NutritionFoods, Photosynthesis and Digestion

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.

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

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.

Functions of Nutrients1. 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.

Functions of Nutrients4. 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.

NUTRIENTSNutrients are needed in specific proportionsThey 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 nutsVegetables

Food from animals

FruitsFats and substitutes

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.

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

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)

The Leaf

Site of Photosynthesis

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

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

Leaf StructurePhotos highlighting veins in leaves

Cross Section diagram of leaf showing types of cells

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.

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.

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

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.

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

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

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

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.

Drawing of the stomach

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)

The VillusThe 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

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

Digestion

1. Digestion begins in the mouth with

salivary amylase.2. Pepsin in the stomach changes proteins into

polypeptides

3. In the ileum, enzymes work on all three nutrients

4. In the small intestine, simple foods are absorbed

into the blood

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

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.

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.

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.

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