Biology Chapter on Genetic Diversity

Defining Biological Terms

• Species: A group of organisms that can interbreed to produce viable, fertile offspring (e.g., Grey squirrels, Hazel trees).
• Population: All the organisms of one species in a particular place at a particular time (e.g., the Human population of Britain in 2014).
• Community: All the populations of all the species in a particular place at a particular time (i.e., all life in an area including animals, plants, fungi, bacteria...everything living).
• Habitat: The place, with a distinctive set of conditions, where an organism lives.
• Niche: The role an organism plays in its environment or how an organism exploits (uses) its environment. Most importantly it describes what it eats/where it is located in a food chain/its trophic level. But it also includes where it shelters and the times it is active. Only one species can survive in a single niche. If a second species inhabits exactly the same niche they will compete and one species will die out.
• Environment: The external surroundings including all of the biotic (living) and abiotic (non-living) factors.
• Interspecific Competition: Competition for resources (e.g., light, space, food, minerals) between individuals of different species.
• Intraspecific Competition: Competition for resources (e.g., light, space, food, minerals) between individuals of the same species.

Adaptations

• Behavioral Adaptations: Actions by an organism that help them to survive or reproduce. Examples include hibernation, migration, hunting strategies, herding together for protection, burying acorns to store food for winter.
• Physiological Adaptations: Features of an organism's body chemistry that help them survive or reproduce. Examples include chemicals acting as pigments for coloration, modified hemoglobin to work at high altitudes, venom, anti-venom, digestive enzymes, and bacterial with thermostable enzymes.
• Anatomical Adaptations: Structures that an organism has that help them survive or reproduce. Examples include lungs adapted to have a large surface area, muscles in arterioles to adjust rate of blood flow to particular organs, antlers on deer, claws, and large ears on an elephant.

Natural Selection

• Natural Selection Steps:
• A population has naturally-occurring genetic variation with new alleles created through mutations.
• A change in the environment causes a change in the selection pressures acting on the population.
• An allele which was previously of no particular advantage now becomes favorable.
• Organisms with the allele are more likely to survive, reproduce, and so produce offspring.
• Their offspring are more likely to have the allele, so it becomes more common in the population.

Gene Pool and Genetic Diversity

• Gene Pool: All the alleles of all the genes in a population at a given time.
• Genetic Diversity: The variety of alleles in a gene pool (often derived from meiosis – crossing over, independent assortment – or from mutations and random fertilization). The more different alleles there are in a gene pool, the greater the genetic diversity.

Hardy-Weinberg Equation Assumptions

• Large Population: To prevent in-breeding effects
• Random Mating: Individuals with a particular genotype must not tend to mate with other individuals of the same genotype.
• No Selection: This would affect the frequency of particular alleles.
• No Mutations: This would affect the frequency of particular alleles.
• No Immigration/Emigration (Gene Flow): No gene flow into or out of the population – as this would affect the frequency of particular alleles.

Biodiversity

• Biodiversity Components:
• Genetic Diversity: A measure of the variety of alleles in a gene pool (tends to increase over time as mutations accumulate, meiosis).
• Species Diversity: The number of individuals and the number of species in a community (should increase over time).

Sources of Genetic Diversity

• Mutations to DNA: Either by a mutagen (e.g., ionizing radiation, toxins from cigarette smoke) or randomly by inaccurate copying of DNA during the S phase of the cell cycle.
• Meiosis:
• Crossing Over: When non-sister chromatids exchange alleles.
• Independent Assortment: Homologous pairs line up at the equator, but their orientation with respect to maternal and paternal chromosomes is random.

Defining Biodiversity Terms

• Species Richness: The number of different species present in a particular habitat at a particular time – but tells us nothing about their abundance.
• Biodiveristy: Made up of 2 main components: Genetic diversity - there is genetic variation between members of a species. However, if a population falls below the level of 50 breeding adults, there is likely to be genetic inbreeding, usually resulting in the accumulation of harmful recessive alleles. Species diversity - a measure of both the number of individuals and the number of species in a community.
• Endemism: Where an organism's distribution is restricted to specific geographical areas. Islands which have been isolated for a long time often have endemic species. The longer the isolation, the greater the number of endemic species present.

Simpson's Biodiversity Index

• A statistical test (Simpson's Biodiversity Diversity Index) can quantify species diversity.
• Its formula involves the total number of organisms of all species and the total number of organisms of a particular species.

Plant Cell Organelles

• Cell Wall: Provides support and protection.
• Chloroplasts: Site of photosynthesis
• Amyloplasts: Storage of starch.
• Vacuole: Contains cell sap. Keeps cells turgid when water enters.
• Tonoplast: The membrane around the vacuole.
• Plasmodesmata: Allows movement of dissolved substances directly from one cell to another without having to pass through the cell membrane.
• Pits: Areas of very thin cell walls that help movement of substances between cells.
• Middle Lamella: The layer between the cell walls of adjacent cells.

Cellulose Structure and Function

• Cellulose has a high tensile strength due to its structure. It is made of beta-glucose, joined by beta(1-4) glycosidic bonds. Cellulose molecules are unbranched and straight. Many lie next to each other, bonded with hydrogen bonds. This forms microfibrils. Cellulose is also insoluble in water due to its large size.

Starch vs Cellulose

Xylem Vessels, Phloem Sieve Tubes, and Sclerenchyma Fibres in Plant Stems

• Vascular bundles are near the outer edge of the stem.
• Sclerenchyma is outermost.
• Then phloem.
• Then xylem

Xylem Vessels Structure and Function

• Xylem is tissue that transports water and mineral ions from the root to the stems and leaves, and supports the stem.
• Xylem vessels are large cells with thick cell walls (like drain pipes)
• The cross walls are missing, allowing a structure that acts like a continuous tube for water transport in one direction
• The walls are strengthened with lignin, making them waterproof and supporting the plant
• The tonoplast breaks down and the cell contents dissolve (dead cells)

Phloem Structure and Function

• Phloem transports products of photosynthesis (sucrose and other organic solutes) from leaves to other plant parts.
• Phloem is made of sieve tubes and companion cells.
• Sieve tubes are long, individual cells arranged end-to-end, perforated walls (sieve plates), allowing fluid movement between lumens of adjacent cells .
• Companion cells have a lot of ribosomes and mitochondria, and their cellular functions support the activities of the sieve elements.

Sclerenchyma Fibres Structure and Function

• Sclerenchyma fibres are a type of supporting tissue in plants.
• They have very thick cell walls, strengthened with lignin, small lumen.
• They lack cytoplasm and are dead cells.
• They are different from xylem vessels because they have cross-walls and don’t form tubes.

Measuring Mineral Deficiencies in Plants

• Method steps:
  1. Prepare solutions with different mineral concentrations or a mineral missing.
  2. Maintain all conditions constant except the mineral being investigated.
  3. Cover the tops of test tubes with a clear film above the solution. Attach the seedling with roots in the solution and stem out.
  4. Use 10 repeats per solution
  5. Control temperature and light intensity.
  6. Control for the age of seedling for consistent results
  7. Leave to grow for 3 weeks.
  8. Measure changes in length, stem mass, number of leaves, and colour to evaluate results.

Inorganic Ions Required by Plants

• Nitrate ions: Needed to make amino acids, proteins, chlorophyll, and nucleic acids; deficiency causes stunted growth and yellow leaves.
• Magnesium ions: Needed to make chlorophyll; deficiency causes yellow leaves but veins remain green.
• Calcium ions: Needed to build cell walls, pectins, and for cell membrane permeability; deficiency causes stunted growth and misshapen leaves.

Measuring Tensile Strength of Plant Fibres

• Method steps:
  1. Extract plant fibres from standardized way - e.g. retting or scraping.
  2. Use plants of the same age/ leaves collected the same time ago.
  3. Attach the plants to a clamp with a hook
  4. Add increasing mass to the fibres and see what mass makes the fibre break
  5. Repeat these steps 10 times for each plant fibre type.
  6. Control for temperature and humidity.

Drug Testing Process

• Pre-clinical Testing: Animal studies and tissue cultures identify active ingredients. Tests for safety and toxicity.
• Phase 1: Small group of healthy volunteers checks for safety in humans. Identifies side effects and maximum tolerated dose.
• Phase 2: Small group of patients with the illness tests for treatment effectiveness.
• Phase 3: Large group of patients with the illness, double blind tests for treatment effectiveness testing a new drug against a placebo to identify statistically significant results.
• Post-licensing: Data collection continues once the drug is licensed to identify rare or long-term side effects and ensure the clinical trials were correct.

Conditions for Bacterial Growth

• Warm temperature: For efficient enzyme reactions.
• Moisture: For chemical reactions (like respiration).
• Oxygen (Aerobic Bacteria Only): For aerobic respiration.
• pH: For efficient enzyme reactions.

Investigating Antimicrobial Properties of Plants

• Method steps:
  1. Prepare a plant extract. (e.g., 5g of plant material in 10cm³ ethanol)
  2. Soak filter paper discs into the extract. Dry.
  3. Prepare a bacterial lawn on an agar plate.
  4. Place dried discs onto the agar plate seeded with bacteria.
  5. Tape the lid of the agar plate in quarters to prevent opening.
  6. Incubate at a controlled temperature (25°C).
  7. Observe and measure the zone of inhibition around each disc.
  8. Repeat the experiment at least 10 times for each plant.
  9. Compare the mean sizes of the clear zones around each disc.
  10. Greater zone size = more effective antimicrobial properties. Measure clear zones (diameters).

Sustainability

• Sustainability: The principle that the use of resources (or the environment in general) should only be permitted if it can be done without damaging the environment or reducing those resources in the long term.

Fossil Fuels as Carbon Sinks

• Carbon Sink: A long-term store of carbon where carbon is prevented from cycling around the carbon cycle.
• Dead plant or animal matter in anaerobic conditions (e.g., swamps, bottom of the sea) doesn't decay.
• This matter is turned into fossil fuels (coal, oil, gas).
• Carbon in fossil fuels stays there for long time, preventing its release back into the environment.
• However, combustion releases this carbon into the atmosphere as carbon dioxide.

Captive Breeding Programs

• Increasing Population: Increase the number of individuals of a species successfully.
• Maintaining Genetic Diversity: Collect data on individuals and decide which ones to breed together. Collaborate with other zoos to increase the effective population size (minimum 50 individuals).
• Reintroduction: Train animals in captivity. Over exposure to humans might affect behaviour and chances of survival in the wild.

Seed Bank Storage Processes

• Seed Collection: Collect seeds from the wild, identifying the species.
• Viability Check: X-ray seeds to check for embryo presence/ viability.
• Preparation: Dry, sterilize, and package seeds.
• Storage: Store seeds in large numbers at low temperatures (-20°C) to prevent germination and decomposition.
• Monitoring: Periodic germination trials to check seed viability.

Test your knowledge on genetic diversity and organism classification in this biology quiz. Explore key concepts such as species richness, kingdoms of life, and the processes contributing to genetic variation. Perfect for students delving into biological sciences and genetics.