BIOL1001 Lecture Notes - Lecture 3: Homeostasis, Smallest Organisms

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2 Aug 2016
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Lecture 3
All living organisms share several key characteristics or
functions: order, sensitivity or response to the
environment, reproduction, growth and development,
regulation, homeostasis, and energy processing.
When viewed together, these eight characteristics serve
to define life.
Organisms are highly organized, coordinated structures
that consist of one or more cells.
Even very simple, single-celled organisms are remarkably
complex: inside each cell, atoms make up molecules;
these in turn make up cell organelles and other cellular
In multicellular organisms , similar cells form tissues.
A toad represents a highly organized structure consisting
of cells, tissues, organs, and organ systems.
Plants can grow toward a source of light, climb on fences
and walls, or respond to touch.
Even tiny bacteria can move toward or away from
chemicals or light.
Movement toward a stimulus is considered a positive
response, while movement away from a stimulus is
considered a negative response.
The leaves of this sensitive plant will instantly droop and
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fold when touched.
Single-celled organisms reproduce by first duplicating
their DNA. They then divide it equally as the cell prepares
to divide to form two new cells.
Multicellular organisms often produce specialized
reproductive germline cells that will form new individuals.
When reproduction occurs, genes containing DNA are
passed along to an organism's offspring.
These genes ensure that the offspring will belong to the
same species and will have similar characteristics, such
as size and shape.
Although no two look alike, these kittens have inherited
genes from both parents and share many of the same
All organisms grow and develop following specific
instructions coded for by their genes.
These genes provide instructions that will direct cellular
growth and development, ensuring that a species' young
will grow up to exhibit many of the same characteristics
as its parents.
Even the smallest organisms are complex and require
multiple regulatory mechanisms to coordinate internal
functions, respond to stimuli, and cope with
environmental stresses.
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Two examples of internal functions regulated in an
organism are nutrient transport and blood flow.
Organs perform specific functions, such as carrying
oxygen throughout the body, removing wastes, delivering
nutrients to every cell, and cooling the body.
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