Nutrition in Animals - KCSE Form 1 Biology Notes

​Heterotrophism

Meaning and Types of Heterotrophism

• This is a mode of nutrition whereby organisms feed on complex organic matter from other plants or animals.
• All animals are heterotrophs.
• Their mode of feeding is also said to be holozoic to distinguish it from other special types of heterotrophic nutrition namely:
  • Saprophytism
  • Parasitism
• Saprophytism/saprotrophysim- occurs in most fungi and some forms of bacteria.
• Saprophytes feed on dead organic matter and cause its decomposition or decay.
• Parasitism is a mode of feeding whereby one organism called the parasite feeds on or lives in another organism called the host and harms it. 

Leech

​Modes of Feeding in Animals 

1. Animals have developed various structures to capture and ingest food.
2. The type of structures present depend on the method of feeding and the type of food.
3. Carnivorous animals feed on whole animals or portions of their flesh.
4. Herbivorous animals feed on plant material.
5. Omnivorous animals feed on both plants and animal materials.

​​Feeding in Mammals

• The jaws and teeth of mammals are modified according to the type of food eaten.
• Mammals have different kinds of teeth.
• Each type of teeth has a particular role to play in the feeding process.

​Feeding in Mammals

• The jaws and teeth of mammals are modified according to the type of food eaten.
• Mammals have different kinds of teeth.
• Each type of teeth has a particular role to play in the feeding process.

​Feeding in Mammals

• The jaws and teeth of mammals are modified according to the type of food eaten.
• Mammals have different kinds of teeth.
• Each type of teeth has a particular role to play in the feeding process.
• This condition is described as heterodont.
• The teeth of reptiles and amphibians are all similar in shape and carry out the same function.
• They are said to be homodont. 

​Types of Mammalian Teeth

• Mammals have four kinds of teeth.
• The incisors are found at the front of the jaw.
• They are sharp-edged and are used for biting.
• The canines are located at the sides of the jaw.
• They are pointed and are used for tearing and piercing.
• The premolars are next to the canines and the molars are at the back of the jaw.
• Both premolars and molars are used for crushing and grinding.
• Teeth are replaced only once in a lifetime.
• The first set is the milk or deciduous teeth.
• These are replaced by the second set or the permanent teeth.

• Dentition refers to the type of teeth, the number and their arrangement in the jaw.
• A dental formula shows the type and number of teeth in each half of the jaw.
• The number of teeth in half of the upper jaw is represented above a line and those on the lower jaw below the line.
• The first letter of each type of teeth is used in the formula i.e. i = incisors, c = canines, pm = premolars and m = molars.
• The total number is obtained by multiplying by two (for the two halves of each jaw).

Adaptation of Teeth to Feeding
In general, incisors are for cutting, canines for tearing while premolars and molars are for grinding.
However, specific modifications are observed in different mammals as an adaptation to the type of food they eat.
Teeth of Herbivores

• Incisors are long and flat with a sharp chisel like edge for cutting.
• The enamel coating is thicker in front than at the back so that as the tooth wears out, a sharp edge is maintained.
• Canines are reduced or absent.
• If absent, the space left is called the diastema.
• The diastema allows the tongue to hold food and push it to the grinding teeth at the back of the mouth.

Premolars and molars:

• These are transversely ridged.
• The ridges on the upper teeth fit into grooves on the lower ones.
• This gives a sideways grinding surface.
• The teeth of herbivores have open roots i.e., wide opening into the pulp cavity.
• This ensures a continued adequate supply of food and oxygen to the tooth.
• In some herbivores, such as rabbits and elephants, the incisors continue to grow throughout life.

Teeth of Carnivores

• Incisors are reduced in size and pointed.
• They are well suited for grasping food and holding prey.
• Canines are long, pointed and curved.
• They are used for piercing and tearing flesh as well as for attack and defence.
• Premolars and molars: In general, they are long and longitudinally ridged to increase surface area for crushing.
• Carnassial Teeth: These are the last premolars on the upper jaw and the first molars on the lower one.
• They are enlarged for cutting flesh.
• They act as a pair of shears.
• They also crush bones.
• The teeth of carnivores have closed roots i.e., only a very small opening of the pulp cavity to allow food and oxygen to keep teeth alive.
• Once broken, no re-growth can take place.

Teeth of Omnivores

• Incisors have a wide surface for cutting.
• Canines are bluntly pointed for tearing.
• Premolars and molars have cusps for crushing and grinding.
• The premolars have two blunt cusps while the molars have three to four.

​Internal Structure of tooth

​The tooth consists of two main parts:
Crown: The portion above the gum; it is covered by the enamel.
Root: The portion below the gum; it is covered by the cement.
The tooth has two roots.
Neck: Is the region at the same level with the gum.

• It forms the junction between the crown and the root.
• It is covered by enamel. Incisors and canines have one root only.
• Premolars have one or two roots while molars have two to three roots each.
• Internally, the bulk of the tooth is made up of dentine which consists of living cells and extends to the root.
• It is composed of calcium salts, collagen and water.
• It is harder than bone but wears out with use.
• This is why it is covered by enamel which is the hardest substance in a mammal's body.

Pulp Cavity: Contains blood vessels which provide nutrients to the dentine and remove waste products. It also contains nerve endings which detect heat, cold and pain.
Cement: Fixes the tooth firmly to the jaw bone.

​Common Dental Diseases 

Dental Carries
Dental carries are the holes or cavities that are formed as acid corrodes enamel and eventually the dentine.
Causes

• This is caused by bacteria acting on the food left between teeth and on the cusp.
• Acids are formed that eventually corrode the enamel.
• The pulp cavity is eventually reached.
• A lot of pain is experienced then.
• The bacteria then infect the pulp cavity and the whole tooth decays.

Treatment
Treatment depends on the extent of the dental caries:
Extraction of Tooth.
Filling
This involves replacing the dentine with amalgam, a mixture of hard elements e.g. silver and tin.
Root Canal Treatment
This involves surgery and reconstruction.
It saves severely damaged teeth.
The nerves in the root canal are surgically severed.
The tooth is cleaned and filled up with amalgam.
Periodontal Diseases

• These are diseases of the gum.
• The gum becomes inflamed, and starts bleeding.
• Progression of the disease leads to infection of the fibres in the periodontal membranes and the tooth becomes loose.
• This condition is known as pyorrhoea.
• The diseases are caused by poor cleaning of the teeth.
• The accumulation of food particles leading to formation of plaque, lack of adequate vitamin A and C in the diet.

Treatment

• Nutrition - by taking adequate balanced diet rich in vitamins A and C.
• Antibiotics are used to kill bacteria.
• Anti-inflammatory drugs are given.
• Antiseptic is prescribed to use in cleaning the mouth daily to prevent further proliferation of bacteria.
• The plaque is removed-drilled away - a procedure known as scaling.

​Care of Teeth 

In order to maintain healthy teeth the following points should be observed:

• A proper diet that includes calcium and vitamins, particularly vitamin D is essential.
• The diet should also contain very small quantities of fluorine to strengthen the enamel.
• Large quantities of fluorine are harmful.
• The enamel becomes brown, a condition known as dental fluorosis.
• Chewing of hard fibrous foods like carrots and sugar cane to strengthen and cleanse the teeth.
• Proper use of teeth e.g. not using teeth to open bottles and cut thread.
• Regular and thorough brushing of teeth after meals.
• Dental floss can be used to clean between the teeth.
• Not eating sweets and sugary foods between meals.
• Regular visits to the dentist for checkups.
• Washing the mouth with strong salt solution or with any other mouth wash with antiseptic properties. 

Digestive System and Digestion in Humans
Organs that are involved with feeding in humans constitute the digestive system.
Digestive System and Associated Glands

• Human digestive system starts at the mouth and ends at the anus.
• This is the alimentary canal.
• Digestion takes place inside the lumen of the alimentary canal.
• The epithelial wall that faces the lumen has mucus glands (goblet cells).
• These secrete mucus that lubricate food and prevent the wall from being digested by digestive enzymes.
• Present at specific regions are glands that secrete digestive enzymes.
• The liver and pancreas are organs that are closely associated with the alimentary canal.
• Their secretions get into the lumen and assist in digestions.

Digestive system consists of:

• Mouth.
• Oesophagus.
• Stomach.
• Small intestines - consist of duodenum, the first part next to the stomach, ileum - the last part that ends up in a vestigial caecum and appendix which are nonfunctional.
• Large intestines consist of: colon and rectum that ends in the anus. 

Ingestion, Digestion and Absorption

• Feeding in humans involves the following processes:
• Ingestion: This is the introduction of the food into the mouth.
• Digestion: This is the mechanical and chemical breakdown of the food into simpler, soluble and absorbable units.
• Absorption: Taking into blood the digested products.
• Assimilation: Use of food in body cells.
• Mechanical breakdown of the food takes place with the help of the teeth.
• Chemical digestion involves enzymes.

Digestion in the Mouth

• In the mouth, both mechanical and chemical digestion takes place.
• Food is mixed with saliva and is broken into smaller particles by the action of teeth.
• Saliva contains the enzyme amylase.
• It also contains water and mucus which lubricate and soften food in order to make swallowing easy.
• Saliva is slightly alkaline and thus provides a suitable pH for amylase to act on cooked starch, changing it to maltose.
• The food is then swallowed in the form of semisolid balls known as boluses.
• Each bolus moves down the oesophagus by a process known as peristalsis.
• Circular and longitudinal muscles along the wall of the alimentary canal contract and relax pushing the food along.

Digestion in the Stomach

• In the stomach, the food is mixed with gastric juice secreted by gastric glands in the stomach wall.
• Gastric juice contains pepsin, rennin and hydrochloric acid.
• The acid provides a low pH of 1.5-2.0 suitable for the action of pepsin.
• Pepsin breaks down protein into peptides.
• Rennin coagulates the milk protein casein.
• The stomach wall has strong circular and longitudinal muscles whose contraction mixes the food with digestive juices in the stomach. 

Digestion in the Duodenum

• In the duodenum the food is mixed with bile and pancreatic juice.
• Bile contains bile salts and bile pigments.
• The salts emulsify fats, thus providing a large surface area for action of lipase.
• Pancreatic juice contains three enzymes:
  • Trypsin which breaks down proteins into peptides and amino acids,
  • Amylase which breaks down starch into maltose, and
  • Lipase which breaks down lipids into fatty acids and glycerol.
• These enzymes act best in an alkaline medium which is provided for by the bile.

Digestion in ileum

• Epithelial cells in ileum secrete intestinal juice, also known as succus entericus.
• This contains enzymes which complete the digestion of protein into amino acids, carbohydrates into monosaccharides and lipids into fatty acids and glycerol.

Absorption

• This is the diffusion of the products of digestion into the blood of the animal.
• It takes place mainly in the small intestines though alcohol and some glucose are absorbed in the stomach.

The ileum is adapted for absorption in the following ways:

• It is highly coiled.
• The coiling ensures that food moves along slowly to allow time for its digestion and absorption.
• It is long to provide a large surface area for absorption.
• The epithelium has many finger-like projections called villi (singular villus).
• They greatly increase the surface area for absorption.
• Villi have microvilli that further increase the surface area for absorption.
• The wall of villi has thin epithelial lining to facilitate fast diffusion of products of digestion.
• Has numerous blood vessels for transport of the end products of digestion.
• Has lacteal vessels; for absorption of fatty acids and glycerol and transport of lipids.

Absorption of Glucose and Amino Acids

• Glucose and other monosaccharides as well as amino acids are absorbed through the villi epithelium and directly into the blood capillaries.
• First they are carried to the liver through the hepatic portal vein, then taken to all organs via circulatory system. 

Absorption of Fatty Acids and Glycerol

• Fatty acids and glycerol diffuse through the epithelial cells of villi and into the lacteal.
• When inside the villi epithelial cells, the fatty acids combine with glycerol to make tiny fat droplets which give the lacteal a milky appearance.
• The lacteals join the main lymph vessel that empties its contents into the bloodstream in the thoracic region.
• Once inside the blood, the lipid droplets are hydrolysed to fatty acids and glycerol.

Absorption of Vitamins and Mineral Salts

• Vitamins and mineral salts are absorbed into the blood capillaries in' the villi. Water is mainly absorbed in the colon.
• As a result the undigested food is in a semi-solid form (faeces) when it reaches the rectum.
• Egestion: This is removal of undigested or indigestible material from the body. Faeces are temporarily stored in the rectum then voided through the anus. Opening of the anus is controlled by sphincter muscles
• Assimilation: This is the incorporation of the food into the cells where it is used for various chemical processes.

Carbohydrates

• Carbohydrates are used to provide energy for the body.
• Excess glucose is converted to glycogen and stored in the liver and muscles.
• Some of the excess carbohydrates are also converted into fat in the liver and stored in the adipose tissue' (fat storage tissue), in the mesenteries and in the connective tissue under the skin, around the heart and other internal organs.

Proteins

• Amino acids are used to build new cells and repair worn out ones.
• They are also used for the synthesis of protein compounds.
• Excess amino acids are deaminated in the liver.
• Urea is formed from the nitrogen part.
• The remaining carbohydrate portion is used for energy or it is converted to glycogen or fat and stored.

Lipids

• Fats are primarily stored in the fat storage tissues.
• When carbohydrates intake is low in the body, fats are oxidised to provide energy.
• They are also used as structural materials e.g. phospholipids in cell membrane. They act as cushion, protecting delicate organs like the heart.
• Stored fats under the skin act as heat insulators.

Summary of digestion in humans

Importance of Vitamins, Mineral Salts, Roughage and Water in Human Nutrition 

Vitamins

• These are organic compounds that are essential for proper growth, development and functioning of the body.
• Vitamins are required in very small quantities.
• They are not stored and must be included in the diet.
• Vitamins Band C are soluble in water, the rest are soluble in fat.
• Various vitamins are used in different ways.

Mineral Salts

• Mineral ions are needed in the human body.
• Some are needed in small amounts while others are needed in very small amounts (trace).
• All are vital to human health.
• Nevertheless, their absence results in noticeable malfunction of the body processes.

Water

• Water is a constituent of blood and intercellular fluid.
• It is also a constituent of cytoplasm.
• Water makes up to 60-70% of total fresh weight in humans.
• No life can exist without water.

Functions of Water

• Acts as a medium in which chemical reactions in the body takes place.
• Acts as a solvent and it is used to transport materials within the body.
• Acts as a coolant due to its high latent heat of vaporisation.
• Hence, evaporation of sweat lowers body temperature.
• Takes part in chemical reactions i.e. hydrolysis. 

​Vitamins, sources, uses and the deficiency disease resulting from their absence in diet

Roughage

• Roughage is dietary fibre and it consists mainly of cellulose.
• It adds bulk to the food and provides grip for the gut muscles to enhance peristalsis.
• Roughage does not provide any nutritional value because humans and all animals not produce cellulase enzyme to digest cellulose.
• In herbivores symbiotic bacteria in the gut produce cellulase that digests cellulose.

Factors Determining Energy Requirements in Humans

• Age: Infants, for instance, need a greater proportion of protein than adults.
• Sex: males generally require more carbohydrates than females.
• The requirements of specific nutrients for females depends on the stage of development in the life cycle.
• Adolescent girls require more iron in their diet; expectant and nursing mothers require a lot of proteins and mineral salts.
• State of Health: A sick individual requires more of certain nutrients e.g. proteins, than a healthy one.
• Occupation: An office worker needs less nutrients than a manual worker.

Balanced Diet
A diet is balanced when it contains all the body's nutrient requirements and in the right amounts or proportions.
A balanced diet should contain the following:

• Carbohydrates
• Proteins
• Lipids
• Vitamins
• Mineral Salts  
• Water
• Dietary fibre or roughage

Malnutrition
This is faulty or bad feeding where the intake of either less or more than the required amount of food or total lack of some food components.
Deficiency Diseases
Deficiency diseases result from prolonged absence of certain components in the diet.
Examples are:
Marasmus:
Lack of enough food results in thin arms and legs, severe loss of fluid, general body wasting, sunken eyes.
Kwashiorkor
Lack of protein in the diet of children. The symptoms of kwashiorkor include wasting of the body, red thin hair, swollen abdomen and scaly skin.
Other deficiency diseases are due to lack of accessory food factors (vitamins and mineral salts.). Such diseases include rickets, goitre and anaemia.
Treatment of these deficiency diseases is by supplying the patient with the component missing in the diet. 

​Practical Activities

• Experiments to show that Carbon (IV) Oxide is necessary for Photosynthesis
• Experiment to Show Effect of Light on Photosynthesis
• Experiment to Show the Effect of Chlorophyll on Photosynthesis
• Experiment To Observe Stomata Distribution in Different Leaves
• Test for Reducing Sugar
• Test for non-reducing sugar
• Test for Lipids;

         a)      Grease Spot Test         b)      Emulsion Test

• Test for Proteins -Biuret Test
• Experiment To Investigate Presence of Enzyme in Living Tissue
• Dissection of a Rabbit to show the Digestive System

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