Download Through the microscope - NSW Department of Education

Science Stage 4
Set 3: Lessons 11 to 15
NEW SOUTH WALES
DEPARTMENT
OF EDUCATION
AND TRAINING
Through the microscope
Set 3: Looking at cells
Number: 31719
Title: Through the Microscope
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Extracts from Science Syllabus Years 7-10 © Board of Studies, NSW 2003
Unit Outline
pp vi-viii
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i
Through the microscope
Here are the names of the lessons in this unit.
Set 1
☞
Looking more closely
Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5
What does living mean?
What keeps your body alive?
What can you see with a hand lens?
How to draw diagrams
Why use a microscope?
Set 2
Making things look bigger
Lesson 6
Using a microscope
Lessons 7 and 8
Making a slide
Lesson 9
What is tissue made of?
Lesson 10
Tissue is made of cells
Set 3
Looking at cells
Lessons 11 and 12
Lessons 13 and 14
Lesson 15
Animal cells
Plant cells
Comparing plant and animal cells
Taking another look
Lesson 16
Lesson 17
Lesson 18
Lesson 19
Lesson 20
Living cells
Cell division
Unicellular organisms
Multicellular organisms
Looking back
Set 4
Through the microscope
Set 3
ii
Set 3: Looking at cells
Contents
What will you learn in Set 3? ...................................................................iii
What do you need for Set 3? .....................................................................v
Lessons 11 and 12
Animal cells............................................................1
Lessons 13 and 14
Plant cells................................................................7
Lesson 15
Comparing plant and animal cells....................11
Suggested answers ...................................................................................19
Send-in pages ............................................................................................21
Through the microscope
Set 3
iii
What will you learn in Set 3?
When you have finished Set 3, you should be able to answer these questions.
Under each question is a list of things you should be able to do
to answer the question.
12. What are the functions of the parts of a typical animal cell?
(a) Name the parts of a typical animal cell.
(b) Give the function of the parts of a typical animal cell.
(c) Draw a diagram of a typical animal cell.
(d) Label a diagram of a typical animal cell.
13. What are the functions of the parts of a typical plant cell?
(a) Name the parts of a typical plant cell.
(b) Give the function of the parts of a typical plant cell.
(c) Draw a diagram of a typical plant cell.
(d) Label a diagram of a typical plant cell.
14. How do you compare and contrast objects?
(a) Say how two things are similar.
(b) Say how two things are different.
(c) Identify a cell as plant or animal from the parts present.
Through the microscope
Set 3
iv
You should also be able to pronounce, spell, explain and use
these words correctly:
cell membrane
nucleus
cytoplasm
cell wall
vacuole
chloroplast
calculate
micron
specialised
function.
Through the microscope
Set 3
v
What do you need for Set 3?
Here is a reminder of the items you need for Set 3. To save time,
it might be a good idea to get all these things ready before you start.
Lessons 11 and 12
•
packet of jelly crystals, preferably yellow
•
hot water
•
basin or bowl
•
plastic bag, about 6 x 12 cm
•
large lolly, such as jaffa
•
cup
•
stirring spoon
•
sticky tape
•
fridge
Lessons 13 and 14
•
rest of jelly crystals
•
basin
•
cup
•
stirring spoon
•
hot water
•
fridge
•
large lolly
•
several smaller lollies, such as green Smarties
•
plastic drink bottle, about 250 mL
•
rubber band or string
•
small plastic bag, about 2 x 4 cm
Lesson 15
•
model animal cell from Lessons 11 and 12
•
model plant cell from Lessons 13 and 14
Through the microscope
Set 3
vi
Through the microscope
Set 3
1
Lessons 11 and 12
Animal cells
There are thousands of millions of cells in your body.
Someone estimated that an adult human body contains
about 60 billion (million million) cells.
The cells in your body lead double lives. One part of a cell's life
is carrying out those activities that keep the cell alive.
All cells have features in common that are used to keep the cell alive.
In this part of a cell's life it acts on its own.
The other part of the life of a cell is its action as part of a tissue.
Here it contributes to the life of the organism it is found in.
To do its special job as part of a tissue, cells often have special sizes,
shapes or features. Scientists say that the cells are specialised.
It’s much the same as saying that a person becomes specialised in a job.
A doctor may become specialised as a surgeon. A mechanic may specialise
in fixing one kind of car.
Here are some examples of specialised cells.
Muscle cells are specialised
to contract and shorten,
over and over again.
Red blood cells are specialised
to carry oxygen around the body.
Nerve cells are specialised to
carry electrical messages from
one part of the body to another.
Figure 11.1
Some examples of specialised animal cells
Through the microscope
Set 3
2
Parts of an animal cell
An animal cell is the smallest part of an animal that can show
the characteristics of life. But what are the parts of an animal cell?
Cell membrane
Each cell has a definite edge or boundary. This boundary is called
the cell membrane. It is a very thin outside wrapper of the cell.
The function, or job, of the cell membrane is to surround the cell and
to control which substances move in and out of it.
If you would like to see a cell membrane, have a look at an egg
next time someone is going to cook one. Carefully break the egg
onto a saucer – try not to break the yolk. Rinse out the shell and
use a pair of tweezers to peel off some of the rubbery layer
inside the shell. This is one sort of membrane in an egg.
There is also a membrane around the yolk. Use the point of a sharp knife
to break the membrane around the yolk and pull it to one side.
Did you notice it was thinner than the one inside the shell?
The membranes around most cells are much thinner than the membranes
you find in an egg.
Nucleus
Have you noticed a large dark spot somewhere near the centre of
most cells you have seen in this unit? (Look back through the
photographs and drawings in Lesson 9 and 10.) This spot is
called the nucleus and it acts as the control centre of the cell.
It directs the growth of the cell and the activities that
go on inside the cell.
You cannot always see the nucleus, but every cell must have one.
That is, all cells except red blood cells. This is another way that
red blood cells are specialised.
Cytoplasm
The rest of the cell is a jelly-like material called cytoplasm.
Many chemical reactions occur in the cytoplasm.
These reactions help to keep the cell alive and do its specialised job.
Through the microscope
Set 3
3
A typical animal cell
Some parts of the cell that keep the cell alive are the membrane,
the cytoplasm and the nucleus. Even though all the animal cells
you have seen are different sizes and shapes, they have these things
in common. Figure 11.2 is a diagram of a typical animal cell.
It shows these common features.
Figure 11.2
A diagram of a typical animal cell
The diagram in Figure 11.2 shows that animal cells are
roughly round, have a cell membrane, a nucleus and cytoplasm.
Now look back through the information on page 2.
Underline the function of each part of the animal cell.
Use the information to complete these sentences.
1.
The cell membrane surrounds … ___________________________________
2.
The nucleus directs … ______________________________________________
3.
The cytoplasm is where chemical reactions occur to …
Please compare your sentences with the ones in the answer pages.
Exercise 11
Make your own drawing of a typical animal cell
in send-in Exercise 11. Make sure you label your diagram.
Through the microscope
Set 3
4
Model of a typical animal cell
In science, a model is often a simple thing which helps you understand
a more complicated idea. It is often not very like the real object
but it helps you picture what the real object is like or how it works.
A model may have some or all of the features of the real object.
A cell is not really like the model you're going to make,
but it can give you some idea of what a cell is like.
The model you will make shows the parts of an animal cell.
You’ll need jelly crystals, hot water and a basin to make up the jelly,
and a plastic bag and large lolly.
You will use your completed model in Lesson 15.
1.
Which part of an animal cell could be represented by the:
•
plastic bag?
___________________________________________________
•
large lolly?
____________________________________________________
•
jelly?
__________________________________________________________
The plastic bag is the cell membrane, the lolly is the nucleus and
the jelly is the cytoplasm.
2.
Here are some bits of sentences that describe how
parts of your model resemble the real cell parts.
Use lines to join the sentences together correctly.
A nucleus is
like cytoplasm.
A cell membrane
is thin like a plastic bag.
Jelly contains dissolved substances,
approximately round like a lolly.
If your sentences are scientifically true, they should also be good sentences.
If you’d like, you can compare them with the ones in the answer pages.
Through the microscope
Set 3
5
Making your model
1
Use about 5 of the packet of jelly crystals and keep the rest of the packet
for your next lesson. Put the crystals in a basin and add half a cup
of hot (not boiling) water. Stir until all the jelly crystals have dissolved.
When the jelly has cooled down a bit, pour some of the mixture
into the plastic bag until it is about half full. Put the bag with
the jelly in a cup so that it does not spill and put the cup in a freezer
or fridge. When the jelly has partly set, take it out of the fridge,
add the lolly and almost fill the bag with the rest of the jelly solution.
Put the cup back in the fridge until the jelly sets. Fold over the top
of the plastic bag and seal it with sticky tape.
Keep your model animal cell in the fridge until Lesson 15.
Important
For your next lesson, you will need:
•
the rest of the jelly crystals
•
a basin
•
a cup
•
a stirring spoon
•
hot water
•
a fridge
•
another large lolly
•
several smaller lollies – green Smarties would be ideal
•
a plastic drink bottle – about 250 mL
•
a rubber band or string
•
a small plastic bag about 2 x 4 cm
If you don’t have one, use the corner of a larger plastic bag.
You’ll need scissors to trim away the extra plastic bag
from a large bag.
Through the microscope
Set 3
6
Through the microscope
Set 3
7
Lessons 13 and 14
Plant cells
Plants are living things and so they are also made of cells.
Plant cells have to carry out activities to stay alive and
they also have special features which allow them to contribute to
the life of the organism.
The onion cells that you looked at in Set 2 are an example of plant
cells. Here are some more examples.
Plants contain cells that act as pipes
to carry water and dissolved substances
throughout the plant.
These cells are grouped into tissue
called xylem and phloem vessels.
The surface (epidermis) cells of plants
are not all the same. Some of them
are kidney-shaped and work in pairs
to control water loss from the plant.
Figure 13.1
Some examples of specialised plant cells
Through the microscope
Set 3
8
Parts of a plant cell
Plant cells are like animal cells because they have a cell membrane,
a nucleus and cytoplasm. As well, plant cells have other parts.
Cell wall
Look at the pictures of the plant cells on page 7.
Did you observe that plant cells have thicker edges than animal cells?
You may have thought that plants have a thick cell membrane,
but they do not. Plants do not have bones or shells to let them
keep their shape. Instead of bones, each cell has an outside coating
of waxy, non-living material. This coating is made by the cytoplasm.
The coating is called the cell wall and its function is to help plant cells
keep their shape and so keep the whole plant upright when it is growing.
Vacuole
In many plant cells, there is a part of the cell that looks clearer
than the rest of the cytoplasm. It is called the vacuole.
A vacuole is like a blister inside the cytoplasm. It is a bag made
from membrane that contains water with substances dissolved in it.
Vacuoles are not often present in animal cells but some plant cells
have very large vacuoles. Most plant vacuoles store food for the plant
and help control the amount of water in the plant cell.
Chloroplast
The green parts of a plant make the food for the plant.
This is carried out in special parts of the cells called chloroplasts.
Chloroplasts often look like tiny green footballs spread throughout
the cytoplasm.
Why do you think the cells in the onion skin have no chloroplasts?
That's right, the cells in the skin of an onion are not green and
do not make food, so they do not have chloroplasts.
Would you expect to find chloroplasts in root cells?
No, because root cells do not make food either.
Through the microscope
Set 3
9
A typical plant cell
Here is a diagram that shows the most common features of plant cells.
Figure 13.2 A diagram of a typical plant cell
The cell membrane is like an inner tube of a tyre.
It is usually pressed against the cell wall in the same way that
an inner tube is pressed against the outer part of a tyre.
Usually you cannot see the cell membrane as a separate line
in a photograph or diagram. You must infer it is there,
around the inside of the cell wall.
And remember that the vacuole is not an empty space
but is filled with fluid.
Now check that you know the function of each part of a plant cell.
Underline the functions of the parts on page 8. If you need to,
look back at page 2 to remind yourself of the functions of the cell
membrane, nucleus and cytoplasm.
Then point to each name on the diagram above and say aloud
the function of that part. Practise until you feel confident that you
know the names and functions of all the parts of the cell.
Exercise 13
Make your own drawing of a typical plant cell in the send-in pages.
Label all the parts of the cell.
Through the microscope
Set 3
10
Model of a typical plant cell
Your model will contain objects to represent the parts of a typical plant cell.
In the animal cell model, jelly was used to represent the cytoplasm
and a large lolly represented the nucleus. These parts of your plant model
can be the same.
But you need extra things for a plant cell model.
Can you guess which part of a plant cell could be represented by:
•
green Smarties?
___________________________________________________
•
a plastic bottle?
____________________________________________________
•
a small plastic bag filled with water?
_____________________________
The Smarties can represent chloroplasts, the plastic bottle is the cell wall and
the plastic bag will represent the vacuole.
Where do you think the cell membrane will be on your model?
You will have to imagine that the cell membrane is the inside surface
of the plastic bottle.
Making your model
1
Make up the rest of the jelly crystals, this time using 12 cups of hot water.
Again, let the jelly cool before you handle it.
1
Pour jelly into the plastic bottle until the bottle is about 3 full.
Add some of the small, green lollies and put the bottle in the fridge
until the jelly partly sets.
While the jelly is setting, take the small plastic bag, put about two spoonfuls
of water into it and tie off the neck with a rubber band. When the jelly
is partly set, take it out of the fridge and add the plastic bag and
the large lolly to the bottle.
2
Pour in jelly until the jar is about 3 full. Again, partly set the jelly.
Add the last of the green lollies and the rest of the jelly. Set the jelly.
Important
For the next lesson, you will need:
•
your models of the animal and plant cells
•
a computer with Internet access.
Through the microscope
Set 3
11
Lesson 15
Comparing plant and animal cells
Comparing objects
Comparing usually means finding things in common.
If you were asked to compare the two pictures below,
you would look for similarities (things that are the same).
Picture 1
Picture 2
Figure 15.1 Two pictures of some objects you might find on an office desk
Through the microscope
Set 3
12
Make a list of the things that are in each picture in Figure 15.1.
You can try it as a memory task, if you like. Look at the picture,
then try to write all the items without looking again.
And don’t forget to check that you have remembered everything!
Picture 1
Picture 2
Which things appear on both lists?
Write a sentence for your answer on the lines below.
These are the things that are similar in the two pictures.
You can look at the list in the answer pages if you like.
Through the microscope
Set 3
13
Contrasting objects
If you were asked to contrast two things, you would look for
differences between them. The first sort of difference you can look for
in the two pictures in Figure 15.1 are things that are present in one picture
but not in the other.
What things are in Picture 1 that are not in Picture 2?
Write a sentence for your answer.
As well as things that are not present in one of the pictures,
you could also look for things that are not exactly the same
in the two pictures. You can look for differences in properties
such as size, shape, hardness or colour.
Can you see an object which is present in both pictures
but is a different size in each?
Check your answers in the answer pages.
Through the microscope
Set 3
14
Similarities and differences of cells
You will use your jelly models of the plant and animal cell to
compare and contrast some of the parts and properties of cells.
Make a list of the parts of cells that are represented in your models
of animal and plant cells.
Animal cells
Plant cells
Now compare the two types of cells by saying
what parts are present in both.
What parts are present in the plant cell but not in the animal cell?
This is one of the differences between plant and animal cells.
Plant cells have parts which are not normally found in animal cells.
Through the microscope
Set 3
15
What happens if you gently squeeze each of your model cells?
Would you say that they both behaved in exactly the same way?
You should find that the plant cell is more difficult to squeeze
out of shape – the cell is more rigid. This is another difference
between plant and animal cells.
Exercise 15.1
Compare plant and animal cells by filling in the table in Exercise 15.1
in the send-in pages. The table also asks you to describe the function
of each part of a cell.
There is one more activity for you to do in this lesson.
It is on the next page.
Through the microscope
Set 3
16
Can you find the missing cells?
Some cells have been stolen from a laboratory
and a reward has been offered for their return.
Can you find them hidden in the drawing below?
(Hint: The missing cells are shown on the next page.)
Figure 15.2 Search for the missing cells
There is a solution in the answer pages.
Through the microscope
Set 3
17
Here are diagrams of the missing cells.
Figure 15.3 Diagrams of the lost cells
Exercise 15.2
In this exercise you’ll record more words and their meanings.
Please complete this exercise now.
Through the microscope
Set 3
18
Through the microscope
Set 3
19
Suggested answers
Lessons
11 and 12
Page 3
Animal cells
A typical animal cell
These sentences describe the functions of the parts of an animal cell.
1. The cell membrane surrounds the cell and controls which substances
move in and out of the cell.
2. The nucleus directs the growth of the cell and the activities that go on
inside the cell.
3. The cytoplasm is where chemical reactions occur to keep the cell alive
and do its specialised job.
Model of a typical animal cell
Page 4
Lesson15
Here are the correct sentences.
• A nucleus is approximately round like a lolly.
• A cell membrane is thin like a plastic bag.
• Jelly contains dissolved substances, like cytoplasm.
Comparing plant and animal cells
Comparing objects
Page 12
Did you list these objects?
Picture 1
Picture 2
stapler
thumb tack (or drawing pin)
fold-back clip
sticky tape
pencil
dark-coloured pen
light-coloured pen
scissors
ink pen
stapler
fold-back clip
sticky tape
pencil
dark-coloured pen
scissors
ink pen
The things that are on both lists are the stapler, fold-back clip,
sticky tape, pencil, dark-coloured pen, scissors and ink pen.
Through the microscope
Set 3
20
Contrasting objects
Page 13
The things that are in Picture 1 but not in Picture 2 are the thumb
tack and the light-coloured pen.
The pencil is present in both pictures, but it is smaller in Picture 2.
Similarities and differences of cells
Page 14
Did you include these parts from your models?
Animal cells
Plant cells
cytoplasm
cytoplasm
nucleus
nucleus
cell membrane
cell membrane
vacuole
chloroplasts
cell wall
Both animal and plant cells have cytoplasm, a nucleus and
a cell membrane.
A plant cell contains a vacuole, chloroplasts and a cell wall
but an animal cell does not.
Can you find the missing cells?
Page 30
The missing cells are shown inside the circles.
Through the microscope
Set 3
21
Send-in page
Name
______________________________
Lessons 11 and 12: Animal cells
Exercise 11
Draw and label a typical animal cell.
Through the microscope
Set 3
22
Through the microscope
Set 3
23
Send-in page
Name
______________________________
Lessons 13 and 14: Plant cells
Exercise 13
Draw and label a typical plant cell.
Through the microscope
Set 3
24
Through the microscope
Set 3
25
Send-in page
Name
______________________________
Lesson 15: Comparing plant and animal cells
Exercise 15.1
Fill in the spaces in the following table.
Put a tick, ✓, if the part named is usually present and
a cross, ✗, if it is not normally present.
For function, write the normal job of that part of a cell.
Part
Present in
Present in
animal cells plant cells
Function
nucleus
cytoplasm
cell
membrane
cell wall
chloroplast
vacuole
Through the microscope
Set 3
26
Exercise 15.2
1.
Listen to the audio file called Through the microscope track 4.
Access this at: http://www.cli.nsw.edu.au/kto12.
Go to Science, then Stage 4 Junior Science,
then Through the microscope.
Concentrate on hearing how these ten words are pronounced.
cell membrane
nucleus
cytoplasm
cell wall
vacuole
chloroplast
calculate
micron
specialised
function
SPEAK
2.
Practise saying the ten words listed above.
3.
What does each word mean? Say each word aloud,
then use your own words to explain what it means.
4.
Record each word onto an audiotape or computer and then
say what you think the word means in your own words.
❒
Tick this box when you have finished your recording.
Do not send your recording to your teacher
with these send-in pages. You will add more words to it
in the next set.
Through the microscope
Set 3