AQUATIC HABITAT

AQUATIC HABITAT

An aquatic habitat is a natural body of water in which certain organisms live naturally. There are three types of aquatic habitats:

1. Marine habitat (salt water habitat)
2. Estuarine habitat (brackish water habitat)
3. Fresh water habitat

MARINE HABITAT

Marine habitat is an aquatic habitat that contain salt water e.g. oceans, seas, lakes, sea shores.

Characteristics of marine habitat

1. Salinity: salinity of marine habitats is high, at about 35.2 parts of salt per thousand (35‰)
2. Size: size of marine habitats is very large
3. Density: density of marine water is high at about 1.028g/cm³; this causes organisms to float in it.
4. Pressure: the water pressure of marine habitat increases with depth at one atmosphere for every 10m. The pressure at the bottom is high.
5. Temperature: the temperature of marine habitats decreases with increase in depth. The temperature is about 30̊C at the top and 4̊C at the ocean floor.
6. Oxygen concentration: the oxygen content of marine water is highest at the top where atmospheric oxygen dissolves in the water and decreases with depth.
7. Hydrogen ion concentration (pH): marine water is alkaline with a pH of 8.0 - 9.0.
8. Light penetration: light penetrates the marine habitat to a depth of about 200m. This is due to water turbidity.
9. Marine habitats are usually affected by waves, ocean currents and tides.

Major Ecological Zones of Marine Habitat

1. Supratidal zone (splash zone): this is the exposed zone of the marine habitat; it is land where water splashes when waves break at the sea shore.
2. Intertidal zone (neritic zone): this zone is exposed at low tide and submerged at high tide.
3. Subtidal zone: is about 200m deep and constantly submerged by water.
4. Bathyal zone: this zone is about 3000m deep and is characterized by low light penetration
5. Abyssal zone: this zone is ab0ut 7000m deep. It is characterized by low temperature, low light penetration and high pressure
6. Hadal zone: this zone is up to about 10000m deep. It is characterized by no light penetration, very low temperature, high pressure and no photosynthetic activity.

On the basis of light penetration, marine habitat can be categorized into:

• i. Euphotic zone: has enough light penetration. Photosynthetic activities are high. Producers, consumers and decomposers are present here.
• ii. Disphotic zone: has dim light. Only consumers and decomposers are present.
• iii. Aphotic zone is the dark ocean bottom with no light penetration. Very few organisms are present here.

Distribution of organisms in marine habitat

Plants in the splash zone include grasses and Ipomea. Animals found here are sand crab and ghost crab.

Organisms in the intertidal zone include starfish, bivalve mollusc, mole crab, Limpet, barnacles, crabs, sea anemones, sea urchins, crabs and worms. Plants found here include Sargassum, sea lettuce and brown algae.

Organisms in the subtidal zone include starfish, polychaete worms, brown algae, red algae, prawn, shrimp, phytoplankton, zooplankton, squid, cartilaginous fish and bony fishes.

Other organisms of the deep ocean are shark, ray, sea catfish, croaker and angler fish.

Adaptive features of Organisms in Marine habitat

1. Star fish, bivalve mollusc, mole crab, sand crab and ghost-crab burrow into the soil to prevent being washed away by waves and to avoid desiccation during low tide.  They also possess gills for gaseous exchange in water and spongy tissue for gaseous exchange on land.
2. Star fish and bivalve mollusc have protective colouration like sand to prevent being detected by predators.
3. Limpets, barnacles, sea urchins and sea anemones attach themselves firmly to the rocks by the feet to prevent being washed away by waves
4. Barnacles have protective shell and enclose water in its shell to prevent desiccation.
5. Sea weeds possess hold fast for attachment and air bladder for buoyancy.
6. Algae, phytoplankton have small sizes to enable them float to reach light for photosynthesis.
7. Prawns and shrimps have gills for gaseous exchange, appendages for locomotion and exoskeleton to prevent water-loss from the body.
8. Bony and cartilaginous fish have gills for gaseous exchange, scales to prevent water-loss from the body and air bladder to adjust its depth within the water body.
9. Organisms of the benthic zone have fluorescent organs that produce light to attract their prey, have large mouths to capture their prey and can withstand high pressure and low oxygen concentration.

Food chain in marine habitat

Diatom → krill → squid → whale

Algae → limpet → whelk → seagull

ESTUARINE HABITAT

Estuarine habitat is a body of water where salt water from the sea mixes with fresh water from the land to produce brackish water. In Nigeria, estuaries are found in coastal zones of Lagos, Ondo, Edo, Delta, Akwa Ibom, Bayelsa, Rivers and Cross rivers.

Types of Estuaries

There are three types of estuaries

    a.  Bay: a little portion of sea water that enters into land to mix with fresh water.

    b.  Delta: where a river divides into many channels before entering the sea.

    c.  Lagoon: this is when sea/ocean water enters into land by means of a canal.

Characteristics of Estuarine Habitat

1. Fluctuations in salinity: the salinity of an estuary is lower at the mouth of the river and higher towards the sea
2. Turbidity: the turbidity of estuarine habitat increases especially during the rainy season due to the debris brought by flood water.
3. Shallowness of water: estuarine habitat is shallow due to deposition of debris by rivers. It is not as deep as marine habitat
4. High level of nutrients: estuarine habitat is characterized by high amount of nutrients
5. Low oxygen content: the oxygen content of an estuarine habitat is very low
6. Low species diversity: the species diversity of estuarine habitat is lower compared to that of marine habitat.

Distribution of Organisms in Estuarine Habitat

Plants in the estuary are phytoplankton, algae and epiphytic plants, Spartina, Salicornia, sedges, bulrush, saltgrass, Thalassia, red mangrove (Rhizophora racemosa), white mangrove (Avicennia nitida).
The animals are oysters, anemones, clams, crabs, lobster, shrimps and salmon fish

Adaptive Features of Organisms in Estuarine Habitats

1. Planktons / Diatoms possess air spaces in their tissues for buoyancy so as to reach light. They also have rhizoids/false feet for attachment to rocky shores
2. Algae possess chlorophyll for photosynthesis and air bladder for floating.
3. White mangrove possess breathing root (Pneumatophores) for exchange of gases.
4. Mosquito larva has breathing trumpets for gaseous exchange
5. Mudskipper fish have fins adapted for crawling when on land and swimming when in water
6. Worms have strong protective and impermeable covering against high salinity.
7. Crabs burrow fast into the mud to escape predators, strong waves or tides.

Food chain in Estuarine habitat

Detritus → shrimp → Salmon

Detritus → worms → snail → bird

FRESH WATER HABITAT

Fresh water habitat is an aquatic habitat that contain very low level of salinity e.g. rivers, springs, streams, lakes.

Characteristics of freshwater habitat

1. Low salinity: freshwater habitats contain no significant amount of salt
2. Small size: the body of freshwater habitats are small compared to marine habitats.
3. Variation in temperature: the temperature of freshwater habitat varies with depth and season. The temperature at the top is slightly higher at the top than at the bottom. The temperature during the hot season is also higher than the temperature during the cold season.
4. Shallow depth: freshwater habitats are usually shallow; this allows light penetrate through to the bottom.
5. High concentration of oxygen content: the concentration of oxygen in freshwater habitats is high and evenly distributed round the water body.
6. Seasonal variation: some rivers dry up during the dry season and increases in volume during the rainy season.
7. Currents: currents are present in freshwater which affects the distribution of gases and nutrients.

Types of freshwater habitats

There are two types of freshwater habitats on the basis of their mobility:

1.  Lentic freshwater: these are standing or stagnant water e.g. ponds, pools, lakes, swamps, dams
2.  Lotic freshwater: these are running waters which flow continuously in one direction e.g. rivers, streams, springs

Major Ecological Zones of Freshwater Habitats

Lentic freshwater habitat is divided into two zones:

a)  Littoral zone: this is the shallow part of the freshwater habitat. It contains several plants and animals.

b)  Benthic zone: this is the deepest part of the freshwater habitat. It does not have as much plants as littoral zone.

Lotic freshwater is also divided into two zones:

    a)  Pool zone: this is where the rate of water flow is slow and calm

    b)  Rapid zone: this is where the speed of water flow is very fast. 

Distribution of Organisms in a Freshwater Habitat

Some of the organisms found in the littoral zone of the freshwater habitat include Spirogyra, Chlamydomonas, water lettuce, water fern, duckweed, diatoms, reeds, sedges, water fleas, water snails, water skater, ducks, frogs, toads, tadpoles, hydra, snakes, crocodiles, waterbuck and hippopotamus.

Organisms found at the benthic region of freshwater habitat include water lily, ferns, commelina, hydra, Tilapia fish, mud fish, cat fish, leech, pupae of mosquito, crayfish, water snail, water scorpion, water boatman and water bug.

Adaptive features of organisms in freshwater habitat

1. Water hyacinth and water lily have air bladders, intercellular space and light weight that enable them float in the water. They also have broad leaves that helps in absorbing sunlight for photosynthesis.
2. Spirogyra has mucilaginous cover which protect them in water.
3. Water lettuce has hairs on their leaves which help them to trap air and enable them to float
4. Water boatman carries hair bubbles with it to the bottom of the pond for respiration under water
5. Water skater has long legs with which it skates on water surface
6. Lungfish carries out gaseous exchange with gills under water and when the river dries out, it burrows into the soil and begin to use lungs

Food Chain in Freshwater Habitat

Algae → Tadpole → Dragonfly larva → water stick insect

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SS2 Third Term Scheme of work

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TRANSPORT SYSTEM

TRANSPORT SYSTEM

Transport system refers to the movement of metabolic materials from various parts of an organism where they are produced or obtained to parts where they are used, stored or removed from the body.

The Need for Transportation in Small and Large Organisms

1. Distribution of essential materials
2. Removal and disposal of metabolic wastes
3. Movement of hormones
4. Transport of substances to storage sites
5. Regulation of body temperature and distribution of heat
6. Distribution of water, mineral salt and manufactured food in plants

Need for Transport System in Large Organisms

The surface area to volume ratio (A/V) is too small. Many cells are situated far away from others. Materials need to move great distances. Materials to be distributed are too large in quantity. Hence, the need for efficient transport system.

Shape	Surface area	Volume		A/V ratio
A	6cm2	1cm3	6/1	6
B	10cm2	2cm3
C	16cm2	4cm3
D	24cm2	8cm3

Materials Transported in Animals

1. Oxygen
2. Carbon(IV)oxide
3. Water
4. Salts
5. Hormones
6. Antibodies
7. Food
8. Excretory products e.g. urea

Media of Transportation in Animals

1. Cytoplasm: used in lower organisms e.g. Amoeba, Paramecium
2. Blood: used in higher animals e.g. vertebrates
3. Lymph: used in higher animals
4. Cell sap or latex: used in plants

Composition and Function of Mammalian Blood

Blood is a tissue that contains cells.

1. Blood cells (corpuscles): contains red blood cell, white blood cell and blood platelets. This constitutes 45% of whole blood.
2. Plasma: the fluid portion of the blood. This constitutes 55% of whole blood. Plasma consists of proteins, food materials, mineral salts, hormones and excretory products.

Red blood cells (RBCs or Erythrocytes): these are tiny biconcave discs with no nucleus. There are about five million RBCs in each mm³ of blood. Red blood cells are produced in the bone marrow which is a spongy red tissue in bones. The lifespan of a red blood cell is about 120days. Old and worn out RBCs are destroyed in the spleen and liver. Red blood cells contain haemoglobin which helps it to transport oxygen from lungs to the cells and assist in the formation of blood clot.

White blood cells (WBCs or Leucocytes): these are colourless, irregular and amoeboid in shape. They are larger than RBCs and contain a nucleus. There are between 5,000 and 10,000 WBCs per mm³ of blood. They could be phagocytes which ingest bacteria or lymphocytes which produce antibodies. White blood cells keep the body healthy by fighting off disease.

Blood platelets are tiny fragments of cells which help in the formation of blood clot.

Plasma is the liquid component of blood. It contains soluble proteins (e.g. albumin, globulin), dissolved mineral salts, food substances, excretory products and hormones. Plasma help in transportation of substances dissolved in it.

General Functions of Blood

           1.      Transport medium

a.       For digested food to all parts of the body

b.      Excretory products

c.       Hormones

d.      Oxygen

e.       heat

           2.      Defence against diseases and infections

a.       Phagocytosis

b.      Production of antibodies

c.       Clotting of blood

           3.      Regulation of body temperature

           4.      Homeostasis

ASSIGNMENT: Describe the process by which blood clot forms during an injury

Circulatory System in Mammals

The mammalian circulation consists of heart (a pump) and blood vessels (arteries, veins and capillaries).

Structure of Mammalian Heart

The Mammalian Heart

The human heart is a hollow, conical, muscular organ which keeps blood circulating around the body throughout the life of a person. The heart is protected by a membrane called pericardium.

The muscles of the heart are called cardiac muscles. There are four (4) chambers in the mammalian heart: the right and left auricles or atria (singular- atrium) and the right and left ventricles. A thick septum separates the heart into two (2) sides. The right auricle communicates with the right ventricle by the tricuspid valve while the left auricle communicates with the left ventricle by the bicuspid valve. The valves ensure blood flows only in one direction.

The heart beats at about 70-75 times per minute. During a heartbeat, the resting period is known as diastole while the period the heart contracts is known as systole. The cycle between systole and diastole is known as pulse and takes about 0.8seconds.

Arteries

An artery is a blood vessel which carries blood away from the heart e.g. aorta. The walls are thicker, more elastic, has a small lumen and are more muscular than those of veins. The pressure in arteries is usually high and they are situated deep in muscles. Arteries carry oxygenated blood except for pulmonary artery. They branch out to arterioles and do not have valves.

Veins

Veins are blood vessels that return blood to the heart e.g. vena cava, pulmonary vein. The walls are less muscular, thinner, has a larger lumen and are less elastic compared to arteries. The pressure in veins is relatively lower and they are superficially located close to the skin surface. Veins carry deoxygenated blood except for pulmonary vein. They have valves.

Capillaries

These are microscopic blood vessels that form a network of linking arterioles to venules. Exchange of materials between tissues takes place in capillaries. Their walls are only one cell thick in order to facilitate diffusion of materials between the cells and the blood.

The diagram below shows the direction of blood flow in the body.

Types and Mechanisms of Circulation

     A.    Open and Closed Circulation

Open blood circulatory system is found in most invertebrates e.g. roundworms, insects and molluscs. The heart pumps blood into haemocoel, the organs and tissues are bathed in the blood (which is colourless) while the blood is returned to the heart through paired ostia. There is no system of blood vessels. Fluid flow in open circulation is slow.

Closed circulatory system occurs when blood leaves the heart in closed blood vessels and capillaries and circulates around the body and returns to the heart without being exposed. The blood flows from the heart to the arteries which branch out into arterioles, then capillaries where the exchange of material takes place with the body cells. The capillaries then form venules which connect together to form veins which return the blood to the heart.

     B.    Single and Double Circulation

In the single circulatory system, blood flows through the heart once in one cycle. This occurs in organisms such as fish which has a two-chambered heart (one atrium and one ventricle). Blood flows from the ventricle to the gills through the aorta, the blood picks oxygen which is distributed to various organs of the body through arteries which branch out to all parts of the body.

In the double circulatory system, blood flows through the heart twice in one cycle. This occurs in mammals.

The amphibians, the atrium is divided into right and left chambers. However, the ventricle is just one.

The mammalian heart is completely divided into right and left chambers, oxygenated blood does not mix with deoxygenated blood.

    C.    Pulmonary and Systemic Circulation

Pulmonary circulation involves the movement of blood between the heart and the lungs. From the right ventricle, deoxygenated blood is pumped into the pulmonary artery which branches to the right and left lungs. From the lungs, oxygenated blood is returned to the left atrium through the pulmonary vein.

Systemic circulation involves the movement of blood between the heart and all other parts of the body. Oxygenated blood collected by the left atrium is forced into the left ventricle, then to the aorta to be distributed around the body. The superior and inferior vena cava returns the deoxygenated blood from the body to the right atrium.

Coronary circulation involves the supply of blood to the muscles of the heart.

TRANSPORT SYSTEM IN PLANTS

The major materials transported in plants are gases, CO₂, oxygen, water, mineral salts, manufactured food, pigments and hormones.

The main transport media in plants are cytoplasm, cell sap and latex.

Transportation in Lower Plants

Lower plants use their cytoplasm for movement and distribution of materials. Gases enter the lower plants mainly by diffusion while water enters by osmosis

Transportation in Higher Plants

Vascular bundles are conducting vessels of plants and they consist of xylem and phloem.

Phloem tissues consist of thin-walled living cells with dense cytoplasm and have perforated cross-walls. Phloem translocates manufactured food from the leaves to living cells and storage organs. Xylem tissues consist of dead cells with lignified walls. Xylem vessels are responsible for upward conduction of soil nutrient and water from root to the leaves.

Translocation

This is the transport of manufactured food from the leaves to other parts of the plant where they are needed or stored.

EXPERIMENT: (Ringing Experiment)

AIM: To show that translocation takes place in phloem tissue.

MATERIALS: Two potted plants, knife

METHOD: use the knife to remove the bark of one of the potted plants together with the phloem tissues. The other plant is left untouched. Both plants are observed for a period of 2-5 weeks.

OBSERVATION: the potted plant with the removed bark and phloem tissues show swellings just under the part where the tissues have been removed. The other plant remains unchanged.

CONCLUSION: the swelling observed at the top of the ringed region is as a result of the accumulation of food which have passed down from the leaves. This shows that phloem is responsible for translocation of food from the leaves to other parts of the plant.

Transpiration

This is the loss of water vapour from the shoots of plants through the stomata of the leaves to the atmosphere. Water-loss from the stomata is known as stomatal transpiration, water-loss from the cuticles of plants are known as cuticular transpiration while water-loss through the lenticels is known as lenticular transpiration.

Measurement of Transpiration

1. Weighing method
2. Use of photometer
3. Use of cobalt chloride paper

EXPERIMENT

AIM:	To show that plants lose water from their leaves by transpiration
MATERIALS:	Two polythene bags, two bell jars, two potted plants (one having its stem cut), white copper(II)tetraoxosulphate VI (CuSO4) and crucible
METHOD:	Place the CuSO4 in a crucible along with the potted plants covering the soil with the polythene bag. Repeat the same procedure with the potted plant with the cut stem which serves as control. Cover the setups with bell jars
OBSERVATION:	The white anhydrous CuSO4 in the main test experiment changes colour to blue due to the water released by the plant while the CuSO4 in the control experiment did not
CONCLUSION:	Colour change from white to blue is due to water given off during transpiration of the leaves

Factors Affecting Transpiration

           A.    Plant factors

1)      Leaf area

2)      Leaf structure

3)      Root system

          B.     Atmospheric factors

1)      Sunlight

2)      Humidity

3)      Temperature

4)      Wind

          C.     Soil factor

1)      Availability of water

2)      Temperature

Importance of Transpiration

1. Cooling effect
2. Translocation of mineral salts
3. Good growth of plants

Absorption of Water and Mineral Salts

1. Uptake of soil water: the root hairs absorb water from the soil by osmosis.
2. Uptake of mineral salts: mineral salts are absorbed into the root hairs by active transport

Transport of Water in Xylem Tissue

Transport of water in xylem tissue is due to root pressure, capillary action and transpiration pull.

Root pressure: as the root accumulate water absorbed by root hairs, pressure is developed which causes water to move across root cells up the xylem vessels.

Capillary action: xylem vessels form fine capillary tubes. Water rises up along the tubes as a result of attraction between water molecules and the wall of xylem vessels.

Transpiration pull: as water evaporates from the leaves by transpiration and more sugar molecules are produced by photosynthesis, the osmotic pressure increases, and this causes water to flow into the leaf cells from xylem vessels.

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DIGESTIVE SYSTEM

DIGESTIVE SYSTEM

The digestive system includes the alimentary tract and all glands and organs associated with digestion and assimilation of food in animals.

Digestion is the breakdown of large molecules of food into simple and absorbable form for use by animals. Ingestion is the taking in of food from outside through the mouth. Egestion is the discharge of undigested and unabsorbed food from the alimentary canal. Absorption is the passage of food through the wall of the alimentary canal. Assimilation is the manufacture of the body’s own materials from the absorbed substances and their use in metabolism.

TYPES OF DIGESTIVE TRACTS

There are two types of digestive tracts:

A.    Incomplete digestive tract: has only one opening- the mouth which serve for ingestion and egestion e.g Hydra, Planaria

B.     Complete digestive tract: has two openings to the outside world- mouth (for ingestion) and anus (for egestion) e.g. earthworm, goat

Complete digestive system has an advantage that incoming food does not mix with outgoing undigested food materials and each part is specialized to perform different functions.

Alimentary Canal of invertebrates

Animals have different alimentary tracts which vary in size, complexity, mode of feeding or the type of diet.

Alimentary canal of Planaria

Planaria is a free-living flatworm that feeds on small aquatic animals- zooplankton. It has a simple digestive tract with one opening- the mouth. The digestive tract consist of a ventrally placed mouth, muscular pharynx and intestine. The pharynx can be protruded when attacking a prey. Digestion is intracellular and undigested food is egested through the mouth. Digested food is distributed through the body by diffusion.

Alimentary canal of Earthworm

The earthworm has a complete digestive tract.

The mouth has a lip-like structure called prostomium which leads into the buccal cavity. The pharynx secrete mucus and protein digesting enzymes into the pharyngeal cavity. The oesophagus secrete CaCO3 [calcium trioxocarbonate(IV)] which removes excess calcium from ingested food. The crop acts as temporary storage chamber. Food is ground into small particles by the churning action of the gizzard. Digestion of food takes place in the intestine. Indigestible materials are removes from the body through the anus as casts.

Alimentary canal of Cockroach

The digestive tract of Cockroach consist of mouth (mandibles) which is modified for cutting and chewing. Oesophagus is short, narrow and tubular and connects the mouth with the crop. The crop acts as temporary storage. Most digestion occur in the crop. The gizzard is muscular and grinding of food takes place here. Digestion and absorption take place in the midgut. The rectum absorbs water and faeces is passed out through the anus.

Alimentary canal of birds

The mouth parts have been modified to beak with no teeth. Food is passed from the mouth through the oesophagus into the crop where it is stored temporarily. The food then passes to the stomach consisting of the true stomach (proventriculus) and muscular gizzard. The proventriculus also known as glandular stomach has glands which secrete digestive enzymes. The food then proceeds into the gizzard (grindular stomach) where grinding takes place. Bile and pancreatic juice is secreted in the first part of the intestine (duodenum) while digestion is completed and absorption takes place in the lower intestine. Undigested food passes into the rectum and anus (cloaca) to be discharged as faeces.

Similarities in the alimentary canal of Birds and Cockroach

1.         Possession of narrow oesophagus;
2.         Possession of crop;
3.         Possession of caecum;
4.         Possession of muscular gizzard;
5.         Possession of mid-gut/intestine;
6.          Possession of rectum.

Differences between the alimentary Canal of Birds and Cockroach

Bird	Cockroach
-mouth is modified into beak for pecking	mouth modified for chewing and biting;
- tongue is present in the mouth	tongue is absent in the mouth;
- duodenum is present	duodenum is absent;
- alimentary canal is long	alimentary canal is relatively short;
- hindgut terminates into cloaca	hindgut terminates into anus;
- malpighian tubules are not attached to the alimentary canal	malpighian tubules are attached to to the alimentary canal
- liver/pancreas present in the alimentary canal	liver/pancreas absent in the alimentary canal;
- salivary gland absent	salivary gland present.

Alimentary canal of Rabbit

The rabbit is an herbivore that feeds mainly on grasses and leaves. It digestive system consist of mouth, oesophagus, stomach, small intestine, large intestine, caecum, rectum and anus.

Food is physically broken-down in the mouth by the teeth. The food then passes into the stomach where gastric juice breaks down the food into simpler substances. Digested food is absorbed into the bloodstream through the walls of the small intestine. The rabbit has a very large caecum which contains a large number of beneficial microorganisms. These microorganisms digest fine food materials and undigested food from the caecum form soft moist pellets which are excreted through the anus.

Alimentary canal in Man

The mouth contains teeth, tongue and salivary glands. The teeth are used to cut, grind or chew (masticate) the food into tiny particles. The tongue rolls the food into bolus, allows mixing of the food with ptyalin and aids swallowing the food. Saliva contains the enzyme ptyalin, serve as lubricant for the mouth and solvent for the food. Food passes through the oesophagus through peristaltic movement into the stomach.

The stomach secretes renin (curdles milk) and pepsin (breaks down proteins into peptones). It also secretes HCl an acid which helps to kill some bacteria in the stomach. Churning movement of the stomach convert the food into semi-liquid called chyme.

Duodenum secrete amylase (convert starch to maltose), lipase (convert protein into peptones) and bile. The food is now in liquid form- chyle. Absorption and digestion takes place in the ileum. Enzymes secreted in the ileum include lipase, erepsin, maltase, sucrase and lactase.

Water is absorbed in the large intestine while undigested food is converted to faeces and egested through the anus.

The liver secretes bile which is temporarily stored in the gall bladder. Bile aid digestion of fats. The pancreas produce the pancreatic juice which contains digestive enzymes and produces the hormone – insulin which regulates the amount of sugar in the blood.

Digestion in Man

Enzyme	Secretion	Source	Site of action	Substrate	Product
Ptyalin	Saliva	Salivary glands	Mouth	Cooked starch	maltose
Pepsin	Gastric juice	Gastric glands	Stomach	Protein	Polypeptides (Peptone)
Renin	Gastric juice	Gastric glands	Stomach	Soluble casein (milk protein)	Insoluble casein
Amylase	Pancreatic juice	Pancreas	Small intestine (Duodenum)	Starch	Maltose
Trypsin	Pancreatic juice	Pancreas	Small intestine (Duodenum)	Protein	Polypeptides (peptones)
Lipase	Pancreatic juice	Pancreas	Small intestine (Duodenum)	Fats	Fatty acids and glycerol
Erepsin	Intestinal juice	Intestinal glands	Small intestine (Ileum)	Polypeptides (peptones)	Amino acids
Maltase	Intestinal juice	Intestinal glands	Small intestine (Ileum)	Maltose	Glucose
Lactase	Intestinal juice	Intestinal glands	Small intestine (Ileum)	Lactose	Glucose and galactose
Sucrose	Intestinal juice	Intestinal glands	Small intestine (Ileum)	Sucrose	Glucose and fructose
Lipase	Intestinal juice	Intestinal glands	Small intestine (Ileum)	Fats	Fatty acids and glycerol

Similarities in Alimentary Canal of Birds and Grasshopper

1. Both have narrow oesophagus
2. Both have crop for temporary storage of food
3. Both have muscular gizzard
4. Both have midgut

Differences in Alimentary Canal of Birds and Grasshopper

	Birds	Grasshopper
1	Mouth is modified into beaks	Mouth is modified into mandible and maxillae for biting and chewing
2	Duodenum is present	Duodenum is absent
3	The alimentary canal is relatively longer	The alimentary canal is relatively shorter
4	Alimentary canal ends in cloaca	Alimentary canal ends in anus
5	Malpighian tubules are absent	Malpighian tubules are present
6	Pancreas is present	Pancreas is absent
7	Tongue is present in the mouth	Tongue is absent in the mouth

FEEDING MECHANISMS IN SOME ANIMALS

A.          Absorbing mechanism: e.g. Tapeworm. They do not have alimentary canal, they possess a scolex or head with a rostellum surrounded by hooks and four suckers for attachment; they possess a flat body for large surface area for absorption; entire body surface adapted for absorption and thick cuticle to resist digestion by digestive enzymes.

B.           Biting and chewing mechanism: e.g. grasshopper, cockroach. They have four different mouth parts:

• -          Labrum (upper lip): this prevents food from falling off the mouth
• -    Mandibles: these are heavy toothed and law-like structure for cutting and chewing food materials
• -     Maxillae: a biting blade which breaks down the food chewed by mandibles into smaller particles
• -          Labium (lower lip): this prevent wastage of food from the mouth

C.     Sucking mechanism: e.g. mosquito, butterfly and housefly. The mosquito has piercing mouth parts called proboscis, which is used for sucking blood of animals. The mouth produce saliva to prevent clotting of the blood.

The butterfly has long coiled proboscis used for sucking nectars of flowers. The proboscis can be coiled or extended when in use.

The housefly has enlarged labella for sucking liquid food. It uses a sponging mechanism to absorb the food.

D.    Grinding mechanism: this is common among mammals. The grinding is aided by hard, strong teeth made of enamel and dentine. The teeth can withstand biting, chewing, grinding or cracking of food. There are different sets of teeth for special purposes- incissors for cutting bits of food, canine for tearing food, pre-molars and molars with wide surfaces for grinding.

E.     Trapping and absorbing mechanism: this is common in carnivorous (insectivorous) plants e.g. bladderwort, sundew. The plants have structures for trapping small insects. Sundew has long hairs which carry digestive glands which digest insects and digested food is absorbed into the plant.

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