MICROORGANISMS REMEMBER!! TO BE CLASSIFIED AS A LIVING, THE ORGANISM MUST DISPLAY THE FOLLOWING CHARACTERISTICS: M – movement; R - respiration; S – sensitivity to the environment; G - growth; R - reproduction; E - excrete; N – nutrition. Movement Living organisms are capable of movement. Animals move from one place to the next in response to what they see, smell, hear and feel. Even bacteria – they use their flagella to move. Plants respond to light, water availability and gravity. They move towards the light (eg sunflowers) or the flowers close when the sun goes down and roots grow towards water. Roots grow downwards – this is called positive geotropism; shoots grow upwards - against the pull of gravity or negatively geotropically. Movement is closely linked to Sensitivity to the environment. (WHY DO WE SAY THIS?) Respiration Living organisms all respire. They function effectively by using energy, which is made available to them during the process of respiration. This process takes place in the hundreds of mitochondria in each of the cells in their bodies. Even plants respire. They convert the sun’s energy (radiation energy) into stored chemical potential energy in glucose molecules during the process of photosynthesis that occurs in the chloroplasts. The glucose is then broken down during the process of respiration to release energy for all the other processes that occur in the cell. Sensitivity to the environment Living organisms respond to environmental stimuli. A simple example is found in plants - Some plants secrete allelochemicals into the soil to inhibit the growth of other roots in the near vicinity – other plants’roots sense these chemicals and will grow away from the allelochemicals. A more complex example is the temperature receptors in our skin. For example, if we place our hand on a hot iron, the receptors in our skin receive the stimulus from the environment, the message is carried to the brain by nerve impulses and the brain interprets the message and sends a message via other nerves to our biceps to contract so that our hand is removed from the hot iron. All this happens in milliseconds. Growth Living organisms make organic molecules, which serve as a building material and increase their body size mainly by the process of cell division called mitosis (you will learn about mitosis in Form 3). Each multicellular organisms originates from a single cell, and through mitosis more and more cells develop each with a specific function. All the cells with a similar function group together to form a tissue. Tissues group together into organs to form a specific function. Reproduction Living organisms reproduce to sustain life (ensure the continuation of their species). Reproduction can be asexual or sexual. In asexual reproduction, only one organism are required. For example, unicellular organisms such as amoeba, simply divide into two. Certain plants, such as aloes, can grow a whole new plant from a slipping (a leaf or stem cutting). For sexual reproduction, a male and a female are required. Even plants have sexual reproduction – the pollen fertilises the ovary to produce the seed that grows into a new plant that has genes from both the male and the female plant. Excretion All living organisms must excrete the waste products that are produced in their bodies by the normal metabolism which occurs in all their cells. Any waste products that are allowed to build up in our bodies will become toxic to our systems. Carbon dioxide is a waste product of respiration. The carbon dioxide that is produced in plants is either used in the process of photosynthesis or diffuses out of the plants through the pores (called stomata) on the leaf and stem surfaces. In most animals (mammals, birds, and reptiles) carbon dioxide is secreted by all their cells into the blood which transports it their lungs where it is breathed out. Nitrogenous wastes, excess salts, toxins, and excess water must also be excreted. These are filtered out of the blood by the kidneys and are excreted in the urine. (Undigested food remains are excreted as faeces). Nutrition Living organisms sustain their complex organisation and metabolic processes by taking in energy from the environment. Plants use the sun’s energy and convert this into a form that can be converted into usable energy by the animals that eat the plants (herbivores and omnivores). Carnivores obtain their energy from the animals that they eat. Refer to the section on food chains later on in this book. Unicellular organisms such as amoeba take in food particles by a process of phagocytosis. THE 5-KINGDOM CLASSIFICATION SYSTEM MONERA The rest of the Kingdoms consist of EUKARYOTIC organisms. Eukaryotes have a true nucleus – the DNA is enclosed by the nuclear membrane. Monera are simple, unicellular (ie an organism made up of only onecell) PROKARYOTIC organisms. Prokaryotes have NO TRUE NUCLEUS and their nucleic material (strand of DNA) is not enclosed within a membrane. They do not have membrane bound organelles (like chloroplasts and mitochondria). Reproduction is mostly ASEXUAL, but some sexual reproduction is also seen. Asexual reproduction is by BINARY FISSION. Movement is assisted by flagellae. NUTRITION ➢ Autotrophic bacteria - Bacteria which prepare their own food are autotrophic. (Example Cyanobacteria) ➢ Heterotrophic bacteria - Bacteria which are dependent on other organisms for their food are heterotrophic. (Example Escherichia coli in our intestines) Monerans are found everywhere, from hot springs, under ice, in deep ocean floor, in deserts and on or inside the body of plants and animals. PROTISTA (Algae – plant-like algae and Animal-like protozoans) These are unicellular and multicellular organisms. They have no protection from drying out, therefore they can only live in a moist environment. The species range from microscopic organisms to those that are 100m long (kelp) NUTRITION Some species are Heterotrophic (animal-like, called protozoans) and some are autotrophic (plant-like, called algae). They display sexual and asexual reproduction. FUNGI (mushrooms, bread mould, Athlete’s foot, Thrush) Some are macroscopic but MOST are microscopic. Most are multicellular but some are unicellular. They are found in a wide variety of habitats - soil, air, dead organic matter. Heterotrophs – saprophytic or parastic (eg athlete’s foot; rust in plants) Some live in symbiotic relationships (eg lichen; mycorrhizea). Fungi display sexual and asexual reproduction. PLANTAE Multicellular, complex organisms (have different cell types and organs). All are photosynthetic. Display both sexual and asexual reproduction. ANIMALIA Multicellular, complex organisms (have different cell types and organs). All are heterotrophic. A few display asexual reproduction and most reproduce sexually. VIRUSES Viruses may be regarded as non-living because they cannot reproduce without a host cell; they are acellular as they do not have a nucleus, cytoplasm or organelles. ➢ They, therefore, do not fit into any one of these kingdoms. ➢ Viruses cannot be seen with a compound light microscope. They are much smaller than bacteria. Viruses are obligate intracellular parasite composed of: o Nucleic acid - either DNA or RNA o Protein coat or capsid; some have envelopes ( a lipid bilayer) to protect the virus from the host cell’s nuclease enzymes which would harm the virus cell’s nuclear material (DNA or RNA). ➢ Multiply inside living cells using the host cell nuclear material ➢ They are classified according to the host cell that they invade, for such as Bacteriophages infect bacteria. They have different shapes: POLYHEDRAL, HELICAL, COMPLEX Other characteristics: Viruses can become dormant when environmental conditions are unsuitable for their requirements. When dormant, they are called VIRON. A VIROID is even smaller than a virus and is an infectious RNA particle. NOTE: It is difficult to study viruses because they must live within a living host cell (animal, plant or bacteria, and they destroy the host cell. Can you see the difficulty a researcher would have in cultivating viruses? BACTERIA (Know the characteristics of Monera) • Bacteria have a protective rigid cell wall and a cell membrane. The membrane serves as a mitochondrion, endoplasmic reticulum and sometimes a chloroplast. • The nuclear material is a simple loop of DNA. • Many bacteria that cause disease, especially bacilli, are surrounded by a waxy capsule, which protect it from the defences of the host’s body. • Some have flagella that help them move. Bacteria are classified according to their shape: Spiral = spirilla Rod-shaped = bacilli Round = cocci Reproduce by BINARY FISSION during favourable conditions (can divide every 10 -15 minutes – doubling of population in this time) In unfavourable conditions – bacteria become dormant and form spores with a thick coat around each bacterium - when favourable conditions return the coat splits and releases the bacterium (spore ‘germinates’). Bacteria are mostly useful but some are pathogenic (disease-causing). Some, such as Escherichia coli are useful to us in that they exist in a mutualistic relationship with us in our intestines. The bacteria get nutrients from undigested food and a suitable environment to grow. The human benefits by gaining vitamin K2 which the E. coli produce (used in humans for blood clotting) AND E. coli protect against the growth of pathogenic bacteria in the intestines. But other bacteria cause us to become very ill. How bacteria affect our bodies: 1. Destroy body cells and then use components as a food source 2. Absorb materials from body fluid 3. Release toxins that cause a rash or high temperature or block metabolic pathways eg meningitis; tetanus. Bacteria that cause tetanus, Clostridium tetani, are found in soil, dust and animal faeces. If they enter a deep flesh wound, spores of the bacteria may produce a powerful toxin, tetanospasmin, which actively impairs your motor neurons, nerves that control your muscles. The toxin caus muscle stiffness and spasms. Another example of a symbiotic relationship that bacteria form is nitrogen-fixing bacteria and plants. Nitrogen-fixing bacteria such as Rhizobium live in root nodules of legumes and have a mutualistic relationship with the legume. Rhizobium gets nutrients from the root and a favourable environment to grow. The plant gets ammonia from the Rhizobiumand uses ammonia to make amino acids and therefore proteins. FACT The legume–Rhizobium symbiosis provides 20% of all nitrogen inputs into global agriculture PROTISTA PLANT-LIKE PROTISTA (ALGAE) • • • • Green algae; Contain chlorophyll Mostly free-floating but some are attached eg kelp Unicellular (eg diatoms and dinoflagellates) or multicellular (eg seaweeds) Reproduce asexually GROUPS OF ALGAE Red algae Brown algae Diatoms (have silica cell walls) Dinoflagellates (have flagella) GREEN ALGAE RED ALGAE DINOFLAGELLATES DIATOMS ANIMAL-LIKE PROTISTA (PROTOZOANS) • • • • ALL unicellular All heterotrophs – absorb nutrients from water OR ingest by engulfing food particles (phagocytosis) Actively seek their food. Classified according to their form of locomotion AMOEBA PROTOZOAN GROUPS AMOEBOIDS(use pseudopodia to move and feed. These are temporary cytoplasmic projectio FLAGELLATES (Use flagella to swim) PARASITIC (Non motile) Plasmodium (malaria-causing parasite) inside red blood cells LIFE CYCLE OF THE MALARIA PARASITE 1. A female Anopheles mosquito carrying malaria-causing parasites (Plasmodium) feeds on a human and injects the parasites in the form of sporozoites into the bloodstream. The sporozoites travel to the liver and invade liver cells. 2. Over 5-16 days (depending on the species of Plasmodium), the sporozoites grow, divide, and produce tens of thousands of haploid forms, called merozoites, per liver cell. Some malaria parasite species remain dormant for extended periods in the liver, causing relapses weeks or months later. 3. The merozoites exit the liver cells and re-enter the bloodstream, beginning a cycle of invasion of red blood cells, asexual replication, and release of newly formed merozoites from the red blood cells repeatedly over 1-3 days (depending on the species of Plasmodium). This multiplication can result in thousands of parasite-infected cells in the host bloodstream, leading to illness and complications of malaria that can last for months if not treated. 4. Some of the merozoite-infected blood cells leave the cycle of asexual multiplication. Instead of replicating, the merozoites in these cells develop into sexual forms of the parasite, called male and female gametocytes, that circulate in the bloodstream. 5. When a mosquito bites an infected human, it ingests the gametocytes. In the mosquito gut, the infected human blood cells burst, releasing the gametocytes, which develop further into mature sex cells called gametes. Male and female gametes fuse to form diploid zygotes, which develop into actively moving ookinetes that burrow into the mosquito midgut wall and form oocysts. 6. Growth and division of each oocyst produce thousands of active haploid forms called sporozoites. After 8-15 days (depending on the species of Plasmodium), the oocyst bursts, releasing sporozoites into the body cavity of the mosquito, from which they travel to and invade the mosquito salivary glands. The cycle of human infection re-starts when the mosquito takes a blood meal, injecting the sporozoites from its salivary glands into the human bloodstream. PLANKTON - protista floating on the oceans and can be divided into: • Phytoplankton - plant-like unicellular algae • Zooplankton - bacteria and animal unicellular protozoans FUNGI SOME LIVE IN A SYMBIOTIC RELATIONSHIP, EG LICHEN, AND MYCORRHIZAE Lichen is the mutualistic symbiotic relationship between an algae and a fungus. Like all fungi, lichen fungi require carbon as a food source; this is provided by their symbiotic algae that are photosynthetic. The algae require a moist environment to grow in and this is provided by the fungus. Mycorrhizal fungi and plant roots form a mutualistic relationship Mycorrhizal fungi gain glucose from the plant and the plant gains nutrients in return. The white hyphal tissue shows the increased surface uptake area provided by the fungus. Fungi form symbioses with about 90% of all plants, including tomatoes, onions and maize. Bread mould reproduces asexuallly by means of spores.
