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CELL STRUCTURE AND FUNCTION

Author: Janice HoLungNote: Diagrams in text, unless otherwise acknowledged, are by by author.

Iconos images courtesy of NEPA, Jamaica. Source of other images acknowledged below each one.

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OBJECTIVES

• You will be able to describe the structure of simple unspecialized plant and animal cells

• You will be able to differentiate between plant and animal cells

• You will be able to state the functions and explain the importance of selected cell organelles.

• You will be able to make simple line drawings of unspecialized cells

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Components of CellsLiving things are made up of cells.Often we are asked what are the characteristics of living things, and we obediently recite: Living things eat; they excrete; they reproduce and so on.But, one of the most important characteristics of living things is often forgotten……….that living things are made up of minute structures called cells.In this unit, you will learn about their structures, and how different cells look. You will also learn how to draw cells.

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WHAT DO CELLS LOOK LIKE?

• See these photos of plant and animal cells under the microscope.

http://www.umanitoba.ca/faculties/science/biological_sciences/lab3/biolab3_2.html

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Are all the cells the same?• Did those two photos of cells look alike? No

they didn’t. All cells are not the same, although nearly all cells have the same parts or components.

• Cells in plants have cell walls made of cellulose, while cells of animals do not have cell walls. Both types of cells have an outer covering called a cell membrane.

• Animal cells usually have small vacuoles or spaces containing different chemicals or water, while plant cells have large vacuoles.

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Parts of a Cell

• Look at the two diagrams on the next slide, which show the common parts of plant cells and animal cells.

• What are these parts?• Yes, you can find the common

parts of plant and animal cells quite easily.

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Diagrams of CellsComponents

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What structures are found inside cells?

• If you looked carefully at those two diagrams, you can identify the parts that are found inside cells.

• Notice the shapes and locations of the cell wall, cell membrane, nucleus, the cytoplasm, vacuoles, mitochondria, and chloroplasts.

• These are the important parts of the cell that you need to remember.

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Learning to Draw

• Look at the following photographs of drawings and diagrams

• Can you identify which are clear and easy to understand?

• Think of reasons why this is so for these diagrams and drawings

• These reasons will guide you as you learn to draw good diagrams

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Look at these photographs

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Look at these other photos

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Look at the last one !

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DRAWING A CELL• Now try to draw one cell of the tissue that your teacher has set

up under the microscope. Is it a plant or animal tissue? So, it will have which organelles ?? Have you noticed these organelles? If yes, which ones? If no, which ones can you see?

• Remember to draw using a sharp pencil, and use only a single line for the outline of the cell structures. Do not shade. If you wish to differentiate between structures, use large/small dots or stripes.

• Make sure that your diagram looks similar to the cell under the microscope, or similar to the diagram in the book that you are using. Your teacher should be able to recognize which cell you drew.

• Now, consider, have you labeled them correctly? Check back with the earlier slide that had labels. Make sure that you have labeled on the right hand side of the diagram.

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WHAT SIZE IS A CELL?

• Cells are extremely small. Generally they cannot be seen with the naked eye alone.

• A microscope with magnifying lenses is needed to make the tiny cells look larger to our eyes.

• Let us explain how this works by using an easier example.

• Look at the next slide.

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ICONOS PHOTO• This is an Iconos (name of satellite) photo of

a part of Kingston where Spanish Town Road, Maxfield Ave and Waltham Park Road meet. Can you see the three roads?

• Notice the large structures. What do you think they are?

• Do you notice a lot of green? Those are trees, pastures and lawns.

• Did you see that there were many homes?

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SAME PHOTO –LARGER IMAGE

• Have you noticed that this photo only shows a small part of the first one?

• What else can you see in this photo?• Anything that you could not see in the

first one?

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AN EVEN LARGER IMAGE

• Notice that this picture seems ‘fuzzy’. This is because it has been enlarged to show greater details of the area, but the sharpness of the images have deteriorated

• What else can you now see that you could not see before?

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AND FINALLY…….

• The photo shows a close up view of homes and factories in one community. We could enlarge this view still further to show the rooms inside the home, as is seen in the next slide.

• Can you guess which one is the living room, which are the two bedrooms, the bathroom and the kitchen?

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Floor Plan of House

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CELLS ARE TINY• You can see by the example of the satellite

photograph, that just as we can use complex cameras to take photos from far away of large objects, microscopes are used to see cells that are really minute

• Other, more complicated microscopes can magnify cells much more than the school microscope, and can show the structure of each of the cell’s organelles.

• These microscopes are called electron microscopes; while your school microscope is called a light microscope.

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USING YOUR IMAGINATION!• It is easy to remember the functions of the different

organelles in a cell, if a comparison is made between the plan of a house with its components AND the cell.

• For example, the walls of the house can be likened to the walls or membranes covering the cell. What do the walls of the house do?

• If you look at the next slide, you will see how to compare these two very different things!

• What about the other organelles in the cell? What is their function? (You can get the clues from considering the functions of the different parts of a house)

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Comparing Floor Plan with Cell Structures

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Functions of different parts of the cell• It is very useful to know the functions of the

different parts of the cell.• These parts are called organelles, as they

function almost like tiny organs.• It is easy to figure out the nucleus…..because

that is always the centre of everything, or the ruler of everything!

• Look up in your textbook to check if your guesses before were correct about the functions of all the organelles.

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TIME TO REVIEW

• All cells have some common components or organelles

• Each organelle within the cell does a different function

• Cells are minute, and can be seen only with microscopes.

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LOOK AT ANIMAL CELLS

• These diagrams show different animal cells.

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LOOK AT ANIMAL CELLS

• Observe their structures carefully to notice how different they are from the typical cell that you drew earlier.

• What is the function of each of these cells?• How does the structure suit their function?

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NOT ALL CELLS ARE THE SAME….

• Remember that you looked at plant cells and animal cells and considered how their different structures suited their different functions.

• Look at these next riddles about cells and guess their identity.

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WHAT AM I?• I am thin, am round or rectangular, am

closely attached to my neighbours, found in animals only, and look like a pavement. What am I?

• I am tiny, found in male animals only, have a tail, and contain a ‘body’ with many mitochondria. What am I?

• I am tall, with a cell wall, a large vacuole and contain many chloroplasts. I am very strong and found only in plants.

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LET’S CHECK !• Did you guess correctly? Did you guess the first one

was cells found on the outside of the body? What about the second one? Was it a sperm cell? And the third? Was that a palisade cell?

• The structure of cells is suited to their function. For example, if an animal cell is long and slim, with a small nucleus, it probably holds things together or helps hold things upright. Another example: if a cell is short and fat and contains many small particles and vacuoles, it probably works to produce mucous or enzymes or other important chemicals.

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MANY CELLS MAKE UP……

• Of course, many cells of the same kind make up a tissue.

• In a tissue, the cells work together to do the same function

• Different tissues make up organs, and organ systems.

• Finally, many organs make up the body of the organism.

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SOME EXAMPLES

• Can you think of four different tissues in your body?

• What about at least two different tissues in the plant’s body?

• Now, consider your important organ, your stomach. What kinds of tissues should it have? (Remember what kind of work it needs to do, and then suggest at least two kinds of different tissues that it should have)

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The Stomach• What has the stomach got to do? (Yes, you are

right……it has to help digest food)• Consider…..what types of tissues and cells does the

stomach need to do this?• Does it need to hold food for a while? Does it need

to send out chemicals, e.g., enzymes to work on the food?

• Does it need to move the food around, for the food to get well mixed with the enzymes?

• Therefore……………..what kinds of tissues should it be made of?

• Look at the diagram on the next page to check if your guesses were correct !

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http://content.answers.com/main/content/img/ahd4/A4stomac.jpg

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DIFFERENT CELLS & TISSUES ARE IMPORTANT

• Different tissues are important for organs. You have seen how useful it is that the stomach (an organ) has different types of tissues.

• How many different tissues did it contain? (Yes, you are correct, in the stomach are seen different layers of muscle tissue as well as mucous membrane on the inside; the stomach also contains tissue on the outside for protection.)

• That is just one example of an organ with different tissues, made up of different cells. Do you see why it is important to have different cells and different tissues?

• Did you remember that cells make up tissues and organs? And that organs make up the body of the plant or the animal?

• When tissues have different cells of different kinds, they can specialize in doing certain types of work.

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REALLY, HOW DO CELLS WORK or FUNCTION?

• It is important to remember that all materials are made of tiny particles called atoms, just as bodies of organisms are made of tiny bodies called cells.

• Atoms are always moving, and this movement is useful to a cell’s working or functioning, because generally atoms or their molecules move from areas where there are lots of them to areas where there are few of them………..this process is called diffusion. The molecules move along what is called a concentration gradient. This is the phrase used to describe the concentrations of the material found in or near a place. That is, there is an area with many molecules, beside an area with some molecules, next to an area with a few molecules, next to the area with no molecules. The next slide shows a picture of this.

• This means that particles of chemicals that are needed by cells or in short supply, can move inside the cells, and particles of chemicals that are NOT needed by cells, or are there in too great a quantity, can move outside of cells.

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HOW CELLS FUNCTION (2)

• When the molecules of water need to move in or out of the cell, this is a special type of diffusion called osmosis.

• Generally speaking, cells are protected on their outside by cell membranes. These membranes are selectively or partly/partially permeable. This means that although they control the entry and exit of chemicals into and out of the cell, they do not allow all materials in or out.

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CELL FUNCTIONING• Diffusion and osmosis work without using up much

energy at all. They work because of a normal behaviour of molecules, moving from a region where they are concentrated to an area where they are dilute.

• As you can imagine, not all materials can move into/out of cells in this manner. Some materials move in the opposite way to diffusion and osmosis. They move from an area where they are scarce to an area where they are in great supply.

• This way they have to move against the concentration gradient, and to do this they need energy which they obtain from respiration.

• This type of materials movement is called active transport.

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REVIEW TIME- Do you remember these?

• Cells function because all materials are made of tiny particles (atoms & molecules).

• Since they are small, they are able to move through cell membrane materials, by diffusion and by osmosis.

• Some materials move in a different way, by active transport, which uses up energy.