cytology

Question 1

what is cytology??

Answer 1

Cytology is the study of cells – cell structure and cell function

Question 2

The Modern Cell Theory (also referred to as the cell doctrine) states that:

Answer 2

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

Question 3

What is a cell?

Answer 3

A cell is the smallest unit that contains all the structures and molecules that are essential for life.

Question 4

Functions of living cells

Answer 4

a) Responsiveness/Irritability:
b) Conduction:
c) Respiration:
d) Contractibility:
e) Absorption:
f) Metabolism:
g) Secretion/Excretion:
h) Growth and reproduction:

Question 5

a) Responsiveness/Irritability:

Answer 5

All living cells are able to react to a suitable stimulus.

Question 6

b) Conduction:

Answer 6

Indicates the ability to conduct a stimulus along the surface of a cell. This character is highly developed in nerve cells.

Question 7

c) Respiration:

Answer 7

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).

Question 8

d) Contractibility:

Answer 8

Ability of cells to change form after a suitable stimulus. This character is highly developed in muscle cells, for example, shortening of the cell.

Question 9

e) Absorption

Answer 9

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).

Question 10

f) Metabolism:

Answer 10

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.

Question 11

g) Secretion/Excretion

Answer 11

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.

Question 12

h) Growth and reproduction:

Answer 12

*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.

Question 13

Metabolism

Answer 13

*anabolism
*catabolism

Question 14

anabolism

Answer 14

chemical process where larger molecules are built

Question 15

catabolism

Answer 15

chemical process where larger molecules are broken down to smaller molecules

Question 16

Metabolism involves three processes:

Answer 16

1. Feeding
   2.Respiration
   3.Synthesis

Question 17

1.feeding

Answer 17

*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:

Question 18

Organic nutrients can be obtained in two different ways:

Answer 18

a) Autotrophic nutrition
b) Heterotrophic nutrition

Question 19

a) Autotrophic nutrition

Answer 19

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.

Question 20

b) Heterotrophic nutrition

Answer 20

Organisms like animals, fungi, most bacteria and nongreen plants feed on other plants or animals to obtain energy by degrading their organic molecules.

Question 21

Respiration

Answer 21

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

Question 22

Synthesis

Answer 22

A process by which more complex cell components are built, using organic compounds as building blocks. These reactions are usually reduction reactions, requiring energy

Question 23

4. Cell size

Answer 23

*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.

Question 24

4. Cell size

Answer 24

4.1 Minimum cell size
4.2 Maximum cell size
4.3 Surface/Volume ratio of cells
4.4 Specialisation of cells

Question 25

4.1 Minimum cell size

Answer 25

*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

Question 26

Mycoplasms

Answer 26

smallest cells or bacteria sized 0,1 µm in diameter

Question 27

4.2 Maximum cell size

Answer 27

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

Question 28

4.3 Surface/Volume ratio of cells

Answer 28

*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.

Question 29

Surface/volume ratio of cells is mainly limited for the following reasons:

Answer 29

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!).

Question 30

The following table illustrates the effect of an increase in cell size on the surface/volume ratio.

Answer 30

refer to notes

Question 31

4.4 Specialisation of cells

Answer 31

*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:

Question 32

Some large cells are modified for special functions. Examples include:

Answer 32

a) large plant cells
b) Eggs of birds
c) Skeletal muscle cells
d) Nerve cells
e) Microvilli

Question 33

a) large plant cells

Answer 33

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.

Question 34

b) Eggs of birds

Answer 34

*These are extremely large cells
* They consist of large amounts of food reserves and the cells are not metabolically active.

Question 35

c) Skeletal muscle cells

Answer 35

• More than one nucleus
• extremely long cells (fibres) have more than one nucleus for protein synthesis.

Question 36

d) Nerve cells

Answer 36

*Long narrow cylinders
*all cytoplasm near the cell surface.

Question 37

e) Microvilli