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The organisation of living beings
All living things have certain characteristics:
Biology is the study of living things, which are often called organisms. Living
organisms have several features or characteristics which make them different
from objects which are not alive.
1 They reproduce.
2 They feed.
3 They breath – that is, they release energy from their food, often by combining it
with oxygen.
4 They grow.
5 They excrete – that is, they get rid of substances which they do not want.
6 They move.
7 They are sensitive – that is, they can sense and respond to changes in their
surroundings.
8 They are made of cells.
Fig. 1 Typical animal and plant cells
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Let’s make a comparison between animal and plant cells
Similarities
1 Both have a cell surface membrane surrounding the cell.
2 Both have a cytoplasm.
3 Both contain a nucleus.
4 Both contain mitochondria.
5 Both contain endoplasmic reticulum.
6 Both contain ribosomes.
Differences
Plant cells
Animal cells
Have a cellulose cell wall outside cell
surface membrane
No cell wall
Often have chloroplasts containing
chlorophyll
No chloroplasts
Often have very large vacuoles,
containing cell sap
Only have small vacuoles
Often have starch granules
Never have starch granules;
sometimes have glycogen granules
Often regular shape
Often irregular shape
Animal and plant cells obtain their food in different ways.
Plants make their own food, so their cells contain chloroplasts. Starch granules
store some of the food they make. This is made easier if their cells do not have a
rigid wall.
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There is a division of labour between cells.
A large organism such as yourself may contain many millions of cells, but not all
the cells are alike. Many cells specialize in some of the functions of living cells
and they do it better than other cells do. Muscle cells, for example, are specially
adapted for movement.
Similar cells are grouped to form tissues.
A group of cells which specialize in the same activity is called a tissue. For
example: these cells make enzymes to help to digest food.
Fig. 2 Schematic tissue
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An organ contains tissues working together
All the tissues in the stomach work together, although they each have their own job
to do. A group of tissues like this make up an organ. The stomach is an organ.
A group of organs, in turn, may become a system or an apparatus? The two terms
are not synonymous: look at figures 3a and 3b and try to discover the difference.
to nose
mouth
cavity
to nose
to ears
mouth
cavity
pharynx
mouth
salivary
gland
to lungs
pharynx
mouth
salivary
gland
to lungs
esophagus
liver
to ears
esophagus
gallbladder
stomach
stomach
pancreas
small
intestine
small
intestine
large
intestine
large
intestine
anus
anus
Fig 3a, 3b Compare these two figures and try to learn the name of the organs
The stomach and the other organs in fig. 3a are directly connected to each other to
form the gastrointestinal tract or gut. All the organs are in anatomical contact to form
the animal’s alimentary canal or apparatus. The organs in fig. 3b make up the
digestive system because they aren’t always anatomically connected but they
collaborate for the same function. For example you can only say nervous system.
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About positions
Now it’s time to look at an anatomical model of the human body.
We have to learn something about the positions of the various organs of the
digestive system.
Fig. 4
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About positions
In this model, the skin, the muscles and parts of the thoracic wall have been removed
in order to make the internal organs visible. The diaphragm subdivides our model in
two cavities. In the upper zone, we find the thoracic cavity, in the lower zone lies the
abdominal cavity. Now, have a look at the position of the different organs, going
from top to bottom and according to their site within each cavity.
Upper cavity:
Right
Middle
Left
LUNG
LUNG
Below the lungs we will find
HEART
just a little to the left
diaphragm
Lower cavity:
LIVER
STOMACH
under the liver:
GALL BLADDER
PANCREAS
posterior to the stomach
Right KIDNEY
Left KIDNEY
SMALL AND LARGE INTESTINE
SPLEEN
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If we make a transverse section of the body (from above) we can see:
Sternum
Right lung
Left lung
Heart
Chest
Spinal column
Fig. 5a Superior transverse section.
Aorta
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The gastrointestinal tract has a uniform general
histology with some differences which reflect the
specialization in functional anatomy.
Stomach
Intestine
Pancreas
Liver
Spleen
Right kidney
Left kidney
Spinal column
Fig.5b Inferior transverse section seen from above
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Fig.5c Inferior transverse section seen from above
Webquest: Now go to the sites below and, working in pairs, try to describe
the organs using all the new terms.
www.innerbody.com/image/digeov.html
www.kidshealth.org/kid/body/digest_noSW.html
www.kidshealth.org/parent/general/body_basics/digestive.html
www.vivo.colostate.edu/hbooks/pathphys/digestion/index.html
www.bbc.co.uk/ www.digestive.niddk.nih.gov www.enchantedlearning.com
http://training.seer.cancer.gov/module_anatomy/unit1