Cells
The cells1 the basic living structure of an organism. It can be divided into four main parts:
- plasma (cell) membrane, the outer lining membrane which separates the cell from the external environment;
- cytoplasm, the substance between the nucleus and the plasma which surrounds organelles;
- organelles, permanent structures specialised in a specific cellular activity. Organelles include: the nucleus containing hereditary factors, very small granules called ribosomes, the endoplasmic reticulum, the Golgi complex that processes proteins, mitochondria that generate energy, lysosomes with digestive enzymes;
- inclusions, secretions and storage products of cells like melanim, glycogen and lipids.
The science which studies the cells is called Cytology.
There are trillions of cells in a human body which belong to hundreds of different types and whose structure is perfectly suited for the role they perform. Despite their differences, the ceils of the body depend on one another, either directly or indirectly, to keep the body
functioning as one unit.
The following are the most common types of cells: stem, bone, blood, muscle, fat, skin, nerve, endothelial, sex, pancreatic and cancer cells.
WARM UP
Watch the video at the link below and say what it is about.
lnside a human cell posted by Science Photo Library
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1 Foll ow the link to see the image of a plant cell.
Plant Cell
posted by National Geographic
Tissues
Tissues are groups of similar cells that work together. Histology studies the different types of tissue2.
The epithelial tissues cover the surface of the body and some internal organs.
Connective tissues can be classified into embryonic connective tissue and adult connective tissue. Embryonic connective tissue is mainly made of mucosa and is located under the foetus's skin and developing bon s. Adult connective tissues include cartilage, bone and blood tissues.
Nervous tissues contain two main types of cells: neurons and neuroglia.
Neurons are nerve cells sensitive to stimuli that convert into impulses.
Neuroglia are cells that, nourish and support neurons.
Muscle tissues consist of highly specialised cells which provide motion, maintenance of posture and heat production.
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2 A tissue is also a piece of soft paper to absorb liquids, used especially as a handkerchief.
EXCERCISES
5 Decide if the following statements are true (T) or false (F). Then correct the false ones.
1. The plasma membrane separates the nucleus from the cytoplasm. □□
2. The cytoplasm surrounds the nucleus. □□
3. Melanin is a type of organelle. □□
4. The Golgi complex processes proteins and lipids. □□
5. Cartilage is part of the epithelial tissue. □□
6. Neuroglia feed neurons. □□
7. Muscle tissue helps us to keep an erect posture. □□
8. Muscle tissue is responsible for the production of heat. □□
9. Neurons are epithelial cells. □□
10. Both embryonic and adult connective tissues include bones. □□
6 Look at the following picture and compare it with the list of types of cells on the previous page. What is missing in the picture? What is missing in the text? Make a final list that includes both.
7 Look at the picture on the previous page and identify the different parts of the cell.
seize, ehape, colour, poeition, etc.
1. plasma membrane
2. nuclear envelope
3. Golgi apparatus
4. nucleolus
5. lysosome
6. rough endoplasmic reticulum
7. smooth endoplasmic reticulum
8 Read the following text and complete it with the missing numbers. Then, watch the video to check your answers.
► lntroduction to Cells posted by Gregorio Educational Production
10,000 • 100 trillion • 500 quadrillion • thousands • billions
lntroduction to cells
Have you ever wondered what we are all made of?
All life is made of cells. They come in 1 ......................................... .
of shapes and sizes.The human body has over
2 ...................................... of them carrying out the dance of life.
They are so tiny that 3 ............................................. could fit on
the head of a pin.
The cells in our body undergo over 4 ......................................... ..
chemical reactions every second.Their amazing
biochemistry has nurtured life on Earth for
5 ........................................ of years and protected us from harm.
They only ask that we take care of ourselves.
Our Science has barely begun to understand them.
Let's explore cells.
9 Watch the video aga in and identify different cell shapes.
THE ORIGINS OF CYTOLOGY
The earliest phase of Cytology began with the English scientist Robert Hooke's microscopie investigations of cork in 1665. He observed dead cork cells and for the first time used the term cell to describe them. In 1838 the botanist Matthias Schleiden, and in 1939 the biologist Theodor Schwann, were among the first to clearly state that cells are the fundamental partides of both plants and ani mais. This statement was called the cell theory and was widely confirmed and elaborateci by a series of discoveries and interpretations.