Heterotrophic Nutrition Flashcards
1
Q
Define nutrition.
A
Nutrition is the process of acquiring energy and materials for cell activities
2
Q
Define heterotrophic nutrition.
A
Heterotrophic nutrition is the process of obtaining energy metabolic raw materials from organic materials made by other organisms.
3
Q
What are heterotrophs?
A
These are organisms that feed on organic sources of carbon. Their survival is dependent directly or indirectly on the autotrophs.
4
Q
What are the types of heterotrophic nutrition?
A
(a) Holozoic nutrition
(b) Saprotrophic nutrition (Saprophytic nutrition)
(c) Symbiosis:
(i) Parasitism
(ii) Mutualism
(iii) Commensalism
5
Q
What is holozoic nutrition?
A
This is the type of nutrition in which complex organic food is taken in and broken down inside the body of an organism into simple soluble molecules which are then absorbed and assimilated.
6
Q
What is digestion?
A
This refers to the process of reducing large complex food materials into simpler soluble materials.
7
Q
What is absorption?
A
This is the process of taking the soluble molecules from the region of
digestion into the tissues of the organism.
8
Q
Define assimilation.
A
This is the process of using the absorbed nutrients for a particular purpose in the organism’s body.
9
Q
What are the characteristic processes involved in holozoic nutrition?
A
- Ingestion; is the taking in of food.
- Digestion. Is the breakdown of large organic molecules into smaller and simpler molecules.
- There are two types of digestion namely;
• Mechanical digestion, involves mechanical or physical break down of food for example by
teeth.
• Chemical digestion. Involves the activity of enzymes which carry out chemical breakdown
of food by hydrolysis. Digestion can also be intracellular (inside the cell) or extracellular
(outside the cell) - Absorption. This is the uptake of the soluble molecules from the digestive region across a membrane into the body tissues. The food may pass directly into the cells or first into blood stream to be transported other regions of the body.
- Assimilation. This is the process of using the absorbed molecules to provide either energy or materials to be incorporated into the body.
- Egestion. This is the elimination from the body of undigested waste food materials.
10
Q
Define saprophytic nutrition.
A
This is a type of nutrition where organisms feed on dead decaying organic matter.
Organisms which undergo this form of nutrition are called saprotrophs/saprophytes/ saprobionts mainly fungi such as yeast, mucor, and Rhizopus; and bacteria.
- Nucleotidases: catalyse hydrolysis of nucleotides into phosphoric acid, nitrogenous bases and pentose sugars.
- Maltase: catalyses hydrolysis of maltose into glucose molecules, thereby completing starch digestion.
- Sucrase (invertase): catalyses hydrolysis of sucrose into glucose and fructose molecules
- Lactase: catalyses hydrolysis of lactose into glucose and galactose molecules
- Intestinal lipase: catalyses hydrolysis of lipids into fatty acids and glycerol.
- Intestinal amylase: catalyses hydrolysis of starch into maltose.
What is another name for succus entericus?
Intestinal juice
Define food absorption
It is the process by which soluble food substances are absorbed across the gut epithelium into blood circulatory system or lymphatic system to be carried to all body cells.
11
Q
How does saprophytism proceed?
A
These organisms secrete enzymes into their food where it is extracellulary digested.
The soluble end-products are then absorbed assimilated by the saprotrophs.
12
Q
How do Rhizopus feed?
A
Their hyphae (wire-like structures) penetrate the food on which they grow and secrete hydrolyzing enzymes from their tips.
These enzymes then carry out extracellular digestion of starch to glucose and proteins to amino acids respectively.
The thin, branching nature of the mycelium (a mass of hyphae), provides a large surface area for absorption.
Glucose is then used during respiration to provide energy for the organism’s metabolic activities.
More glucose and amino acids are used for growth and repair.
Excess glucose will be converted to glycogen and fats, and excess amino acids to protein granules and stored in the cytoplasm.
Extracellular digestion in a common bread mould (Rhizopus stoloninfer)
13
Q
Define symbiosis.
A
This refers to the process by which two or more organisms of different species form a close relationship involving living together.
14
Q
What is mutualism?
A
This is a relationship between two organisms of different species in which both partners benefit
15
Q
What is parasitism?
A
A relationship between two organisms of different species in which one partner benefits and causes harm to the other
16
Q
What is commensalism?
A
A relationship between two organisms of different species in which one partner benefits but the other receives no harm or benefit.
17
Q
What are examples of mutualistic relationships?
A
• Herbivorous ruminants contain very many cellulose-digesting bacteria and ciliates which can only survive in the anaerobic conditions of a ruminant’s alimentary canal. Bacteria and ciliates feed on the cellulose in host’s diet converting it into simple compounds for further digestion, absorption and assimilation by the ruminant.
• Formation of root nodules by Rhizobium bacteria. The bacteria which inhabit the nodules hence stimulating growth and division of parenchyma cells resulting into swellings (nodules). The bacteria gets sheltered by the plant as the plant benefits from nitrogen fixation done by the bacteria.
• Another example is a mycorrhiza. This is a symbiotic association between a fungus and a plant root. This association is the major route of entry of mineral nutrients into roots. The fungus receives organic nutrients mainly carbohydrates and vitamins from the plant and in return absorbs mineral salts and water which can pass in the plant root.
There are two forms of mycorrhizas are; Ectotrophic mycorrhizas, form a sheath around the root and penetrate the air spaces between the cells in the cortex. Endotrophic mycorrhizas, occurring in virtually all plants, forming an intercellular network and extend into the soil but appear to penetrate cells.
18
Q
What are obligate parasites?
A
Organisms which live their entire life parasitically
19
Q
What are facultative parasites?
A
Organisms which live as parasites for only a short period of their life cycle are termed facultative parasites
20
Q
Give nutrition-related adaptations of parasites.
A
• Many endoparasites such as flat worms have no gut, since they can above pre-digested food through the cuticle.
• The large surface area to volume ratio of the flatworms means that no special internal system is required because materials can rapidly diffuse to all body parts.
• Endoparasites have no special sense organs like eyes, because they live in the dark, constant environments and do not need move looking for food.
• They also lack locomotory devices, since they live in a constant environment except free living flat worms.
• The nervous system of internal parasites is poorly developed compared with free-living ones, because they do not need coordination since they live in a constant environment.
• The ecto parasites have well developed sucking mouse parts such as proboscis, to such blood from their hosts.
• The internal parasites such as tape worms can withstand low oxygen levels of the gut and respire anaerobically, since they live in the gut where there is very little oxygen.
21
Q
What is an example of commensalism?
A
- An egret bird and a grazing cow; the cow chases insects due its feeding method while the egret picks the exposed insects for food.
- In this case the cow (host) doesn’t intend to chase the insects for the egret (commensal) but they fly away from the grass being fed on by the cow.
22
Q
Describe detritus feeding.
A
The term detritus refers to fresh or decaying organic matter commonly found at the soil surface.
23
Q
What is a detritivore?
A
An organism specialized for feeding on detritus for example the earth worm.
24
Q
Briefly explain how earthworms are significant in the maintenance of soil fertility.
A
The earthworm consumes fragments of detritus; pieces of food are torn off, moistened by alkaline secretions of pharynx and then swallowed.
Earthworms can also feed on organic material contained in soil which they swallow during burrowing activity.
Thus nutrients are recycled
25
What organs are a part of the alimentary canal?
- Mouth
- throat
- oesophagus
- stomach
- small intestine (duodenum, jejunum and ileum)
- large intestine (colon, caecum and appendix)
- rectum
- anus.
26
What structures are a part of accessory structures?
- Teeth
- tongue
- salivary glands
- liver
- gall balder
- pancreas
27
What are accessory structures?
These are organs, glands, and tissues that enable digestive processes, e.g. by secreting fluids /chemicals, but the food does not actually pass through them.
28
What are the secretions of the mucous cells, chief cells, and parietal cells known collectively as?
Gastric juice
29
What are the components of gastric juice?
- mucus
- pepsinogen
- hydrochloric acid
30
What do mucus cells secrete?
- Mucus
- Bicarbonate ions
31
What are the functions of the secretions of the mucus cells?
- Mucus is a physical barrier between the lumen and stomach lining
- Bicarbonate ions buffer gastric acid to prevent damage to the epithelium
32
What do chief/peptic/zymogenic cells secrete?
- Pepsinogen
- Prorennin
33
What are the functions of the secretions of the chief cells?
- Pepsinogen is converted to pepsin which digests protein, including collagen
- Gastric lipase: Digests lipids
- Prorennin is converted to Rennin which curdles soluble Caseinogen (milk protein) into insoluble casein whose slow flow enables digestion
34
What do parietal cells secrete?
- HCl
35
What are the functions of the secretions of the parietal cells?
- HCl activates pepsinogen to pepsin, Prorennin to rennin
- HCl kills bacteria in the stomach
36
What do G-cells secrete?
- Gastrin hormone
37
What are the functions of the secretions of the G-cells?
- Gastrin stimulates secretion of gastric juice
- Gastrin Increases contractions of gastro-intestinal tract
- Gastrin hormone relaxes the pyloric sphincter.
38
What do D cells produce?
- HCl
39
What are the functions of the secretions of the D cells?
- HCl activates pepsinogen to pepsin, Prorennin to rennin
- HCl kills bacteria in the stomach
40
What do VIP-producing cells secrete?
Vasoactive intestinal peptide
41
What is the use of the secretions of VIP-producing cells?
- Vasoactive Intestinal Peptide induces smooth muscle relaxation
- It Inhibits gastric acid secretion
- It Stimulates pepsinogen secretion by chief cells
42
Define digestion.
Digestion is the process by which large food molecules are broken down into small soluble molecules which can be absorbed and assimilated into the tissues of the body.
43
What are the two types of processes involved in digestion?
- Mechanical processes; these include the chewing and grinding of food by the teeth and also the churning and mixing of the contents of the stomach to expose more surface area to the enzymes that finish the digestive process.
- Chemical processes; which include hydrolysis action of digestive enzymes, bile, acids.
44
Describe the process of digestion in the mouth.
- It starts with chewing (mastication), which breaks food into pieces small enough to be swallowed
- Chewing also increases the surface area of food to digestive enzymes.
- The sight, taste, smell and thought of food induces salivary glands to secrete saliva.
- During chewing, saliva mixes with food and the different saliva components perform different functions:
(i) Salivary amylase (ptyalin) enzyme catalyses the breakdown of amylose of cooked starch into maltose.
(ii) Water in saliva moistens food and binding it together for swallowing
(iii) Mucin binds and lubricates food; to enable swallowing.
(iv) Chloride ions activate salivary amylase
(v) Lysozymes kill bacteria in the buccal cavity.
45
True or false:
Amylase is usually absent in the saliva of carnivores because of absence of cooked starch in the diet.
True
46
Describe the process of swallowing in man
- Swallowing is a reflex action, which lasts less than 10 seconds.
- The tongue contracts to push the bolus towards the throat, forcing the soft palate upwards to close the nasopharynx
- Larynx and hyoid bone move anteriorly and upwards.
- Epiglottis bends downwards to close larynx (trachea entrance) to prevent food from entering the trachea.
- However, any food that enters into trachea is expelled out by coughing reflex.
- Breathing briefly stops due to closure of glottis.
- Pharynx shortens.
- Upper oesophageal sphincter relaxes, to allow the bolus enter into oesophagus
- In oesophagus the food bolus moves by peristalsis, a sequence of wave-like contractions that squeeze food down the oesophagus.
- Lower oesophageal sphincter (cardiac sphincter) relaxes to allow food into stomach.
47
Describe digestion of food in the stomach.
- Arrival of food in the stomach stimulates secretion of gastrin hormone from G-cells into the blood stream
- Gastrin stimulates the gastric glands to secrete gastric juice, whose components include: mucus, pepsinogen, hydrochloric acid.
- The components of gastric juice are secreted by different cells and perform different roles as follows:
- Mucus cells secrete mucus which forms a barrier at the stomach lining, to prevent tissue digestion.
- Mucus cells also secrete bicarbonate which buffers gastric acid to prevent damage to epithelium
- Chief cells secrete pepsinogen, prorennin and gastric lipase.
- When pepsinogen is activated to pepsin it digests proteins to polypeptides
- Prorennin is activated to rennin which coagulates soluble milk protein Caseinogen into insoluble casein in babies, whose slowed flow enables digestion.
- Gastric lipase digests lipids to fatty acids and glycerol
- Parietal / oxyntic cells secrete Hydrochloric acid this;
- Activates pepsinogen to pepsin, Prorennin to rennin
- Kills most bacteria in the stomach.
- Provides optimum acidic pH for pepsin to hydrolyse proteins into polypeptides.
- Stops the working of salivary amylase enzyme
- Due to churning by the stomach wall, VIP-producing cells are stimulated to secrete the hormone called vasoactive intestinal peptide, which causes relaxation of pyloric sphincter muscle to allow the semi solid chyme flow from the stomach into the duodenum, after a maximum of about four hours.
48
Describe the mechanism of HCl secretion in parietal cells.
- Hydrochloric acid is produced by parietal cells through a complex series of reactions.
- Catalysed by the enzyme carbonic anhydrase, carbon dioxide (which diffused from capillaries) reacts with water to form carbonic acid, which dissociates into bicarbonate ion and hydrogen ion.
- Bicarbonate ion is transported into the blood stream by an ion exchange molecule in plasma membrane which exchanges bicarbonate ions exiting parietal cells for chloride ions entering.
- Hydrogen ions are actively pumped into the duct of gastric gland and the negatively charged chloride ions diffuse with the positively charged hydrogen ions.
- Potassium ions are counter pumped into the parietal cell in exchange for hydrogen ions.
- The net result is production of hydrochloric acid in the parietal cells and its secretion into the duct of gastric gland.
49
Describe the process of digestion in the duodenum.
- Arrival of partially digested, acid food mixture (chyme) in the duodenum stimulates endocrine cells in duodenal walls to secrete the hormones: Secretin, Enterogastrone, Cholecystokinin (CCK) Villikinin and Enterocrinin.
- Secretin hormone secretion is stimulated by presence of acid chyme in duodenum
- Secretin stimulates the liver to secrete bile into the gall bladder.
- It Stimulates pancreatic secretion of (hydrogen carbonate ions) from acinar cells.
- Hydrogen carbonate ions neutralise the acid from the stomach to provide an alkaline pH optimum for pancreatic enzymes.
- Secretin also inhibits secretion of HCl by parietal cells as chyme leaves the stomach.
- Enterogastrone hormone reduces stomach motility
- It inhibits oxyntic cells from secreting hydrochloric acid in order to provide an optimum pH for pancreatic enzymes.
- Signals the stomach to empty slowly when fat is present, allowing much time for digestion of fat already emptied.
- Cholecystokinin hormone (CCK) stimulates contraction of gall bladder to release bile into duodenum.
- Bile salts emulsify fats i.e. fats physically break into droplets which increases their surface area
- CCK also Stimulates the pancreas to secrete pancreatic enzymes
- Pancreatic amylase which catalyses the hydrolysis of starch into maltose
- Enterokinase which activates Trypsinogen to Trypsin.
- Trypsinogen, which is activated by enterokinase to Trypsin.
- Trypsin: Catalyses hydrolysis of polypeptides to peptides.
- Villikinin increases peristalsis in the small intestine and ileum villi movements, in duodenum preparation for incoming food.
50
True or false
High fat diets stimulate enterogastrone production
True
This prolongs food stay in the stomach, and is therefore useful in treating duodenal ulcer.
51
Why are all proteolytic (protein digesting) enzymes along the gut secreted in inactive (precursor) form?
To prevent autolysis (self-digestion) of gut tissues, which are protein in nature.
52
What does the churning action of duodenal walls turn the semi-solid Chyme into?
Chyle
A thin, milky-looking alkaline fluid
53
Describe the process of digestion in the ileum
- Distention of the small intestine by food stimulates the secretion of intestinal juice (Succus entericus)
- This consists of a mixture of substances from crypts of Lieberkühn and Brunner’s glands.
- Some of the components of Succus entericus include the following enzymes:
- Peptidases: catalyse hydrolysis of peptides into amino acids,thereby completing the digestion of proteins.
- Nucleotidases: catalyse hydrolysis of nucleotides into phosphoric acid, nitrogenous bases and pentose sugars.
- Maltase: catalyses hydrolysis of maltose into glucose molecules, thereby completing starch digestion.
- Sucrase (invertase): catalyses hydrolysis of sucrose into glucose and fructose molecules
- Lactase: catalyses hydrolysis of lactose into glucose and galactose molecules
- Intestinal lipase: catalyses hydrolysis of lipids into fatty acids and glycerol.
- Intestinal amylase: catalyses hydrolysis of starch into maltose.
54
What is another name for succus entericus?
Intestinal juice
55
A
56
Define food absorption
It is the process by which soluble food substances are absorbed across the gut epithelium into blood circulatory system or lymphatic system to be carried to all body cells.
57
What processes are involved in absorbing digested food?
(1) Simple diffusion
(2) Facilitated diffusion
(3) Active transport: Direct active transport and Secondary active transport
58
What is secondary active transport?
A form of active transport across a biological membrane in which a transporter protein couples the movement of an ion (e.g. Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient.
Thus, energy stored in the electrochemical gradient of an ion is used to drive the transport of another solute against a concentration or electrochemical gradient.
59
What are the types of secondary active transport?
1. Cotransport (also known as Symport)
2. Exchange (also known as Antiport)
60
What is cotransport?
The direction of transport is the same for both the driving ion and driven ion/molecule.
Examples:
(i) The Na+/glucose cotransporter in enterocytes (small intestine epithelial cell) and kidney proximal tubule epithelial cells simultaneously transports 2 Na+ ions and 1 glucose molecule into the cell across the plasma membrane.
61
Describe exchange in the movement of molecules across a cell membrane
The driving ion and driven ion/molecule move in opposite directions.
Example:
The Na+/Ca2+ exchanger in cardiac muscle cells transports 3 Na+ ions into the cell in exchange for 1 Ca2+ ion transported out of the cell.
62
Give the adaptations of the ileum to absorption of food
(i) Ileum is long and highly folded for increased surface area in absorption of soluble food substances.
(ii) Ileum has numerous finger-like projections called villi which increase the surface area for absorption of soluble food.
(iii) Ileum epithelial cells have microvilli which further increase the surface area for efficient food absorption.
(iv) Ileum epithelium is thin to reduce diffusion distance for soluble food substances to allow fast rate of diffusion.
(v) Ileum epithelium is permeable to allow movement of soluble food substances across with minimum resistance.
(vi) Ileum villi have dense network of blood capillaries to rapidly carry away digested food from the absorption area which maintains a steep diffusion gradient.
(vii) Ileum villi have permeable lacteal, a branch of the lymphatic system for carrying away fats
(viii) Ileum epithelial cells have numerous mitochondria to generate ATP energy for active transport of some ions.
(ix)
Ileum inner surface is lined with a lot of mucus to prevent autolysis (self-digestion) by proteolytic enzymes.
63
Explain how the structure of villi in the small intestine is related to absorption of digested food.
- Large surface area by microvilli / protrusion of exposed parts for fast uptake of soluble substances.
- Epithelium only one layer thick to reduce diffusion distance.
- Protein channels allow facilitated diffusion and active transport.
- Numerous mitochondria provide much ATP for active uptake of some nutrients like glucose and salts.
- Blood capillaries close to epithelium/ surface to reduce diffusion distance during absorption of glucose/ amino acids
- Lacteal / lymphatic vessel is permeable/has large surface area at centre to absorb fatty acids and glycerol.
- Tight junctions between adjacent villi enable controlling absorption of substances
64
What occurs in the colon?
Mainly absorption of:
(i) Water into the blood capillaries by osmosis.
(ii) Na+, Cl- and K+
65
What is the importance of control of digestion?
(i) Secretion of digestive juices depends on respiratory energy, therefore unnecessary secretion must be prevented to avoid wastage of respiratory substrates.
(ii) Secretion of proteolytic enzymes in inactive form prevents autolysis (self-digestion of tissues).
66
State the digestive juices secreted
- Saliva (buccal cavity)
- gastric juice in the stomach;
- pancreatic juice and bile in the duodenum;
- intestinal juice in the ileum;
67
Describe the control of digestion in the mouth
- Sight / smell / thought of food stimulate conditioned reflexes involving the cerebral cortex, hypothalamus and medulla oblongata
- These stimulate salivary glands to secrete saliva.
- Contact of food with tongue taste receptors stimulates nerve impulses via sensory neurons to the hypothalamus and medulla oblongata; relayed along motor neurons to stimulate salivary glands to secrete saliva.
- Salivary amylase in saliva causes hydrolysis of starch to maltose.
- Loss of appetite / depression inhibit cerebral cortex; parasympathetic centre is not stimulated, no secretion of saliva;
68
Describe the control of digestion in the stomach
- Occurs in 3 phases: cephalic; gastric; and intestinal phases;
Cephalic phase / Nervous phase:
- It occurs before food enters the stomach;
- Sight / smell / thought of food stimulate conditioned and unconditioned reflexes; involving the cerebral cortex, hypothalamus and medulla oblongata;
- This stimulates the vagus nerve causing the release of acetylcholine; which stimulates the secretion of the hormone gastrin
- The effects of gastrin are:
(i) Stimulates secretion of gastric juice.
(ii) Increases contractions of gastro-intestinal tract
(iii) Relaxes the pyloric sphincter to let in bolus of food from the gullet;
- Loss of appetite / depression inhibit cerebral cortex; parasympathetic centre is not stimulated, no gastric secretion;
Gastric phase:
- Arrival of food bolus distends / stretches the stomach wall which activates stretch receptors to fire impulses to the Meissner’s plexus in the stomach wall to cause the following effects:
(i) Stimulate local secretory reflexes in the stomach wall to activate gastric glands secrete pepsinogen and HCl;
(ii) Stimulate reflexes in the medulla, via the vagus nerve to activate gastric glands wall to secrete pepsinogen and HCl;
(iii) Stimulate enteroendocrine cells / G-cells to secrete gastrin hormone; which stimulates secretion of gastric juice;
(iv) Stimulate enteroendocrine /enterochromaffin cells to secrete histamine; which activates secretion of gastric juice;
- Partially digested proteins especially peptides / decrease in pH activates chemoreceptors, which stimulate G-cells to secrete gastrin hormone; which stimulates secretion of gastric juice;
- Excessive acidity (PH of less than 2) inhibits G-cells hence gastric juice secretion reduces;
Intestinal phase:
- Distension of duodenum / presence of acid chyme / partially digested food stimulates the secretion of intestinal (enteric) gastrin hormone; which stimulates secretion of gastric juice in the stomach;
- Distension of duodenum / presence of acid chyme / fatty acids / irritants / in the duodenum stimulates the secretion of Intestinal hormones:
(i) Secretin; which stimulates the release of bile from the liver and hydrogen bicarbonate ions in pancreatic juice;
(ii) Cholecystokinin; which stimulates the pancreas to secrete its enzymes;
(iii) Enterogastrone; which inhibits/suppresses gastric activity (any further secretion of acid by the stomach);
(iv) Vasoactive intestinal peptide inhibits gastric acid secretion.
- Distension of duodenum / presence of acid chyme / fatty acids / irritants / in the duodenum initiates gastric-inhibitory impulses in the enterogastric reflex causing suppression of gastric activity; and emptying of stomach;
69
Define Assimilation
The process by which simple soluble food substances are absorbed and used by body cells in the various ways.
70
What is Metabolism?
Chemical processes within cells of an organism.
71
What is Catabolism?
Break down of complex molecules into simpler molecules, with release of energy.
72
What is Anabolism?
Assembly / building up of complex molecules from simple molecules using energy.
73
What is the use of absorbed glucose in the body?
- ATP synthesis in respiration
- Formation of glycoproteins involved in cell to cell recognition mechanisms.
- Excess carbohydrates are stored in the form of glycogen in the liver and muscles.
74
How does the body deal with excess glucose?
- Stored in the liver as glycogen.
- Excess carbohydrates may be converted into fats for storage.
75
What is the use of absorbed amino acids in the body?
- Formation of protoplasm of cells during growth
- Production of enzymes and antibodies
- Formation of body structures such as hairs, nails, hooves, cell membranes
- Oxidised to release ATP energy during severe starvation i.e. in the absence of glucose and fats.
- Formation of hormones e.g. insulin
- Formation of plasma membrane components e.g. glycoproteins, channel proteins
76
How does the body deal with excess amino acids?
- Deaminated in the liver to form urea, which is expelled by kidneys.
- Some amino acids are transaminated to produce a different amino acid
77
What is the use of absorbed fatty acids and glycerol in the body?
- The long chain fatty acids are desaturated in the liver and are then broken down to carbon dioxide and water by successive oxidations.
- Some of it can be converted into glucose
- Some used to form various structures which are components of cells e.g. phospholipids
78
How does the body deal with excess fatty acids and glycerol?
- Stored as fat under the skin
79
What roles does the liver play in food digestion?
- On stimulation by secretin hormone, the liver secretes bile into the gall bladder.
- On stimulation by CCK hormone, gall bladder contracts to release bile salts which emulsify fats i.e. fats physically break into droplets due to reduced surface tension, which increases their surface area
80
What roles does the pancreas play in food digestion?
- On stimulation by cholecystokinin hormone, the pancreas secretes enzymes whose effects are as follows:
(i) Amylase catalyses hydrolysis of starch into maltose
(ii) Enterokinase enzyme which activates Trypsinogen to Trypsin.
(iii) Trypsin:
(1) Catalyses hydrolysis of polypeptides to peptides.
(iv) Lipase hydrolyses fats to fatty acids and glycerol
(v) Nuclease hydrolyses nucleic acids to nucleotides
(vi) Polypeptidase hydrolyses polypeptides to amino acids.
- On stimulation by secretin hormone, the pancreas secretes hydrogen carbonate ions from acinar cells, which neutralise the acid chyme from the stomach to provide an alkaline pH optimum for pancreatic enzymes.
81
What roles does the liver play in metabolism of absorbed products?
1. The Liver regulates blood glucose:
(i) If in excess (above 90mg/100cm3), glucose is converted into glycogen for storage.
(ii) If little (below 90mg/100cm3), glycogen is converted into glucose for use.
2. The liver regulates amino acids in the body: Excess amino acids are not stored in the body, but undergo deamination process. i.e. the amino group (NH2) from the amino acid is removed to form ammonia, which later forms urea that is carried in blood to kidneys for excretion.
3. The liver regulates lipids (fats) in the body: It synthesizes and degrades phospholipids and cholesterol.
4. The liver forms red blood cells in foetus and breaks down worn out red blood cells in adults.
5. The liver forms plasma proteins from amino acids
6. The liver stores fat soluble vitamins A, D, E, K and water soluble vitamins B12 and C
7. The liver stores minerals like Iron, potassium, copper, zinc and trace elements.
8. The liver detoxifies poisonous substances i.e. toxic substances are turned harmless by the liver cells e.g. alcohol, cholesterol and hydrogen peroxide.
82
What roles does the pancreas play in metabolism of absorbed products?
i) If in excess glucose(above 90mg/100cm3), the pancreas is stimulated to secrete insulin hormone which causes conversion of glucose to glycogen for storage, fat or metabolizing it to energy and CO2.
(ii) If little glucose(below 90mg/100cm3), the pancreas is stimulated to secrete glucagon hormone which causes conversion of glucagon to glucose hence increasing the blood glucose level.
83
What are causes of starvation?
- Prolonged fasting
- anorexia
- deprivation
- disease
84
Give symptoms of starvation
- Weight loss
- dehydration
- apathy
- increased susceptibility to infectious disease
- discoloured hair color
- flaky skin
85
Describe the changes in energy reserves when one undergoes prolonged fasting
- Glycogen, proteins, and fats are all metabolized during starvation.
- Exhaustion of blood glucose stimulates glucagon secretion and insulin secretion is inhibited.
- Within the first 24 hours, the very low glycogen amount stored in the liver and muscles decreases rapidly to depletion because glycogen is broken down into glucose for oxidation to release energy, while the amounts of fats and protein remain high.
- Anaerobic breakdown of glycogen in skeletal muscle is also stimulated.
- Within week 1, after depletion of carbohydrate/glycogen, the amount of fats decreases rapidly while the amount of protein decreases gradually until about 6 weeks of starvation.
- This is because fats are hydrolysed rapidly into fatty acids and glycerol while oxidation of amino acids releases energy.
- The liver metabolizes fatty acids into ketone bodies that are degraded to release energy.
- Accumulation of ketones causes ketosis, by condition characterised by blood becoming acidic
- Fatty acids in skeletal muscles are broken down to release energy, thus decreasing the use of glucose by tissues other than the brain.
- Glycerol is converted into small amount of glucose, but most of the glucose is formed from the amino acids of proteins.
- The brain begins to use ketone bodies, as wells as glucose, for energy.
- Dependency on fats for energy release decreases the demand for glucose, protein breakdown reduces but does not stop.
- The liver degrades non-essential proteins into glucose for the brain in a process called gluconeogenesis, which involves converting carbon skeletons into pyruvate or Krebs’ cycle intermediates and excreting amino groups from the body as urea.
- From 6 weeks to 8 weeks, amount of fat decreases slowly to very low levels, while amount of protein decreases rapidly.
- This is because as fat reserves / stores are getting depleted, metabolism of fats to release energy occurs gradually and the body begins to rapidly break down essential proteins, leading to loss of liver and heart function as these organs are broken down for fuel metabolizing proteins as the major energy source.
- Muscles, the largest source of protein in the body, are rapidly depleted.
86
Differentiate between grazers and browsers
Grazers mainly feed on grass while browsers mainly feed on leaves of shrubs and trees
87
What are the adaptations of carnivores to finding and capturing prey?
- Well-developed sense of smell for locating prey
- Fast moving to outpace and capture prey
- Well-built body to manipulate and capture prey.
- Very sharp claws for gripping and killing prey.
- Keen eye sight for locating prey from a distance
- Foot pads enable stealth movement to ambush prey.
- Long, sticky tongue for reaching distant prey e.g. toads.
- Elongated canines for digging up prey e.g. walrus
88
What are the adaptations of herbivores to grazing or browsing?
- Upper jaw lacks incisors to provide a hard pad against which lower incisors press and cut grass.
- Tongue is highly muscular for manipulating food during chewing.
89
What are the adaptations of carnivores for ingesting food?
- Sharp pointed canines for tearing the fresh of prey
- Flat molars to crush prey
- Incisors pointed for nipping and biting.
- Carnassial teeth present for shearing flesh.
- Upper jaw wider than lower jaw to facilitate shearing.
- Up-and-down jaw action only prevents lateral movement hence reducing the danger of dislocation
- Powerful jaw muscles provide much force for chewing
90
What are the adaptations of herbivores for ingesting food?
- Molars and premolars are ridged for maximum grinding of hard cellulose materials.
- Molars and premolars have large surface area for maximum grinding of the hard cellulose materials.
- Articulation of lower jaw permits lateral movement to enable maximum grinding of food.
- Well-developed jaw muscles provide much grinding power for crushing cellulose materials.
- Between the front and cheek teeth, there’s a gap called diastema for separating crushed grass from uncrushed grass for effective chewing.
91
What are the adaptations of carnivores for digestion of food?
- No cellulose in diet hence less developed caecum and appendix to reduce on body weight to enable fast running.
- Relatively short alimentary canal reduces weight, since diet is entirely protein.
92
What are the adaptations of herbivores for digesting food?
- Ruminant stomachs are four chambered to derive maximum nourishment from grass.
- Mutualistic bacteria in caecum and appendix enable chemical digestion of cellulose into glucose.
- Relatively long alimentary canal to digest vegetation
93
What are the nutrition-based differences between carnivores and herbivores?
Carnivores:
- Closed pulp cavity in teeth
- Upper jaw incisors present
- Canines present and well developed
- Carnassial teeth present
- Cheek teeth pointed
- Articulation of lower jaw prevents lateral movement
- Relatively short alimentary canal
- No cellulose digestion
Herbivores:
- Open pulp cavity in teeth
- Upper jaw incisors absent in most herbivores
- Canines small or absent to create a diastema
- Carnassial teeth absent
- Cheek teeth flattened with enamel ridges and dentine grooves
- Articulation of lower jaw permits lateral movement
- Relatively long alimentary canal
- Cellulose digestion occurs in caecum
94
What is diet?
This is the quantity and nature of the food we eat i.e. which nutrients and how much of each.
95
Define a Balanced diet
Is one which contains the correct proportions and quantity of the various nutrients, water and dietary fibre required to maintain health.
96
What is a ruminant?
These are the mammals, which have a 4-chambered stomach for the digestion of plant-based food.
97
Give examples of ruminating mammals
- cattle
- goats
- sheep
- giraffes
- deer
- camels
- antelope,
98
Describe digestion in the rumen
- Bacteria and protozoa in the rumen secrete cellulase enzyme which breaks down cellulose into glucose which undergoes fermentation to form organic acids, carbon dioxide and ethane.
- The fermentation process produces heat that keeps ruminants warm.
99
Describe digestion in the reticulum (Honeycomb bag)
- Here any foreign objects that may have been accidentally swallowed with food settle out in the honeycomb structure of the reticulum’s walls.
- Reticulum is sometimes called “hardware stomach”.
100
Describe digestion in the Omasum (Psalterium / Manyplies)
- It absorbs water from food and also absorbs more nutrients called volatile fatty acids that supply ruminants with energy.
101
Describe digestion in the Abomasum (Reed / True stomach)
- Here, the food particles are digested by hydrochloric acid in the same way it occurs in human stomachs.
- The remaining particles are then passed on to the small intestine where most of the nutrients are absorbed by the body and made available to the ruminant.
102
Describe cellulose digestion in termites
- Guts of wood-eating termites contain a micro-organism called Trichonympha
- It secretes cellulase enzyme to digest cellulose in wood.
- The termite absorbs some of the products of digestion (glucose), while Trichonympha gets sheltered.
103
Describe cellulose digestion in rabbits and non-ruminants
- The caecum and appendix of a rabbit contain bacteria that secrete cellulase enzyme for digesting cellulose into glucose.
- The herbivore gains glucose while the bacteria get shelter.
- In the process described as coprophagy (coprophagia), rabbits eat own faecal pellets while dung beetles feed on cow dung to enable absorption of glucose at the ileum.
104
What challenges are faced by ectoparasites?
- Failure to cling on the host to avoid being dislodged.
- Failure to obtain nutritive molecules from the host.
- Failure to find the right host for dispersal to their final host
105
What challenges are faced by endoparasites?
- Failure to penetrate the host
- Failure to obtain nutritive molecules from the host.
- Destruction by the digestive enzymes and immune responses of the hosts.
- Complete elimination or extinction.
- Fluctuating environment e.g. low oxygen tensions, excess heat, solute concentration, darkness etc.
- Failure to find the right host for dispersal to their final host
106
What are the structural adaptations of parasites?
- Possession of penetrative devices for host entry e.g. fungal haustoria, cutting teeth in hook worms Ancylostoma duodenale)
- Possession of nutrient suckers e.g. leech
- Development of digestive-resistant outer covering to avoid host’s enzyme attack e.g. Ascaris and Taenia etc.
- Camouflaging morphology to increase survival chances e.g. brown ticks on brown cattle.
- Possession of specialised mouth parts in some ecto-parasites to suck hosts e.g. sharp stylets in aphids and tsetse flies.
- Possession of specialised haustorial structures in Cuscuta (Dodder plants) for obtaining nutrients from the host
- Degeneration of non-essential organs e.g. no feeding organs, no locomotory organs, no alimentary canal to reduce body size and fit in intestines /blood vessels and for reducing energy expenditure on such organs for example Fasciola hepatica (liver fluke), tape worm, hook worm etc
107
What are the physiological adaptations of parasites?
- Production of enzymes to digest the host’s tissues during penetration into the host e.g. fungi and plasmodium
- Production of anticoagulants by blood feeding parasitic animals such as mosquitoes and ticks to avoid blood clotting during feeding.
- Highly tolerant to fluctuating environment e.g. anaerobic respiration in areas of low oxygen tensions, high temperatures, darkness and pH changes in places where they live e.g. most endoparasites.
- Rapid means of escape which increases their chances of survival e.g. fleas and mosquitoes.
- Production of much mucus for resisting digestion by host’s enzymes.
- Some endoparasites produce chemicals to protect themselves against the immune response of the host.
108
What are the reproductive adaptations of parasites?
- Some are hermaphrodites with the ability to carry out self fertilisation to increase the rate of reproduction e.g. Fasciola, Taenia.
- Some asexually reproduce for high rate of reproduction to avoid extinction.
- Release of sexually mature forms of the parasites as free living organisms e.g. in some parasitic animals such as the horse hair worms
- Production of large number of infective agents such as eggs, cysts, and spores which increase survival chances to avoid extinction e.g. tape worms.
- Development of reproductive bodies that are highly resistant when out of the host to survive adverse conditions e.g. cysts in amoeba, fungal spores, etc.
- Use of intermediate host (vector) for their transfer to primary host e.g. plasmodium in female anopheles mosquito to man.
- Some parasites localise the strategic points for propagation to the next host e.g. HIV which causes AIDS is localised in the sex organs.
- Some use hereditary transmission for increased spreading i.e. some parasites infect the ovary of primary host which lays parasite infected eggs.
109
What is a Definitive host (final host / primary host)?
This is a host in which a parasite attains sexual maturity.
110
What is an Intermediate host (secondary host)?
This is a host in which a parasite passes one or more of its asexual stages; usually designated first and second, if there is more than one.
111
To what phylum/ division do the following parasites belong?Fasciola hepatica (liver Fluke), Schistosoma mansoni (blood fluke), Taenia solium (Pork tape worm) and Taenia saginata (Cattle tapeworm)
Platyhelminthes
112
What parasite causes Schistosomiasis (Bilharzia)?
Schistosoma mansoni (blood fluke)
113
To what phylum/ division does the following parasite belong? Ascaris lumbricoides (roundworm)
Nematoda
114
To what phylum/ division does the following parasite belong? Plasmodium
Arthropoda
115
Describe the lifecycle of Ascaris lumbricoides
- Adult female in lumen of ileum lays about 200,000 eggs daily, which are passed out in faeces.
- Fertile eggs embryonate and become infective after about three weeks, (optimum conditions: moist, warm, shaded soil).
- On being swallowed by humans, eggs hatch into larvae, which invade intestinal wall, and are carried via the portal, then systemic circulation to lungs.
- Larvae mature further in lungs (10 to 14 days), penetrate alveolar walls, ascend the bronchi to the throat, and are swallowed into gut.
- Upon reaching the ileum, they develop into adult worms.
- Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female.
- Adult worms can live 1 to 2 years.
116
What are the adaptations of ascaris to parasitic life?
- Degeneration of structures reduces space occupied.
- Possession of digestive-resistant cuticle resists destruction by the host’s enzymes.
- Ability to position itself in a habitat where it gains maximum nourishment.
- Eggs have protective/resistant shell which is their main ineffective and resistant stage.
- Tolerance to oxygen deficient environment
- Ability to copulate within the intestines followed by the laying of very many eggs increases survival chances.
117
Describe the lifecycle of Taenia (Tapeworm)
- Humans are the definitive hosts for T. saginata and T. solium.
- Eggs or gravid proglottids are passed out in faeces;
- Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs or gravid proglottids.
- In the animal’s intestine, the oncospheres hatch, invade the intestinal wall, and migrate to striated muscles, where they develop into cysticerci.
- A cysticercus can survive for several years in the animal.
- Humans become infected by ingesting raw or undercooked infected meat.
- In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years.
- Adult tapeworms attach and stay in small intestine by their scolex.
- The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approx 6 per day).
- The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces.
118
Give adaptations of Taenia to parasitism
- Has hooks and suckers for holding tightly onto ileum wall.
- Flattened body increases surface area for absorbing its host’s digested food
- Degeneration of structures reduces on space occupied.
- Lays many eggs to increase survival chances.
- Hooks for boring through the gut of the host
- Eggs have a thick shell for resisting enzyme destruction.
- Being hermaphrodite increases reproductive rate
- Thick cuticle to resist digestion by host‘s enzymes
- No sense organs and reduced body structures to fit in host‘s body.
- Can respire anaerobically in low oxygen.
- Feeds on already digested food from the host.
- Eggs remain viable for a long time.
- Secretes mucus to prevent digestion by host‘s enzyme.
- Has hooks and suckers for holding tightly onto ileum wall.
- Flattened body increases surface area for absorbing its host‘s digested food
- Degeneration of structures reduces on space occupied.
- Lays many eggs to increase survival chances; raising their reproductive success.
- Eggs have a thick shell for resisting enzyme destruction.
- Being hermaphrodite increases reproductive rate.
119
Describe the lifecycle of plasmodium
- Malaria parasite life cycle involves humans as intermediate host and adult female anopheles mosquito as definitive host.
- During a blood meal, a malaria-infected female Anopheles mosquito releases sporozoites into human blood.
- On reaching the liver, sporozoites infect liver cells and mature into schizonts, which rupture and release merozoites.
- After this initial replication in the liver (exo-erythrocytic schizogony), the parasites undergo asexual multiplication in the erythrocytes (erythrocytic schizogony).
- Merozoites infect red blood cells, the ring stage trophozoites mature into schizonts, which rupture releasing merozoites.
- Some parasites differentiate into sexual erythrocytic stages (gametocytes).
- Blood stage parasites are responsible for the clinical manifestations of the disease.
- The gametocytes, male (microgametocytes) and female (macrogametocytes), are ingested by an Anopheles mosquito during a blood meal.
- The parasites’ multiplication in the mosquito is known as the sporogonic cycle.
- While in the mosquito’s stomach, the microgametes penetrate the macrogametes-generating zygotes.
- Zygotes become motile and elongated (ookinetes), invade the midgut wall of the mosquito to develop into oocysts.
- Oocysts grow, rupture, and release sporozoites, which enter the mosquito’s salivary glands.
- Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle.
120
Define saprotrophism
The process of obtaining soluble organic substances from extracellular digestion of dead or decayed organic matter.
121
What is a Saprotroph?
An organism that absorbs soluble nutrients from extracellular digestion of dead/decaying organic matter.
122
What are examples of saprotrophs?
(i) Saprobes: fungi like mushrooms, yeasts and moulds
(ii) Saprophytes: saprotrophic plants e.g. sugar stick
(iii) Saprophages: Animal scavengers, such as dung beetles and vultures
123
What are the similarities between parasites and saprophytes?
Both:
- are heterotrophs
- absorb soluble food
- have simple digestive systems
- have sexual and asexual phases in their reproduction
- produce large numbers of offspring.y
124
What are the differences between parasites and saprophytes?
Parasites:
- Energy derived from living organisms
- Many stages in lifecycle
- Very specific to their host
- Nutritionally highly adapted
- Most plant and animal groups have representatives
- Most are aerobic
Saprophyte:
- Energy derived from dead organisms
- Usually a single adult stage, with spores inclusive
- Use a variety of food sources
- Simple methods of nutrition
- Almost totally fungi and bacteria
- Anaerobic and aerobic
125
What is the importance of saprophytes?
- Recycling of materials e.g. carbon, nitrogen, phosphorus
- Brewing and baking e.g. yeast (Saccharomyces)
- Making antibiotics e.g. Penicillin
- Decomposition of wastes e.g. sewage
- Production of yoghurt and cheese
- Food source e.g. mushrooms
- Industrial applications e.g. leather tanning, production of vitamins, etc.
126
Give similarities between mutualism and parasitism
- Both are nutritional associations between living organisms;
• In both one of the two organisms in the association may live in or on another;
• In both associations the two organisms in association show some specificity to each other;
• Both are interspecific associations;
• In both several grades of association exist from lose to tight associations but in each case the two organisms in the association may not live successfully apart;
• In both associations one of the organisms in the association is usually smaller than the other;
127
What are the differences between parasitism and mutualism?
Parasitism:
- One partner (the parasite) benefits while the other (the host) suffers
- Benefit is almost entirely nutritional
- The parasite may require an intermediate host (vector)
- Requires several modifications (adaptations) that are structural, physiological etc.
- Organisms depend on high reproductive potentials are and are not usually resistant stages in their life cycles;
Mutualism:
- Both partners benefit fully from the association and no harm of any kind suffered;
- Benefit may be nutritional and any other e.g. shelter, protection and even transport;
- No intermediate organisms required
- Modifications are not necessary
- High reproductive potentials are always developed and are not usually
128
Describe how gut bacteria contribute to the well-being of herbivores
- Symbiotic bacteria haboured in enlarged caeca and appendix; release cellulases that digest cellulose, releasing nutrients from plant materials absorbed by the herbivore such as cow, goats;
- Also symbionts in the rumen that is when they die they pass through the digestive system with the food and form an important source of nutrients, especially proteins;
129
Explain how Nitrogen-fixing bacteria contribute to the well-being of herbivores.
- Rhizobium in a mutualistic association with roots of leguminous plants; such as peas, beans, and clover;
- They convert atmospheric nitrogen into ammonia;
- this combines with carboxylic acids formed in Krebs cycle to make a range of amino acids; for synthesis of proteins and nucleic acids;
- constituting plant structures and also stimulate growth of plants which are fed upon by herbivores to obtain nutrients such as vitamins carbohydrates, proteins for nouri- shment of their bodies
130
Explain how the structure of the wall of the ileum is adapted to its function
• Crypts of Lieberkuhn produce new cells to replace those worn off from villi tips secrete intestinal juice;
• Numerous goblet cells; secrete mucus to lubricate food; helping passage through the gut
• Epithelium is single cell layer; reduce diffusion distance for food substances
• Microvilli have enzymes in cell surface membranes; permit contact digestion.
• Numerous tight junctions; ensure digested food passes through epithelial cells
• Dense capillary network within villi; maintains a steep concentration gradient for absorption
• Smooth muscles in the villi allow movement, bringing villi into close contact with digested food.
• Longitudinal and circular muscles that are antagonistic bring about peristalsis and mixing of food
• Folds of wall of ileum; villi, microvilli/ brush border increases surface area for absorption of digested food.
131
Describe filter feeding as a feeding mechanism.
This is a mechanism of feeding where the filter feeders such as most Molluscs strain small particles of organic matter from water.
132
What do D cells produce?
Somatostatin hormone
133
What are the functions of the secretions of the D cells?
- Somatostatin inhibits stomach secretion of gastrin and HCl
- It also inhibits duodenal secretion of secretin and cholecystokinin
- It also inhibits pancreas secretion of glucagon
134
Amylase is secreted into the lumen of the gut, but maltase is attached to the surface of the epithelial cells. Suggest the importance of this difference
Pancreatic amylase hydrolyses amylose to maltose; maltase hydrolyses maltose to glucose most chyme that enters the small intestine contains more amylose than maltose; glucose absorbed by epithelial cells;
