Page 53 - Biology_F5

Biology for Advanced Level Secondary Schools
(c) They are the source of other food
substances, such as a triose sugar in
plants.
(d) Pentose sugar, such as ribose and
deoxyribose sugars are used in the
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synthesis of nucleic acids. Ribose is a
constituent of Ribonucleic acid (RNA)
and deoxyribose is a constituent of
Deoxyribonucleic acid (DNA).
(e) Ribose sugar is also used in the
synthesis of ATP and coenzymes, such
as NAD and NADP.
(f) Carbohydrates such as ribulose (a
five carbon sugar) forms Ribulose
biphosphate, which is used as
carbon dioxide acceptor during light
independent stage of photosynthesis.
(g) In association with proteins and
phospholipids, carbohydrates form
structural parts of a membrane.
(h) They form structural parts of
organisms, such as cellulose in plant
cells and chitin in exoskeleton of
arthropods.
(i) They are important constituents of
connective tissues in animals.
(j) Cellulose fibres in edible fruits and
other foods help to prevent constipation
in humans.
(k) Flower nectar contains sugar, which is
important in the process of pollination.
Activity 1.5: Biochemical test for
carbohydrates
1. Suppose you have been provided with
the following for a practical work:
(a) Solution K containing starch
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(b) Benedict’s solution
(c) Dilute hydrochloric acid
(d) Sodium hydroxide solution
(e) Rubber bands for stimulating
saliva secretion
Questions
1. Show step by step, how you would
go about testing for reducing sugar.
2. It is advised that, before collecting
saliva, one should rinse his or her
mouth with clean safe water. What is
the significance of this?
3. Comment on the final colour change
of the solution.
Exercise 1.11
1. With illustrations, differentiate
monosaccharides from disaccharides.
2. Lactose is a disaccharide formed
from one molecule of galactose and
one molecule of fructose. Apart from
both being disaccharides, give one
similarity and one difference between
the structure of fructose and lactose.
3. Show how two glucose units are
combined to produce maltose. Give
details of chemical reactions involved
and the bond formed.
4. Can sucrose reduce Copper (II) in
Benedict’s solution? Give an annotated
description of your answer.
5. Show how the structure of α-glucose
is maneuvered to produce β-glucose,
galactose and fructose.
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