Page 21 - Science Class 08

Some algae are very small as they consist of For instance, algae can photosynthesise like
only one cell. But others are large with many plants and they possess specialised structures
cells. Some algae float while others remain and cell-organelles including centrioles and
a ached to stones or weeds in water. S ll flagella found only in animals.
others live on bodies of water-animals like the Listed below are some of the general charac-

turtle. Large algae are called sea-weeds. Algae teris cs of algae:
contain chlorophyll and so they prepare their v Algae are photosynthe c organisms.
own food through photosynthesis. As they
v Algae can be either unicellular or mul -
always grow on wet surfaces, they are called
cellular organisms.
water grass as well. Fish and other small water-
v Algae lack a well-defined body, so, structures
animals feed on them.
like roots, stems or leaves are absent.
A type of algae called algal blooms from itself
v Algae are generally found in the ssues of
in thick layers on the materials dumped in
other plants or on the rocks in the moist
water. These materials are sewage, chemicals
places.
and fer lizers. They prove very harmful to the
v Reproduc on in algae occurs in both asexual
animals that live in water.
and sexual forms. Asexual reproduc on
Algae are important as under:
occurs by spore forma on.
v Blue-green algae fix nitrogen of the air. v Most of them are generally found in water

v Algae make the soil fer le by producing and are aqua c in nature, especially
organic ma er. plankton. These are of a free-floa ng type.
v They make the ponds also fer le, i.e., it is Protozoa
eaten by water animals. Protozoa are unicellular organisms with plant-

v Cell of red algae are used to make agar, like or animal-like features. They fall into four
paper, paints and cosme cs. groups in terms of their modes of movement–

v Algae are used in fabric paints. flagellates, sarcodines, ciliates, apicomplexans.
v Many types of sea-weeds (algae) are eaten
as food in China.

v Algae help crop-growth by improving the
capacity of the soil for holding water.

Diatoms are algae that grow on sediments, in
springs, mouths of rivers and in seas. The cell-
wall of a diatom has two overlapping halves
and hence its name– diatom. Diatoms
reproduce sexually as well as vegeta vely.
Characteris cs of Algae : Typically, general Protozoa
characteris cs of algae are common to plants
Protozoa are found in ponds and on animals,
as well as animals.
plants, decaying vegeta on and even in the
soil. The cell of a protozoan has a membrane,

Science-8 21