SACE Stage 2 Biology Exam

Why is high biodiversity important?

More stable and resilient communities. Provide food, fibres, structural materials and medicines.

What is hunting

Hunting is the most direct form of extinction of species such as the black rhino, dodo and Tasmanian tiger.

How does the enhanced greenhouse effect work?

Natural greenhouse gases retain some heat in the atmosphere. Too many greenhouse gases reatin nearly all the heat, changing the average temperature of the earth.

How have humans contributed to global warming?

Burning fossil fuels lead to more carbon dioxide and methane in atmosphere. Deforestation reduced the amount of trees that were taking carbon dioxide out of the atmosphere. Increased greenhouse effect

What is bad about low genetic diversity?

The species is more susceptible to selection pressures that may cause extinction, and more likely to have deformities

Divergent evolution/adaptive radiation

Selection pressures cause two or more species to arise from a common ancestor

Convergent evolution

The aquisition of the same biological trait in unrelated lineages due to similar selection pressures

Evidence in support of endosymbiosis

Mitochondria and Chloroplasts have circular DNA, undergo binary fission, have small ribosomes (able to create thier own proteins), and have double membranes. Structure and biochemistry of chloroplasts is similar to cyanobacteria.

What is the ethical argument for preserving biodiversity?

-The right for all organisms to exist
-Not being wasteful with resources
-The right for future generations to benefit from the aesthetic value of biodiverse ecosystems
-The spiritual and religious context that humans should look after creation

What are ribozymes and what do they do?

RNA molecules that can catalyse reactions (e.g. ribosomes)

Analagous structures

Features that come about by convergent evolution. They look similar and have the same function, but the organisms are unrelated

Homologous structures

Things that evolve from a common structure (common ancestor) to have different functions

What does anthropogenic mean?

caused by humans

Allopatric speciation

When a population is split by a geographical barrier, so that there is no longer gene flow between the two populations. Different selection pressures lead to different traits becoming more frequent, and eventually reproductive isolation arises, creating different species.

Sympatric speciation

Occurs when two species form from a single population in one location. Rare in animals. Common in plants due to polyploidy

Non-disjunction

During meiosis, the homologous chromosomes do not seperate properly and an individual can end up with an extra chromosome or missing chromosomes

What can microplastics do?

Gut blockage, physical injury, change oxygen levels, altered feeding behaviour and reduced energy. Act as carriers for chemicals.

Pollution

The introduction of contaminants into the natural environment that cause adverse change. Can be chemical substances or energy such as heat, light or noise. Pollutions can either be foriegn substances/energies or naturally occuring contaminants

DNA hybridization

DNA from both species is heated to break the hydrogen bonds between complementary strands and allowed to cool. Once they have bonded, they are re-heated and the temperature at which the strands break indicate the degree of relationship. Used mostly for bacteria.

What does deforestation do?

Can cause direct extinction of plants and deprives animals of food and shelter. It divides populations and makes them more susceptible to founder effects, genetic drift etc.

How were other organelles formed?

Infolding of the cell plasma membrane

How did early protocells form?

Spontaneous cell membranes made from lipids, which are able to make hollow balls (vesicles) due to thier polar nature. Different concentrations of chemicals on inside, different reactions inside

What is a mutation?

A permenant change in the genetic sequence caused by miscopying during replication. Mutations accumulate over time.

What are the sources of genetic variation in sexually reproducing organisms?

Independant assortment
Random fertilization
Crossing over
Mutation

Sequencing of common proteins (cytochrome C)

Protein involved in the electron transport chain in the mitochondris. Is found in plants, animals and many unicellular organisms. Is too complex to have evolved independantly. Sequencing amino acids enables comparison between species; the more differences the less related they are

How is DNA sequencing used to determine relationships?

The closer the relationship between species, the shorter time since they diverged from a common ancestor and the fewer mutations that will have occurred. Therefore there are fewer differences between thier DNA

Primary succession

New land. No soil, no previous communities. E.g. Volcanic eruption, glacier retreats and leaves bare rock.

Secondary succession

Small disturbances, leaves soil intact. Previous communities. E.g. bushfire, flood, hurricane, clearing land.

How old is the Earth?

4.5 billion years old. Initially a ball of magma devoid of oxygen. it was in this environment that amino acids formed.

Endosymbiosis

The theory that chloroplasts and mitochondria were once free living prokaryotes that were engulfed by larger prokaryotes and survived to evolve into the modern organelles

What type of tree is used to represent evolutionary relationships?

Phylogenetic tree diagrams

Gene pool

The gene pool comprises all of the alleles in a population, all of the genetic information for that species. Alleles are alternate forms of genes.

Artificial selection

Selective breeding by humans on crops and animals

Morphological similarity

Comparing structure, colour and behaviour. Problematic as two different species can look alike, and there can be lots of variation within a species. Mostly used for grouping fossil organisms into species.

Ring species

Adjacent populations can interbreed but the populations at the 'end of the line' cannot. Shared gene pool, but not all populations can interbreed.

Species

A group of organisms that are more or less alike and can produce fertile offspring in thier natural environment

Community

All of the living organisms (populations of all species) inhabiting the same area at a particular time.

Reproductive Isolation

What prevents one species from breeding with another. reproductive barriers prevent interbreeding

Ecosystem

The interaction between a community and the abiotic factors in an area

Temporal isolation

Species are sexually active or flower at different times. Can be months apart, or as close as day/night

post zygotic barriers

Occur after fertilisatoin and prevent the maturation of fertile offspring. Hybrid inviabilty and hybrid sterility.

pre-zygotic barriers

Prevent mating or fertilization. Temporal, behavioural, mechanical and gamete isolation

Population

A group of organisms of the same species inhabiting the same area

Behavioural Isolation

Animals exhibit courting behaviour or release pheremones to attract mates. Individuals are only attracted to, and will only mate with, members of the opposite sex who perform the appropriate ritual, sing the right song or release the correct chemicals

Hybrid sterility

Two species can mate, the gametes can fuse, an offspring is born, but it cannot produce offspring (sterile)

Hybrid inviabilty

Species where the gametes may fuse, but the embryo does not develop normally and is not born

Gamete isolation

Gametes may be transferred but fertilization does not occur. The environment in the reproductive tract is deadly to the sperm or the sperm and egg do not recognise each other

Natural Selection

Within a population there is genetic variation. Some indivisuals are better able to survive selection pressures and breed. they pass on thier favourable genes/characteristics. over generations the frequency of these alleles increases

Selection Pressure

A factor that causes selection for particular alleles

Population Bottleneck

A sudden reduction in population size, reducing genetic diversity even when the population grows larger again.

Founder Effect

A type of population bottleneck that occurs when a small sample of a population establishes a new population somewhere else

Genetic Drift

Variation in frequency of alleles in small populations owing to the chance disappearance of particular genes as individuals die or do not reproduce

Why are geographical barriers important?

So that there is no longer gene flow between populations

What is the RNA World Hypothesis?

RNA was once the primary carrier of genetic information and that ribozymes assisted in the copying and protection of that RNA due to thier catalystic properties. DNA replaced RNA because it is more stable.

Criteria used to define a species

Morphological similarity, biochemical similarity, sharing a common gene pool, interbreeding

What are the techniques for obtaining evidence of relatedness?

Sequencing of common proteins, DNA-DNA hybridization, DNA sequencing

What happened when chlorophyll appeared in bacteria?

Allowed oxygenic photosynthesis. Increase in oxygen led to:
- Formation of ozone layer, which blocked out UV
- Cataclysmic death of most prokaryotes as oxygen was toxic to them
- Oxygen concentration rose to 0.45% (today it is 21%)

What does sharing a common gene pool mean?

That a species is the largest unit of population in which genetic exchange is possible.

Biochemical Similarity

Comparisons between the DNA and proteins that exist in different organisms

Stromatolites

Oldest known fossils. Ancient bacterial mats that trapped sediments and made mounds that can be seen in the fossil record.
3.7 billions years ago

Mechanical isolation

Anatomical differences (usually in genetalia) make the transwer of gametes impossible. In plants, mechanical isolation occurs when different species have different pollinators that do not service the flowers of other species.

Evolution

Evolution is the change of allele frequency in a population over time

Total non-disjunction

When one of the two cells produced during Meiosis I gets all of the chromosomes. The other cell is not viable and is reabsorbed. Results in two diploid daughter cells instead of four haploid ones. In plants, this can result in a new species as they can self-fertilise

Polyploidy

A cell/organism that has more than two sets of each chromosome due to total non-disjunction. Results in increased size, bigger fruits, and resistance to disease.

How does climate change affect animal populations?

Increasing temperature outside tolerance limits. Migration due to changing temperatures, changing environments, outcompeting natural species. Some species eggs only hatch at a certain temperature, or the temperature indicates the gender of the baby.

PCR

Polymerase Chain Reaction. PCR is a process whereby small samples of DNA can be amplified into many copies where there is enough to analyse and use for other processes

Transgenic Organism

An organism whose own genes have been altered, or new genes inserted from another organism

Compare chromosomes in eukaryotic and prokaryotic cells

Eukaryotes have multiple, linear chromosomes wound around proteins (histones), stored in the nucleus. The genes contain introns. Prokaryotes have only one unbound circular chromosome located in the cytosol. The genes have no introns (only exons)

Chromatin

DNA is wound around histones to make nucleosomes. These are then wound up to form chromatin which further condenses to form a chromosome

Histones

Protein groups that DNA is wound around in eukaryotes. This is called nucleosomes

What is meant by the term 'anti-parallel'?

A term applied to two molecules that are side by side but run in opposite directions. 3' to 5' (three prime to five prime) and 5' to 3'

Macromolecule and Polymer

Macromolecule - very large molecule.
Polymer - a substance which has a molecular structure built up chiefly or completely from a large number of similar units bonded together

What is meant by 'the genetic code is degenerate'?

There are 64 combinations of the 4 nucleotides and only 20 amino acids. Therefore there are heaps of double ups

Describe the bonds between the nitrogenous bases

Adenine and thymine form two hydrogen bonds. Guanine and cytosine form three hydrogen bonds

State the three methods of DNA replication that were proposed initially

Semi-conservative - one old, one new
Conservative - completely new
Dispersive - sections

Glycoproteins

Any class of proteins which have carbohydrate groups attached to the polypeptide chain

Transcription factors

Transcription factors can either activate gene expression by binding to the promotor region upstream of the gene sequence or block gene expression by binding and blocking the attachment of RNA polymerase to the DNA so transcription cannot begin.

Methylation

Genes are not transcribed (switched off) in cells if methyl groups (CH3) are added to the cytosine bases in that gene sequence

Epigenetics

The study of heritable changes in gene function that do not involve changes in the DNA sequence

Zygote

The fertilized egg

Loci

The position of genes on DNA

Chromosomal Mutations

Chromosomal mutations are always harmful. Duplication, deletion, inversion, translocation

What does reducing temperature do to enzymes?

Reduced temperatures slow reactions. As temperature decreases the enzymes and substrates have less energy, move more slowly and encounter each other less often. Kinetic Theory of Matter

Why are inhibitors important?

They allow control of reaction pathways, and can prevent overproduction

Receptor Proteins

Receptor molecules are specific to the molecule they are meant to sense and react to. They can be proteins or glycoproteins. They can be embedded in the cell membrane to recieve external stimuli or inside the cell to react to molecules that can get in

Somatic Cells

Body cells. Any cell of an organism other than germ cells/gametes/reproductive cells

siRNA

Small interfering RNA can cut mRNA after transcription preventing it from being translated

Advantages to breaking reactions into smaller steps

-Lowering activation energy
-Intermediate products produced can be used in other processes
-It is easier to manage the heat released by many small reactions than one big one

Antibodies

Each antibody has two specific antigen binding sites that bind to complementary sites on bacteria and viruses and neutralise them. Produced by white blood cells.

Gel Electrophoresis

DNA samples placed in wells at one end of an agar block. An electric current is applied, and since DNA is negatively charged, it moves towards the positive end. the smaller fragments are able to move faster, so the DNA is seperated by size

STR

Short Tandem Repeating. Used in DNA profiling

Process of DNA extraction

Disrupting the cell and nuclear membrane using detergents (break down lipids). Protease enzyme break down all proteins, including histones. The DNA is precipitated by adding ethanol and centrifugation (spinning)

DNA replication

The DNA helix unwinds with the assistance of helicase, exposing the nitrogenous bases on both strands. Free DNA nucleotides bind complementary to the bases on both template strands with the assistance of DNA polymerase, creating two genetically identical DNA molecules each containing one old (parent) strand and one new (daughter) strand. This is called semi-conservative replication

What can affect the activity of enzymes?

pH, temperature, enzyme concentration, substrate concentration, inhibitors

Gene Therapy

The treatment of genetic disorders by replacing or supplementing defective genes with normal, functional genes. Viral vector usually

DNA/RNA probes

A small single stranded sequence complementary to a known section of the gene of interest is radioactively or fluorescently labelled. The probe is mixed with DNA that has been seperated by heat. When the solution is cooled, the probe will bind to the DNA, locating the gene.

Restriction enzymes

Restriction enzymes cut the DNA double helix at sequence specific sites, called a restriction site (4-8 bases) that is a different sequence for each enzyme

Agrobacterium

Agrobacterium have a special Ti plasmid. The gene is cloned into the Ti plasmid, transferred into agrobacterium and then coated onto plant leaves. The bacterium inserts the Ti plasmid (containing the gene of interest) into the cells, which divide rapidly to produce a timour. The tumour is removed, cut up and used to grow GMO plants

Bacterial Plasmids

Small rings of DNA. Able to exchange DNA with the central chromosome. Can be cut open with restriction enzymes and genes of interest (cut with same enzyme and introns removed) can be inserted using DNA ligase

Quaternary Structure

More than one polypeptide are joined together to form the final protein