Topic 2.1 Cells Theory Board Notes

TOPIC: CELLS

2.1 CELL THEORY - BOARD NOTESBACKGROUND INFORMATION:

Characteristics of Living Things (MRS GREN)

Living things:

Move

Respire: require E. for growth, movement etc.

Organisms can respire:

Aerobic respiration: C6H12O6 (glucose) + 6O2 - 6CO2 + 6H2O + Energy (all cells)

Anaerobic respiration: C6H12O6 (glucose) - 2C2H5OH (ethanol) + 2CO2 + Energy (plant cells)

C6H12O6 (glucose) - 2C3H6O2 (lactic acid) + Energy (animal cells)

Sensitive: respond to stimuli.

Grow: increase in cell size & cell number (cell reproduction).

Reproduce: produce offspring.

2 types of reproduction:

Sexual reproduction: 2 parents required (egg + sperm are produced by meiosis).

Asexual reproduction: 1 parent only (mitosis).

Excrete: release unwanted wastes.

Nutrition: require food which provides E.

Organisms can be classified as:

Autotrophs: make their own food by photosynthesis or chemosynthesis.

Heterotrophs: cannot make their own food; eat other organisms.

One definition of life: "an organized genetic unit capable of metabolism, reproduction and evolution".

CLASSIFICATION OF LIVING THINGSTHINGS

LIVING THINGS (ORGANISMS) NON-LIVING THINGS (NON-CELLULAR)

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Topic 2.1 Cells Theory Board Notes

CELLS VIRUSES

EUKARYOTE CELLS PROKARYOTE CELLS

ANIMAL & PLANT CELLS BACTERIA ALL living things consist of one or more cells.

A cell consists of a cytoplasm surrounded by a membrane & contains genetic material.

Cells can be classified as:

Unicellular organisms: consists of a single cell which carry out all activities essential to life eg eating,

excreting wastes, producing offspring etc).

Multicellular organisms: consists of a many cells, each cell is specialised – has a particular structure &

function.

Eukaryote cells: cells which have a true nucleus & membrane bound organelles eg plant & animal cells.

Prokaryote cells: cells which do not have a true nucleus & membrane bound organelles eg bacteria.

2.1.1 & 2.1.2 Cell Theory & evidence which supports the theoryCell Theory states:

a. Living organisms are composed of cells.

Evidence: organisms observed under the microscope appear to be composed of cells.

b. Cells are the smallest unit of life.

Evidence: a unicellular organism shows all the characteristics of living processes.

Organelles (little organs in the cytoplasm) work together for the successful function of the cell.

c. Cells come from pre-existing cells.

Evidence: cells carry out a form of cell division (mitosis or binary fission) to form identical new cells.

Exceptions: 1. Muscle tissue and many fungi do not have separate cells they are multi-nucleated - have

more than one nucleus per cell.

Muscle cells: Fungal Cells:

2. Mature red blood cells in humans do not have a nucleus.

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Topic 2.1 Cells Theory Board Notes

3. The xylem vessel (transport water ) consists of dead cells .

4. The phloem vessel consists of cells which have lost their nucleus.

5. Surface skin cells of mammals have lost their cytoplasm and nucleus.

2.1.3 Unicellular organisms carry out all the functions of life.Unicellular organisms are able to carry out all the processes which are characteristic of living things such as:

Cellular reactions eg respiration.

Homeostasis - the maintenance and regulation of internal cell conditions.

Reproduction – asexual eg binary fission.

Nutrition eg autotrophic or heterotrophic.

Examples of unicellular organism: Bacteria (prokaryote) & amoeba (eukaryote)

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Topic 2.1 Cells Theory Board Notes

2.1.4 Relative sizes of structure and unicellular organismRelative Sizes:

1 mm (millimetre) = 1 000 µm (micrometre)

1 mm = 1 000 000 nm (nanometre)

nm= nanometer (10-9m)     µm   = micrometer (10-6m)

Relative sizes:1. Molecules (1 nm). 2. Plasma membrane thickness (10 nm). Electron microscope (nm)3. Virus (100 nm).4. Bacteria (1 µm). Light microscope (µm)5. Organelles (< 10 µm).6. Cells (< 100 µm) - generally plant cells (100 µm) are larger than animal cells (50 µm).

  

ToK:

All the biological entities in the above list are beyond our ability to perceive directly. They must be observed through the use of technology such as the light and electron microscope.

Measurements of Cells

1. A light & electron microscope can be used to view & measure the size of cells.

2. An electron microscope has greater resolution & magnification, than a light microscope. Resolution is the ability to distinguish between two points.

3. Measurement of Cells using a Light Microscope:

(a) Scanning Objective Lens (4x): total magnification 4x10 = 40x

Field of vision: Diameter = 5 mm (5 000 um)

(b) Low Power Objective Lens (10x): total magnification 10 x10 =100x

Field of vision:

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5 cells each 1 000

2 cells each 1

Topic 2.1 Cells Theory Board Notes Diameter 2 mm or 2 000 um (view less of the field of vision)

(c) High Power Objective Lens (40x): total magnification 40 x10 = 400x

Field vision: Diameter 0.5 mm or 500 um (view ¼ less of the field of vision)

2.1.5 Calculating the Linear Magnification of DrawingsCalculating the linear magnification of drawingsOn an image of a specimen it is useful to show how much larger/smaller the image is than the real specimen. This is called magnification.

To calculate magnification:

1. Using a ruler measure the size of the image.

2. Convert the units to the same units of measurement - as required. 3. Magnification is calculated as follows:

Magnification = Measured length of the image ……. Must have both units the same!Measured length of the specimen

4. The actual length of the image can be calculated as follows:

Length of the actual specimen = Length on the image Magnification

5. Example: Rose leaf

Image length = 4.2cm Magnification = 0.83.

Real length = 4.2 cm = 5cm 0.83

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1/2 cell shown here only

Topic 2.1 Cells Theory Board Notes

6. Images or diagrams often carry a scale bar which is a horizontal line drawn on the image.

The scale bar shows how long the line is in the real specimen.

7. Example: The scale bar indicates the length of 1 cm = 10um

The diameter of nucleus measures 1.5 cm

………………… therefore its real length = 15 um.

 

2.1.6 Surface area: Volume ratios as a factor limiting cell size: Cells are microscopic. Why?

1.0 cm 2.0 cm 3.0 cm

Calculations:

Surface area = length x width x 6 (cm2)

Volume = length x width x breadth (cm3)

Length (cm) SA (cm2) Volume (cm3) SA: Volume ratio

1 6 1 6 : 1

2 24 8 24 : 8 3 : 1

3 54 27 54 : 27 2 : 1

Conclusion

As the size of a structure decrease the surface area to volume ratio increases.

Therefore the rate of exchange (diffusion/radiation) increases.

This is true for organelles, cells, tissues, organs and organisms.

The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings.

As organisms get bigger their volume and surface area both get bigger, but not by the same amount.

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Topic 2.1 Cells Theory Board Notes

Biological Consequences:

Large organisms the rate of exchange with their surroundings occurs more slowly.

Loxodonta africana (African elephant).

According to the calculations above the elephant should have a small surface are to volume ratio in comparison to smaller animals.

Heat exchange ought to be quite slow which would be a problem for an animal living in a warm region.

The elephant has evolved large ears to increase the surface area for heat exchange allowing the elephant to remain cool.

Small organisms have the opposite problem of a rapid rate of exchange with the environment.

Sorex minutus (pygmy shrew)

Size: Approximately 60mms from tip of nose to base of tail. The tail is around 40mms long. Mass: 4

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Topic 2.1 Cells Theory Board Notesgrams.

This shrew looses body heat so fast that it consumes food at a furious rate simply to produce heat from respiration. I understand that this particular species needs to eat every two hours to stay alive.

2.1.7 Multicellular organisms show emergent propertiesSyllabus: 'Emergent properties arise from the interaction of the component parts; the whole is greater than the sum of the parts'.

'I define life as....a whole that this pre-supposed by all its parts' S. Coleridge

Systems biologists attempt to put together the parts that make up a system and then observe the properties of that 'emerge' from the system but which could not have predicted from the parts themselves.  ToK:

The concept of emergent properties has many implications in Biology. What are they?Life itself can be viewed as an emergent property, and therefore one can discuss the differences of living

and non- living things and the problems about defining death in medical decisions.Background Information:

As a model consider the electric light bulb. The bulb is the system and is composed of a filament made of tungsten, a metal cup, and a glass container. We can study the parts individually how they function and the properties they posses. These would be the properties of tungsten, the properties of the metal cup and the properties of the glass container. When studied individually they do not allow the prediction of the properties of the light bulb. Only when we combine them to form the bulb can these properties be determined. There is nothing supernatural about the emergent properties rather it is simply the combination of the parts that results in new properties being shown.

Biological systems need a different approached, population thinking, which acknowledges the role of variation in a population. Consequently the deterministic laws and theories of the physical sciences do not apply to all aspects of biological systems. The ‘parts’ of the living system vary on both a phenotypic level and at the level of the genetic program. This is an important feature of the biological system (compared to the non-living) that it is not just affected by the physiochemical laws but also by a genetic program.

Theory reduction is the concept that theories and laws in one science field are simply special cases of theories which are to be found in the physical sciences.

Emergence is the occurrence of unexpected characteristics or properties in a complex system. These properties emerge from the interaction of the ‘parts’ of the system. Remember that biology insists on a population thinking so that we know the interacting ‘parts’ vary in themselves and therefore their ‘emerging’ properties can only be generalised. One of the classic examples cited is to think of the emergent properties of water (fluidity) that cannot be predicted from knowledge of the constituent gases hydrogen and oxygen. On a biological scale consider the current debate about the nature of human consciousness or the origin of life itself.

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Topic 2.1 Cells Theory Board Notes1Concise Oxford English Dictionary 10th edition revised: (2002), Oxford University Press: New York2 Mayr, E (2004) What Makes Biology Unique? Cambridge University Press: Cambridge

2.1.8 Multicellular organisms and specialised cell function

Cell differentiation is the process where unspecialized cells develop a specialized structure & function.

ALL cells of an organism contain the same genetic information, only certain genes are activated to produce specialised cells.

The diagram below illustrates how the different cell types develop in the human body:

ADULT FEMALE (46) ADULT MALE (46)

Meiosis (formation of gametes) Meiosis

EGG (23 Haploid Cell) SPERM (23 Haploid Cell)

Fertilisation (union of egg and sperm nuclei)

ZYGOTE (46 Diploid Cell)

Mitosis (identical cells are produced)

EMBRYO (A ball of cells)

Cell DifferentiationCertain genes in the cell are activated and certain genes are decoded to determine the

characteristics of the cell. The genes decoded vary from cell type to cell type.

NERVE CELLS CONNECTIVE EG BLOOD CELLS EPITHELIAL CELLS MUSCLE CELLS

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Topic 2.1 Cells Theory Board Notes

Communication (electrical impulses) Transport O2 Line organs, skin – protection Contraction - movement

Hierarchical structure within multicellular organisms

Cell: Basic building block for all organisms.4 types of cells: muscle, nerve, epithelial & connective cells

Tissues: Group of similar cells with the same structure and function. 4 types of tissues: Muscle – movement (contraction)

Nerve – communication (electrical impulses)Epithelial – protection (lining organs, skin)Connective – various types – red blood cells – transport O2.

Organs: Group of tissues that work together to perform an overall function. Eg heart – pumps blood around the body; lungs – exchanges O2 with CO2.

Organ systems: Groups of organs within an organism that together carry out a process. Eg Cardiovascular system: heart, blood vessels, blood.

The diagram below illustrates the different cells, tissues, organs and organs systems:

2.1.9 Stem cells

Stem cells retain the capacity to divide and have the ability to differentiate along different pathways.

A stem cell is able to divide but has not yet expressed genes to specialise to a particular function.

Under the right conditions stem cells can be induced to express particular genes and differentiate into a specialised cell.

Stem cells can be obtained from embryos / blastocyte OR placenta.

Adults still possess stem cells in some organs but much less than a child.

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Topic 2.1 Cells Theory Board Notes

2.1.10 Therapeutic use of stem cells  Therapeutic use of stem cells is an area of rapid development.

Stem Cells can be used in the following technologies:

1. Embryonic Stem cell therapy

In some treatments of cancers patients requires heavy doses of radiation and or chemotherapy.

This often destroys healthy blood tissue as well as the diseased tissue.

Healthy stem cells or marrow cells are often transplanted (sometimes donated from the patient before

treatment) back to produce healthy blood cells again.

2. Therapeutic cloning

In this process the nucleus of the patient's cell is removed and retained and transferred to the

enucleated cell body.

The cells are then stimulated to divide forming a clone - a blastocyst.

The inner cell mass are called totipotent - cells are capable of being stimulated to become one of any

type of cell.

Cells are stimulated using differentiation factors to become the type of cell required for therapy.

Cells are then transferred to the patient.

Note: these cells have the same immune system identity as the patient therefore there is not immune rejection problem.

Internationalism

Stem cell research has depended on the work of teams of scientists in many countries who share results and so speed up the rate of progress. However, ethical concerns about the procedures have led to restrictions on research in some countries. National governments are influenced by local, cultural and religious traditions, which vary greatly and these therefore have an impact on the work of scientists.

ToK

Issues:

1. Therapeutic cloning has many risks - some stem cells develop into tumours - should therapeutic cloning still be allowed to continue?

2. Should the scientific community convey information about its work to the wider community so that informed decisions about research can be made?

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