Biodiversity Pack 12

Define biodiversity

the variety of living organisms in a community/ habitat

What does biodiversity include?

- Species diversity

- Genetic diversity

Define habitat

Place where an organism lives

Define community

All the organisms in a habitat (for different species)

What is species richness?

The number of different species in a habitat

How can we compare the diversity of 2 different habitats?

- Species diversity index

What does the species diversity index reflect?

- Number of different species present

- Number of individuals in each species

How do we calculate diversity index?

Elaborate on the variables

D = N(N - 1) / Σ n(n - 1)

D is diversity index

N is total number of all species

n total number of organisms of a particular species

Σ sum of

When using the diversity index for comparisons between 2 habitats, which would be more diverse?

Habitat with higher value if D

Why is it more useful to calculate the diversity index rather than just record the number of species present?

- Measures the 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 very high numbers (over/under represented)

What can the diversity index be used to compare?

- Compare diversity of 2 different habitats

- Compared diversity of habitat over time

What doe a high value of D suggest?

- Stable and ancient site

- eg meadow, woodland

- Diverse community

- Usually biotic factors determine which species are present eg competition, predation

- Stable food supplies usually

- Complex food webs so changes in one species generally won't affect the other populations

What does a low value of D suggest?

- Unfavourable / harsh environment

- Agricultural management, deforested area, polluted area

- Few species present with small populations

- Abiotic factors usually determine which species are present

- Few species adapted to survive harsh conditions

Why do we sample and what methods of sampling are there?

- To obtain a representative overview of the community as a whole

- More efficient than sampling the whole area as it would be too time consuming

- produce statistically significant results

- Random, Regular or clumped

What is the only method of gaining unbiased sampling?

Random sampling as it removes sample bias

Describe the method for random sampling

- Grid is laid out across the same area using tape measures

- Random numbers are generated to provide coordinates on the grid which are the sample points where a quadrat frame is placed

- Within each quadrat the community is sampled, species are identified and number of each species are counted

- One sample point isn't representative of the whole population so a large number of randomly placed quadrats are used

How many quadrats are needed for a representative sample?

- 20 quadrats minimum

What is modern intensive farming? - Overview

- Includes removal of existing vegetation and the growth of one crop species - monoculture

- This is to provide the ideal conditions for crop growth to supply a high yield

How does agriculture provide ideal conditions for crop photosynthesis and growth?

- NPK fertilisers added to provide minerals for growth

- Fields irrigated so there is enough water

- Crop species specially selected to grow well in the conditions provided

Give 2 examples of competition?

- Weeds compete crops for resources so are prevented from growing on the farmland

- Animals compete with us by eating the crop such as insect pests which are also removed

How are weeds and pests removed?

- Weeds physically picked out as they start to grow

- Chemical herbicides used which kill the weeds but not the crop plants

- Animal pests (insecticides) are toxic chemicals which usually kill a wide range of similar species

How can we maximise use of land for crops?

- Remove hedgerows and field boundaries, unprofitable pockets of woodland and draining marshy areas

- This removes sources of pests and disease

Why will few species exist, and therefore be low species diversity in the fields of monoculture?

- Low variety of habitats/ niches - places where organisms can live

- Few plant species as just one crop is grown and most weeds are physically removed or killed by herbicides

- Few species of herbivores as little variety of plant food species

- Few types of carnivore as few herbivore species to feed on

- Use of pesticides reduces diversity of insect species

List conservation techniques

- Maintain hedgerows at the best height and shape - A shape is better than rectangular

- Plant hedges instead of fences at field boundaries

- Maintain and create ponds where possible

- Leave wet corners of fields rather than draining them

- Plant native tree species on land with low species diversity rather than species rich areas

- Reduce pesticide use - biological control is better or genetically modify organisms that are resistant to pests

- Use organic than inorganic fertilisers

- Use crop rotation with nitrogen fixing crop, rather than fertilisers - improves soil fertility

- Create natural meadows and use hay instead of grass for silage

- Leave cuttings on verges and field edges until after flowering and when seeds have dispersed

- Introduce conservation headlands - edges of fields where pesticides are used restrictively so wild flowers and insects can breed

Give the effect of using hedgerows as field boundaries

- Increases biodiversity as it contains several plant species which provide a greater variety of habitats and food for animals

Give some advantages for that planting hedgerows might have for a farmer

- Hedges may be habitats for predators of pests. An increase in these should increase yield and reduce pesticide need

- Hedges may be habitats for for pollinating species. An increase in there would improve crop yield

Give some disadvantages of using hedgerows for farmers

- Take up lots of room which reduces area available for growing crops

- Can act as habitats for pests so can lead to an increase in pest population and reduce crop yield

- Crops face increased competition for resources eg minerals, light which reduce yield

Define genetic diversity

number of different alleles of genes in a population

Describe genes and alleles in a population

- Population has same genes - eg for eye colour

- Have different alleles - eg blue or brown colour eyes

- Differences are due to alleles not due to their genes

- When there are many alleles of a gene, the population is said to be genetically diverse

Define gene

section of DNA which codes for a polypeptide

Define allele

Different variation of a gene

Explain the number of alleles in a species

- Set number of alleles in a species - this is the gene pool

- Bigger gene pool has greater genetic diversity

- Leads to better chances of survival of that species

Describe genetic diversity in a population and what happens over time

- Creates variation in a population

- Specific alleles may increase or decrease over time depending on differential changes in survival and reproduction - natural selection

How does genetic diversity within a species occur? (Intraspecific variation)

- Mutations - can result in new allele - adv or disadv

- Meiosis

- Random fusion of gametes - millions of sperm

How do asexually reproducing organisms show variation?

- Mutations only

- No gametes or meiosis is involved

What is a mutation? Give the effects

- Change in the amount or the sequence of of bases in the DNA of an organism

- This changes characteristics of an organism which can be passed onto cells produced by cell division

How can gene mutations lead to non functioning proteins?

- Gene is a sequence of bases in DNA that code for protein production

- If the sequence of bases is altered in a gene by mutation, this changes the sequence of bases in the mRNA strand

- This can change the tertiary structure of the protein as hydrogen, ionic and disulphide bonds form in different places

- This leads to a loss or reduction in function of the protein

- For enzymes the active site changes shape so the substrate is no longer complimentary to fewer ES complexes form

Give the types of mutations which are possible

- Base deletion - results in frame shift changing whole amino acid sequence after that point

- Base substitution - may not have effect due to degenerate nature of the genetic code

- Mutagenic agents increase the rate of gene mutation

Give the 3 main key features about meiosis

- DNA replicates once but there are 2 nuclear divisions so 4 daughter cells form per cell

- Daughter cells are haploid - half the number of chromosomes as the parent cell

- When male and female gametes join at fertilisation, diploid number is restored so chromosome number is constant from one generation to the next

Describe the 2 divisions by meiosis

- Meiosis 1 - homologous pairs separate so cells become haploid

- Meiosis 2 - centromere breaks and chromatids separate

Describe chromosome non - disjunction

- Sometimes homologous chromosomes don't separate properly during meiosis and an extra pair of chromosomes go into the same cell

- This means zygotes can end up with an extras copy of a particular chromosome

- Down's syndrome is caused by having an extra chromosome

Give the ways in which variation occurs in meiosis

- Independent segregation (random assortment)

- Crossing over

Describe Independent segregation/ random assortment in meiosis

- In the first division in meiosis the homologous pairs line up along the equator of the cell in a random orientation

- Subsequent separation results in different gametes forming with different combinations of maternal and paternal chromosomes

How do you calculate the number of combinations of chromosomes?

2^n

n is the number of chromosome pairs

Describe crossing over

- When homologous pairs of chromosomes associate at the start of meiosis they form a bivalent and the chromatids of the homologous chromosomes become wrapped around each other at points - called chiasmata

- This causes sections to break off and re-join on the homologous partner - crossing over

- Alleles are exchanged between maternal and paternal chromosomes - genetic recombination occurs

- When chromosomes move apart and separate during meiosis there are new combinations of alleles on each chromosome resulting in variation in the gametes

Compare chromosome number between mitosis and meiosis

Mitosis 2n ---> 2n

Meiosis 2n ---> n

Compare the divisions between mitosis and meiosis

Mitosis - 1 division forms 2 daughter cells

Meiosis - 2 divisions forms 4 daughter cells

Compare daughter cells genes to parent genes in mitosis and meiosis

Mitosis - Daughter cells have identical genes

Meiosis - Daughter cells have genetic variation to parents