Biology 1.2

         The Variety of Living Organisms
       
 Describe the common features shared by organisms within: plants, animals, fungi, bacteria, protoctists and viruses. Also give named examples and their features as follows

Plants

• All plants are multicellular, which means that they are made up of many cells
• Their main distinguishing feature is that their cells contain chloroplasts, and they carry out photosynthesis (where light changes water and carbon dioxide into complex organic compounds)
• One complex organic compound is a carbohydrate called cellulose, and all plant cell walls are made out of this
• Another such carbohydrate compound is starch, which is often found inside plant cells
• Another carbohydrate produced is sucrose, which is transported around the plant and is sometimes stored in fruits, and other plant organs

An example of a plant is:

•       A flowering plant, such as maize, which is a cereal

•       A herbaceous legume, such as peas

Animals

•  They are multicellular organisms like plants, but their cells do not contain chloroplasts and they cannot carry out photosynthesis
• Animals feed by feeding on other animals (carnivores) or plants (herbivores) or both (omnivores)
• Animals can either be vertebrates, with a vertebral column (backbone) or invertebrates, without one
• Animal cells do not have cell walls, which allows their cells to change shape, which is important to allow them to move from place to place
• Movement in animals often involves coordination by a nervous system
• Most animals store a carbohydrate compound in their cells, called glycogen

An example of an animal is:

•      A mammal, such as humans (homo sapiens)

•      An insect, such as the mosquito

Fungi

• Fungi can be multicellular (E.G. toadstools), where they contain multiple cells, or unicellular (yeast) where they consist of only one cell
• They cannot perform photosynthesis and they have no chloroplasts
•  They have cell walls, but they are made out of a chemical called chitin
• Multicellular fungi have fine, thread-like filaments called hyphae, which exist under the soil, and its cytoplasm contains many nuclei, and it is not divided into separate cells. A mushroom or toadstool is the reproductive organ of the fungus
• The whole network of hyphae is what makes up a fungus, and this network is called mycelium
• Moulds feed by absorbing nutrients from dead (and sometimes living) material, so they are found wherever this is present E.G. in soil or decaying fruit
• Spores are the reproductive cell of a fungus, and when a spore lands on a food source, a hypha grows from it, and eventually a mycelium covers the food
• Unicellular fungi feed by extracellular secretion of digestive enzymes onto food material. They then absorb the organic products, and this is known as saprotrophic nutrition

An example of a Fungus is:

• A multicellular fungus, such as Mucor

• A unicellular fungus, such as Yeast

Bacteria

o   Bacteria are unicellular organisms, and they have three basic structures: Spheres (cocci), rods (bacillus) and spirals (spirilli)

• All bacteria have a cell wall (made of polysaccharides and protein), but they do not contain a nucleus. Instead they have a single chromosome (nucleoid) in the cytoplasm
• They also have a ring of DNA in the cytoplasm, called a plasmid, which contains some of the bacterium’s genes. Not all bacteria have plasmids, only 3/4 do
• Some bacteria can swim, and are propelled by corkscrew-like structures called flagella
• Some bacteria contain chloroplasts and can carry out photosynthesis, but most feed off other living or dead organism

An example of a bacterium is:

 

• A rod-shaped (bacillus) bacterium, such as Lactobacillus bulgarius, which is used in the production of yoghurt from milk

• A spherical-shaped (cocci) bacterium, such as Pneumococcus, that acts as a pathogen and causes Pneumonia

Viruses

• All viruses are parasites, and can only reproduce within living cells. The cell in which the virus lives and reproduces is called the host
• Viruses are small particles (smaller than bacteria), and they can live in and infect plants, animals and even bacteria
• They have a wide variety of shapes and sizes, and have no cellular structure, since they are not made up of cells
• A virus particle has no nucleus or cytoplasm, and is composed of a core of genetic material (either DNA or RNA) surrounded by a protein coat
• The genetic material only consists of a few genes, and that is all that is needed for the virus to reproduce inside the host
• Sometimes a membrane called an envelope may surround a virus, but the virus does not produce this and it is stolen from the surface membrane of the host
• They do not feed, respire, excrete, move, grow or respond to stimuli
• They do not carry out any of the normal characteristics of living organisms except reproduction
• A virus reproduces by entering a host cell (via lock and key) and by taking over the host cell’s genetic machinery, and commanding it to produce more viruses identical to itself. After many viruses are made, the host cell dies and the particles infect more cells

An example of a virus is:

 

• A virus that infects plants, such as the Tobacco Mosaic Virus, that interferes with the tobacco plant’s ability to make chloroplasts, causing mottled patches to develop on the leaves

• A virus that infects animals, such as the Human Immunodeficiency Virus (HIV) which weakens the immune system, and eventually causes Acquired Immunodeficiency Disease Syndrome (AIDS)

Protoctists

• These are microscopic unicellular organisms
• They can have features like an animal cell, or contain chloroplasts and are more like a plant cell
• Some protoctists are pathogens, and can cause diseases
• Some can have cell walls

An example of a protoctist is:

• A protoctist that has animal cell features, such as an Amoeba, that lives in pond water

• A protoctist that has chloroplasts like a plant cell, such as Chlorella

• A protoctist that is a pathogen, such as plasmodium, which causes the disease malaria