chromosome become wrapped around each other at points called chiasmata
· Causes sections of each chromatid to break off and rejoin to chromatid of the homologous partner. This is crossing over.
· Alleles exchanged between the maternal and paternal chromosomes – genetic recombination occurs.
· When chromosomes separate during meiosis there may be new combinations of alleles on each chromosome, resulting in more variation in gametes.
