Transcript Patterns_In_Nature

Patterns in Nature
Cell theory
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Cells are the smallest living units of
organisms
All cells come from pre-existing cells.
Each organism is made of one or more
cells.
Evidence to support cell theory
Cell theory was formulated over a period of
about 300 years in parallel with the development
of the microscope. Microscopes enabled scientists
to make observations of tissues from
organisms. As microscopes
improved scientists began to study
the internal structure of cells and
identify cell organelles.
Development of Cell Theory
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1590 The first compound (two lens) microscope
was made by Hans and Zacharias Janssen.
1665 Robert Hooke studied thin slices of cork
under the microscope and described what he saw
as small boxes or cells.
1676 Anton van Leeuwenhoek, saw
microorganisms under the microscope when he
viewed a few drops of pond water.
Development of Cell Theory
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1824 Frenchman Henri Dutrochet suggested that
all organisms are composed of cells.
1827 Scottish botanist, Robert Brown discovered
and described the nucleus in plant cells.
1838 German biologists Schleiden and Schwann
advanced the idea that all organisms are made of
cells.
1859 German biologist Rudolph Virchow stated
that all cells divide
The light compound microscope
The light compound microscope uses light to view
specimens. It has two lenses.
 Objective lens: is placed over the microscope
slide containing the specimen. It collects light
passing through the object and forms a magnified
image of it.
 Ocular lens (eyepiece): is placed at the top of the
barrel. It collects the magnified image from the
objective lens and further magnifies this image.
Electron microscope
The electron microscope was developed in the
1930s and uses a beam of electrons instead of
light as a source of energy. There are two types
of electron microscope—the transmission
microscope, transmits electrons through the
specimen, and the scanning electron
microscope in which bounces electrons off the
specimen.
Cell Organelles
An organelle is a small structure within a cell that
performs a specific function. Each organelle has a
structure that suits its function. Organelles are
situated in the cytoplasm of cells and include:
- Nucleus & nucleolus
- Vacuoles
- Mitochondria
- Ribosomes
- Endoplasmic reticulum - Golgi bodies
- Lysosomes
Chemicals in Cells
Chemical compounds in cells can be divided into
two groups:
 Organic substances: always contain carbon
atoms. Examples include carbohydrates, lipids
(fats), proteins and nucleic acids
 Inorganic substances: may or may not contain
carbon and are found in living and non-living
things. Examples include water, salts,
phosphates, carbon dioxide and metals such as
potassium.
Volume
Volume is the amount of space occupied by an
object, expressed in cubic units.
Volume
=2x2x2
= 8cm3
2cm
2cm
2cm
Surface area
Surface area is the area of the outer surface of
an object expressed in square units.
SA
=6x2x2
= 24cm2
2cm
2cm
2cm
Surface area to volume ratio
Surface are to volume ratio is the amount of
surface area of an object compared with its
volume.
SA : V
= 24 : 8
=3:1
2cm
2cm
2cm
Surface area to volume ratio
Substances move into and out of cells across the
cell membrane. The cell membrane covers the
surface of the cell and therefore has a surface area.
The contents of the cell occupy a space or volume.
The ratio of SA : V influences the rate at which
substances can move into and out of the cell.
Surface are to volume ratio
As objects become larger their SA : V ratio
decreases. Cells are small because this keeps their
SA : V ratio high. This in turn ensures that transport
of substances across the surface area of the cell is
fast enough to service the metabollic activities in
the volume of the cell.
Cell membrane
Diffusion
Diffusion is the movement of a substance from
where it is more concentrated to where it is less
concentrated.
Osmosis
Osmosis is diffusion
of water across a
semi-permeable
membrane from an
area where it is at a
greater
concentration to an
area where it is
less.
Autotrophs and heterotrophs
Plants are autotrophs which means they are able to
make organic materials from inorganic materials.
They do this by the process of photosynthesis. Other
organisms, such as animals and fungi, that depend
directly or indirectly on the organic compounds
produced by producers are called heterotrophs.
Photosynthesis
Photosynthesis can be
described using a
word equation:
sunlight
water +
carbon
dioxide
oxygen + glucose
Plant structures & photosynthesis
What structures ensure that plants have a ready
supply of the materials needed for photosynthesis?
Leaves
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Flat shape provides a large surface area exposed
to sunlight
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Stomata provide access into the leaf for CO2
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Chloroplasts trap the energy of sunlight
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Xylem and phloem vessels transport materials to
and from the leaves
Plant structures & photosynthesis
Stems
 Xylem vessels give rigidity to stem and transport
water and minerals from the roots to the rest of
the plant
 Branching of stems allows layers of leaves at
different levels thereby increasing total area
available for sunlight
 Phloem transports products of photosynthesis via
the stem to the rest of the plant
Plant structures & photosynthesis
Roots
 Tap water and minerals salts
 Root hairs give a large surface area to volume
ratio and this increases the area available for
absorption of water and mineral salts.
Leaves, stems and roots therefore combine to
provide the sunlight energy, carbon dioxide and
water that plants need for photosynthesis.
Mammalian Digestion
In heterotrophic organisms the digestive system
provides the means by which nutrients are taken in
and broken down. Large insoluble food molecules
are converted into small soluble ones that can be
absorbed and made available to the body cells.
Mammalian teeth
The function of teeth is to physically break down food
into smaller pieces and so increase the surface area
for enzyme activity
(chemical breakdown).
Humans have four
types of teeth: incisors,
canines, premolars
and molars.
Mammalian teeth
Incisors are flat sharp teeth for cutting and biting.
On either side of the four incisors are two canines,
which are adapted for ripping and tearing food.
Premolars and molars are on either side of the
canines and are used for grinding and crushing food.
Carnivore v’s herbivore
Exchange and transport in
multicellular organisms
Multicellular organisms need specialised systems to:
 Obtain nutrients (digestive system)
 Exchange gases with the external environment
(respiratory system)
 Distribute gases and nutrients to cells (circulatory
system)
 Remove cellular wastes (excretory system)
Gas exchange
Gases exchange across the surface of cells all the
time. Oxygen moves into cells and carbon dioxide
moves out. Surfaces where gases enter and leave
the body are called respiratory surfaces. Their
characteristics include:
 All living cells must be moist for gas exchange to
occur. Oxygen and carbon dioxide are dissolved
in water before they diffuse across respiratory
surfaces
Gas exchange
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Respiratory surfaces have a large surface area to
maximise diffusion
Respiratory surfaces have a good blood supply to
carry oxygen to body cells
Respiratory surfaces are thin so that gases can
quickly move into the blood
Different organisms have different strategies for
exchanging gases.
Gas exchange in
mammals
Mammals have lungs.
The respiratory surface
of the alveoli, where
most gas exchange
occurs are protected
within the body.
Alveoli
Gas exchange in frogs
Most amphibians have soft moist skin with an
extensive blood capillary network just below the
surface. As a result gas exchange can occur
directly through the skin. Most carbon dioxide is lost
through the skin.
A frog’s lungs consist of a pair of hollow sacs.
Frogs
first take air into a space behind the mouth called
a buccal cavity.
Gas exchange in frogs
This is separated from the lung by a glottis which
opens and closes to control the movement of air into
and out of the lung.
Gas exchange in fish
Fish need to obtain their oxygen from water. Gills
are the respiratory surfaces fish use for exchanging
dissolved gases with the water around them.
Gas exchange in fish
Gills are protected by bony plates and are
constructed of many thin stacked layers that provide
a large surface area for gas exchange. In addition,
blood capillaries are just inside the surface of the gill
tissue so that diffusion can occur efficiently.
Gas exchange in an insect
Insects have a tracheal system where gases are
transported to and from cells through a network of
fine tubes (tracheae and tracheoles). These tubes
are open to the air at the body surface. The
openings are called spiracles.