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Food and Nutrition in
Humans
Classes of Food Substances
Food Storage
Syllabus Objectives
Students must be able to
perform tests to identify classes of food
substances
Discuss the role of food storage in living
organisms
Identify the products stored and the sites of
storage
Classes of Food Substances
All organisms require organic substances for
their living processes
Green plants make organic compounds from
raw materials that are inorganic
Animals are supplied with organic
compounds in the form of food
Classes of Food Substances - Nutrition
Nutrition is the process of obtaining or
making food
Living organisms require food for
Growth
To provide energy
To maintain health
Classes of Food Substances
Carbohydrates
Fats and Oils
Proteins
Minerals
Vitamins
Classes of Food Substances Carbohydrates
Provide energy
There are 3 types of carbohydrates
Monosaccharides (simple sugars)
Disaccharides (complex sugars)
e.g. glucose, frustose
e.g. maltose, sucrose
Polysaccharides
e.g. starch, cellulose, glycogen
Classes of Food Substances - Fats and
Oils
Provide energy
Usually stored as food reserves
Animals store fats
Plants store oils
Classes of Food Substances - Proteins
Required for growth
Required for repair of damaged or worn out
tissues
Classes of Food Substances - Vitamins
and Minerals
Essential for the maintenance of good health
Control metabolism
Prevent diseases
The role of food storage in plants and
animals
Plants and animals use food for
providing energy
Growth and tissue repair
Controlling metabolism
Preventing disease
Food which is taken in in excess of an organism’s
needs is stored in some form after poisonous or
useless materials are disposed of
The stored material can be utilized in many ways
The role of food storage in plants and
animals cont’d
Food is stored for the following reasons:
Survival when food is scarce or unavailable
Can you give examples of this?
Organisms can survive unfavourable periods of time without
making or taking in food
For use during rapid growth when conditions become favourable
Storage takes place in seeds, fruits and in animals in eggs.
These perform reproductive functions ensuring dispersal and
development of a growing embyro.
Stored products in plants and animals make useful food for man
and other organisms. E.g. cassava, yam, potato, onion
Storage products and sites of storage
Storage in Plants
Storage in plants occur in vegetative organs
(roots, stems and leaves) and reproductive
structures (fruits and seeds)
Temporary storage of starch occur during the day
in leaf cells as the products of photosynthesis
accumulate
Storage in Roots
Food produced by the leaves in the growing season
passes downward and is stored in roots
They can be distinguished from stem tubers
because they lack buds and scale leaves
There are 2 types of vegetative root storage
Root tubers e.g. sweet potato, cassava
Tap root e.g. carrot, radish turnip, beetroot
Root tubers
Sweet potato (Ipomoea
batatas) and cassava
(Manihot esculenta)
both store starch and
very small amounts of
protein
Sweet potato also
stores maltose sugar
Tap root
A swollen tap root is the
main root in carrot,
radish turnip and
beetroot
Carrots store glucose in
the phloem
Storage in Stems
A variety of stem storage organs is found in
nature
Stem tuber
Rhizome
Corm
Stem tuber
Swollen underground stem
Possesses scale leaves or leaf
scars (which distinguish them from
root tubers)
The scale leaves have buds in the
axils (called eyes)
These buds can grow into shoots
utilizing the stored food in the tuber
Examples include:
Yam (Dioscorea)
Irish potato (Solanum) - mainly stores
starch
Rhizome
Swollen, horizontal growing
underground stem
Has nodes at which scale leaves
and axillary buds are present
A terminal bud is present at one end
Adventitious and contractile roots
grow from the rhizome
Examples include:
Canna lily
Ginger (Zingiber),
Stores starch and oils (gives
characteristic smell)
Corm
Short, swollen underground stem
Grows vertically
Covered by scale leaves which grow
from nodes
Buds are present in the axils of the
leaf bases
Adventitious and contractile roots
arise from the base of the corm
A terminal bud is found at the top
Examples include:
Dasheen (Colocasia), cocoyam
which both store starch
Other Storage Stems
Sugar cane has a swollen stem growing
above ground
It stores sucrose sugar
It is cultivated in many tropical countries
It is of great economic importance
Storage in leaves
All plants store food temporarily in their
leaves
Most store starch
Onions chives (escallion) store sugar
Some plants develop underground
storage organs of swollen leaves which
are called bulbs
Storage leaves grow from a flattened
stem and are enclosed by dry, scaly
outer leaves.
The stem bears adventitious roots
Tiny lateral buds are found in the axils of
some of the storage leaves
Storage in Fruits and Seeds
SEEDS
FRUITS
Provide food for young developing embryos for early
growth
Young plants are unable to make their own food until they
form green leaves and are able to photosynthesize
Food reserves in fruits are important for attracting animals
which disperse their seeds.
Fruits and seeds contain varying amounts of
carbohydrates, fats, proteins, vitamins, minerals and
water.
Storage in Fruits
Storage can occur in the fruit wall (pericarp)
or receptacle of fruits
Mango (Mangifera indica) and the West
Indian cherry store sugar in the mesocarp
Sugar is stored in the hairs of the endocarp
in the orange (Citrus sinensis)
Storage in Seeds
Most seeds store food in the cotyledons
Some seeds store food in the endosperm
Endospermic seeds develop another storage
tissue in addition to the cotyledons
This is more common in monocotyledons whose
seeds have only cotyledon
E.g. corn and other cereals and coconut
It is found in some dicotyledons (seeds with two
cotyledons)
E.g. castor oil
Can you identify the different types of storage
organs (a) to (f) represent?
Storage in Animals
Storage in animals occurs mainly in the liver
and muscles
In fat deposits
In eggs
The Liver
When excess carbohydrates are eaten, the
surplus is converted to glycogen by the liver
and stored in liver and muscle cells
Liver cells also store
Fat
Vitamin A, B12 and D
Iron from the breakdown of red blood
cells
Fat deposits…
Excess carbohydrates not converted to glycogen is
converted to FAT for long term storage in animals
Animals can make fat from any excess sugar, fat or
protein in the diet
Fat stored in special fat deposits under the skin of
animals like pig and humans around organs such as
the kidney, heart, ovaries and the gut.
Fat deposits cont’d
Large animals like the polar bear, seals and whales
have thick fat layers under the skin which provide
insulation against heat loss.
In whales and seals this fat layer is called blubber
The hump of a camel, an animal of the hot desert, is
a fat store which when metabolized yields large
amounts of energy and water.
Eggs
Eggs store
Protein
Fat
The fat being concentrated mainly in the yolk.
Some eggs also store simple sugars
Summary Questions
People trying to lose weight eat egg whites
only…why?
What other specific foods would you
recommend for someone trying to lose
weight? Give reasons for your answer.
Site references
http://homepage.smc.edu/hodson_kent/plant
_growth/Angiosperms/ID/basics.htm
http://www.cccmkc.edu.hk/~keikph/Food%20storage%20organ/Food%20sto
rage%20organ.htm