Microorganisms 1

Microorganisms are living organisms too small for us to see with our naked eyes, but which have far-reaching effects on the lives of man, they can only be seen with the help of magnifying lenses.

The branch of biology which involves the study of microorganisms is called microbiology. Some microorganisms are beneficial to us, such as the saprophytic ones that are used in decomposition of organic matter, while some are harmful, those ones are called germs or pathogens.

Microorganisms are found everywhere.

The following scientists worked extensively on microorganisms: Antony Van Leeuwenhoek, Spallanzani, Pasteur, Robert Koch, Lord Lister and Fleming.

Groups/types of microorganisms

Microorganisms include:

1. Viruses

2. Bacteria and blue-green algae

3. Protists (Protozoa)

4. Some fungi

5. Some algae.

Of these, bacteria, viruses, Protozoa and fungi are the most frequently discussed.

Note: viruses have no cell structure, bacteria and blue-green algae are prokaryotes, why protists, fungi and algae are eukaryotes.

Viruses

Viruses are usually seen with the aid of electron microscope. Virus would either contain DNA or RNA. They are meant to cause diseases. Examples are adenovirus, picornavirus, paramyxovirus, coronavirus, togavirus etc.Examples of diseases caused include influenza, HIV/AIDS, mumps, common cold, smallpox etc. 

Bacteria

Bacteria are micro-organisms that can be seen easily with the aid of light microscope. They contain DNA. 

Types of Bacteria

Bacteria are grouped into two types. These are:

A. Bacteria on the basis of the use of oxygen:

1. Aerobic bacteria: These bacteria require oxygen to respire. Examples are Mycobacterium tuberculosis and Vibrio cholera.

2. Anaerobic bacteria: These bacteria do not require oxygen for respiration. Examples are Clostridium tetani and Clostridium botulinum.

3. Falcultative bacteria: These bacteria can live in the moderate or low or no oxygen. Examples are Helicobacter pylori, Salmonella typhi etc.

B. Bacteria on the basis of their shape:

1. Cocci (singular, coccus): These bacteria have spherical/circular(rounded) shape. The spheres may;

(a) form chains i.e Streptococci (Streptococcus pyogens, that cause sore throat) others are S. viridens.

(b) form bunch or cluster i.e staphylococci (Staphylococcus saprophyticus that causes urinary tract infections, S. aureus that causes food poisoning) others are S. epidermidis.

(c) form groups of two; they adhere/stick together in pairs i.e. Diplococci. (Streptococcus pneumoniae  that causes pneumonia)

2. Bacilli (singular, bacillus): These bacteria are rod-shaped, such as Escherichia coli found in the intestines of humans and animals. Such bacteria may be;

(a) chain of rods e.g. Bacillus anthracis .

(b) flagellated rods i.e. those with flagella e.g Salmonella typhi that causes typhoid fever.

(c) spore-former i.e those that form spores in the cells e.g Clostridium botulinum.

3. Spirilla (singular, spirillum): These bacteria have cells spirally twisted or cockscrew shaped. Such cockscrew bacteria could be either ;

(a) spirally rigid, i.e spirillae e.g Spirillum minor found in rats, Helicobacter pylori that causes gastritis. Or

(b) spirally flexible, i.e spirochaetes e.g Treponema pallidum that causes syphilis in humans.

4. Vibrios: These are bacteria with comma-shaped cells. They are rigid curved rod, and are also called comma bacillus. Example is Vibrio cholera that causes cholera. 

Protists (Protozoa and protophyta)

They are microscopic organisms. The protophyta include the autotrophic diatoms, dinoflagellates, Chlamydomonas, Chlorela and some Euglena. The Protozoa are the heterotrophic group such as Amoeba (some species such as Entamoeba histolytica causes amoebic dysentary), Paramecium, Trypanosomes(causes trypanosomiasis), Plasmodium(causes malaria).

Fungi

Some fungi are microscopic and some are large enough to be seen. Fungi are either saprophytes or parasites. Those that are parasitic include Tinia that causes ringworm. Some fungi are beneficial to man such as Penicillium notatum which is an antibiotic.

Algae

Algae are microscopic green plants, they live in aquatic habitat. Examples are diatoms, spirogyra, volvox, nostoc etc.

CULTURE

The technique used to grow micro-organisms for study in the laboratory in special media is termed culture. The medium used for growing most micro-organisms consists of:

- Agar, a jelly-like material obtained from sea-weed, and 

- Nutrient agar/broth.

NOTE:

1. Viruses can only grow and multiply inside living cells. So they cannot be grown in a culture medium like the other micro-organisms. Other micro-organisms that can be cultured are bacteria, fungi, and algae.

2. Culturing disease-causing micro-organisms are always difficult. Therefore, there is need to enrich the culture media with blood to enrich the nutrient agar.

3. During culture, the culture media are usually poured into sterile petri dishes, or test-tubes kept in a slanting position and covered at once. The main reason for keeping the test-tubes in a slanting manner is to provide a large surface area for micro-organisms growth.

Procedures to Culture Micro-Organisms

The major procedures used to culture micro-organisms in the laboratory are the aseptic techniques. The procedures include:

• Sterilizing culture media and all glassware (that will come in contact with the specimen). Such sterilizing instrument is autoclave. The main purpose of sterilizing is to kill all micro-organisms and spores.

• Flaming all equipment used for the transfer of micro-organisms just before use to avoid contamination by unwanted micro-organisms in the air.

• Keeping all petri-dishes, flasks and test-tubes involved covered, and open them near the presence of blue bunsen flame only when necessary for as short a time as possible.

• Wiping the work area with cloth or cotton wool soaked in a strong disinfectant.

Caution: do not touch bacteria cultures with your bare hands. Always wash your hands throughly at the end of any laboratory exercise. All equipment used must be boiled and washed with a strong disinfectant at the end of the experiment.

To prepare a culture of Paramecia

Place some dry grass in a beaker and cover it with water. Leave the preparation for about five days. This preparation is called an 'hay infusion'. The organisms exist in cyst-form on the grass. After this period, you will see a number of white specks moving about near the surface of the water. These are almost certainly Paramecia.

How to examine the Paramecia cultured:

- obtain a clean microscope slide, use a pipette to draw a drop of water from the beaker containing a colony of Paramecia and place the drop on the microscope slide.

- Cover the drop with a cover slip, and watch how the animal moves. The movement is usually rapid but can be slowed down by entangling the animals in a few fibers of cotton wool placed under the cover slip.

- Examine the organism under the microscope , lift the cover slip slightly and place a little iodine solution under it. This stains the nuclear safety. Replace the cover slip and examine the structure of the animal in greater detail under the light microscope. 

- Make a leveled diagram of one Paramecium.

Tissue Culture

The method used to culture the cells of multicellular plants and animals, usually in a single layer of cells on a solid surface or as a suspension in a fluid medium.

Importance of Tissue Culture

Tissue culture is used to study:

1. Hereditary mechanism;

2. Growth and development;

3. Viruses and damage they do cause to cells they affect;

4. Special properties of various types of cells;

5. The nature of specific inherited disorders; and

6. Details of cell structure and metabolism.

Application/Uses of Tissue Culture

1. Production of vaccines against viral diseases;

2. To diagnose defects linked to certain types of mental illness in unborn children;

3. For the culture of viruses;

4. For the production of interferon (an anti-viral protein formed by animal cells that are invaded by viruses);

5. To diagnose inherited disorders.

Classwork

1. List five instruments used/required for the preparation of culture solution.

2. Itemize five precautions to be taken during preparation of culture solution.

Identification of micro-organisms 

Students are divided into five working groups, with each group provided with a sterilized petri-dishes containing culture medium.The petri-dishes are labeled A, B, C, and D, to be used to collect micro-organisms from air, pond, river, stream, respectively and the fifth one remain sterilized to serve as control. Observe the petri-dishes under the microscope after 3 days. Record your observation and discuss with the teacher.

Staining

We can observe size, shape, cell arrangements, and cell structures such as flagella, capsules and spores of the microorganisms observed using the following stains:

1. Simple stains like methylene blue and crystal violet to observe size, shape and cell arrangements of the microorganisms;

2. Differential stains like Gram's stain to bring out structures such as flagella, capsules, and spores. The Gram's stain divides bacteria into two groups: purple stained called gram-positive bacteria and red stained called gram-negative bacteria.

Staining procedure

Fix and stain cultured medium microorganisms as follows:

1. To fix, pass a slide quickly across the flame of a Bunsen burner three times. The smear on the slide is then dried on it.

2. Allow slide to cool for 2 or 3 minutes.

3. Stain the slide by addition of a few drops on the smear of any one of the following stains: methylene blue or cotton blue, crystal violet and carbon-fuschin for 2 or 3 minutes.

4. Tilt the slide and allow the stain to run off.

5. Allow 5 minutes for the air to dry the slide.

6. Rinse the slides to clear them of excess stain by running clear water over them gently.

7. Use absorbent paper to dry the slide.

8. View the slide once again and microorganisms will at this time be seen distinctly.

Class Activities

Activity 1: To show that microorganisms are present in our body

Method: Scrape the dirt under the nail with a sterilized knife into a petri-dish or use a tooth-pick or a short piece of washed broom-stick to remove the remain of food around the gum of your teeth. Add five drops of distilled water to the dirt or scrape in the petri-dish (the petri-dish contains the nutrient agar and stir very well with a sterilized needle). Cover it up quickly, and label it petri-dish A. Set-up a controlled experiment containing distilled water and agar solution alone in petri-dish without the scrape, cover and label it petri-dish B. Keep under controlled temperature(room temperature).

Results: After three days, coloured patches are seen on the surface of petri-dish A. Stain it with methylene blue, view it under microscope, different bacteria shape could be seen. Fungi such as Mucor and Rhizopus can be seen. No colour patches are observed in petri-dish B.

Conclusion: Microorganisms are present in our body.

Note: The same method could be employed in determining the presence of microorganisms in food, air and water.

How micro-organisms enter the body.

Pathogenic microorganisms after our body through the following ways:

1. Through cuts, wounds and abrasions on the skin, e.g. Clostridium tetani.

2. Through the nose and mouth, e.g. Influenza virus.

3. Through the mouth and oesophagus, e.g. Entamoeba histolytica.

4. Through direct contact, e.g. Ringworm fungi and the spirocahete (e.g. Treponema pallidium).

5. Through urinogenital tracts, e.g. Neisseria gonorrhoea.

6. Through placenta; a foetus is infected of syphilis and measles through the placenta, if the mother is infected.

7. Through insect bites, e.g. Mosquito bites releases pathogens into the body.

8. Through mammalian bite, such as the case of rabies and lassa fever which are caused as a result of dog and rat bites respectively.

CARRIERS AND VECTORS OF MICROORGANISMS

A carrier of microorganism is any organism that only carries pathogen usually on its body, but does not bring about the development of pathogens within its body e.g. Housefly. A vector is an organism (usually insect or other arthropods) which allows the pathogens to develop within its body and transmits it, hence causing the spread of an infectious disease from one organism to another e.g. Mosquitoes. Examples are:

Vector/carrier Microorganism Disease caused

female anopheles mosquito Plasmodium malaria

Tse-tse fly Trypanosome sleeping sickness/trypanosomiasis 

Housefly Vibrio cholera cholera and typhoid

Rat flea/body louse Ricketsia typhus

Aedes mosquito Virus yellow fever and dengue fever

Rat fleas bacterium plague

Dog virus rabies

Activity 2: To show that housefly is a carrier

Method: Kill a housefly using a broom, detach its: A. Proboscis, B. Legs, C. Wings, and D. Hairy abdomen. Place each of A-D on culture medium, in separate petri-dishes. Cover them and label them accordingly. Set up a controlled experiment containing only cultured medium in a petridish. Place in an incubator/cupboard for 3 days. Observe and record your observation using the format below:

Part Colour Pattern of growth General appearance

A (proboscis)

B (legs)

C (abdomen)

D (wings)

E (control)

Habitat

HABITATS The habitat of an organism is the type of environment or place where an organism live and survive normally. There are two main classes/kinds of habitat, they are aquatic and terrestrial. AQUATIC HABITATS/BIOMES An aquatic habitat is an environment consisting of water which ensures survival of some organisms. Aquatic habitats are divided into three broad divisions, marine or salt water, freshwater and estuarine or brackish-water. There are three main conditions which distinguish freshwater habitat from marine habitat. These are: 1. The salt content of fresh water is very low and that of marine is very high; 2. Strong, swift currents (except ponds and large lakes) are common features of freshwater habitat and marine habitat does not experience strong and swift current; 3. Climate and weather often affect freshwater habitats (except very large lakes) much more easily than marine habitat. The marine habitat As explained above, marine habitat contains high proportion of salt, hence the name salt water habitat. Examples include salt water lake, oceans, the shore and open sea. Characteristics of the marine habitat 1. Salinity is very high and its average is put at 35.2 per thousand. 2. Density of marine water is higher than that of freshwater, hence many organisms can float in it. The density is put on the average of 1.028, while that of freshwater is 1.00 3. Size of marine habitat is very large, occupying more than two thirds of the earth's surface. 4. Pressure in marine habitat increases at 1 atmosphere at the surface to 1000 atmospheres at the bottom. In other words, this means at a depth of about 1000m, the pressure would be about 100 atmospheres. 5. Turbidity is very high due to the suspended particles washed into it from land and rivers. 6. Light can only penetrate to about 200 metres due to high turbidity. Therefore plant life is limited to the upper layers of the ocean where light can penetrate. 7. Dissolved gases are usually oxygen and carbon dioxide. More oxygen are dissolved at the surface due to the wave action at the surface and due to the photosynthetic activities of phytoplanktons; oxygen level reduces as one goes deep in the sea due to increase in turbidity, and hence more carbon dioxide are concentrated at the bottom due to decomposition and respiration of some organisms that inhabit the bottom zones of the sea. 8. pH (hydrogen ion concentration): the pH of the surface water ranges from 8.0 to 8.5. This means that it is alkaline near the surface. 9. Currents are produced at the surface of the ocean by wind actions, rotation of the earth and differences in water density but not strong and swift. A current is a directional movement. 10. Waves: A wave is undirectional movement of water caused by the blowing of winds against the water surface. Wave action is common in marine habitats. Waves bring about mixing of dissolved oxygen. 11. Tides: This is the rise and fall of the ocean water twice a day. It is caused by the gravitational pull on the earth. Tides have huge effects on the lives of organisms living in lagoon and estuaries because high tide fills the lagoon and estuaries with water while low tides makes the water levels fall drastically, hence much water may not be available to some organisms, especially during dry season when the rivers are dried. MAJOR ECOLOGICAL ZONES OF THE MARINE HABITAT The major ecological zones of the marine habitats include: A. Littoral (euphotic) zone: This is the region that extends over the continental shelf to a depth of about 200 metres. The littoral zone can be subdivided into the: 1. splash (supratidal) zone; 2. intertidal (neritic) zone; and 3. subtidal zone; B. Benthic zone: This is the zone beyond the littoral zone, it can extend to a depth of 10 000 metres. The benthic zone can be subdivided into the: 1. bathyal (disphotic) zone; 2. abyssal (aphotic) zone and 3. hadal (aphotic) zone. 1. Splash or supratidal zone: This is really not part of the marine habitat, but of the terrestrial habitat. It is the area where water splashes when the waves break at the shore; it is just above the high-tide mark and is wetted by the spray from the breaking waves. It is exposed and usually moistened by the splashed water. Plants in the splash zone include halophytes such as Sesuvium. Adaptation of Sesuvium include: - Reduced thick leaves for water conservation; - Chloroplasts for photosynthesis. Animals in the splash zone include crabs. Adaptation of crabs include: - Presence of gills for gaseous exchange; - Possession of powerful chelipeds for seizing food; - Possession of exoskeleton to prevent desiccation on land; - Ability to dig hole to water level to escape predator and strong waves. 2. Intertidal or neritic zone: This zone is purely marine zone. It is the zone along the substratum between the high tide mark and low tide mark. Characteristics of intertidal zone: a. It is exposed to drying conditions of the air at low tides and covered by water at high tides; b. It receives abundant sunlight; hence the name euphotic and photosynthetic activity is very high than respiration; c. Water temperature fluctuates; d. Exposed to wave action; e. The substratum is unstable; f. It is about 150 - 190 metres deep. Plants in the intertidal zone include algae such as Kelp and Sargassum. Adaptive features of Sargassum: - Possession of chloroplast for photosynthesis; - Possession of hold fasts for firm attachment to the substratum; - Presence of air bladders for buoyancy; - Presence of mucilage on the body to reduce desiccation during low tide; - Possession of flattened lamina leaves for buoyancy; - Tough/leathery thallus body/flexible stripe to withstand wave action. Animals in the intertidal zone include periwinkles, crabs, barnacles, starfish. Adaptive features of barnacles: - Presence of shell to prevent desiccation during low tide; - Presence of cilia for filter feeding; - Presence of basal disc for attachment to the substratum during low tide; - Ability to clamp down the mantle during low tide to prevent desiccation. Other adaptive features of animals in the intertidal zone includes: - Ability to dig holes/burrows into thin soil substratum to avoid desiccation/drying; - Body fluid isotonic with sea water to prevent loss/gain of water; - Possession of gills for respiration. 3. Subtidal zone: This zone extends from the low tide zone to the end of the continental shelf. It is the zone between the neritic and oceanic. Characteristics of subtidal zone: a. It is about 200 metres deep; b. It is always covered with water; c. It receives sufficient light (euphotic); d. High rate of photosynthesis. Organisms found here are those found in the neritic and some from the disphotic zone. 4. Bathyal zone: This zone extends from the end of the continental shelf down the oceanic. Characteristics of bathyal zone: a. It is about 3000 metres in depth; b. It receives dim light, hence the name disphotic; c. It is the beginning of the deep ocean; d. Slight water movement; e. Photosynthetic activity is low due to low light penetration, while the rates of respiration exceeds those of photosynthesis. Organisms find this place and beyond difficult to survive. Only few animals live in the entire benthic zone. 5. Abyssal zone: This zone extends from the end of the bathyal zone to a depth of 7000m. Characteristics of abyssal zone: a. The water is uniformly cold and quiet; b. Pressure is high; c. No light penetration, hence the name aphotic. d. Primary food production is by chemosynthesis; e. Very little oxygen dissolved. 6. Hadal zone: This zone is the substratum of very deep water, it goes beyond 7000m depth. Characteristics of hadal zone : As in abyssal zone. Animals in benthic zone include cartilaginous fish such as dog fish, sharks and sting rays, and the bony fish such as sardine, barracuda. Adaptation of animals in benthic zone: Cartilaginous fish: - Ability to retain urea in their body to cope with high salinity; hence prevent water loss from the blood by osmosis; - Ability to excrete excess salts from the blood to avoid accumulation of salt than that of the marine water; - Presence of gills for gaseous exchange; - Possession of large liver which contains large amount of oil which gives the fish low density to remain afloat. - Presence of tail for locomotion and fins for steering - Presence of scales on the skin to prevent loss or entry of water into the fish. Bony fish: - Ability to drink salt water continuously to replace the water they are losing by osmosis; - Ability to eliminate excess salt ingested through the special cells called chloride cells; - Presence of gas-filled bladder for buoyancy. Other adaptive features common to all benthic zone animals include: - Possession of large stomachs to store as much food as possible whenever food is available. - Presence of wide mouth with sharp teeth to catch prey. - Presence of fluorescent organs to attract prey, such as the one possessed by the hatchet fish. Food chain in marine habitat Phytoplankton(e.g. Diatoms)→zooplankton(e.g. Paramecium, amoeba, molluscs)→small fish(e.g. Tilapia)→larger fish(e.g. Shark). Note: In the neritic and euphotic zones, producers, consumers and decomposers are present here; in the disphotic and aphotic zones, the consumers and decomposers are found here. The freshwater habitat Characteristics of freshwater habitat: - Contains no significant amount of salt; - The body is relatively small compared to oceans; - There is significant seasonal variation; - It is shallow compared to oceans; - There is greater light penetration to the bottom; - There is varying temperature from surface to the bottom and from morning, afternoon and evening; - Oxygen is usually available in all parts of the water Types of freshwater habitat Freshwater habitats are classified into two main kinds, based on their mobility. These types are: (i) Lentic fresh waters: These are standing/stagnant bodies of water. They do not flow and are calm. Examples include pools, lakes, ponds, dams and swamps. (ii) Lotic fresh waters: These are running/flowing waters which move on a particular direction on land. Examples include rivers, springs, and streams. Characteristics of freshwater habitats 1. Small size: they are relatively small in size. 2. Seasonal variation: they experience significant seasonal variations as some rivers dry up during dry season, and increases during rainy season. 3. Low salinity: they contain very low level of salts, about 0.5% of salt compared to about 3.5% for sea water. 4. Variation in temperature: their temperature varies with season and depth. 5. Light penetration: light reaches almost all depth due to shallowness of the water. 6. Turbidity is usually very high during rainy season due to movement of wastes from land into water. 7. Oxygen concentration: oxygen is usually available in all parts of the fresh water. 8. Currents: current is very common, especially in lotic habitats. This affects distribution of gases and organisms. Ecological zones of fresh water habitats There are two major zones in a lentic fresh water habitat. These are littoral and benthic zones. The littoral zone is the shallow part of the bottom. The benthic zone is the deeper part. The main difference between littoral zone and benthic zone is that the littoral zone has rooted vegetation at its base while the benthic zone with well developed root systems plants in the mud. Assignment: list three differences between littoral zone and benthic zone of freshwater habitat. In lotic freshwater habitats, there are two zones, the pool zone, where the water is relatively slow and calm, and the rapid zone where the flow is fast. Plants in the freshwater zones include deep rooted plants such as: ferns (Naphrolepis), water lily (Nymphaea), water arum (Cytosperma senegalense), commelina grasses and sedges. The floating plants include: Spirogyra, Chlamydomonas, water lettuce (Pistia), duckweeds (Wolffia), water ferns, bladderwort (Utricularia) and bluegreen algae. Animals in the freshwater zones include zooplankton (they are abundant in lentic freshwater), such as Cyclops and Daphnia which are both copepods. Other animals include water skater, Tilapia, cat fish leeches, larvae and pupae of mosquitoes, water snails crustaceans such as crayfish, water scorpion, crabs. Others are amphibians such as toads, frogs, reptiles such as crocodiles, birds such as ducks, heron, and mammals such as waterduck and hippopotamus. Note: Nekton are active animals which can swim against water currents (directional movement). Adaptative features of freshwater plants: - Presence of large air space/parenchyma in roots and leaves to provide support for buoyancy; e.g. Nymphaea/water lily; - Presence of hairs on the leaves to prevent blockage of stomata; e.g. Pistia/water lettuce; - Stomatal pores occur only at the upper epidermis of the leaves to aid transpiration; - Numerous adventitious roots and root hairs to aid water and mineral salts absorption; - Small size of the plant for buoyancy/floating in water; e.g. Lemna/duckweed - Waxy upper surface of the leaf to prevent clogging of the leaf by water; - Long petiole/leaf stalk to support or expose the broad lamina for photosynthesis; - Long flower stalk to expose flower for pollination; - Presence of breathing roots/pneumatophores for breathing/gaseous exchange; - Thin cuticle for absorption of sunlight for photosynthesis - The entire plant is flattened to aid floating, e.g. Lemna/duckweed; - Ribbon-shaped/finely dissected leaves to allow free flow water current, e.g. Hornwort Adaptive features of freshwater animals: - Presence of swim bladders for buoyancy; e.g. Tilapia; - Presence of webbed digit feet for easy swimming/locomotion; e.g. Duck; - Possession of contractile vacuole for osmoregulation; e.g. Protozoa; - Possession of serrated beak for sieving food into the mouth; e.g. Duck; - Possession of long legs to skate on water surface; e.g. Skaters; - Presence of gills for gaseous exchange; e.g. Tilapia. Why green plants are absent at the lower depth of some lake: Light intensity decreases with depth in water bodies, so at certain depths in water, there is no light for photosynthesis to occur. Energy flow in a freshwater habitat: Common aquatic plants suc as Pistia or Spirogyra use energy from the sun to photosynthesis or produce food. This food is eaten by primary consumers or small aquatic animals which would in turn be eaten by bigger aquatic animals or secondary consumers. In the process of feeding, energy flows from one trophic level to another and decreases progressively; dead animals or plants also decompose, hence this leads to energy loss. Food chain in fresh water biome: Diatoms→Fishfry→Tilapia. Spirogyra→Tadpoles→Carps→Kingfishers. Detritus→Worm→Shrimp→Bird. ESTUARINE This is the place/point where a river enters the ocean/sea into which the tides flow, freshwater mixes with saltwater to form a brackish water. Characteristics of the estuarine habitat 1. The land is low lying; 2. The land is flat or has a small gradient towards the sea; 3. Salinity varies as a result of tides and season; 4. Waves and current are mild compared with the sea; 5. There may be overflow of banks, this leads to frequent flooding; 6. It is a disturbed area as a result of tidal flowing in and out of it; 7. Estuary water has lower specific gravity than sea water, hence marine animals which float in sea water may sink and not do well in estuarine water. Note: the main factor affecting distribution of organisms in an estruary is the salinity levels. Plants in estuary include diatoms, algae, red mangrove, white mangrove, bulrush. Animals in an estuary include mudskipper, barnacles, hermit crabs, oyster, lagoon tulip. Adaptive features of red mangrove to estuary: 1. Ability of the seeds to withstand tides, current and wind until it reaches a mud bank; 2. Possession of rootlets to absorb water and mineral salts; 3. Possession of thick leathery leaves to reduce loss of water by transpiration; 4. Presence of spongy tissue with many air spaces in roots to obtain air. Adaptive features of hermit crab 1. Ability to live in the empty shell of a snail to withstand waves and tides action; 2. Its body remains in the shell for protection; 3. It has specially modified legs for holding tightly to the shell; 4. It has physiological tolerance to variations in salinity. Food chains in an estuarine: Phytoplanktons→Barnacles→Fish→Bird. Detritus→Worm→Mollusc→Bird. Detritus→Shrimp→Fish→Bird. TERRESTRIAL HABITATS/BIOMES This is the life on land. Life begins in water, and over time, organisms that were suitably adapted migrated on to land. There are four kinds of terrestrial habitats: marsh, forest, savannah, and arid lands. MARSHES A marsh is a lowland habitat which is flooded or water-logged at all times, and in which grasses and shrubs grow. It is the transitional habitat between the aquatic and terrestrial habitats. It is a treeles land, but rather dominated by grasses, reeds, sedges and water plants. Characteristics of a marsh 1. It is a flat lowland; 2. It has a high relative humidity atmosphere; 3. Its ground is flooded most of the time; 4. It has high rate of decomposition due to increase in decaying organic matter; 5. There is a decrease in oxygen content in the marsh water; 6. The soil is wet, soft and water-logged. Why some marshes are very strongly acidic: The increased rate of decomposition results in decrease in oxygen content of the marsh water. This results in increased anaerobic conditions of the marsh, which results in the release of foul-smelling gases such as hydrogen sulphide and methane which are acidic gases. This results in acidic marsh. Formation of marshes Marshes occur in lowlands near rivers or estuaries where drainage is poor. Marshes may also develop when river overflows its bank to accumulate on the low land area.. a marsh may also be formed by accumulation of debris in a lake, hence turning aquatic habitat into a wet land. Types of marshes There are two major types of marshes. These are: 1. Freshwater marshes: These type of marshes occur in inland. During their formation, rivers overflow its bank and accumulates debris on the lowland to form a wetland. 2. Saltwater marshes: These type of marshes occur along the coastal areas, when salt water along the coast mixes up with freshwater from rivers to form brackish water. Characteristics of salt marsh habitat: - presence of low oxygen; - High salinity; - Soft muddy environment; - Low light penetration; - Its a flat lowland; - Presence of changing water levels; - Swampy/water-logged. Plants that live in the marshes include duckweed/Lemna sp, aquatic fern/Salvinia, water lettuce/Pistia, water arum/Cyrtosperma, white mangrove, red mangrove. Modification/adaptation of plants to salt marsh - Plants grow long roots/numerous roots to hold to substratum; - Possession of stilt roots for anchorage. Animals that live in the marshes include mangrove-crab, lagoon crab, hermit crab, mudskipper fish, oysters, barnacles, toads, frogs and birds (e.g. heron). Evolution of new habitat in the marsh through succession: As sediments and organic deposits raise the bottom of a marsh above the water table, aquatic vegetation will be replaced gradually by shrubs and eventually by a terrestrial ecosystem of upland grasses or forest trees over time. Food chain in marshes Humus→Earthworms→Frogs→Snakes. Flowering plants→Insects→frogs. SWAMP A swamp is a special form of a marsh, where trees are found with the usual grasses and shrubs, which are known to be found in the marsh. Types of swamp 1. Tropical freshwater swamp forests; 2. Temperate freshwater swamp forests; 3. Mangrove swamp forests. Mangrove swamp forest is found in coast especially in states like Delta, Cross River, Rivers, Ogun, Lagos, Akwa-Ibom and Bayelsa. Characteristics of swamp forest 1. It has tall woody trees; 2. Plants mainly have aerial roots; 3. It has evergreen trees with broad leaves; 4. It has high rainfall; 5. Its water is a combination of fresh water and salt water; 6. It has a very high relative humidity. Adaptive features of mangrove plants 1. Possession of prop rots for support in the soft muddy substratum, e.g Rhizophora and Pandanus. 2. Possession of air roots or pneumatophores to take in atmospheric oxygen because the waterlogged soil is low in oxygen content, e.g. Avicennia. 3. Their seeds undergo viviparous seedlings, that is the seeds germinate while they are still on the parent tree, this prevent them from being washed away. FOREST A forest is a plant community in which tree species are dominant, hence forming a biome. The main forest biomes include the tropical rain forests, the temperate deciduous forests and the coniferous forests. Characteristics and climate of temperate forests: 1. Forests mainly of broad-leaved deciduous trees; 2. Trees shed their leaves during the winter (the coldest period; between December and February); 3. Forests are less dense than tropical forests; 4. Sunlight penetrates into the forests enabling the growth of plants at many levels from ground; 5. Moderately wet climate with a dry or a cold season. Characteristics and climate of coniferous forests: 1. Forests of needle-leaved evergreen conifers such as pines, firs and spruces; 2. Forest has two layers --- a dense layer of tall trees forming the upper storey and a layer of shrubs, ferns and mosses forming the lower layer; 3. Few types of trees are found here, unlike the tropical forests; 4. The Forest floor is covered with a thick layer of conifer needles as decomposition is slow at temperatures; 5. Cool temperate climate with light rainfall and snow. Characteristics and climate of tropical rain forests: 1. It is a dense forest with many types of trees, epiphytes and climbers; 2. There is abundant rainfall and an average temperature of 27oC throughout the year; 3. Presence of broad leaves; 4. Presence of buttress roots which give additional support to them and prevent falling due to wind actions; 5. The vegetation has a pattern of arrangement in stores or layers; 6. Presence of tall trees; 7. Presence of a large amount of fallen leaves on the forest floor; 8. Presence of many climbing plants such as epiphytes, e.g ferns. Examples of plants found in the tropical forests include: Mahogany, teak, Iroko, oil palm, liverworts, mistletoe, African walnut etc. Examples of animals found in the tropical forests include: bats, monkeys, snakes, squirrels, birds, lizards, earthworms, millipedes etc. Strata in a tropical rain forest 1. The upper layer/storey is made up of the tallest trees, over 40m tall, called emergents. The crowns of the emergents do not normally touch one another. Examples of plants in this category are Iroko, Obeche, Mahogany etc. 2. The middle layer/storey is made up of tall trees, between 16m and 40m tall. Their crowns touch, forming a continuous canopy below the emergents. 3. The lower layer/storey is made up of small trees, less than 16m tall, which also form a continuous canopy below the second or middle storey. 4. The shrub layer/storey is made up of small trees, 1-5 metres in height. 5. The ground layer or forest floor which consists of shade-tolerant plants, including mosses and ferns. Adaptive features/ adaptations of forest plants 1. Presence of strong tap root system to hold the trees firmly/anchorage and to absorb water. 2. Presence of large amounts of strengthening tissues such as xylem for support. 3. Presence of stomata and lenticels for gaseous exchange. 4. Presence of broad leaves to increase rate of transpiration. 5. Presence of thin barks to increase water loss. 6. Presence of chloroplasts for photosynthesis. Adaptive features/ adaptations of forest animals 1. Presence of prehensile tail tail to climb and hang onto branches, e.g. Climbing Pangolin. 2. Presence of wing-like structures for gliding, e.g. Flying squirrel and gliding lizard. 3. Possession of opposable digits on the hands and feet to climb trees and grasp slender branches, e.g. Chameleon. 4. Ability to change skin colour to match the forest background to escape predators, e.g. Chameleon. 5. Possession of long sticky tongue to catch prey, i.e. Chameleon. 6. Slim elongated bodies to enable balance on branches by coiling, i.e. Tree snakes. 7. Presence of wings to fly to escape predators and search for food, e.g. Birds, bats. 8. Possession of water permeable cuticle to reduce water loss and prevent drying up, e.g. Earthworm and snail. 9. Movement in groups to protect themselves from predators, e.g Apes such as Gorilla. Abiotic factors affecting tropical rainforest 1. Temperature, 2. Rainfall, 3. Relative humidity, 4. Sunlight, 5. pH of the soil, 6. Wind. Food chains in a tropical rain forest habitat Green plants/herbs/shrubs→herbivores/insects/rats/monkeys→carnivores/leopard. Herbs→grasshoppers→Toads→Hawks. Shrubs→Caterpillars→Lizards→Snakes→HawksTrees→grasshoppers→Chameleons. Detritus→Eartwoms→Birds GRASSLANDS OR SAVANNA A grassland is a plant community in which grass species are dominant, but trees and shrubs may be present. It is an intermediary between forests and deserts. Characteristics of grassland 1. The soil is usually sandy. 2. Intense sunshine. 3. Predominance of grasses. 4. Predominance of bush fires in the dry season. 5. Moderate and low rainfall and high temperature. 6. Presence of drought resistant trees due to low rainfall. 7. Presence of short but scattered trees. Types of grassland The major grassland biomes of the world are: 1. The temperate grasslands, 2. The tropical grasslands. The temperate grasslands: This type of grasslands experience low rainfall, a hot wet summer and a cold dry winter. Temperate grasslands include: a. Prairies in United States of America; b. Steppes in Russia and Asia; c. Pampas in Argentina; d. Veldt in South Africa; e. Downs in Australia. The tropical grasslands: This type of grasslands experience a high temperature throughout the year, and a distinct wet season and a dry season. Tropical grasslands are called savannah, such as in West Africa. Savanna/savannah In Nigeria, there are different types of savannah, they include: I. Southern Guinea savannah, II. Northern Guinea savannah, III. Sahel savannah, IV. Derived savannah. Southern Guinea Savannah Location: This biotic community is found in states like Enugu, Kogi, Benue, Kwara, Oyo, Ebonyi, Osun and Ekiti. Characteristics of southern Guinean savanna 1. It is the largest of all the biotic communities in Nigeria. 2. It has moderate rainfall of between 250mm to 500mm per annum. 3. It has tall grasses. 4. Scattered deciduous trees and shrubs. 5. Predominant of bush fires in the dry season. 6. The common tree species are fire resistant. Trees found here include locusts bean trees, shea-butter and Bridellia etc. Animals found here include antelopes, lions, leopards etc. Nothern Guinea Savanna Location:This biotic community is found in states like Plateau, Kaduna, Bauchi, Kano, Taraba, Niger and Adamawa. Characteristics of Northen Guinea Savanna 1. The rainfall is low (100mm to 300mm per annum). 2. Presence of short grasses. 3. It has scattered and short deciduous trees. 4. Presence of short and scattered trees. Trees in this zone include acacia, date palm, silk cotton plants and baobab. Animals include snakes, lizards, deer, lions, antelopes etc. Sahel Savannah Location: This type of savanna occurs only in Nigeria on the eastern tip of Borno State, around Lake Chad, and some parts of northern states such as Yobe, Kebbi, Zamfara, Kano, Sokoto, Jigawa and Katsina. Characteristics of sahel savanna 1. Presence of short grasses and small trees; 2. Low rainfall, which is spread over only a few months of the year; 3. High temperature; 4. Many drought-resistant and scattered plants. Trees in this biome include Acacia spp, date palm, gum arabic. Shrubs found here include Salvadoran persica, Leptadenia pyroteshnica etc. Animals found here include those found in other types of grassland. Derived Savanna This is a type of grassland existing due to human activities such as farming, house construction and bush burning. It is an artificial savannah, which will revert to its original biome (e.g. Rain forest in Nigeria) when human influence is withdrawn. Adaptive features/ adaptations of savannah plants 1. Possession of broad and succulent trunks/barks to store excess water, e.g. Baobab tree; 2. Possession of long roots to search for ground water, e.g. Acacia; 3. Possession of cluster of shoots which protect the buds during burning e.g. Elephant grass; 4. Possession of very small and thick leaves to reduce transpiration e.g. Acacia; 5. Presence of spines on the body of the plant to protect the plant from being damaged by animal, e.g Acacia. 6. Shedding of leaves during dry season to reduce transpiration i.e deciduous plants, e.g. Locust bean tree. 7. Possessionof rhizomes which regenerate new shoots immediately after bush fire, e.g. Spear grass. Adaptive features/ adaptations of savannah animals 1. Presence of chitinous exoskeleton to prevent desiccation and external damage e.g. Grasshopper; 2. Possession of efficient tracheal system for respiration, e.g insects; 3. Ability to burrow into the soil to avoid excessive heat of the sun and fire; 4. Camouflage body colors to escape predators, e.g Zebras, grasshoppers, and giraffes; 5. Movement of animals in group to achieve strength e.g elephants, and lions; 6. Snails retreat into their shells during dry season to prevent desiccation. This is called hibernation. Abiotic factors affecting Savannah 1. Temperature 2. Rainfall 3. Wind 4. Soil fertility. Soil in the grassland are usually fertile as most of the nutrients are not leached because of low rainfall. 5. Low relative humidity 6. High light intensity. Food chains in the grassland Grasses→grasshoppers→Lizards→Hawks. Wood→Termites→Aardvark//anteater→Lynx. Grasses→Zebras→Lions. ARID LANDS OR DESERT HABITATS An arid land is a biome where water is very difficult to obtain, either because it is scarce or because it is frozen. Types of arid lands There are two major types of deserts, they are: 1. Hot arid lands, which are hot deserts and semi-deserts. Examples of hot deserts are Sahara desert (North Africa), Arabian desert and Kalahari deserts (South Africa), Great Australia desert (Australia) and Atacama desert of South America; and 2. Cold arid lands, which are cold deserts or tundra. The desert is found in interior of Eurasia, North America and in Patagonia (South America). Characteristics of hot arid lands 1. The soils are sandy or rocky; 2. Predominance of strong winds; 3. Little or no vegetation; 4. High sunshine; 5. Hot temperature during the day, but become very low at night; 6. Water is very scarce because rainfall is very low (below 250mm per annum); 7. Low relative humidity due to low rainfall, high temperature and scanty vegetation. 8. Presence of ephemeral. These are plants that complete their life cycles from seeds to plants in a few weeks. They are common in the desert, during the brief rainy season. 9. Plants are widely spaced so that each plant has a maximum area from which to draw available water. Note: The main difference between hot arid land and the tundra/cold arid land is that the tundra is very cold and the ground surface is covered with ice throughout the year, except during the short summer. Location of desert biome in Nigeria: Desert biome is located at the northern borders of Sokoto, Katsina, Jigawa, Yobe and Bornu States. Distribution of plants in arid lands or hot deserts The following are examples of plants found in the desert: Euphorbia,Aloe, Cacti and Date palms (occurring around oases; areas where there is a local source of water). Note: Vegetation which is adapted to dry environmental conditions is called xerophytic and such plants are called xerophytes. Adaptive features of xerophytes/desert plants 1. Leaves are reduced to spines to reduce loss of water/transpiration, e.g Cactus. 2. Possession of thick succulent stem and side branches to store water/conserve water, e.g Cactus. 3. Possession of deep root systems to tap subsoil water, e.g Acacia, and Oleander. 4. Possession of waxy, hairy leaves to reduce transpiration, e.g Baobab. 5. Presence of spines to prevent the plants from being eaten up by browsing animals, e.g the spines on the Cactus. 6. Green modified stem for photosynthesis, e.g Cactus. 7. Presence of sunken stomata or hairs on leaves to reduce transpiration, e.g Eucalyptus Distribution of animals in arid lands or hot deserts The following are common animals found in the desert: camel, rats, lizards, zebras, snakes, locusts, ants, moths, butterflies, hedgehog, fox etc. Adaptive features of desert animals or Ways by which animals in arid land are adapted to droughts and high temperature 1. Possession of hard, impermeable body-coverings to reduce water loss from the body surface by evaporation, e.g insects and reptiles. 2. Presence of wax-covered integumentary which are permeable to water at high temperature, e.g insects. 3. Excretion of concentrated liquid (i.e urea; to be excreted by mammals e.g camel) or solid (i.e uric acid, to be excreted by e.g reptiles, birds and insects) wastes to conserve water. 4. Ability to live in burrows during the day to conserve water and come out at night to feed, e.g desert rats. 5. Ability to live on dry seeds, hence to get the water they need from the food(the seeds) e.g Jerboa rat and from metabolic reactions(e.g by absorbing moisture from the air through their outer body coverings, e.g some desert insects) 6. Presence of fringed feet to move rapidly over sand, e.g lizards. 7. Presence of broader and flatter body shapes to allow sidewinding movements and to sink in the sand, e.g snakes. 8. Presence of scales on the body to limit rate of water loss, e.g lizards and snakes. 9. Possession of muscular nostrils that can close during a sandstorm to prevent entering of dusts into its nasal cavity, e.g Camel. Food chain in arid land habitat Grasses→grasshoppers→Lizards→Snakes. Plants→Ant-lions→Scorpions→Snakes. Factors affecting arid lands/Sahara desert: The following are abiotic factors affecting arid lands: 1. Low rainfall. 2. High temperature. 3. Very low relative humidity at noon but high at night. 4. Strong winds. 5. Intense sunlight.

PLANT NUTRITION A British clergyman and chemist demonstrated in the year 11772, that when a plant or animal was kept alone in an airtight jar, it died, but when a plant and animal were put together in an airtight jar, both lived. Jan Ingen-Housz later showed that sunlight was necessary for plants to produce oxygen although he knew nothing about oxygen. Jean Senebier was was a Swiss Pastor showed that plants use carbon dioxide when they produce oxygen; he suggested that carbon dioxide was converted to oxygen during photosynthesis. Senebier called this gas that was converted "fixed air." EARLY EXPERIMENT TO SHOW THAT CHLOROPHYLL IS IMPORTANT DURING PHOTOSYNTHESIS AND THAT CHLOROPLASTS DO NOT ABSORB GREEN WAVELENGTHS. T. W. Engelmann, in the year 1883 studied the algae Spirogyra sp., which has distinctively long, spiral chloroplasts. He used a prism to direct specific wavelengths of light to different parts of the Spirogyra. After this, he put oxygen-dependent (aerobic) bacteria to the solution containing the Spirogyra, expecting that when the Spirogyra was getting the best light for photosynthesis, the Spirogyra would release the most oxygen. He was of the believe that, the bacteria would cluster where more oxygen is found. It was found out that the greatest numbers of bacteria clustered where the chloroplasts were absorbing the bands of red and blue light not by the green wavelengths. This experiment concluded that oxygen was being produced where the red and blue wavelengths were being absorbed.therefore, chloroplasts do not absorb green wavelengths from spectrum. Green plants obtain their food through: 1. Photosynthesis and 2. Mineral salts uptake. Explanation why most leaves look green: This is because while the leaves absorb the red and blue wavelengths, the green passes through. That is when white light falls on a leaf, it absorbs all the components of light except the green component. This green component is reflected, hence giving a green appearance of leaf. Examples of photosynthetic pigments include: chlorophyll, carotenoids, xanthophylls and anthocyanins. PHOTOSYNTHESIS There are two major types of nutrition, they are autotrophic (self-feeders) and heterotrophic (dependent-feeders). Plants, algae and green bacteria are all examples of autotrophs, while animals, fungi and most bacteria are all examples of heterotrophs. Photosynthesis is an example of autotrophic nutrition. Photosynthesis This is a biochemical process in green plants, in which, their chlorophyll (found in the chloroplasts) manufacture food/sugar (organic food) using inorganic substances such as carbon dioxide and water in the presence of sunlight, giving off oxygen as a by-product. 6CO2 + 6H2O →C6H12O6 + 6O2 Note: Photosynthesis is an example of holophytic nutrition because inorganic compounds are converted into organic compounds. Mechanism/process/stages of photosynthesis The process of photosynthesis is broadly grouped into two: 1. Light reaction; 2. Dark reaction. Light Reaction This stage involves: a. Capturing of light energy from the sunlight. Certain wavelengths of the light energy are been trapped by the chlorophyll. Red and blue light energy are trapped the most efficiently, while green light energy is trapped the least. The chlorophyll is therefore energized. b. The conversion of light energy into chemical energy. The energy released from the electrons in the chlorophyll when it traps light energy is used to do two things: (i) split water molecules and (ii) make ATP. The process of splitting water is called photolysis. During photolysis, water molecule is splited to form hydrogen ions (H+) and hydroxyl ions, while oxygen is given out as a by-product from the hydroxyl ion. i.e 4H2O → 4H+ + 4OH- 4(OH-) → 2H2O + O2 The hydrogen atom (H2) released is collected by a coenzyme called NADP (Nicotinamide adenosine dinucleotide phosphate), this is done to prevent its escape from the cell or recombining with oxygen to form water. This process reduces the NADP to NADPH2, because it (NADP) have accepted hydrogen atoms and serve as electron carrier of hydrogen ions. This coenzyme brings the hydrogen atom to the next step of photosynthesis process. In the next step, the light energy which has been stored as a low chemical energy carrier called ADP (Adenosine diphosphate) gets more energy from the extra or unused energy from photolysis to form a high chemical energy carrier called ATP. This energy is stored in the grana part of chloroplasts for dark reaction. The major products of light stage/light-dependent stage of photosynthesis and their importances include: 1. ATP (Adenosine triphosphate)/energy, to generate energy for the dark stage reaction. 2. H+ (Hydrogen ion), reduces NADP to NADPH2. 3. OH- (Hydroxyl ion), splits into water and oxygen escapes. 4. NADPH2 (reduced nicotinamide adenine dinucleotide phosphate), generates hydrogen ions/to reduce carbon dioxide to form carbohydrate in the dark stage. 5. O2 (Oxygen gas), is given off into the atmosphere form animals/other organisms to use for respiration. DARK REACTION. This is also called Calvin cycle. This stage does not require absorption of light energy. During this process, carbon dioxide is reduced by the hydrogen ions produced in the light stage. This is done together with the energy provided by ATP. This process leads to formation of sugars through a series of reactions, controlled by enzyme. These processes take place in the stroma of the chloroplasts. i.e 4H + CO2 → CH2O + H2O. This is a reduction process and enzyme is involved. 6CO2 + 12H2 →C6H12O6 + 6H2O (This equation only shows the overall reaction of the dark stage). The overall mathematical reactions of photosynthesis look like this: Light stage: 12H2 O → 12H2 + 6O2............(i) Dark stage: 6CO2 + 12H2 →C6H12O6 + 6H2O.........(ii) Add equation (i) and (ii). 12H2 O + 6CO2 + 12H2 → 12H2 + 6O2 + C6H12O6 + 6H2O Collect like terms: 12H2 O - 6H2 O + 6CO2 →C6H12O6 + O2 6H2 O + 6CO2 →C6H12O6 + 6O2 Note: 1. Dark reaction is not called the dark reaction because it occurs at night, but because the steps of this process do not involve the absorption of light energy. 2. In the reaction for dark stage, the name of the first real carbohydrate produced is a 3-carbon molecule called PGAL (phosphoglyceraldehyde), which is used to make other macromolecules such as fats, oils, proteins and carbohydrate derivatives. 3. Chloroplast is a special organelle found in plants, which contains a special pigment molecule called chlorophyll. Chlorophyll is found in little sacs called thylakoids (a coin like structures). The thylakoids stack up on each other like coins to form grana. The grana are surrounded by a fluid called stroma. Factors/conditions (materials) that affect the rate of food production in a green plant or in photosynthesis The rate of photosynthesis is affected by the following factors: 1. The wavelength of light available/ light intensity as moderately high light intensity favours photosynthesis. 2. An optimum temperature is required as very high or too low temperature may alter enzymes reaction. 3. The carbon dioxide must be adequately supplied to the chlorophyll for faster photosynthesis. 4. The concentration of chlorophyll available within the organisms determine the rate of photosynthesis; if its low, photosynthesis rate will be slower. 5. Water. Water must be adequate. 6. Oxygen concentration. The higher the concentration level in the atmosphere, the slower the rate of photosynthesis. 7. Leaf structure. A broad leaf will undergo more photosynthesis than a leaf that is reduced (such as to a spine). 8. Inhibitors, such as herbicides and urea will alter rate of photosynthesis. 9. Pollutants, such as sulphur dioxidea dn ozone damage leaves and hence, alter photosynthesis. Experiment to show that oxygen is given out as a by-product of photosynthesis Method/procedure: Water plant such as Elodea or Spirogyra is placed in a beaker of water covered with a funnel and a test tube filled with water is turned upside down/inverted over the funnel stem. The experimental set-up is placed in sunlight for about 3 hours/few hours while an identical control experiment is setup and placed in a dark cupboard for about 3 hours/few hours to prevent photosynthesis taking place. Observation: Bubbles of gas were observed in the test-tube of the experimental setup, while no gas bubbles were observed in the control. The gas was tested with glowing splint which was rekindled/burst into flames. Conclusion: This showed that oxygen gas is produced during photosynthesis. How leaf of a flowering plant is adapted for photosynthesis 1. The guard cells have chloroplast for the absorption of sunlight. 2. Large vacuoles of the palisade cells store photosynthetic products. 3. Phloem transports manufactured food to other parts of the plants. 4. Xylem conducts water into the leaves for photosynthesis. 5. Broad/flat leaf lamella exposes large surface area for maximum absorption of light. 6. Large intracellular air spaces in the spongy mesophyll allow oxygen/carbon dioxide to diffuse in/out of the chlorophyllus cells/gaseous exchange. 7. Thin lamella allows light penetration into leaf tissue of mesophyll. 8. Palisade mesophyll cells contain a lot of chloroplast/chlorophyll for maximum absorption of light. 9. The stomata open easily when it becomes turgid for diffusion of gases/carbon dioxide/oxygen. 10. The bean-shaped structure of the guard cell is to allow oxygen/carbon dioxide exchange. Importance of photosynthesis to humans 1. Food produced by photosynthesis is consumed/eaten by all humans. 2. Provides humans with fossil fuel. 3. Oxygen produced during photosynthesis is taken in by man during breathing/for respiration. 4. Provides raw materials for industries, such as medicinal herbs. 5. It maintains carbon dioxide balance in the atmosphere by reducing them, because they could become a pollutant. It means it brings purification of air. Importance of photosynthesis to living things/nature 1. Production of food for both plants and animals. 2. Purification of the atmosphere by maintaining oxygen-carbon balance. 3. It releases oxygen for plants and animals to use for respiration. 4. It is the building blocks for other substances in the body of organisms, such as building of fats, proteins etc. EXPERIMENTS ON PHOTOSYNTHESIS Activities on Photosynthesis: 1. To show the materials and conditions necessary for photosynthesis. The following external conditions are necessary for photosynthesis: a. Sunlight b. Carbon dioxide c. Chlorophyll d. Water a. Sunlight: ✓ Ensure that the leaf used is a fresh green leaf, which is still attached to the parent plant. This will allow the leaf receives a continuous supply of water and mineral salts; ✓ Cover both surfaces of the leaf with strips of black paper with a pattern cut on it; ✓ Make sure the plant-leaf is left in sunlight for few hours; and ✓ Pluck the leaf after some few hours, and test for starch. ✓ Only the parts of the leaf exposed to sunlight turn blue-black. ✓ This change on the the part of the leaf exposed to sunlight shows that sunlight is needed for photosynthesis. b. Carbon dioxide: • Enclose the leaf of a potted plant attached to the plant in a flask/bell jar containing caustic soda/caustic potash (sodium hydroxide/potassium hydroxide) solution. The caustic soda/caustic potash will absorb carbon dioxide; • Ensure that the experiment set-up is done early in the morning, and allow to stand in exposed bright sunlight for 4-6 hours; and • Detach the leaf, and test for starch. The result will be no sign of starch. • Set up a control experiment labelled ‘B’, ensure that there is no soda lime, also, let water replaces caustic soda/potash. Hence, ‘B’ receives sufficient carbon dioxide from the air. It will be observed that only leaf in ‘B’ is tested positive to starch presence, because it receives carbon dioxide. • This change in B shows that carbon dioxide is necessary for photosynthesis. Precaution: 1. If you are using conical flask, smear the flask with Vaseline at the neck so that it is air-tight, but if you are using bell jar, use soda lime to prevent entry of more carbon dioxide. 2. Make sure that the experiment start early before day light so as to ensure that plant has not started manufacturing food. 3. Ensure that in both set up, the soil is covered with polythene to prevent the release of carbon dioxide by the micro-organisms in the soil. Another description of Experiments to show that carbon dioxide is necessary for photosynthesis Experiment 1: Method: Two potted plants are de-starched by placing them in a dark cupboard for 24 hours; a leaf each from both plants are then tested for starch to ensure they have no starch/have been de-starched; the potted plants are placed on a board each; a beaker containing caustic soda is placed beside plant A to absorb carbon dioxide, while a beaker containing water is placed beside plant B as control. They are both covered with bell jars labelled A and B respectively. The mid/edge is smeared with vaseline/petroleum jelly to make it air tight. The setup is exposed to sunlight/light for 4-6 hours, then a leaf each from both plants are plucked and tested for starch. Observation: It is observed that leaf from plant A is negative/does not contain starch/remains brown in colour while leaf from plant B is positive/contains starch/turns blue-black. Conclusion: Carbon dioxide is necessary for photosynthesis. Experiment 2: Method: De-starch a well-watered potted plant by putting it in darkness for 48 hours. Insert a leaf into a flask containing KOH/potassium hydroxide/caustic potash, ensure both flasks are air tight by smearing the split corks with vaseline. Leave the potted plant in a well-lit place for 6 to 9 hours. Detach the leaves and test them for starch. Observation: It is observed that the leaf in the flask containing caustic potash contains no starch while the leaf in the controlled experiment contained starch Conclusion: Carbon dioxide is necessary for photosynthesis. c. Water: ▪ Take a potted plant and get it well watered; ▪ Keep the potted plant in a dark cupboard for at least 24hours or overnight. This will destarch the leaves; ▪ Enclose the destarched potted plant in a conical flask containing alkaline pyrogallol solution. The alkaline pyrogallol solution will absorb water, and remove any trace of water inside the flask; ▪ Set-up a control experiment, without destarching the leaves; exposed to all conditions necessary for photosynthesis; ▪ The destarched leaves show negative result, by showing a yellowish-brown colour, while the control leaves turn blue-black, when iodine test was conducted. ▪ The negative result in test experiment shows that water is released during photosynthesis. d. Chlorophyll: • Take a variegated leaf (e.g. leaf of Croton, Acalypha,or Coleus plant) that has been exposed to sunlight for a few hours; • Draw a diagram to show the distribution of the green colour of the leaf; and • Test the leaf for starch. Only the green parts containing starch will turn blue-black, others will not. • The change in green colour to blue-black when tested with iodine shows that chlorophyll is needed for photosynthesis. Variegated leaf: A leaf with different colour parts/patches/green and non-green parts. The only part of it that would be positive when treated with iodine solution is the green part, because there is presence of chlorophyll for tapping solar energy to manufacture starch which turns blue-black with iodine. 2. To show that starch is a product of photosynthesis. I. Pluck the leaf of a plant which has been exposed to sunlight for a few hours to ensure that food is manufactured; II. Place the plucked leaf in boiling water for 30 seconds to kill the leaf; III. Remove the leaf from boiling water, then place it in hot alcohol (use a water bath) to decolorize the leaf; IV. Dip the decolorized leaf in hot water to soften it; V. Place the leaf on tile and add iodine solution to it to test for starch presence. Experiment to show the effect of light intensity on photosynthesis/or how the intensity of light affects the rate of photosynthesis Get a table lamp/torch, a beaker, a water plant such as Elodea or Spirogyra, pond water, prepare 0.5% solution of sodium bicarbonate/baking soda/bicarbonate of soda and a beaker. Prepare the set-up as follows in the dark room: Fill the beaker with the pond water, add a small amount of 0.5% sodium bicarbonate solution to the pond water to saturate the water with carbon (IV) oxide and thus make it readily available to the plant for photosynthesis. Insert the water plant through the test-tube. Then, place the lamp/torch 15 cm from the set-up, switch on the lamp. Take three 1-minute counts of the number of bubbles produced. The bubbles are oxygen given off by the plant; which can be confirmed using a glowing splint placed over the mouth of the test-tube after the experiment. The splint is rekindled/glows brighter, which confirms that the gas is rich in oxygen. Calculate the average number of counts. Repeat the procedure several times, each time moving the lamp further away from the set-up. The farther it is, the slower the bubbles counts. This shows that light intensity affects rate of photosynthesis. Fate of photosynthetic products The only product of photosynthesis is the sugar. The sugar is used as either glucose or stored as starch, which may by used to make other substances. The glucose is used to generate energy during respiration. The energy produced is stored as ATP, which is used for life activities such as growth and reproduction. Excess starch are broken down to form glucose and as well converted to substances such as sucrose, and oils, which are stored in the plant for other uses. Such uses may be in the plant tissues or useful to human when we eat plant, where they provide energy to human and to build-up the many organic compounds that we need. Fate of photosynthetic by-product The by-product of photosynthesis is oxygen. Oxygen gas is released and is used by animals for respiration and as well by plants during respiration. It breaks down sugar (glucose) to release energy for the organisms cells and tissues in order to carry out life activities. Mineral requirements of plants Plants obtain mineral salts majorly from the soil, while others are gotten from gases (such as carbon, hydrogen and oxygen) and use them to react with the carbohydrates made during photosynthesis to make proteins and as well for healthy growth. For example, nitrogen is needed to make proteins. Mineral salts are not required in the same quantity, hence they are grouped into: a. Macro-nutrients or major elements and b. Micro-nutrients or trace elements. a. Macro-nutrients or major/essential elements: These are elements required by plants in large quantities for growth and development. Examples include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulphur, calcium, iron and magnesium. b. Micro-nutrients or trace/minor/non-essential elements: These are elements that are needed in plants, which must be present for growth and development but in small quantities. They are required for the activity of enzymes. Their absence or over dose is disastrous to plants. Examples include copper, boron, cobalt, chlorine, molybdenum, zinc and manganese When a plant lacks any of these elements, it shows certain signs called deficiency symptoms. The functions and deficiency symptoms of these elements are shown below: Element Function/importance Deficiency symptoms Nitrogen (N) 1. Protein synthesis/synthesis of amino acids 2. Synthesis of nucleic acids/nitrogenous bases 3. Synthesis/formation of chlorophyll 1. Stunted growth. 2. Chlorosis/yellow leaves 3. Small/reduced leaves Phosphorus (P) 1. Formation of nucloeproteins 2. Formation of coenzymes 3. Formation of ATP, DNA and RNA 4. Controls nuclear division 5. Controls stem and root formation 1. Poor/stunted growth 2. Stems and leaves appear purplish/reddish brown 3. Poor root development 4. Mottling of lower leaves Potassium (K) 1. Cell formation 2. Protein synthesis 3. Regulates respiration and photosynthesis 1. Leaves/leaves margins turn orange or brown 2. Delayed growth/ poor growth 3. Premature death Sulphur (S) Forms components of some amino acids and proteins 1. Yellow leaves/ chlorosis 2. Stunted growth 3. Weak stem/ slender stem Calcium (Ca) 1. Formation of cell wall 2. Neutralizes organic acids 3. Activates some enzymes 4. Gives rigidity to plant 1. Stunted growth 2. Weak stem 3. Poor root development Magnesium (Mg) 1. Formation of chlorophyll 2. Promotes growth 1. Yellow leaves 2. Stunted growth Iron (Fe) 1. Formation of chlorophyll 2. Formation of protein 1. Yellow leaves 2. Poor growth Manganese (Mn) 1. Activates some enzymes 2. Regulates certain cell activities such as respiration 1. Death of shoot Zinc (Zn) 1. Activates some enzymes 2. Necessary for the synthesis of the starting material of auxin 1. Poor growth 2. Poor leaf formation Molybdenum (Mo) 1. Activates some enzymes such as the enzyme that reduces nitrates to nitrite 2. Aids nitrogen fixation 1. Retarded growth 2. Necrosis of leaf tissue Water Culture This is the method of growing plants in distilled water containing all the necessary elements in the correct quantities in a medium. Examples of water culture solution prepared in the laboratory include Knop's culture solution and Sach's culture solution. Both culture solutions are called complete culture solutions. Water Culture Experiments We can determine the deficiency symptoms of some elements using water culture experiments, by preparing media where each medium lacks a specific element. A control experiment where seedlings are grown in a complete culture medium is done. Precautions to be taken while carrying out the water culture experiment 1. Use dry cotton wool or stoppers to hold the stem to prevent rottening of the stem. 2. Cover the gas jar with black paper or paint it black to prevent alagbo growth in the culture solution. 3. All the jars used must be kept under the same light and temperature to prevent the effect of other variables. 4. All culture vessels must be sterilized before the experiment to avoid contamination with pollutants and microorganims. 5. Air/oxygen must be blown in daily into the the culture solution through the bent glass tubing to aerate/replenish the oxygen used up by the plant. 6. Use healthy growing seedlings of the same age and size to give accurate growth rate. 7. Replace culture solutions every two weeks to avoid depletion of nutrients. Experiment on mineral deficiency/ to show the effects of mineral deficiency in plants