UEC Senior 1 Biology 独中高一生物

1. 4.2 Levels of biological structure

2. Levels of biological structure
• Life starts as unicellular organism, i.e. they are life at
the cellular level. Example: protozoa, bacteria.
• Then cells work together and form colonies. Example:
volvox and sponges
• Cells become specialize and yet they group together to
form tissue. Lower animal such as coelenterates, are
tissue-level multicellular organism.
• Larger organisms may develop organs, that are formed
from different tissues with specific functions. For
examples, roots, stems, leaves, flowers, fruits and
seeds in plants; stomach, kidney and heart in animals.
• Different types of organs group together to perform a
particular function is called system. For example, the
digestive system, the nervous system etc.
• Different structures and functions of various systems
group together to form a multicellular organism.
Cells
Cell colony
Tissue
Organ
bacteria
sponge
Coelenterate
Higher plants, animals
腔腸動物(刺胞動物+櫛水母)

3. 4.3 Advantages of
multicellular
organisms

4. Advantages of multicellular organism
• The organism can be larger as growth of
unicellular organisms are limited.
• Cell can undergo differentiation.
• The organisms to be more complex.
• The organism can increase the efficiency of
physiological activities.
• The organisms to adapt to new environment
with more ease.
Unicellular amoeba
Amoeba colony