Food and Nutrition in Humans

1
Food and Nutrition in Humans

• Classes of Food Substances
• Food Storage

2
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

3
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

4
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

5
Classes of Food Substances

• Carbohydrates
• Fats and Oils
• Proteins
• Minerals
• Vitamins

6
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

7
Classes of Food Substances - Fats and Oils

• Provide energy
• Usually stored as food reserves
• Animals store fats
• Plants store oils

8
Classes of Food Substances - Proteins

• Required for growth
• Required for repair of damaged or worn out tissues

9
Classes of Food Substances - Vitamins and Minerals

• Essential for the maintenance of good health
• Control metabolism
• Prevent diseases

10
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 organisms
  needs is stored in some form after poisonous or
  useless materials are disposed of
• The stored material can be utilized in many ways

11
The role of food storage in plants and animals
contd

• 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

12
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

13
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

14
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

15
Tap root

• A swollen tap root is the main root in carrot,
  radish turnip and beetroot
• Carrots store glucose in the phloem

16
Storage in Stems

• A variety of stem storage organs is found in
  nature
• Stem tuber
• Rhizome
• Corm

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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

18
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)

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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

20
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

21
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

22
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.

23
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)

24
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

25

• Can you identify the different types of storage
  organs (a) to (f) represent?

26
Storage in Animals

• Storage in animals occurs mainly in the liver and
  muscles
• In fat deposits
• In eggs

27
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

28
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.

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Fat deposits contd

• 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.

30
Eggs

• Eggs store
• Protein
• Fat
• The fat being concentrated mainly in the yolk.
• Some eggs also store simple sugars

31
Summary Questions

• People trying to lose weight eat egg whites
  onlywhy?
• What other specific foods would you recommend for
  someone trying to lose weight? Give reasons for
  your answer.

32
Site references

• http//homepage.smc.edu/hodson_kent/plant_growth/A
  ngiosperms/ID/basics.htm
• http//www.cccmkc.edu.hk/kei-kph/Food20storage2
  0organ/Food20storage20organ.htm