Cells The basic Unit of life Chapter Notes - Natural Science Grade 9 PDF
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Cells as the basic units of life
KEY QUESTIONS:
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What are cells?
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Why are cells so small?
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What does it mean to be microscopic?
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Are there different types of cells?
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What is inside a cell and why is it there?
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Are plant and animal cells the same?
NEW WORDS • cell • cytoplasm • eukaryote • membrane • microscope • microscopic • nucleus • organism • prokaryote
In this chapter we will learn about the basic units of life which enable all of functions within living organisms -cells.
1.1 Cell structure
What are cells?
All living organisms, including plants, animals, bacteria and fungi, are made up of cells. Cells are the smallest parts of all living organisms.
If we look at all the living organisms in the world we see that there are two main types of organisms based on the structures of their cells. The most important difference in structure is the presence of a nucleus. Cells that contain a nucleus are classified as eukaryotic cells, while those without a nucleus are prokaryotic cells. In this chapter we will specifically look at eukaryotic cells that make up organisms such as plants and animals. Examples of organisms with prokaryotic cells are bacteria.
DID YOU KNOW? All the New words listed in the boxes in the
We can say that cells are the basic structural and functional units of all living organisms. You cannot see individual cells with the naked eye, because they are too small -you need to use a microscope to be able to see cells. We say cells are microscopic because they can only be seen under a microscope.
margin are defined in the glossary at the end of this strand.
Robert Hooke (1635 -1703)
Robert Hooke was the first cytologist to identify cells under his microscope in 1665. He decided to call the microscopic shapes that he saw in a slice of cork "cells" because the shapes reminded him of the cells (rooms) that the monks in the nearby monastery lived in.
ACTIVITY: Brainstorm the Seven Functions of Life
Do you remember the test you learnt about in previous grades to decide whether an organism is living or non-living? Perhaps you had an mnemonic to remember the seven processes, such as "MRS GREN".
1.
Work in your group and see how many of the seven functions of life you can remember. Write them down below.
2. Do you think that an individual cell is living? Explain your answer.
Robert Hooke was the first to use the term 'cell' when he studied thin slices of cork with a microscope.
Robert Hooke's microscope that he used to first view cells.
TAKE NOTE
In this section you'll often read the prefix cyto-as in cytoplasm, cytosol or cytoskeleton. Cyto-means 'cell' so if you read cytoskeleton it actually says: 'cell-skeleton'.
TAKE NOTE
The Visit boxes in the margins contain links to interesting websites and videos. Simply type the link exactly as it is into the address bar in your browser.
Different types of cells
NEW WORDS
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carbon dioxide
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cell membrane
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cellular respiration
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DNA • hereditary • inherited
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medium
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mitochondria
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nuclear
membrane
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nucleolus • organelle
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oxygen • protein
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selectively permeable
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specialised
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species
• vacuoles • variation
Your body is made up of many different kinds of cells. We say your cells are specialised to perform a specific function. Depending on the function of the cell, it can be specialised by having a different shape or size or may have some components which other cells do not have. Have a look at the differences between nerve cells and red blood cells in the images.
These nerve cells appear green under a fluorescence microscope.
Red blood cells have a round, biconcave shape.
Even though there are many different types of cells, there are components of the cell structure which are common to all cells. There are also some structures which most, but not all, cells have. Let us take a look at this in the next section.
DID YOU KNOW? We call the study of cells cytology, cyto-meaning 'cell' and -logy meaning 'study', while -logist refers to the person who does the studying. The cytoplasm (cytosol and organelles) and the nucleus together is referred to as protoplasm.
Cell Structure
As we have mentioned before, all cells have some common structures. These are:
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a cell membrane
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cytoplasm; and
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in most eukaryotic cells, a nucleus
Let's now have a look at the structure of these components of the cell, and some of the other organelles common to cells. An organelle is a specialised structure within the cell that performs a function for the cell. Examples of organelles in cells are vacuoles and mitochondria. Look at the diagram which identifies the different components in a simple animal cell.
A drawing of a typical animal cell
Cell membranes
All cells have a cell membrane around them. The cell membrane is a thin layer that encloses the cell's contents and separates the cell from its environment.
Many different substances have to pass in and out of a cell in order for it to function. The cell membrane controls which substances are allowed to enter and leave the cell. We say the cell membrane is selectively permeable. The organelles are also surrounded by membranes.
Cytoplasm
The cytoplasm includes all living parts of the cell within the cell membrane, but excluding the nucleus. The cytoplasm is made up of the cytosol and the cell organelles. The cytosol is a watery, jelly-like medium made of 70%-90% water, and is usually colourless.
The cytosol is a mixture of different substances dissolved in water. Do you remember what a mixture is from Matter and Materials? These substances within the cytosol include salts, various elements, such as sodium and potassium, and more complex molecules, such as proteins.
The cytosol is also where many chemical reactions take place. Next term, in Matter and Materials, we will learn more about chemical reactions.
The cell organelles making up the cytoplasm include mitochondria, chloroplasts and vacuoles. Vacuoles are organelles enclosed by a membrane and contain mostly water with other molecules in solution. The size and number of vacuoles within a cell varies greatly and depends on the type and function of the cell.
(VISIT Videos about the cell and cell organelles. and
TAKE NOTE If something is 'permeable', then it means that substances, such as gases and liquids, can pass through it freely.
TAKE NOTE
In Natural Sciences we speak of a medium when we talk about a solution in which organelles, cells or organs are grown or suspended. Can you think of other meanings for the word medium?
TAKE NOTE
The difference between eukaryotic and prokaryotic cells is that eukaryotic cells have a nucleus which contains the genetic material surrounded by a membrane. Prokaryotic DNA floats in the cytoplasm without a membrane.
DID YOU KNOW?
Identical twins come from the same fertilised egg which splits in two. They have the same DNA. However, they are not exactly the same due to environmental factors that can influence how they develop. Non-identical twins developed from two different eggs and two different sperm.
This is a micrograph of a plant cell. Can you see the clear, white organelles, which are the vacuoles? The cytoplasm appears very granular in this image.
Nucleus
Plant and animal cells have a nucleus inside the cytoplasm. It controls all the processes and chemical reactions that take place inside the cell. The nucleus also contains the cell's genetic material which is organised into long DNA molecules.
The nucleus is structured as follows:
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A double membrane called the nuclear membrane encloses the DNA. This nuclear membrane contains pores (holes) for substances to pass through.
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There is a nucleolus inside the nucleus. This is often seen as a darker area within the nucleus.
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The DNA contains information about inherited characteristics (hereditary), such as whether the person will have blue, brown or green eyes.
Have a look at the micrograph of a nucleus and the diagram of the nucleus.
Left) A Diagram of a nucleus. Right) A micrograph of a cell nucleus.
DNA is a very important part of all cells and therefore of all life. DNA contains information that encodes all our inherited traits or characteristics. This refers to characteristics which are passed down in families, such as your skin and eye colour, whether you have allergies and also the likelihood of contracting different types of illnesses.
Every organism has unique DNA. The difference in DNA that occurs between individuals is called variation. Even the slightest difference in DNA might cause significant variations within species and between species. Within species DNA differences or variations can lead to albino animals or the transference of similar illnesses, like sickle cell anemia.
An albino (white) lion lacks pigment due to an alteration in the lion's DNA.
Mitochondria
Do you remember that we spoke about food as the energy source for our bodies? Just as wood is burned to use the stored potential energy to make a fire to heat some water, the food that we eat needs to be broken down in order to release the energy so that our bodies can function. Mitochondria are responsible for doing this.
Diagram of a mitochondrion.
Mitochondria are organelles enclosed by a double membrane. Cells that are very active would typically have more mitochondria than cells that are less active. Which type of cell, do you think, will have more mitochondria: a muscle cell or a bone cell?
A micrograph of muscle tissue in a mouse. Can you see all the darker grey circles? These are mitochondria.
Once food molecules enter the cells and pass into the mitochondria, they are used by the mitochondria in a process called cellular respiration. During respiration the mitochondrion can combine molecules from food with oxygen to
(VISIT Learn more about genes
TAKE NOTE
Singular or Plural? mitochondrion is the singular and mitochondria is the plural form of the word.
DID YOU KNOW?
Mitochondria have their own mitochondrial DNA that is completely different to the DNA in the nucleus. What do you think we can we deduce from this fact?
VISIT
If you would like to find out how mitochondrial DNA (mtDNA) is responsible for 'old age', read this article by Dr Barry Starr from Stanford University (
release energy that the cell can use. Carbon dioxide, water and waste materials are by-products of this process.
Micrograph of a mitochondrion within a cell.
Look at the micrograph of the mitochondrion in the image. What differences can you see between this mitochondrion and the diagram shown previously? In the diagram, it was very clear that the inner membrane folds, whereas in the micrograph it is not as easy to see this. This is because of the way that the cell was sectioned (cut) before it was viewed on the transmission electron microscope. In a diagram, we show an ideal representation of the organelle. But, when we view an actual organelle under a microscope, it may look quite different depending on how it was cut into a very thin section to view.
ACTIVITY: : Summarise what you have learnt
Now that you've studied the internal structure of a cell, let us summarise what we have learnt so far. Complete this table filling in the main function of each of the cell structures.
Cell Structure
Function(s)
Cell membrane
Cytoplasm
Nucleus
Mitochondrion
Vacuole
1.2 Difference between plant and animal cells
Now that we know what the main similarities are between all plant and animal cells, let's see how they are different.
Plant cells differ from animal cells
Why do plant and animal cells have differences? Plant and animal cells differ because they have to perform different functions.
ACTIVITY: Identify differences between plant and animal cells
1.
Study the pictures below. On the left is a picture of plant cells and on the right is a picture of some animal cells, which have been stained blue.
2.
Write differences that you observe in the table below the pictures of the cells.
Plant cells
Animal cells
NEW WORDS • cell wall • cellulose • chloroplast • turgid • flaccid
Cell wall
All animal and plant cells are enclosed or surrounded by a cell membrane as we learned before. However, as you probably noticed in the previous activity, animal cells often have an irregular shape, whereas plant cells have a much more regular, rigid shape.
Plant cells have an additional layer surrounding the cell on the outside of the cell
DID YOU KNOW?
Other organisms also have cell walls, like bacteria or fungi, but in these organisms their cell walls are not the same as plant cell walls. Only plant cells are made of cellulose.
membrane. This is called the cell wall. This wall provides a protective framework for support and stability for the plant cell.
The cell wall is formed from various compounds, the main one being cellulose. Cellulose helps maintain the shape of the plant cell. This allows the plant to remain rigid and upright even if it grows to great heights.
Chloroplasts
You might remember learning about photosynthesis in previous grades. Can you still remember why photosynthesis is so important to all life on earth?
Did you notice the green organelles present in plant cells which were not there in the animal cells in the previous activity? These are chloroplasts. Chloroplasts are the only cell organelles that can produce food from the sun's energy. Only plants with chloroplasts are able to photosynthesise because they contain the very important green pigment, chlorophyll. Chlorophyll can absorb radiant energy from the sun and convert this to chemical energy that plants and animals can use. Animal cells lack chloroplasts and are not able to photosynthesise.
DID YOU KNOW?
The sea slug,Elysia chlorotica, has evolved to take up the chloroplasts from the algae that it eats and incorporate them into its own cells where the chloroplasts function as if in a plant!
A large chloroplast next to the cell wall is visible in this section of a cell.
Vacuoles
Does a plant have a skeleton? Turn to a friend and discuss what could possibly be used in a plant cell as a skeleton. Think for example of a blade of grass or a long stemmed rose.
Vacuoles in plant cells are usually quite large organelles that can occupy as much as 90% of the cell's volume. The liquid in the vacuole, called cell sap, helps to support the plant. The full vacuoles push out against the cell wall and make the cells, and therefore the plant, rigid. We say the cells are turgid in this condition. The opposite to turgid is flaccid.
You can easily see when a plant's vacuoles are full and when they are not. When the vacuoles are full the plant's stem and leaves will be held upright and firm. However, if the leaves and stem are drooping, the vacuoles might have lost a lot of water because the soil is too dry and the cell was forced to use up this water to survive.
Left: A plant with turgid vacuoles is rigid and stands upright. Right: A plant with flaccid vacuoles droops (called wilting).
(VISIT Article and video on the solar powered sea slug, Elysia chlorotica.
Vacuoles are only present in some animal cells and they are typically very small and have a short life-span.
ACTIVITY: Comparing plant and animal cells
Study the two diagrams of plant and animal cells below.
1.
Draw a table of differences between the two cell types in the space provided. Give your table a suitable heading.
2.
Also provide labels for the different cell structures and organelles.
A typical animal cell.
A typical plant cell.
ACTIVITY: 3D model of a cell
In a 3D cell model, we will be making built models out of materials where we will use other objects to represent the actual parts of the cell.
INSTRUCTIONS :
1.
You must create a 3D model of a cell.
2.
You may use whatever materials or 'media' you choose to create your cell.
3.
Your model must clearly show the following:
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cell membrane
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nucleus with nuclear membrane
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cytoplasm
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mitochondria
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vacuoles
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chloroplasts
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Any other organelles that you might have learnt about
Requirements for your cell model:
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Your model and the examples of the organelles need to show some resemblance to the real organelle that we have learnt about so far.
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Your model needs to be clearly marked with a heading and your name.
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Each organelle needs to be clearly labelled and with each label you need to add a description of the function of that particular organelle.
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You also need to make an accompanying drawing (at least the size of an A4 page) including the labels of the structure of a basic plant and animal cell.
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Your teacher will assess your model according to a rubric.
1.3 Cells in tissues, organs and systems
Now that you have learnt all about different cells, are you ready to see them for yourself?
Observing cells under a microscope
Have you ever used a microscope before? Microscopes are instruments that are used to look at and study objects that are too small to be seen with the naked eye. Since the days of Hooke's observations, the development of microscopes has come a long way. Today we have incredibly powerful microscopes called electron microscopes which use electrons instead of light to observe very fine detail -even as small as a single column of atoms!
A modern electron microscope
Before we start working with microscopes, let's have a look at the different parts of a basic light microscope and the safety precautions we need to follow when using these pieces of equipment.
A basic light microscope
NEW WORDS • multicellular organisms • cover slip • slide • specimen • unicellular • wet mount
(VISIT Citizen science: Help out in cancer research from your own home!
A microscope allows you to see detail in specimens that you cannot see with the naked eye. The image you see needs to be:
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well lit with enough light provided to see the specimen
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well focused
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contrasted with its surroundings to clearly see details
(VISIT Video on making a wet mount slide.
The next image explains the different parts of a light microscope and what they are used for.
When you use a microscope, make sure to follow these safety precautions:
1.
There is a special way to carry the microscope: one hand supports the base and the other holds the frame of the microscope.
2.
Put it down on a stable, horizontal, clear counter.
3.
Before using the microscope, clean the lenses with proper lens paper. Do not touch the lenses with your fingers! Make sure the stage and slides are clean.
4.
When handling the slides, do not use broken or cracked slides and handle cover slips by the edges.
5.
When focusing with the objectives:
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Focus smoothly and slowly
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Be careful with the objectives and do not scratch them
6.
When you are done:
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Always turn the lowest magnification objective into place before storing the microscope.
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Make sure that the stage and slides are clean before putting everything away.
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Always store the microscope in a box or covered with a dust jacket to avoid dust from settling on the lenses.
To view cells under a microscope, we need to make and prepare something called a specimen on a slide.
A specimen is a small part or slice, or an example of an organism that we want to examine. When we view a specimen under a microscope it needs to let light pass through the specimen so we can see it. Therefore we need to prepare the specimen and cut extremely thin slices of less than 0.5 mm. Specimens are then placed on a glass slide.
We can prepare samples or specimens on a slide using these different techniques:
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wet mount -good for observing living organisms and is especially used for aquatic samples
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dry mount -good for observing hair, feathers, pollen grains or dust
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smears are often made of blood or slime that is smeared over the slide and allowed to dry before observing them.
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stains are added to wet or dry mounts by dropping colouring chemicals onto the specimens, like iodine solution, methylene blue or crystal violet. We use staining to improve the colour contrasts on the slide.
DID YOU KNOW?
We can use water, brine (salt water), glycerine or immersion oil for wet mounts.
ACTIVITY: Evaluating microscopic images
INSTRUCTIONS:
1.
Carefully study this image of onion cells that have been stained blue. Evaluate this image in terms of the focus, light and contrast visible in the photo.
2.
These same onion cells were viewed under a microscope which had not been adjusted properly and the following photos were taken. Identify what is wrong with the photograph compared to the one above.
Image
What is wrong with the image?
How could the image have been adjusted and corrected, using what part of the microscope?
ACTIVITY: Making a wet mount with onion and cheek cells
There is a very specific way to prepare slides for viewing under a microscope. You will use this technique very often in Life Sciences to study specimens.
MATERIALS:
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onion
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scalpel or knife
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dissecting needle
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forceps
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microscope slides
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coverslips
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dropper
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tissue paper or filter paper
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distilled water
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iodine solution
•
light microscope
INSTRUCTIONS:
Step 1: Prepare your microscope and slides as discussed in the safety methods above.
Step 2: Cut the onion into blocks of about 1 cm square with a sharp knife or scalpel.
Step 3: Use forceps to pull or peel a small piece of the very thin membrane-like epidermis lining off one of the inner layers of the onion.
Step 4: Place a drop of iodine solution onto the slide.
Step 5: Place the membrane directly in the drop on the slide.
Cutting the onion to expose the layers.
Carefully pulling the lining off the onion layer.
Adding iodine solution to the slide.
TAKE NOTE You will need to work quite quickly as the onion cells will dry out!
Step 6: Gently lower a coverslip at an angle onto the onion cells. Hold the coverslip up with a dissection needle and gently lower the slip. This prevents air bubbles from getting trapped under the cover slip.
TAKE NOTE If you accidentally trapped an air bubble, gently press on the middle of the coverslip to get rid of any trapped air using the dissecting needle or drop some extra fluid right next to the edge of the coverslip.
Step 7: Wipe off excess fluid around the edge of the coverslip with tissue paper or filter paper. Step 8: Make sure the lowest power objective lens (this is the shortest lens) is in line with the eyepiece. Switch on the lamp or use the mirror to reflect the light onto your stage. Place the prepared slide onto the stage and secure it with the stage clips.
Step 9: While on the low power, look from the side and lower the objective lens to just above the coverslip. Then look through the eyepiece and use the fine focus to focus your image. Step 10: Magnify your cells by swapping the objective lens to a higher powered lens. Only use the fine focus adjustment to focus clearly. Step 11: Make careful drawings of your observations in the space below and remember to label what you see. Add a heading including the specimen, the stain used and the magnification.
The slide secured on the microscope stage.
Onion cells.
Now that you have prepared slides of onion cell specimens, use a toothpick to gently scrape the inside of your cheek to collect cheek cells using the side of the toothpick or ice cream stick. Follow the same instructions as above to prepare the cheek cell specimen and to view it under the microscope. Draw and label the cheek cells that you viewed under the microscope in the space below.
Did you see something like this?
Some cheek cells stained with methylene blue
1.
What are some of the differences and similarities you noted between the animal and cheek cells?
ACTIVITY: Research the discovery of light and electron microscopes
The invention and improvement of microscopes has lead to incredible cellular discoveries (among others) in the last 400 years. Without microscopes, many of the microscopic organisms we know of today would never have been identified!
INSTRUCTIONS:
1.
You can work individually or in groups for this task.
2.
Research the history and discovery of the light and electron microscopes and how they are used today.
3.
Design a brochure for the local Science museum where you tell visitors about the history of the development of microscopes.
4.
Remember that a brochure must be informative, but not contain too much text.
5.
Include some photographs or drawings.
Cells differ in shape and size
NEW WORDS • stem cell • differentiation
We looked at the basic differences between plant and animal cells. However, not all plant cells and not all animal cells are the same. Cells within an organism need to have different shapes and sizes because they fulfill different functions.
Look at the photo of the rose. Do you think the cells in the roots, stem, leaves, and petals of the rose all look the same?
The cells in the different parts of the rose all have to perform very specific functions and therefore have different sizes and shapes.
The rose's petals are red due to pigments in the vacuoles of the petal cells which are round.
Cells in the leaves are full of chloroplasts for photosynthesis. They are long and rectangular in shape.
Your body contains a great number of specialised cells, meaning they have different functions. They have differences in their structures allowing them to have different functions. We say they have differentiated.
Do you remember we spoke about nerve cells and red blood cells briefly in the beginning of the chapter? Some of them are summarised in the following table.
Specialised cell
Structure
Function
Epithelial cells -they are mostly flat
They cover the surface of the body for protection.
Muscle cells - some are long and spindle shaped
Muscle cells can contract and relax allowing for movement within your body
Nerve cells - the are very long and have branched ends
Nerve cells are specialised to carry messages that coordinate the functions of the body.
Red blood cells -Round and biconcave shape
Red blood cells carry carry oxygen and carbon dioxide throughout the body.
DID YOU KNOW?
Stem cells are also harvested from the umbilical cord at birth and used for research. There are many ethical concerns regarding stem cell research. What do you think?
Stem Cells
TAKE NOTE
Microscopic and macroscopic describe whether an organism can be seen with the naked eye, while unicellular and multicellular refer to the number of cells an organism has.
Stem cells are unspecialised cells which can divide and develop into many different types of specialised cells. Stem cells are quite amazing as they can divide and multiply while at the same time keeping their ability to develop into any other type of cell. Embryonic stem cells are the little ball of 50 -150 cells that forms 4-5 days after conception. Embryonic stem cells are very special as they can become absolutely any cell in the body, for example, blood cells, nerve cells, muscle cells or brain cells.
For this reason, scientists are using stem cells to conduct research. There are many benefits in doing this, but there are also many controversial and ethical issues surrounding stem cell research.
Are you curious about stem cell research? Find out more and discover the possibilities!
Microscopic and Macroscopic organisms
We have just looked at specialised cells within organisms. The organisms that we discussed, plants and animals, consist of many, many cells. Your body has millions of cells! Did you know that there are some organisms which consist of only a single cell? We have many different specialised cells to perform the different functions within our body whereas in a single-celled organism, all the functions it performs are done in this one cell. We can make a distinction between organisms that are made of one cell (unicellular) and those that are made of many cells (multicellular).
Microscopic organisms
We call one cell organisms that can only be seen with the help of a microscope microscopic organisms. There are many single-celled microscopic organisms. Have a look at the images.
A group of Escherichia coli bacteria which are found in the intestines of many animals.
An amoebae which is a single cell organism that lives in water.
Red blood cells showing some which have been infected with malaria (purple dots).
A single-celled algae called a desmid.
Macroscopic organisms
In contrast to microscopic single-celled organisms, macroscopic organisms are visible to the naked eye and consist of many cells. Macroscopic organisms can have a few cells working together or trillions of cells that form larger organisms.
Organisation of cells in macroscopic organisms
In microscopic single-celled organisms, the individual cell has to perform all the life processes for that microscopic organism.
So what about the cells in macroscopic organisms that consist of many cells? We have already learnt about specialised cells in macroscopic organisms, so we know that not all cells perform all the processes -they are specialised to perform a specific function.
Specialised cells that perform a specific function, group together to form a tissue. For example, muscle cells will group together to form muscle tissue, epithelial cells will group together to form the skin, and nerve cells will group together to form the brain and nerves.
Groups of tissues that work together form organs. Think of the stomach for example -it is made of many different specialised cells that form muscle tissue to make it contract and epithelial tissue (made from specialised epithelial cells) which lines the inside of the stomach and produces mucus.
When organs work together we say they form systems or organ systems. There are many different systems in your body where specific organs work closely together to make your body function. Have a look at the following diagram which shows how cells are organised into tissues in the stomach which form part of the digestive system in a human (the organism).
VISIT Take a virtual tour of the human body (
(VISIT Learn more about the different systems in your body
All the systems work together to form an organism. We will be looking at some of these systems later on in the term.
Have you noticed the VISIT boxes in the margins which contain links? You simply need to type this whole link into the address bar in your internet browser, either on your PC, tablet or mobile phone, and press enter, like this:
It will direct you to our website where you can watch the video or visit the webpage online. Be curious and discover more online on our website!
SUMMARY:
Key Concepts
•
Cells are the basic structural and functional units of all living organisms.
•
Cells are microscopic and can only be seen under a microscope.
•
Plant and animal cells have cell membranes, cytoplasm, a nucleus and organelles such as mitochondria and sometimes vacuoles.
•
The cell membrane encloses the contents of the cell and separates it from its environment.
•
Cell membranes are selectively permeable, which means they only allow certain substances to pass into and out of the cell.
•
The cytoplasm includes the organelles and the cytosol. The cytosol is the jelly-like medium in which many chemical reactions take place in the cell. Everything inside the cell membrane, except the nucleus, is considered the cytoplasm.
•
The nucleus in eukaryotic cells is enclosed by a nuclear membrane and contains the DNA.
•
DNA contains inherited characteristics of an organism and controls the cell's activities. It is unique to each organism, resulting in variation within a species.
•
Mitochondria are responsible for cellular respiration, which is the release of energy from food.
•
Plant cells have a cell wall around the cell membrane that is rigid and provides support and protection of the cell's content.
•
Plants have chloroplasts with the pigment chlorophyll to photosynthesise and produce glucose.
•
Plant cells also have large vacuoles to store water and glucose, and to provide support for the plant.
•
Vacuoles in animal cells are temporary (or absent) and much smaller.
•
Cells come in many different shapes and sizes.
•
Stem cells are cells that have the ability to divide and develop into many different cell types.
•
Microscopic organisms can only be seen under a microscope. All single-celled organisms, such as bacteria, are microscopic. However, some multicellular organisms such as dust mites are also too small to see with the naked eye.
•
Macroscopic organisms consist of many cells and can be seen with the naked eye.
•
Specialised cells perform special functions. Specialised cells that work together to perform a specific function form a tissue.
•
A group of different tissues makes up an organ.
•
Organs working together in groups form systems or organ systems.
•
Organ systems make up an organism, such as a human,
Concept Map
This year in Natural Sciences, we are going to learn more about how to make our own concept maps.
In the summary, we first have the "Key concepts" for this chapter. This is a written summary and the information from this chapter is summarised using words. We can also create a concept map of this chapter which is a map of how all the concepts (ideas and topics) in this chapter fit together and are linked to each other. A concept map gives us a more visual way of summarizing information.
Different people like to learn and study in different ways; some people like to make written summaries, whilst others like to draw their own concept maps when studying and learning. These are useful skills to have, especially for later in high school and after school!
Have a look at the concept map which shows what we have learned about the cell in this chapter and how these concepts link together. Can you see how the arrows show the direction in which you must "read" the concept map?
There are some empty spaces in the concept map that you need to fill in. For example, some of the common structures in cells have been left out. You need to look at the concepts linking from these bubbles to work out which structure goes where. For example, what structure in a cell encloses the cell contents? Write the answer in the correct space. On the left hand side of the concept map there are also empty spaces -can you see that this describes the hierarchy of how cells are organised into tissues, which are organised into organs, and so on? Fill in each level of organisation into the spaces.
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REVISION:
1.
Why would you say cells are considered to be the smallest unit of life? [2 marks]
2.
Explain what selectively permeable means when referring to the cell membrane. [1 mark]
3.
Eukaryotic and prokaryotic cells differ. What is the main difference between these two types of cells? [2 marks]
4.
What is the main function of the nucleus and what is the function of the DNA? [2 marks]
5.
When a Gr. 9 learner labelled one of the cell organelles 'Powerhouse', their teacher marked it wrong. What should the learner rather have written? [1 mark]
6.
A plant and an animal cell are similar in some ways yet very different in others. Compare the two types of cells in a paragraph. [10 marks]
7.
Make two drawings to show the differences between plant and animal cells using the examples of plant and animal cells you studied under the microscope. Follow the drawing guidelines for making scientific drawings. [10 marks]
8.
There are different types of specialised cells and tissues in plants and animals that perform different functions. Match each function to the corresponding tissue. [3 marks]
Smooth muscle tissue
receives and sends messages and helps the body respond to stimuli
Nerve cell
carry oxygen around the body in mammals
Red blood cells
contracts and enables movement
9.
Use words from this box to complete the sentences below. Write the sentences out in full. [4 marks]
•
organs
•
tissues
•
organ systems
•
specialised cells
Macroscopic organisms consist
of many different
that are
made of individual
that work together in a very particular
way. These are formed from
that are in turned created
when groups of
function together in a specific way.
Total [35 marks]
Here is your chance to discover the possibilities. What can this apple become?
