Core Practicals:
CORE PRACTICAL 6:
Identify sclerenchyma fibres, phloem sieve tubes and xylem vessels and their location within stems through a light
microscope.
CORE PRACTICAL 7:
Investigate plant mineral deficiencies.
CORE PRACTICAL 8:
Determine the tensile strength of plant fibres.
CORE PRACTICAL 9:
Investigate the antimicrobial properties of plants, including aseptic techniques for the safe handling of bacteria.
,Topic Checklist
4.1 Know that over time the variety of life has become extensive but is now being threatened by human activity.
4.2 i) Understand the terms biodiversity and endemism. (P3)
ii) Know how biodiversity can be measured within a habitat using species richness and within a species using
genetic diversity by calculating the heterozygosity index (H) (P3)
iii) Understand how biodiversity can be compared in different habitats using a formula to calculate an index of
diversity (D) (P3)
4.3 Understand the concept of niche and be able to discuss examples of adaptation of organisms to their
environment (behavioural, physiological and anatomical). (P4-5)
4.4 Understand how natural selection can lead to adaptation and evolution. (P5)
4.5 i) Understand how the Hardy-Weinberg equation can be used to see whether a change in allele frequency is
occurring in a population over time. (P7)
ii) Understand that reproductive isolation can lead to accumulation of different genetic information in
populations, potentially leading to the formation of new species. (P6)
4.6 i) Understand that classification is a means of organising the variety of life based on relationships between
organisms using differences and similarities in phenotypes and in genotypes, and is built around the species
concept. (P8)
ii) Understand the process and importance of critical evaluation of new data by the scientific community,
which leads to new taxonomic groupings, including the three domains of life based on molecular phylogeny,
which are Bacteria, Archaea, Eukaryota. (P8)
4.7 Know the ultrastructure of plant cells (cell walls, chloroplasts, amyloplasts, vacuole, tonoplast,
plasmodesmata, pits and middle lamella) and be able to compare it with animal cells. (P11-12)
4.8 Be able to recognise the organelles in 4.7 from electron microscope (EM) images. (P11-12)
4.9 Understand the structure and function of the polysaccharides starch and cellulose, including the role of
hydrogen bonds between β-glucose molecules in the formation of cellulose microfibrils. (P15-16)
4.10 Understand how the arrangement of cellulose microfibrils and secondary thickening in plant cell walls
contributes to the physical properties of xylem vessels and sclerenchyma fibres in plant fibres that can be
exploited by humans. (P16)
4.11 Know the similarities and differences between the structures, position in the stem and function of
sclerenchyma fibres (support), xylem vessels (support and transport of water and mineral ions) and phloem
(translocation of organic solutes). (P13-14)
4.12 Understand the importance of water and inorganic ions (nitrate, calcium ions and magnesium ions) to plants.
(P18)
4.13 Understand the development of drug testing from historic to contemporary protocols, including William
Withering’s digitalis soup, double blind trials, placebo, three-phased testing. (P17)
4.14 Understand the conditions required for bacterial growth. (P14)
4.15 Understand how the uses of plant fibres and starch may contribute to sustainability, including plant-based
products to replace oil-based plastics. (P18)
4.16 Be able to evaluate the methods used by zoos and seed banks in the conservation of endangered species and
their genetic diversity, including scientific research, captive breeding programmes, reintroduction
programmes and education. (P9-10)
2
,Biodiversity
Biodiversity
• Biodiversity: The range of organisms found in a particular area.
• Endemism: The ecological state of a species being unique to a defined geographical location, such as an
island, nation, country, or other defined zone / habitat type.
Species Diversity
• Species Diversity takes into account both species richness and species evenness:
o Species Richness: The number of different species found in a particular area.
o Species Evenness: A measure of how evenly distributed the different species are in a particular are.
Genetic Diversity
• Genetic Diversity: The variation of alleles within a species (or a population of a species).
• Gene Pool: The complete set of alleles in a species (or population).
• Individuals of the same species vary because they have different alleles.
• The greater the variety of alleles, the greater the genetic diversity.
• Sources of genetic variation:
o Meiosis (Crossing Over)
o Meiosis (Independent Assortment)
o Mutations
o Reproduction
Measuring Genetic Diversity
• Samples of an organism’s DNA can be taken and the sequence of base pairs analysed.
• The order of bases in different alleles is slightly different.
• By sequencing the DNA of individuals of the same species, you can compare the alleles within a species for
similarities and differences.
The Heterozygosity Index
• The heterozygosity index is used to measure genetic diversity within a species.
• Heterozygotes have two different alleles at a particular locus (the position of a gene on a chromosome).
• A higher proportion of heterozygotes in a population means that the population has greater genetic diversity.
H= ______Number of Heterozygotes______
Number of Individuals in the Population
• You can find an average value of H at many loci – this can be used to estimate genetic diversity in the whole
genome of a population.
The Index of Diversity
• An index of diversity is calculated using an equation that takes both the number of species (species richness)
and the abundance of each species (population size) into account.
D: Index of Diversity
N: Total Number of organisms of all species
n: Total Number of organisms of one species
• The higher the index of diversity (D), the more diverse the area is.
• If all the individuals are of the same species (i.e. no biodiversity) then the D=1.
3
, Niche
The Environment
• Environment: All the factors in a habitat which affect an organism; these may be biotic or abiotic.
• Habitat: The geographical area occupied by an ecosystem.
• Biotic: Factors referring to the living organisms in the ecosystem.
o E.g. Predation, competition, disease, parasites, mates.
• Abiotic: Factors referring to non-living physical and chemical elements in the ecosystem.
o E.g. Humidity, nutrient availability, temperature, light intensity, wind speed, oxygen concentrations,
water availability, soil pH.
Niche
• Niche: The role of a species within an ecosystem.
• This includes its relationship with living organisms and the non-living environment.
• Every species has its own niche – a niche can only be occupied by one species.
• If two species try to occupy the same niche, they will compete with each other; one species will be more
successful than the other and the other will struggle to survive.
(Extra) Fundamental Niche Vs. Realised Niche
• Fundamental Niche: The full range of environmental conditions (biological and physical) under which an
organism can exist.
• Realised Niche: The limited range of environmental conditions that a species is forced to occupy due to direct
and indirect interactions with other species.
Competition
• Interspecific Competition: Competition between individuals of different species.
• Intraspecific Competition: Competition between individuals of the same species.
• Competition forces species to occupy a narrower (realised) niche than their full (fundamental) niche.
(Extra) Effect of Competition on Realised Niche
Interspecific Competition
• Interspecific competition is between different species, and different species will have different niches.
• However there may be some overlap of resources between these niches and there will be competition between
the species for these resources.
• As a result, the species will be forced to specialise towards the resources within their niche that are not apart
of the overlap.
• Hence interspecific competition makes niches narrower.
Intraspecific Competition
• Intraspecific competition is between the same species, and the same species will have the same niche.
• As such these species will be competing for exactly the same resources, which there will likely not be enough
of.
• As a result, the species will be forced to move outside of their optimum range and specialise towards new
resources.
• Hence intraspecific competition makes broadens niches.
4
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