Zusammenfassung der Ressource
Biology 3a
- Osmosis
- Osmosis is a Special
Case if Diffusion
- Osmosis is the movement if water
molecules across a partially
permeable membrane from a region
of high water concentration to a
region of low water concentration
- A partially permeable membrane is just
one with very small boles in it. So small
that only tiny molecules (like water) can
pass through them, and bigger molecules
can't
- The water molecules usually pass
both ways through the membrane
during osmosis. This happens
because water molecules move
about randomly all the time
- But because there are more water molecules on
one side than on the other, there's a steady net flow
of water into the region with fewer water
molecules, i.e. into the stronger sugar solution
- This means the strong sugar solution gets more
dilute. The water acts like it's trying to "even up" the
concentration either side of the membrane
- Osmosis is a type of diffusion -
passive movement of water
particles from an area of high
water concentration to an area
of low water concentration
- Water moves into
and out of cells by
osmosis
- Tissue fluid surrounds the cells in the body - this is basically just water
with oxygen, glucose and other stuff dissolved in it. It's squeezed out of
the blood capillaries to supply the cells with everything they need
- The tissue fluid will usually have a different concentration
to the fluid inside a cell. This means that water will either
move into the cell, or out of the cell, by osmosis
- If a cell is short of water, the solution inside
will become quite concentrated. This usually
means the solution outside is more dilute, and
so water will move into the cell by osmosis
- If a cell has lots of water, the solution inside will
be more dilute, and water will be draw out of
the cell and into the fluid outside by osmosis
- Osmosis
experiment
- You cut up potato into individual cylinders, and you
get some beakers with different sugar solutions in
them. One should be pure water, another should be a
very concentrated sugar solution. Then you can have
a few others with concentrations in between
- You measure the length of the cylinders, then leave a few cylinders in each beaker for half an
hour or so. Then you take them out and measure their lengths again. If the cylinders have drawn
in water by osmosis, they'll he a bit longer. If water has been drawn out, they'll have shrunk a bit
- Gas and Solute
Exchange
- Substances move by
diffusion, osmosis and
active transport
- 1) Life processes need
gases or other dissolved
substances before they
can happen
- 2) For example, for photosynthesis to
happen, carbon dioxide and water
have to get into plant cells and for
respiration to take place, glucose and
oxygen both have to be inside the cell
- 3) Waste substances also need to move out of
the cell so that the organism can get rid of them
- 4) These substances move where they need to
be by diffusion, osmosis and active transport
- Diffusion is where particles move from an area of high concentration to an
area of low concentration. For example, gases can just just diffuse through
one another, like a smell spreading through a room. Alternatively, dissolved
particles can diffuse in and out of cells through cell membranes
- Diffusion and osmosis both involve stuff moving from an
are of high concentration to an area of lower
concentration. Sometimes substances need to move in the
other direction - which is where active transport comes in
- 5) In life processes, the gases and dissolved substances
have to move through some sort of exchange surfaces.
The exchange surface structures have to allow enough of
the necessary substance to pass through
- 6) Exchange surfaces are ADAPTED
to maximise effectiveness
- They are thin, so
substances only have a
short distance to diffuse
- They have a large surface
are so lots of a substance
can diffuse at once
- Exchange surfaces in animals have
lots if blood vessels, to get stuff
into and out of the blood quickly
- Gas exchange surfaces in animals are often
ventilated too - air moves in and out
- 7) Exchanging substances get more difficult in bigger and more
complex organisms - the place where the substances are
needed ends up being a long way away exchange surfaces
- The structure of leaves
lets gases diffuse in
and out of cells
- Carbon dioxide diffuses into the air spaces within the leaf, then
it diffuses into the cells where photosynthesis happens. The
leaf's structure is adapted so that this can happen easily
- The underneath of the leaf is the exchange
surface. It's covered in little holes called stomata
which the carbon dioxide diffuses through
- Oxygen (produced in photosynthesis)
and water vapor also diffuses in and
out through the stomata
- The size of the stomata are controlled by the guard
cells. These close the stomata if the plant is loosing
water faster than it is being replaced by the roots.
Without these guard cells the plant will soon wilt
- The flattened shape of the leaf increases the area of
this exchange surface so that it's more effective
- The walls of the cells inside the leaf form another
exchange surface. the air spaces inside the leaf
increase the area of this surface ares so there's
more chance of carbon dioxide to get into the cells
- The water vapor evaporates from the cell inside the
leaf. Then it escapes by diffusion because there's a lot
of it inside the leaf and less of it in the air outside.
Evaporation is quickest in hot, dry, windy conditions
- The Breathing
System
- The lungs are
in the thorax
- The thorax is the top
part of your 'body'
- It's separated from the lower
part of the body (the
abdomen) by the diaphragm
- The lungs are like big pink sponges
and are protected by the ribs
- The air that you breath in goes through
the trachea. This splits into two tubes
called the bronchi (each one is called 'a
bronchus'), one going into each lung
- The Bronchi splits into
progressively smaller
tubes called bronchioles
- The bronchioles finally ends at small bags called
alveoli where the gas exchange takes place
- Ventilation is
breathing in and out
- Breathing in
- Intercostal muscles
and diaphragm
contract
- Thorax volume
increases
- This decreases pressure
and draws air in
- Breathing out
- Intercostal muscles
and diaphragm relax
- Thorax volume
decreases
- This increases the pressure,
so air is forces out
- Artificial ventilators
help people to breath
- Ventilators are machines that move air
(often with extra oxygen) into or out of the
lungs, They help people who can't breath by
themselves, e.g. if they're under general
anaesthetic, or have a lung injury or disease
- They used to be a giant case (an 'iron lung') from the neck
to the abdomen, with only the patient's head poking out.
Air was pumped out of the case, pressure dropped, the
lung expanded so air was drawn into the lungs. Air
pumped into the case has the opposite effect, forcing air
out of the lungs. However, they could interfere with the
blood flow to the lower body
- Nowadays , most ventilators work by pumping air into
the lungs. This expands the ribcage - when they stop
pumping, the rubcage relaxes and pushes air back out
of the lungs. This doesn't interfere with the blood flow
but it can occasionally cause damage (e.g. burst
alveoli) if the lungs can't cope with the artificial air flow
- Diffusion Through
Cell Membranes
- Gas exchange happens
in the lungs
- 1) The job of the lungs is to transfer
oxygen to the blood and to remove
waste carbon dioxide from it.
- 2) To do this the lings contain
millions of little air sacs called alveoli
where gas exchange takes place
- 3) The alveoli are
specilised to maximise the
diffusion of oxygen and
carbon dioxide. They have:
- An enormous
surface area
- A moist lining for
dissolving gases
- Very thin walls
- A good blood
supply
- The Villi provide a
really big surface area
- 1) The inside of the
small intestine is
covered in millions of
these tiny little
projections called villi
- 2) they increase the surface area in a big
way so that digested food is absorbed
much more quickly into the blood
- Notice they have
- A single layer of
surface cells
- A very good blood supply
to assist quick absorption
- Active Transport
- Root hairs are
specilised for absorbing
water and minerals
- The cells on the surface
of plant roots grow into
long "hairs" which stick
out into the soil
- This gives the plant a
big surface area for
absorbing water and
minerals from the soil
- Most of the water and
mineral ions that get into
a plant are absorbed by
the root hair cells
- Root hairs take in
minerals using
active transport
- The concentration of minerals is
usually higher in the root hair
cell than in the soil around it
- So normal diffusion doesn't
explain how minerals are taken
up into the root hair cells
- They should go the other way
if they follow if they followed
the rules of diffusion
- The answer is that a conveniently
mysterious process called "active
transport" is responsible
- Active transport allows the plant to absorb
minerals from a very dilute solution, against
a concentration gradient. This is essential
for it's growth. But active transport needs
energy from respiration to make it work
- Active transport also happens
in humans, for example in
taking glucose from the gut
and from the kidney tubules
- We need active transport
to stop us starving
- Active transport is used in the
gut when there is a low
concentration of nutrients in
the gut but a high concentration
of nutrients in the blood
- When there is a higher
concentration of glucose
and amino acids in the
gut the diffuse naturally
into the blood
- But - sometimes there's a lower
concentration of nutrients in the
gut then there is in the blood
- This means the concentration
gradient is the wrong way
- Active transport allows nutrients to be taken
into the blood despite the fact that the
concentration gradient is the wrong way round
- Water Flow
Through Plants
- Flowering plants have 2 separate types of vessel - Xylem and
Phloem - for transporting stuff around. Both types of vessel
go to every part of the plant, but they are totally separate
- Phloem Tubes
transport food
- Made of columns of living cells with small holes
in the ends to allow stuff to flow through them
- They transport food substances (mainly
dissolved in sugars) made in the leaves to
growing regions (e.g. new shoots) and storage
organs (e.g. root tubers) of the plant
- The transport goes
in both directions
- Xylem tubes
take water up
- Made of dead cells joined end to
end with no end walls between
them and a hole down the middle
- They carry water and minerals
from the roots to the stem and
leaves in the transpiration stream
- Transpiration is the loss
of water from the plant
- Transpiration is caused by the
evaporation and diffusion of
water from inside the leaves
- This crates a slight shortage of water in the leaf,
and so more water is drawn from the rest of the
plant through the xylem vessels to replace it
- This in tern means more water is drawn up from
the roots, and so there's a constant
transpiration stream of water through the plant
- Transpiration is just a side-effect of the way
leaves are adapted for photosynthesis. They have
to have stomata in them so that gases can be
exchanged easily. Because there's more water
inside the plant then in the air outside, the water
escapes from the leaves through the stomata
- Circulatory System
- The Heart
- The double
circulatory system
- Humans have a double
circulatory system - two
circuits joined together
- The first one pumps deoxygenated
blood to the lungs to take in oxygen.
The blood is then returned to the heart
- The second one pumps oxygenated
blood around all the other organs of
the body. The blood gives up it's oxygen
at the body cells and the deoxygenated
blood returns to the heart to be
pumped out to the lungs again
- The heart contracts to pump
blood around the body
- the heart is a pumping organ that keeps the
blood flowing around the body. The walls of
the heart are mostly made of muscle tissue