cytology Flashcards
what is cytology??
Cytology is the study of cells – cell structure and cell function
The Modern Cell Theory (also referred to as the cell doctrine) states that:
a) Life occurs only in cells – thus, organisms consist of cells. The cell is the basic unit through which matter and energy are obtained, converted, stored and utilized.
b) Cells are self-producing. cells originate from the reproduction of previously existing cells.
c)Structure is related to function! There is relationship between the structure and the function of a cell
What is a cell?
A cell is the smallest unit that contains all the structures and molecules that are essential for life.
Functions of living cells
a) Responsiveness/Irritability:
b) Conduction:
c) Respiration:
d) Contractibility:
e) Absorption:
f) Metabolism:
g) Secretion/Excretion:
h) Growth and reproduction:
a) Responsiveness/Irritability:
All living cells are able to react to a suitable stimulus.
b) Conduction:
Indicates the ability to conduct a stimulus along the surface of a cell. This character is highly developed in nerve cells.
c) Respiration:
c) Respiration: Is the breakdown/oxidation of energy-rich molecules (e.g. sugar molecules) to release useful energy for the cell. Water and CO2 are by-products and O2 is usually essential for the reaction (exception: anaerobic organisms).
d) Contractibility:
Ability of cells to change form after a suitable stimulus. This character is highly developed in muscle cells, for example, shortening of the cell.
e) Absorption
e) All cells have the ability to take up substances from their surroundings, using them to extract useful energy and to synthesise their own molecules (metabolism and assimilation).
f) Metabolism:
Refers to the chemical processes which take place in the body. Subdivided into anabolic processes, where larger molecules are built up, and catabolic processes, where large molecules are broken down into small molecules.
g) Secretion/Excretion
The release of essential substances from the cell. Some of the substances are useful (e.g. digesting enzymes and hormones). Some substances are waste products (even toxic) and must be excreted.
h) Growth and reproduction:
*cell growth is determined by the increased number of cells after cell division
Cell growth takes place by means of an increase in the amount of protoplasm and/or increase in the number of cells after cell division.
Metabolism
*anabolism
*catabolism
anabolism
chemical process where larger molecules are built
catabolism
chemical process where larger molecules are broken down to smaller molecules
Metabolism involves three processes:
- Feeding
2.Respiration
3.Synthesis
1.feeding
*Organisms constantly take in and assimilate materials for growth, maintenance and energy.
* Nutrients can be: inorganic (water and minerals, directly obtained from the environment) or
*organic (carbohydrates, fats, proteins etc.). Organic nutrients can be obtained in two different ways:
Organic nutrients can be obtained in two different ways:
a) Autotrophic nutrition
b) Heterotrophic nutrition
a) Autotrophic nutrition
Organisms like plants, algae and some bacteria synthesise their own organic foodstuff by using inorganic compounds and obtaining energy e.g. from the sun – photosynthesis or by chemosynthesis.
b) Heterotrophic nutrition
Organisms like animals, fungi, most bacteria and nongreen plants feed on other plants or animals to obtain energy by degrading their organic molecules.
Respiration
This is the oxidation of organic molecules to CO2 and H2O to obtain energy. Organisms do not only use absorbed organic foodstuff as ‘fuel’, but they can also use their own body particles, especially worn-out body particles that need to be replaced
Synthesis
A process by which more complex cell components are built, using organic compounds as building blocks. These reactions are usually reduction reactions, requiring energy
- Cell size
*Most cells are between 10-100 µm in diameter
*Thus too small to study without a microscope (exceptions: egg cells of frogs or others such as bird eggs).
* Cells can easily be studied with a light microscope.
- Cell size
4.1 Minimum cell size
4.2 Maximum cell size
4.3 Surface/Volume ratio of cells
4.4 Specialisation of cells
4.1 Minimum cell size
*The smallest known cells are the so-called Mycoplasms (obligate parasites) with a diameter of about 0,1 µm (100 nm). These bacteria can only be observed with an electron microscope.
*Living organisms can most probably not be smaller than this, because then the cells would not have enough room for all the proteins necessary to perform the functions of life
Mycoplasms
smallest cells or bacteria sized 0,1 µm in diameter
4.2 Maximum cell size
Why are cells not large?
*Instead of a single-celled elephant, an elephant consists of millions of small cells.
What is the advantage of smaller cells over large cells?
*The answer lies in biological communication.
effective biological communication is not determined by the size of the cell but the number of cells
4.3 Surface/Volume ratio of cells
*Each cell needs to absorb substances and to excrete products
*plasmalemma plasmalemma plasmalemma
*absorbtion and excretion occurs only through the cell surface membrane (plasmalemma).
*The cell surface should be large enough to meet the needs of its volume.
Surface/volume ratio of cells is mainly limited for the following reasons:
a) As a cell grows its volume increases at a rate faster than its surface area; thus it causes problems in the uptake of nutrients and the excretion of waste products
b) There is a relationship between the volume of the nucleus and the volume of the cytoplasm; thus the nucleus can attend only to a limited amount of cytoplasm (for protein synthesis).
c) Substances in larger cells must move further by diffusion than those in small cells; thus the ratio of the surface area of the cell to the volume of the cell is greater for small cells (more surface for business!).
The following table illustrates the effect of an increase in cell size on the surface/volume ratio.
refer to notes
4.4 Specialisation of cells
*The development of multicellular organisms brings along the advantage of cell specialisation to optimise metabolism in the cell.
* Some large cells are modified for special functions. Examples include:
Some large cells are modified for special functions. Examples include:
a) large plant cells
b) Eggs of birds
c) Skeletal muscle cells
d) Nerve cells
e) Microvilli
a) large plant cells
i) Have large vacuoles. a vacuole with a watery content (which does not take part in the cell metabolism).
cytoplasmic streaming cytoplasmic streaming cytoplasmic streaming
ii)Undergo cytoplasmic streaming where organelles and fluids flow together through the cell.
b) Eggs of birds
*These are extremely large cells
* They consist of large amounts of food reserves and the cells are not metabolically active.
c) Skeletal muscle cells
- More than one nucleus
- extremely long cells (fibres) have more than one nucleus for protein synthesis.
d) Nerve cells
*Long narrow cylinders
*all cytoplasm near the cell surface.
e) Microvilli
