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) e.g. glucose, frustose
Disaccharides (complex sugars) 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 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 FRUITS
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/~kei-kph/Food%20storage%20organ/Food%20storage%20organ.htm