Download HETEROTROPHIC NUTRITION

AL notes Heterotrophic Nutrition P.1
HETEROTROPHIC NUTRITION
H
eterotrophic organisms are unable to make their o_______ foods and must obtain it in organic
form from their environment. Heterotrophs can be holozoic, saprophytic or parasitic.
Most animals are h___________: Ing______ eaters-- majority of animals, use a mouth to ingest food.
Abso______ feeders, such as tapeworms, live in a digestive system of another animal and absorb
nutrients from that animal directly through their body wall. Fil___ feeders, such as oysters and
mussels, collect small organisms and particles from the surrounding water. Det____ feeders, such as
earthworms, eat the material (detritus) they burrow through. Flu___ feeders, such as aphids, pierce
the body of a plant or animal and withdraw fluids.
I) Holozoic Nutrition
Q1.
Name the 5 stages and describe the action of each stage in holozoic nutrition
AL notes Heterotrophic Nutrition P.2
The digestive system uses mec________ and ch_________ methods to break food down into nutrient
molecules that can be absorbed into the blood.
There are two types of plans and two locations of digestion. Sac-like plans are found in many
invertebrates e.g. Coelenterates, who have a single opening for food intake and the discharge of
wastes. Vertebrates use the more efficient tube-within-a-tube plan with food entering through one
opening (the mouth) and wastes leaving through another (the anus).
Intra_________ digestion: food is taken into cells by phago_______ with digestive enzymes being
secreted into the phagocytic vesicles; occurs in coelenterates and most protozoans.
_______cellular digestion: digestion occurs in the lum___ (opening) of the digestive system, with the
nutrient molecules being transferred to the blood or body fluid; e.g. vertebrates, crustaceans.
A) TEETH AND DENTITION IN MAMMAL
Enamel:
the outer part of the tooth / the h________tissue in the body / consists of rods of
mineral salts embedded in keratin fibres.
Dentine:
a slightly softer material containing the protein fibres collagen running through a
calcified matrix.
Pulp cavity:
At the centre of the tooth / containing blood c________ and sensory n______ fibres.
Tooth cement:
modified bone / holds the tooth in its socket in the jaw.
periodontal membrane: found between the cement and the tooth socket. The collagen fibres of the
periodontal membrane fixed the tooth in the socket and which allows it to flex slightly
without breaking when subject to s______.
 only the teeth of ma______ vary in appearance and function at different points along the
jaws--unlike other vertebrates where all the teeth are similar and usually cone-shaped..
 most teeth stop growing at a certain size, but herbivores' teeth usually grow con________, being
constantly w___ away by the food. These teeth retain a very wide opening to the pulp cavity so
there is a good bl_____ supply throughout life.
Enamel ridges on molar and
premolars of herbivores:
The relative rates of wear of the
enamel, dentine and tooth
cement mean that the herbivore's
teeth are virtually self-sharpening.
Look up for the Dental formulas of a carnivore and a herbivore.
How are they related to their different diet?
AL notes Heterotrophic Nutrition P.3
Comparison of Herbivorous and Carnivorous adaptations in mammals
Herbivorous adaptations
Carnivorous adaptations
Sharp chi___-shaped incisors for cutting or
gnawing
Incisors sharp, sometimes pointed, for nipping and
biting
Upper incisors sometimes absent, e.g. in cattle &
sheep
Upper incisors never absent
Canines, if present, small and incisor-like
Canines long and po____ for piercing and tearing
D________
Diastema never present
present
Molars and premolars flattened with ri______ of
enamel for grinding food
Molars and premolars have p______d cusps for
shearing food
Carnassial teeth absent
Last upper premolars and first molars form
ca____________ teeth
O_____ pulp cavity means teeth can grow
continuously to compensate for wear
Closed p____ c_____ means teeth do not continue to
grow once full size
Teeth of upper jaws meet those of lower jaw end on
to allow grinding of food
Teeth of upper jaw sl_____ past the outside of those
in the lower jaw to allow shearing of food
L_______ movement of lower jaw aids g_______
of food
Absence of lateral movement of lower jaw helps
prevent dislocation when capturing prey
Jaw muscles relatively small Less well developed
processes for muscle attachment
J___ muscles relatively large W____- developed
processes for muscle attachment
Specialized pouches in esophagus or caecum
and appendix to accommodate symbiotic
c__________ digesting micro- organisms
No specialized adaptation of stomach; caecum and
appendix small
Relatively long alimentary canal
Relatively s______ alimentary canal
Dental formula e.g.
Dental formula e.g.
B)
THE
ALIMENTARY
a)
Ingestion
CANAL
IN MAN
In the mouth, or buccal cavity, food is chewed and mixed with saliva. The three pairs of salivary
glands are stimulated when food is seen, smell, or enter the mouth.
i) Action of Saliva
Q2.
What is the composition of the saliva?
Q3.
Give the physical and chemical action of saliva and explain their significance.
AL notes Heterotrophic Nutrition P.4
ii) The Swallowing reflex
 After mastication / ch______ the t_______ moulds the food turning it into a ball or b_____.
 A 'flap' called the e___________ closes off the entrance to the trachea, the s_____ palate closes off
the internal openings to the nose
 Food is swallowed through the p______ into the o_________. The swallowing r______ is
controlled by the m______ oblongata of the brain and briefly inh_____ breathing so that choking
is avoided.
b)
Digestion
i) Digestion in the Stomach
The food is forced down the oesophagus by the contraction of its c________and l__________
muscles, called p_____________.
 The stomach wall produces gas_____ juices in response to the si____, sm____ and ta___ of food.
Involving both n_______ and hormonal control.
AL notes Heterotrophic Nutrition P.5
 Two types of cell produce the gastric juice inside gastric p___ in the stomach wall.
H__________ acid was secreted (by parietal cells) to give the juice a pH of 1.5 to 2. The other
component is pepsinogen (by chief cells), an enzyme precursor that, in the presence of
hydrochloric acid, is act_______to pep___ and hydrolyses proteins to large poly________.
 These cells also secrete pro-_______ which in its active form rennin, coag______ the soluble
milk protein caesinogen to in_______ c_____. Rennin is probably absent from adults, but is
important in babies. Milk is more easily digested in this co_________ form.
 The acid provides a suitable ___ for the enzymes and kills bacteria* entering with the food.
 The cells of the upper part of each gastric pit secrete m_____ which helps to p______ the stomach
lining from digestion and formation of a gastric ul___. Pepsin is inactivated when it comes into
contact with the mucus.
 As well as the c________ and l____________ muscles present along the rest of the length of the
gut, the stomach has oblique muscles. These cause a pendular swinging movement when they
contract and help to m__ the stomach contents and the gastric juice.
 After one to two hours in the stomach the food has a semi-fluid consistency and is called chy___. It
is released in small amounts through the py_____ sphincter into the duodenum.
 Alc_____ and some drugs are absorbed through the stomach lining into the blood.
AL notes Heterotrophic Nutrition P.6
Reference reading: Activation of pepsinogen
Hydrochloric acid converts pepsinogen to active pepsin by removing a small portion of the molecule and
exposing its active site. Activation of pepsinogen in the stomach is an example of positive feedback.
Once some pepsinogen is activated by acids, a series of chemical reactions occurs because pepsin itself
can activate additional molecules of pepsinogen.
Reference reading : Ulcers
(http://www.helico.com/)
Peptic ulcers result when protective mechanisms fail. Bleeding ulcers result
when tissue damage is so severe that bleeding occurs into the stomach.
Perforated ulcers are life-threatening situations where a hole has formed in the
stomach wall. At least 90% of all peptic ulcers are caused by Helicobacter pylori.
Other factors, including stress and aspirin, can also produce ulcers.
Helicobacter pylori is a spiral-shaped bacterium that lives in the stomach and
duodenum (section of intestine just below stomach). The inside of the stomach is
bathed in about half a gallon of gastric juice every day.
Gastric juice is composed of digestive enzymes and concentrated hydrochloric
acid, which can readily tear apart the toughest food or microorganism, bacteria
and viruses. It used to be thought that the stomach contained no bacteria and
was actually sterile, but Helicobacter pylori changed that. The stomach is protected
from its own gastric juice by a thick layer of mucus that covers the stomach
lining. H. pylori takes advantage of this protection by living in the mucus lining.
H. pylori fights the stomach acid with an enzyme called urease. Urease converts urea, (from saliva and
gastric juices), into bicarbonate and ammonia, which are strong bases. This creates a cloud of acid
neutralizing chemicals around the H. pylori, protecting it from the acid in the stomach:
C=O(NH2)2 + H+ + 2H2O ---urease---> HCO3- + 2(NH4+)
Another defense H. pylori has is that the body's natural defenses cannot reach the bacterium in the
mucus lining of the stomach. The immune system will respond to an H. pylori infection by sending white
cells, killer T cells, and other infection fighting agents. However, these potential H. pylori eradicators
cannot reach the infection, because they cannot easily get through stomach lining. They do not go away
either, though, and the immune response grows and grows. White cells die, and spill their destructive
compounds (superoxide radicals) on stomach lining cells. Extra nutrients are sent to reinforce the white
cells, and the H. pylori can feed on this. Within a few days, gastritis and perhaps eventually a peptic ulcer
results. It may not be H. pylori itself which causes peptic ulcer, but the inflammation of the stomach lining;
i.e. the response to H. pylori.
ii) Digestion in the small intestine
The small intestine is about 7m long in man and
consists of a straight d__________ and a coiled
i______. Opening into the duodenum is a combined
duct formed from the union of the b____ duct and
p_________ duct.
The wall of the small intestine has the usual four
layers. Its inner surface has folds, which help to
sl___ down the passage of food.
All over the surface are tiny finger-like projections
called v_____ about 20-40 per mm2 which, together
with the folds provide a large s______ area for
digestion and absorption of food. The villi also
cont____ and sway, thus contacting more food.
AL notes Heterotrophic Nutrition P.7
The duodenum receives digestive juices made by the l_____, p_______ and the i_________ wall.
a. Bile
 Bile is made in the liver / stored in the g____ bladder / released down the bile duct to the
duodenum.
 A yellowish-green watery fluid of pH 8 containing bile s____, bile pig_____, mucin and
chol________.
 It contains no e_______ but its alk_______ helps to neutralise the acid chyme entering the
duodenum and aids the activity of enzymes in the pancreatic and intestinal juices. The bile
salts help to e_______ fats, breaking them up and providing a larger surface area for digestion.
The bile pigments are excr_______ products formed during the breakdown of old r__ blood
cells by the liver.
Reference reading : Bile salt
Bile salts, primarily cholic acid
and chenodeoxycholic acids, are
cholesterol derivatives. In
addition to their role in
emulsifying fats, they also help
in fat and cholesterol
absorption.
Although many substances
secreted in the bile leaves the
body in faeces, bile salt are
conserved by a recycling
system in they are reabsorbed
into the blood by the ileum,
returned to the liver via the
hepatic portal vein.
b. Pancreatic juice
 colourless with a pH about 8.8, due to
the sodium b__________ present.
 It also contains two enzyme precursors,
trypsinogen and chymotrypsinogen,
which are only activated when they
contact the enzyme entero______
produced by the intestinal en_____.
(a brush border enzyme).
The del__ in activating them ensures
that these protein-digesting enzymes
do not digest the pancreatic duct as
they pass along it. In their active
forms tryp___ and ______trypsin
digest proteins to large polypeptides.
 Pancreas secretes an am____ similar to that in saliva, which continues the digestion of starch
to m______.
 Also present are lip____ which hydrolyse f___ to g_______ and f____ acids.
 Nucleases are responsible for the hydrolysis of nucleic acids into nucleo______.
AL notes Heterotrophic Nutrition P.8
c. The intestinal juice
It is a watery solution of pH about 7.4-7.8. Although most digestion action takes place in the small
intestine, intestinal juice provides little of what is needed to perform these functions. Except for
the b______ border enzymes, most substances required for chemical digestion is imported from
the l_____ and the p________.
 In the duodenum is an additional type of gland called Brunner's gland, which secretes an
al________ fluid containing mucus. This helps to maintain the correct ____ for digestion and
also p______ the duodenum from the acidic chyme.
d. Epithelium of small intestine (Brush border)
Attached to the epithelium of small intestine
are a number of e_______ (brush border
enzymes) that complete the final stages of
digestion. These enzymes are built into the
membranes of the intestinal epithelium, which
is also the site of ab_________.
 Carbohydr____ / disaccharidases:
sucrase (invertase) converts sucrose to
glucose and fructose; maltase converts
maltose to glucose; and lactase converts
lactose to glucose and galactose.

Nucleotid_____ break down nucleotides into
nitrogen bases, sugar and phosphates.

Carboxypeptidase & aminopeptidase
hydrolyse small polypeptides to a_____
acids. .Dipeptidases break down
dipeptides into amino acids.
 Peristalsis and hydrolysing enzymes reduce
the food to a fluid called chy__.
AL notes Heterotrophic Nutrition P.9
Enzyme digestion in the Human digestive system
Carbohydrate
digestion
Oral cavity,
Pharynx,
Oesophagus
Protein digestion
Fat digestion
Nucleic acid
digestion
Fat g
DNA, RNA
Salivary
amylase
Smaller
polysaccharides
Maltose
Stomach
P
P
Small p
Lumen of
Small
Intestine
Polysaccharides
Polypeptides
T
C
P
a
Maltose and other
di
Smaller
Polypeptides
Carboxypeptidases
A
Epithelium
of Small
Intestine
(Brush
Border)
B
s
Fat d
(emulsified)
N
N
L
Glycerol, fatty
acids,
Glycerides
acids
Small peptides
N
Di
Di
Monosaccharides
Amino acids
N
s
b
,p
AL notes Heterotrophic Nutrition P.10
Reference reading : Lactose intolerance
The enzyme lactase hydrolyses lactose to its constituent monosaccharides. This enzyme is found in all
human babies, but is only found in adults from northern Europe and a few African tribes. Most other human
groups, including Orientals, Arabs, Jews, most Africans, Indians and Mediterranean peoples produce little
or no lactase as adults and may even show lactose intolerance.
The undigested lactose sugar creates osmotic gradients not only prevent water from being absorbed but
also pull water from the interstitial space into the small and large intestines, resulting in diarrhoea. Bacterial
metabolism of the undigested sugar produces large amount of gas that results in flatulence and cramping
pain. The solution to this problem is simple—add lactase enzyme ’drops’ to your milk or take a lactose
tablet before meals containing milk products
c)
Absorption
i)
The Small intestine
Very little absorption of food occurs in the stomach,
mainly w____ and glu____. The bulk of absorption
takes place in the il____ when the food has been
digested to molecules of hexose sugars, amino acids,
glycerol and fatty acids, which are small enough to
pass through the gut wall.
In man, and other mammals, absorption is aided by
the large surface area provided by the villi and their
covering of _______villi.
Note the abundance of mitochondria in the epithelial cells. What
do you think are their roles in the process of absorption?
 villus has a c_________ network
supplied by a small arteriole.
 Each villus has a surface covered in
m________ that form on top of an
epithelial cell known as a brush
b_______.
 Some absorbed substances pass through
the brush border into the capillary by
p________ transport. E.g. fructose
 Most cross the epithelial cell
membranes by a_____ transport.
e.g. Pep____ fragments and a_____
a____, vit_____, glu____ and some
simple sugars.
 Malt___, sucr___, and lact___ are
also absorbed by the microvilli.
En______ in the cells (brush border
enzymes) convert these disaccharides
into mono__________ that then leave
the cell and enter the capillary.
Heterotrophic nutrition P11
Absorption of specific nutrients
1. Carbohydrates
 Glucose and galactose are actively taken up and carried into the epithelial cells by common
protein car______ and then move into the capillary blood.
 Th carriers which are located very closely with the disaccharidases on the brush border, they
combine with the monosaccharides as soon as the disaccharides are broken down.
 Fructose transport is not ATP dependent, it moves entirely by fac_______ transport.
Reference reading : The Na+-glucose secondary transport mechanism
A secondary active transport system uses the Na+-K+ pump as the first step, generating a strong Na+ gradient
across the cell membrane. Then the glucose-Na+ symport protein uses that Na+ gradient to transport glucose
into the cell.
This system is used in a novel way in human gut epithelial cells. These cells take in glucose and Na+ from the
intestines and transport them through to the blood stream using the concerted actions of Na+-glucose symports,
glucose permeases (a glucose facilitated diffusion protein), and Na+-K+ pumps. Note that the epithelial cells are
joined together by tight junctions to prevent anything from leaking through from the intestines to the blood
stream without first being filtered by the epithelial cells.
2. Proteins
 Several types of carriers a_______ transport the different classes of amino acids.
 Short ch___ of amino acids (tripeptides and dipeptides) are also actively transported, but they
are di_____ to their amino acids within the epithelial cells before they enter the capillary blood.
Although whole proteins are not usually absorbed, in rare cases intact proteins are taken up by endocytosis
and released on the other side of the epithelial cells by exocytosis. This process is most common in newborn
infant, reflecting their immaturity and accounts for many early food allergies. The mechanism may also
provide a route for antibodies from breast-milk to reach an infant’s blood—passive immmuity.
3. Fats
Just as bile salts accelerate lipid d______, they are essential for the ab_____ of its digested products .
The products of fat digestion, the monoglycerides and fatty acids, are relatively water-in______.
They readily associate with the bile salts to form tiny micelles.
M______ are collection of fatty elements clustered together with the bile salts in a way that the
Heterotrophic nutrition P12
pol__ end of the molecules face the water and the non____ portions form the micelle core. Also
nested within the hydrophobic core are chol________ and f__-soluble vitamins. They are similar to
emulsion droplets but are much smaller so that they can easily diffuse between microvilli and come
into close contact with the mucosal membrane.
The fatty substances, cholesterol, and fat-soluble vitamins then leave the micelles and, because of
their high lipid solubility, move through the li____ phase of the membrane by simple d_________.
Once inside the epithelial cells, the free fatty acids and the monoglycerides are re_________into
tri__________ The triglycerides are then combined with small amount of phospholipids and
cholesterol, and coated with a ‘skin’ of proteins to form water soluble lipoprotein droplets called
chylomicrons, which are processed by the Golgi apparatus for extrusion from the cell.
The milky-white chylomicrons are too large to pass through the wall of the blood capillaries, instead
they enter the more permeable l______. Thus most fat enters the lym_____ stream and is
eventually emptied into the venous b_____.
4. Vitamins
Small intestine absorb dietary vitamins, the l_____ intestine absorb some of the __ and __ vitamins
made by the bacteria.
 Most water-soluble vitamins (B &C) are absorbed readily by d________.
 Fat-s_______ vitamins (A,D,E, K) dissolve in dietary f___, become incorporated into the
mi_____, and move across the epithelium by passive d________.
5. Electrolytes
 Most ions are a_______ absorbed along the entire length of the small intestine.
 Absorption of sodium is coupled with the absorption of glu____ and a_____ acids.
most part, anions follows the electrical potential established by sodium transport.
For the
 Calcium absorption is regulated by vitamin ___.
Q4.
Mechanisms for absorption in the small intestine
As we have seen, glucose, galactose, and fructose are examples of
hexose sugars with the empirical formula C6H12O6. Xylose and
arabinose are pentose sugars with the empirical formula C5H10O5.
Results from experiments on the rates of absorption of these sugars by
pieces of living intestine and by pieces of intestine poisoned with
cyanide are given in table below. The rates are shown in relation to the
rate of absorption of glucose by the living intestine.
a What relationship is shown between molecular size and rate of
absorption ?
b
Suggest a reason for the difference in the rates of absorption of glucose
and galactose by living and by poisoned intestine.
c
Suggest a reason for the difference in the rates of absorption of glucose
and galactose when compared with that of fructose.
Rate of absorption
Sugar
By living
intestine
Glucose
1.00
By
poisoned
intestine
0.33
Galactose
1.10
0.53
Fructose
0.43
0.37
Xylose
0.30
0.31
Arabinose
0.29
0.29
Heterotrophic nutrition P13
Pieces of a rat's intestine bathed in a solution of sodium sulphate absorb
glucose at a rapid rate. Pieces bathed in lithium sulphate solution absorb
glucose much more slowly. The results of a demonstration of this effect are
shown in the graph above.
d
ii)
On the basis of these results and those summarized in table above,
comment on the absorption of glucose from the small intestine.
The large intestine
The large intestine is about one and a half metres long and divided into a cae___ and app_____,
rec___ and a___ canal.
The caecum is large in diameter and has a bl___-ending appendix projecting from it. In some
herbivores, such as the rabbit the caecum and appendix are important as sites of cel_____ digestion
by s________ bacteria, but in man it does not have this function and indeed may sometimes trap food
that putrefies and causes inflam________, resulting in appendicitis.
Heterotrophic nutrition P14
The colon has three regions, the ascending, transverse and descending limbs. It bends round to become
the rectum, leading to the anus that is closed by a sph_______ muscle.
The wall of the large intestine has the usual four layers but no villi, though mucus-secreting gl____
are present and there are large patches of lymphoid tissue that presumably eliminate bacterial toxins.
The main function of the large intestine is the absorption of w____ so that the contents gradually
become more solid and consist of insoluble waste materials referred to collectively as faeces. These
vary in content with the diet, but may contain undigested roug_____, d____ cells from the gut lining,
living and dead bact_____, unwanted m______ salts, including iron, calcium and magnesium,
usually as phosphates, bile p_______ from bile, hydrogen sulp____, ammonia and indole and
skatole---products of amino acid breakdown responsible for the offensive smell. Surprisingly the water
content may still be as high as 60 to 70%.
Faecal movement along the gut is slow, usually in
powerful waves particularly when more food is
taken in. This gives t____ for water absorption
and mineral salt secretion. Faeces may take from
14hrs to 3 days or more to pass to the rectum and
their arrival there stimulates defaecation
(egestion).
Q. Explain how the structure of the small intestine is related to its functions
d)
Assimilation
Assimilation is the incorporation of f____
into the body for growth and repair. In a
mammal the nutrients absorbed from the gut
are brought to the l_____ that stores, changes
or re-directs them as required.
(85 IIA3)
6m
Heterotrophic nutrition P15
Protein metabolism
 Neither proteins nor amino acids can be stored in the body. They must be used or altered
immediately by one of two processes: de____________ or trans__________. These processes
are particularly rapid in the liver and kidney.
 In deamination the amino group (NH2)
is removed from the amino acid in the
form of am______, but the ammonia is
highly toxic and is converted into less
poisonous u____.
 Transamination is the transference of
amino groups between amino acids to
make another kind. This is performed
by the liver. All the non-e_________
amino acids can be made in this way,
but the essential ones must be taken in
in the diet.
 It works by the reversible transfer of
an amino group from an amino acid
to what was originally an -keto acid,
forming a new keto acid and a new
amino acid.
 The residue of the amino acid after the
amino group has been removed by any
of these processes is called a ____
acid, some can be converted to glucose
and enter car__________
metabolism.
Carbohydrate and fat metabolism
Carbohydrate metabolism revolves around the maintenance of a steady level of gl______ in the
blood. This is kept to approximately 0.1 g per 100 cm3 regardless of the level of sugar in the diet.
The level is maintained by the interconversion of gl______ and gl_______, the latter being formed
mainly in the liver and muscles.
 A rise in blood sugar level results in increased production of insulin from the -cells of the islets of
Langerhans in the p_______. The effect of insulin is to accelerate the conversion of glucose to
glycogen so that the blood sugar level falls again.
 If the level drops too low, the -cells of the islets of Langerhans would be stimulated to produce
glucagon. This hor______ facilitates the conversion of glycogen to glucose and the level will
rise again (the reverse effect of in________).
 If the intake of carbohydrate is excessive the glycogen storage capacity of the liver (about 100 g)
and muscles (about 300 g) may be exceeded and the additional carbohydrate is then converted
to f___ for storage. E.g. the connective tissues under the skin, and around many organs.
Heterotrophic nutrition P16
 Adipose tissue is a collection of cells in which fat accumulates. The fat forms a large globule in the
cell pushing the nucleus and cytoplasm to the periphery.
 The conversion of carbohydrate to fat begins with its breakdown to py______ acid which is then
decarboxylated to a______ coenzyme A (2 carbon fragments). Repeating reactions of adding
the 2C fragments together leads to the formation of the f____ acids. These are finally
combined with g______ produced from to form fats for storage.
e)
The accessory glands of the gut
i)
The mammalian liver
Structure of liver tissue
 The liver is the l_______ gland in the body.
The liver receives oxygenated blood from
the hepatic a______ and blood rich in
f____ from the hepatic p_____ v____.
 Inside the liver, these vessels divide into a
network of cap______ or sinusoids, which
ramify throughout the tissue and eventually
drain into the hepatic v____, in which
products released by the liver are carried
away.
 In the walls of the sinusoids are occasional
phago_____ cells. These are responsible
for destroying old r___ blood cells,
bact____ and any for____ matter passing
through the sinusoids.
Functions of the liver










C___________ metabolism and regulation of blood sugar level;
De____________ and trans___________ of amino acids;
F___ metabolism;
Secretion of b____;
Storage of i____ released from the breakdown of old red blood cells;
Storage of vit_______ A and D and B12
Manufacture of plasma p_______ including those used in blood clotting;
Produces h____ by its active metabolism and this is subsequently distributed by the blood;
De_______ by the phagocytic cells removing old red blood cells, bacteria etc.;
De___________. This includes the breakdown of ammonia from ___aminated amino acids
into less toxic urea; the destruction of hor_____ therefore limiting their period of
effectiveness; and modification of dr___ and al_____ prior to their excretion by the kidney.
Q. Describe the roles played by the liver in the homeostatic mechanisms of mammals. (90 II B5)
10m
Heterotrophic nutrition P17
ii)
The pancreas
The pancreas lies between the stomach and duodenum. It is composed of secretory cells secrete
pancreatic j______which is carried away by the pancreatic duct.
Scattered at intervals are small masses of cells called the islets of L__________ which are ductless
or endo______ glands and secrete the hormones in______ and glu______ directly into the b_____.
II)
SAPROPHYTES

Saprophytes feed on d___ animals and plants and include many bacteria and fungi.

They secrete a range of en_____ through their body surfaces on to the food where ______cellular
digestion occurs.

The soluble food is then ab_____ into the saprophyte's body. These organisms are particularly
important in promoting the d____ of dead animal and plant material so that the elements locked up
in it can be re______.



Heterotrophic nutrition P18
III)
PARASITES

Parasites feed on the living tissues of plants and animals. Many bacteria and fungi are parasitic
causing a variety of plant and animal diseases.

There are even a few parasitic flowering plants such as the dodder. They don’t contain
chlorophyll and each feeds by sending outgrowths which penetrate the hosts' vascular tissues.

Animal parasites vary a good deal in the closeness of their association with the host, some merely
visiting it for food like a mosquito, others remaining with the host and feeding at intervals like a flea,
and some like tapeworms being internal parasites which never leave the host.

The adaptations they show for feeding vary accordingly, from the biting and sucking mouthparts of
some insects to the absence of mouthparts, or even a gut, in some internal parasites (like the
tapeworm, which absorbs digested food all over its surface).
E.g.
Tapeworm as an internal parasite
Problems and adaptations of Tapeworm to the parasitic mode of life
Problems
encountered by
tapeworm living as a
parasite
1
2
Adaptations found in Tapeworm
Heterotrophic nutrition P19
3
4
5
6
Specialisations of some common parasites:
Features
Type of modification
Attachment organs such as hooks or suckers.
Feeding
Highly specialised mouthparts as in fluid feeders.
Anticoagulant production in blood feeders.
Degeneration of
unnecessary
organs
Degeneracy of sense organs associated with the constancy of
the parasite's environment.
Respiration
Reproduction
Taenia,
Leech,
mosquito,
Aphids
Mosquito,
Leech
Taenia,
Absence or degeneration of feeding and locomotory organs characteristic of gut parasites.
Resistant outer covering.
Against Host
reaction
Examples
Taenia
Production of anti-enzymes for gut parasites
Ability to respire in anaerobic conditions.
Taenia,
Enormous numbers of reproductive bodies, i.e. eggs, cysts and
spores.
Taenia,
Employment of specialised reproductive phases in life cycle.
Taenia,
Use of secondary hosts as vectors.
Taenia,
Plasmodium
Taenia,
Hermaphrodite condition thus aiding possible self- fertilisation.
Q. a) List the similarities and differences between saprophytic and parasitic nutrition.
4m
b) With reference to a named example, show how the structure of a saprophyte is related to its mode of
nutrition.
4m
c) i) Draw labelled diagrams to show the life cycles of a named parasitic animal and a named parasitic fungus.
ii) Discuss the common adaptive features shown in the life cycles of both organisms to their parasitic mode
of life.
(89IIB 7)
12m
Heterotrophic nutrition P20
IV)
CARNIVOROUS PLANTS
Carnivorous or insectivorous plants feed autotrophically using their green leaves but also have
modifications which allow them to trap insects so that they also feed heterotrophically. This enables
them to live in nit_____-deficient habitats augmenting their supply from insect protein. eg. the
pitcher plant has pitcher-shaped leaves containing digestive juices into which the insects fall.
V)
APPENDIX : Details of the source and function of vitamins
Vitamin
Source
Function
Effect of deficiency
A (Retinol)
Fish liver oils, liver,
kidney, dairy produce and
eggs. Vegetable products
(e.g. spinach, carrots)
contain carotene and
other caro- tenoids. These
may be converted to
vitamin A during
absorption in the small
intestine.
Essential for vision in dim
light. Maintenance of healthy
skin and surface tissues,
especially those which secrete
mucus.
Night blindness.
Increased chance of
respiratory and intestinal
infections. Roughening
of the skin.
B1 (Thiamin)
Wholemeal bread and
whole grain cereals, yeast
extract.
Steady and continuous release
of energy from carbohydrate.
Component of coenzyme
Beriberi. Weakness of
limbs, possible
paralysis.
B3 (Nicotinic acid,
Niacin)
Instant coffee, liver, meat,
fish, tea, eggs, legumes.
Also involved in utilisation of
food energy. Essential part of
NAD+ and NADP (hydrogen
acceptors).
C (Ascorbic acid)
Rose-hips, blackcurrants,
citrus fruits. Raw fruits
and vegetables.
Maintenance of healthy
connective tissue. Role in
biological redox reactions.
Scurvy. Bleeding from
small blood vessels and
into the gums. Wounds
heal more slowly.
D (Calciferols)
Cod liver oil, fish,
margarine. Action of
sunlight on skin.
Necessary for maintaining
levels of calcium and
phosphorus in blood enhances absorption of
dietary calcium from intestine
and regulates interchange of
calcium between blood and
bone.
Rickets - deformed limb
bones too weak to
support weight of body.
Q. Discuss the importance of carbohydrates, lipids, proteins and roughage in the human diet. (90 II B3)
End
8m