2.4 Adaptations for Nutrition

Question 1

Define autotroph

Answer 1

An autotroph is an organism that synthesises its own complex organic molecules from simpler molecules using either light or chemical energy.

Autotrophs use simple, inorganic raw materials carbon dioxide and water to produce their organic molecules.

Question 2

What are the 2 types of autotrophs?

Answer 2

Photoautotrophs and Chemoautotrophs

Question 3

Explain photoautotrophic organisms

Answer 3

Photoautotrophic Organisms (photoautotrophs) use light as the energy source and perform photosynthesis. They are green plants, some protoctists and some bacteria. This type of nutrition is described as holophytic.

Question 4

Explain chemoautotrophic organisms

Answer 4

Chemoautotrophic Organisms (chemoautotrophs) use the energy from chemical reactions. These organisms are all prokaryotes and they perform chemosynthesis. This is less efficient than photosynthesis and the organisms that do this are no longer dominant life forms.

Question 5

What can’t heterotrophic organisms do and what do they do instead?

Answer 5

Heterotrophic organisms cannot make their own food and consume complex organic molecules produced by autotrophs so they are consumers. They either eat autotrophs or organisms that have themselves eaten autotrophs.

Question 6

What do heterotrophs include?

Answer 6

Heterotrophs include animals, fungi, some protists and some bacteria.

Question 7

Define saprotroph

Answer 7

A saprotroph is an organism that derives energy and raw materials for growth from the extracellular digestion of dead or decaying material.

Question 8

What do saprotrophs include?

Answer 8

This includes all fungi and some bacteria.

Question 9

What do saprotrophs not have in digestion and what do they do instead?

Answer 9

They have no specialised digestive system and they secrete enzymes onto food material outside the body for extracellular digestion. They absorb the soluble products of digestion across their cell membranes by diffusion and active transport.

Question 10

What are decomposers?

Answer 10

Decomposers are microscopic saprotrophs and their activities are important in decaying leaf litter and recycling nutrients such as nitrogen.

Question 11

What are parasites?

Answer 11

Parasites are highly specialised organisms that live in or on another living organism and obtain their nutrition at the expense of the host organism.

Question 12

What are endoparasites?

Answer 12

Endoparasites live in the body of the host while ectoparasites live on its surface. A parasite’s host always suffers some harm and often death. Parasites have adapted in many ways and are highly specialised for their way of life.

Question 13

What is holozoic nutrition?

Answer 13

Holozoic nutrition is the internal digestion of food substances

Question 14

How does holozoic nutrition work?

Answer 14

Holozoic nutrition is used by most animals, they ingest food, digest it and egest the indigestible remains. The food is processed inside the body, in a specialised digestive system. Digested material is absorbed into the body tissues and used by the cells.

Question 15

Diet of Herbivore, Carnivore, Omnivore, Detritivores

Answer 15

Animals that eat plant material only are herbivores and those that eat other animals only are carnivores. Those that eat both plant and animal material are omnivores. Detritivores feed on dead and decaying material.

Question 16

Who uses holozoic nutrition?

Answer 16

Unicellular organisms such as Amoeba use holozoic nutrition.

Question 17

How do unicellular organisms use holozoic nutrition?

Answer 17

Unicellular organisms (amoeba) have a large surface area to volume ratio. They obtain all the nutrients that they need by diffusion, facilitated diffusion or by active transport across the cell membrane. They take in larger molecules and microbes by endocytosis into food vacuoles which fuse with lysosomes and their contents are digested by lysosomal enzymes. The products of digestion are absorbed into the cytoplasm and indigestible remains are egested by exocytosis.

Question 18

Explain single body opening nutrition (hydra)

Answer 18

Hydra is more complex than Amoeba. It is related to sea anemones and like them is diploblastic (comprises two layers of cells, an ectoderm and an endoderm separated by a jelly layer containing a network of nerve fibers). Hydra is cylindrical and has tentacles at the top (usually six) surrounding its mouth and the only body opening. Hydra lives in freshwater, attached to leaves or twigs by a basal disc. When hungry it extends its tentacles and when small organisms brush against the tentacles their stinging cells discharge and paralyse the prey. The tentacles move the prey through the mouth into the hollow body cavity. Some endodermal cells secrete protease and lipase, though not amylase. The prey is digested extracellularly and the products of digestion are absorbed into the cells. Other endodermal cells are phagocytic and engulf food particles which they digest in food vacuoles. Indigestible remains are egested through the mouth.

Question 19

Explain a tube gut

Answer 19

Many animals have a distinct anterior and posterior end and a digestive system that is a tube with 2 openings. Food is ingested at the mouth and indigestible wastes are egested at the anus. More complex animals have a more complex gut including different sections with different roles.

Question 20

Why must food be digested?

Answer 20

Food must be digested because the molecules are :

• Insoluble and too big to cross membranes and be absorbed into the blood.
• Polymers, and must be converted to their monomers so they can be rebuilt into molecules needed by body cells.

Question 21

Where does digestion and absorption occur in humans?

Answer 21

Digestion and absorption occur in the gut, a long, hollow, muscular tube. It allows movement of its contents in one direction only. Each section is specialised and performs particular steps in the processes of mechanical and chemical digestion and absorption. The food is propelled along the gut by peristalsis.

Question 22

Define peristalsis

Answer 22

Peristalsis is the rhythmic wave of coordinated muscular contractions in the circular and longitudinal muscle of the gut wall, passing food along the gut in one direction only.

Question 23

What are the 4 main functions of the gut?

Answer 23

Ingestion

Digestion

Absorption

Egestion

Question 24

Explain ingestion

Answer 24

Ingestion : taking food into the body through the buccal cavity (mouth).

Question 25

Explain digestion

Answer 25

Digestion : the breakdown of large insoluble molecules into soluble molecules that are small enough to be absorbed into the blood.

Question 26

What are the 2 types of digestion?

Answer 26

Mechanical digestion : cutting and crushing by teeth and muscle contractions of the gut wall increase the surface area over which enzymes can act. Chemical digestion : digestive enzymes, bile and stomach acid contribute to the breakdown of food.

Question 27

Explain absorption

Answer 27

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

Question 28

Explain egestion

Answer 28

Egestion : the elimination of waste not made by the body, including food that cannot be digested

Question 29

What are the 4 tissue layers of the gut?

Answer 29

Outer layer - Serosa Muscularis Externa Submucosa Inner layer - Mucosa

Question 30

Structure and function of serosa

Answer 30

Made up of tough connective tissue Protects the gut wall and resists damage from friction with other abdominal organs.

Question 31

Longitudinal muscle in muscularis externa structure

Answer 31

Outer layer and fibres lie length ways

Question 32

Circular muscle in muscularis externa structure

Answer 32

Inner layer and fibres lie around the wall

Question 33

Muscularis externa function

Answer 33

Behind the bolus of food, circular muscles contract and longitudinal muscles relax, pushing the food along by peristalsis. Also aids the mixing of food with secretions in the gut.

Question 34

Submucosa structure and function

Answer 34

Connective tissue which contains collagen (Strength) and elastin (Stretch and recoil). Blood and lymph vessels which remove absorbed products of digestion. Nerves which stimulate the smooth muscle to coordinate peristalsis.

Question 35

Mucosa 3 layers

Answer 35

Muscularis mucosa (Outer layer) Lamina propria (Middle layer) Epithelium (Inner layer)

Question 36

What is the mucosa responsible for?

Answer 36

Secretion and absorption

Question 37

Muscularis mucosa structure and function

Answer 37

Muscularis mucosa is a thin layer of smooth muscle that supports the mucosa and provides it with the ability to move and fold.

Question 38

Lamina propria structure

Answer 38

The lamina propria contains connective tissue and cells of the immune system

Question 39

Epithelium structure and function

Answer 39

Epithelium is one cell thick. Contains goblet cells to secrete mucus, to lubricate the food and to protect the mucosa. In different regions of the gut there are specialised epithelial cells which produce different secretions (e.g. enzymes).

Question 40

How are carbohydrates digested?

Answer 40

Carbohydrates : Polysaccharides are digested into disaccharides and then monosaccharides. Amylase hydrolyses starch and glycogen. Similarly, sucrase digests sucrose and lactase digests lactose. The general name for carbohydrate-digesting enzymes is carbohydrase.

Question 41

How are proteins digested?

Answer 41

Proteins are extremely large molecules. They are digested into polypeptides, then dipeptides and then amino acids. The general names for protein-digesting enzymes are protease and peptidase. Endopeptidases hydrolyse peptide bonds within the protein molecule, then exopeptidases hydrolyse the terminal or penultimate peptide bonds at the ends of these shorter polypeptides.

Question 42

How is fat digested?

Answer 42

Fats are digested to fatty acids and monoglycerides by one enzyme, lipase.

Question 43

What does the buccal cavity do?

Answer 43

Mechanical digestion begins in the mouth or buccal cavity, where food is mixed with saliva by the tongue and chewed with the teeth. The food's surface area increases, giving enzymes more access.

Question 44

What does saliva contain?

Answer 44

- Salivary amylase, beginning the digestion of starch and glycogen into maltose - HCO3- and CO32- ions. The pH of the saliva varies. - Mucus, lubricating the food's passage down the oesophagus. - Water which dissolves the soluble parts of food.

Question 45

What role does the oesophagus play in digestion?

Answer 45

The oesophagus has no role in digestion. It carries food to the stomach, as a bolus by peristalsis.

Question 46

Structure of the stomach

Answer 46

The stomach is a muscular sac with sphincter muscles at each end to control the entry and exit of food with a volume of about 2dm3. The stomach has an extra layer of muscle, the oblique muscles at an angle to the circular and longitudinal muscles which provide extra contraction in order to churn the food rhythmically which is a form of mechanical digestion. The mucosa of the stomach is highly folded, the folds are known as rugae and the pits that form are known as gastric pits.

Question 47

Explain the sphincters in the stomach

Answer 47

When the cardiac sphincter (junction with the oesophagus) relaxes, food enters the stomach. The pyloric sphincter (junction with the duodenum) remains contracted so food is held in the stomach for several hours. When the pyloric sphincter relaxes, the partially digested food is released into the duodenum as chyme (semi-solid).

Question 48

Where is gastric juice secreted?

Answer 48

Gastric juice is secreted from glands in depressions in the mucosa called gastric pits.

Question 49

What does gastric juice contain?

Answer 49

- Peptidases secreted by zymogen, or chief cells at the base of the gastric pit. Pepsinogen, an inactive enzyme, is secreted and activated by H+ ions to pepsin, an endopeptidase which hydrolyses protein to polypeptides. - Hydrochloric acid, secreted by oxyntic cells. It lowers the pH of the stomach contents to about pH2, the optimum pH for the enzymes and kills most bacteria in the food. - Mucus, secreted by goblet cells, at the top of the gastric pit. Mucus forms a lining which protects the stomach wall from the enzymes and lubricates the food. - Water for hydrolysis reactions and soluble products of digestion to dissolve.

Question 50

What are the 2 regions of the small intestine?

Answer 50

The small intestine has 2 regions : the duodenum and ileum.

Question 51

How is partially digested food allowed into the duodenum?

Answer 51

Relaxation of the pyloric sphincter muscle at the base of the stomach allows partially digested food into the duodenum, a little at a time.

Question 52

What does the duodenum receive?

Answer 52

It receives secretions from the liver and pancreas.

Question 53

Where is bile made and stored?

Answer 53

Bile is made in the liver. It is stored in the gallbladder then passes through the bile duct into the duodenum.

Question 54

What does bile contain?

Answer 54

Contains bile salts which are amphipathic. They emulsify lipids in the food, by lowering their surface tension and breaking up large globules into smaller globules which increases the surface area. This makes digestion by lipase more efficient.

Question 55

What is the benefit of bile being alkaline?

Answer 55

Bile is alkaline and neutralises the acid in food coming from the stomach. It provides a suitable pH for the enzymes in the small intestine.

Question 56

Where is chyme transported?

Answer 56

Chyme from the stomach is released into the duodenum.

Question 57

Where is pancreatic juice secreted?

Answer 57

Pancreatic juice is secreted by islet cells which are exocrine glands in the pancreas. It enters the duodenum through the pancreatic duct.

Question 58

What enzymes are secreted in the small enzyme?

Answer 58

Trypsinogen : Inactive enzyme converted into the endopeptidase trypsin by the duodenal enzyme, enterokinase Endopeptidases : Hydrolyse proteins and polypeptides to peptides Amylase : Digests any remaining starch to maltose Lipase : Hydrolyses lipids into fatty acids and monoglycerides

Question 59

What is a zymogen?

Answer 59

A zymogen is an inactive precursor of an enzyme. Protease enzymes are stored in their inactive form so that they do not digest the proteins within the cell or in the cell membrane

Question 60

What does sodium hydrogen carbonate do?

Answer 60

Raises the pH to make pancreatic juice slightly alkaline and contributes to : - Neutralising acid from the stomach - Providing the appropriate pH for the pancreatic enzymes to work efficiently

Question 61

What happens to the food coming from the stomach?

Answer 61

The food coming from the stomach is lubricated by mucus and neutralised by alkaline secretions from cells at the base of the crypts of Lieberkühn, called Brunner's glands.

Question 62

What synthesises digestive enzymes?

Answer 62

The epithelial cells lining the ileum have finger-like projections called villi which synthesise digestive enzymes

Question 63

Endopeptidases and exopeptidases location and function

Answer 63

Peptidases are secreted by villus epithelial cells and digestion continues in the gut lumen. Dipeptidases in the cell surface membranes digest dipeptides to amino acids.

Question 64

Where does absorption occur?

Answer 64

Mainly in the small intestine by diffusion, facilitated diffusion and active transport.

Question 65

Active transport needs ATP so .... cells ....

Answer 65

Active transport needs ATP so epithelial cells have many mitochondria.

Question 66

How is the ileum well adapted for absorption?

Answer 66

In humans it is very long, several metres, and its lining is folded. One the surface of the folds are villi and their epithelial cells have microscopic projections called microvilli. The folds, villi and microvilli produce a very large surface area for absorption.

Question 67

How are amino acids absorbed into the epithelial cells?

Answer 67

Amino acids are absorbed into the epithelial cells by active transport and as individual amino acids they pass into the capillaries by facilitated diffusion. They are water-soluble dissolve in the plasma.

Question 68

How is glucose absorbed into the epithelial cells?

Answer 68

Glucose passes into the epithelial cells with sodium ions, by cotransport. They move into the capillaries, sodium by active transport and glucose by facilitated diffusion, and dissolve in the plasma. Diffusion and facilitated diffusion are slow and not all the glucose is absorbed. To prevent it leaving the body in the faeces, some is absorbed by active transport.

Question 69

How are fatty acids and monoglycerides absorbed into epithelial cells and lacteals?

Answer 69

Fatty acids and monoglycerides diffuse into the epithelial cells and into the lacteals. Lacteals are blindly-ending lymph capillaries in the villi. They are part of the lymphatic system, which transports fat-soluble molecules to the left subclavian vein near the heart.

Question 70

How are minerals absorbed into the blood?

Answer 70

Minerals are taken into the blood by diffusion, facilitated diffusion and active transport and dissolve in the plasma.

Question 71

How is vitamin B and C absorbed into blood?

Answer 71

Vitamins B and C are water-soluble and are absorbed into the blood.

Question 72

How is vitamin A, D and E absorbed into the lacteals?

Answer 72

Vitamins A, D and E are fat-soluble and are absorbed into lacteals.

Question 73

How is water absorbed?

Answer 73

Water is absorbed into the epithelial cells in the ileum and into the capillaries by osmosis.

Question 74

What are lipids used for?

Answer 74

Lipids are used in membranes and to make some hormones but excess is stored.

Question 75

What is glucose used for?

Answer 75

Glucose is taken to body cells and respired for energy or stored as glycogen, in liver and muscle cells. Excess is stored as fat.

Question 76

What are amino acids used for?

Answer 76

Amino acids are taken to the body cells for protein synthesis. Excess cannot be stored so the liver deaminates the amino acids and converts - NH2 groups to urea, which is carried in the blood and excreted at the kidney. The remains of the amino acid molecules are converted into carbohydrate for storage or conversion to fat.

Question 77

Where are other molecules taken to?

Answer 77

Other molecules are taken in the hepatic portal vein to the liver.

Question 78

What does the large intestine comprise of?

Answer 78

The large intestine is about 1.5 metres long and comprises the caecum, the appendix, the colon and the rectum.

Question 79

What passes into the colon?

Answer 79

Undigested food, mucus, bacteria and dead cells pass into the colon.

Question 80

Structure of the colon wall?

Answer 80

The colon wall has fewer villi than the ileum and these villi have a major role in water absorption.

Question 81

What does the colon do?

Answer 81

Vitamin K and folic acid are secreted by mutualistic microorganisms living in the colon, and minerals are absorbed from the colon. As material passes along the colon, water is absorbed, and by the time it reaches the rectum, the material is semi-solid. It passes along the rectum and is egested as faeces, in a process called defecation.

Question 82

What is a carnivore's diet and its gut adaptations?

Answer 82

A carnivore eats only animals and so its diet is mostly protein. Its small intestine is short in relation to its body length, reflecting the ease with which protein is digested.

Question 83

What is a herbivore's diet and its gut adaptations?

Answer 83

A herbivore eats only plant material. Its small intestine is long in relation to its body length, because plant material is not readily digested and a long gut allows enough time for digestion and absorption of nutrients.

Question 84

What is an omnivore's diet and its gut adaptations?

Answer 84

Omnivores eat both animals and plants. The gut of an omnivore, such as a human, is intermediate in length.

Question 85

What is a carnivore's large intestine like?

Answer 85

The carnivore's large intestine is straight with a smooth lining.

Question 86

What is a herbivore or omnivores large intestine like?

Answer 86

That of a herbivore or omnivore is pouched. It can stretch to accommodate the larger volume of faeces produced in digesting plants, much of which is cellulose. The large intestine is also long, with villi, where water is absorbed.

Question 87

Adaptations for a grazing herbivore e.g. cow or sheep?

Answer 87

A grazing herbivore, such as a cow or sheep, has incisors on the lower jaw only, and the canine teeth are indistinguishable from the incisors, in shape and size. The animal wraps its tongue around the grass and pulls it tight across the leathery 'dental pad' on its upper jaw then the lower incisors and canines slice through it.

Question 88

What is the diastema?

Answer 88

Herbivores - A gap called the diastema separates the front teeth from the side teeth, or premolars. The tongue and cheeks operate in this gap moving the freshly cut grass to the large grinding surfaces of the cheek teeth or molars.

Question 89

How do molars in herbivores move?

Answer 89

The molars interlock and the lower jaw moves from side to side and produces a circular grinding action in a horizontal plane. With time, the grinding surfaces on the teeth become worn, exposing sharp-edged enamel ridges, which further increase the efficiency of grinding. The teeth have open, unrestricted roots, so they continue to grow throughout the animal's life, replacing material worn down by chewing.

Question 90

Why does a herbivore not need strong muscles attached to its jaws?

Answer 90

A herbivore does not need strong muscles attached to its jaws because its food is not likely to escape.

Question 91

What are incisors for?

Answer 91

Carnivores - The sharp incisors grip and tear muscle from bone.

Question 92

What are canines for?

Answer 92

Carnivore - The canine teeth are large, curved and pointed from piercing and seizing prey, for tearing muscle and killing.

Question 93

What are the specialised cheek teeth in carnivores?

Answer 93

Carnivores have a pair of specialised cheek teeth, called carnassials on each side which slide past each other like scissor blades. These shear the muscle off the bone. They are large and easily identifiable.

Question 94

How does the lower jaw move in carnivores?

Answer 94

The lower jaw moves vertically. Carnivores open their jaws very wide when they deal with prey and side-to-side movement could dislocate their jaw.

Question 95

Do carnivores have strong jaw muscles?

Answer 95

The jaw muscles are well developed and powerful, enabling the carnivore to grip the prey firmly and crush bone. There are protrusions on the skull, where these muscles insert into the bone.

Question 96

What are ruminants?

Answer 96

The ruminants are a group of herbivores including cows and sheep that use a rumen in digesting their food.

Question 97

What do ruminants rely on for digestion?

Answer 97

Since much of their food is cell wall material, mainly cellulose. Animals do not make cellulase and cannot digest the β-glycosidic bonds in cellulose. Ruminants rely on mutualistic microbes living in their gut to secrete the enzymes instead.

Question 98

What do mutualistic microbes include?

Answer 98

These microbes include bacteria, fungi and Protoctista which live in a 150dm3 chamber, the rumen.

Question 99

How does cellulose digestion take place from the mouth to the rumen.

Answer 99

- The grass is cut by the teeth and mixed with saliva to form the cud, which is swallowed down the oesophagus to the rumen. - The rumen is the chamber in which the food mixes with microbes. The microbes secrete enzymes which digest cellulose into glucose. The glucose is fermented to organic acids that are absorbed into the blood, and are an energy source for the cow. The waste products, carbon dioxide and methane, are released.

Question 100

How does cellulose digestion take place from the reticulum to the blood?

Answer 100

The fermented grass passes to the reticulum and is re-formed into cud. It is regurgitated into the mouth for further chewing. Cud may be swallowed and regurgitated to the mouth several times. The cud passes next into the omasum where water and organic acids made from fermented glucose are absorbed into the blood. The fourth chamber, the abomasum is the 'true' stomach, where protein is digested by pepsin at pH2. Digested food passes to the small intestine, from where the products of digestion are absorbed into the blood.

Question 101

What do non-ruminant herbivores have?

Answer 101

Non-ruminant herbivores have mutualistic microbes in their caecum and appendix therefore these are relatively large.

Question 102

Where does absorption of nutrients take place in non-ruminant herbivores?

Answer 102

Absorption of nutrients takes place in the ileum which is located between the caecum and appendix.

Question 103

What happens if the absorption of cellulose has not taken place in non-ruminant herbivores?

Answer 103

If absorption of cellulose has not taken place the faecal pellets produced will be green. The herbivore will eat the green faecal pellets in a process known as reflection in order to absorb the digested products in the ileum. This should result in the production of brown faecal pellets which will not be eaten.

Question 104

What is Taenia Solium?

Answer 104

The gut parasite/the pork tapeworm

Question 105

What type of parasite is taenia solium?

Answer 105

An endoparasite

Question 106

Explain the tapeworm's life cycle

Answer 106

The primary host is the human and the secondary host in the pig, in which the larval forms develop. The pig becomes infected when its food is contaminated with human faeces. Humans are infected by eating undercooked pork containing live larval forms.

Question 107

What hostile conditions does the tapeworm experience?

Answer 107

It is surrounded by digestive juices and mucus It must withstand peristalsis It experiences pH changes as it moves down the gut to the duodenum It is exposed to the host's immune system If the host dies, the parasite dies too

Question 108

Structural modifications of the tapeworm?

Answer 108

A scolex with suckers and a double row of curved hooks attach it strongly to the duodenum wall. A thick body covering, the cuticle, protects it from the host's enzymes and immune system. It makes enzyme inhibitors (anti-enzymes) which prevent the host's enzymes digesting it. It has a very reduced gut, a large surface area to volume ratio lets it absorb pre-digested food over its whole surface.

Question 109

Structural adaptations of the tapeworm's eggs?

Answer 109

The tapeworm is hermaphrodite-each proglottid has male and female reproductive organs. An infected gut usually has only one tapeworm, but each mature proglottid may contain many eggs which pass out of the host's body with the faeces. This huge number of eggs increases the chances of infecting a secondary host. The eggs have resistant shells and survive until eaten by a pig. Then the embryos hatch and move through the intestine wall into the pig's muscles. They remain dormant there until the meat is eaten by a human.

Question 110

What are lice?

Answer 110

Lice are wingless insects. They cannot fly and their legs are poorly adapted to jumping and walking so they are transferred from one host to another by direct contact. If removed from the human on which they live, they die. Humans get infected by body lice and their close relatives, head lice.

Question 111

The 3 stages of the louse life cycle?

Answer 111

There are 3 stages in the louse life cycle : Adult, egg and nymph. An adult louse lays eggs which hatch after 1-2 weeks into nymphs, leaving nits, the empty egg cases. The nymph is like an adult but smaller. It becomes an adult after about 10 days and like the adult, feeds on blood which in the case of head lice is sucked from the scalp of the host.