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FOOD PROCUREMENT AND PROCESSING
Plants
Green plants are the producers of food. It contain chloroplasts, the factory where food is
processed and produced.
Leaf - the food factory. Photosynthesis take place primarily in the leaves of plants.
External Structure of the Leaf
Lamina. Thin expanded blade
Petiole. The stalk that attaches the blade to the stem
Stipules. Scale like structure at the base of some petiole
Midrib. The vein in the center of a leaf
Veins and veinlets. vascular bundles that form the branching framework of conducting
and supporting tissues in a leaf.
Margin. The edge of the leaf.
Internal Structure of a Leaf
A cross section through the blade of a typical leaf reveals 4 distinct tissue layers.
1. Upper epidermis. This is a single layer of cells containing few or no chloroplasts. The
cells are quite transparent and permit most of the light that strikes them to pass through to
the underlying cells. The upper surface is covered with a waxy, waterproof cuticle, which
serves to reduce water loss from the leaf.
2. Palisade layer. This consists of one or more layers of cylindrical cells oriented with their
long axis perpendicular to the plane of the leaf. The cells are filled with chloroplasts
(usually several dozen of them) and carry on most of the photosynthesis in the leaf.
3. Spongy layer. Lying beneath the palisade layer, its cells are irregular in shape and
loosely packed. Although they contain a few chloroplasts, their main function seems to
be the temporary storage of sugars and amino acids synthesized in the palisade layer.
They also aid in the exchange of gases between the leaf and the environment. During the
day, these cells give off oxygen and water vapor to the air spaces that surround them.
They also pick up carbon dioxide from the air spaces. The air spaces are interconnected
and eventually open to the outside through pores called stomata (sing., stoma).
4. Lower epidermis. Typically. most of the stomata (thousands per square centimeter) are
located in the lower epidermis. Although most of the cells of the lower epidermis
resemble those of the upper epidermis, each stoma is flanked by two sausage-shaped cells
called guard cells. These differ from the other cells of the lower epidermis not only in
their shape but also in having chloroplasts. The guard cells regulate the opening and
closing of the stomata. Thus they control the exchange of gases between the leaf and the
surrounding atmosphere.
Food Requirements of the Plants
Green plants can manufacture their own food and are called autotrophic organisms. Three types
of substances are needed by green plants to manufacture their food and these are carbon dioxide,
water, and minerals. These are the raw materials for photosynthesis.
DIGESTION AND DIGESTIVE SYSTEM
Digestion in Animals
Food is usually taken in through the mouth and is acted upon within the mouth cavity, by
specialized system of enzymes.
Why is digestion important?
When we eat such things as bread, meat, and vegetables, they are not in a form that the body
can use as nourishment. Our food and drink must be changed into smaller molecules of
nutrients before they can be absorbed into the blood and carried to cells throughout the body.
Digestion is the process by which food and drink are broken down into their smallest parts so
that the body can use them to build and nourish cells and to provide energy.
How is food digested?
Digestion involves the mixing of food, its movement through the digestive tract, and the
chemical breakdown of the large molecules of food into smaller molecules. Digestion begins in
the mouth, when we chew and swallow, and is completed in the small intestine. The chemical
process varies somewhat for different kinds of food.
Digestive System
The digestive system uses mechanical and chemical methods to break food down into nutrient
molecules that can be absorbed into the blood.
Stages in the Digestive Process
1. movement: propels food through the digestive system
2. secretion: release of digestive juices in response to a specific stimulus
3. digestion: breakdown of food into molecular components small enough to cross the
plasma membrane
4. absorption: passage of the molecules into the body's interior and their passage
throughout the body
5. elimination: removal of undigested food and wastes
Components of the Digestive System
The human digestive system is a coiled, muscular tube (6-9 meters long when fully extended)
extending from the mouth to the anus. Several specialized compartments occur along this
length: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus
(The Alimentary Canal). Accessory digestive organs are connected to the main system by a
series of ducts: salivary glands, parts of the pancreas, the liver and gall bladder (bilary system)
The Alimentary Canal
The Mouth, Pharynx, and Esophagus
 Mechanical breakdown begins in the mouth by chewing (teeth) and actions of the
tongue.
 Chemical breakdown of starch by production of salivary amylase from the salivary
glands.
 Salivary glands secrete salivary amylase, an enzyme that begins the breakdown of
starch into glucose.
 Mucus moistens food and lubricates the esophagus. Bicarbonate ions in saliva
neutralize the acids in foods.
 This mixture of food and saliva is then pushed into the pharynx and esophagus..
The Stomach
 Epithelial cells line inner surface of the stomach, and secrete about 2 liters of gastric
juices per day.
 Gastric juice contains hydrochloric acid, pepsinogen, and mucus; ingredients important
in digestion. Hydrochloric acid (HCl) lowers pH of the stomach so pepsin is activated.
 Pepsin is an enzyme that controls the hydrolysis of proteins into peptides.Protein
digestion by pepsin begins in the stomach.
 The stomach also mechanically churns the food. Chyme, the mix of acid and food in the
stomach, leaves the stomach and enters the small intestine.
The Small Intestine
 The small intestine, which has a length of about 6 m is wrinkled and convoluted to
produce a greater surface area for absorption.
 Most enzymatic digestion occurs here. The secretions of the small intestine include
amylase maltase, sucrase, lactase, etc. to digest carbohydrates and lipase to digest
fats.
 Several other associated organs secrete chemicals into the small intestine to aid in
digestion: the pancreas secretes enzymes like trypsin, chymotrypsin, and alkali
solutions like bicarbonate as buffers and the liver and gall bladder make and
secrete bile. Bile contains no enzymes, but salts to emulsify fat so it can be digested.
 Small intestine therefore is responsible for final digestion and absorption of food.
 The sections of the small intestine include:
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the duodenum, the first portion
the jejunum, the second portion
the ileum, the third portion
The Large Intestine
 The large intestine or colon, which begins with a blind pouch called the cecum. In
humans, this terminates in the appendix, a finger-like extension which may function
in the immune system.
 The large intestine functions to re-absorb water and in the further absorption of
nutrients. The remains are formed into brown, semi-solid feces, ready to be removed
from the body.
The Rectum and Anus
 The rectum is the terminal portion of the large intestine and functions for storage of
the feces, the wastes of the digestive tract, until these are eliminated.
 The external opening at the end of the rectum is called the anus.
The Accessory Organs of Digestive System
Liver and gallbladder
 Bile, a watery greenish fluid is produced by the liver. It contains bile salts, bile pigments,
cholesterol and phospholipids.
 Bile salts and phospholipds emulsify fats, the rest are just being excreted. Gallstones are
usually cholesterol based, may block the hepatic or common bile ducts causing pain,
jaundice.
Pancreas
 The pancreas, like the stomach, makes powerful digestive juices called enzymes
which help to digest food further as it enters the small intestines.
Salivary glands
 Saliva is a mixture of mucus and serous fluids, each produced to various extents in
various glands. Also contains salivary amylase, (starts to break down starch)
lysozyme (antibacterial).
Facts:
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HOW LONG ARE YOUR INTESTINES? At least 25 feet in an adult.
Be glad you're not a full-grown horse -- their coiled-up intestines are 89
feet long!
Chewing food takes from 5-30 seconds
Swallowing takes about 10 seconds
Food sloshing in the stomach can last 3-4 hours
It takes 3 hours for food to move through the intestine
Food drying up and hanging out in the large intestine can last 18 hours to
2 days!
In your lifetime, your digestive system may handle about 50 tons!!