Cell Biology: Cell Structure and Function PDF

Here is the transcription of the document in a structured markdown format. # 3 Cells **In this chapter you will learn:** * that all organisms are made of cells * that microorganisms are usually made up of only one cell - they are single-celled * to give reasons for classifying virus as livin...

Here is the transcription of the document in a structured markdown format. # 3 Cells **In this chapter you will learn:** * that all organisms are made of cells * that microorganisms are usually made up of only one cell - they are single-celled * to give reasons for classifying virus as living or non-living * to identify and describe cell structures * how the structures of cells are related to their functions * about the similarities and difference between the structures of plant and animal cells * how cells can be grouped together to form tissues, organs and organ systems > DID YOU KNOW? > The average human adult body may be composed of up to 40 trillion cells. Nobody is sure of the exact number. ## Science in context **The discovery of cells** * The discovery of cells began with the careful dissection of dead human bodies to reveal the organs. * Such dissections were first carried out over 2000 years ago, in Greece, by two doctors called Herophilus and Erasistratus. * Their work encouraged other scientists who lived around 400 years ago to investigate further. ## Do you remember? * In your previous science courses, you will have learnt about some systems of the human body. These systems are made up of a number of organs working together. * The digestive system is made up from a number of organs. What are they? * What is the main organ of the circulatory system and what does it do to the blood? * What are the main organs of the respiratory system? What do they do and where are they found? * In this chapter, you are going to find out what organs are made from. ## What is a cell? * You may have met the word 'cell' when studying electricity, and found that it is a source of electricity, sometimes called a 'battery' when there is more than one cell. * In biology, the word 'cell' means something very different. It can be described as the basic unit of life and is a very small structure from which all organisms are made. It has all the characteristics of life that you learnt about in Chapter 1. --- ## BIOLOGY In the 16th century, scientists in Europe began studying the human body by dissection. This work has continued ever since. *The image shows a painting by Rembrandt shows Dr Nicolaes Tulp making a dissection in Holland in 1632.* * Marie-François X Bichat (1771-1802) was a French doctor that examined many bodies after they had died. * This is what is known as a post-mortem examination. In the last year of his life, he carried out 600 post-mortem examinations. * He cut up the bodies of dead people to find out how they had died. From this, he discovered that organs were made of layers of materials. He called tissues and identified 21 different kind. For a while, scientists thought that tissues were made of simple non-living materials. * In 1665, long before Bichat was born, an English scientist, Robert Hooke (1635-1703), used a microscope to investigate the structure of a very thin sheet of cork, which is the outer covering (called the bark) of a type of oak tree. He discovered that it had tiny compartments in it. He thought of them as rooms and called them cells, after the small rooms in monasteries - which are the buildings where monks live, work and meditate. * Bichat did not examine the tissues he had found under a microscope because most microscopes of that time did not produce very clear images. When better microscopes were made, scientists investigated pieces of plants and found that, like cork, they also had a cell structure. The cells in Hooke's piece of cork had been empty, but other plant cells were found to contain structures. * A Scottish scientist, Robert Brown *(1773–1858)*, studied plant cells and noticed that each one had a dark spot inside it. In 1831, he named the spot the nucleus, which means 'little nut'. *The image shows compartments in cork that Hooke saw using his microscope. He called them cells.* --- ## 3 Cells * Matthias Schleiden (1804-1881) was a German scientist who studied the parts of many plants. * In 1838, he put forward a theory that all plants were made of cells. A year later Theodor Schwann(1810-1882), another German scientist, stated that animals were also made of cells. * The ideas of Schleiden and Schwann became known as ***'cell theory'***. * It led other scientists to make more discoveries about cells and showed that tissues are made up of groups of similar cells. > LET'S TALK > > How do you feel about being made up from trillions of tiny cells all working together to keep you alive? > DID YOU KNOW? > > Biologists use the word ***'Specimen'*** to describe an object such as a plant, an animal or a part of one, such as a group of cells. The objects that they place on microscope slides are callen ***'specimens'***. 1. Where did Bichat get his idea that organs were made from tissues? 2. Who first described cells ans where did the idea for the word come from? 3. Who named the nucleus and what does the word mean? 4. What instrument was essential for the study of cells? 5. How could cell theory have been developed sooner? 6. Arrange these parts of a body in order of size stating with the largest: * Cell * Organ * Tissue * Organ system 7. Which scientific activity did Bichat perform to think up his idea that organs were made from tissues? 8. Which was the final scientific activity that led Schleiden and Schwann to set up cell theory? ## The microscope * The microscope is a laboratory instrument used to observe very tiny objects. It does this by procuring a highly magnified view of the object. * Most laboratory microscopes give a magnification up to about 200 times, but some can give a magnification of over 1000 times. * The microscope must also provide a clear view, and this is achieved by controlling the amount of light shining onto the specimen. ## How do we see cells? You will need: * A microscope and light source, and a prepared slide with a specimen on it (the specimen could be like the one shown in Figure 3.3 on the next page). * The microscope is used to see very tiny objects such as cells. It does this by making a highly magnified view of them, as in Figure 3.3 on the next page. --- ## BIOLOGY *The image shows a very thin slice through human skin which has been stained to make the cells easier to see.* * Figure 3.4 shows the main parts of a microscope. Many older microscopes (such as the one shown in Figure 3.4) have a mirror for collecting light. * Microscopes made today have an illuminator instead of a mirror, as shown in Figure 3.5. * The illuminator has an LED lamp inside it and a light control on the side. *The image shows Figure 3.4 The main parts of a microscope. Some labels are: ocular tube, focusing knob, stage clips, mirror, eyepiece lens, nosepiece, objective lenses, stage, lamp.* *The image shows Figure 3.5 A modern microscope. Some labels are: eyepiece, ocular tube, nosepiece, objective lenses, stage, stage clips, focusing knob, and illuminator.* **Process** 1. The objective lenses have different magnifying powers. This is shown on their sides, such as $x5$, $x10$ or $x20$. Select the lowest-power objective lens and click it into a position under the ocular tube. 2. Put the slide with the specimen on it onto the stage. Make sure that the specimen is in the centre of the hole on the stage. --- ## 3 Cells > LET'S TALK > > The microscope is very important piece of scientific equipment. Did you find it easy to use? What was the most difficult task in seeing the specimen? What did you think of the specimen when you saw it magnified under the microscope? 1. Carefully place the stage clips on the slide without moving it. 2. If the microscope has a mirror and lamp, look down the eyepiece to see that the specimen is in a circle of light. If it is not, move the mirror slowly, as instructed by your teacher, to point the mirror at the lamp from a slightly different direction. 3. Look at the side of the microscope and turn the focusing knob so that the objective lens moves closer to the slide but does not touch it. 4. Look down the eyepiece and turn the focusing knob slowly, so that the objective lens moves up and away from the specimen on the slide. As you do this, keep looking at the specimen through the eyepiece until you can see it clearly. The microscope is now focused on the specimen. 5. Describe what you see, either in words or by making a drawing. ### CHALLENGE YOURSELF Look at the microscopes in your laboratory and use Figures 3.4 and 3.5 to identify their parts. Learn to point at each part and say its name without looking at the figures. What would yu do to see a more powerful magnification of the specimen than in the enquiry? check your plan with your teacher and, if approved, tru it. ### Science extra: The magnification of the microscope Above the state is the ocular tube. This has an eyepiece lens at the top and one or more objective lenses at the bottom. The magnification of the two lenses is written on them. Any eyepiece lens may give a magnification of $x5$ or $x10$. An objective lens may give a magnification of $x10$, $x15$ or $x20$. The magnification provided by both the eyepiece lens and the objective lens is found by multiple their magnificent power together. 9. What magnification would you get by using an eyepiece of $x5$ magnification with an objective lens of $x10$ magnification? 10. If you had a microscope with $x5$ and $x10$ eyepieces and objective lenses of $x10$, $x15$ and $x20$, what powers of magnification could it provide? ## Basic parts of cells **The parts of a cell** All cells (in animals and plants) have some parts in common. **Nucleus** The nucleus is the control centre of the cell. It controls all the life processes which take place to keep the cell alive. --- * An image showing an animal cell. There are labels for the following: * cytoplasm * cell membrane * nucleus * mitochondrion > DID YOU KNOW? > > DNA are letters which stand for a chemical found in every plant and animal cell. DNA controls how living things grow and develop their life processes, and can sometimes me found in the surroundings close to where a plant and animal lives. > DID YOU KNOW? > > The largest human cell is the ovum or egg cell. It is about $1 mm$ across and can be seen without a microscope. You were once that size! ### Cytoplasm * Cytoplasm is a watery jelly that fills most of each animal cell. It can move around inside the cell. The cytoplasm may contain stored food in the form of grains. Most of the chemical reactions that keep the cell alive take place in the cytoplasm. ### Cell membrane *The cell membrane has tiny holds in it called pores that control the movement of chemicals in or out of the cell. Dissolved substances such as food, oxygen and carbon dioxide can pass through the cell membrane. Some harmful chemicals are stopped from entering the cell by the membrane.* ### Mitochondria *Mitochondria are tiny structures in the cytoplasm. In each mitochondrion, chemical reactions take place which release for life processes in the cell. Mitochondria are shown in the first few cell diagrams in this chapter, but not in all of the other cell diagrams, to allow different structures to be seen clearly. Even when they are not shown, it is important to remember that mitochondria are in the cytoplasm, helping to keep the cell alive.* 11. Imagine that you are looking down a microscope as a slide labeled 'Cells'. You can see a coloured substance woth dots in it and lines that divide the substances into rectangular shapes. a. What are the dots? b. What are the lines? c. What is the coloured substance? 12. How does the cell membrane protect the cell? * An image showing a typical plant cell. There are labels for the following: * cell wall * cell membrane * vacuole * chloroplast * cytoplasm * mitochondrion * nucleus ### Cell wall *The cell wall is found outside the membrane of a plants. It is made of cellulose, which is a tough material which gives support to the cell.* --- 13. Name two things that give support to a plant cell. 14. Would you expeact to find chloroplasts in a root cell? Explain your answer. 15. Why do plants wilt if they are not watered regularly? ### Chloroplasts * Chloroplasts are found in the cytoplasm of many plant cells. They contain a green pigment which traps a small amount of the energy in sunlight. That energy is used by the plant ti make food. Chloroplasts are found in many leaf cells and in the stem cells of some plants. ### Sap-vacuole *The vacuole is a large sapce in the cytoplasm of a plant cell that is filled with a liquid, called cell sap, containing dissolved sugars and salts. When the vacuole is full of cell sap, the liquid pushes onwards on the cell wall and gives it support. If the plant is short of water, the support is lost and the plant wilts.* The features of animal and plant cells can be compared by setting thrm out in a table, as Table 3.1 shows. **Table 3.1 Features of animal and plant cells.** | Feature | Animal cell | Plant cell | | :------------ | :---------- | :--------- | | nucleus | present | present | | cytoplasm | present | present | | cell membrane | present | present | | mitochondria | present | present | | cell wall | absent | present | | chloroplasts | absent | present | | sap vacuole | absent | present | > LET'S TALK > > Imagine that you are a cell in an animal. How would you describe yourself ? If you were a plant cell, how would you be different? Spend a little time jotting down your ideas then read them out to the group. ## Looking at plant cells with a microscope In the next enquiry, you will learn how to make a wet mount - placing a specimen in water for examination - and repeat the skills you have learnt in the previous scientific enquiry. ## What makes a leaf green? You will need: * a microscope and light source, a slide, a cover-slip, a small beaker of water, a dropping pipette, a pair of forceps, a mounted needle, a moss plant growing on a sone or log (or another suitable green plant you can find locally), an HB (hard black/ medium hard) or a number 2 grade pencil and an A4 sheet of paper. ### Hypothesis The green colour of the moss leaf is made by a pigment in the chloroplasts. Is that hypothesis testable? Explain your answer. --- ## BIOLOGY ### Prediction Where will the green colour in the moss cells be found? Make a prediction. ### Investigation 1. Use a pipette to place a drop of water on a microscope slide. 2. Use a pair of forceps to pull a leaf off a moss plant (or other suitable green plant). 3. lower the leaf gently into the drop of water. 4. Lower a cover-slip over the leaf in the water with a mounted needle. * An image showing steps 1 to 4. 5. Examine the slide for air bubbles. They will appear as circles with dark walls. If you find any, gently raise the cover-slip with the mounted needle and lower it again carefully as you check to see that no more bubbles form. --- ### 3 Cells 1. Set up the side on the microscope and examines it under the low-power lens. Make a drawing out what you see. You do not need to draw a circle; just draw about six to ten cells on the paper. 2. Repeat step 6 with the medium- and high-power lenses. Draw fewer cells, if neccessary. > Work safely > > Hands should be washed throughly after handling living of preserved specimens. > > Microscope mirrors should not be turned to catch direct sunlight. ### Examining the results Compare your drawings with figure 3.7. ### Conclusion Compare your drawings with the hypothesis and prediction and make a conclusion. ## Adaptation in cells The word adaptation means the change of an existing design for e particular task. You learnt about the basic structure of animals and plants cells in the last section. However, many cells are adopted, which allows them to perform a more specific task and became specialized. Here are some common examples of the different types of plant and animal cells have become specialized. ### Adaptations in plant cells **Root hair cells** 16. What changes have taken place in the basic plant cell to produce a root hair cell? 17. Why would it be a problem if root hair cell extansions were short and stubby? *Root hair cells are plant cells that grow a short distance behind the root tip. The sales have long thin extensions that allow them to grow easily between the soil particles. The shapes of those extensions gives the root hair sells a large service area through which water can be taken up from the soil.* *An image shows a root hair cell. The image also lists the fallowing:* * nucleus * cell wall * cell membrane * cytoplasm * vacuole --- ## BIOLOGY ### Can you see root hairs on germinating seeds? You will need: * A soaked bean seed, a dump paper towel, a dish, a hand lens (magnifying glass), a ruler, some A4 paper and a an HB (hard back / medium hard) or a number 2 grade pencil. ### Hypothesis As the root hairs grow out from the root surface, you may be able to see them. Is the hypothesis testable? Explain your answer. ### Prediction A germinating speed produces a root eitch searches for water. It may produce the route held cells along its length to help it in its task. ### Investigation 1. Wrap a soaked bean seed in a dump paper towel and put the towel on a plate. 2. Keep the plate and well in a warm place it does not have to be in the light. 3. unwrap the towel earefully every day to look at the being for sounds of germination and root production then drop up the bean carefully again make sure that the day will stay dumb 4. repeat step 3 until a route begins to appear then rock up the bean less slightly so the route has wrong to grow inside the tower 5. repeat step 3 for for more days Take care not to damage their route as you unlock the wrapper on the tower 1. Look for root hairs with a hand lens by taking the calling steps: hold the hand lens close to your eye 2. pick up the bean with its root and bring them close to your hand lens until you see it would clearly 3. Repeat step 6 once a day for a call of the you see changes than the route with them down and make drawings of the route > Work safely > > wash your hands for all handling living or reserve the specimens! ### Examining the results Compare your written description and drawings. ### Conclusion compare your descriptions and drawings with the hypothesis and production and make a conclusion --- ## 3 Cells *An image shows a palisade cell. The image also lists the following:* * cell wall * cell membrane * vacuole * Chloroplast * Cytoplasm * Nucleus * Mitochondria ### Palisade cells *Palisade cells have a shape that allows them to pack closely together in the upper part of a leaf, near the light. They have large numbers of chloroplasts in them to trap as much light energy as possible.* 18. How is a palisade cell different from a root hair cell? Explain these differences. 19. Why are there differnet kinds of cells? ## Adaptation in animal cells ### Skin cells There are a numbers of different types of the skin cells, and skin cells have more than ine function. However, one of the main functions of skin cells is to protect the surface of the body. After thy have informed by cell division below the skin surface, they rise up inform a laser of dead cells which stop water microorganisms entering the body. If you stay in the water in a swimming pool or bath for a long time, you make notice sometimes that when you dry yourself , you may notice that part of our skin flakes off. Then sales are made of dead skins you are losing your skin cells all the time, but on a less obvious way AS your call if rub against your skin, they pulled of tiny flex which of that into the air and settle in the dust. A small part of the dirt that swept up at the end of a school day comes form the skin that you have left behind In the 1870 it was discovered that dyes could be made form all their cold tackily black liquid which produced a can with their cold that the black liquid which produced a can with their cold that with stain different parts of the cell cell biologist found they cook stain the news of the cells different cells ### How can skin cells be exanimated? You will need: a microscope and light source, clear stich tap, and a pair of forcep, a microscope slide, chemical resident gloves, a bottle of math lane with all a stains as the glasses so A4 paper or an HBD black media and hard or am number 2 grade pencils --- ## BIOLOGY ### Hypothesis The outer surface of the skin is covered with dead skins that might be easily removed by stich tap is they had the thesis example Explain your answer made your wrong perfection bastons ### The investigation is as fallows one 1 but of a 2 cm long 2 but on a glove to pick it up as this will printing printing forming in the glow 3 Press the tax from the arm tap 4 Use for apps to lift the tarpa from your scanda 5 put a microscope 10 is the put on the other globe and use to have the 6 Usd the four apps to left one and all bit 7 you step for left one and all bit Use drop one but but your is the type I used the for apps the fully longer the top back on the song If will form or leave the table a exami exami and move to the right or left to fine objects > Work sately > > My call a cell the top > Be carefully that I can ### Exams exams compar the a Conclusion compared on 1 --- ## 3 Cells *The image shows a Red blood cell. * **Red blood cells** * Red blood cells travel through all the arteries, veins and capillaries in the body. * They are disc-shaped but their centres dip inwards. This structure is called a biconcave disc. * It is also flexible, which allows the cells to bend and fold to pass through the smallest of capillaries. It does not have a nucleus so that it can be completely filled with a red substance, called haemoglobin, which carries oxygen to all the other cells in the body. 20 If blood cells had a nucleus, how would this affect the oxygen supply to the other body cells? *The image shows the nervous system. The nervous system is the collection of nerves, spinal cord and brain. Labels include: brain, spinal cord, nerve.* *The image shows the a nerve cell. * * Labels include: * cell body * nucleus * nerve fibre ### Nerve cells * Nerves are made from nerve cells or **neurones**, which have long thread-like extensions. These nerve cells are connected to other nerve cells in the spinal cord. The nerve cells in the spinal cord are then connected to nerve cells in the brain. * A nerve cell can conduct tiny electrical signals through its body. In the nerve cell shown in Figure 3.13, the signals are collected from other nerve cells (perhaps in a sense organ or a muscle) by the fibres on the cell body, and are transported through the nerve fibre to the projections at the far end. Once they reach these places, they set off another electrical signal in the next cell. Electrical signals are moved around the body in this way, from sense organs to the brain, and from the brain down the spinal column, and along nerves to the muscles to make them move. ### Ciliated epithelial cells * Cells that line the surface of structures are called **epithelial cells**. **Cilia** are microscopic hair-like extensions of the cytoplasm. Cells with one surface covered in cilia are described as being ciliated. (See Figure 3.14 on the next page showing these cells.) --- ##BIOLOGY **The image shows Ciliated epithelial cells.* * Labels include: * cilia * cytoplasm *cell membrane *nucleus 21 Smoking damages the cilia lining the breathing tubes. What effect might this have on breathing? **Ciliated epithelial cells lined the Throat. Air entering the throat contains dust that becomes trapped in the MUCUS OF THE THROAT lining the cilia wave tot and FOR AND CARRY the dust trapped I the mucus away for the LungS. THE previous the examples of cells are found onThe previous three examples of cells are found on the inside of the human Body. * Next Scientific Inquiry * gives YOU the chance to see the Summer of YOU can sell from inside you.