Transcript File - JLooby Biology

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