Agriculture food supply and population in our environment

RELEVANCE OF BIOLOGY TO AGRICULTURE
Biology is the stdy of living things Agricuitun the growing of plants and the rearing farm animals to provide our needs the cultural activities a basic knowledge of biology is necessary. Such knowledge includes

. the structure, function and nutrition of plants and animals

* diseases which affect plants and animals and the organisms which cause them ;

* ecological systems
*soil ; and
* genetics.


Classification Of Plants

Plant can be classified in several ways. In Botany (the study of plants), all plants are grouped into the plant kingdom and subdivided as on pages 15 to 20. This classification, which is based mainly on structure, function and evolu- fo
tionary trends, is not particularly useful to a farmer. However,more useful and appropriate ways of classifying plants include grouping them

. into annuals, biennials and perennials; and
. for agricultural purposes.

Annuals, Biennials and Perennials Plants are commonly grouped into annuals, biennials and perennials according to the span of their life cycles.

This classification applies mainly to flowering plants, the group to which most crop plants belong.

It is a practical way of classifying crop plants as it helps a farmer to
plan how to use his land to meet his goals.

Annuals These plants complete their entire life cycles and die within one growing season which may be from a few months to a year.

Many im-portant agricultural plants are annuals. Examples include rice, wheat, maize, bean, flax, jute and sunflower


Biennials These plants grow and store food during the first growing season, and use it in the second growing season to produce flowers, fruits and seeds before they die example include cabbage, radish and turnip which are harvested for food immediately after the first growing season.

Perennials These include trees, shrubs and herbs which continue to grow from year to year producing flowers, fruits and seeds for many years. Agriculturally important perennials include herbaceous ones such as ginger and onion, and woody ones like rubber, oil palm, cacao, mango and coconut.

Agricultural Classifications
In agriculture, cultivated plants or crops are usually grouped according to the products for which they are grown as given below

Cereals These plants belong to the grass fam
ily. They include maize, rice millet, Guinea corn and wheat. They are grown for their
grains which form the bulk of the world's food supply. The grains have a high starch content and contain varying amounts of proteins, oils and vitamins.

The legumes are an important source of dietary protein. They also supply
protein-rich fodder for livestock in tropical countries. In addition, legumes replenish soil nitrogen because nodules on their roots contain nitrogen-fixing bacteria. This makes them important in crop rotation. Legumes include bean, groundnut, cowpea, soya bean, oil bean,Legumes lima bean and yam bean.

Root crops They are grown mainly for starch and form the staple food of the people in many tropical countries. They include cassava, yam and sweet potato.

Vegetables Various kinds of vegetables are grown to supply dietary vitamins and certain minerals like calcium. Examples include to-mato, okra, onion, pepper and spinach.

Fruits Many plants are grown for their fruits which are rich sources of vitamins, especially vitamins A and C, minerals and sugars. Most fruits are eaten raw. Examples include orange pineapple, banana, plantain, mango, pawpaw and native pear.

Beverages and drugs The crops which yield ese products include cacao, coffee, tobacco and quinine. The products, cocoa and coffee,

are food drinks; tobacco is a stifnulant; and quinine is used as a medicine.

Spices Pepper, ginger, cinnamon and cloves belong to this group. They are used mainly for flavouring food.

Oils The fruits and seeds of certain plants are rich in oil. Such oil crops include oil palm, Shea butter, coconut and sunflower.

Forage crops These are the grasses and leg-umes that are grown for animal feed.

Latex When a cut is made on the trunks of certain trees, a. milky fluid called latex flows out. The rubber tree is grown in tropical coun-tries for its latex which is used to make natural rubber.

Fibres Plants such as jute, hemp and cotton are grown for their fibres which are used for making ropes and cloth.

Soil
Soil is very important in agriculture. It provides anchorage for plants. It also supplies water and mineral salts that are essential for their nutrition. Animals, including humans, depend on plants for food, and as such, indirectly depend on the soil.

Soil characteristics
Most sails are made up of a misture of sand silt and chay with varying amounts of humus

A sandy aoti has very little humus Since the particles in a sandy soll are large, it has a
oarse lesture wüh plenty of space between the particles Hence, it is well aerated but water dvains through it quiekly leaving it dry. It is not a good suil tor erop culivation

A clayey soil is made up of very fine parti-cles with very little space in between them. Asa result, it becomes easily water logged during the wet season and is poorly aerated, During the dry season, it hardens and cracks. It is also not a good soid for erop cultivation

Loamy soil contains a misture of sand and clay particles with plenty of humus. It has a good crumb structure which allows water to drain through it while holdi!男back just enough for plant growth It is well aerated and rich in plant nutrients. This is the best type of soil for crop cultivation

Soil Erosion
Brosion is the wearing away and removal of fertile topsoil from an area by the wind and water (during a heavy rainfal).

Plants cannot
grow on eroded land. Erosion is, therefore, a serious problem as it affects the economy of a country that depends on agriculture for sup-plying its needs Erosion is often due to bad farming prac-tices such as overgrazing of pastures, continual cropping without fallowing or adding fertiliz-ers, and exposing soil surfaces for long periods Farmers can prevent erosion by good farming practices.

This includes the following:
Growing fast-growing cover crops in be-tween slow-growing crop plants such as oil
palms. Cut grass and crop residue can be spread over bare ground to protect it. This
is known as mulching.
Contour ploughing or ploughing along the contour of the land to reduce water runoff.

Gaseous Exchange of Respiration and Respiratory Systems

Every time we breathe we take in life-supporting oxygen from the surrounding air. Oxygen is extremely important for life : we can survive for weeks without food and for days without water but only a few minutes without oxygen.

In our bodies oxygen is used to release energy stored in the chemical fuel we consume as food. This energy is vital for powering our life process. Broadly, the sequence of processes leading to the release of energy in living cell is called respiration. In most multicellular animals, it involves

*the intake and absorption of oxygen from the surrounding environment ;
*the transport of oxygen to the individual cell in the body and
*using oxygen to release energy as (ATP) from energy - rich substance via the kreb's cycle.

The above metabolic process which uses oxygen to release energy at ATP in living cell is known as cellular respiration, and has been discussed in chapter 11 in this chapter, we shall discuss the respiratory system that are concerned with the intake of oxygen and it entry into the circulatory system for distribution to the individual cell in the bodies of various organisms.

The same system also get rid of carbon dioxide and water, the waste products of cellular respiration in fact, the intake and absorption of oxygen Is automatically accompanied by the elimination of carbon dioxide and water in the surrounding. Thus, these respiratory system are also known as Gaseous exchange systems.

TYPES OF ANIMAL RESPIRATORY SYSTEMS
well - developed respiratory system are found in higher animals. Simple organisms, like monerans, protists, fungi and some multicellular animals and plant, do not have any particular respiratory system. The games simple diffuse through their cell or body surfaces.
The following are important Gaseous exchange or respiratory structures found in protists and animals : body surface, gills, trachea and lungs.

DIFFUSION AND RESPIRATORY STRUCTURE.
gases enter and leave the cell of an organism by diffusion. The gases, however must first be dissolved in water before they can diffuse across cell membrane. Hence respiratory structure must have Gaseous exchange surface that are bathed in water or Moist.

Respiratory structure must also have ways of increasing the rate of Gaseous diffusion to do this

*the Gaseous exchange surface must be large
*the barrier (I.e the membrane) across which the gases diffuse must be thin;
*there must be ventilation mechanisms to maintain a big difference in the concentration of the gas across the barrier (I.e maintain a steep diffusion gradient) and
* the Gaseous exchange surface must be closely linked to the transport system.

Note by removing and distributing the diffusing gas, the transport system would also help to maintain a steep diffusion gradient across the Gaseous exchange surface.

BODY SURFACE
unicellular organisms like amoeba, Gaseous exchange take place through the plasma membrane the size of such an organism is small to ensure the sufficient oxygen reaches all parts of the organisms to maintain its life processes. In amoeba, all parts of it protoplasm are within a distance of 0.5mm from the plasma membrane. Thus there is no necessity for a special respiratory structure.

MULTICELLULAR ANIMALS
multicellular animals can have larger body surface for Gaseous exchange than unicellular organisms. However, these organisms too cannot grow beyond a certain size since the body surface area does not increase as rapidly as body size or volume thus only few simple multicellular animals carry out Gaseous exchange thorough their body surface or skin without using specialized respiratory structures. Such animals are fairly inactive so that their energy requirement and as a result, their oxygen demands are low

GASEOUS EXCHANGE BODY SURFACE IN SOME SIMPLE ANIMALS
Sponge and coelenterates in these simple animals all their body cells are in direct contact with the surrounding aquatic medium Thus cell can get it own supply of oxygen

FLATWORM
in flatworm the body is extremely flattened and elongated in the free living planaria the body is 10mm long and only 0.6mm thick this is the body form

* increases the surface area to volume ratio and
*brings the innermost cells very close to the body surface.

It is therefore, possible for these worms to meet their oxygen requirements through diffusion over their body surface. In addition free living flatworms are found in well aerated flowing waters so that oxygen concentration in the water surrounding them is high.

Note parasitic flatworms are anaerobes as the oxygen concentration in their environment is very low.

ANNELIDS
In this more advanced worms, Gaseous exchange occur by diffusion over their body surface this is possible because

*their cylindrical shape give a high surface area to volume ratio so that the rate at which oxygen diffuse is sufficient to meet the worms requirements and

* the cell in their body surface (epidermis)  have rich supply of blood capillaries.

AMPHIBIANS
these more advanced group of animals live on land and water. They have lungs which are not properly developed to meet their oxygen demands. As a result many amphibians, like frog, obtain much of their oxygen through their Moist skin. This is known as cutaneous respiration. It is possible for the skin of a frog to carry out Gaseous exchange because the skin is

* richly supplied with blood capillaries and
*kept Moist by mucus secreted by glands.

AQUATIC RESPIRATORY STRUCTURE:

THE GILL Gill are specially respiratory organ used for absorbing dissolved oxygen from an aquatic medium. Basically they are outgrowth from the body which projects into the external environment.
They are very closely linked with circulatory system gills range from very simple form found in certain sea slugs to very complex ones, enclosed in chambers, found in bony fishes

SIMPLE GILLS
external gills are very simple respiratory structures just outgrowth of skin which projects into the water they are however
*highly branced and convoluted exposing a large Gaseous exchange surface to water and
*richly supplied with blood capillaries

External gills are found in certain sea Slugs and many fish and amphibians larvae water only circulate over the gills when these organisms move. Movement on the other hand is hampered by the highly branched gills

Definition of Microorganisms on earth and man as a cell

A Microorganisms also spelled micro-organism, micro organism or Microorganisms or microbe is a microscopic organisms that comprise either a single cell (unicellular)  cell cluster, or multicellular relatively complex organisms. They are indeed, organisms or forms of life requiring magnification with the aid of a microscopic to see and resolve their structures.

 Microorganisms are very diverse ;they include bacteria, fungi, algea, and protozoa ;microscopic plant (green algea) ; and animal such as rotifers and planarians. Some microbiologist also include viruses, but others consider these as nonliving. Most Microorganisms are unicellular (single-celled), but this is not universal, since some multicellular organisms are microscopic, while some unicellular proist and bacteria, like thiomargarita Namibiensis, are microscopic and visible to the naked eye.

Indeed, the word "microscoorganisms"  is general terms that becomes more understandable if it is divided into its principal types as previously mentioned which are predominantly unicellular microbes.  Viruses are also include, although they cannot live or reproduce on their own. They are particles, not cells, they consist of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), but no both. Viruses invade living cells- bacteria, algea, fungi, protozoa, plants, and animals(including humans) and use their host metabolic and genetic machinery to produce thousands of new virus particle. Some virus can transform normal cell to cancer cells. Rickettsias and chlamydiae are very small cell that can grow and multiply only inside other living cells.

 Although bacteria, actiomycetes, yeasts, and molds are cell that must be magnified in order to see them, when cultured on solid media that allow their growth and multiplication, they form visible colonies consisting of millions of cells.

The study of Microorganisms is called microbiology, a subject that began with Anton Van leeuwenhoeks's discovery of Microorganisms in 1675, using a microscopic of his own design. Microorganisms live in all parts of the biosphere where there is liquid water, including soil, hot springs, on ocean floor, high in the atmosphere and deep inside rock within the earth's crust.

Microorganisms are critical to nutrient recycling in ecosystem as they act as decomposers. As some Microorganisms can fix nitrogen, they are vital part of the nitrogen cycle and recent studies indicate that airborne microbes may play a role in precipitation and weather.

Microbes are also exploited by scientists in biotechnology, both in traditional food and beverage preparation, and in modern technologies based on genetic engineering however, pathogenic microbes are harmful, since they invade and grow within other organisims causing diseases that kills human, other animal and plant.

MICROBIAL EVOLUTION
single-celled Microorganisms were the first form of life to develop on earth, approximately 3-4 billion years ago so, for most of the history of life on earth the only form of life were Microorganisms. Fossil microbes have also been found in rocks 3.3 to 3.5billion years old since then, microorganisms have had the principal task of recycling organic matter In the environment. As such they are absolutely essential to the health of the earth. Without them, the earth would be a gigantic, permanent waste dump.

Microorganisms are responsible for recycling the huge masses or organic matter synthesized by plant as life on earth evolved. Furthermore, micro organism -  the cynabacteria or their DNA in the chloroplast of the plant cells - were the source of most of free oxygen in the early atmosphere. They also oxidize ammonia (the universal end product of protein metabolism)  to nitrate, which is the only nitrogen source used by plant and is therefore essential for production of our plant foods.

Microorganisms are also responsible for cellouse hydrolysis in the runmens (first stomach compartments)  of cattle, facilitating the production of animal protein for human consumption. And, in recent times, Microorganisms have been the source of antibiotics that have enabled the cure of numerous diseases.

Blue-green algea (cyanobacteria) are prokaryotes (that is their cell have no distinct nucleus). They are very independent nutritionally since they can carry out photosynthesis using chlorophyll. Thus they can synthesize sugars for energy from carbon dioxide using solar radiation. They also release oxygen. They can respire aerobically and can fix nitrogen, generating amino acid and protein. They require only water, nitrogen gas oxygen carbon dioxide, some minerals and sunlight. The evidence is that they were on earth 3.2billion years ago. The cyanobacteria are among the earliest Microorganisms and very important even today.

Green algea are eukaryotes (that is, their cells have a distinct nucleus). They evolved about one billion years ago. They contain chlorophylls a and b, which enables them to convert carbon dioxide, through radiation, to sugar and to polymerize sugar to starches, hemicelluloses, and cellulose some of our most important source of food energy.

Green algea are still major source of food in the oceans green algea were likely the life forms that evolved into plants which first lived primarily in the oceans but moved to the land about 450 million years ago about the same time as the amphibians and the first land animal evolved. It is believed that the first mammals evolved about 150 millions years later, along with insects and reptiles, which were dominant. Another 150million years later, dinosaurs and first birds evolved, along with the first flowering plants. During the entire period from, 3.6 billion years ago, microorganisms were consuming and recycling the organic matter from themselves and other forms of life as they lived and died.

For several billion years, bacteria, algea, and other Microorganisms serves food for other microbes and for higher animals as they evolved. When plant evolved in the oceans and then subsequently moved to land ; they become major sources of food for other forms of life, including Microorganisms, animals and eventually humans.

Most Microorganisms reproduce rapidly, but slow when the environment is cold and microbes such as bacteria can also freely exchange genes by conjuction, transformation and transduction between widely-divergent species. This horizontal gene transfer, coupled with a high mutation rate and many other means of gene variation, allows Microorganisms to swiftly evolve (Via natural selection) to survive on new environment and respond to environmental stresses. An example of this is the evolution of specialized nylon-eating bacteria, it's also been studied in experimental evolution. This rapid evolution is important in medicine, as it has led to the recent development of super-bugs—pathogenic bacteria that at resistant to morden antibiotics.