Adaptions for Nutrition - Human digestion

Question 1

2 types of Autotrophs

Answer 1

An organism that synthesises its own complex organic molecules from simpler inorganic molecules using either light or chemical energy:

• Photoautotrophs
• Chemoautotrophs

Question 2

Photoautotrophic organisms

Answer 2

Use light energy to build organic molecules via photosynthesis e.g. green plants

Question 3

Chemoautotrophic organisms

Answer 3

Use chemical reactions to build organic molecules from inorganic ones via chemosynthesis e.g. all prokaryotes

Question 4

3 types of Heterotrophs

Answer 4

An organism that obtains complex organic molecules from other organisms:

• Saprotrophic feeders
• Parasitic feeders
• Holozoic feeders

Question 5

Saprotrophic organisms

Answer 5

Derives energy and raw materials for growth from the extracellular digestion of dead or decaying material e.g. all fungi and some bacteria

-Enzymes secreted onto food sources to extracellularly digest and absorb the soluble products by diffusion or active transport

Question 6

Parasitic organisms

Answer 6

Highly specialised organisms that live in or on another living organism, obtaining their nutrition at the expense of the host organism e.g. tapeworm and malarial parasite

Question 7

Holozoic organisms

Answer 7

Internally digest food substances

5 processes:

• Ingestion
• Digestion
• Absorption
• Assimilation
• Egestion

Question 8

Holozoic nutrition in unicellular organisms

Answer 8

Example, Amoeba:

• Large molecules ingested by endocytosis
• Food vacuoles fuse with lysosome and their contents digested by lysosomal enzymes
• Products are absorbed into cytoplasm
• Indigestible remains egested by exocytosis

Question 9

Holozoic nutrition in multicellular organisms

Answer 9

Holozoic multicellular organisms either have:

• A single body opening for both ingestion and egestion (Simple organisms)
• Two different body openings, one for ingestion and one for egestion (Advanced organisms)

Question 10

Holozoic nutrition in simple organisms

Answer 10

Example, Hydra:

• Live in fresh water attached to leaves or twigs
• Cylindrical in shape and have an undifferentiated gut with a sac-like structure
• Mouth is the only body opening

Question 11

Holozoic nutrition in advanced organisms

Answer 11

Advanced organisms have a varied diet, and evolved a tube gut which is divided into various specialised parts along its length to carry out particular functions

Question 12

The human gut

Answer 12

Humans are omnivores, so the gut is adapted to a diet containing both animal and plant material

4 Functions:

Ingestion - taking food into the body through buccal cavity

Digestion - the breakdown of large insoluble into soluble molecules small enough to be absorbed into the blood.
MECHANICAL; Crushing and cutting of food by teeth and muscle contractions of gut wall
CHEMICAL; Digestive enzymes, bile and stomach acid contribute to food breakdown

Absorption - the passage of molecules and ions through the gut wall into the blood

Egestion - the elimination of waste not made by the body, including food that cannot be digested e.g. cellulose

Question 13

The human gut wall structure

Answer 13

• Serosa (Outermost)
• Longitudinal muscle
• Circular muscle
• Submucosa
• Mucosa
• Epithelium (Innermost)

Question 14

Serosa

Answer 14

Protects the gut wall, resisting damage from friction with other abdominal organs

-Made up of tough connective tissue

Question 15

Muscularis externa

Answer 15

Its circular muscles contract behind the bolus of food and longitudinal muscles relax, pushing food along by peristalsis

Two layers of smooth muscle:

• Outer longitudinal muscle have fibres lying length ways
• Inner circular muscle have fibres lying around the wall

Question 16

Submucosa

Answer 16

Its connective tissue contains collagen for strength and elastin for stretch and recoil

Blood and lymph vessels remove absorbed products of digestion

Nerves stimulate smooth muscle to coordinate peristalsis

Contains:

• Connective tissue
• Blood and lymph vessels
• Nerves

Question 17

Mucosa

Answer 17

This layer is responsible for secretion and absorption

• Muscularis mucosa: Thin layer of smooth muscle that supports mucosa and allows it to fold
• Lamina propria: Contains connective tissue and cells of the immune system
• Epithelium

Question 18

Epithelium

Answer 18

• One cell thick
• Contains goblet cells which secrete mucus to lubricate food and protect mucosa
• Specialised epithelial cells found in different regions of the gut, producing different secretions

Question 19

Buccal cavity/Mouth

Answer 19

Function:

• Ingestion
• Digestion of starch and glycogen to maltose

MECHANICAL DIGESTION:
-Takes place using the teeth to break food into smaller pieces (Chewing/mastication).

-The surface area over which enzymes can act is then increased

CHEMICAL DIGESTION:
-Carried out by enzymes within saliva which is secreted from the 3 pairs of salivary glands

• Mucus helps the tongue form food into a bolus to swallow, and lubricates bolus
• Salivary amylase begins digestion of starch and glycogen into maltose

Question 20

Oesophagus

Answer 20

Function:

• Has no direct role in digestion
• Carries food to the stomach by peristalsis

Question 21

The stomach

Answer 21

Function:
-Digestion of protein

MECHANICAL DIGESTION:
-Extra muscles in stomach churn food rhythmically

CHEMICAL DIGESTION:
-Gastric juice secreted by gastric glands containing peptidases, mucus and hydrochloric acid

Question 22

Gastric juice contents

Answer 22

Endopeptidases:

• Secreted by zymogen in gastric pit
• Endopeptidases hydrolyse non-terminal peptide bonds adjacent to specific amino acids
• Peptides hydrolysed to smaller peptides
• Pepsin is an endopeptidase secreted by zymogen as the inactive enzyme pepsinogen
• Pepsinogen is activated to pepsin by H+ ions in hydrochloric acid

Exopeptidases:

• Hydrolyse terminal peptide bonds from the free amino end or the free carboxyl end
• Peptides hydrolysed to amino acids

Hydrochloric acid:

• Secreted by oxyntic cells in gastric pit
• Lowers stomach pH to about pH 2, which is optimum for enzymes
• Also kills most bacteria in food

Mucus:

• Secreted by goblet cells in gastric pit
• Forms a lining protecting stomach walls from the enzymes and lubricates food

Question 23

The small intestine

Answer 23

2 regions:

• Duodenum
• Ileum

Duodenum:
-Digests carbohydrates, fats and proteins

Ileum:

• Digests carbohydrates, fats and proteins
• Absorbs digested food and water

Question 24

Duodenum

Answer 24

Digests carbohydrates, fats and proteins

3 secretions in the duodenum:

• Bile
• Pancreatic juice
• Intestinal juice

Question 25

Bile

Answer 25

Contain no enzymes. Produced by the liver and is stored in the gall bladder. From the gall bladder it is carried to the duodenum via the bile ducts Components: - Bile salts which emulsify lipids by lowering their tension - Hydrogen carbonate ions which neutralise acidity from the stomach for enzymes in duodenum to work

Question 26

Pancreatic juice

Answer 26

Secreted by the pancreas and carried into the duodenum via the pancreatic duct Components: - Sodium hydrogen carbonate ions which neutralise stomach acids and provide optimal pH for pancreatic enzymes - Amylase which hydrolyses any remaining starch or glycogen to maltose - Lipase which hydrolyse triglycerides into monoglycerides and fatty acids - Trypsinogen which is an inactive endopeptidase that is activated to Trypsin by the duodenal enzyme enterokinase - Other endopeptidases

Question 27

Intestinal juice in duodenum

Answer 27

- Mucus to lubricate and protect the wall of the small intestine - Lysozyme to hydrolyse peptidoglycan walls of some bacteria, killing them - Hydrogen carbonate ions to neutralise stomach acids and provide optimal pH for enzyme activity

Question 28

The Ileum

Answer 28

Final stages of digestion take place here, along with absorption of the products of digestion -Digestion and absorption both take place at finger like projections called villi

Question 29

Digestion at the Ileum Villi

Answer 29

Secreted enzymes: - Endopeptidases and Exopeptidases are secreted by cells at the tips of the villi - This continues digestion of polypeptides into smaller peptides and dipeptides Embedded enzymes: - Final stages of digestion of proteins and carbohydrates takes place on the membranes of epithelial cells covering the villi - Enzymes embedded in the membranes of epithelial cells have their active sites exposed and hydrolyse the dipeptides and disaccharides - This is a good adaption as the products of digestion are then concentrated where they are to be absorbed Substrate + Embedded enzyme = Product : Maltose + Maltase = 2x Alpha Glucose Sucrose + Sucrase = Alpha Glucose + Fructose Lactose + Lactase = Alpha Glucose + Galactose Dipeptides + Dipeptidases = Amino acids

Question 30

Adaptions for absorption at the Ileum

Answer 30

-Peristalsis: Ensures food moves through the gut and brings products of digestion in contact with epithelial cells -Good blood supply: Circulation of blood in capillaries in villi ensure a diffusion gradient maintained -Epithelium: One cell thick, providing a short diffusion pathway -Epithelial cell mitochondria: Lots of mitochondria found in epithelial cells of the mucosa to provide ATP for active transport of some molecules/ions -Villi and microvilli: These increase the surface area of the small intestine wall to increase the rate of absorption -Small intestine is long: Provides a large surface area for digestion and absorption to take place

Question 31

Mechanisms of absorption across the small intestine

Answer 31

- Diffusion - Facilitated diffusion - Active transport - Osmosis

Question 32

Absorption of monosaccharides

Answer 32

1) Na+ ions are pumped out of the epithelial cells and into blood by active transport 2) This lowers concentration of Na+ ions in epithelial cell 3) Na+ ions from the gut lumen can then enter epithelial cells via co-transport with glucose on the same carrier protein 4) Glucose concentration inside epithelial cells increases, creating a concentration gradient between the cell and the blood 5) Glucose leaves the epithelial cell and enters the blood by facilitated diffusion 6) Glucose and other monosaccharides in the blood are then transported via the hepatic portal vein to the liver

Question 33

Absorption of amino acids

Answer 33

1) Amino acids are pumped from the gut lumen into the epithelial cells by active transport 2) The concentration of amino acids in the epithelial cells then builds up, creating a concentration gradient between the cells and the blood 3) Amino acids then enter the blood by facilitated diffusion 4) Amino acids in the blood are then transported via the hepatic portal vein to the liver

Question 34

Absorption of fatty acids and glycerol

Answer 34

1) Fatty acids and glycerol pass into the epithelial cells via simple diffusion 2) Within the epithelial cells they are reassembled into triglycerides 3) Triglycerides then pass into the lacteals and are carried via the lymphatic system to the blood

Question 35

Absorption of water

Answer 35

- Water passes down a water potential gradient from the gut lumen, into the epithelial cells and into the blood capillaries by osmosis - The removal of solutes from epithelial cells into the blood maintains a water potential gradient

Question 36

Large intestine

Answer 36

When food reaches the large intestine it has mostly been digested and absorbed Contents of the large intestine: - Undigested food e.g. cellulose - Dead epithelial cells - Water - Bacteria Formed of the: - Caecum - Appendix - Colon - Rectum

Question 37

Colon

Answer 37

- Folded inner surface to provide a large surface area - Fewer but large villi than the ileum Some substances absorbed: - Inorganic ions absorbed by active transport or facilitated diffusion - Water absorbed by osmosis - Vitamin K and folic acid absorbed by active transport or facilitated diffusion

Question 38

Rectum and Anus

Answer 38

- When material gets to the end of the colon it is semi-solid and known faeces - Faeces contains indigestible fibre, some dead cells, some bacteria and a small amount of water Rectum: - Faeces is stored in the rectum - There are receptors in the rectum to allow the brain to detect when the rectum is full Anus: - Faeces is egested through the anus in a process known as defecation - Anus contains sphincter muscles which can contract and relax to control defecation