The document summarizes key aspects of nutrition, including the six main nutrients, how plants obtain nutrients through photosynthesis, and the human digestive system. It explains that carbohydrates, proteins, lipids, vitamins, minerals, and water make up the six nutrients. Photosynthesis allows plants to produce nutrients from sunlight, carbon dioxide, and water. The human digestive system breaks down food through mechanical and chemical processes in the mouth, stomach, and small and large intestines to absorb nutrients.

1. Nutrition
Foods, Photosynthesis and Digestion

2. Introduction
• This presentation summarizes general
information about nutrition.
• It covers foods, enzymes, photosynthesis
and digestion
• It is a useful aid to remind you of the
important aspects in this unit.

3. Objectives
• Students will understand that nutrition is
the means by which living organisms
obtain their energy and material
requirements, and that this occurs in
different ways in different organisms.
• Students will understand the role and
importance of enzymes for digestion

4. Nutrients
• All foods are made up of SIX different nutrients:
lipids (fats), proteins, carbohydrates, vitamins,
minerals, and water.
• Carbohydrates, proteins and lipids are
macromolecules made up of smaller molecules
that are joined together through condensation
reactions.
• These macromolecules can be broken back
down into their smaller constituent molecules if
water is present, i.e. hydrolysis.

5. Functions of Nutrients
1. The main purpose of
eating carbohydratescarbohydrates is
to provide energy for
the functioning of the
body.
2.2. FatsFats also provide energy
and are useful in cell
membrane formation.
3.3. ProteinsProteins are needed to
build and repair the
body.

6. Functions of Nutrients
4. Water makes up the largest
portion of a cell and is
needed for metabolism.
5. Vitamins regulate
metabolism and aid in
various body functions.
6. Minerals are inorganic
substances that are
needed for metabolic
processes in small or
minute amounts. Some of
these minerals are iron, zinc
and copper."
Note.Note. Fibre is not a nutrient,
but is required to aid in the
elimination of undigested
food from the bowels.

7. NUTRIENTS
Nutrients are needed in specific proportions
They can be obtained from the six food groups.
Note.Note. Fibre is not a
nutrient, but is required
to aid in the elimination
of undigested food from
the bowels.
Staples
Legumes and nuts
Vegetables
Food from animals
Fruits
Fats and substitutes

8. Enzymes
• All chemical reactions in cells or organisms
need enzymes in order to speed them up.
• Chemical reactions often need heat, pressure
or catalysts to speed them up.
• Enzymes are biological catalysts. If enzymes did
not exist as biological catalysts, reactions would
probably take too long and life would not exist.

9. Enzymes
• They are proteins
• They are biological catalysts
• Found in all living cells
• Their action is specific to a
substrate/food
• They are affected by temperature and
pH

10. The Origin of Nutrients
• Just where do these nutrients come
from?
• They all originate in plants and plant
foods, since plants manufacture their
own foods, and animals eat plants.
• How do plants get these nutrients?
• By photo (light) – synthesis (manufacture)

11. The Leaf
Site of Photosynthesis

12. Leaf Structure
Bamboo leaf: http://office.microsoft.com, j0438959.jpg
Each part is adapted for photosynthesis:
1. The lamina - broad, flat, thin, green
• broad and flat to catch much
sunlight;
• green with chlorophyll to
capture energy of sunlight;
• thin to allow for fast diffusion of
gases
The lamina

13. Leaf Structure
Bamboo leaf: http://office.microsoft.com, j0438959.jpg
Each part is adapted for photosynthesis:
2. The petiole – firm and flexible
The petiole
• Contains veins with phloem and xylem
vessels - Veins transport water into
leaf and transport manufactured food
out of leaf
• Holds leaf at right angles to sun -
advantageous position to receive
most sunlight

14. Leaf Structure
Photos highlighting veins in leaves

15. Cross Section diagram of leaf showing types of cells

16. Internal Leaf Structure
• 1) Epidermis has a waxy transparent cuticle
which allows sunlight into the leaf but prevents
excessive water loss;
• 2) Mesophyll layers contain cells with
chloroplasts, and also have between them air
spaces which allow exchange of gases.
• 3) Special groups of cells in the epidermis,
called the stomata (pores) allow the gases and
water vapour to move in and out of the leaf.
• 4) Palisade cells are special mesophyll cells with
many chloroplasts lined up to receive maximum
sunlight.

17. Photosynthesis
• Complex organic substances are made
from inorganic & simple materials.
• Chloroplasts capture sunlight energy and
pass it on to ATP, at the same time as
enzymes split water into oxygen and
hydrogen ions.
• A complex set of reactions now change
carbon dioxide into sugar with the
addition of the hydrogen ions.

18. What happens to the sugar produced?
• The glucose produced is
changed into starch
• The glucose may remain
as glucose in the leaves of
onion and escallion
• The glucose may be
changed into sucrose
(cane sugar)
• Glucose may be
converted into proteins
and other complex
carbohydrates

19. Human Digestive System
• The human digestive system is complex: it is
made up of a long tube, along whose length
are attached a number of different organs.
• Some of the organs are secretory in nature, and
send into the tube, a variety of enzymes and
other chemicals.
• Also attached to the tube are blood vessels,
which in some sections, absorb digested food.
• The tube begins at the mouth and ends at the
anus.

20. What happens in the mouth?
• The food is both mechanically broken
down (cut into tiny pieces) and mixed
with liquid (saliva, gastric juices), as well
as chemically broken down (by
enzymes)
• Digestion begins in the mouth, where
teeth break it into pieces, saliva moistens
it into a ball and salivary amylase begins
to change starch into maltose

21. LET’S MAKE A NOTE !
• In your book, prepare a table, with four
columns headed as below:
• When you read a slide, write down what
happens in each part of the digestive
system.
• Start with the mouth that you just read
through.
Location Food acted on Enzyme Food changed into

22. What gets digested in the stomach?
• The stomach pours gastric juice onto the
food, which keeps it moistened and soft
• Enzymes begin to act on proteins and
change them into peptides (an
intermediate compound)
• Acid is present in the stomach to enable
the enzymes to work well

23. Looking closely at the stomach
Do you notice that the
stomach looks like a bag? For
storing food? Why does it store
food? How long does the food stay in
the stomach?
Did you notice the two
ends of the stomach – the top
end that comes from the
oesophagus, and the bottom end
that goes into the small intestine
– that there are little rings there?
These little rings are like
gates; they keep the stomach
contents inside the stomach for a
while, until the enzymes have
acted on the mixture.
Click to show rings.Click to show rings.
Drawing of the stomach

24. How does digestion occur in the small
intestine?
• In the duodenum, additional enzymes are
poured onto the food, breaking the maltose
and peptides further down
• Bile is added (from the gall bladder) to help
emulsify fats, so that the enzymes can act on
them
• In the rest of the small intestine, the tiny folds
and projections (villi) begin to absorb the
simpler molecules into which the foods were
changed (glucose, amino acids, glycerol and
fatty acids)
• Try to remember how this occurs ! (Clue:
diffusion)

25. The Villus
The picture on the right
shows the structure of a
villus. Notice the many
blood vessels inside it
and also the lacteal
vessel (the fat one in
the middle).
You can see how easy
it is for the digested
food to diffuse through
the thin walls (only one
cell thick) into the
vessels. Drawing of the villus

26. Assimilation
The final step in digestion
• The foods are absorbed by the blood
vessels and lacteals inside the villi
• They are taken to the liver
• The liver - processes digested food
(carbohydrate, protein and lipid
metabolism), and stores certain minerals
and vitamins

27. Digestion
1. Digestion begins in
the mouth with
salivary amylase.
1. Digestion begins in
the mouth with
salivary amylase.2. Pepsin in the stomach
changes proteins into
polypeptides
2. Pepsin in the stomach
changes proteins into
polypeptides
3. In the ileum, enzymes
work on all three nutrients
3. In the ileum, enzymes
work on all three nutrients
4. In the small intestine,
simple foods are absorbed
into the blood
4. In the small intestine,
simple foods are absorbed
into the blood
5. Undigested wastes pass
out of the body via the anus
5. Undigested wastes pass
out of the body via the anus
http://www.gutenberg.org/files/18559/18559-h/18559-h.htm
Drawing of the digestive system

28. What happens to those substances that we
do not absorb?
• In the large intestine, water as well as
some inorganic nutrients (minerals) are
absorbed into the bloodstream while the
remaining food materials are passing
through
• Fibre is not digested by humans, so it
forms the bulk needed to keep the
remnants moving along
• The undigested waste is passed out
through the anus at the end of the food
canal.

29. Egestion
• Do not confuse this with excretion !
• Undigested food cannot be absorbed by the
blood and so it remains within the lumen of the
gut until it is expelled at the anus
• We call this E G E S T I O N
• Excretion is totally different ! It relates to
products from metabolic activity, not from
undigested wastes !
• It is important to dispose of egested waste
(faeces) carefully, for it might contain disease
organisms.

30. Let us summarize
• Nutrition is the process by which organisms
obtain their food
• Some organisms can make their own food,
while others have to obtain food by eating
others
• Complex food substances are made by plants
from simple inorganic materials
• Complex food substances eaten by animals
have to be broken down into simpler organic
substances before they can be absorbed into
the body and used
• Enzymes play an important role in nutrition.

31. Photo Credits
• Food display - j0433159.jpg, http://office.microsoft.com
• Girl eating sandwich - j0439576.jpg, http://office.microsoft.com
• Oils - j0386781.jpg, http://microsoft.com
• Salad bowl with salad - j0438794.jpg, http://office.microsoft.com
• Onions - j0402510.jpg, http://office.microsoft.com
• Leaf veins - j0437213.jpg, http://office.microsoft.com
• Bamboo leaf - j0438959.jpg, http://office.microsoft.com
• The Digestive System www.gutenberg.org/files/18559/18559-
h/18559-h.htm