General Biology Bio 101 Notes 2024-2025 PDF

BIO 101: GENERAL BIOLOGY 1 Dr. Justina F. Ogunsola REPRODUCTION Reproduction is the ability of an organism to give rise to new individuals of the same species in order to ensure continuity of life. It is that is not essential for an individual’s survival but for survival of the species. There are...

BIO 101: GENERAL BIOLOGY 1 Dr. Justina F. Ogunsola REPRODUCTION Reproduction is the ability of an organism to give rise to new individuals of the same species in order to ensure continuity of life. It is that is not essential for an individual’s survival but for survival of the species. There are two types of reproduction Sexual and asexual reproduction Sexual Reproduction: is the type of reproduction that involves two parents and the fusion of the male and the female gamete to form a zygote (fertilization). Offspring produced show new variation. The sex cells (gametes) are produced by meiotic cell division (Meiosis) and after fertilization the new individual continue to grow and produce new cells by mitosis. Offspring inherit traits from both parents resulting in genetic variation. Asexual Reproduction: is the process whereby an organism produces an offspring by itself. i.e. only one parent is presence. No gametes involved thus there is no fusion of nuclei, but the cells that give rise to the offspring usually divide by means of mitosis. Offspring produced are identical to the parent in all respect and are called clones. Clone is the term used to describe genetic and morphologic similarities between different individuals Forms of asexual reproduction Binary fission: Fission is the simplest form and involves the division of a single organism into two complete organisms, each identical to the other and to the parent. Fission is common among unicellular organism such as bacteria, many protists and some algae. Budding: The parent organism develops an outgrowth which subsequently forms the new individual organism. These buds break off from the parent without causing any injury and live an independent life. Budding is common in yeast and hydra. 1 Spore formation: Spores are DNA-containing capsules capable of sprouting into new organisms; unlike most seeds, spores are produced without sexual union of gametes, when dispersed, each spore is capable of developing into a new organism. Spores are common in lower organism especially fungi such as Rhizopus and Penicillium Fragmentation: A part of the parent organism breaks up and develops into a new independent organism. This type of reproduction is also called regeneration. Fragmentation is common in spirogyra, Hydra and coelenterates. Vegetative propagation is the major type of asexual reproduction found in flowering plants. It takes place when any vegetative part (stem, root or tuber) detaches from a plant and develop into a new plant. Example of vegetative parts used in this type of reproduction include: stem cuttings, tubers, rhizomes, stolon, corms, bulbs and suckers. Vegetative propagation can be divided into two: 1) Natural vegetative propagation and 2) Artificial vegetative propagation 1. Natural vegetative propagation: This is controlled by nature. For instance, banana/plantain produce suckers which can grow as separate plant before or after the parent plant dies. Natural vegetative propagation involves the use of vegetative parts such as stems, leaves, roots or buds. The part involved must have a stored of food and sometimes able to act as a perenniating organ i.e. enable the plant to survive from one growing season to the next. Organs of vegetative propagation include: Bubil: Axillary buds growing from the leaf margin e.g. Bryophyllum and Begonia Runners or stolon: Stems that creep horizontally on the soil surface. Buds and adventitious roots develop from the nodes of the parent plants e.g. sweet potato, grass. Rhizomes: Underground horizontal stem. It has scaly leaves which cover lateral buds at the nodes. Lateral buds grow into new aerial shoots e.g. ginger, canna lily. 2  Corms: Underground stems which grow vertically in the soil. Bud develop from the axils of scale leaves, grow upward and form leaves and flowers e.g. cocoyam. Stem tubers: Underground stems which have swollen tips. Axillary buds on tuber give rise to new aerial shoot e.g. yam, sweet potato. Suckers: Short underground horizontal branches e.g. banana, pineapple Bulb: Underground condensed shoots with compressed stems and scaly leaves e.g. onion, garlic. 2. Artificial vegetative propagation: This is employed by farmers or gardeners who cut or detach plant part and artificially plant it for rapid multiplication of plants. These include cuttings, layering, grafting or budding. Cutting It is the most common method employed by gardeners to grow new plants. A portion of the stem is cut and planted in the soil, which develops roots and further grows into a new plant e.g. Cassava 3 Grafting In grafting, two closely related plants are used to produce a new plant that has the desired, combined traits of both the parent plants. A twig (Scion) is taken from the variety to be propagated and closely applied to the stem of another plant (stock). A whole shoot or stem of one plant is attached to another plant. One plant is the stock, where the root system is taken and the other is the Scion, where the shoot system is used. The scion is attached to the stock of the second plant with well established root system. Grafting is done between orange and grape. Budding In this method, a bud with a small portion of bark is taken from the desired plant as the scion. The bud is placed in a T shaped slit cut into the bark of the stock and bound as for a graft. It enables to grow a number of new plants on a single stock. Layering: A healthy branch of a plant is bent until it touches the ground. The full end is tied to a strong support and fixes to the ground. The bent portion is fixed in placed by two pegs and it is covered with soil. After sometime, roots are given off and cut from the parent plant and allowed to grow on its own. It is used in plants such as cocoa and roses. 4  Advantages of vegetative propagation  It results in uniform growth in individuals (clone) at germination  They are genetically alike  It saves time and more economical in rapid plant population multiplication  Product of vegetative propagation matures faster than those from reproductive source  Rapid massive production of plants. Disadvantages of vegetative propagation  Vegetative propagated plants are short lived, small compared to seed propagated plants  No new variety can be produced  They are more susceptible to diseases as the entire plant may get affected as there is no genetic variation.  Size of vegetative propagation materials varies because some enlarges in order for it to store nutrients and enable them to survive unfavourable conditions. HEREDITY Heredity: This is the process by which heritable characters/traits (similarity and differences) are transmitted from parents to offspring from one generation to the next. TERMINOLOGIES IN GENETICS AND HEREDITY Gene: discrete unit of information or the hereditary trait transmitted from generation to generations. Basic structural/functional unit of heredity. Genes are segments of DNA that contain the code for a specific protein Allele - Is the alternative forms of a gene e.g. TT and tt. It is also referred to as factors that control the contrasting expression of a single character and located on the same locus of a chromosome. Locus: Position of an allele within a DNA molecule. Trait: are inheritable characteristics that vary from one individual to another. Each trait has two different forms (Tall (T) or Short (t)). 5 Dominant character- The parent character that is maximally expressed in the offspring when a single pair of contrasting characters is considered. The character is expressed in the first filial generation. The phenomenon is referred to as dominance. Recessive character- The parent character that is minimally expressed in the offspring when a single pair of contrasting characters is considered. The character is expressed in the second filial generation. Dominant allele: an allele that is expressed in a heterozygous organism. It is the allele that is expressed in presence of a recessive allele. (When both are present in the same individual. Hh, HH Recessive allele: An allele that is not expressed in the phenotype in the presence of a dominant allele except it is in homozygous form. Homozygous: When a pair of alleles controlling a given character is identical/ similar then the condition is said to be homozygous (TT or tt). Heterozygous: When a pair of alleles controlling a given character is non- identical/different then the condition is said to be heterozygous (Tt). Genotype: Genetic make-up of an individual. Phenotype: Observable characteristics of an individual resulting from interaction between genotype and environment. Phenotype is also referred to as the outward appearance of an organism. Parent generation: generation that supplies gamete to the filial generation Filial generation F1: The first offspring generation. Generation produced by crossing homozygous parental stocks. E.g. crossing tall and short, the offsprings was tall genotypically F2-generation produced by crossing two F1 organisms. Heredity: The transmission of genetic information from parents to offspring. Hybridization: is the mating or crossing of parental generation. Gamete: This is a mature sex or reproductive cell called spermatozoan (in male) and ovum/egg (in female). Hybrid: This is the result of the cross between two parents showing unlike character, also filia generation offspring either the 1st or 2nd. Test Cross: It is a genetic cross between a homozygous recessive individual and corresponding suspected heterozygote to determine the genotype of the unknown. It is used to determine whether the dominant is true breeding (homozygous dominant) or non-true breeding heterozygous. Monohybrid Inheritance: Inheritance of a single pair of contrasting character e.g height Dihybrid inheritance: This is the inheritance of two pairs of contrasting characters e.g height and colour Autosomes: Chromosomes that carried the genes responsible for the majority of all the characters in the body of an organism or individual except the sex character or gene. Sex chromosome: The chromosome that carry the gene responsible for the sex character. It is also called heterosome (XY). E.g. XX and XY Sex-linked genes: These are genes that is on sex chromosome XY and that are therefore inherited differently between male and female. Rhesus: This is the protein/antigen on the surface of red blood cell Albinism: This is the genetic disorder in which the skin lacks the black pigment called melanin Genetic variation: This is the variation in the sequence gene code (DNA sequence) of an organism of same species/ or within a population Mendel’s Experiment 6 The concept of the gene (but not the word) was first proposed in 1865 by Gregor Mendel. Gregor started his experiment in 1856 on pea plants. It was ignored/neglected until 1900 after his demise, his original works were reconsidered which forms the basis of modern genetics when it was rediscovered. In 1905, an English man named William Bateson gave the name Genetics to the science and also gave the name allelemorphs (now shortened to alleles) to identify members of pairs of a gene. Gregor worked with the pea plant by self-fertilizing and crossing the stigma (gynoecium) with the pollen grain (androecium). He studied seven different traits in pea plants i.e. Plant height (tall or short), flower location (Tip of stem or along the stem), pod shape (inflated or constricted), pod colour (Green or yellow), seed shape (Round or wrinkled), seed colour (yellow or green) and flower colour (purple or white). Inheritance of specific traits became clearer due to his discoveries. Plant A Plant B Parent tall plant (pollen grain) short plant (stigma) Genotype: TT tt Gamete: T T t t F1 generation: Tt Tt Tt Tt F1 phenotype: All F1 generation are tall plants F1 genotype: All heterozygous tall offspring 7 Selfing F1 generation Parents: Tall x Tall Genotype: Tt x Tt Gamete: T t T t F2 generation TT Tt Tt tt F2 phenotype: Three tall plants and one short plant F2 genotype; 1 homozygous tall; 2 heterozygous tall; 1 homozygous short plant Mendels observation  He observed that all the plants were tall like the original parent.  He observed that no short plant in F1 generation  Both tall and short plants were present in F2 generation  The ratio of tall to short in F2 is 3:1 which is known as monohybrid ratio  He observed that no blending of features or characters occurred in the plant  He observed that there was no intermediate feature. Mendelian law There are three basic laws of inheritance formulated by Mendel 1) Law of segregation: states that hereditable factors occur in pairs (AA, Aa or aa) which segregate during the formation of gamete and one allele from each parent combine during fertilization 2) Law of independent assortment: states that character behaves as a separate unit and is inherited independently of another character. Or When two contrasting characters are brought together at a cross, the factors controlling them segregate and then recombine at random to form all possible combinations 3) Law of dominance: It states that alleles are dominant while others are recessive, an organism with at least one dominant allele will display the effect of the dominant allele. TYPICAL ILLUSTRATION OF MENDEL’S LAW Law of segregation Mendel principle of segregation is related to events of meiosis. The separation of Homologous chromosome during meiosis results in the segregation. A typical illustration using garden pea with smooth seeds (SS) and wrinkle seeds (ss) which indicates the parental generation Smooth Wrinkle SS ss 8 The F1 generation (First filial generation) after crossing gives all smooth seeds which implies that the smooth seeds are dominant while the wrinkle recessive Parent Smooth plant (pollen grain) Wrinkle plant (stigma) Genotype: SS ss Gamete: S S s s F1 generation: Ss Ss Ss Ss F1 phenotype: All F1 generation are smooth plants F1 genotype: All heterozygous smooth offspring From the cross, all seeds are smooth, though, they are heterozygous i.e. consist of two different alleles (smooth and wrinkled). They are all smooth, because the seeds are dominant to smoothness. The F2 generation consist of 3:1 i.e 3 smooth seeds and 1 wrinkle seeds. Selfing F1 generation Parents: Smooth x Smooth Genotype: Ss x Ss Gamete: S s S s F2 generation SS Ss Ss ss F2 phenotype: Three tall plants and one short plant F2 genotype; 1 homozygous tall; 2 heterozygous tall; 1 homozygous short plant Law of independent assortment (second law) A typical illustration would be done using homozygous pea plant with yellow round seeds i.e. YY and RR where Y is the colour and R is the shape and homozygous pea plant with green wrinkled seeds yy and rr, where y is the green colour and r is the wrinkled seed P1 Yellow Round Green Wrinkle YYRR yyrr P1 gametes YR YR yr yr F1 YyRr YyRr YyRr YyRr Yellow round 9  Selfing F1 generation YyRr x YyRr gamete YR Yr yR yr x YR Yr yR yr F1 gamete YR Yr yR Yr YR YYRR YYRr YyRR YyRr Yr YYRr YYrr YyRr Yyrr yR YyRR YyRr yyRR yyRr Yr YyRr Yyrr yyRr Yyrr This is known as punnett square. This sixteen F2 individual have ratio of 9 yellow round: 3 yellow wrinkled; 3 green round:1 green wrinkled. The table below shows the phenotype genotype of F2 generation of a dihybrid cross between pea plants with yellow round and green wrinkled seeds. No of Individuals Genotype class Phenotype class 1 YYRR Homozygous yellow round 2 YYRr,YYRr Heterozygous Yellow round 2 YyRR, YyRR Heterozygous Yellow round 4 YyRr, YyRr, YyRr, YyRr Heterozygous Yellow round Yellow round =9 1 YYrr Homozygous yellow wrinkled 2 Yyrr, Yyrr Heterozygous yellow wrinkle Yellow wrinkle = 3 1 yyRR Homozygous green round 2 yyRr, yyrR Heterozygous green round Green round =3 1 Yyrr Homozygous green wrinkled =1 16 9:3:3:1 Practice Question 1 10 In an experiment involving crosses in lizards, it was discovered that grey skin colour is dominant over white skin colour, given a cross between a female lizard homozygous for grey colour and male lizard homozygous for white colour. State the colours of F1 and F2 generation of the cross. Practice Question 2 In the cross between tomato plant with red fruit and smooth stem and another with yellow and hairy stem, the resulting F1 generation all have red fruits and smooth stem. What will be the result when F1 is selfed? Using punnet square diagram, explain the result obtained stating the ratio of the genotype of the phenotype. Practice Question 3 In a certain animal, there are two allelles for hair colour: black and white and two alleles for hair length: short and long. In a breeding experiment all of F1 genotype produced from a cross between pure breeding short black haired and pure breeding long white-haired parents had short black hair (a) which is Alleles are dominant? (b) what is the expected proportion of F2 phenotype. Practice Question 4 In pig, black is dominant to brown and a short hair is dominant to long hair. If a homozygous black short haired guinea pig (BBSS) and a homozygous brown long haired guinea pig (bbss) are crossed: using punnet square (i) What are the genotype of the parents (ii) What would be the genotype and phenotype of an F1 guinea pig (iii) What would be the expected genotype and phenotype of the F2 EVOLUTION Evolution is the change in genetic make- up of a population over several generations and relies on the process of natural selection. The theory of evolution is based on the idea that all species are related and gradually change overtime. Theory of evolution doesn’t attempt to explain the origin of life itself (Abiogenesis) but rather the diversification and adaptation of life forms once life emerged Different types of evolution 11 Convergent evolution When the same adaptations evolve independently, under similar selection pressures. For example, flying insects, birds and bats have all evolved the ability to fly, but independently of each other. Co-evolution When two species or groups of species have evolved alongside each other where one adapts to changes in the other. For example, flowering plants and pollinating insects such as bees. Divergent evolution This is the process in which single interbreeding species diverged into two or more evolutionary groups. i.e. Become genetically and phenotypically different from each other. This leads to Speciation. The splitting among species into a number of new forms occurs when a change in the environment makes new resources available or creates new environmental challenges. Example: Mammoths and elephants diverged from a common ancestors (Primelephas sp.) Finches on the Galapagos Islands have developed different shaped beaks to take advantage of the different kinds of food available on different islands. 12 Theory of evolution (Lamarckism) The first theory of evolution was proposed by Jean- Lamarck (1744-1829). His theory was proposed in 1801 that organisms acquire characters during their lifetimes for adapting to environment, and their acquired characters are inherited by the offspring. By accumulation of acquired characters over many generations, the species is modified into a new one. Two main assumptions of Lamarck to explain how species changes over time are: Use and disuse of the organs: He suggested that organs or structures of an organism that are used extensively becomes larger and stronger, while those that are not used become weakened, smaller and gradually disappear (Vestigal organs). Inheritance of acquired characteristics: The character or change acquired during an organism’s lifetime would be inherited by its offspring. Lamarck believed that new species evolved after a long period of time, after many generations by acquiring new character and losing the old character (depending on use or disuse of organs). He explained this using Giraffe e.g. the long neck of giraffe arose from the need to browse on tree tops and since this was a useful adaptation, other generation of giraffe have been inheriting the acquired character. However his postulates or theory were based on the facts that environmental influences are the main causes of evolutionary changes or the formation of new types, thus when an environment of an animal changes, the needs of the animal change and this leads to special demands of certain organs. According to Lamarck, such organs if used more extensively would enlarge and become more efficient, such changed characteristics would be transmitted to the offspring. Lamarck’s contribution to the theory of evolution can be summarized as follows:  Great changes in environment result in corresponding changes in the species.  These changes cause the organism to form new structure or to adjust to the new prevailing environment.  Organism then develop specialised characters by the use and disused of organs.  Frequently used organs become well developed.  Organs not frequently used degenerate and become useless or vestigial 13   Well developed/ dominant acquired characters are inheritable. Lamarckism in evolution theory today Learn behaviour patterns can be changed within a generation. Members of a social group who have acquired the behaviour in their lifetimes will pass these learned skills onto others including their children. The evolution of learnt behaviour is much faster than genetic evolution and it plays an important role in human cultural evolution. This pattern of evolution resembles the Lamarckian pattern. THEORY OF EVOLUTION (DARWINISM) The theory of evolution by natural selection was first formulated in Darwin's book "On the Origin of Species" in 1859. It is the process by which organisms change over time as a result of changes in heritable physical or behavioural traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring. Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including palaeontology, geology, genetics and developmental biology. Darwin’s theory is still generally accepted as the best available explanation of the way life on this planet developed. Charles Darwin’s theory of evolution states that evolution happens by natural selection. Natural selection explains how this evolution has happened: Over-production: More organisms are produced than can survive because of limited resources. Struggle for existence: Organisms struggle for the necessities of life; there is competition for resources.(What do they struggle for ?) Survival of the fittest: Individuals that are better adapted to their environment are more likely to survive, finding food, avoiding predators and resisting disease. These individuals are more likely to reproduce and pass their genes on to their children. Individuals that are poorly adapted to their environment are less likely to survive and reproduce. Therefore their genes are less likely to be passed on to the next generation. They become extinct Origin of new species: As the favourable variations of the fittest animals are inherited to the offspring, these variations accumulate over the generations. In order word, nature selects the individuals that are well adapted to the environment and allows them to survive. Also nature rejects those that are poorly developed. Hence, natural selection is a weeding out process by which only the fittest individuals are selected. 14 Evidence of Evolution Evidence for evolution comes from many different areas of biology: anatomy, molecular biology, biogeography, fossils, & direct observation. 15 Anatomy: Species may share similar physical features because the feature was present in a common ancestor (homologous structures). If two or more species share a unique physical feature, such as a complex bone structure or a body plan, they may all have inherited this feature from a common ancestor. Physical features shared due to evolutionary history (a common ancestor) are said to be homologous. Analogous structures shows that similar selective pressures can produce similar adaptations (beneficial features).e.g. flying insects, birds and bats have all evolved the ability to fly because of similar selection pressure for adaptation. They are similar in appearance and function but different in structure VESTIGAL STRUCTURES Sometimes, organisms have structures that are homologous to important structures in other organisms but that have lost their major ancestral function. These structures, which are often reduced in size, are known as vestigial structures. Examples of vestigial structures include the 16 tailbone of humans (a vestigial tail), the hind leg bones of whales, and the underdeveloped legs found in some snakes Molecular biology: DNA and the genetic code reflect the shared ancestry of life. DNA comparisons can show how related species are. Biologists often compare the sequences of related genes found in different species to figure out how those species are evolutionarily related to one another. The basic idea behind this approach is that two species have the "same" gene because they inherited it from a common ancestor. For instance, humans, cows, chickens, and chimpanzees all have a gene that encodes the hormone insulin, because this gene was already present in their last common ancestor. In general, the more DNA differences in homologous genes (or amino acid differences in the proteins they encode) between two species, the more distantly the species are related. For instance, human and chimpanzee insulin proteins are much more similar (about 98% identical) than human and chicken insulin proteins (about 64% identical), reflecting that humans and chimpanzees are more closely related than humans and chickens 17 Biogeography: The global distribution of organisms and the unique features of island species reflect evolution and geological change.. For instance, there are unique groups of plants and animals on northern and southern continents that can be traced to the split of Pangaea into two supercontinents Fossils Record: Fossils document the existence of now-extinct past species that are related to present-day species. Fossils are the preserved remains of previously living organisms or their traces, dating from the distant past. Fossils are often contained in rocks that build up in layers called strata. The strata provide a sort of timeline, with layers near the top being newer and layers near the bottom being older. Fossils found in different strata at the same site can be ordered by their positions, and "reference" strata with unique features can be used to compare the ages of fossils across locations. In addition, scientists can roughly date fossils using radiometric dating, a process that measures the radioactive decay of certain elements. They can also help scientists reconstruct the evolutionary histories of present-day species 18 Direct observation: Some populations, like those of microbes and some insects, evolve over relatively short time periods and can be observed directly. In some cases, the evidence for evolution is that we can see it taking place around us! Important modern-day examples of evolution include the emergence of drug-resistant bacteria and pesticide-resistant insects. The evolution of DDT resistance in mosquito populations was observed directly in the 1950s as a result of a campaign to eradicate malaria. Resistance to the pesticide evolved over a few years through natural selection Embryology: Some homologous structures can be seen only in embryos. Embryology is an aspect of biology that is concerned with the formation of the embryo as well as its development. It is noticed that early stage of development of the embryo of human look like a fish, an 19 amphibian, reptiles and then a human being. From this we can say that the developmental stage of an embryo were more or less evolutionary in history. For instance, all vertebrate embryos (including humans) have gill slits and a tail during early development. The developmental patterns of these species become more different later on (which is why your embryonic tail is now your tail bone and your gill slits have turned into your jaw and inner ear). Homologous embryonic structures reflect that the developmental programs of vertebrates are variations on a similar plan that existed in their last common ancestor. ECOLOGY Ecology comes from the grek word oiks-home logos-study. Ecology is the study of organisms, the environment and how the organisms interact with each other and their environment. It is studied at various levels, such as organism, population, community, biosphere and ecosystem. Ecosystem: The sum of the organism living within its boundaries and all the abiotic factors with which they interact e.g. A pond is a good example of ecosystem. Biosphere is the part of the earth and atmosphere inhabited by living organisms. Biosphere can be divided into i. Atmosphere: This is the thick layer of air surrounding the earth surface which consists of gases, dust, water vapour and various microscopic light-weight living things. e.g. bacteria, spores of fungi and bacteria, pollen grains of plants that are suspended in it. ii. Hydrosphere: This contains all the water bodies on the surface of the earth and the water reservoirs beneath the earth surface. The water bodies serve as habitats for aquatic plants and animals. iii. Lithosphere: This occupies the outer portion of the earth surface. It is the geologic portion of the biosphere. It is composed of the rocks, soils and their constituents and all the organisms which inhibit the soil such as fungi, algae, worms and animals. The habitat is a specific locality with a particular set of conditions where organisms live. Habitats are categorized into Terrestrial (Land) and aquatic (Water). 20 Niche: The physical space occupied by an organism together with its functional role in the ecosystem and its position in the food web. For example, it feeds on some organisms while it serves as food to others Population: refers to a group of organisms of the same species living together in a habitat at a particular time. For example, in a large abandoned farm land: we may have populations of palm trees, Tridax, snake, birds etc. Community refers to all organisms belonging to different species that interact in the same habitat. A community therefore is made up of populations. For example, a pond, with population of fish tadpoles, algae, water lettuce, bacteria, amoeba, mosquito larvae and pupa, insects etc. form a pond community Biomass is the total dry weight of living organisms at a particular tropic level or per unit area e.g total weight of maize crop per hectare. Carrying Capacity is the maximum number of organisms an area can comfortably support without depletion of the available resources. ECOSYSTEM This is the complex system of interactions between all the living organisms and the non-living physical factors in a given area. Examples include, a rotten log of wood, a school field, a desert, a stream, a farm, a pond, an ocean and an aquarium. Components of ecosystem Ecosystem consist of two main components namely biotic components and abiotic components Ecosystem Abiotic components Biotic components Climate Edaphic Inorganic substance Producer Consumer Decomposer Soil Water Light Primary Topography CO2 Temp. Secondary Oxygen rainfall Tertiary Nitrogen Biotic components The biotic components of the ecosystem are the living things. They are divided into three groups namely: producers, consumers and decomposers.  Producers- Green plants manufacture food for the entire ecosystem through the process of photosynthesis. They are called autotrophs as they absorb water and nutrients from soil, carbon (IV) oxide from the air and capture solar energy for this process. 21   Consumers: called heterotrophs and they consume food synthesized by the autotrophs. Based on food preference, they are grouped into: Herbivores (1o consumers): They feed directly on plants e.g cow, rabbits. Carnivores (2o consumers): animals which eat other animals. E.g lion, dog, cat. Omnivores (3o consumers): are organisms feeding on plants and animals e.g sparrow, human, pigs.  Decomposers: called saprotrophs. These are mostly bacteria and fungi that feed on dead decomposed organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They are also called detrivore or detritus feeders. Abiotic components These are the non- living components of the ecosystem. They include:  Inorganic substances like water, carbon (IV) oxide, oxygen and nitrogen.  Climatic factors like light, temperature and rainfall  Edaphic factors such as soil and topography.  Organic substances like carbohydrates, proteins, lipids etc  Physiological factors such as rocks, mountains, plateau, valleys, seas, river etc Energy flows through ecosystem In a functioning ecosystem, as organism feed on one another, energy and nutrients are transferred steps by steps in a sequence or along the pathway. Each step along this feeding pathway is called feeding level or trophic level. It always begins with producers that manufacture their food followed by the herbivores or primary consumers that feeds on the producers. The secondary consumer that feeds on the primary consumer occupies the third trophic level. Tertiary consumers occupy the 4th trophic level and the last trophic level is always occupied by the decomposers. They feed on the dead bodies of the final consumers. They will release the energy that flow from producers through all the consumers into the environment as heat. They will also release all the nutrients as inorganic substances Trophic level Functional group Energy flow 1 Producers 2 Primary consumers 3 Secondary consumers 4 Tertiary consumers 5 Decomposers FOOD CHAIN A food chain is a linear sequence of feeding relationship which shows the flow of matter and energy from one organism to another. Succession of organism that eat other organisms and may in turn be eaten themselves. A food chain starts with the producer and ends with the predator species or a decomposer. The sun is the source of energy (solar energy) which is used by the green plants (producers) to create their food (carbohydrates) through photosynthesis. The plants are eaten by herbivores (primary consumer) and the energy is transferred to another organism (secondary consumer). 22 Energy is neither created nor destroyed but flows from one level to the other. As the energy goes one level up, the food chain also moves up. Each feeding level is called a trophic level. In a food chain, organisms feed only on one type of organism. Below is food chain in the terrestrial ecosystem. Give one example of food chain in aquatic, savannah and rain forest habitat A FOOD WEB. A food web consists of all food chains in a single ecosystem. It is a graphical model showing the interconnecting food chains in an ecological community. In an ecosystem, a plant may serve as food to several consumers, for examples, grasshopper, rat, stem borer etc may feed on the same plant. Also a consumer may feed on different plants e.g. a bird may feed on tomato fruit, guava fruit etc. Carnivore may feed on more than one kind of prey e.g. Lion can feed on Zebra, antelope, cow etc. This results in many interrelated food chains. It illustrates food chains in an ecosystem. 23 Ecological pyramid/ Trophic pyramid The relationship of organisms to each other at each trophic level in terms of individuals, biomass and energy content is such that these parameters decrease as one move up through the trophic levels from the producers. When these are represented graphically, they give the shape of pyramids, hence the term ecological pyramids. An ecological pyramid is a graphical representation designed to show the biomass or bio productivity at each trophic level in a given ecosystem. 24 Pyramid of numbers represent number of individual organisms at each trophic level. In the food chain, the number of individual organisms at each trophic level generally decreases from the producers through the other trophic levels. For example: The number of grasshoppers that feed on crop plant is lesser. The number of frog is also higher than the number of grasshoppers that feed on them. Likewise, the number of snakes that feed on the frog will be lesser than the number of frog. Few exceptions to this general are found in two instances: a. In tropical rain forest: a few trees can serve as food for a large number of primary consumers. For example, a large number of small insects like grasshoppers, butterflies, ants etc. b. In a food chain containing parasites, a few numbers of hosts may support a large number of parasites e.g. a cow can have many ticks feeding on it. 25 Pyramid of biomass Biomass of an organism is the dry or wet weight of the organism. The dry mass represents the mass of the organism when all the water content has been driven off by heat. The wet mass is the mass of the organism with the water content intact. The pyramid of biomass represents the total wet or dry mass of the organism at each trophic level. It is obtained by first counting the number of organism at each trophic level and then weighing them. The pyramid of biomass therefore estimates both the number and size of the individual at trophic level. Biomass decreases as one move from the first trophic level through other trophic levels. A pyramid of energy represents how much energy, initially from the sun, is retained or stored in the form of new biomass at each trophic level in an ecosystem. Energy flows through the food chains from the producers to the consumers. The energy decreases as it flows from the first trophic level (producer) to the other trophic levels. The pyramid of energy therefore represents the progressive decrease in energy from the first to the last trophic level in a food chain. Typically about 10% of the energy is transferred from one trophic level to the next, thus preventing a large number of trophic levels. Energy pyramids are necessarily upright in healthy 26 ecosystems that are there must always be more energy available at a given level of the pyramid to support the energy and biomass requirement of the next trophic level. A pyramid of energy shows how much energy is retained in the form of new biomass at each trophic level. Assignment: State the laws of thermodynamics Nutrient Cycling in ecosystem Energy cannot be recycled but its continually being supplied to the ecosystem by the sun. Nutrients however are recycled continually in the ecosystem. This is brought about mainly by the decomposers. Feeding 2o to final Sunlight 1o Consumers energy Consumers Death Death Absorption chlorophyl Decomposers 1o Death producers Inorganic Nutrient 27 ECOLOGICAL INTERACTION Different types of interaction exist and they includes: mutualism, parasitism, commensalism, predation, competition Parasitism This is the relationship between two organisms where one called the parasite benefits from another organism called the host. The parasite is sheltered and protected by the host while the host is harmed. Parasites are usually smaller than their hosts. Parasites can be classified into ectoparasites and endoparasites depending on where they are found on the host. Ectoparasites are found on the host’s body. E.g. ticks, lice, fleas, mosquitoes. Endoparasites live within the host body. E.g. Tapeworm, liver fluke, roundworm. When a parasite causes disease and sometimes death of a host, it is called a pathogen. Some plants live and feed on other plants because they cannot produce their food themselves. They get water, nutrients and food from their hosts using a special structure called HAUSTORIUM to pierce the host plant. They are also attached to their hosts by the haustoria. These plants that feed on other plants are referred to as parasitic plants. Examples include Mistletoe (Loranthus), Dodder (Cuscuta), Nepenthes, Striga Mutualism relationship This is an interaction between two organisms of different species in which both of them derive benefit. This is a beneficial association and each member is called a symbiont. Mutualism is either obligate (essential for survival of both species) or facultative (either partner can live alone under certain conditions). The association between nitrogen fixing bacteria of the genus Rhizobium on the root nodules of legumes (beans) is an example of mutualism. Nitrogen fixing bacteria which live inside nodules on the roots of legumes, supply the plants with most of the nitrogen containing compounds. The legumes supply sugars and other energy rich organic molecules to their bacterial. Another example is an acacia tree and ants. The tree provides room and board for ants. The ants eat sugar secreted by the tree. The ants also eat yellow structures at the tip of leaflets these are protein rich. It seems to have no function for the tree except to attract ants. The ants whereas, benefits the tree by attacking virtually anything that touches it. They sting other insects and large herbivores. When ants are removed from the tree, the tree usually dies. This is probably because herbivores damage the tree so much that they are unable to compete with surrounding vegetation for light and growing space. Cattle and the egrets. The white egret flies around cattle and often perch on their back. They help to remove the blood sucking tick from the body of the cattle. The cattle as they graze stir the grass making the green insect to fly into the view of egret which pick them up and eat. Mycorrhiza: This is a close association between roots of higher plants and fungi. The fungi act as root hairs and help to absorb inorganic nutrients like phosphate etc. transferring it to the vascular system of the plant. The plant in turn supplies the fungi with carbohydrates and organic nutrients. 28 Commensalism Commensalism is an interaction in which one species (usually the smaller one) benefit and the other one (the larger organism) is neither harmed nor benefits. Example of commensalism is the relationship between social insects and scavengers such as mites, beetles and millipedes that live in the nest of social insect. Another example is the relationship between a host tree and its epiphytes which are smaller plants. The epiphyte anchors itself to the tree but does not obtain nutrients/water directly from it. Living on the tree enables it to obtain adequate light, water and required minerals. Thus, the epiphyte benefits from the association, whereas the tree is apparently unaffected. Bacterial in the large intestine of man; The bacteria feed on undigested food while man is neither benefit nor loose anything from the association. Predation This occurs when one organism (predator) feeds on another organism (prey). Generally, predation result in the death of the prey. The predator is usually larger and more powerful than its prey. Examples of typical predation are lion (predator) killing and feeding on an antelope (prey), hawk feeding on a chick. Herbivores are predators who feed on plant. Often, the plants eaten may be damaged but not killed. DID YOU KNOW??? Some plants are predators of animals. Carnivorous plants are plants with special structures to attract, trap and secrete enzymes to digest small animals such as insects. They get their nitrogen from the insects they feed on. They are also referred to as insectivorous plants. Examples are Nepenthes (Pitcher plant), Utricularia, Drosera (Sundew) Saprophytism Saprophytism is food relationship in which saprophytes (decomposers) get their food by decomposing food remains or bodies of dead organisms, such as mushroom fungus, Bread mold fungus and Penicillium fungus that decomposes orange fruits. Saprophytic organisms as bread mold fungus get their food by decomposing the food remains (as moist bread) causing the dark green layer on bread. Competition is an interaction between organisms or species in which both require a resource that is in limited supply (such as food, water, or territory). This occurs when 2 or more individuals of the same or different species seek the same resources which are in short supply. If the resources are in abundance, there will be no competition. Competition lowers the fitness of both organisms involved since the presence of one of the organisms always reduces the amount of the resource available to the other. Plants compete for sunlight, nutrients, water and space. While animals compete for space, food, water, mates, light. Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition. 29 Intraspecific competition is usually more intense because the requirements of members of the same species are more similar than that of individuals of different species HABITAT The place where an organism (plant or animal) lives or inhabits naturally Different organisms are found in different habitats. There are two major habitats. These are: 1. Terrestrial habitats, 2. Aquatic habitats. The terrestrial habitat refers to land-based environment. Living organisms found living in terrestrial habitats include human beings, domestic animals, wild animals and plants. The terrestrial habitat can be arboreal (in or on trees), on the ground or under the ground. Monkeys, birds and ants are arboreal. Grasscutter lives on ground, while earthworms live underground. The ground habitat may be of different kinds such as tropical rainforest, savannah, grassland, semi- desert and desert. The variation is widely based on factors such as climate, soil type, vegetation, and topography. Organisms in terrestrial habitats have evolved specific adaptations to cope with challenges such as temperature fluctuations, water availability, and nutrient availability. The aquatic habitat refers to water-based environment. The aquatic habitat contains different kind of animals and plants that are called aquatic organisms. The organisms include: fish, whale, turtles, crocodiles, tadpoles, water lettuce, water lilies etc. Aquatic habitat can be estuarine, marine or fresh water. Estuarine refers to the river mouth where salt and fresh water meet. Examples are such as bays and lagoons. The organisms found in these areas include periwinkles and lobsters. The marine habitat includes the sea and ocean. Marine plants and animals include weeds, octopus, fish, whales and dolphins. The freshwater habitats include lakes, river, pond and streams. The organisms found in fresh water habitat include fish, crayfish and crabs. Aquatic organisms have evolved various adaptations to thrive in their specific water conditions, including gills for respiration, streamlined body shapes, and salt-excreting mechanisms. Characteristics of Habitat Biotic Components: Habitats consist of living organisms, including plants, animals, fungi, and microorganisms. These biotic components interact in complex ways, forming food webs and ecological relationships. Abiotic Components: Abiotic factors encompass the non-living aspects of a habitat, such as temperature, humidity, sunlight, soil composition, water availability, and physical features like rocks and terrain. 30 Niche: A habitat provides a specific ecological niche for each species. A niche includes an organism's role, behavior, and interactions within its environment, including its resource utilization and interactions with other species. Adaptations: Organisms in different habitats develop adaptations to suit their environment. These adaptations can be structural, physiological, or behavioral, helping the organisms survive and reproduce in their specific habitat. Habitat Diversity: Habitats contribute to biodiversity by providing various niches for different species. The diversity of habitats in an area promotes a rich array of species, contributing to ecosystem stability. Habitat Degradation: Human activities, such as deforestation, pollution, and urbanization, can lead to habitat degradation. This can disrupt ecosystems, cause loss of biodiversity, and impact the survival of many species. 31