Nutrition in Animals - Comprehensive Study Notes

HOLOZOIC NUTRITION

• All organisms require food to survive. Nutrition is defined as what an organism needs to eat, how it consumes food, and how that food is used in the body. It provides energy for growth and development.

• Plants

  • Prepare their own food by photosynthesis.

  • Most plants are autotrophs; some are heterotrophs with modes such as parasitic, saprophytic, symbiotic, or insectivorous.

• Animals

  • Obtain food from plants or other animals.

  • Different modes of nutrition include parasitic, saprozoic, symbiotic, and holozoic.

  • Most animals use holozoic nutrition: an heterotrophic mode in which solid or liquid food is taken inside the body through an organ (like the mouth), digested, and undigested parts are ejected.

• Key terms

  • Nutrition: the process of utilisation of food by an organism to obtain energy for growth and development.

  • Holophoic/ holozoic nutrition is contrasted with autotrophic (holophytic) nutrition which uses carbon dioxide and solar energy to produce food.

Stages of HOLOZOIC NUTRITION

• The process involves five main steps: ingestion, digestion, absorption, assimilation, and egestion.

• Ingestion: taking food inside the body through the mouth.

• Digestion: breakdown of complex food molecules into simple soluble molecules with the help of digestive enzymes.

• Absorption: passage of digested nutrients through the intestinal wall into the bloodstream.

• Assimilation: utilisation of absorbed nutrients by body cells for energy, growth, development, and repair.

• Egestion: elimination of undigested food through the anus (defecation).

DIFFERENT WAYS OF TAKING FOOD

• Humans

  • Use hands to put food into the mouth; chew, then swallow.

• Infants

  • Feed on mother’s milk.

• Butterfly

  • Sucks nectar from flowers.

• Snakes

  • Swallow prey whole without chewing.

• Frog

  • Captures prey with a sticky tongue.

• Some aquatic animals

  • Filter tiny particles from water and feed on them.

• Amoeba

  • Engulfs food by extending pseudopodia to surround prey, forming a food vacuole.

• Hydra (multicellular)

  • Uses tentacles and stinging cells to capture prey, then ingests.

• Seahorses

  • Have no teeth and no stomach; food passes quickly, so they must eat almost constantly to stay alive.

NUTRITION IN HUMAN BEINGS

• The digestive system is well developed and consists of an alimentary canal from the mouth to the anus, about
  $9 ext{ to }10 ext{ meters}$ long in humans.

• The canal includes: mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus.

• The canal is coiled in places.

• Ingestion (mouth)

  • Mouth bounded by movable lips; digestion begins here.

• Digestion overview

  • Food is mostly in complex form and needs to be broken down into simple substances (
    carbohydrates, proteins, fats) using digestive enzymes.

• Teeth and their types

  • Temporary (milk) teeth: $20$ teeth.

  • Permanent teeth: $32$ teeth.

  • Types and functions:

  • Incisors: $4 ext{ upper}, 4 ext{ lower} <br>ightarrow ext{total } 8$; cutting and biting.

  • Canines: $2 ext{ upper}, 2 ext{ lower} <br>ightarrow ext{total } 4$; tearing.

  • Premolars: $4 ext{ upper}, 4 ext{ lower} <br>ightarrow ext{total } 8$; chewing and grinding.

  • Molars: $4 ext{ upper}, 4 ext{ lower} <br>ightarrow ext{total } 12$; chewing and grinding.

• The Mouth (Buccal Cavity)

  • Contains teeth, tongue, and salivary glands.

• The Tongue

  • Muscular organ aiding chewing by pushing food to teeth and mixing with saliva.

  • Taste buds are spread on the surface; each taste bud can detect all tastes (sweet, salty, sour, bitter).

• Salivary glands

  • Located near jaws; secrete saliva, a digestive juice with enzymes that partly digest starch.

  • Tongue helps mix saliva with food; digestion of starch begins in the mouth.

• The Oesophagus (Food Pipe)

  • A tube-like organ about $30 ext{ cm}$ long.

  • Muscular walls perform peristalsis to push food toward the stomach.

  • No digestion occurs in the oesophagus.

• Peristalsis and anti-peristalsis

  • Peristalsis: rhythmic contractions to move food along the canal.

  • Anti-peristalsis: reverse movement, e.g., during vomiting.

• The Stomach

  • A J-shaped, muscular organ; churns food with gastric juices to form chyme (semi-solid).

  • Gastric juices contain enzymes and hydrochloric acid (HCl); mucus protects stomach lining.

  • Enzymes in gastric juice digest proteins; HCl kills bacteria and aids enzyme activity.

  • The stomach also secretes mucus to protect its own lining; a mucus layer is renewed about every two weeks.

• The Small Intestine

  • Longest part of the canal; about $7 ext{ m}$ long (roughly $20 ext{ ft}$).

  • Digestion is completed here; receives bile from liver and pancreatic juice from the pancreas.

  • Absorption mainly occurs in the small intestine.

  • Inner wall has villi, increasing surface area by about $5 imes$ for absorption.

  • Villi contain a network of capillaries; digested nutrients pass into the blood.

• Pancreatic and Bile help

  • Pancreatic juice aids digestion of proteins and carbohydrates.

  • Bile from the liver (stored in the gall bladder) makes the intestinal content alkaline and emulsifies fats into tiny droplets.

• The Liver, Gall Bladder, and associated glands

  • Liver secretes bile; gall bladder stores it.

• Absorption and transport

  • Digested food absorbed into blood, transported to cells for energy, growth, and repair.

  • Glucose is used in respiration; amino acids build and repair tissues; fatty acids and glycerol can be stored as fat.

• Assimilation

  • Utilisation of absorbed nutrients by body cells for energy, growth, and repair.

• Egestion and water balance

  • Large intestine absorbs water from digested material; remaining semi-solid material forms faeces.

  • Rectum stores faeces before defecation via the anus.

• Checkpoint-1 (Fill in the blanks)

  • Ingestion

  • Digestion

  • Pseudopodia

  • Food vacuole

  • Egestion

  • Assimilation

• Checkpoint-2 (Key statements)

  • Grass-eating animals are called ruminants.

  • Chewing of cud is known as rumination.

  • Amoeba is a microscopic single-celled organism.

  • When an Amoeba encounters prey, it pushes out two pseudopodia around the organism to eat it.

DIGESTION IN GRASS-EATING ANIMALS (Ruminants)

• Most grass-eating animals cannot digest cellulose with their own enzymes.

• They have a four-chambered stomach: rumen, reticulum, omasum, abomasum.

• Process

  • Step 1: First, half-chewed food is swallowed and goes to the rumen (first chamber).

  • Step 2: In the rumen, bacteria digest cellulose.

  • Step 3: FOOD moves to the reticulum (second chamber) where partly digested material, called cud, is formed.

  • Step 4: Cud is returned to the mouth for rechewing (rumination).

  • Step 5: After cud re-chewing, it moves to omasum (third chamber) for further breakdown.

  • Step 6: Finally, it passes to abomasum (fourth chamber) where enzymes digest the material fully.

• After digestion and absorption in the small intestine, nutrients are carried to cells; undigested material goes to large intestine and is ejected via rectum and anus.

• Examples: cows, goats, buffaloes, sheep, bison, etc.

• Note: The rumen contains cellulose-digesting bacteria essential for cellulose digestion.

NUTRITION IN AMOEBA

• Amoeba is a microscopic, single-celled organism found in ponds and ditches; it constantly changes shape by extending pseudopodia.

• Nutrition in Amoeba involves five stages: Ingestion, Digestion, Absorption, Assimilation, Egestion.

• Ingestion: Amoeba engulfs food by surrounding with pseudopodia to form a food vacuole.

• Digestion: Enzymes from cytoplasm enter the vacuole and break down food into simple substances.

• Absorption: Digested food within the vacuole is absorbed into the cytoplasm.

• Assimilation: Digested nutrients are used for growth, development, and energy release.

• Egestion: Undigested food is expelled when the vacuole ruptures.

• Figure references describe the amoeba’s food vacuole, pseudopodia, and nucleus.

CHECKPOINT-1

• Fill in the blanks based on the text:

  • The grass-eating animals are also called __.

  • Chewing of cud is known as __.

  • Amoeba is a __ single-celled organism.

  • When an Amoeba encounters a suitable organism, it pushes out two __ around the organism to eat it.

CHECKPOINT-2

• Summary statements to verify understanding:

  • Ingestion, Digestion, Absorption, Assimilation, Egestion are the stages of nutrition.

  • Pseudopodia and food vacuoles are used by Amoeba for ingestion and digestion.

  • Ruminants rely on microbial cellulose digestion in their multi-chambered stomach.

  • The small intestine is the primary site of digestion completion and nutrient absorption via villi and capillaries.