Referat Autotrophic And Heterotrophic Nutrition
Mai jos puteti citi fragmente din
Referat Autotrophic And Heterotrophic Nutrition si de asemenea puteti face
Download Referat Autotrophic and heterotrophic nutritionCiteste fragmente din Referat Autotrophic And Heterotrophic Nutrition
Report
On biology
Topic: Nutrition
Chishinau
Autotrophic and heterotrophic nutrition:
Exist 4 kinds of nutrition and depends on organism. Autotrophic and
heterotrophic is characteristic only for plants and animals. Humans,
like all animals eat food which has be made by other organisms. The food
we eat contains organic substances, especially carbohydrates, fats and
proteins which have been made by plants. Plants are able to make these
substances from inorganic ones; they use carbon dioxide and water to
make carbohydrates by photosynthesis. The addition of a few inorganic
minerals ion, such as nitrates and phosphates, enables them to
synthesize all the other substance which they require ,such as proteins
and nucleic acids.
All animals on organic substances which have originally been made by
plants, both for their source of energy and for materials from which to
build their bodies. Animals are therefore said to be heterotrophic
,while plants are autotrophic .Hetero means ‘different’ or
‘other’, whereas means ‘auto’ or ‘self’. Animals are
depend on food produced by other organism, but plants can make our own
food.
Animals are not only group of organism which feed heterotrophically.
Fungi also are hetrotrophs, as are many protoctist and prokaryotes.
All of them are dependent on food made by autotrophs.
Types of heterotrophic nutrition:
Heterotrophic organisms have evolved many different ways of obtaining
the organic nutrients they need.
Holozoic nutrirtion
Is the method by which humans and other mammals feed, as well as many
other animals such as insects .food, in solid or liquid form is taken
into a tube called the alimentary canal where it is digested and
absorded into the body.
Saprotrophic nutrition
Is the method by which fungi and many prokaryotes feed. They live and
grow on their substance , which can be anything organic, such as milk
bread or dead body .They secrete enzymes from their bodies, and digest
the food material around them before absorbing it.
Parasitic nutrition
Is the method of feeding which has evolved in many different groups of
organisms, including various kinds of worms and fungi and a few plants.
Parasites fed on, and live in close association with, a living organism
of a different species, called their host. They can feed either
holozoically biting their host or sucking fluids from it, or they can
feed saprotrophically ,absorbing soluble food into their bodies.
Holozoic nutrition-feeding in humans:
Humans like all other animals are heterotrophs .This means that we need
to eat food containing organic molecules. These organic molecules
includes carbohydrates, fats and proteins. This all are our only source
of energy. In contrast autotrophs such as green plants do not need to
take in any organic molecules at all. They obtain their energy from
sunlight, and can use their energy to built organic molecules from
inorganic one. They produce carbohydrates from carbon dioxide and water,
by photosynthesis and can them use these carbohydrates, plus inorganic
ions such as nitrate, phosphate and magnesium , to manufacture all the
organic molecules that they require .Heterotrophs therefore depend on
autotrophs for the supply of organic molecules on which they feed. Some
of them feed directly on plants, while others feed further along a food
chain. But eventually all of our food can be traced back to green
plants, and the energy of sunlight.
The structure of the human alimentary canal:
The alimentary canal is a long hollow tube which runs from the mouth to
the anus .Together with several other organs, including the liver and
the pancreas, it makes up the digestive system.
The total length of the human alimentary canal is between 5 and 6 m,
from anus to mouth. To fit this considerable length into body, parts of
the canal are folded and coiled inside the abdomen .The mucus is a
substance secreted along the tube by cells lining its walls .Mucus helps
food to slide through the canal without doing too much damage to the
lining. It also forms a protective covering which keeps the digestive
juices, which are inside the lumen of the canal, from coming into
contact with the living cells of the walls. Along the whole length of
the alimentary canal there are muscles in the walls. These produce
waves, of
Contraction and relaxation called peristaltic waves, which move food
along the alimentary canal and help to mix the contents. Each region of
the alimentary canal has it own function and different structure. There
are 4 basic layers in the wall of the alimentary canal. Working from the
inside these are: a) the mucosa b) the submucosa c) the muscularis
externa d) the serosa. Many of this names came from Latin origin.
The mucosa is made up of 3 layers. The innermost layer is the
epithelium. The structure of the epithelium varies in different parts
of
the alimentary canal, but it always contains cells which secrete mucus.
Beneath it is a layer of connective tissue called lamina propria, which
means ‘closest layer’. And beneath that is a layer of smooth muscle
called the muscular is mucosa.
The sub mucosa is made up of areole connective tissue. This is an
open-textured stretchy tissue, containing many elastic fibred and
collagen fibres. Running through it are numerous blood vessels and
nerves.
The muscularis externa ia made of two layers of muscle. The innermost
layer has fibres running around the tube, and is called circular muscle.
The outermost layer has fibres running along the tube and it is called
longitudinal muscle.
The serosa is a very thin layer, made up of connective tissue covered
with a single layer of thin, smooth closely fitting cells.
We can observe in detail each part of the human alimentary canal
structure in this diagram.
The mouth:
Taking food into the mouth is called ingestion. We use lips, tongue and
teeth. The tongue is also important in tasting food, to tell you whether
it is good to eat; if not it will be ejected from the mouth rather than
swallowed.
The main purpose of the human teeth is to break up large pieces of food,
thus beginning the process of the mechanical digestion. This is done by
chewing, or mastication. Strong muscle is the jaws move the lower jaw up
and down from side to side, grinding the teeth in the lower jaw against
those in the upper jaw.
The premolar and molar teeth have ridges and grooves, which trap food
between them and crush it as chew. Mastication greatly increases the
surface area of the food, bringing more of it into direct contact with
enzymes in the digestive juice and so speeding up chemical digestion.
Three pairs of salivary glands secrete watery liquid saliva, which pours
along ducts into the mouth. Like all secretions along the alimentary
canal, saliva is mostly water. It contains mucus, which mixes with the
food as it is chewed, helping to glue it loosely together into a ball
called a bolus. The mucus also makes the bolus slippery, so that is
easier to swallow.
Saliva contains the enzyme amylase, which catalyses the hydrolysis of
starch. .
Thus, digestion by amylase produces maltose and small chain made up of
three, four or more glucose molecules on the end of a chain . Thus ,
digestion by amylase produces maltose and small chains made up three,
four or more glucose molecules linked together, but it does not produce
individual glucose molecules.
Saliva also contains an enzyme called lysozyme. This enzyme, which is
also found in tears, can destroy several types of bacteria which can
cause infection in the mouth and throat, including Staphylococcus and
Streptococcus. The lysozyme,
together with a general ‘washing’ action of saliva, and a small
amount of hydrogen carbonate ions in it ( which partly neutralizes
acids on teeth ) appear to
help reduce the incidence of tooth decay.
The stomach:
When a bolus of food is swallowed ,it is moved swiftly down to the
esophagus by peristalsis and into stomach.
The stomach is a muscular sac, with a capacity of up 5 dm.. In some
parts of the stomach the muscle layers of the muscularis externa are
thicker than in most other parts of the alimentary canal. They produce
strong, rhythmic, churning movements when there is food in the stomach.
This not only mixes the food with the juices secreted in the stomach,
but also helps to continue the process of mechanical breakdown begun by
chewing in the mouth.
The inner layer of the stomach wall, the mucosa, is specialized to
produce large quantities of gastric juice, up to 2 dm each day. Gastric
juice contains protease and lipase, as well as hydrochloric acid
(HCL).To protect the cells in the wall from damage by the acid and
proteases, they are covered with a slimy coat of mucus containing
hydrogen carbonate ions which neutralize the acid.
The protease secrete in gastric juice is pepsin. Pepsin is secreted from
large cells in the gastric glands called chief cells .It is secreted in
an inactive form, as pepsinogen ,to prevent it from digesting proteins
in the cells which produce it. Pepsinogen is a larger molecule than
pespsin, and it is activated by removing a strip of several amino acids
from it. This happens automatically when it is exposed to the acidic
conditions inside the stomach. It is also achieved by pepsin molecules
which have already been activated; they ‘digest’ pepsinogen
molecules to convert them into more pepsin.
Pepsin catalyses the hydrolysis of peptide bonds within protein
molecules; it does not break the bonds holding the ‘end’ amino acids
of the polypeptide chains. Proteases which do this are called
endopeptidases (‘endo’ means ‘within’).Pepsin therefore breaks
protein molecules into short chains of amino acids called peptides, but
produces almost no individual amino acid molecules. Pepsin molecules are
unusual proteins in that they are only stable in acidic conditions. The
optimum pH for the pepsin found in the human stomach is about 2 or
3.This is, of course the pH which is found in the stomach when gastric
juice has been secreted because this juice contains large amounts of
hydrochloric acid. Hydrochloric acid helps to destroy many potentially
harmful microorganisms which might be present in food. It is secreted
from parietal cells in the gastric glands.
The lipase in gastric juice begins to hydrolyze triglycerides into fatty
acids and glycerol. However, the majority of the digestion of
triglycerides and other lipids happens later, in the small intestine.
Gastric juice also contains a substance called intrinsic factor. This
is a glycoprotein which binds to vitamin B and protects it from begin
digested. Later, in the ileum, the intrinsic factor-vitamin B complex
sticks to the surfaces of the cells of the ileum wall, which adsorb it.
People who don’t secrete intrinsic factor cannot absorb vitamin B
,however much the eat in their diet. They suffer from pernicious
anaemia, an illness in which not enough red blood cells are formed. Food
may be kept in the stomach for several hours. The acidic mixture of
partly digested food and water, called chyme, cannot pass on the next
part of the alimentary canal, the duodenum, until a band muscle called
the pyloric sphincter relaxes. When this happens depends on many factors
which seem to relate to how
quickly the duodenum will be able to deal with what is being sent into
it.
For example; if there is a lot of fat chyme ,it will be allowed into
the duodenum only in small amounts at a time, to give the duodenum a
chance to deal with it.
The small intestine:
The duodenum and the ileum together make up the small intestine.
(The first part of the ileum is sometimes known as the jejunum.) The
overall length of the small intestine is about 5m, of which the
duodenum makes up the first 25m.
It is within the duodenum and the ileum that most digestion and
absorption occurs.
The mucosa of the whole of the small intestine is greatly folded,
forming tiny projections called villi. In the duodenum, these are
flattened with a rather leaf-like shape, while in the ileum the are more
finger-like. A villus is about 0.5mm to 1.0mm long; villi are very thin
and make the inner surface of the small intestine look rather like
velvet. As in the mucosa layer of all parts of the alimentary canal,
this mucosa is made up of three layers an epithelium, a layer of
connective tissue
and the muscular is mucosa. .The muscles of the muscular is mucosa
contract and relax, so that the villi sway about. This helps to bring
their surfaces into contact with more of the contents of the small
intestine than if they remained still.
The cells which make up the epithelium of the villi have a very folded
cell surface membrane on the side nearest to the lumen of the small
intestine; these little folds are called microvilli. Seen under the
microscope, the surface of the cells looks like the bristles of a burst
and it is called a bursh border. The villi and the microvilli produce
an enormous surface area within the small intestine, which greatly
increase the rate at which absorption can take place.
In the ‘troughs’ between the villi in the duodenum are glands, known
as crypts of Lieberkuhn which secrete mucus. The crypts also constantly
produce new cells, which move up the villi until they ‘fall off’ at
the top. This constant replacement of the surface cells is essential, as
individual cells do not last long. Deeper in the walls of the duodenum,
in the submucosa , Brunner’s glands are found. These glands secrete a
watery mucus that contains hydrogencarbonate ions to help neutralize the
acidic chyme flowing into the duodenum from the stomach.
Digestion in the small intestine:
Digestion in the small intestine is brought about by enzymes from 2
sources.
One of these is the cells which cover the surface of the vili, and the
other is the pancreas.
The pancreas secretes pancreatic juice. This flows into the duodenum
along the pancreatic duct. The pancreas has another role as part of the
endocrine system, where it helps in the regulation of blood glucose
levels.
Pancreatic juice contains hydrogencarbonate ions and a number of
enzymes, especially amylase, the three proteases trypsin, chymotrypsin
and carboxypeptidase and lipase. The enzyme in pancreatic juice
continue to digest the partly digested substances which flow into the
small intestine from the stomach. Digestion is completed by enzymes
which are produced by the cells on the surface of the villi and remain
on their surfaces. Indeed , some of the pancreatic enzymes become
absorbed onto these surfaces, so that much of the digestion in the small
intestine takes place on the brush border of the villi. This is useful
because it means that the products of digestion are right next to the
surface across which they can be absorbed, which probably increases the
speed at which they are taken up into the cells.
Absorption in the small intestine:
The small intestine is the area of the alimentary canal in which all
absorption of nutrients occurs. The very large surface area provided by
the villi, and the microvilli in the surfaces of the cells which cover
them, greatly speed up absorption. Inside each villus is blood
capillary, which can transfer absorbed nutrients to a branch of the
hepatic portal vein. There is also a lymph vessel, called a lacteal,
which you will see is important in the adsorption of lipids.
To get into either the blood capillary or the lacteal, nutrient
molecules must first cross the cells surface membrane on the ‘outer’
surface of the one of the cells on the surface of villus. Then they must
cross the cell and leave it across the cell surface membrane on the side
furthest away from the lumen. Then they have to across either the wall
of the blood capillary or the wall of the lacteal. This last part of the
journey does not cause too many difficulties, as these walls are adapted
to allow various substance to pass in and out. molecules across the
cells surface membranes of the villus cells by diffusion and
endocytosis.
Glucose is absorbed into the cells by indirect active transport,
involving the co-transport of sodium ions. Then the glucose moves out of
the opposite side of the cells by facilitated diffusion and simple
diffusion ,into the tissue fluid inside the villus and then into blood
capillary.
Amino-acids are absorbed into the villus cells by active transport and
pass out of the opposite side by diffusion. In a fetus a newly born baby
, some entire undigested proteins can be absorbed by pinocytosis. This
is how babies are able to absorb some of their mother’s antibodies
from the milk. This can also happen to a small extent adults.
Fatty acids and glycerol are easily absorbed across the cell surface
membrane of the villus cells because they are lipid-soluble; they move
across by simple diffusion. Once inside the cells, they are taken to the
smooth endoplasmic reticulum where some are reconverted to
triglycerides. They are moved to the Golgi apparatus, where they are
surrounded in a coat of protein, phospholipids and cholesterol to from
chylomicrons. These tiny structures ranging from 100 to 600nm in
diameter ,are moved out of the far side of the cell into the tissue
fluid in the villus by exocytosis. Although they are very small, they
are too big to get through the even smaller holes in the walls of the
blood capillaries, and so they do not enter the blood. They can,
however, readily enter the lacteals .The chylomicrons suspended in the
lymph inside the lacteals from a milky emulsion, which is what gives
these structures their name. (‘Lact’ means ‘to do with milk’).
Considerable amounts of water and inorganic ions, such as sodium,
chloride, calcium, and irons are also adsorbed in small intestine .The
absorption of calcium is helped by the presence of vitamin D. The
adsorption of irons is helped by citrate ions and ascorbic acid, both of
which is found in citrus fruits. This is probably why fresh fruits and
vegetables in the diet can help to prevent anaemia. On the other hand,
drinking to much tea can hinder irons absorption, because tannins in
the tea react with irons to produce compounds which cannot be adsorbed.
Vitamins are also absorbed in the small intestine. The fat-soluble
vitamins A, D, and E can simply cross the cell surface membranes by
diffusion; you have seen how bile salts help to bring them to the
surface of the villi along with fatty acid. The water –soluble
vitamins, such as vitamin C and the many types of B vitamins are moved
across the cells surface membranes by specific transport. Vitamin B can
only be adsorbed in combination with intrinsic factor.
The colon and rectum:
By the time the food has reached the end of the small intestine,
virtually everything which could be absorbed has entered the villi. What
is left? The undigested, unabsorbed remains are mostly fibre; humans
cannot digest cellulose or lignin.
At the entrance of the colon from the small intestine, there is a
blind-ending side branch-the caecum and appendix. The appendix has no
function in humans. The colon however is very important indeed as it is
here that much of the remaining water is adsorbed into the
blood,together with sodium and chloride ions. These processes also occur
in the caecum. The colon has no villi but it does have a large surface
area produced by many folds in its wall, to increase the efficiency of a
absorption. The rectum is a short straight section of the alimentary
canal, which leads from the colon to the anus and thus to the outside
world. It is usually empty only receiving the contents of the colon now
called faeces when they are ready to be passed out of the anus.
The control of secretions in the alimentary canal:
As food passed along the alimentary canal, numerous sections are
produced to help to digest it. It is important that this secretions are
only produced when needed. Various mechanism are used to ensure that
this happens.
Saliva is produced by a reflex actions resulting from a stimulus of the
thought sight smell or taste of food. Gastric juice like saliva beings
to be secreted even before anything has been eaten just at the smelling
food. This impulses came from brain and along a branch of the vagus
nerve to the gastric glands. In animals such as dog this impulses also
cause the release of a hormone called gastrin. Like all hormones gastrin
is secreted into the blood and it is carrying in the blood to the
gastric glands. The secretion to the pancreatic juice into the duodenum
is controlled in similar way. Most secretions happens when chyme from
the stomach enters in duodenum. Acid entering the duodenum causes cells
in it wall secrete a hormone called secretin, which is carried in the
blood to the pancreas and increases the production and release of
pancreatic juice especially rich in ions. Another hormone with a similar
effect to secret in is called cholecystokinin or CCK and old name
pancreozynim. This hormone it is found in brain and it is secreted by
the walls of the duodenum when chyme enters from the stomach. CCK
stimulates the secretion of bile, walls of the gall bladder. It is also
stimulates the production of pancreatic juice especially rich in
enzymes.
Contents:
Autotrophic and heterotrophic nutrition
Types of heterotrophic nutrition
Holozoic nutrition-feeding inn humans
the structure of the human alimentary canal
a) The mouth
b) The stomach
c) The small intestine
5. Digestion in the small intestine
6. Absorption in the small intestine
7. The colon and rectum
8. The control of secretion in the alimentary canal
Bibliography:
The book of Advanced Biology
Authors: Mary Jones and Geoff Jones.
ì¥Â`
