Back to: O level Biology NOTES Uganda syllabus
This refers to the movement of materials from one part of the organism to another. In plants, it is called translocation. It involves diffusion, osmosis and active transport in simple organisms and active transport in simple organisms and transport systems in large higher organisms, (Vascular & circulatory systems).
THE NECESSITY FOR TRANSPORT SYSTEM
All living things need a continuous exchange of certain substances between their cells and the environment e.g. oxygen, food, materials carbon dioxide, waste products.
In large complex animals, most of the cells are located far from the surface thus the need for a transport system.
Flat worms are flattened to shorter distance for transport.
Requirements of transport system
The materials to be transported
The medium of transport
The channels of transport
Energy
Materials to be transported
In animals, they include respiratory gases oxygen and carbon dioxide, nitrogenous excretory products e.g. uric acid, nutrients e.g. glucose, amino acid.
In plants, they include oxygen and carbon dioxide.
Mineral elements for plant growth
Manufactured food (autotrophs)
Absorbed food (in saprophytes)
Vitamins, amino acids auxins
The medium of transport
The medium of transport in plants and lower animals is water and it is blood in vertebrates and in a few invertebrates like arthropods, annelids (earth worm).
The channels of transport
In most animals, these are blood vessels, in others e.g. earth worms, it is the body cavity (coelom). In higher plants, there is a vascular system or system of xylem and phloem.
Energy
Circulation of blood in animals requires energy supplied from respiration used in pumping of the heart and muscle contractions.
TRANSPORT IN PLANTS
Transporting tissue in plant is xylem and phloem. It involves movement of water, salts and organic molecules (manufactured food).
THE XYLEM
This Consists of xylem vessels and tracheids. Xylem vessels develop from cylindrical cells, arranged end to end, in which the cytoplasm die and cross- walls disappear leaving a dead empty tube. Through this:
Water, mineral salts, move from roots, stems, up to leaves. Xylem vessels are strengthened by lignin in their walls.
This strength gives support to the soft tissue of roots, stems, and leaves: it also prevents collapse of the vessels under tension as sap pressure changes.
Structure of xylem
Tracheids
They are similar to xylem vessels; except that they are typically 5 or 6 sided. In cross- section, instead of being open at each end, their tapering end walls are perforated by pit (tiny holes in lignified walls). Even xylem has pits in their walls.
NB
Tracheids are more primitive- they are found in gymnosperms e.g. cypress where there is control of transpiration, for water does not move very fast through them.
Characteristics of xylem tubes
a) Consist of dead tubes
b) They are hollow
c) Its walls are lignified
d) Has no protein filaments
e) Has no cytoplasm
f) Transports water and salts
g) Transports water and mineral salts in one direction