TOPIC 1-CLASSIFICATION KINGDOM FUNGI
SIGNIFICANT OF FOOD CHAINS AND FOOD
WEBS
i) Food chains and food webs
facilitate the flow of energy in the environment.
ii) Helps to maintain the balance of
the total numbers of organisms in the environment
TRANSPORTATION OF MATERIALS
Introduction
The basic characteristics of all
living things are nutrition, respiration, excretion, growth and development,
movement, reproduction and sensitivity. In order for these life processes to
take place, there must be transportation of materials. Materials are
transported either from the environment into the organism or from one part of
the organism to another. They can also be transported from the organism into
the environment.
For example, during nutrition,
organisms take in food substances that they need to provide them with energy.
The food must also be transported to all parts of the organism. Respiration
requires oxygen, which must be taken in from the environment. During excretion,
waste materials from the organism are transported to the excretory organs and
removed from the body. Growth requires the production and transportation of
growth hormones to the growing parts of the organism. Movement and locomotion
are made possible by the transportation of impulses to the relevant organs.
Reproduction requires the movement of gametes (sex cells) or the transportation
of genetic material. Sensitivity is made possible by the transportation of
messages about the presence of a certain thing in the environment.
Transportation is therefore very
important for the survival of living things.
Transportation is therefore very
important for the survival of living things.
Ways of transportation of materials
Life processes in organisms take
place at the cell level. Therefore, it is necessary for substances to move in
and out of the cells. There are two ways through which substances can move
across the cell membrane:
Passive transport;
which occurs spontaneously without the need of energy to transport materials
through the cell membrane.
Active transport;
where the cell has to use energy to move materials across the cell membrane.
Processes like diffusion, osmosis
and mass flow involve passive transport.
Diffusion
Diffusion is the movement of
particles from an area of high concentration to one of low concentration.
A difference in the concentration of
a substance between two regions is known as a concentration gradient. Diffusion
causes particles to move from the area of high concentration to a low
concentration area. This process continues until the particles are distributed
evenly throughout the liquid. Figure below shows the diffusion of potassium
permanganate in water.
FACTORS AFFECTING RATE OF DIFFUTION
- Concentration gradient: high diffusion rate with higher concentration and vice versa
- Surface area to volume ratio: the higher it faster the diffusion rate.
- Distance over which diffusion takes place: example a thin layer of cells increases diffusion rate
Osmosis
Osmosis is a form of passive
transport considered as a special form of diffusion involves movement of water
molecules through semi-permeable membrane.
Osmosis defined as the process by
which water move from a weak solution into a strong through a semi-permeable
membrane. The semi permeable membrane is only permeable to some solutes
(dissolved substances).
For osmosis to take place there must
be two separated solution by a semi-permeable membrane. One solution should
have greater water and a lesser quantity of solute than other solution. This
solution is hypotonic, it has a lower water potential. The second should have a
lesser volume of water andvolume of solute than the other solution. This
solution is hypertonic, meaning it has greater water potential.
Two solutions have the same water
potential are said to be isotonic
