Biology Department

BIOLOGY DEPARTMENT

Unit 2 - Adaptations for nutrition

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Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the terms autotrophic and heterotrophic and that autotrophic organisms can be photoautotrophic or chemoautotrophic (b) the terms saprotrophic/saprobiotic, holozoic, parasitic in relation to heterotrophic organisms (c) saprotrophic nutrition involving the secretion of enzymes, external digestion of food substances followed by absorption of the products of digestion into the organism, e.g. fungi (d) holozoic nutrition, the internal digestion of food substances (e) nutrition in unicellular organisms, e.g. Amoeba, food particles are absorbed and digestion is carried out intracellularly (f) the adaptation of multicellular organisms for nutrition showing increasing levels of adaptation from a simple, undifferentiated, sac-like gut with a single opening, e.g. Hydra, to a tube gut with different openings for ingestion and egestion and specialised regions for the digestion of different food substances (g) the adaptations of the human gut to a mixed, omnivorous diet that includes both plant and animal material, including examination of microscope slides of duodenum and ileum (h) the efficient digestion of different food substances requiring different enzymes and different conditions (i) the adaptations of herbivore guts and dentition, in particular ruminants to a high cellulose diet and the adaptations of carnivore guts and dentition to a high protein diet, including examination of skulls and dentition of a herbivore and a carnivore (j) parasites; highly specialised organisms that obtain their nutrition at the expense of a host organism e.g. Taenia and Pediculus, including examination of specimens and slides of tapeworm e.g. Taenia.

Different ways of obtaining food

This topic is an overview of the adaptations for nutrition in a variety of organisms. As organisms increase in size and complexity, there is an increased need for specialised digestive systems.

Autotrophs use simple inorganic materials to manufacture complex organic compounds and can be photoautotrophic and chemoautotrophic. Heterotrophs consume complex organic food material. Heterotrophic organisms can be saprotrophic, holozoic or parasitic.

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TASK 1: Write a definition for each of the words in bold in the information above. Find examples of organisms that feed in each way.

Type of feeding Description of feeding Examples of method organisms Photoautotroph

Chemoautotroph

Saprotroph

Holozoic

Parasite

Saprotrophic organisms, which include all bacteria and some fungi, feed by secreting enzymes onto the food material outside of their bodies and then absorb the soluble products across the cell membrane. This is known as extracellular digestion. https://www.youtube.com/watch?v=6rS5asxv3fI

TASK 2: Use the animation above to explain using series of diagrams how extracellular digestion takes place.

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Nutrition in simpler organisms

Amoebae are single celled protoctists that live in water.

TASK 3: Watch the video link below without the sound. Using your knowledge of cells and cell transport, write a script for this video clip. Key words: pseudopodia, endocytosis, vacuole, lysosome, enzymes, digestion, exocytosis. https://www.youtube.com/watch?v=mv6Ehv06mXY

Hydra are small carnivorous invertebrates, related to sea anemones.

TASK 4: Use the web page below to describe how hydra catch their prey and digest them. http://www.countrysideinfo.co.uk/hydra.htm https://www.youtube.com/watch?v=LBseo9NtR Bc

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Human alimentary canal

In simple organisms, the gut is undifferentiated. In larger, more complex organisms, the gut is divided into various parts along its length and each part is specialised to carry out particular functions.

TASK 5: Define the following words: Ingestion - Digestion -

Absorption - Egestion -

TASK 6: Use a textbook/internet to label each part of the digestive system.

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TASK 7: Use a textbook or the internet to find out what happens in the following regions of the alimentary canal. State whether ingestion, digestion, absorption or egestion occurs there and the names of any enzymes released.

What happens here Buccal Cavity What does saliva contain? What are these substances for?

Oesophagus

Stomach Why is acid produced? Where is acid secreted from?

Duodenum Which glands secrete substances into here?

Ileum Which substances are absorbed?

Colon

Rectum and anus

TASK 8: Explain how the pancreas and liver contribute to digestion in the gut.

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Digestion

Digestion of food can be mechanical or chemical.

TASK 9: Which two parts of the alimentary canal carry out mechanical digestion?

•

•

Chemical digestion is caused by enzymes. Organisms with a varied diet require more than one type of enzyme of carry out the digestion of the different food substances and usually more than one type of enzyme is needed for the complete digestion of a particular food.

TASK 10: Complete the table to show which enzymes carry out digestion in the gut.

Enzyme: Where released: Action:

Amylase

Exopeptidase

Endopeptidase

Sucrase

Lipase

Maltase

Lactase

What is the difference between exopeptidases and endopeptidases?

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Structure of the stomach

Several substances are secreted into the stomach of mammals to aid digestion. The cells responsible for each substance are located in gastric pits.

TASK 11: On the picture of a gastric pit below write down which substance is secreted by the parietal/oxyntic cells, the chief/zymogen cells and the mucous cells. Describe the function of each substance.

Pepsin is an exopeptidase that is secreted in the inactive form of pepsinogen.

TASK 12: Explain why it is secreted in an inactive form and how it is activated in the stomach.

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Most chemical digestion by enzymes takes place in the duodenum.

TASK 13: Draw an epithelial cell and label the microvilli.

The mucosa is folded and the millions of microscopic projections created by this folding of the inner surface of the wall are called villi. In between the villi are intestinal glands (or crypts of Leiberkuhn) which secrete intestinal juice.

What is the purpose of villi and microvilli in the duodenum/ileum?

What are goblet cells for?

The epithelial cells produce various enzymes that are not released into the lumen but are bound to the cell surface of the microvilli (also called brush border because of its appearance).

Other enzymes, found free in the lumen of the duodenum have been produced and released by the pancreas. As well as these enzymes, sodium bicarbonate solution (an alkali) is secreted into the duodenum to provide the optimal pH for the enzymes found in this region of the gut.

Why is sodium bicarbonate solution secreted into the duodenum?

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The gut wall consist of five layers surrounding a central cavity – serosa, longitudinal muscle layer, circular muscle layer, submucosa and mucosa.

TASK 14: Use the pictures below to identify each layer on microscope slides of the duodenum and ileum. Make labelled drawings of the tissues you can see on the slides. Write a brief description of the function of each layer.

Absorption of digested food

Large molecules have now been chemically digested into their constituent subunits by enzymes. They now need to be absorbed through the intestine wall, along with mucus and the digestive juices.

Absorption takes place by simple diffusion, facilitated diffusion and active transport.

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TASK 15: Read the following information about how the products of digestion are absorbed into the blood. Draw a series of pictures to illustrate the process.

Monosaccharides, amino acids, dipeptides and tripeptides are actively transported into the epithelial cells lining the wall. It is thought that their absorption is coupled with the absorption of sodium. This would mean that the carrier proteins have 2 receptor sites, one for sodium and one for glucose. Only when both are filled would they be actively transported from the lumen side of the epithelium, and into the cells. From here they diffuse into the capillaries by facilitated diffusion.

The fatty acids, glycerol and monoglycerides form complexes with bile salts called micelles. The micelles come into contact with epithelium cells and the fat-soluble fat components diffuse into the epithelium cell, leaving behind the fat insoluble bile salts.

In the epithelium, the fatty acids and glycerol are reformed by the endoplasmic reticulum to make triglycerides. They are packaged into globules with cholesterol and phospholipids and then coated with protein to be passed out from the epithelial cell into the lacteal and are transported in the lymphatic system.

Eventually these packages, called chylomicrons, are emptied into the blood. http://www.kscience.co.uk/animations/duodenum.htm

Http://www.s-cool.co.uk/alevel/biology/nutrition-and-digestion/human- digestive-system.html#ileum

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What happens to food after it has been absorbed?

TASK 16: Complete the sentences below using the words in the box to help you.

Glucose is absorbed from the blood to cells, for energy release in ______and any excess is stored as _____.

Amino acids are absorbed to synthesise ______. Excess cannot be stored so is ______where the ______groups are removed and made into ______. The rest of the molecule is converted into ______and stored.

Lipids are used for ______and hormones and the excess is stored as ______.

Membranes respiration carbohydrate Deaminated amino urea Fat fat protein

In the Colon

Most water is reabsorbed, along with soluble nutrients, in the small intestine. The colon absorbs the remaining water, together with vitamins which are secreted by micro organisms in the colon in order to produce solid faeces. Undigested cellulose, bacteria and sloughed cells pass along the colon to be egested as faeces. Fibre is required to provide bulk and stimulate peristalsis.

Which carbohydrate, found in cell walls, makes up fibre? Why can’t we digest it?

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Dentition in Herbivore and Carnivores

Mammals have evolved different types of teeth which each type being specialised for a different function.

TASK 17: On the picture below, label the incisors, canines, premolars and molars and state the function of each.

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Look at the pictures of a cat’s teeth and a sheep’s teeth.

TASK 18: Compare the teeth of carnivores and herbivores. Explain the function of each type of teeth and how they enable the animal to eat its food.

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Ruminants

Animals like cows and sheep eat mainly grass, a large proportion of which contains cellulose. As mammals do not produce cellulose, they are unable to digest cellulose directly and have a specialized stomach or rumen to aid cellulose digestion.

TASK 19: Read the information below and summarise it in a flow diagram. http://science.jburroughs.org/mbahe/BioA/starranimations/chapter36/videos_ani mations/ruminant.swf

The cow's digestive tract consists of the mouth, oesophagus, a complex four- compartment stomach, small intestine and large intestine (figure 1). The stomach includes the rumen, reticulum, the omasum and the abomasum.

The rumen. The rumen acts as a fermentation chamber where food, mixed with saliva, undergoes fermentation by mutualistic bacteria. Many of these produce cellulases which digest cellulose. Their presence is essential to the ruminant as it is unable to manufacture cellulase itself. The bacteria require anaerobic

conditions provided by the rumen and obtain their energy requirements through fermentation. The products of fermentation are absorbed by the cow who uses them as a source of energy. The cow also digests bacteria and uses them as a protein source.

Rumination. A ruminant is able to regurgitate and rechew partially digested material from the rumen. This is called rumination or 'chewing the cud'. The food is reswallowed and undergoes further fermentation.

Eventually the partially digested food is passed through the initial compartments of the alimentary canal until it reaches the abomasum which is similar to the stomach in humans. The small intestine contains the usual mammalian digestive enzymes. 15

Parasitic Nutrition

A parasite is ………………………………………………………………………………………………………………………

………………………………………………………………………………………………………………………………………………

Research task: Use the internet and textbooks to find out about the life cycles of two common parasites, Taenia solium (pork tapeworm) and Pediculus sp. (head louse). Use the information you have found to complete the table below. Find or draw labelled pictures of both parasites and attach them to this booklet.

Taenia solium Pediculus

What do they feed on and how do they obtain it?

How do they attach to the host?

How are they adapted to survive in their environment?

How do they reproduce?

How do they infect other hosts?

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Folder Check: Nutrition

Check whether you have detailed notes on Notes Teacher/Student following. complete? Comments Definitions of the different types of feeders. Description of extracellular digestion. Description of feeding in Amoeba and Hydra. Labelled diagram of the digestive system and descriptions of the function of each organ. An explanation of why larger organisms need a more complex digestive system. Descriptions of the different enzymes involved in digestion including where they are made and secreted. Drawings of TS ileum and duodenum, with layers of the gut labelled. Description of digestion and absorption of carbohydrates, proteins and lipids. Description of the fates of amino acids and carbohydrates once digested. Comparison of the digestive systems of carnivores and herbivores, including dentition, length of digestive system and the presence of a rumen. Details of the adaptations of the parasites Taenia and Pediculus.

General Organisation Y or N Student/teacher comments. Are student notes up to date?

Are their notes accurate?

Is the folder organised?

Is there evidence of independent learning? Has all homework been handed in?

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Test Mark (%) Grade Target Grade

Teacher Comments

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