Bio IGCSE (1)
Bio IGCSE (1)
1 The nature & variety of living organisms
(a) Characteristics of Living Organisms
Living organisms share the following characteristics:
- Movement - An action by an organism or part of an organism that causes a change in position or place
- Respiration - Chemical reactions that break down nutrient molecules in living cells to release energy
- Sensitivity - Ability to detect stimuli in their surroundings and to make responses
- Homeostasis - The ability to control their internal conditions.
- Growth - Permanent increase in size and dry mass by an increase in the number of cells, the cell size or both
- Reproduction - Processes that make more of the same kind
- Excretion - Removal of toxic materials from organisms. Waste products of metabolism and substances in excess
- 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:
- Movement - An action by an organism or part of an organism that causes a change in position or place
- Respiration - Chemical reactions that break down nutrient molecules in living cells to release energy
- Sensitivity - Ability to detect stimuli in their surroundings and to make responses
- Homeostasis - The ability to control their internal conditions.
- Growth - Permanent increase in size and dry mass by an increase in the number of cells, the cell size or both
- Reproduction - Processes that make more of the same kind
- Excretion - Removal of toxic materials from organisms. Waste products of metabolism and substances in excess
- 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