2.0: Nutrition- biology topic for secondary school (form two)
2.0: N U T R I T I O N
Topic outline:
2.1 Concept of nutrition and food
nutrients
2.2 Heterotrophic nutrition (nutrition in
man)
2.3 Digestive system and digestion
2.4 Nutrition in plant (Autotrophic
nutrition)
2.5 Food processing, preservation and
storage
2.1
Concept of Nutrition and Food Nutrients
Nutrition –is
the process whereby organisms acquire raw materials(nutrients) needed for body
activities. The raw materials (food)
used for body activities such as growth, repair, protection and energy.
Nutrition stages in animals includes; ingestion, digestion, absorption and
assimilation. In plants it involves synthesis.
(i) Provide
materials for body growth and development
(ii) Provide
materials for body protection against diseases
(iii) Provide
materials for repair of body parts
(iv) Provide
materials for body energy
(v) Provide
materials for transmission of nerve impulse
Modes/types of nutrition
i) Autotrophic
nutrition –is the manufacture of organic food compounds
from inorganic
materials using chemical or light energy.
E.g. in green
plants, manufacture complex organic food
(eg; glucose C6H12O6) from simple inorganic
materials: water and carbon dioxide by using light.
Autotrophs –are
the organisms that able to manufacture their own complex food molecules from
simple inorganic materials.
E.g. green plants, manufacture their own food by using
light energy (photosynthesis).
ii) Heterotrophic nutrition–is the breaking down of manufactured organic food into simpler form that can be absorbed and utilized by cells.
Heterotrophs –are the organisms that breaking down of already
manufactured complex food molecules into smaller absorbable particles.
E.g. animals. They are not able to manufacture their own
food, but use food manufactured by plants.
Forms of heterotrophic nutrition
i. Holozoic nutrition –taking of complex food substance and converting to simple form.
Types
of holozoic nutrition;
a) Herbivorous
–organism feed on plants. Eg; cow
b) Carnivorous
–organism feed on other animals fresh meat. Eg; lion
c) Omnivorous
–organism feed on both plants and meat.
Eg; man
ii. Saprophytic –feeding on dead organic matters. Eg fungi i.e. mushroom.
iii. Symbiosis –feeding relationship between two species living together.
Types
of symbiosis;
a) Commensalism –feeding relationship between two species whereby one benefit while the other neither benefit nor harmed. Eg; small plants growing on other plants
b) Mutualism –feeding
relationship between two species whereby both benefit. Eg; bacteria and legume
plants, bacteria in ruminant digestive system.
c) Parasitism –feeding relationship between two species whereby one benefit while the other is harmed. Eg; tapeworm in human gut, plasmodium and human etc.
2.2 Heterotrophic Nutrition
Heterotrophic
nutrition–is the breaking down of manufactured organic food into
simpler form that can be absorbed and utilized by cells.
Types of food substance and their uses in the body
Food
nutrients –are organic and inorganic chemical substances present in food
stuff.
| Food | Function | Example of food sources |
|---|---|---|
|
1. Carbohydrate |
- provide body energy - for structural materials |
- cassava - sugar cane - maize - bread |
|
2. Protein |
- for growth and repair - for body protection (immunity) - provide body energy - for structural formation - formation of enzymes, hormones, and other substances |
- milk - legumes, e.g., beans - egg white - meat, fish |
|
3. Lipids: fat & oil |
- provide body energy - provide water when respired - provide insulation, avoid heat loss - protect organs such as kidney - for structural materials, e.g., cell membrane |
- seeds - coconut - butter - milk - oils |
|
4. Vitamins |
- prevent deficiency diseases - promote health - regulate body processes |
- fruits, e.g., oranges - vegetables - meat, liver - dairy products |
|
5. Minerals |
Ca -strong bones & teeth, conduct nerve impulse Fe -formation of haemoglobin P -part of ATP and nucleic acid, tissues growth Cl -produce hydrochloric acid, water balance, activate enzymes Na, K, Mg –muscle contraction and conduction of nerve impulse |
-vegetable -unpolished cereals -egg |
Food nutrients –their sources and principal functions
Balance diet
-is the regular meal containing all necessary food
nutrients in a correct proportion.
The components of balance diet are;
carbohydrate, protein, lipid, water, mineral salts,
vitamins, and roughage.
Importance of balance diet
- Provide materials for body growth and development
- Provide materials for body protection against diseases
- Provide materials for repair of body parts
- Provide materials for body energy
- Provide materials for transmission of nerve impulse
Nutritional
requirement for different groups of people
Type and amount of food required by the body depend
on;
- ActivityBody
- size
- Sex
- Ageweight
- State of health
a) Expectant mothers and lactating mothers -Require more food with high amount of protein; for growth and development of the foetus and milk production.
b) Young children
-Require balance diet with high amount of protein and vitamin; for growth, protection (immunity) and good health
c) Elderly (old age)
-Require balance diet with high amount of protein and vitamin; for body repair, protection and good health.
Vitamins –their source and principal functions
d) Sick e.g. living with HIV/AIDS
-Require balance diet with high amount of protein and vitamin for strong immunity to fight the disease.
e)
Manual workers (hard workers)
-Require more energy giving food like carbohydrates.
f) Sedentary workers
-Require food with little
amount of lipid and carbohydrates (little energy).
Causes of
lack of balance diet among Tanzania societies
•
Poverty –no money to buy some of the food
required for balance diet
•
Ignorance –no education of food required and
their important functions
•
Traditions and taboos –some avoid eating some
types of food; e.g. pregnant mother is avoided to eat some kind of foods such
as eggs in some societies.
•
Some types of food required are not available in some
areas
Nutritional
Deficiencies and Disorders
Malnutrition:
-is the condition result from too little food, too much food or food lacking
some nutrients.
Malnutritiondisorders and diseases include; , Anorexia, Beriberi, Constipation, Anaemia, Night blindness, Etc.
Nutritional
deficiency diseases and disorder in human
2.3 Digestive System and Digestion
Digestion –is
the broken down of complex food substance into simple soluble form for
absorption in the alimentary canal.
Mechanical digestion
–food is broken down by teeth (mastication
or chewing) and by gut muscles(churning)
into small particles.
Chemical digestion
–food is broken down chemically
by enzymes into simple soluble form for absorption
Food taken by organism passes through different stages
before it is become usable by the body:-
i)
Ingestion –taking in food into alimentary canal ii) Digestion
iii) Absorption
–diffusion of food nutrients into the body/blood after digestion
iv) Assimilation
–utilization of food nutrients for the
body activities
v)
Egestion (Defecation) –removal of undigested food
materials through the anus.
The process of
digestion is taking place in the alimentary canal.
The Human Digestive System (alimentary canal)
Fig. 7.1 The human alimentary canal
Alimentary canal: Parts and Functions
• Teeth –chew
food into small particles (mechanical digestion)
• Tongue
–roll food into bolus and push food into oesophagus
• Salivary
glands –produces saliva
• Epiglottis
–prevent food from entering the air passage
(trachea)
• Oesophagus
–pass food by peristalsis
Peristalsis –is the
movement of food into the stomach by contraction of oesophagus muscles
NB: -Person can swallow food while standing on his
head upside down because peristalsis is not influenced by gravity.
Fig. 2.2 Peristaltic
movement of food
• Cardiac
sphincter –avoid back flow of food from stomach to oesophagus.
• Stomach –muscular
chamber to store food, mix food by churning and digest protein
• Pyloric
sphincter –control movement of food (chyme) into the duodenum
• Duodenum
–is the first portion of small intestine, liver(gall bladder) and pancreas are connected to this part.
• Liver
–produce bile and store some food products. Bile –it emulsify fat into tiny droplets; it is a greenish yellow
fluid produced by the liver and stored in the gall bladder.
• Pancreas
–produce pancreatic juice to digest protein, lipid, starch and neutralize the
acidic food (chime)
• Ileum –is
the coiled long portion of small intestine for digestion and absorption.
-It contains villi
for absorption of end products of food. -Ileum produces intestinal juice
which digests all types of food.
• Colon and
appendix –absorbs water, salts and some vitamin
Alimentary canal: Digestion
A:
Digestion in the mouth
-The food digested in the mouth is starch only
Saliva –dissolve,
digest and lubricate food, and enable person to talk.
Saliva contain:
ptyalin enzyme (to digest starch to maltose), water(to dissolve food), mucus
(to
lubricate food) and minerals ions.
B: Digestion in the stomach
-Food digested in the stomach is protein only Stomach gland produce gastric juice which contain:- hydrochloric acid, mucus and enzymes
pepsin and rennin.
i. Hydrochloric acid; -kill bacteria present
in food
-provide acidic medium for enzymes activity
-convert complex sugar into simple sugar -activate enzymes; pepsin from pepsinogen and rennin from prorenin
iii. Enzymes; pepsin and renin Pepsin –digest protein into
peptides
Rennin
–solidify milk protein in young mammal. It is to enable the milk protein to
stay long in the gut for digestion.
NB: Pepsin and
renin are produced in their inactive forms (pepsinogen and prorenin) to avoid digesting the
cells that produce them. They digest proteins; also cells are protein in
nature.
C:
Digestion in the duodenum
Food digested is protein, lipids and starch. It is the first part where digestion of
lipids takes place.
Pancreas is connected to duodenum by pancreatic duct,
pancreas produce pancreatic juice.
Pancreatic
juice contain:
•
Enzymes;
Lipase –digest lipids to fatty acid and glycerol
Trypsin –digest protein into peptides
Pancreatic amylase –digest starch into maltose
•
Hydrogen carbonate salt –to neutralize the
acidic food (chyme) from the stomach.
D:
Digestion in the ileum.
The digestion of all types of food ends in the ileum Ileum produces intestinal juice.
Intestinal
juice contains enzymes
•
Lipase –digest lipids into fatty acids and
glycerols
•
Maltase –digest maltose into glucose
•
Lactase –digest lactose into glucose and
galactose
•
Sucrase –digest sucrose into glucose and
fructose
•
Peptidase (Erepsin) –digest peptides into amino
acids
Absorption and fate of end products of digestion
Absorption mostly takes place at ileum by villli.
•
Villi –are the finger like projections in the
ileum which increase surface area for absorption of food nutrients
-Amino acids and glucose enter the blood vessels of villi, the
glycerol and fatty acids packed as lipoprotein and enter lymph vessel
(lacteals) of villi.
Structure of vill
- It is long –food stay for long time for maximum absorption
- It is coiled –food move slowly, take long time for maximum absorption
- It has numerous villi –to increase surface area for absorption.
- It has thin wall –for the food nutrients to diffuse easily
- It is well supplied with blood –to transport the absorbed food nutrients.
2.4 Nutrition in Plants (Autotrophic nutrition)
–Manufacture of complex organic food molecules from simple inorganic
materials using chemical or light energy.
E.g. Green
plants; manufacture complex organic food (eg; glucose C6H12O6)
from simple inorganic materials:
water and carbon dioxide, by using light.
Plants are autotrophs, they manufacture their own
food by using sunlight (photosynthesis)
To manufacture food, plants also need mineral salt elements from the
soil.
Plant mineral nutrients are of two categories;
i) Macro elements –needed by plants in large amount; nitrogen, phosphorus and potassium (N, P, K) ii) Micro elements –needed by plants in small/trace amount. Eg; zinc, copper, manganese Essential mineral
Elements in plant and their roles
Photosynthesis
-is the process by which green plants manufacture their own organic
food compounds from inorganic materials using light
energy.
Site of photosynthesis: photosynthesis take place in the chloroplast.
Chloroplast are found in the green parts of plant ie; leaves
Internal structure of leaf
•
Vein –transport materials in leave
•
Lamina –green with chlorophyll for
photosynthesis
(trap sun light)
•
Petiole –attaches leave to stem
• Cuticle
–waxy
thin layer to protect and avoid water loss
• Epidermis
–thin outer layer to protect inner parts
• Palisade
mesophyll –has many chloroplasts to trap sun light for photosynthesis
• Spongy
mesophyll –loosely cells layer with air spaces to allow gas to circulate easily
• Stomata
–allow gas and water to pass
• Guard
cell –with many chloroplasts to control close and opening of stomata. Control
amount of water and gas passing in and out.
• Xylem
–transport water and mineral salts
• Phloem
–transport manufactured food
Condition necessary for photosynthesis
i.
Light –provide energy for the process and
photolysis
of water.
ii.
Chlorophyll –trap sunlight
Raw materials for photosynthesis
iii. Carbon dioxide iv. Water –provide hydrogen during photolysis. -The hydrogen combines with the carbon dioxide to form glucose food.
Photolysis –is the splitting of water molecule by light to produce hydrogen and oxygen.
Therefore; photosynthesis takes place through 2 tages;
i)
Light stage –water split into hydrogen and oxygen by light energy.
ii) Dark reaction(light independent) –the hydrogen combine
with carbon dioxide to form glucose food
Equation of photosynthesis Word equation:
End products of
photosynthesis i) Glucose ii)
Oxygen gas iii) Water
Fate of the end products of photosynthesis
•
Glucose is store as starch in plant and some is
used during respiration to release energy. Also can be converted into oil or
protein.
•
Oxygen is used during respiration and the excess
is removed out to be used by other organisms.
•
Water is used back for photosynthesis, the
excess water is removed out during transpiration.
•
Some glucose sugar is converted into lipids.
Protein is formed by addition of mineral ions from the soil.
Importance of photosynthesis
Ø Food production
Ø Energy
conversion; it convert light energy from the sun to chemical energy used by
organisms
Ø Balance
atmospheric gases (carbon dioxide and oxygen)
Ø Produce
oxygen used by organism in respiration
Factors affecting the rate of photosynthesis
•
Light intensity –photosynthesis increase with
increase in light intensity to optimum.
•
Carbon dioxide concentration
• Temperature –photosynthesis increase with increase in temperature up to optimum. Too much temperature damage leaves chlorophyll and decrease photosynthesis
•
Water
Examples of plant storage organs;
•
Leaves –E.g. onion
•
Root –E.g. cassava, carrot, potatoes
•
Stem –E.g. sugar cane, yam,
•
Seed and grain –E.g. bean, maize, ground nut
Experiments on photosynthesis
1. To test for starch in a leaf Procedures;
•
Take a green leaf from a plant in sunlight and
dip it in boiling water for 20 seconds
•
Remove the leaf from water and dip it in a
boiling ethanol using water bath for
2minutes.
•
Remove the leaf from ethanol and dip again in
the water to soften it and remove the ethanol.
•
Add few drops of iodine to the leaf, wash and
observe the colour change Observation/Results:
The leaf turn blue black, this indicate the presence of starch.
Inference
and conclusion:
-Therefore during photosynthesis starch is formed.
Questions:
i. Why the leaf dipped in boiling
water? ii. Why the leaf dipped in boiling ethanol? iii. Why water bath
was used? iv. Why should the leaf from ethanol washed again in the water?
v. Why it was necessary to remove the
chlorophyll? vi. Why the leaf washed after adding iodine?
Answers:
i. To kill protoplasm ii. To
remove chlorophyll (decolourize) iii. Ethanol is flammable, it would catch
fire if boiled
directly
iv.
To soften the leaf and remove the ethanol
v.
To seen the colour change properly, (chlorophyll
would mask the colour change)
vi.
To remove excess iodine
2. To test the necessity of light in photosynthesis Procedures;
•
Fix a piece of hard cardboard on upper and
lower surface of leaf in a green plant early in the morning.
•
Detach the leaf after several hours and dip it
in a boiling water for 20 seconds
•
Remove the leaf from water and dip it in a
boiling ethanol, use water bath.
•
Remove the leaf from ethanol and dip again in
the boiling water, or wash.
Set-up to investigate
necessity of light for photosynthesis
|
2.5 Food processing, preservation and
storage
Food
processing
-are the processes of treating food to make it good, safe
and stay for a long time.
Food preservation
–process of adding preservatives
chemicals to the food to prevent deterioration (decay)
Preservatives
–chemical that stop food deterioration by preventing life and activities of
microorganism. Examples of preservatives are:-
salts, sugar, honey, sulphur
dioxide, organic acids etc.
Importance of food processing and preservation
Ø Prolong
life of the food
Ø Prevent
food decay and spoilt
Ø Keep
reserve for the future
Ø Preserve
natural state of the food
Methods of food processing and preservation
Natural methods
•
Smoking –applying smoke to the food, the carbon
monoxide kills destructive organisms.
Examples:- for food such as fish, meat, cassava, seeds
•
Drying –remove water from the food prevent life
of microorganisms, organisms cannot live without water.
Examples:-for food such as cassava, meat, fish, cereals,
seeds, vegetables
•
Salting –adding much salt to the food increase
concentration to prevent life of microorganisms by osmosis.
Examples:- for food like meat, fish
•
Boiling –high temperature kill microorganisms
•
Pickling –putting food in preservative like
honey. Eg; for food like meat
Modern methods
•
Freezing
–keeping food at very low temperature, microorganism are not active at very
low temperature.
Examples:-for food like meat, fish, vegetables
•
Canning
and bottling –food is heated to kill microorganisms and sealed in airtight
can or bottle to avoid oxygen, organisms cannot live without oxygen. Examples:- for food like fruits, drinks,
fish, tomatoes,
meat
•
Additives
–chemical preservatives are added to the food to prevent growth and life of
microorganisms. The preservatives are like salt, sugar, sulphur dioxide,
organic acids etc.
Examples:- for food such as meat, fish, drinks etc.
•
Pasteurizing
(Heating) –Overheating the food to above 600C for several
minutes to destroy microorganisms and their enzymes.
Example:- for milk
•
Refrigeration –keeping food at low temperature,
avoid activities and life of microorganisms. Eg; fruits, vegetables
Differences
between traditional and modern methods of food processing and preservation
Properties of food substances
Carbohydrates
-Compound of carbon, hydrogen and oxygen
Types
i) Monosaccharide (simple sugars) –composed of single
molecule. E.g; glucose and fructose ii) Disaccharides (complex sugar) –formed
by condensation of two monosaccharide molecules. E.g; sucrose (from sugar cane), maltose, and
lactose (from milk) iii) Polysaccharides (complex sugar) –formed by
condensation of large number of monosaccharides. E.g.
Starch, cellulose
Lipids
-Compound of carbon, hydrogen and oxygen. More hydrogen
than carbohydrate, but lower oxygen content.
Lipids are polymers made of monomers; faty acids and glycerols.
Ø Insoluble
in water, soluble in organic solvent
Ø Fat is
solid at room temperature while oil is liquid at room temperature
Ø In paper
cause it to become translucent
|
|
Ø Oil react with osmic acid and turn black
Protein
-Compound of carbon, hydrogen, oxygen and nitrogen;
some contain sulphur and phosphorus as well.
Proteins are polymers made of monomers called amino
acids.
Ø Proteins
are insoluble in water
Ø React with
Million’s reagent to form purple/reddish colour
Ø React with
sodium hydroxide and copper sulphate to produce a violet colour. This is called
Biuret test.
Vitamins
Formed by combination of glucose and some mineral
elements.
Most vitamin are synthesized by autotrophs (green plant),
mammals can synthesize vitamin A and D.
