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Bio IGCSE (1)

Bio IGCSE (1)

1 The nature & variety of living organisms

(a) Characteristics of Living Organisms

Living organisms share the following characteristics:

  1.  Movement - An action by an organism or part of an organism that causes a change in position or place
  2. Respiration - Chemical reactions that break down nutrient molecules in living cells to release energy
  3. Sensitivity - Ability to detect stimuli in their surroundings and to make responses
  4. Homeostasis - The ability to control their internal conditions.
  5. Growth - Permanent increase in size and dry mass by an increase in the number of cells, the cell size or both
  6. Reproduction - Processes that make more of the same kind
  7. Excretion - Removal of toxic materials from organisms. Waste products of metabolism and substances in excess
  8. Nutrition - The taking in of materials for energy, growth and development

   MRS H. GREN - an acronym for the 8 characteristics of the living organisms


(b) Variety of Living Organisms

Eukaryotic Organisms

  • Plants
    • they are multicellular organisms
    • their cells contain chloroplasts to carry out photosynthesis
    • their cells have cellulose cell walls
    • they store carbohydrates as starch or sucrose.
      • Examples include :
      • flowering plants,
      • such as a cereal (for example, maize),
      • and a herbaceous legume (for example, peas or beans).
  • Animals
    • these are multicellular organisms
    • their cells do not contain chloroplasts and are not able to carry out photosynthesis
    • they have no cell walls; they usually have nervous co-ordination and are able to move from one place to another
    • they often store carbohydrate as glycogen. 
      • Examples include :
      • mammals (for example, humans) 
      • and insects (for example, housefly and mosquito)
  • Fungi
    • these are organisms that are not able to carry out photosynthesis; 
    • their body is usually organised into a mycelium made from thread-like structures called hyphae, which contain many nuclei; 
    • some examples are single-celled; 
    • cells walls are made of chitin; 
    • they feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products; 
    • this is known as saprotrophic nutrition;
    • they may store carbohydrate as glycogen. 
      • Examples include:
      • Mucor, which has the typical fungal hyphal structure, 
      • Yeast, which is single-celled.
  • Protoctists
    • these are microscopic single-celled organisms. 
    • some, like Amoeba, that live in pond water, have features like an animal cell, 
    • while others, like Chlorella, have chloroplasts and are more like plants.
      • Example is
      • Plasmodium, responsible for causing malaria.

Prokaryotic Organisms

  • Bacteria
    • these are microscopic single-celled organisms
    • they have a cell wall, cell membrane, cytoplasm and plasmids
    • they lack a nucleus but contain a circular chromosome of DNA; 
    • some bacteria can carry out photosynthesis 
    • but most feed off other living or dead organisms.
      • Examples include 
      • Lactobacillus bulgaricus, a rod-shaped bacterium used in the production of yoghurt from milk,
      • and Pneumococcus, a spherical bacterium that acts as the pathogen causing pneumonia.

Pathogens

Pathogens are disease-causing organisms. Fungi, protoctists, bacteria and viruses can all be classified as pathogens

  • Virus
    • these are not living organisms. 
    • they are small particles, smaller than bacteria; 
    • they are parasitic and can reproduce only inside living cells; 
    • they infect every type of living organism. 
    • they have a wide variety of shapes and sizes; 
    • they have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA.
      • Examples include 
      • the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, 
      • the influenza virus that causes ‘flu’ 
      • the HIV virus that causes AIDS

Bio IGCSE (1)

1 The nature & variety of living organisms

(a) Characteristics of Living Organisms

Living organisms share the following characteristics:

  1.  Movement - An action by an organism or part of an organism that causes a change in position or place
  2. Respiration - Chemical reactions that break down nutrient molecules in living cells to release energy
  3. Sensitivity - Ability to detect stimuli in their surroundings and to make responses
  4. Homeostasis - The ability to control their internal conditions.
  5. Growth - Permanent increase in size and dry mass by an increase in the number of cells, the cell size or both
  6. Reproduction - Processes that make more of the same kind
  7. Excretion - Removal of toxic materials from organisms. Waste products of metabolism and substances in excess
  8. Nutrition - The taking in of materials for energy, growth and development

   MRS H. GREN - an acronym for the 8 characteristics of the living organisms


(b) Variety of Living Organisms

Eukaryotic Organisms

  • Plants
    • they are multicellular organisms
    • their cells contain chloroplasts to carry out photosynthesis
    • their cells have cellulose cell walls
    • they store carbohydrates as starch or sucrose.
      • Examples include :
      • flowering plants,
      • such as a cereal (for example, maize),
      • and a herbaceous legume (for example, peas or beans).
  • Animals
    • these are multicellular organisms
    • their cells do not contain chloroplasts and are not able to carry out photosynthesis
    • they have no cell walls; they usually have nervous co-ordination and are able to move from one place to another
    • they often store carbohydrate as glycogen. 
      • Examples include :
      • mammals (for example, humans) 
      • and insects (for example, housefly and mosquito)
  • Fungi
    • these are organisms that are not able to carry out photosynthesis; 
    • their body is usually organised into a mycelium made from thread-like structures called hyphae, which contain many nuclei; 
    • some examples are single-celled; 
    • cells walls are made of chitin; 
    • they feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products; 
    • this is known as saprotrophic nutrition;
    • they may store carbohydrate as glycogen. 
      • Examples include:
      • Mucor, which has the typical fungal hyphal structure, 
      • Yeast, which is single-celled.
  • Protoctists
    • these are microscopic single-celled organisms. 
    • some, like Amoeba, that live in pond water, have features like an animal cell, 
    • while others, like Chlorella, have chloroplasts and are more like plants.
      • Example is
      • Plasmodium, responsible for causing malaria.

Prokaryotic Organisms

  • Bacteria
    • these are microscopic single-celled organisms
    • they have a cell wall, cell membrane, cytoplasm and plasmids
    • they lack a nucleus but contain a circular chromosome of DNA; 
    • some bacteria can carry out photosynthesis 
    • but most feed off other living or dead organisms.
      • Examples include 
      • Lactobacillus bulgaricus, a rod-shaped bacterium used in the production of yoghurt from milk,
      • and Pneumococcus, a spherical bacterium that acts as the pathogen causing pneumonia.

Pathogens

Pathogens are disease-causing organisms. Fungi, protoctists, bacteria and viruses can all be classified as pathogens

  • Virus
    • these are not living organisms. 
    • they are small particles, smaller than bacteria; 
    • they are parasitic and can reproduce only inside living cells; 
    • they infect every type of living organism. 
    • they have a wide variety of shapes and sizes; 
    • they have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA.
      • Examples include 
      • the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, 
      • the influenza virus that causes ‘flu’ 
      • the HIV virus that causes AIDS