Biology 1&2 PDF

[ **Topic 1 -- Genes & Inheritance**] Definitions: - Autosomal - Involving a gene carried on one of the 22 pairs of non-sex chromosomes - Bivalents - A pair of homologous chromosomes held together at the chiasmata - Carrier - Heterozygous for a recessive trait - Chiasmata - The point at which chromosomes cross over - Chromatin - The material of which chromosomes are made of - Consists of DNA wrapped around histones - Diploid Cell (2n) - Having two of each chromosome (homologous pair) - 23 pairs = 46 chromosomes total - Gametes - Human sex cells (sperm and egg cells) - Germ Cells - Reproductive tissues in the gonads (testes in males and ovaries in females) - Haploid Cell (n) - Having one of each chromosome - 23 chromosomes total - Histone - A protein found in eukaryotic chromosomes that assists in packing the DNA - Homologous Chromosomes - A pair of chromosomes of the same length and which contain the same gene - Kinetochore - A protein structure in eukaryotic cells where the spindle fibres attach during cell division to pull sister chromatids apart - Nucleosome - A section of supercoiled DNA around histones - Nucleotide: - A sub-unit of DNA consisting of a phosphate group, a nitrogenous base and a sugar - Punnet Square - A square diagram used to predict the genotypes of a cross product - Sister Chromatids - A pair of identical chromosomes that result from duplication and are connected to each other at the centromere - Synapse - When chromosomes come into contact with each other - Telomeres - The ends of the chromosomes - X-Linked - Involving a gene carried on the X-chromosome DNA - Deoxyribonucleic acid - All genetic material is made up of DNA Structure: - Double Helix: - Two polymer strands wrapped around each other in a double helix - Made up of lots of monomers - Each monomer is called a nucleotide - Each one is made up of a phosphate, a pentose sugar and a base - Each nucleotide has the exact same phosphate and sugar - Four bases: - Purines: - Adenine - Guanine - Pyrimidines: - Cytosine - Thymine - The phosphate of one nucleotide bonds to the sugar of the next nucleotide - This process repeats for thousands of nucleotides, making up the sugar-phosphate backbone - The outer casing of the DNA helix - The bases hold the two strands together - Only complimentary bases can pair together however - Adenine and Thymine - Guanine and Cytosine - This is complimentary base pairing - Sequencing: - Genetic code refers to the sequence of bases - Thus a gene is a particular sequence of bases that codes for a protein - Each group of three bases is called a triplet (codon) - This codes for a specific amino acid - Determines the order of the amino acid monomers in the polypeptide - In RNA there are Anticodons however, not codons - Proteins: - Each unique shape carries out a particular function - The main uses of them are: - Enzymes: - Act as biological catalysts - Hormones: - Carry messages around the body - Structural proteins: - Add strength to cells and tissues - RNA: - Messenger RNA - Sends coded intructions for how to build specific proteins - 4 bases: - Cytosine - Guanine - Adenine - Thymine replaced by Uracil - Transfer RNA - Remains as transfer RNA - Ribosomal RNA - 60% of a ribosome\'s composition Chromosomes: - Structure: - Each molecule of DNA is wrapped around histones - Each histone with DNA wrapped around it is called a Nucleosome - Large chunks of nucleosomes are called chromatin - Chromatin is coiled and wrapped around itself to make up a chromosome - Each human cell has 46 chromosomes in it - The DNA is separated into the 46 chromosomes - However there is only 23 different types - This is because we have two of each type - These are called chromosome pairs - Sex Chromosomes: - 23^rd^ pair, either X or Y - XX -- female - XY -- male - Are only in an X shape just before cell division - Connected by the centromere (middle) - Usually are separated however ![](media/image2.png) Genes & Genomes: Genes: - A length of DNA that contains the coded instructions for building a gene product (usually a polypeptide or protein) - A small segment of a chromosome - This segment is a code for a specific sequence of amino acids - When these amino acids are combined in the specific sequence, it creates a unique protein Genomes: - The term genome refers to all the genetic information in a cell, individual, or a species, depending on what is being discussed - Complete human genome: - This allows us to identify genes that are linked to certain types of diseases - These are inherited diseases - We can trace the migrations of our ancestors through the genome Meiosis: Summary: - The basis of sexual production - The goal is to make daughter cells with exactly half as many chromosomes - And then create gametes from those daughter cells - When an egg and sperm join in fertilization the two haploid sets of chromosomes form a complete diploid set: a new genome Purpose: - To enable sexual reproduction to happen without an increase in the number of chromosomes in an individual's offspring - To take diploid cells and produce sexual gametes from each Process: - Interphase and introduction: - Meiosis takes place in germ cells - During the S Phase of Interphase, chromosomes are duplicated, resulting in each chromosome having two identical sister chromatids. - Begin as diploid cells but divide by meiosis into haploid gametes - Meiosis 1: - Prophase 1: - Early prophase 1 - Nucleolus disappears and the chromatin starts to condense and become visible - Mid Prophase 1: - Chromatin condenses into X shaped conformations - Each conformation has two sister chromatids visible - Each conformation's telomeres attach to the inside of the nuclear membrane - Late Prophase 1: - Each chromosome moves around the nuclear membrane until they find their homologue - Crossing Over: - They synapse and become anchored together at genetically similar points called chiasmata - During this phase equivalent sections of sister chromatids break and are recombined - In this way genes are exchanged between homologous chromosomes - A pair of homologous chromosomes held together at chiasmata are called bivalents - End of Prophase 1: - Nuclear membrane breaks down - Centrioles separate - Microtubule spindle forms between them - Bivalents start to move to the equator of the cell - Metaphase 1 - Bivalents assemble along the equator of the cell in a completely random arrangement - This is called independent assortment which increases genetic diversity - The kinetochore at each chromosome's centromere extends kinetochore fibres that attach to the spindle fibres - Anaphase 1 - Spindle fibres shorten - This splits each bivalent dragging the homologous chromosomes to opposite poles of the cells - Telophase 1 - Early Telophase 1: - Chromosomes begin to decondense - Nuclear envelope reforms in some cells - Mid Telophase 1: - A contractile ring of protein fibres and motor proteins forms, creating a cleavage furrow in the cell membrane - Late Telophase 1: - The contractile ring constricts and cytokinesis starts. - Cytokinesis/Interkinesis: - When the contractile ring has full constricted, membrane vesicles move to the constriction and fuse the membrane, creating two separate haploid cells - In many cells there is a period of rest called interkinesis - In other cells however, the second stage of meiosis begins almost immediately after the completion of cytokinesis. - These cells are called independent daughter cells - Meiosis 2: - Prophase 2 - Early Prophase 2: - Chromosomes begin to condense again - Centrioles separate and begin to move toward opposite poles of the cell - Spindle fibre begins to form between them - Late Prophase 2: - Chromosomes are fully condensed - Each chromosome still consists of two sister chromatids - Metaphase 2 - The chromosomes line up along the equator of the cell in a single line - Perpendicular to the direction they lined up in during Metaphase 1 - Each chromosomes kinetochores extend fibres which attach to a spindle fibre - Anaphase 2 - Spindle fibres contract - The sister chromatids of each chromosome separate and one chromatid goes to each side of the cell - Telophase 2 - A contractile ring of protein fibres and motor proteins forms - This creates a cleavage furrow - Cytokinesis starts - Cytokinesis: - Nuclear membrane has reformed - Chromatin decondenses - Nucleolus reappears in each nucleus - The second meiotic division is complete - The original diploid germ cell has now been divided to make four non-identical haploid cells - Gametogenesis: - Following meiosis, the haploid cells further develop to become gametes - Either sperm cells (through spermatogenesis) - Or egg cells (through oogenesis) ![Meiosis](media/image4.png) Alleles: - An allele is a different version of the same gene - This is because there is multiple forms of the same protein - Two alleles (one from each parent) - Homozygous: - The same allele - Can be homozygous recessive or homozygous dominant - Heterozygous: - Two different alleles - Dominant: - The allele that is expressed in the phenotype - Recessive: - The allele that is not expressed phenotype - Genotype: - The array of alleles we have for each gene - Phenotype: - The characteristics that you get from your genotype that are physically expressed - Sex Linked Alleles: - If a trait is sex-linked the gene involved is carried on one of the sex chromosomes - If the gene locus is on the X chromosome, it is said to be X-linked. - If it is carried on the Y chromosome, it is said to be Y-linked. - Because males only have one X chromosome, the sex of a baby affects how likely it is to express an X-linked trait. - Only males have Y-linked traits since females lack the Y chromosome. - As sex matters when predicting the outcome of a cross involving sex-linked genes, the allele symbols are written as a superscript to an X - Examples: - Red Green colour blindness - A recessive X linked trait - Affects about 8% of males but only 0.5% of females - Several types but the most common one is deuteranopia - The alleles are X^R^ for normal vision and X^r^ for deuteranopia - This means normal vision genotype would be any of the following: - X^R^X^R^ - X^R^X^r^ - X^R^Y - This means deuteranopia genotype would be either of the following: - X^r^X^r^ - X^r^Y Mutations: What are they? - A change in the DNA base sequence - Happen spontaneously in our cells all the time - Particularly during DNA replication (like before mitosis) - Increase risk of mutations: - Carcinogens: - Harmful chemicals - Certain types of radiation - Such as X-Rays or Gamma Rays Consequences: - There would be a change because the overall sequence of amino acids would be different - A different protein would be formed - - Usually doesn't have any significant effect - Often only affect a protein very slightly - Most mutations occur in non-coding DNA - Not part of any gene as it doesn't code for a protein - This DNA plays an important role in the expression of a gene - Whether it is on or off Types of mutations: - Substitutions: - One of the bases in a sequence is changed (substituted) for another random base - This changes the codon and thus the amino acid - Insertions: - An extra base is inserted into the sequence - Worse than substitutions - All subsequence bases are shifted along by one - Alters all subsequent codons - Amino acid chain becomes completely different - Deletions: - One of the bases is deleted from a sequence - All the bases are shifted left to fill the gap - This too alters all subsequent codons - Which also changes the amino acid chain Variation and Evolution: Variation - Different phenotypes in a population - Everyone has a unique genome - The environment can also be a factor in the phenotype characteristics - Most characteristics are determined by the interaction between genes and the environment - Variations are due to mutations - Individuals with beneficial mutations are more likely to survive - And thus more likely to reproduce and pass along their mutated genes Evolution: - Inheritance of certain characteristics in a population, over multiple generations, could lead to a change in the whole species - Or sometimes even the development of a new species - Theory of evolution by natural selection implies that all living species evolved from simple life forms that first developed billions of years ago - The natural selection of genetic changes that give rise to phenotypes that are best suited to the environment - Given enough time if phenotypes of two different populations within a species become so different that they can no longer interbreed, they are considered two new species' Phenotype Variation: Modes of Inheritance: - Complete Dominance - One trait is fully dominant the other is recessive - Dominant vs Recessive: - A recessive phenotype is determined by an allele which encodes a protein that does not influence the phenotype of a heterozygote. - If one phenotype is recessive, the phenotype determined by the other allele is said to be dominant - In other words, the dominant trait is the one expressed in the phenotype of a heterozygote - Allele Symbols: - It is conventional to assign the allele for a dominant trait a capital letter, and the allele for a recessive trait a lowercase letter of the same letter - E.g: B for black fur, and b for white. - BB, Bb, Bb, or bb - Codominance: - This is when there are two different alleles for the gene locus, and both alleles are expressed in the phenotype - Common examples include multicoloured animals - Allele Symbols: - Superscripts are used on the capital letter to differentiate between alleles - Incomplete Dominance: - Similar to codominance - Two available alleles, however the phenotype is an intermediate between both homozygote phenotypes - This is also called partial dominance - An example is flower colours: - F^R^ F^R^ would manifest as red coloured - F^W^ F^W^ would manifest as white coloured - F^R^ F^W^ would manifest as a midway between the two, and in this case, pink - Multiple alleles - Very often there are more than only two alleles for each gene locus - When multiple alleles exist, there can be a hierarchy or series of dominance patterns - An example is ABO blood type in humans Karyotypes: Summary: - A visual representation of a person's chromosomes - To create a karyotype, the chromosomes are isolated, stained, cut out, and then arranged in order of size - Karyotypes can be used to determine a number of things about an individual including: - Species - Sex - XX is female - XY is male - Genetic abnormalities - 22 pairs of autosomes and 1 pair of sex chromosomes in each person's diploid cell Genetic Abnormalities: - Turner Syndrome: - Missing Y chromosome or second X chromosome - The individual would be female because being male is determined by the absence or presence of a Y chromosome - Edward syndrome: - Extra copy of chromosome 18 - Most children born with this syndrome don't make it to adulthood - Down syndrome: - Extra copy of chromosome 21 - Patau syndrome: - Extra copy of chromosome 13 Diversity: - Macrochromosome: - A chromosome that is more than 40 megabases in length - Microchromosomes: - A chromosome that is less than 20 megabases in length - Examples: - Scarlet Macaw have 22 macrochromosomes and 40 microchromosomes - Jack jumper ants have only a single pair of chromosomes - Some ferns have 720 chromosome pairs - Absence of X and Y chromosome: - Birds do not have X and Y chromosomes - Males have two Z chromosomes - Females have a W and a Z chromosome - Turtles and crocodiles do not have any sex chromosomes Aneuploidy - Occurs when a single chromosome is missing or added to a normal set - This results in 3 homologous chromosomes (trisomy) or 1 chromosome (monosomy) - Most autosomal aneuploidies result in spontaneous abortion as the missing or extra genes are catastrophic for development - Trisomy 21 -- Down Syndrome - 1 in every 1,100 births - Extra copy of chromosome 21 is inherited as a result of a non-disjunction during meiosis of a parent gamete - Symptoms include: - Physical and intellectual disabilities - Poor immune function - Increased risk of a number of other health problems (congenital heart defect, epilepsy, leukaemia, thyroid diseases, etc) - Klinefelter (XXY) - Occurs in 1 in 650 men - Many are never diagnosed - Two X chromosomes and one Y chromosome - Symptoms may include: - Small testes and underdeveloped male secondary sexual characteristics - Behavioural and learning difficulties - Infertility - Osteoporosis - Turner syndrome (XO) - 1 in 2000 females - Syndrome occurs when an individual receives only an X chromosome and no Y chromosomes - Appear female - Symptoms vary but include short stature and infertility - Aneuploidies and maternal age - Incidence of aneuploidy increases with the age of the mother Epigenetics: Summary: - The study of heritable phenotype changes that do not involve alterations in the DNA nucleotide sequence - Two individuals may have identical alleles of a gene, but due to epigenetic factors they may have different phenotypes expressed Molecular Tags: - Types: - Histone methyltransferase / demethylase - Enzymes that add/remove methyl groups to histones - Histone acetyltransferase / deacetylase - Enzymes that add/remove acetyl groups to histones - DNA methyltransferase - An enzyme that methylates the cytosine in DNA - The most well-known epigenetic mechanisms are methylation and acetylation of histones and methylation of DNA. - These epigenetic markers act as tags which tell the cell to increase or decrease gene transcription (and therefore the gene expression) - 75% of the DNA in mammals is methylated - Essentially is like a tag being added to DNA that prevents that DNA from being used by the cell - Methylation involves a methyl group (CH~3~) being added to cytosine to create 5-methylcytosine (5mC). - This happens at CpG sites, - This is where C precedes G in a 5' -- 3' direction Examples: - Agouti Mice: - The agouti gene is methylated in thin, brown mice but unmethylated in obese, yellow mice. - These mice are genetically identical - Diet can affect the phenotype of the mice and these changes can be inherited by their offspring - Female mice fed a diet high in folic acid (A B-group vitamin found in leafy green vegetables) have more pups with the thin, brown phenotype. - BPA (A chemical added to many plastics) exposure has the opposite effects - Cannabis Rats: - Rats exposed to cannabis have pups who are predisposed to heroin addiction - Starvation: - Descendants of humans who survived starvation have a higher incidence of diabetes and cardiovascular problems Research is underway on many other examples of epigenetic inheritance, including the effect of exercise and childhood abuse. Monohybrid Crosses: - A cross between two alleles - Autosomal Monohybrid Inheritance: - Since both males and females have a homologous pair of each of the 22 autosomes, there is no difference between the likelihood of a male or a female inheriting a particular trait - The possible gametes produced are the ones written outside the punnet square, not the genotype - X-Linked Monohybrid Inheritance: - Because males only have one X chromosome, the sex of a baby affects how likely it is to express an X-linked trait - Males are more likely to express X-linked traits rather than females Mother - Heterozygous Carrier ------------------------------- ---------- ---------- ---------- X-Linked X^H^ X^h^ Father -- No Gene X^H^ X^H^X^H^ X^H^X^h^ Y X^H^Y X^h^X - Examples: Mother - Heterozygous ------------------------ ----------- ---- ---- Autosomal D D Father -- Heterozygous D DD Dd d Dd dd The phenotype chance is D 75% and d 25%. Dihybrid Crosses: - The study of a genetic cross between two individuals considering two genetic traits in combination - When writing in a cross, it is important to remember to write the possible gametes not the genotype DA Da dA da ---- ------ ------ ------ ------ DA DDAA DDAa DdAA DdAa Da DDAa DDaa DdAa Ddaa dA DdAA DdAa ddAA ddAa da DdAa Ddaa ddAa ddaa 9:3:3:1 for two heterozygous - FOIL -- Front, Outer, Inner, Last - Simulated Meiosis to find potential genotypes of offspring - Linked Genes: - Genes located close together on the same chromosome which tend to be inherited together - E.g: - DA are linked - da are linked - Linked Genes are written with a slash - E.g: - DA/da instead of Dd AA - Recombinant traits are those with alleles that aren't linked and don't tend to be together - This is because of crossing over - Usually quite rare - E.g: - DD Aa - Dd AA - The percentage of recombinant offspring directly equates to the distance the two genes are apart in "map units" - E.g: - If 5% of the offspring are recombinant, the genes D and A are 5mu apart Test Crosses: Monohybrid: - When an individual has a dominant phenotype, we don't know by simply looking at it whether it is a homozygous or heterozygous genotype. - A "test cross" involves crossing such an individual with an individual that is homozygous recessive to reveal it's genotype - You would need multiple offspring to figure out the genotype however - Example - B (black coat) is dominant to b (brown coat) - Black guinea-pig might be either BB or Bb - If a BB mates with a bb, all offspring will be Bb - If a Bb mates with a bb, half offspring will be Bb and half will be bb Dihybrid: - A cross between an individual heterozygous at both gene loci and another individual homozygous recessive at both gene loci. - A dihybrid test cross is used to determine the linkage relationship between two genes. Pedigree Charts: Summary: - A diagram that shows the occurrence of phenotypes in an individual and its ancestors from one generation to the next - ![](media/image6.png) - Definitions: - Consanguineous Mating - Marriage between two people who are related - Monozygous Twins - Identical twins - Dizygous Twins - Non identical twins - Refer to individuals by the Generation number and then Sequence number horizontally - E.g: - II-4 - IV-3 Analysis: - Analysis is used to determine the pattern of inheritance - A useful way is to propose a hypothesis and then test it against the evidence presented in the pedigree - Modes of inheritance: - X-Linked Dominant - X-Linked Recessive - Autosomal Dominant - Autosomal Recessive - Faster Approach: - Is there any individual who is different to both their parents? - If yes there is at least one individual different to both parents, the individual has the recessive trait - If every individual has a parent with the same phenotype, the shaded trait is most likely dominant - Highlight all females with the recessive phenotype - Examine every one of them. Do any have a non-matching father or son? - If yes then the trait must be autosomal - If no, then the trait is probably X-Linked **[Topic 2 -- Reproduction:]** Definitions: - Asexual Reproduction: - A type of reproduction that does not require the fusion of gametes, where offspring arise from a single parent and are genetically identical to that parent - Clones: - Groups of cells, organisms or genes with identical genetic make-up - Binary Fission: - A process of cell multiplication in bacteria and other unicellular organisms in which there is no formation of spindle fibres and no chromosomal condensation - Mitosis: - Process involved in the production of new cells genetically identical to the original cell - An essential process in asexual reproduction - Halophiles: - An organism that grows in or can tolerate saline conditions - Multiple Fission: - A process of division in which multiple cells are produced from a single starting cell - Spore: - In bacteria usually; but also formed by fungi and some plants - A reproductive structure resistant to heat and desiccation - Cytokinesis: - One of the stages of mitosis that cells in your body are currently going through - In this stage the cytoplasm divides into two, producing two new daughter cells - Sporangia: - A plane aerial structure in fungi where spores are formed by mitosis - Mycelium: - The vegetative part of a fungus, consisting of a network of fine, white filaments - Meiosis: - A type of cell division that produced haploid gametes - Gametophyte: - The sexual phase in the life cycle of plants and algae - Vegetative Propagation: - Asexual reproduction in plants - Meristematic Tissue: - Plant tissue found in tips of roots and shoots that is made of unspecialised cells that can reproduce by mitosis - Runners: - Stem-like growths extending from a mother plant's growing point - Cuttings: - A type of vegetative propagation that involves taking pieces of shoots, roots or leaves and planting them - Rhizomes: - Horizontal underground stems - Tubers: - A thickened underground part of a stem or rhizome - Bulbs: - An underground storage organ with short stems, a central bud and many closely packed, fleshy leaves - Corms: - A rounded underground storage organ present in plants, consisting of a swollen stem base covered with scaly leaves - Plantlets: - Tiny young plants that develop from the meristematic tissue along plant margins - Parthenogenesis: - A form of asexual reproduction in which new individuals are produced from unfertilised eggs - Obligate Parthenogenesis: - A type of parthenogenesis in which a species can reproduce only through asexual reproduction - Genetic Variation: - Variation exhibited among members of a population owing to the action of genes - Genetic Diversity - Genomic differences between individuals within a population - Fitness - The quality of a trait that confers an individual an increased chance of survival or reproduction - Vector - Any particle or organism used as a vehicle to artificially carry DNA into another cell to be replicated - Gametes: - A reproductive cell of an animal or plant - Gonads: - A reproductive organ that produces gametes - Hermaphrodites: - An organism with both male and female reproductive organs - External Fertilisation - The union of sperm and egg cells occurring outside the body of the female parent - Zygote: - A fertilised egg cell that results from the union of a female gamete with a male gamete - Brief stage in the embryonic development of animals - Internal Fertilisation: - Union of sperm and egg occurring inside the body of the female parent - Monotremes: - The order of non-placental mammals that lay leathery-shelled eggs and secrete milk through pores in the skin - Marsupials: - The order of non-placental mammals that are born at a very early stage of development and then grow inside their mother's pouch - Chiasma: - A point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands Genetic Diversity: - The production of gametes via meiosis results in genetic variation due to independent assortment of chromosomes and crossing over - The point at which this occurs is called the chiasma - The mechanism of evolution - A concept identified by Charles Darwin - He made a few observations: - 1\. There is a phenotypic variation between members of a species - 2\. Offspring tend to look like their parents - 3\. Individuals produce more offspring than needed to replace themselves - 4\. Some offspring don't survive to reach sexual maturity. - Darwin made two inferences from these observations: - Individuals whose traits give them more chance to survive and reproduce leave more offspring than other individuals - The unequal chance of reproduction will lead to the accumulation of favourable (fit) traits in the population over generations. Asexual Reproduction: Summary: - The ability to produce new offspring without having to find a mate - Because there is only one organism contributing genetic material, the offspring are genetically identical to the parent - They are called clones Methods of Asexual Reproduction: - Binary Fission in Prokaryotes - Process: - Replication of the circular molecule of DNA of the cell - Attachment of the two DNA molecules to the plasma membrane - Lengthening of the cell - Division of the cell into two via a constriction across the middle of the cell and the formation of the septum - This results in each new daughter cell containing an identical circular molecule of DNA - ![A diagram of a cell division Description automatically generated](media/image8.png) - Binary Fission in Eukaryotes: - Unicellular Eukaryotes - Reproduce asexually by splitting into two - Although it occurs in eukaryotic cells, it is known as binary fission - This binary fission is different from that occurring in bacterial cells - In Eukaryotes, the formation of new cells by binary division involves the process of mitosis - A diagram of a cell Description automatically generated - Multiple Fission: - Amoebae can undergo multiple fission - This means mitosis occurs repeatedly and many nuclei form within a single cell - Each nucleus then comes enclosed within a small amount of cytoplasm and forms a spore - These spores can later develop into new amoebae - Multicellular Eukaryotes - Simple multicellular animals can reproduce asexually by splitting into two - Each of the parts then grows into a complete animal - This kind of splitting does not occur in other multicellular organisms because their structure is more complex, being built of many different tissues and organs. - Examples: - Flatworms - Anemones - Coral Polyps - Mitosis in Eukaryotes: - Mitosis is ongoing in all eukaryotic organisms in order to: - Provide new cells for growth - Repair damaged cells - Replace worn out cells - Spore Formation in Fungi - Summary: - Asexual reproduction forms spores in algae and some fungi - These spores are true asexual spores produced by mitosis - After dispersal, the spores develop into new organisms that are genetically identical to each other and the parent - Process: - Spores are formed by mitosis in aerial structures called sporangia - When released from a sporangium the spores are carried away by air currents - If a spore lands on a moist location, the spores germinate and form a branching structure or fungal network (called mycelium) - Soon after, new sporangia containing spores develop - The cycle continues - Plants: - Some plants such as mosses and ferns also produce spores in their life cycles - However, because these spores are produced by meiosis and not mitosis, the spores are not genetically identical to the plant that produced them or to each other - Each spore then develops into a new plant, called a gametophyte, by the process of mitosis - Vegetative Propagation: - Summary: - Asexual reproduction common in plants - Made possible due to meristematic tissue - These consist of undifferentiated cells and are found in stems, leaves and the tips of roots - Meristematic tissue cells rapidly divide by mitosis to allow fast and extensive plant growth - Types: - Runner - Description: - Stem like grows from a parent plant that run along the ground - New buds develop into roots, leaves, flowers and fruit - Examples: - Strawberries - Water hyacinth - Cuttings - Description: - The cloning of plants by taking cuttings of shoots, roots or leaves and planting them - Examples: - Lavender - Geraniums - Hydrangea - Sage - Oregano - Rhizomes - Description: - Underground stems that grow horizontally - Buds and roots sprout from nodes along a rhizome and produce new daughter plants - Can be distinguished from plant rotos by the presence of buds, nodes and often tiny, scale-like leaves - Typically thick in structure because they have a food reserve, mainly in the form of starch. - Examples: - Irises - Grasses - Kikuyu Grass (*Pennisetum Clandestinum)* - Couch Grass (*Cynodon Dactylon*) - Austral Bracken - (*Pteridium Esculentum)* - Many types of reeds - Tubers - Description: - Swollen underground stems from which buds sprout - If cut, a piece of tuber with a bud can grow into a new plant - A type of asexual reproduction known as fragmentation - Examples: - Potatoes - Yams - Bulbs - Description: - Underground structures with short stems, a central bud, and many closely packed fleshy leaves - The leaves are the food source for the plant - Examples: - Onions - Garlic - Daffodils - Tulips - Hyacinths - Corms - Description: - Enlarged, bulb-like underground stems, with a solid stem tissue typically surrounded by papery leaves - Examples: - Taro - Gladioli - Plantlets - Description: - Tiny young plants that develop from the meristem tissue along plant margins - When they reach a particular size, the plantlets drop from the parent plant and take root - Examples: - (*Asplenium Bulbiferum*) - (*Bryophyllum*) - Fragmentation: - Summary: - A form of asexual reproduction where an organism is split into fragments and each fragment can develop into a mature organism - As this is a form of asexual reproduction, offspring are genetically identical to the parent - Examples: - Filamentous Cyanobacteria - Sponges - Acoel Flatworms - Annelid Worms - Sea Stars - Budding: - Summary: - A form of asexual reproduction where a new organism develops through cell division, from an outgrowth on the parent - Examples: - Sponges - Hydra - Parthenogenesis: - Summary: - An unusual form of asexual reproduction in animals, referred to as 'virgin birth' - Defined as reproduction without fertilisation and almost always involves the development of an unfertilised egg. - Offspring are produced from unfertilised eggs -- no sperm is necessary - These eggs are produced by mitosis and develop into offspring identical to the female parent. - Seen in many invertebrate animals, and is rare in vertebrate species. - Populations that reproduce using parthenogenesis are typically all-female - This can be obligate parthenogenesis, meaning this is the only way a species can reproduce. - Examples: - Aphids - Komodo Dragons - Whiptail lizards - (*Aspidoscelis*) - Some shark species - Some snakes, rock lizards and Australian geckoes - (*Lacerta*) - (*Heteronotia*) Advantages and Disadvantages of Asexual Reproduction: Advantages: - Able to quickly colonise an area - Grow with exponential growth Best of Both: - Summary: - For organisms that have become isolated from the main population, the ability to reproduce asexually allows them to produce offspring without having to find a mate. - The switch from asexual to sexual reproduction may occur in advance of a seasonal change to less favourable and more unstable conditions - Being able to reproduce asexually conserves both energy and time spent looking for a mate - Asexual reproduction is advantageous in stable environments - As the parent has been able to survive and reproduce, likely due to their genome, they are well-suited to the environment, and therefore their identical offspring will also be well-suited to it. - Asexual reproduction can also be advantageous in unstable environments - Should the organism be suited to the changes in the environment, no time is wasted in seeking a mate - For example, drought provides opportunities for organisms that have lower water requirements to colonise the area and outcompete other organisms for resources - Examples: - Aphids - Fairy Shrimp - Komodo Dragons - Volvox Disadvantages: - If conditions were to change, the population lacks genetic variation. - Should a population produced via asexual reproduction not be suited to the new environmental conditions, all members of the population are susceptible to extinction. - The ability of an organism to reproduce asexually and populate quickly can increase competition for resources within the population - Environments have a finite amount of resources available and exponential growth of organisms can place pressure on such resources Sexual Reproduction Fusion of Gametes: - The genetic material from the two contributing parents come from gametes, which are produced in specialised organs called gonads - In animals, the gametes are: - Eggs produced by females in the ovaries - Sperm produced by males in the testes - In sexual reproduction, the two parental contributions fuse to produce a gamete that develops into an animal or a plant - Even in the case of animals that are hermaphrodites, the gametes typically come from two separate animals, rather than self-fertilisation occurring External Fertilisation: - Occurs when animals release their gametes into the external environment so fertilisation occurs outside the body of females - Features include: - Very large numbers of gametes are produced - Large numbers of gametes increase the chance of fertilisation but also mean there is much gamete wastage - In nature, it is limited to animals that either live in aquatic environments or reproduce in a watery environment, as sperm need a watery environment to swim to an egg - Oysters, for example, each produce about 500 million eggs in a single season - Occurs in aquatic invertebrates, bony fish, and amphibians - External fertilisation in nature can be a chancy process. Thus, some species that use external fertilisation have developed strategies to increase the chance that fertilisation will occur: - Fish: - Behaviours such as courtships before spawning can lead to an improved chance of fertilisation - Through a courtship display a female can recognise that a male is a member of her species and, if she is ready o release her eggs, the eggs will be released in close proximity to the male - In turn, the male will release sperm nearby so that the likelihood of fertilisation is increased - Courtship has a high energy cost - Frogs - A behavioural adaptation in males increases the chance of fertilisation - When a female frog is ready to lay eggs, she goes into a nearby pond or pool - A male tightly clasps her and remains on her back until she releases her eggs - As the female releases her eggs, the male is stimulated to release sperm over the eggs, fertilising them - The fertilised eggs then undergo embryonic development Internal Fertilisation: - Summary: - Occurs when males deliver sperm directly into the reproductive tract of females so that fertilisation of eggs occurs inside the body of the females - Features include the following: - Energy cost of finding, attracting and securing a female mate - Has the benefit of increasing the chances of the gametes meeting, and therefore increases the chances of fertilisation - Occurs in some aquatic organisms as well as in terrestrial organisms - All terrestrial animals use internal fertilisation, except for amphibians, such as frogs and toads, that mate in the water - Marine animals: - Sharks: - In sharks the male of the species has claspers that are appendages of his pectoral fins - The male shark inserts his claspers into the vagina of a female and releases his sperm inside her, via her cloaca, which is carried by water pressure that he generated - Octopi: - In males, one of his eight arms is shorter than the other arms - This arm is specialised for the direct transfer of a parcel of sperm to a female - Insects: - Complex genital structures at the end of the abdomen of a male insect enables him to couple with a female and transfer sperm packages into her reproductive tract - Reptiles: - First vertebrates to evolve a male copulatory organ - The presence of this organ enables male reptiles to transfer sperm directly into the reproductive tract of a female - Apart from sharks, reptiles were the first vertebrates that did not need to release their gametes into water for fertilisation to occur. - Internal fertilisation freed the ancestral terrestrial reptiles and their descendants, from the need to return to water for reproduction. - Birds: - Males lack a penis - Sperm transfer takes place through close contact of the urogenital openings (cloacae) of male and female birds - Mammals: - Monotremes: - Mammals that lay eggs - Only surviving monotremes are platypus and echidna - In these animals the fertilised egg becomes enclosed within a shell and embryonic development occurs within the shelled egg, similar to reptiles - Unlike other mammals, they feed their young through pores in the belly that secrete milk, as opposed to teats. - Marsupials: - Retain the fertilised egg in their bodies and embryonic development proceeds within the uterus - Young marsupials are born at a very undeveloped stage - Their young continue to develop in a pouch on the mother's stomach - Placental Mammals: - Retain the fertilised egg in their bodies and embryonic development proceeds within the uterus - Born at a more developed stage - The biological advantage is that they are better able to cope with the environment, and thus increasing their chance of survival. - The young survive in utero through being connected to the mother via the placenta, receiving food and oxygen and returning waste before being born. Advantages and Disadvantages of Sexual Reproduction: Advantages of Sexual Reproduction: - The biggest advantage is that it creates genetic diversity - This helps a species to thrive or to survive - This is done in a number of ways: - Mixing of genetic information between two parents - Random mating within the population - Independent assortment of non-homologous chromosomes at Metaphase I in Meiosis - Crossing over and recombination at Prophase I in Meiosis Disadvantages of Sexual Reproduction: - Genetic variation comes at a great cost in other ways: - Uses time and energy - Quite inefficient - Only half the population can reproduce (carry a baby) - Often depends on a vector - Depends on a 3^rd^ party species to do some work - Risk to life - While trying to attract a mate, organisms don't focus on staying safe from predators Differences between Asexual and Sexual Reproduction: Asexual Reproduction Sexual Reproduction --------------------------------------------------------- ------------------------------------------------------------------- One parent contributes genetic material Two parents contribute genetic material Daughter cells are usually identical to the parent cell Daughter cells are different to the parent cells No exchange of genetic material Exchange of genetic material through crossing over of chromosomes Chromosomes are not assorted Chromosomes are assorted independently Less energy required Energy invested in finding a mate Does not affect genetic diversity Increases genetic diversity in a population Biological advantages and disadvantages of sexual reproduction: Advantages of Sexual Reproduction: Disadvantages of Sexual Reproduction: ------------------------------------------------------------------------------------------------------------- --------------------------------------------------------------------- Genetic diversity within the species Energy expended to find a mate Variation increases survival chances should conditions change Some organisms can be injured (or killed) in competition for a mate Variation between members of the same family due to crossing over and independent assortment during meiosis More traits to select for when choosing a mate -- allows natural selection to occur **[Topic 3 - Cloning Technologies and Procedures:]** Definitions: - Clone: - An organism or cell produced from one ancestor to which they are genetically identical - Reproductive Cloning: - (Also known as whole organism cloning) Usually refers to techniques that are used to create genetic copies of an organism - Effectiveness: - How well a process works to achieve the desired outcome - Telomere: - The caps at the end of a chromosome that protect the chromosome - (Like aglets on a shoelace) - Plant Tissue Culture: - A technique used to clone plants in large numbers - Embryo Splitting: - The process of separating the totipotent cells of a very early embryo, so that the resultant cells are each able to form a complete embryo - Somatic Cell Nuclear Transfer: - A cloning technique that involves the nucleus of a somatic cell being transferred into the cytoplasm of an enucleated cell, that is then stimulated to divide. - Enucleated Cell: - A cell from which the nucleus has been removed - Adult Somatic Cells: - Body cells that have differentiated into their cell type - Totipotent: - A cell that is able to give rise to all different cell types Reproductive Cloning Technology in Plants: Vegetative Propagation: - One example is taking a cutting from a plant to produce new plants that are all genetic copies of the original parent plant - Using the technology of plant tissue culture, many clones of a plant can be produced from a small amount of starting tissue - This technique is mainly used with ornamental plants (such as orchids and carnations), and Australian native plants (such as bottlebrush, the flannel flower and various eucalypts) - Tissue culturing can also be used with endangered or very rare plants, since only a few specimens exist in the wild, in order to try save the species. - Tissue culturing cloning has several advantages: - Slow-growing plants can be produced in large numbers - Plants can be cultured all year round (in controlled conditions of temperature and day length) rather than relying on seasonal growth - Virus-free tissue can be used to produce a large number of plants that do not carry the virus - Cultured plants can be transported from country to country. - The sterile conditions in which they are cultured also ensures that the plants are pest-free, so lengthy quarantine periods are avoided - How does it work? - ![](media/image10.png) Reproductive Cloning Technologies in Animals: Embryo splitting to make identical copies: - Summary: - Occurs when the cells of an early embryo are artificially separated - Typically into two masses - This process mimics the natural process of embryo splitting that produced identical twins or triplets - Embryo-splitting technology has been used for stockbreeding for many years - Although it has become a relatively simple technique, it is usually limited to twinning - Features: - Parents can be chosen because of desirable inherited characteristics that they exhibit - Typically, embryos to be split are produced through IVF (in-vitro fertilisation) - The embryo is divided using a very fine glass needle - Each small embryo is then implanted into the uterus of a surrogate female parent, where embryonic development continues - The small embryos from the splitting of one embryo are identical, as will be the adults that develop from them. - However, the two offspring from the splitting of one embryo are not genetically identical copies of either the organisms that produced the egg or the organism that provided the sperm used to produce the embryo that was split. - The two offspring are genetically identical to each other and are identical copies of the fertilised egg from which the embryo came. Somatic cell nuclear transfer (SCNT) - Process: - The nucleus of the cell is removed, creating an enucleated cell - The nucleus of another cell can be transferred to an enucleated cell to form a redesigned nucleated cell - An enucleated cell can be fused with a somatic cell using a short electrical pulse - Dolly the Sheep SCNT Process: - Took an egg cell from a Scottish blackface ewe and enucleated it (took the nucleus out of it) - Took a mammary gland cell from a Finn-Dorset ewe - Somatic cell from a different breed of sheep - Fused the mammary gland cell with the enucleated egg cell - Allowed it to divide by mitosis until a blastocyst was formed - The blastocyst was then implanted into the Scottish blackface ewe - The resulting baby was a Finn-Dorset ewe which was named Dolly Reproductive Cloning Issues: Inefficiency: - To this point cloning is very ineffective - There have been a significant number of species which have been successfully cloned using SCNT, but the efficiency rate is very low - Took 277 attempts to make Dolly - 123 attempts for a dog - 87 attempts for a cat - 189 attempts for a cow Health of Clones: - An ethical issue surrounding cloning is the health and longevity of the cloned organism - Although a typical Finn-Dorset sheep has a life expectancy of 11-12 years, Dolly the sheep only lived to 6.5 years of age, after which she was euthanised due to severe arthritis and a progressive lung disease - It is not fully known why clones have a shorter life than naturally conceived animals - A likely reason is that the telomeres of the chromosomes from the somatic cells are already shortened - Telomeres shorten as you age - In other words, the cloned organism isn't really born at an age of 0 years Ethics: - Some people consider cloning to be immoral to due religious beliefs or due to social values about human or animal dignity - Others are concerned that the technology may soon be used to clone humans, since there is no technical reason why this could not be done - Therapeutic cloning involves making a cloned embryo with the intention of using its cells to research or treat disease in an individual - To date there is no evidence that this has ever taken place **[Topic 4 -- Adaptations for Survival:]** Definitions: - SA:V Ratio - The ratio of ski surface to the volume of the animal - Crepuscular - Appearing or active in twilight - mOsmol/L - Mili osmols per Litre; A measure of Osmolatirty; the concentration of a solute in a solvent - Xerophyte - A plant adapted to an arid environment - Isobilateral - The same on both sides - Malic Acid - An organic compound with the molecular formula C~4~H~6~O~6~ - Adaptations - Features or traits that appear to equip an organism for survival in a particular habitat - Maladaptation - Features or traits of an organism that inhibits survival in a particular habitat - Abiotic Factors - Nonliving factors that can affect population size - Desiccation - Drying out - Tolerance Range - The extent of variation in an environmental factor within which a particular species can survive - Tolerance Limits - The upper and lower limits of a particular environmental condition in which a species can survive - Limiting Factor - An environmental condition that restricts the types of organism that can survive in a given habitat - Hyperthermia - A condition in which the core body temperature exceeds the upper end of the normal range without any change in the temperature set point - Free-Standing Water - Water available for an animal to use, including to drink - Plasma - The fluid portion of blood in which blood cells are suspended - Water Balance: - The way in which an organism maintains a constant amount of internal water in hot or dry conditions - Interstitial Fluid: - Fluid that fills the spaces between cells and bathes their plasma membranes - Humidity: - A measurement of the amount of water vapour in the atmosphere - Ephemeral - A short lived or lasting a short period of time - Dormancy - Condition of inactivity resulting from extreme lowering of metabolic rate in an organism - Operculum - \[In fish\] the flaps covering the gills - \[in molluscs\] a hard impenetrable lid that closes the shell, making a watertight compartment for the animal inside - Hummock Grassland: - Major vegetation type dominated by spinifex grasses - Occurring over one quarter of Australia - Acacia Shrublands - Major vegetation type dominated by mulga, a species of acacia - Occurring in arid inland Australia - Chenopod Shrublands - Major vegetation type dominated by saltbushes and bluebushes - Occurs in arid regions with salty soils - Drought Tolerant - Being able to tolerate a period of time without water - Drought Resistant - Being able to store water and hence live for long periods of time without water - Water Tappers - Trees that have a single main root extending to depths near the watertable before forming lateral branches - Transpiration - Loss of water from the surface of a plant - Stomata - Pores on a plant - Each surrounded by two guard cells that regulate the opening and closing of the pores - Cuticle: - A waxy layer on the outer side of epidermal cells - Waxy outer layer on leaves - Antifreeze - A chemical substance produced by an organism to prevent freezing of body fluids or tissue when in a sub-zero environment - Insulating Layers - Layers of fat under the skin of mammals that retain heat within the body - Countercurrent Exchange System: - A situation in which two fluid systems flowing adjacent to each other, but in opposite directions, enables the transfer of heat or compounds from one system to the other by diffusion Adaptations: Summary: - An adaptation is a structural, behavioural or physiological feature that enhances the survival of an organism in particular environmental conditions. - Adaptative features of an organism are innate - They are built into its genetic makeup - The value of a feature as an adaptation exists in relation to a specific way of life and a particular set of environmental conditions - Thus, in another set of environmental conditions and in a different way of life, the same features may be a maladaptation - As an example, freshwater fish extract dissolved oxygen from the water in which they live using their gills. - Usually, water enters the mouth of the fish, passes to the pharynx, is forced over the gill surfaces and exits, and thus gills are an efficient structure for extracting oxygen from water - However, if removed from the water, the fish gills are maladaptive. - Without the buoyancy of water to support them, the feathery gill filaments collapse, and with no water flowing over them the fish cannot obtain oxygen and suffocates. Tolerance Range: - Summary: - Every habitat contains a number of abiotic factors - These make up the environmental conditions - Such as temperature, desiccation, oxygen concentration, and ultraviolet exposure - The tolerance range for an organism identifies the variations in the particular environmental conditions in which a particular species can successfully live and reproduce. - The tolerance range includes an optimum range, and the extremes of the tolerance range are considered the tolerance limits for that abiotic factor - As the tolerance limits are approached, the species enters a zone of physiological stress - Adaptations to Tolerance Ranges: - If an abiotic factor has a value above or below the range of tolerance of an organism, that organism will not survive unless it can escape from, or somehow compensate for, the change. - In some species, migration is one such escape behaviour, while other species' retreat underground. - Tolerance ranges differ between species and are influenced by structural, physiological and behavioural features of organisms. - For example, the cold tolerance of various mammals is influenced by structural features such as fur density, shape of the body and extent of insulating fat deposits, and by their behaviours, such as hibernating. +-----------------------+-----------------------+-----------------------+ | Type of Adaptation | Definition | Example | +=======================+=======================+=======================+ | Structural | Physical features of | Blubber in seals | | | an organism that | providing a | | | enable them to | protective layer from | | | survive in a given | the cold temperatures | | | environment | of the ocean | +-----------------------+-----------------------+-----------------------+ | Physiological | Internal and/or | Vasoconstriction of | | | cellular features of | blood vessels that | | | an organism that | conserves heat and | | | enable them to | increases blood | | | survive in a given | pressure | | | environment | | +-----------------------+-----------------------+-----------------------+ | Behavioural | Activities that an | Huddling in penguins | | | organism performs in | to stay warm; | | | response to internal | | | | and external stimuli | Migration of birds to | | | | warmer regions over | | | | winter | +-----------------------+-----------------------+-----------------------+ - Limiting Factors for Tolerance - Any condition that approaches or exceeds the limits of tolerance for an organism is said to be a limiting factor for that organism. - Terrestrial and aquatic environments can differ in their limiting factors - Species that can survive under certain environmental conditions have tolerance ranges that accommodate those conditions - The structure and the physiology of plants and animals, and the behaviour of animals, determines their tolerance range - For each organism, the limits of its tolerance range for various abiotic factors are fixed, except for the occurrence of an enabling mutation. Habitat Limiting Factor Extra Info ---------------------------- ------------------------- -------------------------------------------------------------------------------------- Floor of Tropic Rainforest Light Intensity Low light intensity limits the kinds of plants that can survive Desert Water availability Limited water supply means that only plants able to tolerate desiccation can survive Littoral (intertidal) zone Desiccation Exposure to air and sunlight limits the types of organism that survive Polar Region Temperature Low temperatures limit the types of organisms that are found Stagnant Pond Dissolved Oxygen Levels Low dissolved oxygen levels limit the types of organisms that can live there Adaptations for Survival: Arid Climate Animals: Summary: - The key environmental challenges of desert life are avoiding excessive water loss that can result in dehydration, and avoiding overheating that can result in hyperthermia - Both conditions can potentially be deadly Survival without Drinking: - Spinifex Hopping Mouse: - It can survive without drinking liquid water, and thusthe tarrkawarra can endure long periods of drought. - Its kidney tubules reabsorb almost all the water from the kidney filtrate so that it produces highly concentrated and almost solid urine. - Tarrkawarras produce the most concentrated urine of any mammal. - Their kidneys can produce urine with a concentration of 9370 mOsm/L. Survival by Dormancy: - Frogs in the Outback - Some frog species live in arid inland Australia. - Frogs typically live in moist surroundings and need a body of water in which to reproduce. - Some frog species that live near and breed in ephemeral waterholes respond in an amazing manner when the waterholes begin to dry out: - They burrow deeply into the soft mud at the bottom of their waterholes. - Once underground at depths of up to 30 cm, they make a chamber that they seal with a mucous secretion. - The frogs then go into an inactive state known as dormancy, in which both breathing and heart rate are minimal and energy needs are greatly reduced. Their low energy requirements are met from their fat reserves. - They remain buried and are protected from desiccation until the next rains come; this may be a wait of one or two years. - They come out of their dormant state only when soaking rains fall and soil moisture rises. Once activated, the frogs return to the surface to feed and breed in temporary pools. - The completion of the life cycle is very fast. Within days of being laid, eggs undergo embryonic development, hatch, and the resulting tadpoles metamorphose to produce small frogs. - These new populations of frogs feed on larvae of crustaceans and insects that have also hatched from dormant eggs. - Other animal species survive extended periods of drought by sealing themselves off from the drying conditions. - As an example, the univalve freshwater mollusc (*Coxiella striata)* seals itself inside its shell by closing the shell opening with an operculum. - These inland molluscs must stay sealed tightly in their shells for months or years. Survival by Migration - Some species cope with drought by moving from affected areas to areas where conditions are more favourable - Examples: - Banded Stilts (*Cladorhynchus Leucocephalus*) - Live near salt lakes in inland Australia and rely on these lakes for brine shrimps - When one Salt Lake dries up, the birds simply fly to another Salt Lake - Budgeriar (*Melopsittacus Undulatus)* - Flocks of these birds move to more favourable areas of the desert in search of food and water - In order to avoid the desert heat, they travel in the cooler periods of the day. Survival by Reproduction - Survival can be viewed in terms of the successful survival of an individual organism that lives to reproduce on many occasions - It can also be considered in terms of survival of a species - Example: - Shrimp: - Cannot survive long periods of drought and all organisms die when the waterhole dries up - When water is present in abundance, female shrimps produce eggs that are not drought resistant. - Newly hatched shrimp mature and reproduce within a few days - When water is scarce and waterholes begin to dry out, female shrimps produce drought resistant fertilised 'eggs', that are actually cysts that each contain a fully developed embryo encased in a hard protective shell - While the male dies after mating, the female will carry the cysts in a drought-resistant brood sac. - Before the water has dried up, the female will release the cysts and then die. - By the time the water has gone, all the adult shrimps are dead, but the cysts they have left behind can withstand desiccation for long periods. - These cysts are in a state of dormancy and can lie in the dust of dry waterholes for more than 20 years. - The next generation of shrimp will emerge only when the rains come, perhaps years later, when short-lived waterholes and pools reappear. Adaptations for Survival: Arid Climate Plants: Vegetation types of Arid Australia - In arid climates water is scarce and the supply is often unpredictable - In terms of area, the dominant vegetation type in Australia is Hummock Grassland, which covers almost a quarter of the Australian land surface, including the sandy plains and dunes of the major deserts - The second largest vegetation type by area is shrublands - Hummock Grasslands are dominated by species of stiff, drought-resistant spinifex grasses, such as buck spinifex - Different kind of shrublands exist depending upon rainfall and soil type - Acacia shrublands occur across the arid and semi-arid areas and are dominated by mulga - Chenopod shrublands occur in arid regions with salty soils and are dominated by saltbushes and bluebushes +-----------------------------------+-----------------------------------+ | Vegetation Type | Climate | +===================================+===================================+ | Hummock Grasslands | Arid: Lowest and erratic | | | rainfall, high evaporation rates, | | | high temperature | | | | | | Dominated by spinifex grasses | +-----------------------------------+-----------------------------------+ | Acacia Shrublands | Arid and Semi Arid: Low rainfall, | | | high temperature | | | | | | Dominated by mulga | +-----------------------------------+-----------------------------------+ | Chenopod Shrublands | Arid and Semi Arid: Low rainfall, | | | high temperature, salty or | | | alkaline soils | | | | | | Dominated by saltbushes and | | | bluebushes | +-----------------------------------+-----------------------------------+ | Tussock Grasslands | Semi Arid: Annual rainfall | | | between 200 and 500mm, clay soils | | | | | | Dominated by *Astrebla* | +-----------------------------------+-----------------------------------+ | Tropical Grasslands | Tropical: Summer monsoons and | | | winter drought | | | | | | Dominated by *Sorghum* | +-----------------------------------+-----------------------------------+ | Mallee Woodlands | Temperate: Intermediate rainfall, | | | poor soil | +-----------------------------------+-----------------------------------+ | Eucalypt Forests | Temperate: High rainfall, poor | | | soil | +-----------------------------------+-----------------------------------+ | Rainforests | Tropical or Temperate: High and | | | reliable rainfall, rich soil | +-----------------------------------+-----------------------------------+ - Plants that have both structural and physiological adaptations to arid conditions survive by: - maximising water uptake - minimising water loss - producing drought-resistant seeds. - These adaptations result in plants that may be: - drought tolerant --- the plant can tolerate a period of time without water; or - drought resistant --- the plant can store its water and live for long periods of time without water. - Many Australian plants that live in water limited environments would be classified as being drought tolerant Adaptations: Maximising Water Uptake - Two style of root systems: - Water Tappers: - Some trees growing along dry creek beds produce long, unbranched roots that penetrate to moist soil at or near the watertable. - Once moisture is reached, the major root branches and forms lateral roots. - The major root can grow to depths of 30 m. - The part of the root that is located in the upper dry soil is covered by a corky, waterproof layer of cells that prevents water loss. - Shallow, Horizontal Root Systems: - Plants develop extensive root systems that spread out *horizontally*, far beyond the tree canopy but just below the soil surface. - In this case, the plant takes up water from an extensive area around it. Adaptations: Minimising Water Loss - Regulated responses to minimize water loss - Stomatal Opening and Closing: - The major pathway for water loss in plants is through transpiration, controlled by the stomata---tiny pores on the lower surface of leaves. - When stomata close, plants reduce water loss by limiting the escape of water vapor. - However, stomata must also open to allow carbon dioxide in for photosynthesis. - In water-conserving plants, like succulents, stomata open at night to take in carbon dioxide, reducing water loss during the hotter day. - Leaf Rolling: - In response to water stress or high temperatures, some plants like maize (corn) use leaf rolling to minimize water loss. - Bulliform cells in the leaf lose turgor pressure as temperatures rise, causing the leaf to curl inward. - This creates a humid environment inside the rolled leaf and reduces exposure to wind and sun, effectively minimizing water loss. - When the temperature drops, the cells regain turgor and the leaf unrolls. - Structural features to minimise water loss - Structural features of plants are constitutive and genetically determined traits that are present in plants regardless of whether the plant is in water deficit. - However, when plants are in water deficit, these structural features reduce or prevent water loss from leaves - The features are summarised in the following table: **Adaptation** **How it prevents water loss** ------------------------------------------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Presence of a thick cuticle Water loss is minimised as the cuticle is composed of a waterproof material called cutin Reduced number of stomata Fewer stomata per unit area of leaves means that water loss by transpiration is reduced. Presence of sunken stomata Sunken stomata, located in pits below the leaf's surface, called crypts, create a region of relatively higher humidity in the air space immediately surrounding the stomata. This reduces water loss by transpiration as the concentration gradient of water vapour between the air and the leaf is closer Water storage tissue Succulents have thick, fleshy leaves or stems that store water in their vacuoles after rainfall. Cacti stems have pleats that allow it to expand and contract quickly. Large-stem succulents may have water storage tissue in their trunks, such as the Queensland bottle. Others have water storage tissue in tubers and enlarged roots, such as magenta storksbill No visible leaves Succulent plants such as cacti have leaves that are reduced to spines, significantly reducing surface Altering leaf margins The larger the ratio of edge length to surface area, the faster a leaf will cool. Cooler leaves have lower transpiration rates Altering leaf orientation and pendant branches Leaves with a vertical orientation have less exposure to sunshine and so gain less heat and are cooler. Cooler leaves lose less water. Pendant branches may also develop, which move with the wind, creating water-catching wells in the soil under the tree Silver leaves Silver or grey leaves reflect sunlight and help keep the leaf cool, which reduces water loss. Hairs on leaf surface When hairs are present on leaf surfaces, they slow the flow of air across the leaves, reducing the rate of water lost through transpiration. Leaves that are not leaves Members of the genus *Acacia* have had their feathery leaves replaced by flattened leaf stalks called phyllodes. Phyllodes enable plants to survive in arid conditions because they provide a store of water in large parenchyma cells at their centre, and phyllodes have fewer stomata than true leaves and so lose less water by transpiration. Shedding leaves When plants become stressed in drought conditions, they conserve water by dropping their leaves. Drought-resistant seeds The outer coating of the seeds contains a water-soluble chemical that inhibits germination. Dry conditions equals no germination. Adaptations for Survival: Cold Climate Animals: Dangers of cold and ice - Processes that are essential for life include chemical reactions that take place between substances that are dissolved in liquid water. - These processes cannot take place in solid water (ice) - Thus if all the liquid water in a living organism was replaced by solid water, the life would be destroyed. - This is because when ice forms, the solid water expands. - If the cells were to freeze, the expanding ice crystals would rupture the cell membrane and kill the cells. - To combat this, many organisms have special features or behaviours that enable them to survive in extremely low temperatures. Physiological Adaptations: - Production of Antifreeze substances - Some insects, fishes, frogs and turtles that can survive in cold winters make antifreeze substances such as glycerol, amino acids and sugars, or mixtures of substances, at the start of the freezing season - These antifreeze substances are released into their body fluids, which lowers the fluids' freezing point to well below that of the surrounding water temperatures. This means that the body fluids of these organisms stay liquid. Behavioural Adaptations: - Burrowing - Some frogs and toads - Hibernation - Such as pygmy possums or bears - Huddling - Emperor penguins huddle in large groups to conserve heat Structural Adaptations: - Growth of thick fur and layers of fat. - The fat layers can be a physiological insulating layer of fat under the skin, a layer of thick fur, and birds even have layers of feathers. - These insulating layers of fat are very important in cold climate marine animals Adaptations for Survival: Cold Climate Plants: Summary - Many plants can survive in sub-zero temperatures without being damaged by the extremely low temperatures - Unlike animals, plants do not produce an antifreeze. - They gradually become resistant to the potential danger of ice forming in their tissues as the temperature falls below 0°C ![A diagram of cell division Description automatically generated](media/image12.png) - Ultimately, if there is an excessive drop in the surrounding temperature, ice crystals form inside the cells and they die, and so the tree may die. - It has been suggested that an excessive drop in temperature damages the protein molecules that form part of the cell membranes, so ions can leak out of the cell. - Australia does not experience the sustained extremes of low temperatures found in many other countries and low temperature is rarely a limiting factor for plant growth. - Growth of native plants in Australia is determined by whether a plant has the adaptations to survive the various altitude zones and their associated temperatures. - Some plants, particularly exotic garden plants, may be killed or damaged by an unusually severe frost. **[Topic 5 -- Interactions within an Ecosystem]** Definitions: Biotic Factors: - Living factors that can affect population size Abiotic Factors: - Non living factors that can affect population size Ecology: - The study of communities in their habitats and the interactions between them and their environment Population: - Members of one species living in one region at a particular time Community: - A biological unit consisting of all the populations living in a specific area at a specific time Diversity: - Measure of 'species richness' or the number of different species in a community Producers: - Photosynthetic organisms and chemosynthetic bacteria that, given a source of energy, can build organic matter from simple inorganic substances Consumers: - Organisms that obtain their energy and organic matter by eating or ingesting the organic matter of other organisms; - Also termed heterotrophs Decomposers: - Organisms, such as fungi, that can break down and absorb organic matter of dead organisms or their products Autotrophs: - Organisms that, given a source of energy, can produce their own food from simple inorganic substances; - Also known as producers Heterotrophs: - An organism that ingests or absorbs food in the form of organic material from their environment; - Also known as a consumer Herbivores: - An organism that eats living plants or parts of them Carnivores: - An organism that kills and eats animals Omnivores: - An organism that eats both plants and animals Detritivores: - An organism that eats particles of organic matter found in soil or water Detritus: - Fragments of organic material present in soil and water Keystone Species: - A species whose presence in an ecosystem is essential for the maintenance of that ecosystem Competition: - Interaction between individuals of the same or different species that use one or more of the same resources in the same ecosystem Intraspecific Competition: - Competition for resources in an ecosystem involving members of the same species Interspecific Competition: - Competition for resources in an ecosystem involving members of one species and members of other species Amensalism: - Any relationship between organisms of different species in which one organism is inhibited or destroyed, while the other organism gains no specific benefit and remains unaffected in any significant way Predator-Prey Relationship: - A form of interaction within a community that involves the eating of one species, they prey, by another species, the predator Camouflage: - An adaptation that allows organisms to blend into their environment Mimicry: - A situation in which one species has an appearance similar to that of a different but distasteful species, where that similarity apparently gives protection against predators Warning Colouration: - A conspicuous colouring that warns a predator that an organism is toxic or distasteful Herbivore-Plant Relationship: - A form of interaction within a community between plants and the animals that eat them Parasitism: - A form of interaction within a community that involves one species, the parasite, living on or in another species, the host, typically without killing the host. Parasite: - An organism that lives in or on another organism and feeds from it, usually without killing it Host: - An organism on or in which a specific parasite lives Exoparasites: - A parasite that lives on its host Endoparasites: - A parasite that lives inside its host Hemiparasitism: - A form of parasitism in which a plant parasite obtains some nutrients and water from its host plant but also makes some of its own food through photosynthesis Haustoria: - A thin strand of tissue though which a plant parasite makes connection with its host - Singular = haustorium Holoparasitism: - A form of parasitism in which a plant parasite depends completely on its host for nutrients and water Mutualism: - An association between two different species in a community in which both gain some benefit Mycorrhiza: - Fine threads formed by a fungus that form a large surface area for uptake of nutrients Nitrogen-Fixing Bacteria: - Bacteria able to convert nitrogen from the atmosphere into ammonium ions Sulfur-Oxidising Producer Bacteria: - One group of bacteria that gain their energy by oxidising sulfuric compounds Trophosome: - An organ found within deep sea worms that is colonised by bacteria that supply the host worm with food and energy Commensalism: - Association between two different species in a community in which one benefits and the second neither gains nor is harmed Symbiosis: - Prolonged association between different species in a community in which at least one partner benefits; - Includes parasitism, mutualism and commensalism Primary Ecological Events: - In population dynamics, the factors that contribute directly to population density, such as births and deaths Growth Rates: - The change in population size over a set period of time Positive Growth Rates: - Population increases over the stated period of time Negative Growth Rates: - Population decreases over the stated period of time Zero Population Growth: - Occurs when growth by births and immigration matches losses by death and emigration over a stated period of time Open Populations: - Refers to populations that experience migration of individuals into the population (immigration) or out of the population (emigration) Closed Populations: - Refers to populations that do not experience migration as they are isolated from other populations of the same species Secondary Ecological Events: - In population dynamics, abiotic or biotic factors that influence changes in population density, such as temperature Density-Independent Factors: - A factor whose impact on members of a population is not affected by the size of the population Density-Dependent Factors: - A factor whose impact on members of a population is dependent on the size of the population Exponential Growth: - Population growth that follows a J-shaped curve but cannot continue indefinitely Carrying Capacity: - The maximum population size that a habitat can support in a sustained manner R -- Selected: - Organisms that live in unstable environments and produce many offspring with the likelihood that few will survive to adulthood K -- Selected: - Organisms that live in stable environments and produce few offspring in each litter with a greater chance of survival to adulthood What is an Ecosystem: Summary: - In biology, it is possible to focus on different levels of organisation - Different levels of biological organisation are shown: A diagram of a diagram of life cycle Description automatically generated - An ecosystem is the most complex level of organisation Ecosystem: - Each ecosystem includes the following: - Biotic Factors \[Living - The populations of various species that live in a given environment - Abiotic Factors - Non-Living - The non-living surroundings and their environmental conditions - The interactions within and between species and their local environment - The continuation of an ecosystem depends on the intactness of the parts and on the interactions between them. - Thus, an ecosystem depends on its parts and may be destroyed if one part is removed or altered. - Ecosystems can vary in size but must be large enough to allow the interactions that are necessary to maintain them. - An ecosystem may be as small as a freshwater pond or a terrarium, or as large as an extensive area of mulga scrubland in inland Australia. - An ecosystem may be terrestrial or marine. - The study of ecosystems is the science known as ecology Ecological Communities: Summary: - A population is defined as all the individuals of one particular species living in same area at the same time - A community is made up of all the populations of various organisms living in the same location at the same time. - Different communities can be compared in terms of their diversity - Two factors are used by ecologists to measure the diversity of a community - The richness or the number of different species present in the sample of the community (species diversity) - The evenness or the relative abundance of the different species in the sample - As richness and evenness increase, the diversity of a community increases Factors affecting species diversity: - Physical Area in Which the Community Lives - The number of different populations in terrestrial communities in the same region is related to the physical size of the available area. - In general, if an island has an area ten times that of another in the same region, the larger island can be expected to have about twice the number of different species. - Latitude (Distance from the Equator) - In general, as we move from the poles to the equator, species richness of terrestrial communities increases. - This means that more species, and hence more populations, exist in a given area of a tropical rainforest ecosystem than in a similar area of a temperate forest ecosystem. - In turn, an area of temperate forest ecosystem has more populations than a similar area of a conifer (boreal) forest ecosystem in cold regions of the northern hemisphere. Members of a community: - Members of the living community in an ecosystem can be identified as belonging to one of the following groups: Producers, Consumers and Decomposers Producers - These are the members of the community that bring energy from an external source, into the ecosystem - Producers are autotrophic organisms that use photosynthesis to capture sunlight energy and transform it into chemical energy in the form of sugars (such as glucose) making it available within the community. - In aquatic ecosystems, such as seas, lakes and rivers, the producers are microscopic phytoplankton, macroscopic algae, bacteria and seagrasses - In terrestrial ecosystems, producer organisms include photosynthetic microbes and familiar green plants. - These, in turn, include trees and grasses, other flowering plants, cone-bearing plants such as pines, as well as ferns and mosses - The organic compounds made by producer organisms provide the chemical energy that supports both their own needs and, (either directly or indirectly), all oth

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