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Topic 4: Classification
Different forms of Life.
The evolutionary development of unicellular life forms into multicellular life forms.
Most scientists used to think that all living things had remained the same since the Earth was created. But as they learned more about the different plants and animals, some scientists started learning that species had changed and that new species are being formed. They think that similar species descended from a common ancestor by a process of gradual change. This is the Theory of Evolution. The first person to suggest this theory was Charles Darwin.
Darwin was a British naturalist. In 1831, he set sail on the survey ship HMS Beagle. He travelled around the world and visited many different islands studying wildlife. He was impressed by the huge variety of plants and animals that he found. He brought back a large collection of plants and animals and fossils and studied them. After, he published the book “The Origin of Species”, in which he described how evolution might have taken place. He called it the “theory of natural selection”
From unicellular to multicellular.
The first organisms that appeared on Earth are believed to have been unicellular ones. After millions of years, multicellular organisms started forming.
Unicellular organisms are so small, that their surface area is enough to serve all living purposes
e.g. when a unicellular feeds, it doesn’t need a mouth to do so, but diffusion is enough;
or when the organism breathes, it does so by diffusion through the cell membrane;
or when it excretes, it doesn’t need an excretory system because diffusion through cell membrane is enough.
However, as multicellular organisms started forming, their surface area was much smaller than the volume and hence, they required specified systems to perform the vital functions e.g. a digestive system for feeding, a respiratory system for breathing, an excretory system for excreting wastes, a reproductive system to reproduce (e.g. a human being cannot reproduce by cell division! ! ! ), skeletal system to bring about movement, etc. etc.
Surface area to volume ratio. Work out.
A B
Surface area = length x breath x 6 faces
______
Volume = length x breath x height
______
Surface area to volume ratio = ______
The study of viruses began in 1898 when a Dutch botanist named Martinus Beijerinck realized that something smaller than bacteria can cause disease. He named this particle “virus”, a Latin word meaning ‘poison’. Although viruses have no means of propelling themselves, they can reproduce and have characteristics which are transmitted from 1 generation to the next. However, they cannot do this by themselves because they do not possess all the enzymes necessary for multiplication. They can only reproduce inside the living cell of a host. In so doing, they destroy the cell. For this reason viruses are always associated with disease e.g. small pox, measles, poliomyelitis, common cold, and some plant diseases too.
What do viruses look like?
v Extremely small; can be seen with an electron microscope
v Consist of DNA / RNA surrounded by a protein coat called CAPSID.
v No nucleus, no cytoplasm, no cell organelles, no cell membrane.
References: Biology for you pg. 164; GCSE Biology pg. 311-317
Life Cycle of Viruses.
Viral Diseases.
Viruses do not produce toxins. They cause harm by destroying the cell they invade. When cells are destroyed, they are very likely to be invaded by bacteria and so a secondary infection develops.
Viral diseases:
1. AIDS (Acquired Immune Deficiency Syndrome).
2. Food and Mouth Disease – in cattle
3. Viral Diseases in Plants e.g. Tobacco Mosaic Virus.
A bacterium is said to be a prokaryotic cell i.e. without a true nucleus and no membrane bound organelles. The Kingdom Monera includes bacteria and blue-green algae.
Structure of bacterium.
Each bacterial cell contains a single chromosome consisting of a circular strand of DNA. The chromosome is not enclosed in a nuclear membrane but is coiled up to occupy part of the cell.
Nutrition.
Some bacteria can have chlorophyll and therefore, they photosynthesise.
Others, produce and release enzymes which digest the food outside the cell.
Respiration.
Aerobic bacteria are those bacteria which need oxygen for respiration.
Anaerobic bacteria are those bacteria which do not need oxygen for respiration e.g. those which digest sewage.
Reproduction.
Bacteria reproduce by cell division, or every 20 minutes. Bacterial cells multiply by binary fission; the genetic material is duplicated and the bacterium elongates, constricts near the middle, and then undergoes complete division, forming two daughter cells essentially identical to the parent cell.
Effect of heat.
Some bacteria are killed by
heating. Others are not killed by heating because they produce spores which are resistant to heat. Others survive even very cold temperatures. As you can see there are so many different types of bacteria adapted in different ways.
Important Aspects of Bacteria.
1. Some bacteria are important for recycling nutrients in the environment. These break down (decompose) dead remains of animals by secreting extracellular enzymes on them. These dead bodies start decaying and the nutrients flow back to the soil, to be used up by plants. These bacteria are called saprophytic or decomposers.
2. Some bacteria live in or on other living organisms such that the bacteria and the other organism are both at an advantage. Their relationship is called symbiotic. There are some symbiotic bacteria that live in the alimentary canal of animals. These take food from the products of digestion and in turn digest some foods that are not normally digested by the organism. Example, herbivores have symbiotic bacteria that digest cellulose.
3. Some bacteria are photosynthetic and they use up hydrogen sulphide instead of water.
Harmful aspects of bacteria.
1. Some bacteria are parasitic because they live in or on other organisms harming them as a result of this relationship. These cause diseases or death e.g. Mycobacterium tuberculosis causes the disease tuberculosis in humans, and Salmonella typhimurium causes food poisoning in humans.
g The kingdom Protista includes unicellular organisms.
g These are different from bacteria because they are eukaryotic i.e. they have a nucleus and membrane bound organelles, and also, they feed in different ways from bacteria which are prokaryotic.
g Some protists feed like animals, i.e. they take in solid or liquid food from the surroundings. These are called protozoans e.g. Amoeba and Paramecium.
g Some protists feed like plants, i.e. they photosynthesise. These are called unicellular algae or protophyta.
Amoeba.
It is a protozoan because it feeds by picking up bacteria and other microscopic organisms and digest them.
It moves by flowing its cytoplasm towards the direction it wants to move to.
Chlamydomoonas, Chlorella and Euglena.
They have chloroplasts in their cells and feed like plants by photosynthesis. Also, their cell membrane is enclosed by a cellulose cell wall.
Euglena.
Read “Biology for Life” pg. 22-23
: The organisms in this kingdom are not made up of cells but of microscopic threads called hyphae.
: The hyphae spread through the material on which the fungus is growing and absorb food from it.
: The hyphae grows to become mycelium.
: Mushrooms and toadstoals are the reproductive structures “fruiting bodies” of an extensive mycelium that spreads through the soil or the dead wood on which the fungus is growing.
Structure.
: The hyphae contain cytoplasm.
: In the center of the older hyphae there is a vacuole.
: The cytoplasm contains organelles, lipid droplets, granules of glycogen, and nuclei.
: The hyphal wall may contain cellulose or chitin.
: In some species of fungi there are incomplete cross walls called septa dividing the hyphae into cell like regions but the cytoplasm is free to flow through large pores in these walls.
: In other species there are no cross walls (septa) and there are more than one nucleus in each compartment.
Nutrition.
Saprophytic Parasitic
living on dead organic matter: the hyphae secrete enzymes on organic material and digest it to liquid products which are absorbed in the hyphae. / the hyphae penetrate the tissues of their host plant and digest the cells and their content.Reproduction.
J Fungi release spores from the tips of special hyphae.
J The spores are dispersed in air currents or by other methods.
J When a spore lands on suitable organic matter or on a new host, it germinates to produce a mycelium.
Diagram of Mucor which is a common mould-fungus that grows on bread and other food.
Yeast.
L Not all fungi are large enough for us to see. Mucor is small, but yeast is even smaller. They are ______fungi.
Structure of a yeast.
v Most of the yeasts remain as separate spherical ______and only few form true hyphae.
v They live in the presence of ______e.g. surface of fruits, nectar of flowers etc
Nutrition.
Yeasts contain certain enzymes which can break down sugars by a process called alcoholic ______. This is a form of respiration where sugars are broken down into simpler compounds.
Reproduction.
C Some yeasts reproduce by simple cell ______i.e. the cell divides into 2 complete yeast cells.
C Other yeasts reproduce by a method that is called ______.
C A bud develops on the surface of a yeast ______.
C The ______of the cell then divides into 2, one of which moves into the bud.
C The bud separates and is capable of starting a life of its own as a new ______.
Budding.
Bryophytes (Mosses)
h Mosses are simple land plants.
h Each plant has a slender stem with numerous small leaves arising from it.
h Every leaf does not have specialised cells.
h The inner most cells conduct water and food.
h There are no proper roots, but there are rhizoids which are like multicellular root hairs.
h Mosses reproduce sexually but do not form seeds. The male and female gametes fuse at the tip of a moss plant to produce a spore capsule on the end of a long stalk. The spore capsule opens to release single celled spores which are scattered and grow into new moss plants.
The Ferns
v Ferns are land plants, much larger than bryophytes and more highly developed.
v They are common in damp places of the woods, ravines and rocky crevices. Only deserts and the polar regions have no ferns.
v Ferns are non-flowering plants that grow from spores instead of from seeds.
v Their stems, leaves and roots are very similar to those of the flowering plants.
v The leaves are called fronds.
v Fronds have a single midrib, with small leaflets branching off from either side.
v On the underside of a fertile frond are clusters of brown dots. The dots are called sori (singular sorus). These are made up of many spore cases called sporangia.
v The stem takes the form of a rhizome.
v The stem and leaves have sieve tubes and water conducting cells similar to those in the xylem and phloem and flowering plants.
v Ferns also have multicellular roots with vascular tissue.
Differences between Conifers (Gymnosperms) and Flowering Plants (Angiosperms)
Gymnosperms / AngiospermsThe seeds are not enclosed in an ovary / Seeds are enclosed in an ovary
Spores develop on cones / Spores develop in flowers
No fruit because no ovary / After fertilisation, the ovary develops into a fruit
No vessels in xylem, no companion cells in phloem / Xylem contains vessels, phloem contains companion cells.
Phylum Angiosperms: Flowering Plants.
This phylum includes plants that have seeds formed within the ovaries of flowers and not naked like in the previous phylum conifers. There are two main groups: the moncots and the dicots.
Differences between Dicotyledons and Monocotyledons.
Dicots / MonocotsEmbryo has 2 cotyledons / Embryo has 1 cotyledon
Leaf with net like patterns / Veins are parallel in leaves
Stem with ring of vascular bundles / Stem with scattered vascular bundles
Few groups of xylem in root / Many groups of xylem in roots
A main root with lateral roots / Fibrous root system
Flower parts are mainly in 4’s, or 5’s / Parts usually in 3’s
Often insect pollinated / Often wind pollinated
Example: rose / Example: grass.
1. Invertebrates are animals which do not have a vertebral column.
2. Vertebrates are animals which do have a vertebral column.
The Invertebrates.
[ Phylum Coelenterates (cnidarians)
[ Phylum Flatworms (platyhelminthes)
[ Phylum Roundworms (nematodes)
[ Phylum Segmented worms (annelids)
[ Phylum Molluscs
[ Phylum Arthropods - Insects
[ Phylum Echinoderms
General characteristics of the following groups:
Coelenterates (Cnidarians): have a sac-like body with a single opening surrounded by tentacles armed with stinging cells. They live in a watery environment.
Flatworms (platyhelminthes): due to the absence of a circulatory system, the body is thin and flat to facilitate the diffusion of oxygen. Many are animal parasites.
Roundworms (nematodes): have a long thread-like body, round in cross-section. Some live in soil, but many are plant or animal parasites.
Segmented worms (annelids): have a long segmented body and a digestive tract with a mouth and anus.
Molluscs: have a soft unsegmented body. Most have an external or an internal shell. They live in aquatic or moist environments.
Arthropods: have a segmented body covered by a hard cuticle (exoskeleton) that is shed and replaced by a new one when the animal outgrows it (moulting). They have jointed appendages. The phylum includes Crustaceans, Insects, Myriapods and Arachnids in which the number of legs is a major distinguishing feature.