Page 182 - Biology_F5

Comparative studies of natural groups of organisms

(g) Under natural conditions, earthworms (c) They are used as source of nutritious
are less active; this limits oxygen food rich in proteins and vitamins for
consumption. fish and carnivorous birds.

(h) They have looped surface vessels, (d) They are ecological decomposers; hence,
which facilitate absorption of oxygen they contribute to nutrient circulation;
over a short diffusion distance. since they feed on decaying organic
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matter.
(i) Their haemoglobin has high affinity to
oxygen. (e) They are used for removing soil
pollutants from the soil and clean the
(j) The head is less elaborate. The worm environment by transforming organic
has tactile and photoreceptive cells for wastes during feeding as a way of waste
locating food at night and sensing light management.
during the day respectively. (f) Their excretory wastes in the form of

(k) They have chaetae that are used for casts increase cementing effects of
movement. soil particles; hence, increasing water-
holding capacity.
Economic importance of Annelids
Annelids are both ecologically and (g) They are used as specimens in biological
economically important; even though on studies.
the other side, they have some drawbacks.
Disadvantages of Annelids

Advantages of Annelids (a) They increase soil porosity and aeration,
(a) They improve soil aeration, drainage and which is detrimental to paddy fields (rice
increase depth of the top soil through plants in the field).
burrowing and mixing of soil layers. (b) They damage young roots of the growing
(b) They are used as bait in fishing industry, plants.
example earthworms. (c) Leeches are harmful to mammals,
reptiles, and fishes, as they suck blood.

Activity 3.11

S S S
1 2 3
Figure 3.47 Specimens S , S , and S 3
1
2
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