Patterns in nature - lrr.cli.det.nsw.edu.aulrr.cli.det.nsw.edu.au/legacy/Science/43209_P4_lo.pdf ·...

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BiologyPreliminary CourseStage 6

Patterns in nature

Part 4: Electron microscope and cell organelles

Incorporating October 2002

AMENDMENTS

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Part 4: Electron microscope and cell organelles 1

Contents

Introduction................................................................................ 2

The electron microscope ........................................................... 3

Using an electron microscope .............................................................4

Structure and function..........................................................................5

Tissues, organs and organ systems ........................................ 14

Summary ................................................................................. 15

Suggested answers ................................................................. 17

Exercises–Part 4 ..................................................................... 21

2 Patterns in nature

Introduction

Plants and animals have specialised structures to obtain nutrients from

their environment. You may recall that plants and animals obtain

nutrients differently. Plants rely on the Sun to manufacture food by a

process called photosynthesis. Plants are autotrophic organisms.

Animals cannot manufacture their own food; they consume or eat other

organisms in order to gain the nutrients they require for life processes.

Animals are heterotrophic organisms.

Plants and animals have specialised cells, tissues and organs to obtain the

nutrition they require and carry out their body processes. Some of these

will be investigated in this part.

In this part you will be given opportunities to learn to:

• identify cell organelles seen with an electron microscope

• describe the relationship between the structure of cell organelles and

their function

• identify some examples that demonstrate the structural and

functional relationships between cells, tissues, organs and organ

systems in multicellular organinsms

In this part you will be given opportunities to:

• process information from secondary sources to analyse electron

micrographs of cells and identify mitochondria, chloroplasts, Golgi

bodies, lysosomes, endoplasmic reticulum and cell membranes.

Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally

issued 1999. The most up-to-date version can be found on the Board’s website

at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.

This version November 2002.

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The electron microscopes

There are two main types of electron microscopes:

• the transmission electron microscope and

• the scanning electron microscope.

Unlike light microscopes that use a beam of light passing through the

specimen electron microscopes use a beam of electrons.

The transmission electron microscope uses the electrons that pass

through very thin specimens, to show detailed images of internal

structures. The scanning electron microscope produces images of the

surface features of objects, often coated with a very thin layer of metal

atoms to enhance the image.

One disadvantage of using electron microscopes is that the preparation of

specimens is very expensive. For example, the specimen must be kept in

a vacuum to avoid scattering the electron beam or it must be fixed in

heavy metal compounds eg. gold. This means that it is not possible to

view live specimens, also a disadvantage. It is unclear whether such

harsh treatment of specimens might actually distort the true nature of the

structure of the cells.

An electron microscope


The advantage of the electron microscope is that the magnification

(x 1 million) and the resolution (0.0002 micrometre) are very high.

Do Exercise 4.1 now.

Using an electron microscope

Under a light microscope there is a limit to the organelles that are visible

even with the latest technology. The story is different however, under an

electron microscope where there are many more organelles visible.

The table below lists the cell structures that are visible with an

electron microscope.

Cell structure Animal cells Plant cells

nucleus

nucleolus

cell membrane

cytoplasm

nuclear membrane

mitochondria

Golgi bodies

ribosomes

endoplasmic reticulum

lysosomes

cell wall

chloroplasts

vacuole

present

present

present

present

present

present

present

present

present

present

absent

absent

absent

present

present

present

present

present

present

present

present

present

absent

present

present

present

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Structure and function

The nucleus

The nucleus is usually large and spherical. The nucleus is enclosed by a

double membrane. This membrane has pores that allow fairly large

molecules to move in and out of the nucleus.

The nucleus often contains a nucleolus which is involved in the

manufacture of proteins in the cell. (Refer to the electron micrograph

below showing the nucleus and other organelles.)

Nucleus in a rat intestinal wall. (g—Golgi bodies, m—mitochondrion,nu—nucleolus, n—nucleus, rer—rough endoplasmic reticulum)© Australian Key Centre for Microscopy.

The nucleus controls the activities of the cell. It does this largely by

controlling the formation of proteins in the cell. The nucleus contains the

chromosomes, which carry the genes. Genes are units of inheritance and

determine which types of proteins are formed.


What sort of structural feature/s does the nucleus have that makes it suited

for its function?

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

Plastids and chloroplasts

Plastids are oval–shaped organelles. Some store substances such as food

made by plants eg. starch. Other plastids contain pigments such as the

green pigment, chlorophyll. Plastids that contain chlorophyll are

called chloroplasts.

Chloroplast in soybean leaf. (g — granum, r — ribosomes, s — starch grains)© Australian Key Centre for Microscopy.

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Look at the three dimensional drawing of a chloroplast below.

Note that it has, like a nucleus, a double membrane. Within a chloroplast

is a membrane known as the lamella. In some areas, the lamella is

densely packed into grana (singular granum). These resemble stacks of

coins and increase the surface area. The grana are embedded in a

colourless substance called the stroma.

stack of grana(thylakoids)

ring of DNA

lamella

double membrane

starch grain

stroma

ribosome

Photosynthesis occurs in chloroplasts. So, essentially, the chloroplasts

are the food–making organelles of plants. The chlorophyll is contained

in the grana. It is the chlorophyll that absorbs light energy which makes

the process of photosynthesis possible.

Describe how the structure of a plastid such as a chloroplast assists the

process of photosynthesis in plant cells.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

The cell membrane

The cell membrane, also known as the plasma membrane, surrounds all

cells. It is a physical barrier but it is thin and contains pores that allow

selected materials to pass through. In plant cells the cell membrane is

surrounded and protected by the cell wall.

The function of the cell membrane, apart from keeping the cell together,

is to regulate the flow of substances into and out of the cell.

The membrane is described as selectively permeable. This means it

allows some substances to pass through while stopping other substances.


Describe how the structure of the cell membrane enables it to carry out the

function described here.

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

A summary

Following is a summary of important points so far. Fill in the missing

words as you read this summary.

1 The _____________ is a large spherical organelle that controls the

activities of the cell. This organelle is surrounded by a

_____________ membrane that has _____________ in it.

2 Chloroplasts are one type of _____________. They are green coloured

because they contain the green pigment, _____________. Like the

nucleus, the chloroplast is surrounded by a _____________ membrane.

Chloroplasts absorb _____________ energy, which drives the

food–making process called _____________.

3 The cell or plasma membrane keeps the cell intact. It allows some

substances to enter and leave while preventing others from entering or

leaving. It is therefore described as _____________ permeable.

Check your answers.

Mitochondria

Cells may contain several or hundreds of mitochondria. The more active

a cell is, the more mitochondria there are.

1 Make a prediction to explain why there are more mitochondria in an

active cell than one not involved in activity.

_____________________________________________________

_____________________________________________________ .

A mitochondrion is surrounded by a double membrane.

Look at the photomicrograph on the next page, which shows some

mitochondria. You can see that the inner membrane is highly folded.

Folded membranes like this provide a very large surface within a

small space.

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Mitochondria in unicellular algae.© Australian Key Centre for Microscopy.

Mitochondria are the organelles in which the final stages of cellular

respiration occur. They are the organelles in which the energy produced

is released by cellular respiration. The wastes from this process, carbon

dioxide and water, are also formed in these structures. Mitochondria are

often referred to as the powerhouses of the cell because they are the

organelles which provide energy for the cell.

2 How does the structure of a mitochondrion support its function?

_____________________________________________________

_____________________________________________________

Check your answers.

Golgi bodies

A Golgi body was first observed and identified as an organelle by

Camillo Golgi (1844–1926), an Italian histologist. Hence, Golgi is

always spelt with a capital letter. We are inclined to get the impression

that these not so well known organelles were discovered when the

electron microscope came into use. This is not so.


The Golgi body was actually discovered when Golgi used an optical

microscope and a dye containing a silver compound. There was

originally much argument as to whether or not it was a new organelle or

simply a product of the staining technique he used. The matter was not

resolved for about 60 years when electron microscopes verified

Golgi’s claims.

Find the Golgi body in the electron micrograph below. Note that the

Golgi body consists of stacks of membranes which bulge out in places to

travel through the cell.

Small Golgi body in a grass leaf cell. (g — Golgi body, rer — roughendoplasmic reticulum, cw — cell wall)© Australian Key Centre for Microscopy.

The Golgi body has been found in nearly all types of cells, but is

particularly abundant in cells that secrete substances eg. the

salivary glands.

The Golgi apparatus can absorb amino acids and sugars and use them to

synthesise more complex proteins and carbohydrates. These chemicals

are contained in the vesicles, which become detached from the Golgi

apparatus. These vesicles appear to move away from the Golgi apparatus

across the cytoplasm to the cell membrane. Finally, the small vesicles

fuse with the cell membrane and the protein–carbohydrate substances are

discharged (secreted) from the cell.

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So, the Golgi body prepares and secretes various chemicals for use either

within or outside the cell.

How is the function of a Golgi body supported by its structure?

_________________________________________________________

_________________________________________________________

Check your answer.

Ribosomes

Compared to the nucleus, mitochondria, chloroplasts and Golgi body,

ribosomes are very small indeed. They are tiny, spherical organelles

which are found throughout the cell.

Ribosomes are found within other organelles such as the nucleus and

chloroplasts. They are also found attached to a membrane system known

as the endoplasmic reticulum.

Rough endoplasmic reticulum in rat intestine. (Arrowheads indicate ribosomesattached to the surface of the rough endoplasmic reticulum).

© Australian Key Centre for Microscopy.


Ribosomes are the organelles where proteins are made. They are most

numerous in cells that produce proteins. The small size of ribosomes

gives a high surface area to volume ratio.

How does the structure of a ribosome enable it to produce proteins?

_________________________________________________________

_________________________________________________________

Check your answer.

Endoplasmic reticulum

The endoplasmic reticulum is a network of membranes that run through

the cytoplasm. The rough endoplasmic reticulum looks rough because

there are ribosomes attached to it. Smooth endoplasmic reticulum has no

ribosomes on it. The endoplasmic reticulum is an intricate combination

of canals.

Rough endoplasmic reticulum in mouse intestine. Parallel sheets of roughendoplasmic reticulum can be seen surrounding the nucleus. (n — nucleus,nu — nucleolus, m — mitochondria, rer — rough endoplasmic reticulum)

© Australian Key Centre for Microscopy.

The endoplasmic reticulum forms a complex system of canals or

channels along which substances are transported throughout the cell.

Smooth endoplasmic reticulum is involved in the formation of lipids

(fats). It also helps inactivate some drugs.

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How does the structure of endoplasmic reticulum relate to its function?

_________________________________________________________

_________________________________________________________

Check your answer.

Lysosomes

Lysosomes were first described in the 1950s. They are smaller than

mitochondria and are enclosed by single membranes. The membrane

does not permit the movement of enzymes from within and is capable of

resisting their digestive action. Lysosomes are more commonly found in

animal cells.

The lysosome is thought to contain enzymes that take in and break down

older cell organelles. If a lysosome should rupture (break) the enzymes

would break down and destroy the cell.

How is the structure of a lysosome relevant for the function it performs?

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answers.

You will need to look carefully at the micrographs throughout the module

and familiarise yourself with them, as you may be required to identify such

pictures/diagrams at a later stage. Use other secondary sources of electron

micrographs to identify mitochondria, chloroplasts, Golgi body, lysosomes,

endoplasmic reticulum and cell membranes. Use the electron micrographs

on the previous pages and the LMP Science webpage for more sources of

pictures. Make sure you can identify the above cell organelles.

Complete Exercise 4.2.


Tissues, organs and organ systems

Cells are not a disorganised mass of matter. Instead cells are grouped

together to form tissues, tissues make up organs and organs make up

organ systems. The table below summarises this information.

Definition Animal example Plant example

tissue a group of cells of the same typewith the same function

blood phloem

organ part of an animal or plant forming astructural and functional unit whichis made up of one or more tissues

heart leaf

organ system a group of organs that functiontogether as a unit

blood system vascular system

Explain the difference between tissues, organs and organ systems.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

Do Exercise 4.3 to complete this part.

In the next part you will go on to investigate how specialised structures

are used by organisms to obtain nutrients from their surroundings.

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Summary

Self–correcting summary.

1 a) What are two advantages of using electron microscopes over

light microscopes?

_________________________________________________

_________________________________________________

b) In what way is the use of the electron microscope limited?

_________________________________________________

c) Which organelles would you be able to see using an electron

microscope that were not visible using a compound or light

microscope?

_________________________________________________

2 Complete the summary of cell organelle structure and function

following by filling in the missing words.

a) Mitochondria (singular ________________ ) are organelles with

a double ________________. The inner membrane is highly

________________ producing a large surface area.

Mitochondria are described as the powerhouses of cells because

they provide cells with ________________ to do work. The

final stages of the energy–releasing change called

________________ occur in these organelles.

b) A Golgi body consists of ________________. These

membranes bulge out to form ________________. These

vesicles contain various chemicals which are used whether

within the cell or ________________ by the cell for use

elsewhere.

c) ________________ are small, spherical structures which are the

site of protein synthesis.


d) The endoplasmic reticulum is a network of ________________

which form canals or passageways. The canals

________________ a variety of substances throughout the cell.

Endoplasmic reticulum with ribosomes attached is called

________________ endoplasmic reticulum.

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Suggested answers

The nucleus

The nucleolus is involved in the formation of proteins which controls the

activities of the cell. Substances are able to move in and out of the cell

through the pores in the nuclear membrane.

Plastids and chloroplasts

The stack of grana in chloroplasts increases the surface area available

within the chloroplast for photosynthesis.

Chloroplasts contain chlorophyll which absorbs light energy and makes

photosynthesis possible.

The cell membrane

The cell membrane is a physical barrier, it is thin and contains tiny pores

to enable the diffusion of matter across it.

A summary1 The nucleus is a large spherical organelle which controls the

activities of the cell. This organelle is surrounded by a double

membrane that has pores in it.

2 Chloroplasts are one type of plastid. They are green coloured

because they contain the green pigment, chlorophyll. Like the

nucleus, the chloroplast is surrounded by a double membrane.

Chloroplasts absorb light energy, which drives the food–making

process called photosynthesis.

3 The cell or plasma membrane keeps the cell intact. It allows some

substances to enter and leave while preventing others from entering


or leaving. It is therefore described as selectively (or semi)

permeable.

Mitochondria1 Active cells require large amounts of energy. Energy in cells is

provided by the process of respiration. Mitochondria might be the

site where respiration occurs, therefore providing the energy needed.

2 The highly folded inner membrane increases the surface area for

respiration. The large surface area provided by a folded membrane

provides more places for respiration to occur. So, respiration can

occur on a large–scale.

Golgi body

The Golgi consist of stacks of membranes which increase the surface

area for diffusion and synthesis of complex molecules. The vesicles

function is transporting these molecules to the cell membrane.

Ribosomes

The large surface area to volume ratio enables efficient movement of

materials across the ribosome’s membrane.

Endoplasmic reticulum

The large surface area enables the endoplasmic reticulum to efficiently

transport materials around the cell.

Lysosome

The semipermeable nature of the membrane prevents the enzymes

escaping into the cell and destroying it.

Tissues, organs and organ systems

Cells are fundamental units that make up a living thing. Similar cells

work together to form tissues and different tissues work together in

an organ.

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Summary1 a) Greater magnification and resolution

b) Specimens are killed in the process of preparation for viewing

with an electron microscope. No guarantee that the resulting

images are true representations of the original living tissue. The

cost of electron microscope technology is very high.

c) Nucleolus, Golgi, endoplasmic reticulum (rough and smooth),

lysosome, mitochondria, ribosomes.

2 a) Mitochondria (singular mitochondrion) are organelles with a

double membrane. The inner membrane is highly folded

producing a large surface area. Mitochondria are described as

the powerhouses of cells because they provide cells with energy

to do work. The final stages of the energy–releasing change

called respiration occur in these organelles.

b) A Golgi body consists of membranes. These membranes bulge

out to form vesicles. These vesicles contain various chemicals

which are used whether within the cell or secreted by the cell for

use elsewhere.

c) Ribosomes are small, spherical structures which are the site of

protein synthesis.

d) The endoplasmic reticulum is a network of membranes, which

form canals or passageways. The canals transport a variety of

substances throughout the cell. Endoplasmic reticulum with

ribosomes attached is called rough endoplasmic reticulum.

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Exercises – Part 4

Exercises 4.1 to 4.3 Name: _________________________________

Exercise 4.1: The electron microscopea) Identify two types of electron microscopes.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Describe two disadvantages of using an electron microscope.

_____________________________________________________

____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

c) What magnification and resolution are available with an electron

microscope?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________


Exercise 4.2: Observing plant and animal cells

The following diagrams show the structure of a generalised plant and

animal cell, as viewed with an electron microscope.

Golgi apparatus

cell wall

plasma membrane

nucleus

nucleolus

chloroplast

endoplasmic reticulum

mitochondrion

vacuole

ribosomes

cytoplasm

Plant cell (as seen with an electron microscope).

mitochondrion

Golgi apparatus

smoothendoplasmicreticulum

lysosome

nucleolus

nucleus

roughendoplasmicreticulum

plasma membrane

Animal cell (as seen with an electron microscope).

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a) Which structures are you able to see with an electron

microscope that are not possible to see with a light microscope?

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

b) Identify differences between plant and animal cells.

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

c) You are a biologist working in a research laboratory comparing

plant and animal cells. Prepare a comparison of the two types of

cells, their structure and function.

You may find it more convenient to put this information into a

table. A suggested table with headings is provided here for you.

You may select headings of your own.

For each organelle state how the structure enables it to carry out

its specific function.


Organelle structure Function Found inanimal cells

Found inplant cells

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Exercise 4.3: Tissues, organs and organ systemsa) Define the following terms

tissues _______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

organs _______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

organ systems _________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Organ systems in multicellular organisms supply the needs of cells.

For example, the circulatory system transports oxygen from the

lungs to the cells. Outline how one other organ system supplies the

needs of cells.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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