Biology IB

Where does variation come from? (5)

Where does variation come from? (5)

- Sexual reproduction
- Genetic mutations
- Errors in DNA
- Viral injection of foreign DNA
- Environmental effects on gene expression

Biological species concept

Species consist of populations of organisms that can
- Successfully reproduce with one another to have fertile offspring
- Are reproductively isolated from other populations

Problems raised in Biological species concept (2)

- Assumes genetic variation within a population, problem for asexually reproducing organisms whose offspring are genetically identical.
- Assumes genetic information is passed on vertically, when in bacteria it can be horizontal.

DNA barcode

A short sequence of DNA inside and organism's cells that can be used quickly identify the species. It converts into a barcode identification number

Mutation:

Any change in DNA that results in a change of characteristics

Behavioural (Reproductive isolating mechanisms)

- Different mating calls, active at different times in the day

Post Zygotic reproductive isolating mechanisms

- Reduced hybrid viability
- Reduced hybrid fertility
- Hybrid breakdown (stillborn, eggs don't hatch...)

Speciation named case study: Congo River bonobo's and common chimpanzees.

With climate change and a shifting African place, the Congo River formed, a fast flowing river up to half a kilometre wide. This became an impassable barrier to the chimpanzees, and split the population. Different selection pressures led to the evolution of the common chimpanzee on the north bank, and the bonobo on the south bank. In the north bank, the bonobos were able to exploit resources formally used by the extinct gorillas, which the chimpanzees were unable to do, leading to more stable groups and different social structures and behaviour to the chimpanzees.

Later change in the range of the common chimpanzee formed a new subspecies, meaning it has range similar to the bonobos, but they are now behaviourally different enough to not interbreed between bonobos and chimpanzees.

Extinction (3)

When the last individuals of a species dies out. Happens when the rate of change is to fast, and a species doesn't have enough time to evolve for changing conditions. Unless extinction occurs, diversity of life will increase.

Cryptic species

Species which are impossible to differentiate with the naked eye, as they have the same morphology and only differ genetically.

Phylogenetic species concept:

A species is a group or organisms that share a common ancestor and can be distinguished from all other groups of organisms, based on genetic comparison and DNA analysis. Makes finding cryptic species possible

Morphological/phenetic species concept

All organisms with the same body structure/morphology are considered a species. This is useful in paleontology where there is limited/no genetic data

Formation of chromosomes

In the nucleus, DNA is wrapped around proteins called Histones to form regions called nucleosomes. This bundled DNA is called chromatin. During normal cell function (interphase), it is unravelled. As it prepares for replication, the chromatin condenses and supercoils, forming chromosomes.

Nucleoid

The region where naked DNA is more concentrated in a prokaryote.

DNA in prokaryotes

- Found as a singular circular chromosome, not found in the membrane bound organelle.
- Additional genetic material in small circular plasmids.
- DNA is naked, not associated with any proteins or histones.
- Generally haploid

DNA in eukaryotes

- DNA is organised in linear chromosomes and enclosed in the nucleus
- No plasmids, but mitochondria and chloroplast contain their own DNA which exist in circular plasmid like structures.
- DNA is associated with histone proteins
- Generally diploid, two copies of each autosomal chromosome

Plasmids

Where DNA is exchanged through horizontal gene transfer

Diversity of life reflected in chromosomal variation

- Individuals of same species have same number of chromosomes (except some species)
- Closely related species often have different chromosome counts, despite having similar genes.

Why is the number of chromosomes not a reflection of genetic complexity?

Because the chromosomes may have joined or split during a species evolution. In some case, more genetically complex organisms have less chromosomes than simple ones.

Karyograms (4)

- A photo of chromosomes in a cell during metaphase.
- Arranged in order of size, centromere position, and banding pattern
- Provides information on sex, species, and genetic disorder
- Made by lysing a cell where the cell membrane is broken down, then staining them to see chromosomes, cut out and arranged by hand.

All diploid organisms have...

an even number of chromosomes (excluding those with genetic disorders)

Fusion hypothesis

It is hypothesised that the human chromosomes 2 is a result of fusion between chromosomes 2a and 2b in an ancestral species.

Single nucleotide polymorhic (SNP's) (4)

Regions where there are multiple options for a nucleotide base.
- Majority are found in the non-coding DNA
- This gives each individual variability from others
- Humans have over 100 million SNP's

Single nucleotide polymorphic are used for (3)

- Paternity testing
- Genetic testing
- Forensic DNA testing

Genome size (3)

- High degree of variability among taxonomic groups
- Correlation between genome size and number of genes coding for a protein however...
- No correlation between genome size and organismal complexity, at least among eukaryotes.

Genome sequencing current uses (2)

- Comparison to work out evolutionary relationships
- Conservation of biodiversity

Genome sequencing future uses (2)

- Identification, prevention, and control of infectious diseases caused by pathogens
- Identification of SNP's or alleles that lead to increased risk of certain illnesses/disorders, allowing personalised medication and treatments.

For evolution to occur there must be (3)

- Variation within a population
- A mechanism of inheritance (DNA)
- A selection pressure

Selection pressures

Factors in the environment that are uneven in the effects they have on different individuals.

Selection pressures example

Biotic: Predation, disease, competition for mating and resources. Sexual selection
Abiotic: Temperature, oxygen levels, rainfall, light intensity

Fitness (2)

How well an individual is able to survive given selection pressures. Potential for an individual to survive and reproduce.
It is measured as an average contribution of an individual to the gene pool of the next generation.

Evidence for evolution: Convergent and divergent evolution

When similar traits or features arise in unrelated species, resulting in analogous structures in different species. They have similar function, but different structure, because they are analogous.

Adaptive radiation

A fast more extreme version of divergent evolution. It allows closely related species to coexist without competing, thereby increasing biodiversity in ecosystems where there are vacant niches

Evidence for evolution: Genetics

Shared ancestry should be reflected in DNA. DNA should have the same structure across all organisms, code for amino acids using the same code, and reflect time since speciation (more recently diverged species should have more similar DNA)

Evidence for evolution: Genes

Commonality of certain genes and gene families across different species points to a common origin. Genes taken from one organisms and implanted into another will perform the same function.

Speciation

The process by which populations diverge to become distinct species

Covalent bonds

Electrons are shared between non metals. They are very strong and contain lots of energy.

Water and metabolism

Water is the medium for metabolic reactions, making it essential to all living things. The way molecules interact with the water based cytoplasm allows cells to control their composition and maintain functions of life.

Cohesion in water

Is a result of polarity between water and ability to form hydrogen bonds. Bonds between water molecules are weak, however the large number of bonds present gives cohesive forces great strength, so water has strong cohesive properties.

Surface tension

Causes by cohesive hydrogen bonding resisting an object trying to penetrate the surface. These forces can counteracr gravity.

Water and... Ice density

Density of ice is lower than density of water, because when water starts to solidify, the hydrogen bonds form crystalline structures that space molecules apart more evenly, making ice less dense than water.

Specific heat capacity practical elements

- Water has higher SHC than air, because hydrogen bonds must be overcome in water molecules
- It is hard to heat up or cool down the oceans, they are giant heat sinks regulating the temperature of our planet

Water as a...solvent!

Water can dissolve many substances that have polar regions.
The polar attraction of large quantities of water can disrupt intra-molecular forces, resulting in the dissociation of atoms in other substances.

Water as a Solvent practical elements (2)

- Water solvent properties provide multicellular organisms with a medium to transport materials between cells.
- Some materials needing transportation are non-polar and so cannot be dissolved in water. They require special means of transportation such as the protein haemoglobin which binds and carries oxygen gas.

Hydrophilic

Chemically attracted to water. Includes all substances that dissolve in water, polar and charged particles, and substances that adhere to water, like cellulose.

Properties of water: Buoyancy

Upward forces exerted by a fluid on an object in the opposite direction to the weight of that object. If the density is higher than the fluid, the object will sink and vice versa. Water has high buoyancy, meaning less materials can float.

Properties of water: Thermal conductivity

How readily a material conducts heat. Materials with high TC transfer heat quickly. Water has high thermal conductivity compared to air.

Black throated loon - Thermal conductivity and SHC (3)

A thick layer of down feathers insulating it from the water. These are covered by contour feathers which form an impenetrable seal to the water. A preening gland exudes oil, further waterproofing the contour feathers.

Monomer

A small molecule that joins with other monomers to make a large polymer molecule

Polymer

Large molecules or macromolecules formed by combining smaller compounds called monomers

Condensation reaction

When two or more molecules combine to make a larger molecule and water is released. They are anabolic meaning they builds things up, and are endothermic. They create a covalent bond called a phosphodiester bond.

Nucleic acid

Chains of repeating monomers called nucleotides. These nucleotides join together to form a polymer by a condensation reaction called polymerisation. Nucleotides are the building blocks of nucleic acids.

Bonds of DNA and RNA

Covalent bonds form between the phosphate group attached to the 5'C of one deoxyribose sugar and the -OH group attached to the 3'C of another sugar, releasing one molecule of water with the use of energy, and forming a continuous chain.

Purines

bases that have two rings in their structure - Adenine + Guanine

Nucleosomes

A length of DNA wrapped around a core of eight histones and a special histone called histone 1 which locks everything in place. The extra histone attaches to a piece of linker DNA which links nucleosomes, binding around the DNA using its terminal amino acid tail

Euchromatin

Regions of the DNA where nucleosomes are loosely bound and can be transcribed

Extra terrestrial origins of water

Planets formed 4.6 by a from spinning discs of gas around the newly formed proto-sun
Heavier elements closer to sun, lighter elements further out.
Collision between earth and Theia caused remelting of earth and formation of moon
Asteroids containing hydrogen and water bombarded earth
Asteroids melt, releasing the water.
Crust forms on the earth
Very pressurised atmosphere ensured water stayed liquid despite being heated to several hundred degrees
Earth cools, atmosphere loses gasses, temperature falls to accommodate life

The goldilocks zone

A region around a star where conditions are right for water to exist in liquid form. Planets falling outside this zone are less likely to have water

Chargaff's data

- DNA was thought to be single stranded containing equal amounts of each base
- This was the tetranucleotide hypothesis
- He analysed different samples of DNA using paper chromatography to separate components of DNA.
- He increased the number of species he tested and includes some viruses
- He found that amount of A was equal to T, and amount of C was equal to G, supporting double helix model and giving clues to complementary base pairings.

Capillary action in xylem vessels

Xylem vessels transport water from the roots to the leaves. Water bonds to the sides of the xylem vessel using adhesion, and the rest of the water follows because of cohesion

Three things that all cells have

Lipid based plasma membrane, DNA, Cytoplasm

Prokaryotes have what organelles?

Cell wall, Plasma membrane, Cytoplasm, Naked DNA, 70s Ribosomes, Plasmids, Flagellum, Pili,

What are prokaryotes?

The earlies form of cells that originated around 3.5 BYA, and do not contain membrane bound organelles. They are generally smaller and less complex then eukaryotic cells.

Prokaryotes: Cell wall

Found outside the plasma membrane and protects the cell against toxins in the external environment and maintains the shape of the cell. Made up of peptidoglycan

Prokaryotes + Eukaryotes : Plasma Membrane

Separates the cell's interior from external environment and controls what enters and exits the cell. Amphipathic

Prokaryotes + Eukaryotes: Cytoplasm

Water based jelly like fluid that fills the cell, suspends ions, organic molecules, DNA and ribosomes, and is the site of metabolic reactions

Prokaryotes: DNA

Contains naked DNA in a loop, not associated with any proteins and mostly found in the nuceloid.

Prokaryotes: Ribosomes

70s

Compartmentalisation in Eukaryotic cells.

Containing membrane bounds organelles allows for the interior of the organelles to have separate conditions to the cytoplasm, allowing for the separation of toxins from the rest of the cell, creating higher concentrations of substances within the organelles, and maintaining optimum condition for enzymes in organelles.

Eukaryotes: Mitochondria

Double membrane bound organelle that converts glucose into ATP

Eukaryotes: Ribosomes

80s Ribosome: Where protein synthesis occurs. Some attached and some free floating. Larger and more mass that in prokaryotes. 70s ribosomes are found in the Mitochondria and Chloroplasts

Eukaryotes: Nucleus

Contains nucleolus which is involved in producing ribosomes. Has a double membrane containing pores through which certain molecules can pass through including glucose, ions, and RNA

Eukaryotes: Smooth ER

Produces and stores lipids including steroids

Eukaryotes: Rough ER

Has ribosomes attached to its surface which produce proteins usually destined for use outside the cell

Eukaryotes: Golgi Apparatus

Processes and packages proteins, which are then released in Golgi vessels

Eukaryotes: Vesicle

Small sac that releases substances produced within the cell by fusing it with the cell membrane

Eukaryotes: Vacuole

Helps to maintain the osmotic balance of the cell, used to store substances, and sometimes has hydrolytic functions similar to lysosomes

Eukaryotes: Cytoskeleton

A system of protein fibres called microtubules and microfilaments. It helps to hold organelles in place and maintain the structure and shape of the cell

Eukaryotes: Lysosomes

Plasma membrane sacks containing digestive enzymes

Eukaryotes: DNA

Linear, organised into chromosomes. Often diploid and bound into nucleosomes

Unicellular organisms

All prokaryotic cells and some eukaryotic cells are unicellular

Eight processes of life

Metabolism
Reproduction
Homeostasis
Movement
Growth
Response to stimuli
Excretion
Nutrition

Homeostasis

The maintenance of constant internal conditions despite changes in external environment

Nutrition

Intake or production of nutrients

Animals cells contain...(4)

Centrioles, lysosomes, small vacuoles, cilia.

Centrioles

Two cylindrical organelles that help to establish and organise the microtubules, playing an important role in cell division

Lysosomes

Membrane bound bags of hydrolytic enzymes that break down and destroy biological molecules and old cellular organelles

Plant cells contain...(4)

Cell wall, chloroplasts, large vacuole, plastids

Chloroplasts (2)

Double membrane bound organelles that convert light energy into chemical energy through photosynthesis. Green of chloroplasts comes from chlorophyll.

Plastids (2)

Double-membrane bound organelles involved in food production/storage. Main form is chloroplasts however they can also be chromoplasts and leucoplasts

Centrioles in Fungi

The main function is to produce cilia during interphase and the aster and spindle during cell division

Fungi cells can be...

Unicellular or multicellular and reproduce through a process called budding.

Atypical cell structure in Eukaryotes

Typically, prokaryotes don't contain a nucleus and eukaryotes do. However some eukaryotic cells contain no nucleus or multiple.

Atypical cell structure in Eukaryotes: Skeletal muscle

Multinucleated, one single cell contains multiple nuclei. This is because the muscle cell has formed from muscle cells that have fused together

Atypical cell structure in Eukaryotes: Red blood cells

Anucleate. This means the cell has greater haemoglobin capacity and can transport more oxygen

Atypical cell structure in Eukaryotes: Fungal hyphae

Normally, the hyphae of fungi contain septates which separate cellular structures and organelles whilst still allowing the movement of substances between cells. Aseptate hyphae in fungi do not have cellular partitions that are normally present, and so contain multiple nuclei in a single cellular unit, therefore are multinucleated.

Atypical cell structure in Eukaryotes: Sieve tube elements

Anucleate. They also contain very little cytoplasm and few organelles. This means there is low resistance for substances moving through the sieve tube element.

Endosymbiotic theory

Organelles originated as symbiosis between separate single-celled organisms.

Endosymbiont

A cell that lives within another cell with mutual benefit.

Development of the Nucleus (3)

1) Prokaryote grows in size and develops folds in its membrane to maintain sufficient surface area
2) The infoldings are pinched off forming an internal membrane
3) Nucleoid region is enclosed in the internal membrane and becomes the nucleus