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