CORE UNIT 8.3: PATTERNS IN NATURE CONTEXTUAL OUTLINE · PDF file... PATTERNS IN NATURE...

© The School For Excellence 2016 Summer School – Year 11 Biology – Book 1 Page 49

CORE UNIT 8.3: PATTERNS IN NATURE

CONTEXTUAL OUTLINE

From NSW Board of Studies Stage 6 Biology Syllabus, Page 25 Detailed examination of one or two species of living things does not provide an overview of the general features of living things. By looking across the range of commonly occurring living organisms, patterns in structure and function can be identified. These patterns reflect the fundamental inputs and outputs of living things – the absorption of necessary chemicals and the release of wastes. At a microscopic level, there are patterns in the structure and function of cells. The fundamental structural similarities exist because the biochemical processes are similar. Some important differences between plant and animal cells reflect the fundamental differences between plants and animals – the process of photosynthesis in plants. Many living things have evolved complex and efficient systems with large surface areas to facilitate the intake and removal of substances. Transport systems allow distribution and collection of nutrients and wastes. This module increases students’ understanding of the history, applications and uses of biology.


BASELINE

WHAT CAN YOU REMEMBER FROM YOUR PREVIOUS SCIENCE STUDIES?

Self-Assessment: Five focus areas:

Concept

One thing I remember about this is...

In thinking about this, I would assess myself as

1. I can construct word equations from observations and written descriptions of a range of chemical reactions.

Remember everything

Remember about half

Don’t remember

2. I can explain that systems in multicellular organisms serve the needs of cells.

Remember everything

Remember about half

Don’t remember

3. I can identify the role of cell division in growth, repair and reproduction in multicellular organisms.

Remember everything

Remember about half

Don’t remember

4. I can identify that information is transferred as DNA on chromosomes when cells reproduce themselves

Remember everything

Remember about half

Don’t remember

5. I can identify that genes are part of DNA

Remember everything

Remember about half

Don’t remember


CONTEXT POINT 1: ORGANISMS ARE MADE OF CELLS THAT HAVE SIMILAR STRUCTURAL CHARACTERISTICS

• Outline the historical development of the cell theory, in particular, the

contributions of Robert Hooke and Robert Brown. Biology is the study of living organisms, how they function, and how they relate to the external environment. In order to understand how organisms function it is necessary to study how the different parts of an organism work together. The relationship between structure and function is critical to the study of Biology and can provide information about how organisms interact with their environments. Before studying the diversity of life, it is important to have an understanding of what a ‘living organism’ is. When we study Chemistry, it is critical to have an understanding of the atom. The atom is the currency; the smallest discrete unit of Chemistry. In Biology, the currency is the cell. An understanding of the cell, its structures and functions and differences between different cells affects our view of Biology as a discipline.

CELLS Cells are the smallest living units of any organism. They come in a wide variety of shapes according to their wide variety of functions. Root hair cells of a plant, for example, have a distinctly different shape to skeletal muscle cells in a human. Some organisms are composed of a single cell. These organisms are said to be unicellular (e.g. amoebas and bacteria), while other organisms are composed of many cells and are said to be multicellular (e.g. all plants and animals).

Amoeba Wim van Egmond


CELL THEORY The cell theory is a very important biological concept. It had its origins in the first half of the 19th century. Many microscopists provided evidence. Many scientists helped developed ideas, until the cell theory emerged. The Cell Theory states: • All living things are made up of cells

• Cells are the smallest building blocks of life

• All cells come from pre-existing cells.

We can recognise a number of key events in the development of the cell theory. It should be fairly obvious that there is a direct link between the development of microscopes and our understanding of cells.

A BRIEF HISTORY OF THE DEVELOPMENT OF THE CELL THEORY

QUESTION 19 The timeline shown above is drawn incorrectly. Redraw the timeline so it is scientifically acceptable.

1676 1824 1827 1859 1880 1938 1485 1590 1665

Robert Hooke observed thin slices of

cork and saw cells

Rene Dutrochet"all living things are composed of cells”

Rudolph Virchow “all cells divide and

that is how new cells are made”

First functional scanning electron

microscope

Walther Flemming Observed and

described mitosis in stained cells

Robert Brown observed an

opaque spot in the cell, which he

named the nucleus and suggested its vital role in cell

function

Hans and Zacharias Janssen First compound microscope

Anton Van Leeuwenhook

observed microorganisms in

pond water

Leonardo Da Vinci First magnifying

glass

Schleiden and Schwann

formulated the original cell theory (the first 2 parts)

© The School For Excellence 2016 Summer School – Year 11 Biology – Book 1 3

QUESTION 20 Discuss the contributions of Robert Hooke and Robert Brown to the development of the cell theory.

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DESCRIBE EVIDENCE TO SUPPORT THE CELL THEORY QUESTION 21 Restate the Cell Theory and outline evidence for each point.

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*EXTENSION WORK At the cellular level, all cells can be divided into two main groups: prokaryotic and eukaryotic.

PROKARYOTIC CELLS The most primitive cells on earth, which lack membrane-bound organelles, are prokaryotic. All forms of bacteria are prokaryotes. Each bacterium has a circular chromosome which floats freely in its cytoplasm, i.e. it has no nucleus. Bacteria have few distinctive organelles. • Photosynthetic bacteria (cyanobacteria) contain free floating chlorophyll. • Divide by binary fission. • Examples are bacteria and cyanobacteria (blue-green algae).


EUKARYOTIC CELLS

Eukaryotic organisms (all organisms except bacteria) possess cells with membrane-bound organelles, including a nucleus. Other membrane-bound organelles include chloroplasts, mitochondria etc. The nucleus contains linear chromosomes enclosed within a nuclear membrane. Eukaryote cells also contain non membrane-bound organelles such as the protein-producing ribosomes. • Examples include animals, plants, fungi and protists. • Somatic (body) cells divide by mitosis.

From the development of the first lenses until now, people have been examining cells. The timeline highlighted the link between the development of lenses and the constructions of simple microscopes and our understanding of cellular structures. Robert Hooke contributed the first significant evidence about cells through his description of cork cells seen with a compound light microscope. From this description of ‘box-like’ cells generations of scientists were inspired to look at cells under the microscope. Van Leeuwenhoek described cells he observed under pond water, Dutrochet defined the cell, Robert Brown described the nucleus and Virchow and Wiseman contributed to cellular reproduction and evolution. The growth and support for the cell theory came through successive confirmations that all living things were made from cells and all organisms seemed to be made of simple single cells, such as the prokaryotes, or aggregates of cells, such as the eukaryotes. When microscopes became sufficiently sophisticated to allow direct observation of cell division, similar to the division describe first by Virchow, there was evidence to support the assertion that cells came from pre-existing cells. Better microscopes, particularly the development of electron microscopes, enabled scientists to look directly at the cellular organelles and start to understand their function and their ubiquitous nature. All cells not only seemed similar but they contained the same types of organelles.


QUESTION 22 Distinguish between prokaryotic and eukaryotic cells.

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DISCUSS THE SIGNIFICANCE OF TECHNOLOGICAL ADVANCES TO DEVELOPMENTS IN THE CELL THEORY

As has already been discussed there is a direct link between the development of microscopes and our understanding of cells. To better understand this link, it is necessary to look at different types of microscopes to identify what types of cells and/or microstructures can be resolved through them.

MICROSCOPES Two main types of microscopes exist: The light and electron microscopes. The light microscope increases the ability to see minute objects using lens systems which magnify images of specimens using light. Light microscopes widely used in schools contain two lenses, the _________________

and _____________________ lenses, and are referred to as compound microscopes. • Total magnification is determined by multiplying the individual eyepiece and objective

lens magnification values.

• All images are presented in two dimensions. The electron microscope uses beams of electrons to reveal complex internal structures of cells, or to magnify the surface textures of specimens.

Cells described

Single celled organisms identified

Nucleus described

Cell reproduction observed

Cell division described


• Transmission electron microscope (TEM): is used to reveal the internal detail of stained dead cells.

• Scanning electron microscope (SEM): provides detailed images of surfaces of cells or specimens.

Resolution is a measure of the image detail or clarity of an image produced by a particular microscope, i.e. the minimum distance required to distinguish between two lines. The table below compares the light and electron microscope, including the advantages and disadvantages of each.

Light Microscope Electron Microscope

Used to Create Image Light Electrons

Magnification

Up to 2,000x (Disadvantage)

Up to 2 000 000x (Advantage)

Resolution

200 nm (human eye requires 0.1 mm or

100,000 nm) (Disadvantage)

0.2 nm (Advantage)

Specimens

Living or dead, true colour, staining if desired

(Advantage)

_________________ (Disadvantage)

Thickness

Thin – fixation not required (Advantage)

Very thin – fixation required (Disadvantage)

(Cost)

Cheap, low magnification microscopes are available, however high magnification

microscopes are costly

Microscopes are costly

(Size)

Low magnification microscopes are fairly small,

but high magnification microscopes can be quite

large

Can be quite large


To adjust the view under a light microscope you can increase the magnification, use the fine focus adjustor or adjust the light using the iris diaphragm or condenser.


Fluorescence microscopes highlight chemicals in cells such as DNA. Stains improve the visibility of structures within a cell. E.g. Iodine stains _____________________ Methylene Blue stains the nucleus Measuring cells: Cells are measured in units called micrometres (microns), i.e. 1 mm = 1000 µm. How to determine the size of a cell: • Measure width/diameter of field of view (FOV) using minigrid. If the field of view is

measured at a low magnification and then the microscope is changed to a high magnification, calculate the new FOV diameter based on the magnification e.g. if the low magnification is 100x and the high magnification is 400x, then divide the diameter of the low magnification FOV by 4.

• Estimate the number of cells that fit across FOV.

• Divide FOV by the number of cells that would fit across FOV.

• At 100x magnification, Field of View might be 1.5 mm. That would equal 1500 µm.

• The number of this type of cell that would fit across the FOV would be about 5.

• Therefore the approximate width of one cell would be 1500 µm ÷ 5 and would be

300 µm.

Field of View (FOV)

Diameter of FOV

Cell


QUESTION 23 (a) Use the lines on the grid at x100 magnification to calculate the diameter of the field of

view. (b) Calculate the FOV diameter at x600.

(c) Count the number of red blood cells that fit across the FOV at x600.

(d) Calculate the size of a red blood cell.

x100

x600


While light microscopes are far better that when they were first developed, there is a limit to their resolution. Such microscopes are only effective to around 2000x magnifications. Clearly several of the microstructures within cells would have remained a mystery without the development of the higher resolution electron microscopes. These microscopes are now capable of resolving images down almost to the level of molecules. As a result, biologists now know much more about the structures inside of cells that before.

QUESTION 24 Describe ways of obtaining an image of cells, or the structures within cells, using a microscope. You answer should contrast light microscopes with electron microscopes and include any features which may enhance or change the images.

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QUESTION 25 What is the size of a red blood cell from Question 23 (viewed at 1000x), if you use the following FOV at 100x magnification?

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