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Learning Outcomes What you need to know Unit 2 Tick off each piece of information once you have learned it. A) ECOSYSTEMS Habitat = The place where an organism lives (e.g. pondwater, garden soil, mountain top, bark of tree, small village. Population = A group of organisms of the same species (e.g. a pack of wolves, a shoal of herring, the human inhabitants of a town, the oak trees in a wood. Community =The sum total of all the populations of plants, animals and micro-organisms living together in an ecosystem. e.g. the leaves that support the greenfly + ladybirds and small insect-eating birds. Ecosystem = Is a natural unit made up of one or more habitats and the communities of plants and animals living there e.g. woodland Within an ecosystem there can be a number of different habitats each with its own community. Green plants are called producers because they are able to produce their own food using light from the sun by photosynthesis. Animals (and non-green plants like fungi) cannot produce their own food so need to consume plants or other animals to get their energy. They are called consumers. A herbivore (e.g. sheep) eats plant material only. A carnivore (e.g. tiger) eats animal material only (meat). An omnivore (e.g. pig) eats both plant and animal material. An animal which hunts another for food is called a predator. The animal that is hunted is called the prey. Decomposers are micro-organisms, such as bacteria and fungi that obtain their energy by breaking down waste materials and dead bodies using enzymes. A food chain shows the relationship between organisms where one organism feeds on the previous one. It always begins with a green plant. The arrow indicates the ‘direction of energy flow’. Example of a food chain Heather mountain hare eagle Heather is the producer Mountain hare is the primary consumer Eagle is the secondary consumer Many interconnecting food chains are called a food web. E.g. Eagle Mountain hare Fox Merlin Grouse Skylark Moth larva Heather As energy flows through a food chain or food web energy is lost. The energy is lost in undigested food or as heat during movement. Only energy used for growth can be passed on to the next organism. A pyramid of numbers is a diagram which represents the number of organisms at each stage in a food chain Tertiary consumer e.g. pike Secondary consumer e.g. stickleback Primary consumer e.g. water flea Producer e.g. alga •A pyramid of biomass is a diagram which represents the total mass of organisms at each stage in a food chain. A pyramid of energy is a diagram which represents the quantity of energy at each stage in a food chain. Biodiversity is the term used to describe the variety or range of species present in an ecosystem. A species is defined as a group of organisms which can interbreed to produce fertile offspring. The ecological niche of an organism is the role that it plays within an ecosystem e.g. brown trout lives in freshwater, it is an insect eating consumer suffering intense competition from introduced rainbow trout A stable ecosystem has a wide range of species and food webs. An ecosystem with little variety of species is unstable and unlikely to last. Few links in a chain: removing 1 animal can have a severe effect -> unstable Lots of links in a chain: removing 1 animal doesn’t have such a severe effect. -> Stable ADAPTATIONS Organisms show adaptations which allow them to successfully occupy a particular niche. Adaptations may involve body structure and behaviour. An adaptation is an inherited characteristic that makes an organism well suited to survival in its environment. Darwin’s finches The main differences between the finch types are their beaks (size and shape) and feeding habits. These differences allow them to exploit different ecological niches and this will in turn increase their chances of survival. Desert Plants -Long roots to absorb water deep underground -Leaves are reduced to a spine to avoid water loss - Some leaves have thick, waxy cuticles to further avoid water loss. GRAZING A high intensity of grazing will maintain species diversity. Very high or low intensity grazing will decrease species diversity. POLLUTION Pollution and habitat destruction will lead to a decrease in species diversity. COMPETITION In Plants Compete mainly for water, light and soil nutrients. In Animals Compete for food, water and shelter. BEHAVIOURAL ADAPTATIONS All animals show behavioural adaptations. They are often reactions by the animal to changes in its environment. Such changes are called environmental stimuli e.g. light, humidity The animal’s reaction is called a behavioural response. Woodlice and humidity When woodlice enter a dry environment their rate of movement increases. When they enter a damp area they slow down again. This response to humidity ensures that woodlice remain mainly in a moist/humid environment and are less likely to die from drying out. Woodlice and light When given the choice in a choice chamber, woodlice will move to the dark side. By staying in dark places, this behaviour will increase their chance of survival. Factors affecting Variation in a species Continuous variation A characteristic shows continuous variation when it varies in a smooth continuous way from one extreme to the other and does not fall into naturally distinct groups. e.g. height, weight, eye colour, hand span in humans, tail length in mice, body length in salmon. Discontinuous variation A characteristic shows discontinuous variation if it can be used to divide up the members of a species into 2 or more distinct groups e.g. human blood group, tongueroller/non-roller, human fingerprint type. FERTILISATION Mammals Mammalian gametes (sex cells) are eggs and sperm. Eggs are produced in the ovaries. Sperm are produced in the testes. Sperm and eggs both contain a nucleus. Fertilisation is when these 2 nuclei fuse together to form a zygote (a fertilised egg cell). Variation within the zygote is produced by a random combination of parental gametes. Flowering plants The sex cells or gametes in flowering plants are found in:pollen and ovules. Pollen is produced by the anther. Pollen contains the male gamete. Ovules are produced by the ovary which contains the female gamete. A pollen grain lands and becomes attached to the stigma. The pollen grain bursts open and then starts to grow a pollen tube which grows towards the ovule. • The nucleus of the male sex cell in the pollen fuses with the nucleus of the female sex cell in the ovule. This is called fertilisation. When the male and female nuclei fuse together a zygote is formed which contains the genetic information of both parent plants. GENETICS Chromosomes contain genetic information that gives rise to an organisms’ characteristics. Chromosomes are described in terms of a chain of DNA bases. The order of the DNA bases encodes information for the sequence of amino acids in proteins. These in turn dictate the structures and therefore functions of these proteins. e.g. the protein haemoglobin gives red blood cells their characteristic colour. DIVISION OF THE NUCLEUS IN GAMETE PRODUCTION Gametes have 1 set of chromosomes. Body cells have 2 matching sets of chromosomes. The reduction in number of chromosomes to a single set occurs during gamete formation (meiosis) The 2 sets of chromosomes are restored at fertilisation. Matching chromosomes pair and then separate during meiosis. The random assortment of chromosomes during meiosis leads to variation in offspring. CHROMOSOME NUMBERS IN DIFFERENT SPECIES Humans have 23 chromosomes in one set giving a total of 46 chromosomes in a normal body cell. Different species have different numbers of chromosomes (chromosome complement). SEX DETERMINATION In humans, each male gamete has an X or a Y chromosome. Each female gamete has an X chromosome. Female = XX Male = XY CHARACTERSITCS CONTROLLED BY FORMS OF A GENE CALLED ALLELES Genes are part of chromosomes. Different forms of a gene are called alleles. Each gamete carries 1 allele of the gene. HOMOZYGOUS = An individual with 2 of the same allele e.g. TT or tt. HETEROZYGOUS = An individual with 2 different alleles of a gene, e.g Tt The genetic symbols an individual has is its GENOTYPE, e.g. Tt The physical appearance an individual has is its PHENOTYPE e.g. Tall If a tall plant and a dwarf plant cross, the offspring are all tall. This means that ‘Tall’ is dominant. ‘Dwarf’ is recessive. The dominant form of the gene always gets a capital letter e.g. T = tall. The recessive form of the gene always gets the same letter but lower case e.g. t = dwarf TRUE BREEDING When 2 lilac parent plants cross, the offspring are all lilac. When the lilac offspring cross, all their offspring are lilac. SO: - When the flower colour of the offspring is identical to the parent flower colour, the members of the strain are true breeding. (they are always homozygous, e.g. LL) MONHYBRID CROSSES P = parent F1 = 1st filial generation F2 = 2nd filial generation A monohybrid cross is a cross that involves only one difference between the original parents, e.g. flower colour or height. Parents in monohybrid crosses are usually true breeding and show different phenotypes. You should be able to solve monohybrid cross problems following from the P generation to the F2 generation using dominant and recessive alleles. PRORTIONS AND RATIOS OF PHENOTYPES OF THE F1 and F2 OFFSPRING The predicted ratio of F2 offspring is 3:1 from a cross between 2 true breeding parents e.g. Pea plants P Tall TT F1 X Dwarf tt Tt F2…….Cross Tt with Tt Gametes T t and T t T t Genotypic ratio: Phenotypic ratio: T TT Tt t Tt tt 1TT: 2Tt: 1tt 3Tall : 1 dwarf A 3:1 ratio rarely happens in nature since and the observed ratio is not always as predicted since fertilisation is a random process involving an element of chance. CO-DOMINANCE 2 alleles of a gene can be co-dominant when neither is dominant nor recessive. Both alleles are displayed in the phenotype. Example: Black stallion crossed with White mare BB X WW F1 BW Grey roan (mix of black and white hair). You should be able to solve co-dominance problems. POLYGENIC INHERITANCE A range of phenotypes is produced e.g. skin colour in humans, seed mass in plants. The characteristics arise due to the interaction of the alleles of several genes. ENVIRONMENTAL IMPACT ON PHENOTYPE The final appearance of an organism (phenotype) is the result of its genotype and the effects of the environment. If organisms of identical genotype are subject to different environmental conditions they show considerable variation. Such changes have little evolutionary significance as they are not passed from one generation to the next. NATURAL SELECTION Is the process by which organisms that are better adapted to their environment survive and breed, while those less well adapted fail to do so. The better adapted organisms are more likely to pass their characteristics to succeeding generations. E.g. peppered moth. SELECTIVE BREEDING The selective breeding of plants and animals showing desirable characteristics. Over several generations improved offspring may result. Takes a relatively long period of time and the results are not always guaranteed. GENETIC ENGINEERING The stages in the production of a desired product need to be known e.g. insulin, HGH. THE STAGES Identification and removal of required gene from source chromosome Insertion of required gene into bacterial plasmid Insertion of plasmid into bacterial cell Synthesis of required product by bacteria. Advantages of genetic engineering increased range of products and increased rate of production. Disadvantages of genetic engineering possible release of genetically engineered bacteria into the environment and costly to develop.