Topic 4: The Five Kingdoms
Organisms are divided into five kingdoms, which are:
- Kingdom Monera which includes bacteria
- Kingdom Protoctista which includes amoeba
- Kingdom Fungi which includes moulds
- Kingdom Plantae which includes ferns
- Kingdom Animalia which includes insects.
VIRUSES
Viruses do not fit into any of the five kingdoms.
They are obligate parasites i.e. they do not survive outside a host. In fact, outside other living cells, viruses appear as particles that do not feed, respire, excrete, etc.
The only characteristic of living things that they carry out effectively is reproduction; and this is only when inside a living cell.
Size: Viruses are very small ranging from 10 - 300 nm. (NB: 1,000,000,000nm = 1m). So one million viruses could form a single file line of 1 mm length. So viruses cannot be viewed using the light microscope; but only by the powerful electron microscope.
Structure: Viruses consist of a nucleic acid called DNA (deoxyribonucleic acid) which is surrounded by a protein coat.
Below is a diagram to show an example of a virus called the bacteriophage, which infects bacteria.
Life cycle of a bacteriophage virus;
1. Tail fibre attaches virus to host cell
2. Core plate injects DNA into host cell
3. DNA multiplies inside host cell
4. Cell's materials form protein coats for new viruses.
5. The cell bursts releasing many new viruses
6. New viruses invade other cells.
Diseases caused by Viruses:
Tobacco mosaic virus disease: This is caused by a virus transmitted by contact to tobacco plants. It was the first virus to be discovered. The virus attacks outer leaf cells. Control is by burning affected plants.
Rabies: This is caused by a virus transmitted through saliva to dogs and humans. It attacks nerves cells in the brain. Control is by vaccinating dogs and cats.
Influenza and common colds: These are caused by viruses transmitted through air by coughing, sneezing, and breathing. Symptoms are headache, sore throat, high temperature (fever). It is a pandemic disease affecting all parts of the world. It can be controlled by preventing overcrowding.
Yellow fever: This is caused by a virus transmitted through the bite of an Aedes mosquito. The virus affects the liver and kidney causing headache, backache, fever and jaundice where urine is yellow and the eye corneas are yellow.
Control is by: - Destroying all breeding places of mosquitoes.
- Spraying with DDT against adult mosquitoes.
- Sleeping under mosquito nets.
- Quarantine: restriction of movement of people from and to yellow fever areas.
- Inoculation of people traveling to yellow fever areas.
NB: Monkeys act as a reservoir for yellow fever; so their restriction could control the disease.
Measles: Symptoms include fever, skin rush, coughing, continuous temperature rises and falls. Control is by isolation, avoidance of overcrowding and by vaccination.
Poliomyelitis: This is caused by a virus that is transmitted through faeces and water. It attacks the nerve cells of the skeletal muscle finally causing paralysis.
Control is by hygienic preparation of food, clean water supplies and by vaccination by oral dose.
KINGDOM MONERA
This is also called Kingdom Prokaryotae. It includes bacteria and the blue green algae.
Bacteria:
They are larger than viruses i.e. about 1 µm in diameter. So only about 10,000 bacteria would make a single file line of 1 cm. They can thus be viewed under a light microscope.
They may be single cells or colonies.
- They have a cell wall made of protein.
- The slime capsule offers protection from desiccation.
- The flagella help in locomotion.
- There are glycogen granules in the cytoplasm.
- The nuclear matter lacks a nuclear membrane.
Some bacteria are saprophytes feeding on dead matter to fasten decay.
Some are parasites i.e. they feed on a host which suffers injurious effects.
Some are free-living like nitrifying bacteria, which circulate nitrogen in the soil.
Some bacteria carry out aerobic respiration i.e. they need oxygen for respiration.
Other bacteria carry out anaerobic respiration i.e. they do not need oxygen for respiration for example Clostridium tetani, which causes Tetanus.
Bacteria reproduce by binary fussion but in unfavourable conditions they form spores so that they can survive the harsh conditions.
Shapes of bacteria:
1. Some bacteria are spherical or cocci.
Examples:
2. Some bacteria are rod-shaped or bacilli.
Example:
3. Some bacteria are spiral-shaped.
Examples:
Diseases caused by bacteria:
Meningitis: This is an air-borne disease, which invades the brain-covering membranes called meninges. It is controlled by preventing over-crowding and by vaccination.
Pneumonia: This is also an air-borne disease which makes fluids build up in the lungs. It is controlled by preventing over-crowding.
Tetanus: This is caused by Clostridium tetani which enters the body through broken skin. It causes muscular spasms and is controlled by vaccination.
Typhoid fever: This is a water-borne disease caused by Salmonella typhi. Symptoms include fever, muscular pains and diarrhea. It is controlled by proper sanitation of water supplies.
Leprosy: This is caused by a bacillus called Mycobacterium laprae and is transmitted by contact. It attacks nerves fibres and is controlled by isolation.
Tuberclosis (TB): This is an air-borne disease, which is caused by Mycobacterium tuberclosis, which affects the lungs. It is controlled by pasteurizing milk (boiling and cooling); proper ventilation; avoidance of overcrowding and by vaccination using BCG vaccine, a Bacilius invented by Calmette and Guerin.
Other bacterial diseases include diptheria (whooping cough), cholera, gonorrhoea, syphilis.
Importance of bacteria:
- They cause disease to mammals.
- They cause disease to plants.
- They digest cellulose in the rumen of cattle and in the caecum of rabbits and horses.
- They manufacture vitamin B and K in man.
- They improve soil fertility by fixing nitrogen in the soil for example Rhizobium bacteria in the root nodules of legumes like beans.
KINGDOM OF PROTOZOA
These unlike Monera have a nuclear membrane but are also unicellular.
Protoctista kingdom is divided into these major phyla:
- Phylum Euglenoidae for example Euglena.
- Phylum Protozoa for example Amoeba.
- Phylum Chlorophyta for example spirogyra.
Phylum euglenoidae:
These are flagellate unicellular organisms, which contain chlorophyll and are capable of photosynthesis. An example is Euglena, which has a flagellum for locomotion.
It has a photoreceptor which is sensitive to light. Osmoregulation is by a contractile vacuole and reproduction is by binary fission.
Phylum protozoa
The protozoa are divided into the following classes:
- Class Flagellata for example trypanasome.
- Class Rhizopoda for example amoeba.
- Class Ciliata for example paramecium.
- Class Sporozoa for example plasmodium.
CLASS FLAGELLATA
These have long hairs called flagella for locomotion. An example is the trypanasome, which causes sleeping sickness. It lives in the blood plasma of man, cattle and wild animals. It is transmitted form one mammal to another through the bite of the female tsetse fly. Control is by killing tsetse flies using aerial sprays and clearing bushes where it hides. Another form of control is by quarantine regulations.
Class rhizopoda
These are aquatic i.e. they live in water or in moist places.
Some are parasites for example Entamoeba hystorica which causes dysentry.
The Amoeba:
Cytoplasm: This is of two parts: Endoplasm which is fluid and flows more rapidly; and Ectoplasm which is jelly-like.
Cell membrane: This encloses cytoplasm and protects the cell. It is semi-permeable i.e. it allows some substances to pass through but not others. Such substances include water, gases, etc.
Nucleus: This controls cell division and is for reproduction by binary fission.
The Contractile Vacuole: This is for regulating the amount of water in the organism cell i.e. osmo-regulation.
Pseudopodia: These are projections formed by the flowing of cytoplasm to enable locomotion. The pseudopodia also enable the amoeba to feed by engulfing (phagocytosis).
Method of feeding:
The pseudopodia surround the food particles.
The cell membrane becomes the lining of the food vacuole inside cytoplasm
A new membrane forms on the surface at the point where the food particles entered the cell.
Enzymes are secreted into the vacuole to digest food.
Soluble digested materials are absorbed into the surrounding cytoplasm.
Indigested residues are egested through the cell membrane as the amoeba flows on.
Excretion in amoeba of carbon dioxide and nitrogenous wastes is by simple diffusion through the cell membrane. This is because amoeba is small so it has a large surface area to volume ratio.
Amoeba forms a cyst to protect it during unfavourable conditions.
Class ciliata:
These have tiny hairs called cilia which aid in locomotion and capturing food.
They have two nuclei: the meganucleus which controls cell activities and the micronucleus which controls reproduction by binary fission.
An example of a ciliate is the Paramecium.
A paramecium is slipper-shaped i.e. it is rounded at the anterior end (front) and pointed at the posterior end (hind).
Unlike amoeba, paramecium is surrounded by a thick pellicle, which gives it a definite shape.
It has got trichocysts for capturing prey, defence and attachment to solid surfaces.
Gaseous exchange of oxygen and carbon dioxide and elimination of nitrogenous wastes is by simple diffusion through the pellicle.
Reproduction is by binary fission but they can carry out sexual reproduction by conjugation where two of them mate.
The contractile vacuole is for osmoregulation.
Feeding in the paramecium:
The oral groove is lined with cilia.
The cilia beat water currents that have food particles.
The food particles enter a mouth pore, which opens, into a gullet.
A food vacuole is formed at the end of the gullet.
The food vacuole breaks away into the cytoplasm.
Enzymes are secreted into the food vacuole to digest food.
The digested food is absorbed into the cytoplasm.
Undigested residues are egested through the anal pore.
CLASS SPOROZOA:
These are all parasitic. An example is the Plasmodium, which causes malaria fever. It is transmitted to man by the bite of the female Anopheles mosquito.
Life cycle of the plasmodium:
Female Anopheles mosquito bites man infected with plasmodia. The blood enables it to lay eggs.
It first injects its saliva into a host's blood. This is to prevent blood from clothing in its proboscis.
The mosquito then sucks blood from a capillary with plasmodia gametes inclusive.
The plasmodia gametes fertilize and multiply to form sporozoites.
The sporozoites enter the salivary glands of the mosquito.
The mosquito then bites a healthy person and introduces the plasdmodia sporozoites into his blood.
The plasmodia sporozoites enter cells of the liver.
They multiply and enter the red blood cells forming gametes which may attack other red blood cells.
The attacked red blood cells burst releasing more plasmodia gametes.
A mosquito then sucks them up and the cycle repeats itself.
Symptoms of malaria fever include headache, fever, vomiting, convulsions in children, joint pains, miscarriages in the pregnant.
Control of malaria:
- Drainage of breeding places of mosquitoes.
- Destruction of larvae with oil spray
- Destruction of adult mosquito using insecticide.
- Destruction of plasmodia in man using quinine.
- Biological control using minnow fish in ponds to eat larvae.
- The most modern method of control which is also ecologically safe is the biological control of using a bacterium called Bacillus thuringensis which affects mosquito larvae but does not harm man or other water life.
PHYLUM CHLOROPHYTA:
These are green algae, which are aquatic. They contain chlorophyll, which is found in chloroplasts. The cell wall is made of cellulose. An example is the Spirogyra. They reproduce asexually by fragmentation after cell division.
During unfavourable conditions, the spirogyra carries out sexual reproduction by conjugation.
The process of conjugation:
- Two spirogyra filaments lie side by side.
- Protuberances appear at corresponding points on each filament.
- The protuberances form conjugation tubes.
- The points of contact between the conjugation tubes are dissolved away.
- Protoplasm from one filament passes through the conjugation tubes into the adjacent filament.
- The nuclei then fuse to form a zygote.
- A thick outer layer is formed so that the result is a zygospore.
- During favourable conditions the parent wall decays and a new filament emerges.
KINGDOM FUNGI
Fungi vary in size from unicellular like yeasts to multicellular like mushrooms.
The multicellular fungi have a body called a mycelium made of branching threads called hyphae. The cell wall is made of chitin. Fungi have a nucleus.
These many different kinds of organisms that demonstrate the huge diversity within the Kingdom Fungi.
Example of fungi include bread mould mucor, yeasts, a blue mould called penicillium, mushrooms, toadstools and puffballs.
A mushroom
Structure of Fungi
There are a number of characteristics that make fungi different from other eukaryotic organisms:
- Fungi cannot make their own food like plants can, since they do not have chloroplasts and cannot carry out photosynthesis. Fungi are more like animals because they have to obtain their food from outside sources.
- The cell walls in many species of fungi contain chitin. Chitin is a nitrogen-containing material found in the shells of animals such as beetles and lobsters. The cell wall of a plant is made of cellulose, not chitin.
- Unlike many plants, most fungi do not have structures that transfer water and nutrients.
- One characteristic that is unique to fungi is the presence of hyphae, which combine in groups called mycelia, as described above.
Nutrition in fungi:
Fungi lack chlorophyll
Saprophytic fungi depend on dead organic matter. They secrete enzymes onto the food; so the enzymes are extra-cellular (act outside cells). The soluble products of digestion are then absorbed by the fungus.
Parasitic fungi like the one that causes late blight in potatoes get food from the host which suffers injurious effects.
Symbiotic fungi exist as lichens together with algae; each obtaining benefits from the other.
Bracket fungi and lichens on a rotting. Fungi obtain energy from breaking down dead organisms such as this rotting log.
Reproduction in fungi:
This is asexual by spores and in yeast by budding.
Sometimes sexual reproduction takes place. In mucor sexual reproduction follows the following stages:
- Two opposite mycelia lie adjacent to each other i.e. + and - strain.
- They develop suspensors.
- The cross walls dissolve away
- The suspensors join gametes fuse to form a gamete.
- The hard cover develops to form a zygospore.
- During favourable conditions the zygospore germinates to form a new mycelium.
Importance of fungi:
- They are pathogens i.e. they cause diseases. In humans, ringworm and athlete's foot are examples. In plants potato blight is an example.
- Saprophytic fungi decompose plant and animal remains to form humus in the soil.
- They make food become mouldy and thus unpalatable.
- They cause dry rot of timber.
- They form alcohol during fermentation for example yeast.
- They are used to manufacture medical drugs for example penicillin.
Edible and Poisonous Fungi
- Some of the best known types of fungi are mushrooms, which can be edible or poisonous.
- Many species are grown commercially, but others are harvested from the wild. When you order a pizza with mushrooms or add them to your salad, you are most likely eating Agaricus bisporus, the most commonly eaten species.
- Other mushroom species are gathered from the wild for people to eat or for commercial sale. Many mushroom species are poisonous to humans. Some mushrooms will simply give you a stomach ache, while others may kill you.
- Some mushrooms you can eat when they are cooked but are poisonous when raw.
- Have you ever eaten blue cheese? Do you know what makes it blue? You guessed it. Fungus. For certain types of cheeses, producers add fungus spores to milk curds to promote the growth of mold, which makes the cheese blue.
- Molds used in cheese production are safe for humans to eat.
FIGURE 9.13
Some of the best known types of fungi are the edible and the poisonous mushrooms.
Vocabulary
1. budding Asexual reproduction in which part of the body of a fungus, for example, grows and breaks off, eventually becoming a new organism.
2. chitin A nitrogen-containing material found in the cell wall of fungi; also found in the shells of animals such as beetles and lobsters.
3. fruiting body Specialized structure used in sexual reproduction; part of the fungus that produces the spores.
4. hyphae Thread-like structures which interconnect and bunch up into mycelium; helps bring food, such as a worm, inside the fungus.
5. mycelial fragmentation Asexual reproduction involving splitting off of the mycelia; a fragmented piece of mycelia can eventually produce a new colony of fungi.
6. mycelium Help the fungi absorb nutrients from living hosts; composed of hyphae.
7. mycorrhizal symbiosis A relationship between fungi and the roots of plants where both benefit; the plant provides sugar to the fungus; the fungi provides minerals and water to the roots of the plant.
8. parasite The organism that benefits in a relationship between two organisms in which one is harmed.
9. spore The basic reproductive unit of fungi.
KINGDOM PLANTAE
These are multicellular, have nuclei with nuclear membrane and they carry out photosynthesis. There are two major phyla i.e. phylum Bryophyta and phylum Tracheophyta.
Phylum broophyta:
These are green plants that are non - vascular i.e. they lack definite roots, leaves or stems.
They reproduce using spores called gemmae.
Bryophytes are divided into two classes: mosses and liverworts.
Mosses have stem-like and leaf-like structures whereas Liverworts are flattened.
Phylum tracheophyta
These are green plants, which are vascular i.e. they have definite roots, stems and leaves.
They are terrestial i.e. they live on land.
Tracheophytes are divided into several classes, which include Pteridophytes (ferns) and the Spermatophytes (seed-bearing).
PTERIDOPHYTE CLASS:
A fern has an underground rhizome with adventitious roots covered by bases of old leaves.
The compound leaves of ferns are called fronds each with a main axis called a rachis and branching pinnae. Each pinna has branching pinnules. They lack seeds and so reproduce by spores.
Spermatophyte class:
These are seed-bearing plants which are terrestrial and vascular. They are divided intoi two orders: Gymnosperms and Angiosperms.
Gymnosperms Order:
These do not bear flowers and the seeds are found in seed boxes called cones. Examples include conifers and pine.
Angiosperms Order:
These are flowering plants where sexual organs are found in flowers.
Angiosperms are divided into two families:
- Monocotyledons: These have one cotyledon in the seed; have parallel veined leaves; have fibrous root system; have flower parts arranged in three or multiples of three; and carry out hypogeal germination where the cotyledons do not appear above the ground.
Examples are maize, sorghum, grass.
- Dicotyledons: these have two cotyledons in the seed; have net-veined leaves; have a tap root system; have flower parts arranged in fives or multiples of five; and carry out epigeal germination where the cotyledons appear above the ground.
Examples are beans, mango, hibiscus.
KINGDOM ANIMALIA
This consists of animals, which have no chlorophyll.
The kingdom is divided into two:
Vertebrates: which have a backbone or spine or vertebral column for example fish, lizards, frogs, birds, monkeys.
Invertebrates: which do not have a vertebral column for example hydra, worms, snails, insects.
The animal kingdom is divided into the following phyla:
- Coelenterata phylum for example the hydra.
- Platyhelminthes phylum for example tapeworm.
- Nematode phylum for example round worm.
- Annelida phylum for example earthworm.
- Molluscus phylum for example snails.
- Arthropod phylum for example spider.
- Echnodermata phylum for example starfish.
- Vertebrates phylum for example snake.
Coelenterate phylum:
They are aquatic i.e. live in water.
They are diploblastic i.e. they have two body layers of ectoderm and endoderm.
They have a mouth and a cavity called a coelom; so they are coelomates.
They are radially symmetrical i.e. they have many lines of symmetry.
They reproduce asexually by budding.
Their level of organization stops at tissue level.
Muscle cells present aid in somersaulting movement using tentacles; so looping movement results.
Examples of coelenterates include hydra, sea anemones, coral, jellyfish.
Platyhelmithes phylum:
They are bilaterally symmetrical i.e. they have one line of symetry.
They are triploblastic i.e. they have three body layers of ectoderm, mesoderm and endoderm.
They are usually hermaphrodite i.e. they have two sexes.
Cephalisation takes place in them i.e. brain matter starts developing in the head.
They are acoelomates i.e. they have no cavity inside them.
They have no blood system.
Examples of platyhelmithes include:
Planarians which are free-living.
Trematodes (flukes) which are usually endoparasites with a primary and a secondary host. Examples are blood flukes which cause bilharzia (schistosomiasis) and liver flukes.
Tapeworms (Taenia) which are endoparasites with a head called a scolex with hooks and suckers for attachment. It has many segments called proglotides.
Life cycle of a tapeworm:
So man is the primary host and the pig or fish is the secondary host.
Life cycle of a liver fluke:
So the cattle or sheep are primary hosts and the snail is the secondary host.
A cyst stage forms a hard covering which helps the organism withstand unfavourable conditions.
Although the liver fluke is hermaphrodite, it does not carry out self-fertilization; it pairs with a mate to exchange gametes.
Nematode phylum: These include roundworms and hookworms.
They are not true worms because they are not segmented.
They are parasitic and threadlike.
They are unisexual i.e. have one sex.
They have a mouth and an anus.
The round worm is called Ascaris.
Avoid hookworms by wearing shoes.
Annelid phylum: These are the true worms because they are round and segmented.
They are triploblastic.
They are coelomates i.e. they have a body cavity in them.
They have blood vessels.
They show cephalisation i.e. development of brain matter in the head.
Excretion is through tubes called nephridia. An example of annelids are the earthworms.
Molluscus phylum:
- They are bilaterally symmetrical.
- They are coelomates.
- They are not segmented.
- They are usually aquatic.
- They have a head with tentacles.
- They are hermaphrodite.
Examples include snails, slugs, squids and octopuses.
Phylum arthropoda:
They have segmented bodies and jointed legs.
They are bilaterally symmetrical and triploblastic.
They are coelomates which have an exoskeleton.
They have an open blood cirulatory system where blood is poured out to the tissues.
They have a head with antennae, mouth parts, compound eyes and simple eyes.
They are highly cephalised.
Arthropods are divided into four classes: Crusteceans, myriapods, arachnids and insects.
Crustecean class:
- These are aquatic except the woodlice.
- They have a calcerous exoskeleton.
- They have two pairs of antennae.
- They have gill books for breathing.
- They have a larval stage i.e. they carry out metamorphosis i.e. change in form from eggs to adult through stages.
Examples of crusteceans include lobsters, cray fish, crabs, water fleas, wood lice.
Myriapod class:
- These are terrestrial i.e. they live on land.
- They have a long body with many limbs.
- They have spiracles and tracheae for breathing.
- They have malpighian tubules for excretion.
- They have no larval stage i.e. they do not carry out metamorphosis.
Examples include millipedes with two pairs of legs on each segment and centipedes with one pair of legs on each segment.
Arachnid class:
Examples include scorpions, spiders, mites and ticks.
They have two body parts i.e. the prosoma which has a head and legs and the opisthosoma.
They have four pairs of jointed legs.
They have lung books for gaseous exchange.
They have malpighian tubules for excretion.
They have simple eyes but no compound eyes.
They have no larval stage.
Spiders have spinnerets on the opisthosoma which produce a web.
Scorpions have a sting at the tail end.
Mites and ticks are ectoparasites.
Insect class:
These have three body parts i.e. head, thorax and abdomen.
The head has one pair of antennae, a pair of compound eyes and three pairs of jaws.
The thorax has three pairs of jointed legs.
The second and third segment of the thorax has wings for example in grasshoppers.
At times, only the third segment has wings for example in houseflies; and at times there are no wings at all for example in bedbugs.
They breathe by means of spiracles and trachae.
They undergo metamorphosis.
They are terrestrial.
The insect class is divided into the following orders:
Coleoptera order: These have hard elytra covering the wings for example beetles.
Orthoptera order: These have stridation organs on the hind limbs for making sounds to attract the opposite sex. Their hind limbs are also used for jumping. Their outer wings are hard for example grasshoppers, praying mantises, locusts.
Lepidoptera order: These have a maxilla formed into a proboscis. They have powdery scales on their wings for example butterflies, moths.
Hymenoptera order: These are social insects which undergo complete metamorphosis for example bees, wasps.
Isoptera orders: These are social insects which undergo incomplete metamorphosis for example termites (white ants).
Diptera order: These have one pair of wings with halteres for balancing for example flies, mosquitoes.
Hemiptera order: These are wingless sucking insects for example bedbugs, aphids.
N.B: There are many other orders with other insects like the dragonflies which are aquatic.
Further coverage of insects is to be found in the chapter on insects.
Echnodermata phylum:
Examples include the starfish and the sea urchin.
- The are radially symmetrical.
- They are coelomates.
- They are not segmented.
- They are not cephalised.
- They are unisexual.
- They are triploblastic.
- They have a high power of regeneration into new offsprings.
Vertebrates (chordate) phylum:
- They are bilaterally symmetrical.
- They are coelomates.
- They have a dorsal notochord.
- They are highly cephalised.
The vertebrates are divided into two according to the way they respond to temperature changes in the environment.
Poikilothermic vertebrates are those whose body temperature changes according to the changes in the temperature of the surrounding environment for example fish, amphibians and reptiles.
In such animals, their temperature is only slightly higher than that of the environment.
Poikilothermic vertebrates respond to low temperatures by:
Basking on rocks in the sun;
Reducing activity or metabolism.
Poikilothermic vertebrates respond to high temperature by:
Hiding in cool places like under a shade.
¨ Homoithermic vertebrates are those whose body temperature remains constant whatsoever the temperature of the surrounding environment may be for example birds and mammals.
Homoithermic vertebrates respond to low temperatures by:
- Shivering;
- Increasing body reactions (metabolism).
Homoithermic vertebrates respond to high temperatures by:
- Sweating;
- Reducing body metabolism.
Advantages of being homoithermic:
§ Body metabolism is not interrupted by temperature changes in the environment.
§ The animal is active in a wide range of environmental temperatures.
Vertebrates are divided into the following classes:
o Fish or pisces ) These
o Amphibians ) are
o Reptiles ) Poikilothermic
o Birds or aves) These are
o Mammals ) homoithermic
Pisces (fish) class:
- They are aquatic and poikilothermic.
- They carry out external fertilization.
- They have fins for movement.
- They have gills for gaseous exchange.
Fish are divided into:
Cartilaginous fish for example sharks, rays, skates, dogfish.
- They are marine i.e. live in salty water.
- They have dorsal-ventral flattening.
- They have gill slits and no operculum.
Bony fish (teleosts) for example perch, tilapia, lungfish, mudfish.
- Some are marine while others are fresh water fish.
- They are laterally flattened.
- They have a swim bladder which enables them to adjust to different water pressures.
Further coverage of fish is to be found in the chapter on fish.
AMPHIBIANS CLASS:
These are poikilothermic vertebrates which are aquatic-terrestrial.
- They carry out external fertilization.
- They undergo metamorphosis.
- The larvae called tadpoles breathe using gills; adults use lungs.
- They have a pentadactyl limb which ends in five digits.
They are divided into two:
Newts, salamanders and axolotl: which have a tail and breathe by gills.
Frogs and toads: which have no tail or gills except the young.
Further coverage of amphibians is to be found in the chapter on amphibians.
Reptile class:
They are poikilothermic.
They have internal fertilization and external development of eggs; so they are oviparous.
They are homodont i.e. their teeth are of the same shape and function.
- They have a pentadactyl limb.
- They breathe using lungs.
- They are terrestrial.
- They have no larval stage.
Examples include chameleons, lizards, crocodiles, alligators, snakes, tortoises and turtles.
Crocodiles are the most dangerous reptiles in East Africa. They are 7m long and can eat any kind of flesh. They are excellent swimmers in water and fast runners on land. They spend most of their time in water. Crocodiles with open mouths are merely asleep!
Snakes that are poisonous include:
- The green mambas
- The black mambas which attack people unprovoked.
The cobras especially the spitting cobra which spits venom (snake poison) with great accuracy into a victim's eyes causing blindness.
The vipers for example the puff adder with black and yellow stripes which never moves out of the way.
N.B: The python is not a poisonous snake.
Further coverage of reptiles is to be found in the chapter on reptiles.
Aves (birds) class:
They are homoithermic.
They have a pentadactyl limb where the front pair forms wings for flight.
They have feathers except on the legs where there are scales (a resemblance to reptiles).
- They use lungs for breathing.
- They have no larval stage.
Birds are divided into two:
- Flightless birds like the ostrich, emu, kiwi.
- Birds of flight for example fowls, pigeons, ducks.
Further coverage of birds is to be found in the chapter on birds.
Mammals class:
Mammals are different from other vertebrates in the following ways.
- Mammals are viviparous i.e. they have internal fertilization and internal development of the embryo in a uterus; so they produce young ones alive. Other vertebrates are oviparous i.e. lay eggs.
- Mammals suckle their young on milk from the mammary glands of females whereas other vertebrates feed their young on regurgitated food or the young feed themselves.
- Mammals have hair or fur whereas other vertebrates have scales, feathers or bare skin.
- Mammals have external ears (pinnae) whereas other vertebrates have an internal eardrum.
- Mammals are heterodont i.e. their teeth vary in form and function whereas other vertebrates are lacking teeth or are homodont i.e. their teeth are similar both in form and in function.
- Mammals have a body cavity divided into thorax and abdomen by a diaphragm whereas other vertebrates lack a diaphragm.
- Mammals have four-chambered heart whereas other vertebrates (except birds) have a three-chambered heart.
- Mammals have an anus that is separated from the urinogenital system whereas other vertebrates have a cloaca serving as an anus as well as the urinogenital system.
- Mammals have a relatively larger brain whereas other vertebrates have a relatively smaller brain.
N.B: Like birds, mammals are homoithermic.
Mammals are divided into several groups:
1. Monotremes: These are oviparous i.e. egg-laying for example the duck-billed platypus and the spiny anteater.
2. Marsupials: These have internal fertilization but development is partly internal and partly external in a pouch; so they are oviviparous for example kangaroos.
3. Mammals that have a true placenta for development of the embryo are divided into the following orders:
- Insectivores: These eat insects for example shrews, hedgehogs.
- Rodents: These gnaw for example rats, mice, rabbits, hares and squirrels.
- Carnivores: These eat flesh for example cats like the lion, the leopard and tiger and the dogs like the foxes, hyenas, wolves and bears.
4. Odd-toed herbivores: These are ungulates (hoofed) which eat vegetation. They have an odd number of hooves for example horses, zebras, rhinocerouses.
5. Even-toed herbivores: These are ungulates which eat vegetation and have an even number of hooves. Examples include: The grazers which eat grass like the cattle, goats, antelopes, camels, deers; and the browzers which eat leaves off trees and shrubs like giraffes, hippopotamuses, elephants and the hyrax.
6. Whales and Dolphins: These live in the sea and come to the surface to breathe in air using lungs. A whale can be 40 metres long. They are usually hunted for the fat under their skin to make oils. The fats make whales homoithermic. Fertilizers are made from whales' bone.
Dolphins have all adapted to swimming and reproducing in water.
7. Flying mammals: These have no feathers but only skin between their fingers to form the wing for example bats.
8. Primates: These are the most intelligent mammals for example monkeys, apes, and man.
N.B: Man did not come from apes, but man and apes share a common ancestor.
Chimpanzees pictured here belong to the great apes one of the groups of primates.
Lesson Summary
Organisms in the class Mammalia are distinguished by the presence of hair, sweat glands, three middle ear bones and a neocortex area in the brain.
- There is a lot of variation in mammalian reproductive systems. Mammals consist of both the egg-laying monotremes and those that are viviparous. The latter group includes marsupial and placental mammals.
- The 5,400 species of mammals can be grouped according to physical features as well as the type of habitat.
- Mammals have specific adaptations for living on land, in trees, in water and for flight.
- Non-primate mammals have an form important relationships with humans and play key ecological roles.
Review Questions
Recall
1. What are three main characteristics of mammals?
2. What are two ways that monotremes are different from viviparous mammals?
Apply Concepts
3. With respect to characteristics of feet, limbs and tails, what features would you expect mammals to have for:
- Jumping?
- Living in trees?
4. Give examples of two different adaptations of limbs in mammals, naming a mammal species, a structure, and how it is adapted.
Critical Thinking