Page 131 - Biology_F5

Biology for Advanced Level Secondary Schools

Exercise 3.7 phycocolloids, which are widely used in
textile, pharmaceutical, and food industries.
1. A form one student from Makete Chlorophytes are primarily aquatic, and are
observed that all the potato plants in the primary source of energy and oxygen
the school farm are affected by a certain
disease. A form five student isolated a to marine heterotrophs. Few are found in
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leaf specimen, observed it under the special habitats in terrestrial environments.
microsscope and identified the disease Chlorophytes are heterogeneous in their
causing organism as Phytophthora pigmentation, shapes, and size. They range
infestans. Explain the characteristics from microscopic, simple and unicellular
that the student used to confirm the such as Chlorella and Chlamydomonas to
identified organism. giant multicellular macroalgae. Although
they resemble eukaryotic plants in many
2. Why is Phytophthora infestans placed
under kingdom Protoctista? ways, they have no true roots, stem or leaves
and they do not produce seeds. The simplest
3. Explain the effects of Phytophthora structure is unicellular, but they may exist in
infestans to plants and show how colonies or in filaments of several distinct
the spread of this parasite can be cells. Others may be multinucleated with
controlled. interconnected cells that lack cross walls as

in Volvox and Oedogonium, respectively.
Phylum Chlorophyta This section will focus on the characteristics
Members of this phylum were formerly of chlorophytes, structure, and adaptations
classified as plants. They include of Spirogyra.
unicellular, non motile alga (Chlorella
and Acetabularia), a unicellular motile General characteristics of phylum
alga (Chlamydomonas), filamentous alga Chlorophyta
(Spirogyra) and a thalloid marine alga, (a) They are adapted to aquatic
(Ulva). In other classification, chlorophytes environments ranging from fresh
are placed under kingdom plantae, since water to marine water. For example,
they are more phylogenetically related to their sexual reproduction relies on
plants. They are regarded as ancestors of water as they produce motile sperms,
plants, because they have photosynthetic which have to move in water medium
pigments such as chlorophyll a, b and β to fertilise the egg.
'carotenoids' as well as 'xanthophylls', which (b) They are photoautotrophs and have
are characteristics of plants. Additionally, chlorophyll a and b and other
they possess photosynthetic apparatus called photosynthetic pigments, such as
pyrenoid for condensation of glucose to carotenoids used in photosynthesis.
starch, which is the same as photosynthetic (c) They have cell walls made up of
product in plants. Under this phylum there cellulose.
are important species of high economic (d) They store carbohydrates in the form
importance, including sources of agar and of starch.

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