Chapter 15 Heterotrophic Nutrition Introduction Heterotrophic nutrition consumes complex organic food material which originates from autotrophic organisms.

Chapter 15

Heterotrophic Nutrition

• Introduction• Heterotrophic nutrition consumes complex

organic food material which originates from autotrophic organisms.

• There are several forms of heterotrophic nutrition:

• 1.   Saprophytic nutrition

• 2.   Parasitic nutrition

• 3.   Holozoic nutrition

1. Saprophytic nutrition – involves the consumption of complex organic food from the bodies of dead organisms.

• The food is either in soluble form or digested externally into simple molecules to diffuse into the organism,

• e.g bacteria and fungi

2. Parasitism: • some organisms live on or inside other organisms,

obtaining benefits from them and causing harm.

• Organisms have simple digestive system and food is often soluble forms,

• e.g. • Tapeworm (parasite) obtain digested food (benefit)

from man (host) rostellumhook

sucker

immature proglottis

• 3. Holozoic nutrition – involves the consumption of complex (solid) food which is broken down inside the organism into simple molecules which are then absorbed,

• e.g. most animals

15.1 Holozoic Nutrition• Holozoic organisms obtain their energy

from the consumption of complex organic food which is digested within their bodies.

• It involves:• 1. Obtaining food (ingestion) • 2. Ingestion• 3. Physical (mechanical) digestion • 4. Chemical digestion• 5. Absorption• 6. Assimilation• 7. Elimination (egestion)

• According to the type of food ingested, holozoic organisms are classified into:

• Herbivores - those feed on plant material

• Carnivores - those feed on other animals

• Omnivores - those feed on both plants and

animals

• Fluid feeders - those consume liquid

materials

Teeth and dentition in manThe structure of the tooth

Types of teeth

• Milk Teeth and Permanent Teeth

• Milk teeth

• - appear in babies;

• - totally 20 in man

• Permanent teeth

• - replace milk teeth in later years;

• - cannot replaced if damaged;

• - totally 32 in man

Tooth decay

Adaptations to particular dietsHerbivorous adaptations of mammals, e.g. deer

1. A horny pad replaces the upper incisors & canines

2. Diastema - a gap to separate newly nibbled food from those chewing at the back

Skull of deer

Dental formula of a sheep : 0033

3123

3. Cheek teeth with ridged surfaces because of differential wearing of enamel and dentine

4. Jaws can move vertically & laterally - for more efficient grinding by teeth5. Teeth have open roots - teeth grow continuously throughout life to

replace wearing by constant grinding activity6. Stomach is divided into a number of chambers

with micro-organisms to secreted cellulase for the digestion of cellulose (ruminants).

Regurgitation of food from stomach to mouth before passing into the remaining stomach compartments

7. The alimentary canal is relatively long because the digestion of plant material is difficult

• 15.3 Principles of Digestion

• Mechanical breakdown of food has the effect of giving the food a large surface area which aids later digestion.

• The food must be made small enough to pass through cell membranes. Thus chemical digestion with the aid of enzymes occurs.

• amylase - breaks down starch into maltose

• peptidases – break down peptides into amino acids

• endopeptidases – break down peptide bonds in the middle of peptides

Endopeptidases hydrolyse peptide bonds at points along the protein

Carboxypeptidase liberates terminal amino acids

COOH NH2

Exopeptidases acts on terminal amino acids

Aminopeptidase breaks terminal amino acids with –NH2 group

• exopeptidases – break down peptide bonds on terminal amino acids

• aminopeptidases – break down amino acids with a free amino (-NH2) group

• carboxypeptidases – break down amino acids with a free carboxyl (-COOH) group

• lipase - breaks down fats into fatty acids and glycerol

The food vacuoles of protozoans represent the simplest form of digestive system:

• Advantages: • allows the organism to achieve the optimum

concentration of enzymes in a small space within the vacuole

• Disadvantages:1 The organism is restricted to food small enough to be

ingested by phagocytosis2 All enzymes operate within the vacuole without

specialization of certain regions3 Acidic and alkaline phases must be taken within the

same vacuole at separate times

• 15.4 Digestion in Humans

• 15.4.1 Digestion in the mouth

• Mechanical digestion of food begins in the buccal cavity. The tongue manipulates the food during chewing with saliva produced from 3 pairs of salivary glands.

The human digestive system

Digestive System of the Rabbit

• Saliva contains:• 1. Water – over 99%• 2. Salivary amylase – enzyme • 3. Mineral salts • – maintain optimum pH for amylase• 4. Mucin • – bind food particles together and • lubricates food for swallowing• Taste buds allow food to be selected. • The thoroughly chewed food (bolus) is passed

to the back of the mouth for swallowing.

15.4.2 Swallowing and peristalsis

- pharynx leads to both trachea & oesophagus

- when swallowing food, epiglottis closes entrance to trachea to prevent food going into lungs

Peristalsis - longitudinal & circular muscles contract & relax alternately to drive food down oesophagus, small intestine, large intestine & out of the anus as faeces

Gastric mucosa of stomach

15.4.3 Digestion in the stomach

• The stomach is a muscular sac with a folded inner layer (gastric mucosa) with holes (gastric pits) lined with secretory cells which secrete gastric juice:

1. Water - the bulk of the secretion

2. Hydrochloric acid - secreted by the oxyntic cells

• Functions: • Gives an acid pH to kill bacteria and activates enzymes

in the stomach (pepsinogen & prorennin);

• Initiates the hydrolysis of sucrose & nucleoproteins

3. Pepsinogen - secreted by the zymogen (chief cells) in an inactive form to pepsin

• It is activated by HCl

4. Prorennin - secreted by zymogen cells; activated by HCl to rennin to coagulate milk by converting caseinogen (soluble protein in milk) to casein (insoluble)

5. Mucus - secreted by goblet cells to produced a protective layer to prevent autodigestion of the gastric mucosa (thus preventing ulcer)

• It also lubricates food in the stomach

• What is peptic ulcer?

• It is a disease in which a hole has been made in the mucous membrane lining the stomach or duodenum.

• Causes: too much HCl

because of nervous tension, irregular meals, smoking, alcohols, lack of sleeps, etc.

• Cure: antacids

• The churning and mixing action of the muscular stomach wall changes the bolus of food into a creamy fluid (chyme).

• The chyme from any one meal takes 3-4 hours to be released little by little into the duodenum.

• This provides a continuous supply of food for absorption throughout the period between meals.

15.4.4 Digestion in the small intestine

• Duodenum: for digestion

• Ileum: chiefly for absorption

• The walls of the small intestine are folded with villi which contain fibres of smooth muscle.

• These muscles regularly contract and relax to mix food and enzymes so as to facilitate absorption.

• The digestive juices of the small intestines are: