Nature and Variety of Living Organisms

Nature and Variety of Living Organisms
For something to be 'living, it must fulfil the criteria of MRS H GREN. If something does
not carry out all of these processes, it is dead or non-living. For example, a virus is a non-
living particle. The acronym of MRS H GREN stands for:
Movement
Respiration
Sensitivity
Control
Growth
Reproduction
Excretion
Nutrition
Organisms have to have food to provide energy, which is needed for life processes
(movement, respiration and excretion).
Plants use sunlight, carbon dioxide and water to produce both oxygen and glucose in
photosynthesis. Animals consume other organisms to obtain energy, by breaking down
complex molecules into simple molecules (which is called digestion).
An autotroph is an organism which creates its own food for energy, A heterotroph is
where an organism that obtains food from a range of different sources.
Respiration is a chemical reaction that happens in all living organisms, where energy is
released from glucose in either oxygen (aerobic respiration) or in the absence of oxygen
(anaerobic respiration). This results in the creation of carbon dioxide and water as waste
products. Energy is transferred in the form of ATP.
There are five kingdoms to classify living organisms:
1 . Animals
2. Planta
3. Fungi
4. Protoctists
5. Prokaryotes
The first four kingdoms can also be grouped as one; as eukaryotes. A eukaryotic
organism is multicellular or single-celled, with cells containing a nucleus that has a
distinct membrane.

Prokaryotic organisms are in a separate kingdom and are different from eukaryotes as
they're always single-celled and don't contain nuclei. Their nuclear material is in the
cytoplasm.
Generally, prokaryotes are smaller than eukaryotes.
To differentiate between animal cells and plant cells, you must memorise these key
features of animal cells:
multicellular
contain nucleus, distinct membrane
do not have cellulose cell walls
do not contain chloroplasts
unable to carry out photosynthesis
feed on organic substances made by other living things
store carbohydrates as glycogen
have nervous coordination
can move
A plant cell has these features:
multicellular
contain nucleus with distinct membrane
have cell walls made up of cellulose
cells contain chloroplasts
can carry out photosynthesis
store carbohydrates as starch or sucrose
no nervous coordination

Fungi are another type of cell. Here are the main features of a fungal cell:
usually multicellular
some can be single-celled
made up of thread-like structures (hyphae)
hyphae are made of many nuclei and are organised into mycelium
cells contain a nucleus with a distinct membrane
cells have walls made of chitin
cells don't contain chloroplasts

cannot carry out photosynthesis feed by secreting extracellular digestive enzymes onto food and then absorbing digested molecules some are parasitic (feed on living material) some store carbohydrates as glycogen don't have nervous coordination examples include moulds, yeasts, mushrooms Protoctists are another animal kingdom. Their main features are: diverse kingdom mainly microscopic and single-celled some aggragte into larger forms contain nucleus with distinct membrane some have features that are more animal-cell like some have features that are more plant-cell like some photosynthesise no nervous coordination For prokaryotic cells, the nuclear material is found in cytoplasm, such as bacteria. Bacteria have the following characteristics: microscopic, single celled have a cell wall, membrane, cytoplasm, plasmids contain a circular chromosome of DNA no mitochondria Examples of bacteria: Lactobacillus (rod-shaped, used to produce milk from yoghurt) Pneumococcis (spherical, pathogen, causes pneumonia) Methods of feeding for bacteria: Some photosynthesize Most feed on living/dead organisms If something feeds on dead organic matter, it is called a saprobiont. The term saprotrophic nutrition refers to the secretion of extracellular digestive enzymes onto food and then absorbing digested molecules. A pathogen is any microorganism that causes disease in another organism (e.g. in plants or animals) Many microorganisms are pathogens including: Bacteria Fungi Protoctists Viruses Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protoctists are harmless and do not cause disease However, all viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses) Pathogenic bacteria Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces M. tuberculosis causes tuberculosis (TB) in humans The bacteria infect the lungs, causing a chronic cough and bloody mucus It is a disease often associated with poor hygiene and sanitation

M. bovine in cows can also transmit to humans to cause TB
N. meningitidis causes bacterial meningitis in humans
Very few bacteria can cross the barrier created by the meninges (the tissue that
surrounds the brain and spinal cord) however N. meningitidis crosses this barrier to
cause acute inflammation
Inflammation of the meninges causes symptoms such as fever, headache, neck stiffness
and a characteristic rash
Pathogenic fungi
Fungal diseases are much more common in plants than animals
Cattle ringworm and athletes foot are fungal diseases that exist on the surface of the skin
Fungal diseases in plants tend to be much more serious and can threaten entire crops
Black Sigatoka is a fungal disease in bananas
It spreads through the leaves of the plant, reducing its ability to photosynthesise
The lack of photosynthesis causes parts of the leaf to die; producing black streaks
Eventually, the whole leaf dies
Pathogenic protoctists
Plasmodium falciparum is a protist that causes severe forms of malaria in humans
The parasite is spread by mosquitoes
Infected individuals experience fever, chills and fatigue
P. infestans causes the infamous potato blight
The pathogen is unusual as it has some fungal characteristics
It is transmitted via spores
The first signs of potato blight are small, dark brown marks on the leaves which quickly
increase in size and number
The protist destroys potato and tomato crops leaving them completely inedible
Viruses
Viruses are not usually included in the classification of living organisms as they are not
considered to be alive
This is due to the fact that viruses do not carry out the 8 life processes for themselves
In fact, the only life process they seem to display is reproduction but even to carry out this
process they must take over a host cell’s metabolic pathways in order to make multiple copies
of themselves
Viruses, which have a wide variety of shapes and sizes, all share the following biological
characteristics:
They are small particles (always smaller than bacteria)
They are parasitic and can only reproduce inside living cells
They infect every type of living organism

They have no cellular structure but have a protein coat and contain one type of nucleic
acid, either DNA or RNA
Structure of a typical virus
Examples of viruses include:
The tobacco mosaic virus (TMV) causes discolouring of the leaves on tobacco plants by
preventing the formation of chloroplasts
The HIV virus causes AIDS
The influenza virus causes the ‘flu’
Tobacco mosaic virus
Tobacco mosaic virus (TMV) was the first virus to be isolated by scientists
It is a widespread plant pathogen that infects about 150 species of plants including tomato
plants and cucumber

HIV (Human Immunodeficiency Virus) is a virus that can eventually lead to Acquired
Immunodeficiency Syndrome (AIDS)

Influenza virus
Three different influenza viruses infect humans to cause the flu
Influenza A, influenza B and influenza C infect the cells that line the airways
They cause a high temperature, body aches and fatigue
Influenza A is the virus that causes the most cases of flu globally