In this video we are going over some of the basic functions essential for life.
Based on cell theory all living things have a cellular structure, they are made up of
one or more cells.
All forms of life from unicellular bacteria to the large blue whale all share the same
functional characteristics of life.
These characteristics can be remembered by the Mnemonic MR H GREN.
This stands for: Metabolism, Response, Homeostasis, Growth, Reproduction, Excretion and Nutrition.
One of the essential functional characteristic of life is metabolism.
All cells carry out many chemical reactions that are essential for life, metabolism is
the web of all these chemical reactions occurring within cells and organisms.
These include chemical reactions that are catabolic, those that break down compounds,
such as the breaking down of glucose into energy in cellular respiration.
These chemical reactions can also be anabolic, those that are building up and are involved
in the synthesis of compounds, such as the production of proteins and lipids.
Viruses lack metabolism, this is one of the reasons they are not considered living, as
metabolism is considered a characteristic of life.
Another essential functional characteristic of life is response to stimuli, sometimes
referred to as sensitivity.
All living things, whether unicellular bacteria or multicellular complex organisms, are able
to respond to internal and external stimuli.
There is a range of stimuli organisms can respond to such as light, chemical, pressure
and temperature.
In small invertebrates like slaters, the stimulus could invoke a movement that leads them out
of the light.
In plants it can invoke growth towards the light.
In unicellular organisms such as cyanobacteria it can cause movement towards better light
conditions.
These are all examples of a response to the stimulus: light.
Homeostasis is another essential functional characteristics of life.
Living things are able to maintain and regulate their internal environments within a certain
range, such as water levels, pH levels or internal temperature despite changes in their
external environment.
Another essential functional characteristic of life is Growth.
All living things are able to grow and develop.
Growth means that they are able to increase in size over time.
Develop means they are able to transform over time, this allows the young of a species to
develop to have the same features as the adult form.
Reproduction is another essential functional characteristic of life.
All living things produce offspring, this may be through asexual or sexual reproduction.
Asexual reproduction through binary fission or mitosis involves just one parent creating
offspring that are genetically identical to the parent.
Sexual reproduction involves the fusion of sex cells from two parents creating offspring
that are genetically unique.
Excretion is another essential functional characteristic of life.
Living organisms excrete waste products.
In unicellular organisms this occurs through the cell membrane, in plants it can be through
the leaves and roots.
Nutrition is another essential functional characteristic of life.
Living organisms require a source of energy to fuel the metabolic activities also required
for life.
This can be through absorption of organic matter, or by synthesising organic molecules
which is what occurs in photosynthesis.
Unicellular organisms are organisms that consist in their entirety of a single cell, where
with this single cell are able to live an independent life carrying out all the functions
of life.
Paramecium is an example of a heterotrophic unicellular organism, that carries out all
the functions required for life.
Paramecium contain enzymes within their cytoplasms that enable them to digest food particles.
They are heterotrophic and eat smaller uncellular organisms by engulfing them through the oral
groove.
Solids are then excreted through an anal pore, liquids through contractile vacuoles.
Paramecium are covered in small hairs called cilia, these cilia allow them to move around
in response to changes in the environment, this is an example of their responsiveness.
Homeostasis in Paramecium is maintained by the movement of materials through the cell
membrane, such as the diffusion in and out of gases like O2 and CO2, or to maintain water
levels, excess fluid is removed via the cell membrane through vacuoles.
Paramecium grow until they reach a size that affects their surface area to volume ratio
where they divide via asexual reproduction into two smaller unicellular paramecium (reproduction).
Two individuals can also fuse before splitting, in a form of sexual reproduction.
Chlamydomonas is an example of a unicellular autotroph, in other worlds a single-celled
photosynthetic organism, that is able to carry out all the functions of life.
Chlamydomonas have chlorophyll pigments within the chloroplast that produce organic molecules
(sugars) through the chemical reactions involved in photosynthesis.
This is also how they get their nutrition, as they are making their own food through
the process of photosynthesis.
Diffusion allows the excretion of waste products such as oxygen from photosynthesis through
the cell membrane out into the environment around them.
They have a pigment eye spot that can detect bright light, and they have flagella that
enable them to move towards the light.
They have contractile vacuoles that are able to move water out through the cell membrane
to maintain stable water levels within the cell.
They grow by absorbing minerals from the environment around them and through photosynthesis.
They continue to grow until they reach a size that affects their surface area to volume
ratio where they divide via asexual reproduction into two smaller unicellular Chlamydomonas.
The nuclei can also fuse and then divide in a form of sexual reproduction.
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