Feeding and Nutrition In Animals

Proper nutrition is key for overall health, growth, reproduction, and a strong immune system. In order for nutrition to occur, organisms need to feed on food sources. There are various ways to do that:

• Autotrophs → make food for themselves (are able to perform photosynthesis).
• Heterotrophs (consumers) → must eat other organisms for energy.
• Chemotrophs → obtain energy from chemicals (REDOX reactions in their environment).

Types of Consumers:

• Herbivores → only eat vegetation.
• Carnivores → only eat consumers (meat).
• Omnivores → eat both vegetation and other consumers.
• Decomposer → break down organic matter by external digestion (fungi and bacteria).
• Detritivore → break down organic matter internally (worms).
• Parasite → derive nutrients from host at the host’s expense.
• Scavenger → eat off of already dead animals.

Feeding Mechanisms:

• Filter Feeding → obtaining nutrients suspended in water (sponges, whales).
• Deposit feeding → obtaining nutrients from particles suspended in the soil (earthworms).
• Fluid feeding: obtaining nutrients by consuming other organisms' fluids (mosquitos).
• Bulk feeding: ingesting large pieces of food (humans, lions).

Types of Digestive systems:

• Incomplete gut (gastrovascular cavity) → one opening (mouth is also anus) - e.g: cnidarians flatworms.
• Complete gut → separate mouth and anus (most bilaterians - including humans).
• No gut → absorption through skin via diffusion (e.g. some invertebrates).

Special Distinctions (Key for Olympiads):

Intestinal Lengths:

• Carnivores tend to have the shortest intestine lengths because digesting protein is relatively easy.
• Omnivore intestine length falls in between.
• Herbivores have the longest intestines because digesting cellulose requires a lot more attention than other compounds.

Ruminants:

• Herbivorous (e.g. cow, sheep, goat).
• Four-chambered stomach.
• Use microbial fermentation (for cellulose).
• Allows for maximum nutrient extraction from cellulose-rich plant matter (humans can’t digest cellulose).
• *Ecology connection - cows have a symbiotic relationship with the microorganisms in their rumen!

1. Food first enters rumen and reticulum together.
2. Rumen (largest chamber) is where fermentation takes place that breaks down cellulose (also produces methane as a byproduct). Cows get more energy from bacteria’s products than grass itself!
3. Reticulum traps larger particles that haven’t been digested yet. Initiates regurgitation.
4. Regurgitated substance is called cud, which the ruminant chews again.
5. Cud is re-swallowed and enters the omasum, with a large surface area (many folds) that absorbs water and salts.
6. Abomasum (similar to human stomach) - secretes HCl and pepsin to digest proteins.
7. Small interesting absorbs nutrients while large interesting absorbs water (similar to humans).

Bird Digestion:

1. Crop is a storage pouch key for softening food.
2. Proventriculus secretes digestive enzymes (glandular stomach).
3. Gizzard grinds food with swallowed stones (muscular stomack).
4. Small intestine.
5. Ceca (ferments plant matter).
6. Cloaca (one exit for digestive, urinary, and reproductive outputs).

Annelida (earthworms) Digestion:

1. Crop = temporary storage.
2. Gizzard grinds soil using muscular contractions.
3. Intestine for absorption.
4. Typhlosole is a fold in intestinal wall increasing surface area.

Insect Digestion:

1. Foregut (mouth, esophagus, crop, gizzard).
2. Midgut (gastric caeca - secretes enzymes; stomach = ventriculus where chemical digestion actually happens).
3. Hindgut (intestine, rectum, anus).
4. Malpighian tubules → kidneys for insects; collect nitrogen waste (dump waste into hindgut to be excreted).

Written by Josephine Ankomah