Page 286 - Biology_F5

Nutrition

or on dung and faeces. The undigested to be swallowed, as well as for harnessing
food is eliminated from the body, while nutrients from the food during digestion.
the digested soluble food molecules get Additionally, mechanical digestion involves
absorbed and later assimilated to generate mechanical contraction of the gut, which
energy and some are incorporated into the pounds up and mixes the semi-solid foods.
body cells.
Similarly, digestion process is done
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chemically by the action of digestive
Holozoic nutrition in mammals enzymes. Chemical digestion is a complex
The food taken in by mammals in most process that involves a diversity of digestive
cases is in solid form; therefore, it must be enzymes secreted by the alimentary canal,
converted into simpler form, for it to be which convert various food substances
absorbed and assimilated into their bodies. into simpler and absorbable form that
The holozoic nutrition involves ingestion, can be absorbed easily by epithelia cells.
digestion, absorption, assimilation, and For example, polysaccharides are broken
egestion.
down into monosaccharides; proteins are
broken down into amino acids; and fats or
(a) Ingestion lipids are broken down into fatty acids and
This process involves taking in solid or glycerol.
liquid food into the gut or alimentary canal
or gastrointestinal tract of an organism. (c) Absorption
It is aided by structures, such as teeth, Absorption is the uptake of the digested
tentacles and claws through which food soluble products and other substances
substance is taken into the mouth through across the linings of the gut into the
eating or drinking. blood stream and lymphatic system. The
soluble food substances include vitamins
(b) Digestion and minerals. The small intestine is the
Digestion is the process of breaking down site where digested foods are absorbed
large biochemical compounds contained through diffusion or active transport.
in food into smaller and soluble molecules The inner wall of the small intestine,
that can easily be absorbed into the body. It which is also called the mucosa is lined
involves mechanical and chemical digestion. with microscopic finger-like projections
Mechanical digestion involves the physical called villi. The epithelial cells of the
break down of the food into smaller pieces; small intestine have microvilli. Both villi
and this begins in the mouth where the and microvilli have a role of increasing
food is chewed and rolled by the tongue, surface area for nutrients absorption.
while lubricated by the saliva, before it is The villi are equipped with a network of
swallowed. The tongue, teeth and saliva are blood capillaries and lymphatic vessels.
thus important for processing the food from Normally, the absorbed nutrients enter the
large particles into bolus, which can easily be blood vessels and are supplied to different
swallowed for subsequent digestion stages. body organs.
The mastication of food from larger particles
to small ones is necessary for reducing the (d) Assimilation
food into fine particles, which makes it easy Assimilation is the process of incorporating
and using the absorbed food molecules

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