TOPIC- CLASSIFICATION KINGDOM FUNGI
Osmosis is important for the
reabsorption water in the colon and the kidneys. This help to maintain the
body's water balance.
Osmosis and plant cells
In an isotonic solution,
plant cells neither lose nor gain water. In a hypotonic solution cells absorb
water, causing the cell membrane to push against the cell wall. The cell is to
be turgid. It does not burst because membrane exerts pressure on the cell wall
restricts additional intake of water. Turgid plants to maintain their shape.
In a hypertonic solution, plant
cells lose water this causes the vacuole to shrink and their cell membrane to
pull away from wall, making the cell flaccid. Such a cell is to be
plasmolyzedand the process plasmolysis.
If a plasmolyzed cell is placed in a hypotonic
solution, it absorbs water and becomes turgid
Osmosis is importantforthe
absorption of water by plant roots. Opening and closing of stomata also depend
on osmosis. When guard cells absorb water the stomata open and when they lose
water the stomata close.
Osmosis and unicellular organisms
Unicellular organisms that live in
fresh water, for example amoeba and euglena, are hypertonic to surrounding so
water enters the organisms by osmosis. These organisms have a contractile
vacuole. The contractile vacuole collects the excess water and removes it from
the cell. This prevents the cells from bursting
Mass flow
Mass flow
is the bulk movement of substances from one region to another due to the
difference in pressure between the two regions. Mass flow occurs within a cell
or along a vessel.
This mode of transport is important
in large complex organisms where substances are required in large amounts and
also have to be transported over large distances.
Examples of systems where mass flow
occurs are:
- The circulatory system (flow of blood) in animals.
- The lymphatic system (flow of lymph) in animals.
- Transport of manufactured food material in plants from the site of manufacture (mostly leaves) to the point of use (all plant parts) through the phloem. This process is called translocation
Differences between diffusion,
osmosis and mass flow
The following table gives a summary
of the differences between diffusion, osmosis and mass flow.
Differences between diffusion,
osmosis and mass flow
Characteristics
|
Diffusion
|
Osmosis
|
Mass flow
|
Substance transported
|
liquids and gases
|
Water molecules
|
Solids and liquids
|
Transportation
|
None structure
|
Semi permeable membrane
|
Cytoplasm and vessel
|
Causes of movement
|
Diffusion gradient
|
Osmotic pressure
|
Different in pressure
|
Chapter summary
- Transport is necessary for the movement of substances within, into and out of cells so as to enable vital life processes to occur.
- Transport can be carried out through diffusion, osmosis or mass flow.
- Diffusion is the movement of particles from a region of high concentration to a region of low concentration.
- Osmosis is the movement of water molecules from a weak solution to a strong solution through a semi-permeable membrane.
- A hypotonic solution has a lower water potential.
- A hypertonic solution has a higher potential.
- A red blood cell haemolysis in a hypotonic solution and crenates in a hypertonic solution.
- A plant cell becomes turgid in a hypotonic solution and plasmolyzed in a hypertonic solution.
- Mass flow is the bulk movement of substance due to pressure differences in two regions.
TRANSPORTATION IN MAMMALS
Introduction
Mammals are complex multicellular organisms.
Their bodies are made up of numerous cells and tissues. Hence, diffusion alone
is not enough to ensure efficient carrying out of life processes. Mammals
therefore have an elaborate transport system called the circulatory system. The
circulatory system is made up of the heart, the blood and the blood vessels.
The mammalian heart
An example of the mammalian heart is
the human heart. The human heart is approximately the size of a clenched fist.
It is located in the chest cavity between the two lungs.
The external structure of the
mammalian heart
The mammalian heart is broader at the top and
narrower at the bottom. It is enclosed by a double layer of tough inelastic
membranes called the pericardium. The membranes prevent the heart from
over-expanding when it is beating very fast. The pericardium also secretes a
fluid called pericardial fluid. This fluid enables the membranes to move
smoothly against each other