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Summary IGCSE-Biology-Variety of organisms
IGCSE-Biology-Variety of organisms: Summary if the IGCSE content on Variety of organism (Triple award incuded)
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Variety of organismsA cell is the basic structural unit of living organisms.For it to be a living organism it needs to do the 8 life
processes:
Organisms are put into groups, called kingdoms. Members of each kingdom are
descended from a common ancestor.There are 5 kingdoms:
VIRUSES:
Viruses are not considered living organisms. They do not respire, excrete, move,
grow or respond to their environment. Viruses are not made of cells. We consider
them as particles, with DNA enclosed in a protein coat. They are much smaller than
cells. Viruses are parasites. They can only reproduce inside other cells, called host
cells.(They can even infect bacteria). When inside host cells, they can reproduce
rapidly, which destroys the host cell. Because they damage cells, they make their host
ill. Viruses are considered pathogens. Viruses, some bacteria, fungi and protists can
be pathogenic. plasmodium - causes malaria.
Plants Animals Fungi Protoctists Bacteria
Multicellular or Single Multicellular Multicellular Both Single Single
celled?
Does it have a nucleus? Yes Yes Yes Yes No
Do they have chloroplasts Yes No No Some Some have chlorophyll
for photosynthesis?
How does it obtain food for Photosynthesis Eating Saprotrophic Photosynthesis Photosynthesis / feed on
energy? nutrition other organisms
Does it have a cell wall? Yes - made No Yes, Made of Some Yes made from
from cellulose chitin peptidoglycan
How do they store As starch or As glycogen As glycogen Some have flagella to
carbohydrates? sucrose move
Circular DNA. They have a
Unique features: Can move from Some have a Some have single chromosome of
place to place ‘hyphal cells similar to DNA, free in the
Has nervous structure’ plants cytoplasm.
coordination. Others Bacteria are unicellular,
(Amoeba) have but they can group
cells similar to together to form a colony
animals. Bacteria reproduce rapidl
- by a process called
binary fission.
Examples: Maize or Human and Mucor Cholera Lactobacillus bulgaricus -
Legumes Mosquito Yeast (single Amoeba used in producing yoghur
celled) Pneumococcus - causes
pneumonia
WHAT IS YEAST?
, Yeast is a unicellular fungi. One yeast cell can perform all life functions. Yeast is very useful in
biotechnology.
It can be used in baking (making bread), and brewing (making beer).
Yeast can respire aerobically - using oxygen:
Glucose + Oxygen → Carbon dioxide + Water
And anaerobically:
Glucose → Ethanol + carbon dioxide
WHAT ARE MUSHROOMS? Mushrooms are part of the fungi kingdom. These are the reproductive
structure of the organism, called a fruiting body.
WHAT ARE MOULDS? Moulds are similar to mushrooms, but instead of
having a fruiting body, they have spores. These are carried in the air and
land on food. A hypha grows out of the spore, and branches off. This
continues until it grows into a mycelium of hyphae, and covers the food. A
common form of mould is Mucor. Hyphae have cell walls surrounding their
cytoplasm, and the cytoplasm contains many nuclei. The hyphae are not
divided up into separate cells.
Hyphae secrete extracellular digestive enzymes onto food,
which breaks it down into soluble sugars, which are absorbed
by the mould.This is called saprotrophic nutrition - where
digestion occurs outside of the organism.
WHAT ARE DECOMPOSERS? Decomposers play an important role of the recycling of carbon.
Decomposers: Organisms that feed by breaking down the dead remains of other organisms. These
include bacteria and fungi - and are also called saprotrophs
Cells are the basic structural unit of living organisms. In multicellular organisms, cells are usually
specialised, meaning they have a specific function which they are adapted to.
STEM CELLS:
Cell differentiation is the process where cells become specialised to carry out a specific function. This
occurs during the development of an embryo. A stem cell is an undifferentiated cell, which then
differentiate to become specialised. There are 2 types of stem cells in humans:
- Embryonic stem cells - can differentiate into any type of cell. Research and experiments are
being carried out on embryonic stem cells, from unused embryos donated from fertility clinics.
- Adult stem cells - adult bone marrow stem cells can only become a limited number of cells.
Stem cell therapy is the use of stem cells to treat a disease, or repair damaged tissues.
Eukaryotic cells are
cells which contain a
nucleus. Plant and
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