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BiologyPreliminary CourseStage 6

Patterns in nature

Part 8: Growth and repair

Incorporating October 2002

AMENDMENTS

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Part 8: Growth and repair 1

Contents

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

Cell division................................................................................3

Sites of mitosis .....................................................................................4

What happens during mitosis? ............................................................6

Mitosis in plant cells .............................................................................7

Cytokinesis .........................................................................................11

Additional resources ................................................................12

Suggested answers .................................................................15

Exercises–Part 8......................................................................17

Student evaluation of module

2 Patterns in nature

Introduction

Maintenance of organisms requires growth and repair.

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

• identify mitosis as a process of nuclear division and explain its role

• identify the sites of mitosis in plants, insects and mammals

• explain the need for cytokinesis in cell division

• identify that nuclei, mitochondria and chloroplasts contain DNA.

In this part you will be given opportunities to:

• perform a first–hand investigation using a microscope to gather information from

prepared slides to describe the sequence of changes in the nucleus of plant or animal cells

undergoing mitosis

Extract 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/syllabus2000_lista.html

This version November 2002.

Materials required:

• microscope and lamp

• two slides and a cover slip

• onion with fresh roots (you need to soak onion base in water at least a week in advance)

• methyl green pryonin or aceto–orcein stain.

Alternatively use prepared slides of a root tip (if available).

If you do not have access to a microscope or prepared slide, use the photographs provided.

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Part 8: Growth and repair 3

Cell division

A multicellular organism such as a human, begins life as a single cell formed from the union

of two sex cells. From this microscopic beginning the organism grows to become an adult.

This is achieved by the process of cell division. One cell divides forming two cells and then

each of these cells divide forming more cells to continue the process of cell division.

Mitosis is a type of cell division that results in the replication of identical cells. Meiosis is

another type of cell division which produces gametes or sex cells. Meiosis produces cells

that have half the number of chromosomes of the parent cell.

Mitosis results in growth of an organism, is involved in the healing of wounds and the

replacement of cells eg. red blood cells and skin cells. With the exception of gametes (ova

and sperm), all the body cells or somatic cells come from pre–existing cells by mitosis.

1 Write a definition, in your own words, for mitosis.

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2 How is mitosis different from meiosis?

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3 What is the role of cell division in multicellular organisms?

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Check your answers.

Sites of mitosis

Mitosis occurs in areas of rapid growth in organisms. These sites are in different places in

different types of organisms. This is usually due to the need for rapid replication such as

growth points or sites where repair to damaged tissue is required. Multicellular organisms

may also have stages in their life cycle during which mitosis may occur at a greater rate such

as within a developing foetus.

4 Patterns in nature

Plants

Mitosis in plants occurs in special cells called meristematic cells and in the layer of cells in

the stem called cambium. These cells are responsible for the growth in length and width.

In the root there is a protective area called the root cap. Behind this area is the apical

meristem where active cell division is occurring. This is followed by an area of elongation

where the newly formed cells increase in size.

phloem

root hair

cortex

xylem

root cap

grow

th z

one

cell

elon

gatio

nce

lldi

visi

on

Diagram of a root tip showing the growth zone.

In the stems, secondary growth occurs in the cambium. The vascular cambium forms phloem

and xylem cells.

At the tip of the shoots there is the apical meristem where mitosis is occurring rapidly forming

new cells. Buds are another structure that contain meristematic tissue which is capable of

rapid growth.

Insects

Insects have a multiple staged life cycle. During a larval stage the organism increases in size.

This is due to cell enlargement and not cell division. Increased rates of mitosis occur in the

epidermal cells before a moult during the pupal stage. Metamorphosis results in the

breakdown of the larval tissue and the development of the adult insect.

Mammals

In mammals mitosis is occurring in many parts of the body. Skin, hair and nails are

continually growing. Blood cells are made daily to replace those that have died. Any injury

results in rapid mitosis to repair the damage. Young mammals are growing rapidly and at this

stage of life mitosis rates are high.

1 Complete the following table by matching the sites of mitosis in either

plant or mammal.

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Part 8: Growth and repair 5

Site of mitosis Plant/animal

root tip

skin

digestive tract

shoot tip

bone marrow

hair and nails

stems

2 Explain why mitosis is important to insects during metamorphosis.

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Check your answers.

Complete Exercise 8.1.

What happens during mitosis?

When a cell divides, a series of changes occur in the nucleus of cells. The most important

parts of the nucleus involved in the process are the chromosomes. Chromosomes determine

the characteristics of an organism. Genes are found along chromosomes and consist of

sections of DNA (deoxyribose nucleic acid). Most of the DNA in a cell is found in the

nucleus.

1 What is DNA? Why is it important?

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2 The DNA part of chromosomes carries the genetic code as genes.

Each time a cell divides by mitosis, new daughter cells end up with chromosomes, and

hence DNA, which is identical to those of the original parent cell.

The discovery of the structure of DNA and the way it is replicated during cell division,

has been one of the most exciting and important events in 20th century biology. Mitosis

is essentially the replication of chromosomes and their separation into daughter cells.

What major developments in technology do you think assisted in the identification of

DNA?

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6 Patterns in nature

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Check your answers.

Self replicating organelles

Plastids and mitochondria are self–replicating organelles. This means that when mitosis is

occurring these organelles reproduce independently of the nuclear division.

Chloroplasts (a type of plastid) and mitochondria both posses genetic material (DNA) that

enables them to replicate. It is thought that they may be descendants of ancient procaryotic

cells that have since become part of other cells.

1 List the cell organelles that contain DNA.

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2 Most of the cell’s DNA is present in the nucleus. What parts of the nucleus are made of

DNA?

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3 What is the role of DNA in the cell?

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Check your answers.

Complete Exercise 8.2.

Mitosis in plant cells

The process of mitosis in plants is similar to that in animals. However, there are two

differences:

• there are no centrioles in most plants

• the cell does not become constricted in the last stage of the process. In plant cells, the

partition usually starts in the centre of the cell and grows outwards to meet the existing

right cell wall.

1 Why do cells undergo mitosis?

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2 What are the differences between the parent cells undergoing mitosis and the resulting

daughter cells?

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Part 8: Growth and repair 7

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3 What is the significance of division after replication for a cell?

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Check your answers.

Microscopic examination of mitosis in plant cells

As you have already read the root tip is a site of rapid mitosis in plants.

In this experiment you will examine a root tip for the stage of mitosis.

Materials required:

• microscope and lamp

• two slides and a cover slip

• onion with fresh roots (you need to soak onion base in water at least a

week in advance)

• methyl green pryonin or aceto–orcein stain.

Alternatively use prepared slides of a root tip (if available).

If you do not have access to a microscope or prepared slide, use the photographs provided

following.

Procedure:

1 Remove a new root from the base of the onion and place it in the centre of a clean slide

(only the top portion is required if it is very long).

2 Place another slide on top and gently squash the two slides together. This should grind

the root tip.

3 Remove the top slide, ensuring the squashed material remains on the lower slide.

4 Add one drop of stain to the material and cover with the cover slip.

5 Allow to stand for about 20 minutes and then examine under the microscope.

Observe the cells in the slide of the root tip. You are looking for the different stages of

mitosis.

6 Identify cells that have undergone mitosis.

7 Draw diagrams showing the stages in mitosis.

8 Patterns in nature

Slide of root tip showing various stages of mitosis. How many stages can you pick out? (Photo JaneWest)

Interphase (animalcell)

nucleus

Interphase plant cell Your drawing of a plant cell

Prophase (animalcell)

Prophase plant cell Your drawing of a plant cell

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Part 8: Growth and repair 9

Metaphase (animalcell)

Metaphase plant cell Your drawing of a plant cell

Anaphase (animalcell)

Anaphase plant cell Your drawing of a plant cell

Telophase (animalcell)

Telophase plant cell Your drawing of a plant cell

Cytokinesis

Mitosis refers to the changes involving the chromosomes during cell division. Cell division,

however, usually includes the division of the cytoplasm and certain organelles within the

cytoplasm. The division of the cytoplasm is called cytokinesis.

In animal cells cytokinesis is usually achieved by the formation of a cleavage furrow which

deepens to constrict the two parts. In plant cells, a cell wall forms across the middle,

separating the two parts.

1 At what point in mitosis does cytokinesis occur?

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0 Patterns in nature

2 Why is cytokinesis important in cell division?

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Check your answers.

Complete Exercise 8.3.

You have come to the end of the module Patterns in nature. You will have come to recognise

that there are patterns in living things as they adopt similar methods of solving the problems

of surviving.

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Part 8: Growth and repair 11

Additional resources

Phases in mitosis

You do not need to learn the names of the stages of mitosis.

1 Interphase

This stage is sometimes misleadingly called the ‘resting’ stage.

In fact, the cell is very active. It is during this stage that each chromosome becomes

replicated. A cell with four chromosomes would end up with eight at this stage. Cells with

46 chromosomes (a human cell) would end up with 92 and so on.

Organelles, such as mitochondria, ribosomes (and chloroplasts in plants) are also replicated

although how they are replicated is not clearly understood. As well, the centrioles, which are

outside the nucleus, begin to separate. In most of the more complex plants there are no

centrioles.

2 Prophase

During this stage, the chromosomes are visible, first as long, thin strands. As the process

continues, the chromosomes become shorter and thicker. Each chromosome and its replica

are held together by a structure called the centromere. The identical chromosomes at this

stage are called chromatids. The centrioles move to opposite ‘poles’ of the cell and spindle

fibres start to form. This stage ends with the breakdown of the nuclear membrane.

3 Metaphase

The spindle consists of long molecules of protein lying across the cell from pole to pole. The

chromosomes move through the cytoplasm to the spindle and become fastened to it by their

centromere. The centromere becomes attached along a plane about halfway between the

poles.

This plane is called the equator. At this middle stage the chromosomes are in the middle of

the cell.

4 Anaphase

The centromeres divide so that each chromatid has its own centromere. Each chromatid now

is a daughter chromosome. The daughter chromosomes move apart, each member of a pair

moving to opposite poles of the cell. Each group of daughter chromosomes forms a densely

packed group at each pole. Remember: at anaphase the chromosomes are moving apart.

2 Patterns in nature

Notice that four chromosomes move to opposite parts (poles) of the cell. Notice also that the

cells start to become constricted in the centre.

5 Telophase

Nuclear membranes form around each group of daughter chromosomes. The chromosomes

uncoil to become slender threads. A new cell membrane forms at the equator. The cytoplasm

divides and two new daughter cells now exist, where there was originally only one parent cell.

1 interphase 2 early prophase

3 late prophase

4 metaphase

5 anaphase6 telophase

nucleus

centromere

chromatid

spindle

Mitosis in an animal cell with two chromosomes.

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Part 8: Growth and repair 13

Suggested answers

Cell division1 Mitosis is a type of cell division resulting in the replication of identical cells.

2 Meiosis produces cells that have half the number of chromosomes compared to the parent

cell. This process produces the gametes or sex cells.

3 Cell division is responsible for growth, repair and reproduction of multicellular

organisms.

Sites of mitosis

1 Site of mitosis Plant/animal

root tip plant

skin animal

digestive tract animal

shoot tip plant

bone marrow animal

hair and nails animal

stems plant

2 Cells need to be produced rapidly when undergoing metamorphosis compared to other

stages in which no mitosis occurs.

What happens during mitosis?1 DNA makes up the material of inheritance or the genetic material in a cell. Every cell

needs to have its own DNA code for its specific structure and function.

2 The development of the electron microscope and staining techniques.

Self replicating organelles1 The nucleus, chloroplasts and mitochondria all contain DNA.

4 Patterns in nature

2 The chromosomes in the nucleus are made of DNA. A section of DNA with specific

information is called a gene. Genes are part of chromosomes.

3 DNA contains information that is transferred when cells replicate.

Mitosis in plants1 Cells undergo mitosis for growth and repair of body tissue.

2 The parent cells are usually larger than daughter cells initially.

3 Cells must divide after replication otherwise they would end up with double the amount

of genetic material.

Cytokinesis1 After the chromosomes have separated into two nuclei the cytoplasm divides so that the

cells are able to enter interphase.

2 Cytokinesis is important because after mitosis the nucleus has divided and separate

nuclear membranes of the daughter cells have formed. Then the cytoplasm must divide

(cytokinesis) to produce two new cells.

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Part 8: Growth and repair 15

Exercises - Part 8

Exercises 8.1 to 8.3 Name: ________________________

Exercise 8.1: Mitosis

Mitosis is a very significant process in any living thing.

Write a short report to explain the significance of the process of mitosis for plants and

animals.

Your report should include reference to:

• the role of cell division in multicellular organisms

• the activities of chromosomes during mitosis (describe the sequence of change)

• where mitosis occurs in plants, mammals and insects.

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6 Patterns in nature

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Exercise 8.2: What happens during mitosis?

Identify the parts of a cell that contain DNA.

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Exercise 8.3: Cytokinesis

Explain the importance of cytokinesis.

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BIOPRE 43209 Patterns in nature

Student evaluation of the module

Name: ________________________ Location: ______________________

We need your input! Can you please complete this short evaluation to

provide us with information about this module. This information will

help us to improve the design of these materials for future publications.

1 Did you find the information in the module clear and easy to

understand?

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2 What did you most like learning about? Why?

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3 Which sort of learning activity did you enjoy the most? Why?

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4 Did you complete the module within 35 hours? (Please indicate the

approximate length of time spent on the module.)

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5 Do you have access to the appropriate resources? eg a computer, the

internet, scientific equipment, chemicals, people that can provide

information and help with understanding science

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Please return this information to your teacher, who will pass it along to

the materials developers at OTEN – DE.

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NSW Department of Education and Training