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LIFE AND LIVING

THE MICROSCOPIC WORLD OF LIVING THINGS

1. Micro-organisms

Micro-organisms (microbes) are very tiny one-celled/unicellular organisms. They are living organisms and too small to be seen with the naked eye. A microscope is needed in order to observe them.

They play an important role in the decomposition of dead plants and animals. They cause dead matter to decay and spoil.

Micro-organism ensure that essential chemical substances, needed by living organisms, are not used up but are recycled between living organisms.

There are three main types of micro-organisms namely: viruses, bacteria and fungi.

2. Structures

Viruses are smaller than fungi and can only be observed with a powerful electron microscope. They are not true cells and cannot reproduce on their own. They can only live and reproduce and multiply in living cells of other organisms. Humans become ill as a result of their cells being damaged. A virus causes diseases such as influenza, measles, the common cold, chicken pox, fever blisters and AIDS.

Bacteria are bigger than viruses, but still so small that approximately 100 000 of them will fit the full stop at the end of this sentence. Bacteria are found everywhere including on or in unsterilized food. Most of the many different bacteria are harmless to humans and play an important role in food webs – decomposition of dead organisms, re-utilisation of matter and enrichment of the soil. The relatively few bacteria that cause diseases in humans enter the human body cells and use these cells as a source of nutrients necessary for their growth and cell division while giving off poisons. Bacteria can be spherical (coccus), rod shaped (bacillus) or spiral shaped (spirillum)

Fungal cells are 10 to 100 times larger than those of bacterial cells. There are many types of fungi of different shapes and sizes.

Yeast is small unicellular fungus in the making of bread. Mould that grows on stale bread and overripe fruit is made of very thin threads. This gives the

mould a furry or woolly appearance. Mushrooms and toadstools are larger and grow in soil or in compost (humus).

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LIFE AND LIVING

THE MICROSCOPIC WORLD OF LIVING THINGS

3. Habitat

Microbes live in all parts of the biosphere where there is liquid water, including soil, hot springs, on the ocean floor, high in the atmosphere and deep inside rocks within the Earth's crust.

4. Reproduction

Microbes, like humans and other multicellular organisms, exhibit life processes such as reproduction, respiration etc.

After puberty, between the ages of 10 and18, humans are physically capable of reproducing.

Microbes replicate themselves and can multiply within minutes or seconds. For example the HI-virus in the blood of infected person can make thousands or millions of

replicas of itself in one day.

5. Diseases and drugs

A number of microbes cause human diseases. The body is constantly being invaded by microbes, particularly bacteria and viruses. They enter the body through the mouth and nose or through wounds. When harmful organisms penetrate one’s body they begin to reproduce immediately. They damage the body cells or give off poisonous chemicals known as toxins. After a number of cells have been damaged or a large quantity of toxins has built up, one

begins to feel ill.

The effects of microbes on one’s body are called symptoms. These microbes are called pathogens.

5.1 Classification of diseases

There are two main classes of disease

Infectious diseases. These are diseases that can be passed from one individual to another. These diseases can be caused by other organisms, such as microbes. They can be classified according to the way in which they are passed from one individual to

the other. Non - infectious diseases. They are not passed from another individual. They may have a

number of causes.

5.2 Some human diseases and their symptoms

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DiseaseMicrobes that

causes the disease Symptoms Duration of the diseaseDiphtheria bacteria Severe fever, can also

damage the heartA few weeks but damages the heart which remain damaged for life

Athletics’ foot Fungus Itchy and peeling skins Comes and goes for weeks on end at a time

AIDS virus All infections, cough easily Lifelong, sometimes leads to death as a result of pneumonia

5.3 Drugs

In pharmacology, a drug is "a chemical substance used in the treatment, cure, prevention, or diagnosis of disease or used to otherwise enhance physical or mental well-being.

Antibiotics are used to destroy other diseases causing bacteria or preventing them from reproducing.

5.3.1 Microbes can develop resistance to drugs

Harmful microbes in the body can be destroyed by white blood cells that are part of the body’s immune system. White blood cells can – absorb and then digest microbes; produce antibodies that attack microbes; destroy toxins manufactured by harmful microbes.

Beside the white cells producing antibodies, they also make “memory cells” which remain in the blood for many years.

Each type of antibody recognises only one type of harmful microbes and attacks only that microbe.

When the body is infected with a number of organisms, the immune system must manufacture a number of different antibodies to attack microbes.

Microbes change of their own accord, some of them developing resistance to the action of drugs so that they are not destroyed.

These microbes that develop resistance to the drugs live and reproduce quickly and develop as resistant harmful organism. Examples of microbes that resist to drugs are HIV Human Immunodeficiency); MDR-TB (Multi Drug Resistant); XDR – TB (Extensively Drug Resistant).

LIFE AND LIVING

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CELLS AS THE BASIC BUILDING BLOCKS OF LIVING ORGANISMS

1. Cells and Systems

Levels of organisation in organisms

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Just as walls of a building are built from many bricks, all living things (organisms) consist of minute of particles known as cells.

Some organisms are so small that they consist of one cell. Other organisms, such as humans, consist of billions of cells. Therefore a cell can be defined as a basic unit of life. Cells differ in structure depending on their function. Most cells are too small to be observed with the naked eye. Cells are however larger than atoms and molecules. Cells have the same basic structure, they differ in certain regards. Plant cell differ from animal cell and cells in the roots differ from those in the leaves. Groups of cells with similar structure and specific function are called tissues. Tissues cannot function individually and are grouped together to form organs. An organism can only function effectively if all the organs work together. In a multicellular organism, heart organs are grouped together according to their function

and form a system (digestive system) All systems together form an organism.

2. The light or compound microscope

In nature there are few types of cells that can be seen with the naked eye. These cells include the yolk of birds’ egg, frog’s egg and fish egg. Most cells are however too small to be seen without a microscope.

Consider the following diagram for the most important parts of the light microscope

2.1 Functions of the parts of a light microscope

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Eye piece or ocular Is the lens against which eyes is placed that enlarges the object observed, usually 10x.

Tube Holds the lenses of the eye piece at the correct working distance apart.

Coarse adjustment knob Moves the tube up and down to focus the object being observed.

Fine adjustment knob Used for the final focus to obtain clear image.

Arm Join the base and the platform to the tube and supports the adjustment screws.

Rotating nose piece Holds the objectives with low and high power on a rotating disc.

Objectives Lenses of the objectives help to enlarge image:- The shorter one gives a lower magnification x4.- The longer one give a higher magnification (10x

and 40x)Platform Supports the microscope slide over the opening which

transmits light from the mirror or electric source below.Condenser and diaphragm Controls the amount of light directed onto passing

through the object; focuses light rays from the mirror of light source onto the object.

Mirror or electric light source Reflects light upwards through the condenser towards the opening in the platform.

Base It is firm and supports the weight of the microscope

Magnification: If the magnifying power of the eye piece is 10x and that of the objective is 40x, then that total magnification of the object being viewed is 10 x 40; or 400x.

Microscope slide: Consist of a glass slide, the object (specimen) and a cover-slip.

3. The structure of cells

Most cells are too small to be observed, except with a microscope. Each cell has a special function. The structure of a cell depends on its function but all cells have certain similar parts. Cell membrane forms the outer covering of the cell. It controls substances entering and

leaving the cell. Cytoplasm is the living substance of the cell. Cell membrane forms part of the cytoplasm. All

other parts of the cell (organelles) are found in the cytoplasm. Cytoplasm is a sticky, jelly like fluid.

Nucleus is the organelle that controls the function of the cell. It is the largest organelle and can easily be observed through a microscope.

Vacuole is an organelle which contains cell sap and is surrounded by a membrane.

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4. Structure of a plant cell

Plant cells are usually larger than animal cells and consist of the following basic parts:

Cell wall – plant cell is surrounded by a cell wall. It consists of cellulose and is non-living, rigid and strong. The cell wall gives the plant cell its shape and provides strength and protection.

Cell membrane – the cell membrane is found on the inside of the cell wall. It encloses the cytoplasm and is living, thin and flexible. It controls all substances entering and leaving the cell.

Cytoplasm – it is found on the inside of the cell membrane. It is a jelly like and makes up most of the cell content. It contains a large vacuole and many organelles. The vacuole is surrounded by the tonoplast and the cavity is filled with cell sap. The cell sap consists of water, soluble nutrients, mineral salts and waste products. Important organelles found in green plant cells are chloroplasts which contain chlorophyll. Chloroplast is plastids that produce sugar and starch during the process of photosynthesis. Photosynthesis is a process in green plants in which chlorophyll converts the sunlight energy into chemical energy stored in food by using carbon dioxide and water. Oxygen is released during this process.

Nucleus – contains nucleoplasm and is surrounded by a nuclear membrane. It controls the vital functions and processes of the cell. It also plays a role in hereditary.

5. Structure of an animal cell

Animal cell have no cell walls and therefore and therefore have no particular shape.

Cell membrane – the cell membrane is found on the inside of the cell wall. It encloses the cytoplasm and is living, thin and flexible. It controls all substances entering and leaving the cell.

Cytoplasm – as in plant cells, organelles are also found in animal cells but no plastids, such as chloroplast.

Nucleus – contains nucleoplasm and is surrounded by a nuclear membrane. It controls the vital functions and processes of the cell. It also plays a role in hereditary.

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LIFE AND LIVING

LIFE PROCESSES AND SYSTEMS

LIFE PROCESSES OF THE HUMAN BODY

1. Parts and systems

The human body consists of numerous small parts that work together. The work of each part is called its function. The smallest part of the human body id called the cell. Cells with similar function work together in groups called tissues.

Groups of tissues form parts of the body called organs.

Organs work together to form systems.

2. Organ systems of the human body

Some important organ systems of the human body are represented in the diagrams.

The digestive system: the mouth, oesophagus and intestines are digestive system. The respiratory system: the windpipe or trachea, the lungs and the diaphragm are

respiratory organs. The reproductive system: the penis and testicles (in males) and the vagina and uterus (in

females) are reproductive organs. The nervous system: the brain, spinal cord and sensory organs are organs of the nervous

system. The locomotory system: the bones and muscles are organs of the movement. The circulatory system: the heart, blood vessels and circulatory organs.

These are not the only systems in the body, there are also others.

3. Life processes

Each organ system is responsible for a function called a life process. It is the process such as nutrition, respiration, excretion, reproduction, growth, irritability

and movement that sustain life. Nutrition is the process used to obtain nutrients for growth and for energy to sustain other life

process. The digestive system has the nutrition function. Respiration is the process used to produce energy for the body. Energy is produced in the

cells from nutrients and oxygen. The nutrients are obtained from the digestive system and the oxygen from the respiratory system. When the cells use nutrients to produce energy and for growth, waste products are produced that cannot be used. The body get rid of waste products through a process called excretion.

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Reproduction is the process by which babies are produced. For a baby to be produced, a sperm cell from the male testicles must unite with an egg cell from the female ovaries. They make a new cell, called a zygote, which grows in the uterus to form a baby.

The nervous system controls other systems. There are sensory organs in all parts of the body that are connected to the spinal cord and the brain by the nerves. The spinal cord and the brain can control the life processes in this way. Sensory organs such as the eyes and ears send information to the brain regarding activities outside the body.

Movement is the process that is essential for life. In the human body the bones and joints form the skeleton that gives shape to the body and makes movement possible. Muscles provide the force that moves the bones and other parts of the body.

NUTRITION DIGESTION

1. Nutrition

All living things require nutrients to sustain their bodies. Green plants can produce their own food but animals must obtain their own food from other

sources. Animals eat plants or meat of other animals. Nutrition can be defined as the processes by which living organism take in food and use

it for energy, growth and repair.

1.1 Why we require nutrients

We need food to live. Without food our cells will stop functioning and we will die. We require nutrients for:

Growth

Nutrients supply the building blocks for the production of cells and tissues.

Energy

Food is the source of fuel.

Health

Our cells require a variety of nutrients to remain healthy. If we do not eat certain nutrients we can become ill due to lack of these nutrients.

Repair and replacement of worn and damaged cells

Nutrients are required to replace dead cells (for example cells in the skin that are worn) and for the healing of wounds.

Basic nutrient requirements

The small particles that are digested and are used up by cells are called nutrients. Nutrients are chemical compounds that feed the body. Humans require the following nutrients to stay alive:

Nutrient Function SourceProteins The building block for growth

and repairMeat, fish, butter, eggs, beans, dairy products.

Carbohydrates The source of instant energy Sugar and starch, food such as potatoes, rice, maize, meal, bread, pasta, cereals, and certain fruits and vegetables

Fats The reserve source of energy Oils, nuts, butter, certain meat

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and the body’s insulation against the cold

and dairy products

Vitamins Ensure normal growth and development. Keeps your body healthy, important for healthy skin, bones and gums, helps fight infection

Mostly in fresh fruit and vegetables, also in dairy products, whole wheat, meat, fish and eggs

Minerals Ensures normal growth and development. Iron is good for the blood; calcium build strong bones and teeth; magnesium is good for your nerves.

Fresh fruit, vegetables, dairy products, meat and eggs

Water Is the main ingredient of the living body and supplies a fluid medium in which metabolic processes can take place

Drinking water, fruit, drinks and food

Fibre Prevents constipation and certain types of cancers

Cereals, fruit and vegetables

2. Digestion

Digestion is the breaking down of organic food compounds (proteins, fats and carbohydrates) to their simplest forms to be used by the cells. It is the process that changes insoluble food substances to soluble substances.

2.1 Why food must be digested

The most food that people eat consists of very large molecules. These molecules are so large that they cannot enter the bloodstream or cells directly. The cells cannot break down the carbohydrates and fats directly to obtain energy and

they can also not use proteins for growth. These three organic compounds must first be broken down to simplest form.

2.2 What do cells require

Digestion is similar to breaking down a house brick by brick. Bricks are the simplest building materials or building blocks of the house. Proteins are broken down (digested) in a similar way into their simplest and simplest

chemical units, glycerol and fatty acids and carbohydrates must be broken down to simplest sugars.

Building blocks can be taken to another place to build another type of house. Our cells can use the simplest building blocks that have been digested to build new

organic compounds that are required by cells.

Digestion breaks down organic compounds to their simplest building blocks

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2.3 How does digestion take place?

Animals require special mechanism to break down and digest food substances to the smallest possible particle.

This is done in two ways:

Mechanical digestion

Special organs chew, tear, stir, push, mix and grind the food, e.g. the teeth tear, chew and grind the food while the stomach stirs grinds and mixes it.

Chemical digestion

The ground food is broken down further to smaller units by special chemicals called digestive enzymes. These enzymes break down the food substances and change it to liquid form.

Mechanical digestion – food substance Chemical digestion – food substancesare broken down to smaller particles are broken further to smaller units

3. The human digestive system

Your body has a specialised system in which digestion takes place, the digestive system.

The human digestive system consist of two main groups of organs, the alimentary canal and its accessories organs (saliva, glands and teeth).

The alimentary canal is a long, hollow tube through which food passes. It has two openings to the outside: the mouth at the one end and the anus at the other

end.

The following organs form part of the alimentary canal:

(1) The mouth; (2) the oesophagus; (3) the stomach; (4) the small intestines; (5) the large intestines.The accessory organs help with the process of digestion include the teeth, the tongue, the salivary glands, the liver and the pancreas. The teeth and tongue help with mechanical digestion. The glands (namely, the liver and the pancreas) produce and store chemicals (enzymes) that chemically break down the food substances. The different components of the human digestive system are indicated in the following figure.

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3.1 The alimentary canal

3.1.1 The mouth cavity

The opening of the alimentary canal to the outside, namely the mouth, is closed by two lips. The lips prevent food from falling from the mouth. In the mouth cavity the teeth and tongue play an important role in digestion, while the salivary glands are connected to the mouth cavity by ducts.

3.1.2 The teeth

Different types of teeth are found in dental cavities in the upper-and lower jaws. In humans (as in most mammals) two sets are found, namely a milk set (temporary set) and a permanent set. The milk set consist of 20 teeth and the permanent set consists of 32 teeth. To distinguish the teeth they are indicated in the form of a formula, the so called dental formula.

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