RECOGNIZING LIVING THINGS

 

Levels of Organization of Life

The bodies of living things are highly organized. This organization occurs in levels, with the simplest structure occurring at the lowest levels (single cells) which interact to build up more complex structures (multicellular organisms).

The basic levels of organization of life in organisms are; cells, tissues, organs and systems.

(i) Cell: This is the smallest unit of living organism. It is the first and simplest level of organization of life. Plants and animals are made up of cells. One celled organisms are called unicellular organisms. They include Amoeba, Plasmodium, Euglena, Paramecium, etc. Organisms made up of many cells are called multicellular organisms e.g man, mango, trees etc. The single celled organism can carry out all life processes on its own.

(ii) Tissues: This is a group of similar cells which come together to perform a particular function. A tissue consists of two or more different types of cells aggregating together to perform a specific function e.g. the mesophyll layer in leaves, xylem tissue in stems, muscles, blood (a liquid tissue) etc. Organisms which exist at the tissue level include the hydra, jellyfish, sponge etc.

(iii) Organ: Is a group of similar tissues which come together to perform a specific function. Examples in plants are flowers, roots, leaves, seeds, a rhizome, a corm, an onion bulb, a tuber, etc. Examples in animals are the skin, stomach, heart, brain, liver, eyes, ears, kidney, etc.

(iv) System: This is a group of functionally related organs which work together to perform specific functions. Examples in plants include the shoot system and root system. Examples in animals include the digestive, nervous, excretory and circulatory systems. Examples in plants are the transport system, shoot and root system.

 

Complex Multicellular Organisms

The climax of organization in higher living things is the aggregation of systems to form an organism. Complex multicellular organisms are composed of several organ systems which work harmoniously for the benefit of the organism. All animals from Platyhelminthes to Mammals, and all vascular plants are organized on this level.

Complexity of Organization In Higher Animals

As organisms acquire more layers of cells, they become complex in structure, thus there is an increase in complexity from unicellular to multicellular organism.

Advantages of Complexity

1. It leads to cellular differentiation; thus, groups of similar cells are differentiated to form tissues which carry out similar functions
2. It leads to internal structural specialization in which the tissues become specialized to carry out specific functions.
3. There is mutual interdependence between component cells i.e division of labour among the cells.
4. Complexity makes higher organisms to be more efficient in carrying out life processes.
5. Complexity leads to an increase in the size of organisms.
6. It makes it possible for organisms to become more resistant to adverse conditions within the environment.

 

Disadvantages of Complexity

1. The cells lose their independence and become increasingly dependent on one another’s activities.
2. Difficulties in acquisition of materials (such as oxygen and food materials) and removal of waste products by the millions of cells making up a multicellular organism
3. Slower rate of diffusion of oxygen or respiratory gas to individual cells.
4. Slower rate of expulsion of waste products from cells.
5. Decrease in ability to regenerate
6. Difficulties in reproduction.

 

VIRUS

A virus is a microscopic organism which cannot be seen by an ordinary microscope but with an electron microscope Virus does not have a cell structure but is just made up of a cell structure strand of nucleic acid enclosed within a protein coast.

CHARACTERISTICS OF VIRUS

1. Virus is microscopic in nature.
2. It possesses either RNA or DNA.

iii. It cannot reproduce by binary fission.

1. It does not have structures used in the synthesis of protein as in non-living.
2. It does not respire, feed, excrete etc.
3. It is responsible for the causes of many chronic diseases like AIDS, smallpox, influence, measles etc.

VIRUS AS A LIVING (ANIMATE) THING

Virus is often regarded as a living or animate thing because of the following reasons:

1. Virus can reproduce when present in another living cell.
2. It possesses characteristics which can be transmitted from one generation to the next.

VIRUS AS A NON-LIVING (INANIMATE) THING

A virus is often regarded as a non-living (inanimate) thing because of the following reasons:

1. When virus is extracted from a living cell and placed in a non-living medium, it ensures a crystalline form and this becomes non-living.

ii Virus cannot respire, excrete or respond to stimuli.

EUGLENA

Euglena is a protist and atypical example of an organism sharing both the characteristics of plants and animals. However, it is a microscopic, unicellular and aquatic organism.

 

Animal Characteristics of Euglena

Characteristics of Euglena which makes itan animal include:

1. Possession of flagellum used for movement
2. Possession of gullet for passage of food and as reservoir

iii. Possession of contractile vacuole used for excretion

1. Presence of eye spot to enable it to respond to light
2. Possession of pellicle which make its body flexible
3. The presence of myomeres which do aid movement 

Plant Characteristics of Euglena

1. Possession of chloroplast enables it to carry out photosynthesis
2. Possession of pyrenoids where starch is stored

iii. The presence of paramylumgramules forms in which starch is stored.

1. It has holophytic (atrophic) mode of nutrition.

 

CLASSIFICATION OF LIVING THING

Classification of living things consists of placing together in categories to nose living things that resemble each other. It involves placing living things into groups that have certain features in common which distinguish them from other groups.

Note phylum is used for animals, division is used for plants.

 

Kingdom

Phylum (Animal) or division(plant)

Class

Order

Family

Genus

Species

Major group in biological classification using human and dog 

	HUMAN	DOG
Kingdom	Animalia	Animalia
Phylum or Division	Vertebrata	Vertebrata
Class	Mammalia	Mammalia
Order	Primatas	Carnivora
Family	Hominidae	Canidae
Genius	Homo	Canis
Species	H.Sapiens	C. parniliaris

 

Major group of living things

Kingdom Phylum (Pl-phyla) Division

Animalia Porifera (sponge)

Platyhelminthes

Nematode

Annelida

Mollusca

Echinodermata

Arthropoda

Chordata

Thallophyte (Red, brown, green, algae)

Plantae Bryophyta (liver wort& Moses)

Tracheophyte (vascular plant)

Fungi

Protista Protozoa

Euglenophyta

Pyrrophyta

Cryophyte

 

VERTEBRATA

The vertebrata is a sub-phylum of the phylum chordate. Vertebrates are characterized by the presence of a backbone or vertebra columns. They are divided into five classes.

These are:

(i) Pisces (fishes)

(ii) Amphibia (Amphibians)

(iii) Reptilia (Reptiles)

(iv) Aves (Birds) 

(v) Mammalia (Mammals)

ORGANISATION OF LIFE

There are four levels of organization of life in organisms. 

CELLS

The cell is defined as the smallest unit of living organism. It is the first level of organization life. All plants and animals are made up of cells. Some of these plants and animals are made of only one cell hence they are called unicellular organisms while others are made up of many cells and are therefore called multicellular organisms. Examples of unicellular organisms are Amoeba, Euglena, Paramecium, Plasmodium, Trypanosome, Chlamydomonas. Examples of multicellular are flowering plant, man, etc.

TISSUES

A tissue is a group of similar cells forming layer in an organism which performs a particular function. In other words, a tissue consists of two or more different types of cells aggregating together to perform a specific function. Examples of tissues in higher plants are mesophyll layer in leaves. epidermal tissue. Sclerenchyma tissue, xylem tissue, parenchyma tissues in stem. Examples of tissues in higher animals include muscle, bone, cartilages and blood (a liquid tissue). Examples of organismswhich exist at the tissue level of organization life are Hydra, Algae, sponges and fungi.

ORGANS

An organ is a group of similar tissues forming a layer in an organism which performs aspheric function. Examples of organs in plants are leaves, flowers, roots, stems, seeds etc. Examples of organs in animals are the lungs, liver, brain, kidneys, heart, ear, and eye which perform specific functions.  Examples of plants are roots, stems, leaves, flowers, fruits and seeds, bulbs e.g. (onion) 

SYSTEMS

A system is a group of similar organs which work together to perform specific functions. Examples of systems in plant are the shoot system and root system. Examples of systems in animals are digestive, reproductive, respiratory, skeletal, nervous, excretory and circulatory systems. These systems work together to make up an organism. For an organism to perform well, all the cells, tissues, organs and systems must also function normally.

FUNCTION OF SOME HUMAN ORGANS AND SYSTM

NAME	TYPES OF STRUCTURE	MAIN FUNCTIONS
Lung	organ	Exchange of gases containing O, CO2, etc. between the body and the atmosphere
Skin	Organ	Protection, support, irritability body temperature regulation.
Spinal Cord	Organ	Reception and interpretation of response to stimuli.
Digestion system	Organ	Injection, digestion, absorption and egestion
Reproduction system	Organ	Production of offspring

 

THE COMPLEXITY OF MULTICELLULAR ORGANISMS HAS ADVANTAGES AND DISADVANTAGES 

Advantages of Complex Organisation

1. There is division of labour because of presence of specialised organs and systems.
2. Increase in size and complexity to a very great extent.

iii. Specialised organs and system enable them to live and survive in different habitants

1. Efficiency is increases and maintained in the functioning of the organism, because various processes are performed by different organs or system.

Disadvantages of Complex Organisation

1. An efficient system is necessary
2. If an organ/system is damaged/does not function properly, the other organs and systems might not function properly/might be damaged as well.

iii. Some organisms cannot function well if the coordination is poor or impaired.

1. If there is any defect in a system the organism may be endangered.

 

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