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Lesson Note

Subject: Biology
Topic: Recognising Living Things
Lesson Objectives: At the end of the lesson, learners should be able to:
i. State the characteristics of living things,
ii. Give examples of levels of organisation,
iii. State the complexity of organisation in higher organisms.


Biology And Living Things

Biology And Inquiring: Human beings have always been so curious to know more about the existence of things around them especially those which have to do with the ones that have life, hence the study of Biology.

Definition And Branches Of Biology

The term “biology” is coined from two Greek words – bios meaning life and logos meaning to study. Hence, biology can simply be defined as the study of life. In other words, it is defined as the study of plants and animals.

Branches Of Biology

Biology is basically grouped into two main branches. These are:
i. Zoology: The study of animals.
ii. Botany: The study of plants.
iii. Ecology: The study of plants and animals (living things) in relation to their environment.
iv. Morphology: The study of external features of plants and animals.
v. Anatomy: This is the study of internal structures of plants and animals.
vi. Genetics: This is the scientific study of heredity and variation in living things.
vii. Physiology: This is the study of how plants and animals function.

Definition And Usefulness Of Science

Science is defined as the systematic process of making enquiry about the living and non-living things in our environment.

Usefulness Of Science

Science has been put into many good uses for the benefit of man. The usefulness of science finds application in:
i. Medicine: Science has contributed greatly to the manufacture of vaccine and drugs that are used today to cure various diseases of man.
ii. Manufacturing Industries: Various raw materials have been combined to manufacture many finished products commonly used by man.
iii. Construction: Roads, railways, airports etc have neem designed and constructed as a result of the knowledge derived from science.
iv. Engineering: Ship building, skyscrapers, bridges, roads, etc have beem designed and constructed due to the knowledge acquired from science.
v. Agriculture: New breeds of animals and varieties of crops including fertilizers have been developed and these have helped to increase food production.
vi. Technology: Science has helped in the development of computers that have enhanced the efficiency of mankind in their activities.
vii. Communication: Televisions, telephone, telex, fax machines, etc have been developed with the aid of science which now makes communication among countries to be possible.

Processes Or Methods Of Science Or Scientific Approach

The processes or methods of science involves the sequence of making enquiries about an object or thing under study in science. Students of science have to learn to lake clear, systematic and accurate accounts of their scientific investigations.
Scientific methods of science therefore take the following procedures:
i. Observation
ii. Classification
iii. Inference
iv. Measurement
v. Identification
vi. Hypothesis
vii. Experiment
viii. Control or concluded
ix. Theory or law.

The starting point of scientific method is observation which involves the use of the senses to describe what one has seen or felt about an object. The observation then leads to the classification, then to inference and later to measurement and identification of the existing problems. After that, the scientist now forms hypothesis or a tentative answer. The hypothesis is now tested by an experiment. In reporting an experiment, it is very important to use or follow the patterns laid down by scientists. These patterns include:
i. Aim: This is to state the purpose of the experiment.
ii. Apparatus: This stands for the materials that will be used in the experiment.
iii. Method: This is to describe in detail, the procedures that are required or the step-by-step of the experiment.
iv. Observation: This records what one had seen during and after the experiment has been set up.
v. Conclusion: This is to draw conclusions on the outcome of the whole experiment has been set up.
Note: In performing an experiment, a scientist or science student needs to take note of control experiment. In control experiment, the scientist makes sure that during the experiment, the organism or object being observed is not deprived of the particular factor being investigated.
The end of the experiment can then be used to show whether the hypothesis is true or false. If the subsequent experiments show that the hypothesis is false, the whole idea or concept of the matter under investigation is then repeated or at worst discarded. But when the hypothesis has been tested and found to be repeatedly correct within the limits of available evidence, the concept becomes a theory. If a theory has been extensively tested and proven to be true, it becomes a law.

Living And Non-living Things

Everything on earth can be classified either as living or non-living things. Living things include plants and animals that have life, while Non-living things include those things that do not have life. Examples of living things include man, rabbit, hibiscus, elephant, monkey, grass, mango tree, sheep etc while Non-living things include air, stone, water, table, house, book, etc.

Characteristics Of Living Things

Living things are distinguished from non-living things by a number of characteristics which include:
i. Movement or Locomotion: Movement is defined as the ability of an organism to move its own whole body or part of its body from one place to another.
Reasons for movement especially for animals from one place to another including:
a. To search for food
b. To escape from predators
c. To find mates for reproduction.
d. To disperse or reduce competition or overcrowding by moving to new location
e. To avoid danger
Generally, plants can only move parts of their bodies in response to external stimuli.
ii. Nutrition or Feeding: Nutrition is the process involved in obtaining or manufacturing food and utilizing it for growth and maintenance or carry-out life processes like growth, respiration and reproduction. While all green plants can manufacture their own food through the process of photosynthesis (i.e autotrophs or holophytic nutrition) all animals cannot manufacture their own food; hence the type of nutrition is called heterotrophic or holozoic nutrition.
iii. Excretion: Excretion is defined as the removal or getting rid of waste products of cell metabolism from the body. The purpose of excretion is to remove waste products of metabolism e.g water carbon dioxide, etc which are poisonous or toxic to the body if allowed to accumulate. The involvement of getting rid of these poisonous metabolic waste products from the body is called excretion.
iv. Irritability or sensitivity: Irritability is defined as the respond or reactive of organisms towards changes in the environment. Living things exhibit sensitivity in order to enable them survive in their environment. Stimuli include heat, light, pain, water, sound, chemical substance etc which living things respond to.
v. Respiration: Respiration is defined as the breakdown or burning of food substances by aerobic (using oxygen) or anaerobic (i.e without oxygen) respiration, to release energy needed for all process of life.
vi. Growth: Growth is defined as an irreversible or permanent increase in size, dry mass or weight of an organism due to the addition of living photoplasmic materials. The purpose of growth is to enable organisms to repair or replace damaged or old tissues in their bodies. The food eaten provides the basis for growth of organisms. This will lead to complexity and maturation.
vii. Reproduction: Reproduction is defined as the ability of a living organism to give birth to young ones or offspring or individuals of their own kind. The purpose of reproduction is to ensure continuity of life, i.e, it enables life to be passed on from one generation to the next. Reproduction occurs in two forms:
a. Asexual reproduction: This involves only one organism to produce another offspring.
b. Sexual reproduction: This involves two organisms coming together for the purpose of reproduction.
viii. Adaptation: Adaptation is the ability of living organisms to adjust to changes in their various environments in such a manner that they would be comfortable.
ix. Life span/death: All living things must die because they have a definite and limited period of existence. All living things must pass through these five stages of life namely;
Birth – Growth – Maturity – Decline (old age) – Death
x. Competition: This is the ability of living things to struggle for all the necessities of life in order to survive and be in continuous existence.

In summary, all living things carry out all the above characteristics processes, while non-living things cannot.

Organisation Of Life

All living things are highly organised. This organisation occurs in levels. The simplest structures are found at the lowest levels and they interact to build up more complex structures at the next level and so on.

Levels Of Organisation Of Life

There are four levels of organisation of life in organisms. These are the cells, tissues, organs and systems. The simplest of all these levels is the cell.

Cells (First Level)

The cell is defined as the smallest unit of living organism. It is the first level of organisation of life. All plants and animals are made of only one cell hence they are unicellular organism 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. These organisms have only one cell each and are capable of carrying our all life processes such as movement, respiration and reproduction. Examples of cells in higher plants are phloem cells, xylem vessels, while examples of cells in higher animals are rod and cone cells in the eyes, ova or eggs, spermatozoa cells, nerve cells, red blood cells, white blood cells and epidermis cells.

Tissues (Second level)

A tissue is a group of similar cells forming a layer in an organism which performs a particular function. In other words, a tissue consist 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 muscles, bone, cartilages and blood (a liquid tissue). Examples of organisms which exist at the tissue level of organism of life are Hydra, Algae, sponges and fungi.

Organs (Third Level)

An organ is a group of similar tissues forming a layer in an organism which performs a specific function. Examples of organs in plants are leaves, flowers, roots, stems and seeds. Examples of organs in animals are skin, eyes, ears, stomach, brain, kidney, liver and heart. These organs are known to perform specific functions in the body.

Systems (Fourth Level)

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.
Complexity of Organisation in Higher Organisms
There is an increase in complexity from unicellular organisms to multicellular organisms. Even though unicellular organisms can perform all life processes, they still lack vital tissues, organs or systems that is efficient and capable of ensuring their survival. As a result of this, higher organisms have advantages and some disadvantages in complexity over the unicellular organisms.

Advantages Of Complexity In Higher Organisms

i. It leads to cellular differentiation: As a result of complexity, group of similar cells are differentiated to form tissues that carry out similar functions.
ii. It leads to internal structural specialisation: Differentiation: Differentiation leads to internal structural specialisation in which the group of similar cells or tissues become specialised to carry out one or more functions.
iii. Mutual interdependence between component cells: There is always mutual interdependence between component cells. In other words, there is division of labour among the component cells.
iv. Complexity leads to efficiency: Complexity makes higher organism to be efficient in carrying out life processes.
v. Complexity leads to increase in size: Complexity leads to increase in size of organisms because there are spaces between cells for growth.

Disadvantages Of Complexity In Higher Organisms

i. Inability to individual cells to exist on their own: In complexity, cells lose their independence and become increasingly dependent on one another’s activities.
ii. Difficulties in acquisition of oxygen and food materials: Increased size creates difficulties in acquisition of respiratory gas (oxygen), food materials and loss of waste products.
iii. It leads to slower rate of diffusion: Complexity leads to slower rate of diffusion of oxygen or respiratory gas to individual cells.
iv. Slower rate of expansion of waste products: Complexity leads to slower rate of expulsion of waste products from cells.
v. Difficulties in reproduction: Complexity also leads to difficulties in reproduction in higher organisms.

Done studying? See Previous Lessons in Biology

Take a quick test for this lesson
i. What is science?
ii. Define biology
iii. List the stages involved in scientific methods
iv. List five usefulness of science to man
v. Briefly explain the characteristics of living things.
vi. State six differences between plants and animals
vii. State the levels of organisation of life and give three examples for each of the levels.

Questions answered correctly? Kudos!!
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