LEVELS OF ORGANISATIONS Summarized Biology Notes

This should take you about 2 hours to learn, you should not worry if it takes you longer than expected as we all learn at a different pace

In our previous post we looked at the basic structures of both animal and plant cells, here is the link to our previous post if you missed it. In today's post we will look at the levels of organisations closely, you'll see that most cells have variations of this basic structure that help them carry out their functions, you'll also learn how the structure of different cells relates to their functions, we'll also look at how groups of different types of cells are grouped together to produce a larger structure that have a more specialised function and how several of this structures form a even larger system. All systems in one animal or plant function as a whole within the organism itself, this levels increasing system are called levels of organisations hence the title, there are five levels of organisations in biology 1) Cells, 2) Tissues, 3) Organs, and 4) Organ Systems, 5) Organism, we'll look at each level closely

1) CELLS

Cells are the basic structural units of all living things, our bodies are composed with trillions of cells, this cells provide structure for the body, take in nutrients from food, convert those nutrients into energy and carry out specialised functions, cells also contain the body's hereditary Material and can make copies of themselves. Cells have many parts each with a different function, some of this parts called organelles are specialised to perform certain tasks, please refer to the previous post as we talked of cells there

2) TISSUES

When a group of similar cells work together in order to carry out a particular function we call this a tissue, in exam you should define (a tissue as a group of similar cells working together to carry out a particular function) it's almost similar but this is more accurate. Both animals and plants are made up of many different types of cells, these cells have different functions, in a living organism many cells with the same function are usually found together in a group for example, in a plant lot's of very small palisade cells lie side by side in a leaf, here their function is to make food by the process photosynthesis therefore chloroplasts are needed. In a human, lot's of muscle cells are grouped closely together in the biceps muscle in your arm, a group of cells like this made up of similar cells that perform the same function is called a tissue. Down we'll look closer at both plant and animal tissues.

Plant Tissues

Plants have many specialised cells Examples are ( Root hair cells, Xylem vessels, epidermis) for carrying out specific functions:

• Palisade tissues are specialised to make food by photosynthesis

• Root hair cells have a structure that enables them to absorb water and mineral salts from the soil

• Xylem vessels are special cells that run continuously from the roots to the leaves they transport water and salts from the roots up the stem to the leaves and flowers

• Ploem tubes transport food produced by photosynthesis from the leaves to the stem and the roots

• Epidermis lines and protects the leaf surface, and reduces loss of water 

A) Root Hair Cells

A Root hair cell is a very thin, delicate cell that grows out of the side of the root in the soil. Have you ever tried pulling a weed out of a lawn? It is difficult isn't it? this is due to the microscopic root hair cells in every root found near the tip, the image below shows a section through a root tip showing root hairs

Functions Of Root Hair Cells

- The two main functions of the root hair cells are:

• To increase the surface area for the intake of water

• To absorb water and inorganic salts, for example nitrates and phosphates in the form of ions from the soil, an ion is the form in which inorganic salts are absorbed from the soil by plants.

Down is an image of a section through a root hair cell, you can clearly see on the image how the cell is specialised to form part of the outer covering of the root, it also has a long, thin extension growing out into the soil which gives it a large surface area for the absorption of water and inorganic salts.

B) Xylem Vessels

A Xylem vessel is a structure made up of many Xylem cells arranged end to end, the cells are dead and hollow but very strong and they transport water and mineral salts up the plants. A Xylem vessel is made up of many dead, hollow cells arranged end to end hence their definition, they have no end walls or a cytoplasm, their walls are impregnated with a strong substance called lignin this lignin gives the Xylem vessel strength to support the plant, Xylem vessels run from roots to the leaves, they contain a continuous Collum of water in which inorganic salts are dissolved.

Functions Of Xylem Vessels

Just like root hair cells, Xylem vessels have two main functions, they are:

• Transport water and inorganic salts

• Support the plant, with the help of lignin

Above is a transverse section (cut across) image of a stem, it shows how the Xylem vessels fit together like a mass of tubes for transporting water with other living cells.

Below is a longitudinal section (cut along) image along the length of the Xylem vessels, it will help you know how the Xylem vessels are interspersed

C) Epidermis

The epidermis is a thin outer layer of cells that cover the stems, leaves and root. The epidermal cells secrete a waxy substance called cutin which forms the cuticle this cuticle covers the cell walls.

Function Of Epidermis

• Protects the plant from drying out

• Stop the entry of disease causing organisms 

Below is an image/figure which shows some epidermal tissue from a plant, seen with a light microscope

Animal Tissues

Animals have tissues too, examples are ( Epithelium Tissues, Nerve Tissues, Muscle Tissues )

A) Epithelium Tissues

Epithelial tissue is arranged in layers and covers surfaces both inside and outside an animal's body, One type of Epithelium lines the ducts of the salivary gland and the collecting ducts of the kidney, another type of Epithelium lines the breathing tubes, this Epithelium has numerous tiny projections called Cilia which move from side to side and transport mucus along the respiratory passages

Functions Of Epithelial Tissues 

• Protect the body and organs from injury 

• Stop the entry of disease-causing bacteria and viruses 

The Below image shows an epithelial tissue seen under a light microscope

B) Nerve Tissues

A nerve tissue is made of hundreds of nerve cells that are specialised to conduct impulses over long distances in the human body it can go from your big toe to your spine

Functions Of Nerve Tissues

• Conducts/transmit impulses through the body

The figure below will help you see how a nerve cell is adapted for this purpose, by having A very long fibre called an axon, and the myelin sheath which insulates the axon and speeds up the conduction of nerve impulses

C) Muscle Tissues

Make a fist with your hand and bend your arm at your elbow, as demonstrated in the in the image below 

You can feel the muscle in your upper arm bulging, this is the biceps muscle, did you notice how film your muscles became when you raised your hand to the shoulder? The whole is made up of many similar cells that have a striped appearance, when a muscle cell contacts it gets shorter because protein molecules in the cell slide past each other, this has an effect of shortening the muscle and developing a very strong force

Functions Of Muscle Tissues

• Help you lift up heavy weights

• Contracts to move the body (walking, running..)

• Helps you defend yourself

The are many different types of muscle cells in the body but they all perform the same function of contraction that is they have the ability to shorten in length. The following figures will help you see the structures of muscle as seen in transverse and longitudinal section

Transverse Section

Longitudinal Section

D) Red Blood Cells (also tissues)

Do you remember we discussed earlier that Xylem vessels are made up of cells that are dead? In a way are red blood cells are similar, they have a cell membrane and cytoplasm but no nucleus, red blood cells are very small cells that have a strange shape when seen in a cross-section, they have depressions on two surfaces and are described as being biconcave, because the are very small and flexible they are able to move out from the capillaries (small blood vessels) to surround most cells of the body.

Below is a side view of a red blood cell

A surface view of the red blood cell 

Functions Of Red Blood Cells

• To transport oxygen from the lungs to all parts of the body

Red blood cells are packed full of protein called haemoglobin that I of red colour, this haemoglobin is able to take up oxygen where oxygen concentration is high and to release oxygen where the is a low concentration of oxygen we say high concentration of carbon dioxide

E) Ciliated Cells (also tissues)

This are the cells that line in the tubes of respiratory inside the lungs which are covered in special tissues made of Ciliated cells, that's why it's called Ciliated cells instead of tissues. These cells are also found lining the oviduct and in the lining of the trachea (windpipe). Ciliated cells have tiny thread like extensiona called Cilia, the Cilia move rythmically in a wave like motion and move material from one place to another, For example in the breathing passages mucus traps dust particles and Cilia sweep them towards the throat away from the lungs. In the oviduct an ovum is moved towards the uterus

Below is a figure of Ciliated Cells

3) ORGANS

A group of cells with similar structure and function such as a tissue will carry out one or two jobs efficiently, in more complex organisms like human beings and flowering plants more complicated functions depend upon groups of tissues functioning together as an organ, for example in humans the heart, kidney, eye and brain are all organs. In flowering plants the leaf, root and stem are the organs in addition to the palisade cells that you have studied already there are other plant tissue types such as epidermial cells, Xylem vessels, phloem tubes, spongy mesophyll cells and guard cells, all these cells function together to allow the plant to manufacture food in the presence of light from water and carbon dioxide, here is a figure of a transverse section through a leaf

Below are examples of organs

The Heart 

Kidney

A Leaf

A Flower

4) ORGAN SYSTEMS

Finally for several organs to function together in order to carry out some of the most complicated processes found in animals and plants, several organs work together as an organ system, therefore we can define an organ system as a collection of two or more organs or tissues working together to perform closely related functions.

In plants the are only two main Organ Systems:

• The shoot system made up of the stem, leaves, flowers and fruits

• The root system made up of usually roots and associated with storage Organs

Refer to the figure below to help you understand the two systems of a plant

In humans beings organ systems are extremely complex for example the digestive system is made up of the teeth, the pharynx, oesophagus, stomach, small and large intestine, and the rectum, some of this structures are Organs and others are tissues. On the other hand we have the excretion system which consists of the kidney, ureters and the bladder, the circulatory system consists of the heart, blood, and the blood vessels. Below are the figures of various organ systems found in human beings, we'll look at them closely one by one in some of our future posts

The Digestive System

The Respiratory System

The Circulatory System

The Skeletal System

The Muscle System

The Excretory System

The Reproductive System

The Nervous System

5) ORGANISM

An organism is the highest level of structural organisation found in animals and plants, this is a single member of the species that acts as an individual, free living unit for example we have a tree, man, or women, down are the three images of examples of organisms

A Man

A Women

A Plant

I hope by the end of this you learnt something, posted by Mrs Smith Merlin.